1. Possible Life on Enceladus
“The Possible Origin and Persistence of Life on Enceladus and Detection of Biomarkers in the Plume”
Chritopher P. McKay
Carolyn C. Porco
Travis Altheide
Wanda L. Davis
Timothy A. Kral
Sixth Largest Moon of Saturn

2. ENCeladus
• Small, icy moon of Saturn • Studied by the Casinni Spacecraft • One of only three outer Solar System bodies with observed active eruptions

3. Possible Origin and Persistence of Life
•Jets of icy particles and water vapored escaping into space from south pole of Enceladus, along with warmer temperatures in the same area Evidence of an geophysical energy source • Vapor Plume -Simple organic compounds -Water vapor -Methane -Nitrogen gas -Carbon monoxide • Scientists hypothesize the possibility of liquid water beneath the south pole

4. Life possible so Far from Sun?
Hypotheses relate to observed ecosystems on Earth capable of life without reliance on direct sunlight, oxygen, or organics produced at the surface 1) Microbial ecosystems found deep in Volcanic rock -based on consumption by methanogens of hydrogen produced by rock reactions with water 2) Microbial ecosystem deep below surface of South Africa -based on sulfur reducing bacteria consuming hydrogen and sulfate
Out of the Habitable Zone for our Sun!
How is life here possible?

5. So far from the Sun… What is the power source?
Scientific models: • Heat generated within a silicate core or • Heating within outer ice shell Both models assume • Some portion of heat production caused by tidal flexing
Overall, the source of heating remains obscure…

6. Does the Plume originate from subsurface liquid?
Scientists are relatively uncertain!
• Source of water vapor and ice in plume:
-Models suggest the source could
be either subsurface liquid water
or surface ice

7. Source of Methane and Nitrogen in plume?
Possibilities: • Produced when interior temperatures were 300 K – 800 K -Allows decomposition of ammonia into nitrogen and -methane from thermal decomposition of organics

8. If subsurface water exists, how long has it been there?
Duration of subsurface water would need to be long enough for life to originate
Can’t be temporary
No accurate estimates of the age of activity on Eceladus
But…
Geologic features and crater density near plume suggests activity has occurred for several hundred million years

9. Would concentration of solutes in subsurface water allow habitability?
Salts: No salts in plume Expected in any geophysical body of water But… As observed on Earth, water just below ice cover tends to be relatively free of salts Ammonia: No ammonia observed in plume All ammonia once on Enceladus may have already decomposed into nitrogen.

10. Life on Enceladus
Depends on existence of subsurface liquid water being the source of plume
Conclusions:
Based on theories for the origin of life on Earth, subsurface water on Enceledus would give plausible scenarios for life to exist there as well.
Evidence of microbial ecosystems on Earth that do not require sunlight makes Enceladus plausible for containing same types of ecosystems
Methane and other hydrocarbons detected in plume may have biological origin

11. How to detect Life on Enceladus
1) Cassini's instruments measure the ratio of non-methane hydrocarbons to methane
-Low ratio (0.001) indicates biological origin
2) Detection of biomarkers in the plume
Until then,
we will not know!

12. All Images of Enceladus taken from www.nasa.gov