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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
Homework #8
Total Students: 25
Class Average: 7.6
Low: 4
High: 10
Homework are worth 30% of the grade
Quiz #9
Total Students: 22
Class Average: 2.25
Low: 0
High: 3.5
Quizes are worth 20% of the grade
http://www.youtube.com/watch?v=WHCwgc_xs3s&feature=player_detailpage
Europa’s Induced Magnetic Field
Extra Credit Presentation
Sherlyn Popelka
Edgar Granados
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…
Enceladus Small satellite, only 500
km in diameter
Mean density: 1609 kg/m3
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
Enceladus is imbedded in the
E-ring(E-ring is densest around the orbit of Enceladus)
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
Enceladus Surface Temperature
• Energy for geologic activity is not coming from the Sun...
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!)
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
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
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 (Na2CO3)
-Salt lowers the melting temperature of ice-Carbonates suggest that liquid water was in contact with C-bearing rocks
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
Ice along cracks may sublime, venting water vapor and icy
particles
What Process Creates the Plume?Subsurface salty ocean
(or lake)
“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
Cassini Measurements
Cassini detected simple organics in the “tiger stripes“ (sources of Enceladus geysers) including CO2, CH4, C2H6 (ethane) and C2H6 (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
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 CO2, CH4, C2H6 (ethane) and C2H6 (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 forthe origin and evolution of life
Triton
Largest satellite of Neptune
2700 km diameter (7th largest moon in the SS)
Mean density: 2061 kg/m3
Retrograde orbit, synchronous rotation, high axial tilt
Mean surface T ~ 38K
Voyager 2 Flyby 1989
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
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…
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)
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…
Mars• Evidence for surface water
in the past• Are recent gullies formed
by subsurface water seepage?
• Nutrients, carbon, and solar energy are available
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…
Io• Surface temperatures are too hot, even for thermophiles
• No atmosphere to protect it from Jupiter’s radiation
• Very inhospitable to life
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
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?)
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
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!