Homework 9 is due Tuesday, Nov. 23, 5:00 pm

Titan Enceladus

Titan

 Huygens spacecraft landed on surface  Cassini spacecraft has made several close flybys  2 nd largest moon  Only moon with a substantial atmosphere

Saturn’s Titan denser than Earth’s 100K  atmosphere denser than Earth’s but very cold (100K) and composed mostly of N 2 and methane (CH 4 ) smog- like clouds  Completely enshrouded in smog- like clouds  Methane  Methane acts like water (liquid).  Few craters on the surface.  Surface eroded by liquids  Methane/Ethane lakes

View from Cassini Spacecraft during Flyby

Huygens Probe

On the surface! “Rocks” of ice?

View from Huygens Spacecraft during descent to surface

Sunlit side Looking through the atmosphere Hubble view at wavelengths that penetrate atmosphere Thick atmosphere with photochemical hydrocarbon “smog”

Physical Characteristics Size –Among moons, second only to Ganymede (measured by surface, not atmosphere) Mass –Almost double that of our Moon –Density: 1.9 gm/cm 3  equal mixture of rock and ice –Thought to be differentiated: rocky core of silicates with a crust of water ice

Surface Gross features: –Few impact craters  surface Myr old –Tectonics: thin features for hundreds of miles Cryo-volcano: –30 km volcano observed on Titan, including caldera inside –Magma would be mainly CH 4 & H 2 O –Energy?: tidal heating or radioactivity Erosion: –Huygens saw round ice pebbles –Sinuous channels: liquids –East-west dunes near equator with sharp western boundaries: super-rotating winds

Dunes Earth Titan

Possible Earthlike Processes Tectonics Weather, including rain (methane) Erosion by winds and liquids Formation of complex organic compounds Greenhouse effect Volcanism (molten water, not rock) But: all at a much lower temperature

Atmosphere Pressure: 1.5 bar Surface temperature:  C (-290  F) Composition: 92  98% N  6% methane (CH 4 ) Constantly smoggy: UV breaking up CH 4 into radicals Radicals combine to form complex hydrocarbons: C 2 H 6, C 2 H 2, HCN, C 6 H 6

Why does Titan have an atmosphere while the larger Ganymede does not? At Saturn’s distance from the Sun, the protosolar nebula was much colder that at Jupiter. Ammonia (NH 3 ), methane (CH 4 ) & ethane (C 2 H 6 ) ices could condense at Saturn’s distance, but not at Jupiter, where only water ices condensed. Moons formed at Saturn could have significant amount of methane, ethane, ammonia - this provided molecules for UV interactions to form atmosphere Comets and asteroids hit at a smaller velocity (~ half the energy), so collisional losses were smaller.

NH 3 (ammonia) broken up by UV radiation into N 2 and H 2. H 2 escaped, and N 2 stayed behind Expect similar process for CH 4 (methane) CH and CH 2 products of CH 4 breakup help form larger organic molecules, e.g., C 2 H 6 Why are we still seeing CH 4 ? –Possible reservoir of CH 4 and/or C 2 H 6. –Rain or drizzle of CH 4 and/or C 2 H 6  CH 4  C 2 H 6 Ocean? Cassini: no global ocean, but many (relatively) small lakes, and observed a number of clouds

Hydrocarbon lakes River gully? Coastline?

Cold Life? Liquid methane - ethane (CH 4  C 2 H 6 ): –Chemical reaction rates orders of magnitude slower –Poorer solvents than water –No density anomaly: liquids freeze completely –But it’s a liquid Saving graces: –UV forms organic molecules in the upper atmosphere, which sink to the CH 4  C 2 H 6 lakes and the surface –Comet or asteroid impacts can create pockets of water lasting thousands of years? –Underground water ocean heated by radioactivity?

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Enceladus

Enceladus is small

It was not considered a moon of particular interest, until this image was obtained by Cassini

Saturn’s Enceladus 500 km  Small icy moon (500 km) in diameter  Young, crater-free surface regions with like those on Europa  Orbit resonance with Dione  South polar hot spot and ice plumes  Thin “atmosphere” of water vapor  Subsurface ocean!?

“tiger stripes”

Ice Plumes from Enceladus Area of plumes is much warmer than surroundings - evidence of subsurface reservoir of liquid water

Liquid water + energy source + chemicals life?

Neptune Uranus anything of interest?

Ariel Umbriel Titania Oberon Caliban Sycorax Prospero Setebos Stephano Trinculo Cordelia Ophelia Bianca Cressida Desdemona Juliet Portia Rosalind Belinda Puck Miranda Named moons of Uranus

Moons of Uranus No large moons, nothing of particular interest as far as the search for life

Moons of Neptune One location of interest

Neptune’s TritonNeptune’s Triton < 40K icy volcanism. –Extremely cold (< 40K) objects made from volatile materials produce icy volcanism. –Huge geysers of nitrogen! –Pluto and the Kuiper Belt Objects may look and act similarly.

Very unlikely location for life

Solar system beyond Saturn Decline of probability of life –Main factor is temperature –Europa  Ganymede  Callisto  Titan  Enceladus ? Triton –Retrograde rotation  capture –Uneven surface: Cantaloupe terrain, Smooth parts, Frost deposits?, Wind streaks –Few impact craters  recent geological activity (10  100 Myr) Pluto and remaining moons –Too cold and too small –But, amino acids seen in meteorites

Time to reach for the stars!