Life around Saturn, and beyond ASTR 1420 Lecture 15 Sections 9.3

Saturn’s Moons 62 Moons, 53 named (18 above). Mostly icy, some with rocky cores. 62 Moons, 53 named (18 above). Mostly icy, some with rocky cores. Titan is the 2 nd largest moon in our Solar System & only one with a “real” atmosphere with N 2, CH 4, CO 2 (1.5 bar!) Titan is the 2 nd largest moon in our Solar System & only one with a “real” atmosphere with N 2, CH 4, CO 2 (1.5 bar!) 98% of N 2 : (N 2 =77% at Earth) 98% of N 2 : (N 2 =77% at Earth) No appreciable O 2 No appreciable O 2

Titan, the Masked! Voyager 2 image of Titan sunlight 1/100 of Earth sunlight 1/100 of Earth  -180°C A lot of organic molecules A lot of organic molecules  CH 4, C 2 H 2, C 2 H 6, C 3 H 8, …, argon, CO 2, etc. Always covered with thick haze/smog Always covered with thick haze/smog Cassini/Huygens in Cassini/Huygens in 2004+

Cassini + Huygens (2004- )

Titan’s landscape from Huygens descending image… looks like a dry streambed! Water ice as rocks…

Interior of Titan Satellite gravity measurement… Satellite gravity measurement… Similar to Callisto, Titan’s interior is not differentiated! Similar to Callisto, Titan’s interior is not differentiated! It has a subsurface ocean at very low temperature  mixture of water and ammonia It has a subsurface ocean at very low temperature  mixture of water and ammonia Controversial… : some believe that it should have a rocky core + icy mantle… Controversial… : some believe that it should have a rocky core + icy mantle… A lot of NH 3 ! A lot of NH 3 !

Titan’s Atmosphere Multi-layer of haze Multi-layer of haze Titan once was believed to be the largest moon in the solar system because of its extended haze layer (~200 km). Titan once was believed to be the largest moon in the solar system because of its extended haze layer (~200 km). Titan’s solid surface is only 60km smaller than Ganymede… Titan’s solid surface is only 60km smaller than Ganymede… NH 3 + CH 4 + solar UV photons organic molecules… NH 3 + CH 4 + solar UV photons organic molecules… Drizzle of methane and ethane. Possible lakes/oceans of methane Drizzle of methane and ethane. Possible lakes/oceans of methane

Liquid Flow Methane river  A feature most likely formed by a liquid methane flow. Taken by Huygens probe. Theoretical models predict that a single methane rainstorm can produce several inches of rain…

Methane World Cassini pictures of Saturn's moon Titan taken in 2004 and 2005 show that a large methane lake suddenly appeared after what looked like a heavy rainstorm

Sea of Methane on Titan A Cassini radar image juxtaposed with an image of the Lake Superior

Lots of Natural Gases, but no Oxygen to burn with! Temperature range for liquid: Temperature range for liquid: water: 0 to 100C, methane: -182C to -164C, ethane: -183C to -89C Possible ethane world?

Origin of Atmosphere Image of Titan taken from Cassini orbiter 10 times more extended than Earth’s 10 times more extended than Earth’s Key factor  size (gravity) Key factor  size (gravity) How does Titan have an atmosphere when even a larger moon Ganymede doesn’t? How does Titan have an atmosphere when even a larger moon Ganymede doesn’t? 1.distance from the Sun 2.effect of their host planets Ganymede does not have an atmosphere  at Jupiter’s distance, only water ice could condense…, but at Saturn’s distance, ices such as methane and ammonia could condense! Due to the stronger gravity of Jupiter, impacts were generally stronger at Jupiter’s moons than Saturn’s moon. Stronger impacts more easily blew away atmospheres…

More surface feature : Sand Dunes Windblown dunes Namib desert from Space Shuttle

Titan : summary Very similar features with very different composition and temperature! Very similar features with very different composition and temperature! A lot of liquid hydrocarbons! A lot of liquid hydrocarbons! about 200°C colder than liquid water  much slower chemical reaction  slower metabolism A lot of organic material (e.g., organic sand dunes!) A lot of organic material (e.g., organic sand dunes!) Possible life in the upper atmosphere (acetylene [C 2 H 2 ] based) or in the subsurface liquid ocean! Possible life in the upper atmosphere (acetylene [C 2 H 2 ] based) or in the subsurface liquid ocean! interesting to see if we can find right- and left-handed amino acids in life! interesting to see if we can find right- and left-handed amino acids in life! EarthTitan liquid waterliquid methane silicate rockswater ice rocks molten lava volcanoice/slush volcano silicate sand dunesorganic particulate dunes

Titan Complex organic aerosols consisting of CHN and hydrogen gas (H2), which escapes into space. Ethane and methane partly condense, forming clouds and hazes that precipitate, replenishing the lakes and bearing many organic species in solution. (Nature 454, ; 31 July 2008)

Active Enceladus Ice geysers  subsurface liquid water + ammonia mixture Ice geysers  subsurface liquid water + ammonia mixture Although we expect some tidal heating, it is hard to explain all these activities. Although we expect some tidal heating, it is hard to explain all these activities. possible subsurface habitable zone! possible subsurface habitable zone! Tiger stripes = fresh ices  cracks or grooves Tiger stripes = fresh ices  cracks or grooves 6 th largest moon of Saturn

Enceladus

Enceladus creates Saturn’s E-ring Cassini (2006) : APOD

Iapetus : An Intelligence Test for Earthlings? 3 rd largest moon of Saturn

Strange Surface Heavily terraformed satellite? Heavily terraformed satellite? Equatorial bulge (how???) Equatorial bulge (how???)

Iapetus = Alien’s Starship? ?

Iapetus Deathstar!

Triton: Surprising possibility of potential habitability Cryovolcanism… Cryovolcanism… largest moon of Neptune

Triton’s cantalope skin Possibly formed by diapirism (i.e., slow boiling pattern) Possibly formed by diapirism (i.e., slow boiling pattern)

Retrograde motion = Triton orbits Neptune “backward”  captured moon! Retrograde motion = Triton orbits Neptune “backward”  captured moon! Crater count  Triton’s surface is million years old. Crater count  Triton’s surface is million years old. Active ice geysers!! Active ice geysers!! Remnant internal heat from the capture may drive the geological activity… Remnant internal heat from the capture may drive the geological activity…  possible subsurface liquid ocean  even at -230°C, possible habitable world! Triton: Surprising possibility of potential habitability

Cosmic Messengers

Signal from Pioneer A signal from the Pioneer 10 spacecraft, sent from a distance of more than 6 billion kilometers. The spacecraft transmitted the signal with a power of only one watt (about the power of X-mas tree light)! A signal from the Pioneer 10 spacecraft, sent from a distance of more than 6 billion kilometers. The spacecraft transmitted the signal with a power of only one watt (about the power of X-mas tree light)!

In summary… Important Concepts At least six potentially habitable jovian moons!  Europa, Ganymede, Callisto, Titan, Enceladus, and Triton Origin of Titan’s atmosphere Prominent characteristics of Titan, Enceladus, Iapetus, and Triton. Important Terms icy volcanism (cryo-volcanism) Chapter/sections covered in this lecture : 9.3 Next lecture : Exo-planets!