Life around Saturn, and beyond ASTR 1420 Lecture 14 Sections 9.3 Saturn’s Moons • 62 Moons, 53 named (18 above). Mostly icy, some with rocky cores. • Titan is the 2nd largest moon in our Solar System & only one with a “real” atmosphere with N2, CH4, CO2 (1.5 bar!) • 98% of N2 : (N2=77% at Earth) • No appreciable O2 Titan, the Masked! • sunlight 1/100 of Earth -180°C • A lot of organic molecules CH4, C2H2, C2H6, C3H8, …, argon, CO2, etc. • Always covered with thick haze/smog • Cassini/Huygens in 2004+ Voyager 2 image of Titan Cassini + Huygens (2004- ) Titan’s landscape from Huygens descending image… Taken at an altitude of ~8 km. looks like a dried streambed! Water ice as rocks… Interior of Titan • Satellite gravity measurement… • Similar to Callisto, Titan’s interior is not differentiated! • 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… • A lot of NH3 ! Titan’s Atmosphere Ganymede : 2631 km radius Titan : 2576 km radius 55km • 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’s solid surface is only 55km smaller than Ganymede… • NH3 + CH4 + solar UV photons organic molecules… • 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: water: 0 to 100C, methane: -182C to -164C, ethane: -183C to -89C Possible ethane world? -183C Origin of Atmosphere Image of Titan taken from Cassini orbiter • 10 times more extended than Earth’s • Key factor size (gravity) • 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 made of hydrocarbon sediments. Namib desert from Space Shuttle Titan : summary • Very similar features with very different composition and temperature! Earth Titan liquid water liquid methane silicate rocks water ice rocks molten lava volcano ice/slush volcano silicate sand dunes organic particulate dunes • 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!) • Possible life in the upper atmosphere (acetylene [C2H2] based) or in the subsurface liquid ocean! • interesting to see if we can find right- and left-handed amino acids in life! Active Enceladus • Tiger stripes = fresh ices cracks or grooves 6th largest moon of Saturn • Ice geysers subsurface liquid water + ammonia mixture • Although we expect some tidal heating, it is hard to explain all these activities. • possible subsurface habitable zone! Enceladus Cryovolcanism feeding a ring of Saturn Iapetus : An Intelligence Test for Earthlings? a large brightness change (10+ times) over one rotation period! 3rd largest moon of Saturn • Heavily terraformed? Strange Surface • Equatorial bulge (how???) Iapetus = Alien’s Starship? ? No, Iapetus is in fact Deathstar! Triton: Surprising possibility of potential habitability largest moon of Neptune • Cryovolcanism… Triton’s cantalope skin Possibly formed by diapirism (i.e., slow boiling pattern) Triton: Surprising possibility of potential habitability • Retrograde motion = Triton orbits Neptune “backward” captured moon! • Crater count Triton’s surface is 10-100 million years old. • Active ice geysers!! • Remnant internal heat from the capture may drive the geological activity… possible subsurface liquid ocean even at -230°C, possible habitable world! 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)! In summary… Important Concepts Important Terms • At least six potentially habitable jovian moons! Europa, Ganymede, Callisto, Titan, Enceladus, and Triton • icy volcanism (cryo-volcanism) • Origin of Titan’s atmosphere • Prominent characteristics of Titan, Enceladus, Iapetus, and Triton. Chapter/sections covered in this lecture : 9.3 Next lecture : Exo-planets!