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 Universejames.lattimer@stonybrook.edu

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