The Search for Life on Titan By: Charlie Congleton

What do we need for LIFE? A fluid medium for transport of solutes A consistent energy source Environmental constituents and conditions compatible with polymeric chemistry on Titan’s surface {Irwin and Shilze-Makuch, 2001}

Titan Overview Largest moon of Saturn Surface temperature ~95 K Atmospheric pressure ~1.5 bars Nitrogen rich atmosphere (90% N,~5% CH 4 ) “Dirty” water-ice surface (NH 4, C 2 H 2, silicates) Ammonia-water oceans at depth? Hydrocarbon haze and transient clouds CH 4 precipitation and fluvial processes Cryovolcanism

Shulze-Makuch and Grinspoon, 2005

What do we need for LIFE? A fluid medium for transport of solutes –CH 4, NH 4 + H 2 O A consistent energy source –UV radiation, high energy molecules from photochemistry, endogenic geology, lightning Environmental constituents and conditions compatible with polymeric chemistry on Titan’s surface –Likely due to photolysis of CH 4 and N into tholins in atmosphere {Irwin and Shilze-Makuch, 2001}

Tholins Form from photolysis of N and CH 4 in Titan’s upper atmosphere Could fall and make their way into NH 4 -H 2 O Breakdown into amino acids when they dissolve Cause reddish brown tint in atmosphere

Cassini-Huygens Mission

Carbon Cycling How is the CH 4 getting back into the atmosphere? –Methanogens [C2H2 + 3H2 → 2CH4] –Methane clathrates –Cryvolcanism Atmosphere is enriched with heavy nitrogen relative to heavy methane isotopes –Why? Biological? Geological? Shulze-Makuch and Grinspoon, 2005

Earth Analogue? Trainer et al., 2004 suggest that Titan’s haze may be similar to the one that may have covered prebiotic Earth –Greenhouse (CH 4 and CO 2 on Earth) –Formation of organic molecules –Methanogenic organisms –Food?

What To Look For? Could be much larger than water-based life Could metabolize slower Could use different biomolecules Might not use redox reactions Could be something weird we’ve never seen before Everything!

References Atreya, S. K., E. Y. Adams, et al. (2006). "Titan's methane cycle." Planetary and Space Science 54(12): Collins, G. C. (2005). "Relative rates of fluvial bedrock incision on Titan and Earth." Geophys. Res. Lett. 32(L22202). Fischer, G., T. Tokano, et al. (2004). "Energy dissipation of possible Titan lightning strokes." Planetary and Space Science 52(5-6): Hueso, R. and A. Sánchez-Lavega (2006). "Methane storms on Saturn's moon Titan." Nature 442(7101): Irwin, L. N. and D. Schulze-Makuch (2001). "Assessing the Plausibility of Life on Other Worlds." Astrobiology 1(2): Lunine, J. I., Y. L. Yung, et al. (1999). "On the volatile inventory of Titan from isotopic abundances in nitrogen and methane." Planetary and Space Science 47(10-11): Schulze-Makuch, D. and D. H. Grinspoon (2005). Biologically Enhanced Energy and Carbon Cycling on Titan? Astrobiology 5: Sotin, C., R. Jaumann, et al. (2005). "Release of volatiles from a possible cryovolcano from near-infrared imaging of Titan." Nature 435(7043): Stofan, E. R., J. I. Lunine, et al. "Mapping of Titan: Results from the first Titan radar passes." Icarus In Press, Corrected Proof. Tobie, G., J. I. Lunine, et al. (2006). "Episodic outgassing as the origin of atmospheric methane on Titan." Nature 440(7080): Tokano, T., C. P. McKay, et al. (2006). "Methane drizzle on Titan." Nature 442(7101): Tomasko, M. G., B. Archinal, et al. (2005). "Rain, winds and haze during the Huygens probe's descent to Titan's surface." Nature 438(7069): Trainer, M. G., A. A. Pavlov, et al. (2004). Haze Aerosols in the Atmosphere of Early Earth: Manna from Heaven. Astrobiology 4: