Cassini Encounters Enceladus Background and the Discovery of

a South Polar Hot SpotSpencer et al 10 March 2006 Science 311 1401

Presented by Shannon GuilesAstronomy 671April 10 2006

Image Credit NASAJPLGSFC

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeCould frame thy fearful symmetry

Cassini

Cassini entered orbit around Saturn on 1 July

2004 and it will orbit there for four years

Cassini has 12 instruments while the Hyugens probe

(which descended to Titans surface in January

2005) had 6

Cassini had three close flybys of Enceladus between Feb amp July

2005 One more scheduled for Spring

2008Credit NASA

Credit NASA

CIRS

Cassini Composite Infrared Spectrometer

Reference Flazar et al (2004)

In what distant deeps or skiesBurnt the fire of thine eyes

On what wings dare he aspireWhat the hand dare seize the fire

Enceladus

shy discovered in 1789 by William Hershelshy 6th largest moon of Saturnshy orbits close to Saturn at r= 394 r_Saturnshy eccentricity = 00047 in 21 orbital resonance with Dioneshy Voyager found (1981)

shy r_Enceladus = 252 km shy high visual geom albedo implying fresh snow or ice

shy vastly different surfacesshy resides in the middle of Saturns Eshyring and probably its sourceshy surface dominated by water ice with organics and CO2 coincident with tiger stripes Credit NASAJPLSpace Science Institute

Composite of UV (338 nm) green (568 nm) and IR (752 nm)

Why do we care

Scientists like a good puzzle Before Cassini observations of Enceladus South Pole it was expected that Enceladus would be cold

Surprise Enceladus is one of only 3 outer solar system bodies (along with Jupiters Io amp Neptunes Triton) where active geological eruptions have now been seen

What is the origin of Enceladus internal heating Possibility of life

Left Predicted temperatures on Enceladus based on solar heating Right Temperature image from measurements of Enceladus heat radiation from 9 to 165 microns Image

Credit NASAJPLGSFC

The Puzzle

Only previous measurement of Enceladus thermal radiation made by Voyager 2 in 1981 ndash

inferred temperatures of 75 +shy 3 K

And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat

What dread hand and what dread feet

Figure 1(A) of Spencer et al (2006)

Cassini CIRS Observations of Enceladus

FarshyIR brightness temperature images of the thermal emission from the antishySaturn

hemisphere of Enceladus

Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1

Thermal Model Fits to Determine Physical Properties

shy Temperatures near 76 K consistent with Voyager estimates

shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface

shy The high albedo is consistent with Voyager determination of 090 +shy 010

What the hammer what the chainIn what furnace was thy brain

What the anvil what dread graspDare its deadly terrors clasp

Figure 2 of Spencer et al (2006)

Mid-IR Data on Enceladus South Pole

(125 to 16 microm)

Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR

detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)

Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)

Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)

Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies

temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)

They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely

The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)

What Causes the Hot Spot at the South Pole Is it seasonal effects

ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower

How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped

beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice

A heat source from withinndash Quite possibly The hot spot is located in a recently

resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeCould frame thy fearful symmetry

Cassini

Cassini entered orbit around Saturn on 1 July

2004 and it will orbit there for four years

Cassini has 12 instruments while the Hyugens probe

(which descended to Titans surface in January

2005) had 6

Cassini had three close flybys of Enceladus between Feb amp July

2005 One more scheduled for Spring

2008Credit NASA

Credit NASA

CIRS

Cassini Composite Infrared Spectrometer

Reference Flazar et al (2004)

In what distant deeps or skiesBurnt the fire of thine eyes

On what wings dare he aspireWhat the hand dare seize the fire

Enceladus

shy discovered in 1789 by William Hershelshy 6th largest moon of Saturnshy orbits close to Saturn at r= 394 r_Saturnshy eccentricity = 00047 in 21 orbital resonance with Dioneshy Voyager found (1981)

shy r_Enceladus = 252 km shy high visual geom albedo implying fresh snow or ice

shy vastly different surfacesshy resides in the middle of Saturns Eshyring and probably its sourceshy surface dominated by water ice with organics and CO2 coincident with tiger stripes Credit NASAJPLSpace Science Institute

Composite of UV (338 nm) green (568 nm) and IR (752 nm)

Why do we care

Scientists like a good puzzle Before Cassini observations of Enceladus South Pole it was expected that Enceladus would be cold

Surprise Enceladus is one of only 3 outer solar system bodies (along with Jupiters Io amp Neptunes Triton) where active geological eruptions have now been seen

What is the origin of Enceladus internal heating Possibility of life

Left Predicted temperatures on Enceladus based on solar heating Right Temperature image from measurements of Enceladus heat radiation from 9 to 165 microns Image

Credit NASAJPLGSFC

The Puzzle

Only previous measurement of Enceladus thermal radiation made by Voyager 2 in 1981 ndash

inferred temperatures of 75 +shy 3 K

And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat

What dread hand and what dread feet

Figure 1(A) of Spencer et al (2006)

Cassini CIRS Observations of Enceladus

FarshyIR brightness temperature images of the thermal emission from the antishySaturn

hemisphere of Enceladus

Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1

Thermal Model Fits to Determine Physical Properties

shy Temperatures near 76 K consistent with Voyager estimates

shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface

shy The high albedo is consistent with Voyager determination of 090 +shy 010

What the hammer what the chainIn what furnace was thy brain

What the anvil what dread graspDare its deadly terrors clasp

Figure 2 of Spencer et al (2006)

Mid-IR Data on Enceladus South Pole

(125 to 16 microm)

Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR

detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)

Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)

Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)

Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies

temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)

They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely

The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)

What Causes the Hot Spot at the South Pole Is it seasonal effects

ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower

How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped

beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice

A heat source from withinndash Quite possibly The hot spot is located in a recently

resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Cassini

Cassini entered orbit around Saturn on 1 July

2004 and it will orbit there for four years

Cassini has 12 instruments while the Hyugens probe

(which descended to Titans surface in January

2005) had 6

Cassini had three close flybys of Enceladus between Feb amp July

2005 One more scheduled for Spring

2008Credit NASA

Credit NASA

CIRS

Cassini Composite Infrared Spectrometer

Reference Flazar et al (2004)

In what distant deeps or skiesBurnt the fire of thine eyes

On what wings dare he aspireWhat the hand dare seize the fire

Enceladus

shy discovered in 1789 by William Hershelshy 6th largest moon of Saturnshy orbits close to Saturn at r= 394 r_Saturnshy eccentricity = 00047 in 21 orbital resonance with Dioneshy Voyager found (1981)

shy r_Enceladus = 252 km shy high visual geom albedo implying fresh snow or ice

shy vastly different surfacesshy resides in the middle of Saturns Eshyring and probably its sourceshy surface dominated by water ice with organics and CO2 coincident with tiger stripes Credit NASAJPLSpace Science Institute

Composite of UV (338 nm) green (568 nm) and IR (752 nm)

Why do we care

Scientists like a good puzzle Before Cassini observations of Enceladus South Pole it was expected that Enceladus would be cold

Surprise Enceladus is one of only 3 outer solar system bodies (along with Jupiters Io amp Neptunes Triton) where active geological eruptions have now been seen

What is the origin of Enceladus internal heating Possibility of life

Left Predicted temperatures on Enceladus based on solar heating Right Temperature image from measurements of Enceladus heat radiation from 9 to 165 microns Image

Credit NASAJPLGSFC

The Puzzle

Only previous measurement of Enceladus thermal radiation made by Voyager 2 in 1981 ndash

inferred temperatures of 75 +shy 3 K

And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat

What dread hand and what dread feet

Figure 1(A) of Spencer et al (2006)

Cassini CIRS Observations of Enceladus

FarshyIR brightness temperature images of the thermal emission from the antishySaturn

hemisphere of Enceladus

Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1

Thermal Model Fits to Determine Physical Properties

shy Temperatures near 76 K consistent with Voyager estimates

shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface

shy The high albedo is consistent with Voyager determination of 090 +shy 010

What the hammer what the chainIn what furnace was thy brain

What the anvil what dread graspDare its deadly terrors clasp

Figure 2 of Spencer et al (2006)

Mid-IR Data on Enceladus South Pole

(125 to 16 microm)

Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR

detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)

Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)

Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)

Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies

temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)

They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely

The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)

What Causes the Hot Spot at the South Pole Is it seasonal effects

ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower

How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped

beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice

A heat source from withinndash Quite possibly The hot spot is located in a recently

resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Cassini Composite Infrared Spectrometer

Reference Flazar et al (2004)

In what distant deeps or skiesBurnt the fire of thine eyes

On what wings dare he aspireWhat the hand dare seize the fire

Enceladus

shy discovered in 1789 by William Hershelshy 6th largest moon of Saturnshy orbits close to Saturn at r= 394 r_Saturnshy eccentricity = 00047 in 21 orbital resonance with Dioneshy Voyager found (1981)

shy r_Enceladus = 252 km shy high visual geom albedo implying fresh snow or ice

shy vastly different surfacesshy resides in the middle of Saturns Eshyring and probably its sourceshy surface dominated by water ice with organics and CO2 coincident with tiger stripes Credit NASAJPLSpace Science Institute

Composite of UV (338 nm) green (568 nm) and IR (752 nm)

Why do we care

Scientists like a good puzzle Before Cassini observations of Enceladus South Pole it was expected that Enceladus would be cold

Surprise Enceladus is one of only 3 outer solar system bodies (along with Jupiters Io amp Neptunes Triton) where active geological eruptions have now been seen

What is the origin of Enceladus internal heating Possibility of life

Left Predicted temperatures on Enceladus based on solar heating Right Temperature image from measurements of Enceladus heat radiation from 9 to 165 microns Image

Credit NASAJPLGSFC

The Puzzle

Only previous measurement of Enceladus thermal radiation made by Voyager 2 in 1981 ndash

inferred temperatures of 75 +shy 3 K

And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat

What dread hand and what dread feet

Figure 1(A) of Spencer et al (2006)

Cassini CIRS Observations of Enceladus

FarshyIR brightness temperature images of the thermal emission from the antishySaturn

hemisphere of Enceladus

Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1

Thermal Model Fits to Determine Physical Properties

shy Temperatures near 76 K consistent with Voyager estimates

shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface

shy The high albedo is consistent with Voyager determination of 090 +shy 010

What the hammer what the chainIn what furnace was thy brain

What the anvil what dread graspDare its deadly terrors clasp

Figure 2 of Spencer et al (2006)

Mid-IR Data on Enceladus South Pole

(125 to 16 microm)

Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR

detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)

Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)

Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)

Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies

temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)

They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely

The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)

What Causes the Hot Spot at the South Pole Is it seasonal effects

ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower

How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped

beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice

A heat source from withinndash Quite possibly The hot spot is located in a recently

resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

In what distant deeps or skiesBurnt the fire of thine eyes

On what wings dare he aspireWhat the hand dare seize the fire

Enceladus

shy discovered in 1789 by William Hershelshy 6th largest moon of Saturnshy orbits close to Saturn at r= 394 r_Saturnshy eccentricity = 00047 in 21 orbital resonance with Dioneshy Voyager found (1981)

shy r_Enceladus = 252 km shy high visual geom albedo implying fresh snow or ice

shy vastly different surfacesshy resides in the middle of Saturns Eshyring and probably its sourceshy surface dominated by water ice with organics and CO2 coincident with tiger stripes Credit NASAJPLSpace Science Institute

Composite of UV (338 nm) green (568 nm) and IR (752 nm)

Why do we care

Scientists like a good puzzle Before Cassini observations of Enceladus South Pole it was expected that Enceladus would be cold

Surprise Enceladus is one of only 3 outer solar system bodies (along with Jupiters Io amp Neptunes Triton) where active geological eruptions have now been seen

What is the origin of Enceladus internal heating Possibility of life

Left Predicted temperatures on Enceladus based on solar heating Right Temperature image from measurements of Enceladus heat radiation from 9 to 165 microns Image

Credit NASAJPLGSFC

The Puzzle

Only previous measurement of Enceladus thermal radiation made by Voyager 2 in 1981 ndash

inferred temperatures of 75 +shy 3 K

And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat

What dread hand and what dread feet

Figure 1(A) of Spencer et al (2006)

Cassini CIRS Observations of Enceladus

FarshyIR brightness temperature images of the thermal emission from the antishySaturn

hemisphere of Enceladus

Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1

Thermal Model Fits to Determine Physical Properties

shy Temperatures near 76 K consistent with Voyager estimates

shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface

shy The high albedo is consistent with Voyager determination of 090 +shy 010

What the hammer what the chainIn what furnace was thy brain

What the anvil what dread graspDare its deadly terrors clasp

Figure 2 of Spencer et al (2006)

Mid-IR Data on Enceladus South Pole

(125 to 16 microm)

Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR

detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)

Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)

Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)

Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies

temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)

They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely

The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)

What Causes the Hot Spot at the South Pole Is it seasonal effects

ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower

How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped

beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice

A heat source from withinndash Quite possibly The hot spot is located in a recently

resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Enceladus

shy discovered in 1789 by William Hershelshy 6th largest moon of Saturnshy orbits close to Saturn at r= 394 r_Saturnshy eccentricity = 00047 in 21 orbital resonance with Dioneshy Voyager found (1981)

shy r_Enceladus = 252 km shy high visual geom albedo implying fresh snow or ice

shy vastly different surfacesshy resides in the middle of Saturns Eshyring and probably its sourceshy surface dominated by water ice with organics and CO2 coincident with tiger stripes Credit NASAJPLSpace Science Institute

Composite of UV (338 nm) green (568 nm) and IR (752 nm)

Why do we care

Scientists like a good puzzle Before Cassini observations of Enceladus South Pole it was expected that Enceladus would be cold

Surprise Enceladus is one of only 3 outer solar system bodies (along with Jupiters Io amp Neptunes Triton) where active geological eruptions have now been seen

What is the origin of Enceladus internal heating Possibility of life

Left Predicted temperatures on Enceladus based on solar heating Right Temperature image from measurements of Enceladus heat radiation from 9 to 165 microns Image

Credit NASAJPLGSFC

The Puzzle

Only previous measurement of Enceladus thermal radiation made by Voyager 2 in 1981 ndash

inferred temperatures of 75 +shy 3 K

And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat

What dread hand and what dread feet

Figure 1(A) of Spencer et al (2006)

Cassini CIRS Observations of Enceladus

FarshyIR brightness temperature images of the thermal emission from the antishySaturn

hemisphere of Enceladus

Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1

Thermal Model Fits to Determine Physical Properties

shy Temperatures near 76 K consistent with Voyager estimates

shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface

shy The high albedo is consistent with Voyager determination of 090 +shy 010

What the hammer what the chainIn what furnace was thy brain

What the anvil what dread graspDare its deadly terrors clasp

Figure 2 of Spencer et al (2006)

Mid-IR Data on Enceladus South Pole

(125 to 16 microm)

Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR

detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)

Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)

Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)

Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies

temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)

They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely

The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)

What Causes the Hot Spot at the South Pole Is it seasonal effects

ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower

How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped

beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice

A heat source from withinndash Quite possibly The hot spot is located in a recently

resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Why do we care

Scientists like a good puzzle Before Cassini observations of Enceladus South Pole it was expected that Enceladus would be cold

Surprise Enceladus is one of only 3 outer solar system bodies (along with Jupiters Io amp Neptunes Triton) where active geological eruptions have now been seen

What is the origin of Enceladus internal heating Possibility of life

Left Predicted temperatures on Enceladus based on solar heating Right Temperature image from measurements of Enceladus heat radiation from 9 to 165 microns Image

Credit NASAJPLGSFC

The Puzzle

Only previous measurement of Enceladus thermal radiation made by Voyager 2 in 1981 ndash

inferred temperatures of 75 +shy 3 K

And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat

What dread hand and what dread feet

Figure 1(A) of Spencer et al (2006)

Cassini CIRS Observations of Enceladus

FarshyIR brightness temperature images of the thermal emission from the antishySaturn

hemisphere of Enceladus

Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1

Thermal Model Fits to Determine Physical Properties

shy Temperatures near 76 K consistent with Voyager estimates

shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface

shy The high albedo is consistent with Voyager determination of 090 +shy 010

What the hammer what the chainIn what furnace was thy brain

What the anvil what dread graspDare its deadly terrors clasp

Figure 2 of Spencer et al (2006)

Mid-IR Data on Enceladus South Pole

(125 to 16 microm)

Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR

detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)

Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)

Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)

Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies

temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)

They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely

The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)

What Causes the Hot Spot at the South Pole Is it seasonal effects

ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower

How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped

beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice

A heat source from withinndash Quite possibly The hot spot is located in a recently

resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Left Predicted temperatures on Enceladus based on solar heating Right Temperature image from measurements of Enceladus heat radiation from 9 to 165 microns Image

Credit NASAJPLGSFC

The Puzzle

Only previous measurement of Enceladus thermal radiation made by Voyager 2 in 1981 ndash

inferred temperatures of 75 +shy 3 K

And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat

What dread hand and what dread feet

Figure 1(A) of Spencer et al (2006)

Cassini CIRS Observations of Enceladus

FarshyIR brightness temperature images of the thermal emission from the antishySaturn

hemisphere of Enceladus

Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1

Thermal Model Fits to Determine Physical Properties

shy Temperatures near 76 K consistent with Voyager estimates

shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface

shy The high albedo is consistent with Voyager determination of 090 +shy 010

What the hammer what the chainIn what furnace was thy brain

What the anvil what dread graspDare its deadly terrors clasp

Figure 2 of Spencer et al (2006)

Mid-IR Data on Enceladus South Pole

(125 to 16 microm)

Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR

detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)

Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)

Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)

Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies

temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)

They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely

The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)

What Causes the Hot Spot at the South Pole Is it seasonal effects

ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower

How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped

beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice

A heat source from withinndash Quite possibly The hot spot is located in a recently

resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beat

What dread hand and what dread feet

Figure 1(A) of Spencer et al (2006)

Cassini CIRS Observations of Enceladus

FarshyIR brightness temperature images of the thermal emission from the antishySaturn

hemisphere of Enceladus

Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1

Thermal Model Fits to Determine Physical Properties

shy Temperatures near 76 K consistent with Voyager estimates

shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface

shy The high albedo is consistent with Voyager determination of 090 +shy 010

What the hammer what the chainIn what furnace was thy brain

What the anvil what dread graspDare its deadly terrors clasp

Figure 2 of Spencer et al (2006)

Mid-IR Data on Enceladus South Pole

(125 to 16 microm)

Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR

detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)

Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)

Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)

Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies

temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)

They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely

The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)

What Causes the Hot Spot at the South Pole Is it seasonal effects

ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower

How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped

beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice

A heat source from withinndash Quite possibly The hot spot is located in a recently

resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Figure 1(A) of Spencer et al (2006)

Cassini CIRS Observations of Enceladus

FarshyIR brightness temperature images of the thermal emission from the antishySaturn

hemisphere of Enceladus

Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1

Thermal Model Fits to Determine Physical Properties

shy Temperatures near 76 K consistent with Voyager estimates

shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface

shy The high albedo is consistent with Voyager determination of 090 +shy 010

What the hammer what the chainIn what furnace was thy brain

What the anvil what dread graspDare its deadly terrors clasp

Figure 2 of Spencer et al (2006)

Mid-IR Data on Enceladus South Pole

(125 to 16 microm)

Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR

detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)

Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)

Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)

Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies

temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)

They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely

The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)

What Causes the Hot Spot at the South Pole Is it seasonal effects

ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower

How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped

beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice

A heat source from withinndash Quite possibly The hot spot is located in a recently

resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Figure 1 (B) of Spencer et al (2006)Temperatures measured during orbits 3 and 4 Thermal Inertia (TI) in MKS units of J mshy2 sshy12 Kshy1

Thermal Model Fits to Determine Physical Properties

shy Temperatures near 76 K consistent with Voyager estimates

shy Note the large spatial variations in the thermal inertia (TI) TI is 100 x lt TI of solid water ice implying a very lose surface

shy The high albedo is consistent with Voyager determination of 090 +shy 010

What the hammer what the chainIn what furnace was thy brain

What the anvil what dread graspDare its deadly terrors clasp

Figure 2 of Spencer et al (2006)

Mid-IR Data on Enceladus South Pole

(125 to 16 microm)

Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR

detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)

Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)

Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)

Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies

temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)

They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely

The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)

What Causes the Hot Spot at the South Pole Is it seasonal effects

ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower

How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped

beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice

A heat source from withinndash Quite possibly The hot spot is located in a recently

resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

What the hammer what the chainIn what furnace was thy brain

What the anvil what dread graspDare its deadly terrors clasp

Figure 2 of Spencer et al (2006)

Mid-IR Data on Enceladus South Pole

(125 to 16 microm)

Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR

detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)

Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)

Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)

Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies

temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)

They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely

The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)

What Causes the Hot Spot at the South Pole Is it seasonal effects

ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower

How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped

beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice

A heat source from withinndash Quite possibly The hot spot is located in a recently

resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Figure 2 of Spencer et al (2006)

Mid-IR Data on Enceladus South Pole

(125 to 16 microm)

Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR

detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)

Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)

Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)

Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies

temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)

They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely

The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)

What Causes the Hot Spot at the South Pole Is it seasonal effects

ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower

How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped

beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice

A heat source from withinndash Quite possibly The hot spot is located in a recently

resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Mid-IR Data on Enceladus South Pole The FIR detector has low spatial resolution but MIR

detector made a map with resolution of 25 km from 125 to 16 microm (Fig 2 A and B)

Equatorial regions had 650 cmshy1 brightness temperatures ~77 K in agreement with models of passive solar heating based on thermal inertias and albedos determined from FIR observations (Fig 1)

Surprise near the south pole brightness temperatures reach 85 K (thermal models predicted a temperature of ~68 K assuming zero thermal inertia at the pole because of the oblique angle of Suns rays there)

Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies

temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)

They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely

The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)

What Causes the Hot Spot at the South Pole Is it seasonal effects

ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower

How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped

beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice

A heat source from withinndash Quite possibly The hot spot is located in a recently

resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Mid-IR Data on Enceladus South Pole A greybody fit to the south polar spectrum implies

temperatures of 133 +shy 12 K from ~ 050 shy 18 of the area (Fig 2 C)

They used Monte Carlo simulations to determine the uncertainties in the temperature and area found from the spectral fit (Fig 2 DshyE) Temperatures below 110 K are very unlikely

The spectral fit was used to estimate the total radiated power from the southern hot spot of 58 +shy 19 GW (Fig 2F)

What Causes the Hot Spot at the South Pole Is it seasonal effects

ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower

How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped

beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice

A heat source from withinndash Quite possibly The hot spot is located in a recently

resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

What Causes the Hot Spot at the South Pole Is it seasonal effects

ndash No The season is midway between the southern summer solstice amp fall equinox and a nonzero thermal inertia would cause the temperature to be even lower

How about a solid state greenhouse effectndash Probably not This is where solar radiation gets trapped

beneath the surface amp might make warm gases that could escape along fractures and cause plumes Proposed for Neptunes Triton Good in theory difficult in practice

A heat source from withinndash Quite possibly The hot spot is located in a recently

resurfaced region that has four big troughs (tiger stripes ~130 km long ~500 m deep ~2 km wide from ISS imaging)

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Thermal Emission Associated with Individual Tiger Stripes

Figure 3 of Spencer et al (2006)

Precise locations of hot sources A and B MIR FOV is 175 km for source A and 60 km for source B

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Of Hot Spots and Tiger Stripes During the last 25 hours of the approach to

Enceladus South Pole CIRS pointed where the optical cameras pointed These high spatial resolution observations confirm that the hot spots are associated with individual tiger stripe troughs (Fig 3)

Properties of individual hot spots

Table 2 of Spencer et al (2006)

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

When the stars threw down their spearsAnd watered heaven with their tears

Did He smile His work to seeDid He who made the Lamb make thee

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Plume Hot SpotS and Tiger Stripes Likely that warm tiger stripes are the source of the

dust and vapor plume seen by other Cassini instruments

Assuming

ndash the plume originates from thermal sublimation of warm water ice

ndash this warm ice is visible to CIRS Then using

ndash escape rate = (5shy10)x1027 moleculessecondndash mean south polar radiance at 900 cmshy1 of ~

5x10shy10 W cmshy2strshy1(cmshy1)shy1 Get plume source temperature gt 180 K~

Cassini ISS image of ldquoFountains of Enceladusrdquo Credit NASAJPLSpace Science Institute

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Plume Hot SpotS amp Tiger Stripes

In order to produce the escape rate in the plume a 180 K plume source must have an area of ~ 28 km2 consistent with a 50 m width along each of the four tiger stripes

The 345 km2 area of the south polar hot spots is in agreement with all the hot material being concentrated along the tiger stripes

ndash derive a width of ~660 m (4 stripes x 139 km length x 0660 km width = 343 km2 ) consistent with that derived from high resolution spectra

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

In what funace was thy brain - Possible Heat Sources Radioactive decay The max power from this

assuming a meteor (chondritic = silicate blob) composition for nonshyice material in Enceladus is ~ 01 GW ltlt the 6 GW inferred from observations

Tidal heating may generate 1shy10 GW

ndash Enceladus is in a 21 mean motion orbital resonance with Dione

ndash Enceladus may have been in a 14 spinshyorbit resonance in the past (based on the analysis of Enceladus shape Porco et al 2006) This would have caused strong tidal heating from which Enceladus may still be cooling down

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Tiger Tiger burning brightIn the forests of the night

What immortal hand or eyeDare frame thy fearful symmetry

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

Summary

Cassini CIRS found

ndash Enceladus is generating ~ 6 GW from withinndash at temperatures around 150 K

Comparison with Cassini visual images

ndash most if not all of the heat is concentrated along the tiger stripe troughs

Warm troughs probably source of vapor and dust plumes seen by other Cassini instruments

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

References

ldquoCassini Encounters Enceladus Background and the Discovery of a South Polar Hot Spotrdquo Spencer et al (2006) Science 311 1401

ldquoExploring the Saturn System in the Thermal Infrared the Composite Infrared Spectrometerrdquo Flazar et al (2004) Space Science Reviews 115 169

ldquoCassini Observes the Active South Pole of Enceladusrdquo Porco et al (2006) Science 311 1393

wikipedia article on Enceladus at httpenwikipediaorgwikiEnceladus_(moon)

Cassini home page at httpsaturnjplnasagovhomeindexcfm

The Tiger

Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeCould frame thy fearful symmetry In what distant deeps or skiesBurnt the fire of thine eyesOn what wings dare he aspireWhat the hand dare seize the fire And what shoulder and what artCould twist the sinews of thy heartAnd when thy heart began to beatWhat dread hand and what dread feet

What the hammer what the chainIn what furnace was thy brainWhat the anvil what dread graspDare its deadly terrors clasp When the stars threw down their spearsAnd watered heaven with their tearsDid He smile His work to seeDid He who made the Lamb make thee Tiger Tiger burning brightIn the forests of the nightWhat immortal hand or eyeDare frame thy fearful symmetry

shy William Blake (1757shy1827)

Image Credit NASA

Artists Conception of Enceladus

Image Credit NASA

Artists Conception of Enceladus