Cassini Radio Occultation of Saturn's Rings and Atmosphere: Preliminary Results

for the Cassini Radio Science Team

Cassini CHARM PresentationMay 31, 2005

Essam Marouf & Richard French

Twelve Main Cassini Science Instruments

• Microwave Remote Sensing– Radio Science Subsystem (RSS)

– Cassini Radar (RADAR)

• Optical Remote Sensing (ORS)

– Composite Infrared Spectrometer (CIRS)

– Imaging Science Subsystems (ISS)

– Ultraviolet Imaging Spectrograph (UVIS)

– Visual and Infrared Mapping Spectrometer (VIMS)

• Fields, Particles, and Waves– Cassini Plasma Spectrometer (CAPS)

– Cosmic Dust Analyzer (CDA)

– Dual Technique Magnetometer (MAG)

– Ion and Neutral Mass Spectrometer (INMS)

– Magnetospheric Imaging Instrument (MIMI)

– Radio & Plasma Wave Science (RPWS)

To the Deep Space Network (DSN) - Atomic Frequency Standard - X, S: 70 m - Ka, X: 34 m BWGThree Sinusoids Coherent in Phase

(Crystal Oscillator-- USO)

(cm) Pt (W) SNR (dB-Hz)KaX 3.6 19 51S10

€

Δff

~ 10−13

€

Δff

~ 10−14

From Cassini

Goldstone, CA: 70 m

Radio Science Subsystem (RSS): Downlink Configuration

Downlink

Cassini RSS

DSN

S/CSaturn

Downlink Configuration is Used to Conduct:

2- Ring Occultations

3- Bistatic-Scattering From Titan’s Surface

1-Atmospheric / Ionospheric Occultations of Saturn and Titan

From S/C

To DSN

TitanCassini RSS

Hubble Space Telescope

French et al., 2003

Cassini Orbital Tour of the Saturn System

75 Saturn Orbits; 45 Titan Encounters(July 1, 2004 to June 30, 2008)

D. Seal, 2004

Typical Ring Occultation Track Geometry (15 m tick-marks)

(rev 7) 2005 MAY 3,

-23.6, 21.9, 5

(rev 44) 2007 MAY 10,

-15.2, 39.1, 8.3

(rev 46) 2007 JUN 11,

-14.4, 18.4, 5.3(rev 63) 2008 APR 1,

-9.6, 63.8, 6.5

(rev 7) 2005 MAY 3,

-23.6, 21.9, 5

(rev 44) 2007 MAY 10,

-15.2, 39.1, 8.3

(rev 46) 2007 JUN 11,

-14.4, 18.4, 5.3(rev 63) 2008 APR 1,

-9.6, 63.8, 6.5

Occultation Sequence: revs 7 to 14 180° Transfer Sequence: revs 44, 46

High Inc Sequence Orbits 56 to 67

20° ≤ B ≤ 24° B ~ 15°

6 ≤ B ≤ 10°

Rev 7 Rev 44

Rev 46 Rev 63

Cassini RSS

2004 2004.5 2005 2005.5 2006 2006.5 2007 2007.5 2008 2008.5 20090

5

10

15

20

25

30

7

13

28

44

46

53

67

B

I / I0 =exp[− / (sin B)]

/ (sin B) =2.6, ., .6

Cassini Tour

Year

|Rin

g-O

peni

ng-A

ngle

| (|B

°|)

Catching the Open Rings

14

I0

I

Rev 7 Occultation Track

Cassini RSS

04:23 21:23

BL

03:53 ERT 20:53 PDT

06:00 23:00

06:40 23:40

08:00 01:00

08:32 01:32

10:06 03:06

10:36 03:36

10 m

Rev 7 Radio Occultation Track: May 2-3, 2005

View From the Earth

BL

06:50 G: DSS 14, 25, 26

Live Moveable Block (LMB)

11:10 C: DSS 43, 34 02:45

ERT UTC PT

ingress

egress

Cassini

Cassini RSS

* Water-Ice Ring Particles

*Millimeters to Several Meters Main Size Population

Artist Conception!

* Tens of meters thick

B

Direct, or Coherent, Signal

Scattered SignalObservables

• Direct Signal – radial ring structure

– Particle sorting by size

– Thickness of ring edges

• Scattered Signal– Particle size distribution

– Vertical ring profile

– Particle packing and clustering

– Physical ring thickness

Cassini RSS

Direct Signal

Scattered Signal

Cassini ISS

Voyager RSS

I0

I0 esin(B)

Saturn’s Rings

Radio Occultation: Profiling of Radial Ring Structure

Planet Saturn and its Remarkable Ring System(~300,000 km across; ~distance from the Earth to the Moon )

Hubble Space Telescope

Ring C

Ring B

RingA

Cassini Division

Cassini ISS

Rings Structure

Ring F

Saturn’s Inner and Outer Ring C

Cassini ISS

Cassini ISS

Interesting Ring Structure Exists at Every Spatial Scale

Inner Ring C

4 km res

- Colombo Gap

- Titan Ringlet

- W-Features

200 m res

Titan -1:0 Bending Wave

1500 km

OP

AC

ITY

,

[3

.6]

SIG

NA

L L

OS

S (

dB

)

125 km

100 m resolution is not luxury !

Voyager RSS

Fresnel Diffraction by the Inner Edge of the Encke Gap

Voyager RSS

Voyager ISS

Observations are Diffraction-Limited

-W /2 W /2

F = 15 kmΔR = 200 m

OHolographic ReconstructionFinite Observation Interval W (km); T (sec)

Signal phase must remain stable over T

ΔR =2F2

W

FresnelScale:

F ~ DObservationInteval:

T =W /VSC

Radius (km)Voyager RSS

Ring F Example

101 102 1030

0.5

1

1.5

2

2.5

3

3.5

4

Radial Resolution Δ ( )R m

-X Band

SNR=5dB

- : =2Cassini I B deg

- : =5Cassini II B deg

- : =6Cassini III B deg

Voyager

Resolution ΔR (m)

ΔR = 100 m

Thr

esho

ld O

ptic

al D

epth

TH

(SN

R=

1)

B

Cassini RSS: Achievable Radial Resolution

Cassini RSS

Density Waves Bending Waves

Narrow Eccentric Ringlets

Mimas 5:3

Voyager RSS

Opt

ical

Dep

th,

[3

.6]

Sig

na

l Lo

ss (

dB

)

Uranus’ Ring

Occultations at Multiple Longitudes: Dynamical Ring Structure

Encke Gap

Pan’s Wake

Cassini ISS

Voyager RSS

Occultations at Multiple Longitudes: Detection of Embedded Satellites

Cassini Rev 7: Optical Depth Profiles of Ring C (X, 10 km Res)

Cassini RSS

Cassini Rev 7: Optical Depth Profiles of Ring C, S/X/Ka (R/G/B)

Cassini RSS

Cassini Rev 7: Optical Depth Profiles of Ring B (X, 10 km Res)

Cassini RSS

Cassini Rev 7: Optical Depth Profiles of Ring B, S/X/Ka (R/G/B)

Cassini RSS

Cassini Rev 7: Optical Depth Profile of Ring A (X, 10 km Res)

Cassini RSS

Cassini Rev 7: Density Waves in Outer Ring A (Ka, 1.4 km Res)

Cassini RSS

Cassini Rev 7: Optical Depth Profiles of Ring A, S/X/Ka (R/G/B)

Cassini RSS

Small Particles in Ring A (PIA07875)

Cassini RSS

Radio Occultation: Unraveling Saturn’s Rings (PIA07873)

Cassini RSS

Multiple Eyes of Cassini (PIA07874)

http://photojournal.jpl.nasa.gov/catalog/PIA07873•http://photojournal.jpl.nasa.gov/catalog/PIA07872•http://photojournal.jpl.nasa.gov/catalog/PIA07875•http://photojournal.jpl.nasa.gov/catalog/PIA07960•http://photojournal.jpl.nasa.gov/catalog/PIA07874

B

Direct, or Coherent, Signal

Scattered SignalObservables

• Direct Signal – radial ring structure

– Particle sorting by size

– Thickness of ring edges

• Scattered Signal– Particle size distribution

– Vertical ring profile

– Particle packing and clustering

– Physical ring thickness

Direct Signal

Scattered Signal

Cassini RSS

Scattered Signal:

Doppler Contours

Cassini RSS

Scattered Signal:

Meter-Size “Particles”

amax = 3, 5, 10 m

F (kHz)

Cassini RSS

Cassini Rev 7: Outer Ring B Direct & Scattered Signals

Cassini RSS

04:23 21:23

BL

03:53 ERT 20:53 PDT

06:00 23:00

06:40 23:40

08:00 01:00

08:32 01:32

10:06 03:06

10:36 03:36

10 m

Rev 7 Radio Occultation Track: May 2-3, 2005

View From the Earth

BL

06:50 G: DSS 14, 25, 26

Live Moveable Block (LMB)

11:10 C: DSS 43, 34 02:45

ERT UTC PT

ingress

egress

Cassini

Cassini RSS

TITAN EXTENDED ATMOSPHERE

Cassini ISS

Atmospheric Limb-Track Maneuver

“Actual” Earth

“Virtual” Earth “Apparent” Line of Sight

Geometric Line of Sight

Refracted Ray Path

Saturn or TitanVirtual

Actual

Adapted from D. Wait 05/07/04

RSS Saturn Atmosphere

Ka-band Power AttenuationS07 Entry

Time SPM UTC-ERT May 3 2005

21300 21400 21500 21600 21700 21800 21900

Pwer Loss dB

-50

-40

-30

-20

-10

0

10

Ka-band DSS26

Sig

nal L

evel

(dB

)

Cassini RSS

Ka-band Power AttenuationS07 Entry

Time SPM UTC-ERT May 3 2005

21300 21400 21500 21600 21700 21800 21900

Pwer Loss dB

-50

-40

-30

-20

-10

0

10

Ka-band DSS26Ka-band DSS25Ka-band DSS34

Sig

nal L

evel

(dB

)

RSS Saturn Atmosphere

Cassini RSS

X-band Power AttenuationS07 Entry

Time SPM UTC-ERT May 3 2005

21200 21400 21600 21800

Pwer Loss dB

-50

-40

-30

-20

-10

0

10

X-band DSS14

AJK 05/06/2005

Sig

nal L

evel

(dB

)

RSS Saturn Atmosphere

Cassini RSS

X-band Power AttenuationS07 Entry

Time SPM UTC-ERT May 3 2005

21200 21400 21600 21800

Pwer Loss dB

-50

-40

-30

-20

-10

0

10

X-band DSS14X-band DSS25X-band DSS26X-band DSS34X-band DSS43

AJK 05/06/2005

Sig

nal L

evel

(dB

)

RSS Saturn Atmosphere

Cassini RSS

Tri-band Power AttenuationS07 Entry

Time SPM UTC-ERT May 3 2005

21200 21400 21600 21800 22000

Pwer Loss dB

-50

-40

-30

-20

-10

0

10

S-band DSS14

AJK 05/06/2005

Sig

nal L

evel

(dB

)

RSS Saturn Atmosphere

Cassini RSS

Tri-band Power AttenuationS07 Entry

Time SPM UTC-ERT May 3 2005

21200 21400 21600 21800 22000

Pwer Loss dB

-50

-40

-30

-20

-10

0

10

S-band DSS14X-band DSS14Ka-band DSS26

AJK 05/06/2005

Sig

nal L

evel

(dB

)

RSS Saturn Atmosphere

Cassini RSS

Are Saturn’s Winds Changing?

0- 15 -30

100

10

1

Laitude

100125150175200

225

250

275

275

300

325

350

0- 30 -60

100

10

1

Latitude

90

90

95

95

100

100

105

105

110

110

115120 125

130135

140

140

145

145

150155

Latitude–

250 km

Zonal winds: u (m/s)

Winds derived from the thermal wind equation showstrong vertical decay at low latitudes, but the cloudsobserved by HST & Cassini/ISS would have to be >130 km above those seen by Voyager if changing cloudheights explain the changes in observed wind speeds.

Cassini/CIRS: Flasar et al. (2005)

Cloud tracking by HST and Cassini ISSsuggests that Saturn’s equatorial windshave changed or the cloud tops have changed.

Vgr(1980-81)

HST(1996-2002)

CH4 cont.Cassini ISS (2004)

Porcoet al. (2005)

RSS Saturn Ionosphere

Entry Ionosphere Data

Time SPM May 3 2005

20600 20800 21000 21200 21400

Frequency Residual Hz

-0.10

-0.05

0.00

0.05

0.10

DSS 14 S/X

Fre

quen

cy R

esid

ual H

z

Cassini RSS

S07 Ionosphere

Electron Density cm-3

10 100 1000 10000

Altitude (1 bar) km

0

1000

2000

3000

4000

5000

6000

S/X DSS14-entryX/K DSS25-entry

SZA 84o 94o

Lat 7.2 S 9.2 S

AJK 05/20/2005

entry exit

dawn dusk

PIO 11 entryLat=10

o S

SZA= ~ 90o

(exit similar)

Model(Waite and Cravens, 1987)

VGR2 NLat=35

o NVGR2 X

Lat=31o S

Alt

itud

e (1

bar)

km

RSS Saturn Ionosphere

Cassini RSS

Exit Ionosphere Data

Time SPM May 3 2005

30200 30400 30600 30800

Frequency Residual Hz

-0.10

-0.05

0.00

0.05

0.10

DSS 43 S/X

Fre

quen

cy R

esid

ual H

z

RSS Saturn Ionosphere

Cassini RSS

S07 Ionosphere

Electron Density cm-3

10 100 1000 10000

Altitude (1 bar) km

0

1000

2000

3000

4000

5000

6000

S/X DSS14-entryX/K DSS25-entryX/K DSS34-exitS/X DSS43 -exit

SZA 84o 94o

Lat 7.2 S 9.2 S

AJK 05/20/2005

entry exit

dawn dusk

PIO 11 entryLat=10

o S

SZA= ~ 90o

(exit similar)

Model(Waite and Cravens, 1987)

VGR2 NLat=35

o NVGR2 X

Lat=31o S

Alt

itud

e (1

bar)

km

RSS Saturn Ionosphere

Cassini RSS

Scientific Objectives: Ring Occultations

• To profile radial ring structure with resolution ≤ 100 m; characterize structure variability with azimuth, wavelength, ring-opening-angle, and time

• To determine physical particle properties (size distribution, bulk density, surface density, thickness, viscosity)

• To study ring kinematics and dynamics (morphology, interaction with embedded and exterior satellites), and to investigate ring origin and evolution

Cassini RSS

- Determine the global fields of temperature, pressure, and winds in the stratosphere and troposphere of Titan and Saturn

- Determine the small scale structure due to eddies and waves

- Constrain the distribution of methane in Titan’s atmosphere

- Improve the H2/He ratio in Saturn's troposphere- Determine the variations in NH3 abundance in Saturn’s

atmosphere- Search for Titan’s ionosphere; interaction with

Saturn’s magnetosphere- Study the behavior of Saturn’s ionosphere with latitude

and solar zenith angle; investigate its interaction with rings and magnetosphere

Scientific Objectives: Atmospheric/Ionospheric Occultations:

Cassini RSS

Cassini Radio Science Team• NASA/JPL

– Arvydas Kliore (TL)

– Nicole Rappaport (DTL)

– John Anderson

– John Armstrong

• NASA/Goddard– Mike Flasar

• US Universities– Richard French (Wellesely College)

– Essam Marouf (San Jose State University)

– Andrew Nagy (University of Michigan)

• Italy– Roberto Ambrosini (Istituto di Radioastronomia, Bologna)

– Luciano Iess (Universita’ di Roma, Roma )

– Paolo Tortora