1. PTYS 214 – Spring2011  Homework #10 available for download on the class website DUE on Thursday, Apr. 21  Class website: http://www.lpl.arizona.edu/undergrad/classes/spring2011/Pierazzo_214 /  Useful Reading: class website  “Reading Material” http://en.wikipedia.org/wiki/Enceladus_(moon) http://en.wikipedia.org/wiki/Extrasolar_planet Announcements

2. Homework #8  Total Students: 25  Class Average: 7.6  Low: 4  High: 10 Homework are worth 30% of the grade

3. Quiz #9  Total Students: 22  Class Average: 2.25  Low: 0  High: 3.5 Quizes are worth 20% of the grade

4. http://www.youtube.com/watch?v=WHCwgc_xs3s&feature=player_detailpage Europa’s Induced Magnetic Field

5. Extra Credit Presentation Sherlyn Popelka Edgar Granados

6. Moons of Saturn Saturn has 61 confirmed satellites most of which quite small Enceladus is the 4th largest, and revealed some surprises during Cassini flybys…

7. Enceladus  Small satellite, only 500 km in diameter  Mean density: 1609 kg/m 3  Synchronous rotation  Highest albedo in the Solar System: almost 100% of the light that reaches it is reflected!  Surface temperature ranges from 33K to >150K mean surface T ~ 75K

8. Enceladus is imbedded in the E-ring (E-ring is densest around the orbit of Enceladus)

9. Enceladus Surface Geologically it is very active! - Heavily cratered regions, very old in the northern regions - Tectonically deformed regions as young as 100 million years old (mostly in the southern regions) Cassini image

10. Enceladus Surface Temperature Energy for geologic activity is not coming from the Sun...

11. Enceladus South Pole  In the Southern polar region, craters are rare  Surface is covered by fractures, folds, and ridges (remarkable tectonic activity for a relatively small world)  Temperature in the ‘Tiger Stripes’ can as high as than180K (much warmer than anywhere else on the surface) “Tiger stripes” T (K) 21 Sep. 2009 (15 m resolution!)

12. Geysers on Enceladus! At least 8 icy plumes have been identified by Cassini along surface fractures in the south polar region Cassini image – Nov. 2005 Liquid material sprayed directly into space Discharge rates are similar to those of Old Faithful geyser in Yellowstone National Park!  Geyser locations

13. What is ejected by the geysers?: Plume March 2008: Cassini flew through the S. pole’s plume -Plume composition is similar to comets! - no sodium found in plume July/Oct. 2008 flybys: Ammonia detected in plume

14. What is ejected by the geysers?: Grains Dec. 2009: New data shows that at least 50% of plume is ice grains -Supports liquid water erupting into space and freezing (but controversial!) Observations of E-ring ice grains -Sodium rich: salts (NaCl) and carbonates (Na 2 CO 3 ) -Salt lowers the melting temperature of ice -Carbonates suggest that liquid water was in contact with C- bearing rocks

15. Enceladus Heat Source Tidal heating may be sustaining ‘hot spots’ in its interior, causing the surface geological activity Today, there is one hot spot right under Enceladus South Pole

16. Ice along cracks may sublime, venting water vapor and icy particles What Process Creates the Plume? Subsurface salty ocean (or lake)

17. “Perrier Ocean” Hypothesis (Oct. 2010) - gases dissolved in the water lower liquid water density - as water rises, dissolved gases expand and exsolve - gas + water mixture breaks through the ice layer and escapes as a plume

18. Cassini Measurements  Cassini detected simple organics in the “tiger stripes“ (sources of Enceladus geysers) including CO 2, CH 4, C 2 H 6 (ethane) and C 2 H 6 (ethylene)  Water vapor detected in the geysers contains ammonia  Ice grains in E-ring contain salt and carbonates  There is evidence supporting the view that Enceladus has active hydrological, chemical and geochemical cycles

19. Enceladus and life?  Tidal heating may be low but it provides a continuous source of energy  Simple organics in the “tiger stripes“ (sources of Enceladus geysers) including CO 2, CH 4, C 2 H 6 (ethane) and C 2 H 6 (ethylene)  Na has been detected in the E-ring (formed by Enceladus… Support for a subsurface ocean, a.k.a. liquid water? These are all important ingredients for the origin and evolution of life

20. Triton  Largest satellite of Neptune  2700 km diameter (7 th largest moon in the SS)  Mean density: 2061 kg/m 3  Retrograde orbit, synchronous rotation, high axial tilt  Mean surface T ~ 38K Voyager 2 Flyby 1989

21. Triton  Nitrogen and methane ice surface  Few impact craters: 6-50 Ma surface age  Geyser eruptions of N gas from solar heating?  Cryovolcanism with ammonia-water lava?  Flat plains from eruptions  Ridges from tidal flexing

22. Triton and life?  Tidal heating or radiogenic heating from core could melt ice to form a subsurface ocean  Cryovolcanism suggests ammonia is present and lowers the melting temperature of ice  Support for a subsurface ocean, a.k.a. liquid water? No missions have gone to Neptune/Triton since Voyager 2, so it might have more surprises…

23. Recap: Where are we most likely to find life in our Solar System? No environments just like Earth's: all other solar system environments are “extreme” to life (but Earth’s “extreme” could be “normal” somewhere else)

24. Mars may have regions in its deep subsurface permafrost that could harbor endolith communities On Europa, the subsurface water ocean may harbor life, especially at the hypothesized hydrothermal vents at the ocean floor. Venus ’ stable cloud layers, 50 km above the surface, have hospitable climates and chemical disequilibrium, fueling speculations that microbes could live there On Titan, data from Cassini/Huygens suggest a near-surface chemistry consistent with the hypothesis that organisms may be consuming hydrogen, acetylene and ethane, to produce methane (but this is not proof) Earth’s ‘Extreme’ is ‘Normal’ Somewhere Else…

25. Mars Evidence for surface water in the past Are recent gullies formed by subsurface water seepage? Nutrients, carbon, and solar energy are available

26. Venus Surface temperatures are too hot, even for thermophiles Cloud layers might be cooler and harbor acidophiles No water or water vapor makes things difficult…

27. Io Surface temperatures are too hot, even for thermophiles No atmosphere to protect it from Jupiter’s radiation Very inhospitable to life

28. Europa Cold surface temperature and no atmosphere to protect it from Jupiter’s radiation Induced magnetic field  subsurface ocean! (probably due to tidal heating and ammonia in water) Surface features suggest shallow ice layer Life could be possible IF there’s an energy source and nutrients

29. Ganymede, Callisto, Triton All have cold temperatures and high surface radiation Need a subsurface ocean protected by ice… … but not so much ice that life can’t get energy or nutrients (geothermal vents?)

30. Titan Nutrients available and water ice at the surface Methane imbalance suggests production Young, active surface with volcanoes, lakes, evidence for flowing liquid, but the surface is cold No direct evidence for life, but researchers are experimenting with life inTitan-like environments

31. Enceladus Young surface with tidal heating energy Evidence of liquid water in the subsurface Ammonia, salts, nutrients have been observed Surprisingly good conditions for such a small moon!