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!