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AST 248, Lecture 21
James Lattimer
Department of Physics & Astronomy449 ESS Bldg.
Stony Brook University
December 2, 2018
The Search for Intelligent Life in the [email protected]
James Lattimer AST 248, Lecture 21
www.nineplanets.orgJames Lattimer AST 248, Lecture 21
TitanI Only moon with dense atmosphere, 1.5 Earth’sI Saturn’s largest satellite, # 2 in Solar SystemI Spin is tidally locked with SaturnI In a 3:4 orbital resonance with HyperionI Atmosphere’s existence a result of relatively
cold formation temperature and high gravityI Major gases are N2 (98.4%), CH4 (1.6%), ArI a high smog (hydrocarbon, tholin) layerI Lack of noble gases Kr, Xe and Ne suggest
atmosphere formed as a result of outgassingrather than by cometary impacts.
I Haze results in anti-greenhouse effect, cooling;haze is opaque in visibile, but clear in infrared.
I Methane (CH4) is present and must bereplenished, indicating volcanos or lakesof methane or ethane (C2H6).
I Cassini probe mapped surface in 2004.I Surface temperature is 94 K, methane
rain may existI Surface is complex, fluid-processed and
young (H2O and NH3 volcanos?)
Haze
James Lattimer AST 248, Lecture 21
Titan’s Interior
NASA
Evidence for H2O-NH3
sub-surface ocean from
ELF (extremely long
frequency) radio waves
3400 km radius rocky
core surrounded by
several ice layers
Ammonia (NH3) lowers
H2O freeezing point
Systematic shifts of surface
implies crust floats on an
ocean
James Lattimer AST 248, Lecture 21
Titan’s Climate
NASACH4
Methane rains and
ethane snows onto
poles in winter
and evaporate
during summer.
Titan’s year is 30
Earth-years long.
James Lattimer AST 248, Lecture 21
Hydrocarbon lakes
James Lattimer AST 248, Lecture 21
Titan’s Surface
NASA
James Lattimer AST 248, Lecture 21
Titan’s Volcanoes and Lakes
Cryovolcano Sotra Facula
Cryovolcano Tortula Facula
James Lattimer AST 248, Lecture 21
Life on Titan?I Conditions on Titan might be suitable for
some terrestrial psychrophiles, which utilizeorganic chemicals for both food and energy.
I Some key elements are liquid reservoirs,organic molecules and energy sources.
I Ultraviolet light reacting with nitrogen andmethane produces hydrocarbons, visible asorange smog, which fall onto Titan’s surface.
I Large organic molecules (tholins) with atomic weights up to 10,000have been found in Titan’s high atmosphere, and are possiblyresponsible for the haze.
I Natural forces, such as shifting continental plates, wind erosion,lakes of ethane and methane, and volcanos, can alter the landscape.
I There may exist hot springs connnected to hydrocarbon reservoirs.I Possible life could produce energy by mixing acetylene (C2H2),
abundant in Titan’s atmosphere, with hydrogen.I Coldness an impediment, however, with −180◦ C surface making
chemical reactions sluggish at best. Subsurface temperatures in theliquid water layer could be much warmer (−73◦ C).
I Early Titan was warmer, due to radioactivity and warmer Saturn.I In future, as Sun warms and brightens, temperatures will increase,
reaching −70◦ C when the Sun becomes a red giant.James Lattimer AST 248, Lecture 21
EnceladusI Small size, but geologically active
I Surface 90% reflective due to fresh ice
I Ice volcanos may be the source ofSaturn’s E-ring material
I Presence of low melting-point liquid,not pure water, under surface.
I Tidal resonance with Dione or Saturnmay be source of heat
James Lattimer AST 248, Lecture 21
James Lattimer AST 248, Lecture 21
James Lattimer AST 248, Lecture 21
Saturn’s E ring with Enceladus
Enceladussouth polar jets
Tethys
James Lattimer AST 248, Lecture 21
James Lattimer AST 248, Lecture 21
Iapetus
I Iapetus has leading hemisphere which isdark (carbon-rich) and a trailinghemisphere which is bright (ice).
I Dark material may be deposited frommatter chipped off Phoebe, a very darksatellite; this matter may also coat Hyperion.
Orbit is highly inclined.
Equatorial bulge
James Lattimer AST 248, Lecture 21
Phoebe and Hyperion
I Small Saturn satellites
I Phoebe has retrograde orbit and very rocky,indicating it is a captured Kuiper Belt object.
I Phoebe is very dark: albedo is 0.06
I Hyperion is 2nd largest irregular body insolar system; Neptune’s Proteus is larger.
Phoebe
Hyperion
James Lattimer AST 248, Lecture 21
Mimas
I Mimas clears the material from the Cassini Division, the gapbetween Saturn’s two widest rings, because that location is in a 2:1orbital resonance with Mimas
I Impact that produced the large crater (Herschel) almost completelyshattered Mimas; an equivalently-sized crater on the Earth would beas wide as the U.S.
James Lattimer AST 248, Lecture 21
Triton
I Largest satellite of Neptune, 3rd-most massive in solar systemI Only large moon with a retrograde orbit, probably originally a binary
Kuiper Belt object that was captured and disruptedI Decaying orbit will
take Triton withinNeptune’s RocheLimit, causingbreakup in 3.6 Gyr.
I Thin atmosphereof N2 and CH4
I Few craters, active N2,H2O, CH4 cryovolcanosand geysers;relatively young surface< 50 million years old
I No tidal heating, butseasonal solar heatingcreates solid-state (ice)Greenhouse effect;geysers only observednear the subsolar point.
James Lattimer AST 248, Lecture 21
Dark streaks of dust left by nitrogen geysers
James Lattimer AST 248, Lecture 21