POSSIBLE LIFE ON ENCELADUS Sixth Largest Moon of Saturn “The Possible Origin and Persistence of Life on Enceladus and Detection of Biomarkers in the Plume”

POSSIBLE LIFE ON ENCELADUS

Sixth Largest Moon of Saturn

“The Possible Origin and Persistence of Life on Enceladus and Detection of Biomarkers in the Plume”

Chritopher P. McKayCarolyn C. PorcoTravis AltheideWanda L. DavisTimothy A. Kral

ENCELADUS

• Small, icy moon of Saturn

• Studied by the Casinni Spacecraft

• One of only three outer Solar System bodies with observed active eruptions

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

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

How is life here possible?

Out of the Habitable Zone for our Sun!

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…

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

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

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 EceladusBut…

Geologic features and crater density near plume suggests activity has occurred for several hundred million years

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

But…

All ammonia once on Enceladus may have already decomposed into nitrogen.

LIFE ON ENCELADUS

Depends on existence of subsurface liquid water being the source of plume

Conclusions:

1) 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.

2) Evidence of microbial ecosystems on Earth that do not require sunlight makes Enceladus plausible for containing same types of ecosystems

3) Methane and other hydrocarbons detected in plume may have biological origin

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!

All Images of Enceladus taken from www.nasa.gov