1. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 Moons of Jupiter and Saturn Enceladus Cassini Titan Cassini Io New Horizons Europa Galileo

2. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 Announcements Reading Assignment –Chapter 17 5 th homework due now. –The 6 th (and final!) homework is now posted on the website (due Tuesday, April 24 th ) Reminder about term paper – due April 17. –Details of turnitin.com Go to www.turnitin.comwww.turnitin.com Click on “ new users ” usertype  student Class ID: 1868418 Password: Section2

3. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 Announcements (cont.) Mission Updates? Next study-group session is Monday, April 16, from 10:30AM-12:00Noon – in room 330. Movie Night –Monday April 23 rd 6:30PM, this room –Which Movie? “ Deep Impact ” or “ The Day After Tomorrow ”

4. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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

5. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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/m 2 of internal energy (Earth only has 0.06 W/m 2 ) 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.

6. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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:

7. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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

8. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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

9. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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/m 3. 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.

10. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 Cycloidal Features on Europa

11. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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)

12. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 Europa Ridges Often made of multiple ridges Some aren’t straight Not all the same age

13. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 Formation of Ridges on Europa

14. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 Ice Floes on Europa (and Earth)

15. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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

16. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07

17. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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/cm 3 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 !)

18. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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?)

19. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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

20. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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/cm 3

21. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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

22. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 Titan (Moon of Saturn) Discovered by Christiaan Huygens in 1655. 2 nd 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/cm 3 (similar to Ganymede and Callisto) –Probably about ½ rock - ½ ice Synchronous rotation with Saturn

23. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 Titan has a thick, opaque atmosphere rich in methane, nitrogen, and hydrocarbons Titan’s atmosphere is mostly nitrogen –Ammonia (abundant in the outer solar nebula) is disassociated by solar UV –The liberated H 2 escapes (weak gravity) leaving N 2 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

24. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 Beneath the Haze: Images from the Huygens lander

25. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07

26. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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.

27. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07

28. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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)

29. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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/cm 3 More of Saturn’s Moons Closest to Saturn Farthest from Saturn

30. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 Enceladus Discovered by William Herschel (who also discovered Uranus) in 1789 Density –1240 kg/m 3 Its albedo is 0.99 –The highest of any object in the solar system –Reflects nearly all light incident on it!

31. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 Cassini images of a “spray” emanating from Enceladus Evidence of liquid water beneath the surface? Do these particles populate Saturn’s E ring?

32. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 The “Tiger Stripes” of Enceladus: Local hot spots

33. PTYS/ASTR 206Moons of Jupiter and Saturn 4/12/07 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).