# Presentation: 287378

## Organics on Titan, Water on Enceladus: Worlds of possibilities for life

- Chris McKay
- NASA Ames Research Center
- cmckay@mail.arc.nasa.gov
- This talk is a compilation based on the work of many colleagues over many years. My thanks and acknowledgements  to all of them.

## Why is Life on other Worlds Interesting?

- The possibility of a second genesis of life: comparative biochemistry life is common in the universe (yeah!)
- Information about the early planetary environment
- Relevant to the origin of life on Earth

## Jets of H2O on Enceladus

- Jets of H2O on Enceladus

## Slide 4

## Given liquid water on Enceladus is there:

-  a plausible origin of life?
- a plausible ecology?

## OK for Enceladus

- Davis & McKay, *Origins Life Evol. Biosph*. **26**, 61-73, 1996.

## Plausible Ecologies

- The known laws of physicsenergy from thermal gradients, electric fields, radiation
- My favorite “extremophile” *D. radiodurans* radiation resistance, salt tolerance, etc.
- Actual ecosystems actual microbial ecosystems that require no light & no O2

## Examples of ecologically isolated microbial ecosystems (no O2, no light, no organic input) 

- Only three examples are known:
- Two are are based on H2 from rock reactions(H2 + CO2  CH4 + H2O)
- Stevens, T.O. and J.P. McKinley 1995. Lithoautotrophic microbial ecosystems in deep basalt aquifers, Science 270, 450-454.
- Chapelle, F.H., K. O'Neill, P.M. Bradley, B.A. Methe, S.A. Ciufo, L.L. Knobel, and  D.R. Lovley 2002. A hydrogen-based subsurface microbial community dominated by methanogens, Nature 415, 312-315.
- One based on radioactive decay
- Lin, L.-H., et al. 2006. Long-Term Sustainability of a High-Energy, Low-Diversity Crustal Biome, Science 314, 479-482

## 4H2  +  H+  +  SO42-  ----->  H2S  +  2H2O  +  2OH-

- 4H2  +  H+  +  SO42-  ----->  H2S  +  2H2O  +  2OH-

- H2O

- H2

- O2, H2O2

- Radiolysis

- FeS2

- SRB

*Geochemical*
*Reactions*

*Desulfoprofundis tokoloshe*

- Lin et al. 2006, slide courtesy of T. Kieft

## Ice Cover

- Liquid Water

- Biology: H2 + CO2  CH4 + H2O

- Thermal processing, T>500oC: CH4+H2O  H2 + CO2

- CH4

- H2

## Slide 11

## Stardust flys through the Plume of 

- Stardust flys through the Plume of
- Enceladus for a Sample Return Mission

## If we find organic material in the plume of Enceladus (or Europa & Mars) how can we tell if it was ever alive?If its like us then easy, less interestingIf its alien then hard, but interesting

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## Abiotic distributions are smooth

- Biotic distributions are spiked

-  McKay 2004 *PLoS Biol* 2(9)1260-12623

## Abiotic distributions are smooth

- Biotic distributions are spiked

-  McKay 2004 *PLoS Biol* 2(9)1260-12623

**alien**

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## Earth				Titan 

Carbon based			Carbon based
Liquid H2O 			Liquid CH4
Widespread			??

- Carbon based			Carbon based
- Liquid H2O 			Liquid CH4
- Widespread			??

- Possibilities for Widespread Life on Titan

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