The Nature of Possible Life on Europa and Other Planets within our Solar System

© Charles S. Tritt, Ph.D.
Presentated May 24, 1998

A) My definition of life -- Any self replicating process that turns energy into order.

1. One problem is we still have only a single example from which to extrapolate.
2. I'll restrict my discussion chemical based life forms.
3. Finding (or searching carefully and not finding) life in our solar system would answer a number of very important questions about life on Earth.

B) Possible energy sources.

1. Energy source must provide energy to overcome entropy. For every type of life (biochemistry) there is probably a lower limit on the energy flux required to sustain it. The energy must also interact with the mater in the life form ways that can produced controlled chemical reactions.
2. Light (visible solar radiation ). On Earth plants harvest light.
3. Chemical gradients. Generally generated during planetary formation. Stellar energy input might be required to sustain chemical gradients long enough for life to evolve. Used by animals and fungi on Earth. Generated by plants producing reduced carbon compounds and oxygen from sun light. Life around geothermal vents oxidize reduced compounds carried from within the Earth, but the oxidizing potential is only available due to green plants elsewhere.
4. Electromagnetic radiation other than visible light. Must penetrate to zone where life forms exist. Must interact with the life forms in a useful way. Long wave lengths may carry too little energy per photon. Short wave lengths may cause uncontrolled chemical reactions.
5. Electric fields. No known examples on Earth, but lighting does fix significant amounts of nitrogen for use by living things.
6. Subatomic particles. No known examples on Earth. Energy flux must be high enough to be useful and particles must interact with the life forms in a useful way.
7. Thermal gradients. No known examples on Earth. Thermal gradients are very common on planets. Life forms would be living heat engines.
8. Pressure gradients. No known examples on Earth. Hard to imagine how these could be coupled to chemical reactions.
9. Gravitational fields. No known examples on Earth. Density differences could provide motion, but coupling this motion to useful chemical reactions is difficult to imagine.

C) Processes for biogenesis.

1. Still a problem on Earth. Current analyses indicate the early Earth atmosphere was less reducing than those used by Stanley Miller in his famous experiment. Zones near geothermal vents may have been reducing enough.
2. Relatively long periods of are probably required (see Table 1).
3. Environmental changes may be necessary during this period to facilitate the continued development of life forms. In the case of Earth, the oxygen produced by early life forms drastically changed the atmospheric chemistry. This lead to the development of Eukaryotes and ultimately humans.
4. Liquid solvent probably required. Mass transfer too slow in solids. Density too low and mass transfer too fast (due to convection) in gases. Water, ammonia, methane (and/or other hydrocarbons), carbon dioxide certainly possiblities. Should liquid metals be considered?
5. Cosmic seeding a possibility. Separates incompatible chemical processes in space and time. Might involve simple reduced carbon compounds, bio-monomers (nucleic acids and/or amino acids) or complex (prokaryotic) life forms.

D) Tour of planets and their moons.

1. Mercury -- Life very unlikely. No atmosphere or suitable liquid solvent.
2. Venus -- I consider life on Venus to be a possibility. Would be very different from earth life due to harsh chemical conditions. However, Venus has a complex atmosphere and plenty of solar energy input. The absence of life on Venus would support the claim that our DNA/RNA/protein biochemistry is only one that works.
3. Earth -- Life likely (for now). Light driven. Carbon, oxygen and water based. DNA/RNA/protein biochemistry.
• Luna -- Life not likely. No useful atmosphere or liquids.
4. Mars -- Life unlikely now. Previous life pretty likely. The search for fossils is one of best practical reasons I can think of for missions to Mars.
• Martian moons -- Life very unlikely. See Luna.
5. Jupiter -- Life a possibility. Would be very different from earth life due to drastically different chemical conditions.
• Jovian moons -- Life very likely. Lots of chemistry and energy sources. Europa is an excellent candidate.
6. Saturn and its moons -- Life gets less likely as energy flux gets lower. There is some possibility of life on Titan due to its dense atmosphere.
7. Uranus and its moons -- See Saturn.
8. Neptune and its moons -- See Saturn.
9. Pluto -- Life very unlikely. No atmosphere or suitable liquid solvent. Energy flux extremely low.

For more information contact me at tritt@msoe.edu
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