ptys/astr 206moons of jupiter and saturn 4/12/07 moons of jupiter and saturn enceladus cassini titan...

PTYS/ASTR 206 Moons of Jupiter and Saturn4/12/07

Moons of Jupiter and Saturn

EnceladusCassini

TitanCassini

IoNew Horizons

EuropaGalileo


Announcements

• Reading Assignment– Chapter 17

• 5th homework due now.– The 6th (and final!) homework is now posted on the

website (due Tuesday, April 24th)

• Reminder about term paper – due April 17.– Details of turnitin.com

• Go to www.turnitin.com• Click on “new users” usertype student• Class ID: 1868418 Password: Section2


Announcements (cont.)

• Mission Updates?

• Next study-group session is Monday, April 16, from 10:30AM-12:00Noon – in room 330.

• Movie Night– Monday April 23rd 6:30PM, this room– Which Movie?

• “Deep Impact” or “The Day After Tomorrow”


Io• The innermost

Galilean satellite

• Looks like a pizza

• The most geologically active body in the solar system.

• Its surface is the youngest in the solar system– no impact craters

are known.

• Io has so many active volcanoes that its surface is repaved completely (to a dept of 1m) every 100 years


Tidal Flexing of Io

• Io suffers extreme tidal flexing because of the competing pulls of its giant planet and its three neighboring moons. – When Io moves inward (toward Jupiter), the tidal deformation

produced by Jupiter increases;– Has ~2.5W/m2 of internal energy (Earth only has 0.06 W/m2)

• In one 41-hour orbit, parts of Io's surface can rise and fall more than 300 feet, the equivalent of a 30-story building. – During these

repeated deformations friction in the interior of the moon generates tremendous amounts of heat.


Io’s active eruptions and lava flows

• Galileo has imaged an active or recent lava flow, still hot as suggested by its orange color. This is the first time a "living" flow has been seen on any other planetary body:


Io’s plasma torus

• Jupiter’s charged particles bombard Io and Io’s volcanic plume ejecting particles into space

• This creates a huge donut-shaped ring of charged particles (mostly sulfur) around Jupiter the size of Io’s orbit

• This can be seen from Earth with special filters

Aurora on Jupiter linked to Io


Europa

• Smallest of the Galilean satellites

• One of the brightest objects in the solar system– Albedo = 0.64

• Very smooth– No mountains (>1 km)

• Few craters

• The spectrum of reflected sunlight off of its surface closely resembles water ice


Europa

• Europa is crisscrossed by numerous fractures and ridges.

• There are also features reminiscent of ice flows

• It is believed that the surface of Europa consists of 10-30km of ice, which lies over a very deep (100-200km) water ocean– Maintained as a liquid because

of energy arising from tidal forces from Jupiter, and other moons

• Europa’s mean density is about 3000 kg/m3. This is considerably higher than water

• Thus, it is mostly made up of rocky silicates. The water and ice make up the outer layers of the moon.


Cycloidal Features on Europa


Liquid water under Europa’s surface

• The cycloidal geologial features were explained by Randy Tufts and Gregg Hoppa of LPL– They are caused by tidal stresses

arising from Jupiter’s moons Io and Ganymede

• Indicates the presence of large liquid ocean underneath a layer of ice

• More direct evidence came from Galileo measurements of an induced magnetic field that is caused by a conducting layer of salty water (brine)


Europa Ridges

• Often made of multiple ridges

• Some aren’t straight

• Not all the same age


Formation of Ridges on Europa


Ice Floes on Europa (and Earth)


Lenticulae

• Local dark regions are probably due to ruddy, warmer ice rising from below

• This indicates a convection process.

• The energy for this is likely due to tidal forces


Ganymede: The Largest Satellite in the Solar System

• It has a larger diameter than Mercury, but only about half its density– Ganymede density ~1.9 g/cm3

• Many surface craters

• The surface is mostly water ice and is characterized by large bright and dark regions (similar to the moon)– Dark areas are more heavily

cratered• OLDER

– Bright areas are less cratered• YOUNGER

(Note that his is opposite to the case of our Moon !)


Geological Activity on Ganymede

• Two types of terrain are found on the icy surface of Ganymede:– areas of dark, ancient, heavily cratered surface (covered with

a layer darker material?)– regions of heavily grooved, lighter-colored, younger terrain

(younger, icy, reflective material?)


Ganymede’s magnetosphere

• Surprisingly, Ganymede has its own magnetic field (and magnetosphere)– It is the only Moon to

have a strong global magnetic field

– Stronger than Mercury’s magnetic field

• Indicates a moving conducting liquid interior

• Possibly left over heat from formation (odd!)

• Possibly due to electromagnetic heating from Jupiter


Callisto: The outermost Galilean Satellite

• Most heavily cratered body in the solar system– Geologically dead– Oldest surface in the solar

system

• Darkest of the Galilean satellites – but still twice as reflective as

our moon!

• Slightly larger than Mercury, but only 1/3 of its mass– Callisto density ~ 1.9 g/cm3


Callisto

• While it has many craters, there are very few with diameters that are smaller than 1 km

– Unlike Ganymede

– This is puzzling since they both should have the same bombardment history

– Probably eroded away (but how?)

• Covered by layer of rusty-colored material

– Not known what this is


Titan(Moon of Saturn)

• Discovered by Christiaan Huygens in 1655.

• 2nd largest satellite in the solar system (only Ganymede is larger)– Larger than Mercury

• Has a thick atmosphere– Higher pressure than Earth at

its surface (more gas) – by about a factor of 1.5

– Only moon in the solar system with a thick atmosphere

• Density is 1.9 g/cm3 (similar to Ganymede and Callisto)– Probably about ½ rock - ½ ice

• Synchronous rotation with Saturn


Titan has a thick, opaque atmosphere richin methane, nitrogen, and hydrocarbons

• Titan’s atmosphere is mostly nitrogen– Ammonia (abundant in the outer

solar nebula) is disassociated by solar UV

– The liberated H2 escapes (weak gravity) leaving N2

• A variety of hydrocarbons are produced in the atmosphere by the interaction of sunlight with methane

• These compounds form an aerosol layer in Titan’s atmosphere– Which leads to the “haze” that

shields Titan’s surface from view– They can also exist in liquid form

on Titan’s surface


Beneath the Haze: Images from the Huygens lander


Titan’s surface

• Visual evidence from Cassini suggests that Titan’s surface is quite young.– it has few craters and possibly even some evidence of

cryovolcanic activity• Titan’s surface has evidence of lakes of liquid methane.


• The lakes may be filled in by precipitation (a)– methane rain!!

• Or they may be filled in from below through a “methane table” below the surface (b)


• The 6 moderate sized moons of Saturn all rotate in prograde orbits close to Saturn’s equator

• They are all in synchronous rotation with Saturn– Tidally locked

• All have low densities (smaller than the Galilean satellites) indicating they are made primarily of ices with very little rock.– Densities < 1.4 g/cm3

More of Saturn’s Moons

Closest to Saturn

Farthest from Saturn


Enceladus• Discovered by William

Herschel (who also discovered Uranus) in 1789

• Density– 1240 kg/m3

• Its albedo is 0.99– The highest of any

object in the solar system

– Reflects nearly all light incident on it!


Cassini images of a “spray” emanating from EnceladusEvidence of liquid water beneath the surface?

Do these particles populate Saturn’s E ring?


The “Tiger Stripes” of Enceladus: Local hot spots


What is the source of the “Fountains of Enceladus” ?

• The water may be liquid lower down and shot out like a geyser.

• How is the interior kept warm? Enceladus is a small moon and its interior should have died long ago.– In fact, its surface is quite

young (less than 100 million years old)

– Possibly heating from tidal forces from the other moons and Saturn (it is in 2:1 orbital resonance with Dione).

ptys/astr 206moons of jupiter and saturn 4/12/07 moons of jupiter and saturn enceladus cassini titan...

Documents

moons of jupiter

io slide

jupiter increases

moons europas

neighboring moons

water ice slide

tidal flexing of io

section2 slide