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Download Saturn`s Titan
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Homework 9 is due Tuesday, Nov. 23, 5:00 pm Enceladus Titan Titan Titan Huygens spacecraft landed on surface Cassini spacecraft has made several close flybys 2nd largest moon Only moon with a substantial atmosphere Saturn’s Titan atmosphere denser than Earth’s but very cold (100K) and composed mostly of N2 and methane (CH4) Completely enshrouded in smoglike clouds 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 Thick atmosphere with photochemical hydrocarbon “smog” Hubble view at wavelengths that penetrate atmosphere 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/cm3 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 130-300 Myr old – Tectonics: thin features for hundreds of miles • Cryo-volcano: – 30 km volcano observed on Titan, including caldera inside – Magma would be mainly CH4 & H2O – 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: 180C (-290F) • Composition: 9298% N2 + 26% methane (CH4) • Constantly smoggy: UV breaking up CH4 into radicals • Radicals combine to form complex hydrocarbons: C2H6, C2H2, HCN, C6H6 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 (NH3), methane (CH4) & ethane (C2H6) 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. • NH3 (ammonia) broken up by UV radiation into N2 and H2. H2 escaped, and N2 stayed behind • Expect similar process for CH4 (methane) • CH and CH2 products of CH4 breakup help form larger organic molecules, e.g., C2H6 • Why are we still seeing CH4? – Possible reservoir of CH4 and/or C2H6. – Rain or drizzle of CH4 and/or C2H6 CH4C2H6 Ocean? • Cassini: no global ocean, but many (relatively) small lakes, and observed a number of clouds River gully? Coastline? Hydrocarbon lakes Cold Life? • Liquid methane - ethane (CH4C2H6): – 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 CH4C2H6 lakes and the surface – Comet or asteroid impacts can create pockets of water lasting thousands of years? – Underground water ocean heated by radioactivity? ? Enceladus Enceladus is small It was not considered a moon of particular interest, until this image was obtained by Cassini Saturn’s Enceladus 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? Uranus Neptune anything of interest? Named moons of Uranus Cordelia Ophelia Bianca Cressida Desdemona Juliet Portia Rosalind Belinda Puck Miranda Ariel Umbriel Titania Oberon Caliban Sycorax Prospero Setebos Stephano Trinculo 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 Triton – 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 (10100 Myr) • Pluto and remaining moons – Too cold and too small – But, amino acids seen in meteorites Time to reach for the stars!
