28.2 Life in the Solar System

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28.2 Life in the Solar System
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Life as we know it

• Carbon-based
• Originated in a liquid water environment

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The Moon and Mercury

• Lack
• Liquid water
• Protective atmospheres
• Magnetic fields
• So these bodies receive too much UV radiation,
  the solar wind, meteoroids and cosmic rays

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Venus

• Too much atmosphere!
• Its atmosphere is too dense, dry, scorching, hot

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Jovian Planets

• Do not have a solid surface
• Some researchers think that life could have
  evolved in their atmospheres

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Pluto and the Jovian moons

• Most are too cold
• Jupiters moon Europa may have liquid water
  beneath its frozen surface
• Saturns moon Titan has an atmosphere of methane,
  ammonia and may have liquid water but it may be
  too cold

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Europas surface
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Enceladus moon of Saturn, with water geysers
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Mars
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Mars

• Probably the planet most likely to harbor life
• Water is scarce, but present
• The atmosphere is thin
• No magnetism or ozone layer
• Atmosphere was thicker and planet was warmer in
  the past

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Water on Mars

• The Viking and Mars Global Surveyor show
  photographic evidence of flowing and standing
  water.
• In 2004, the European Mars Express confirmed ice
  (water) at the poles.
• Opportunity found evidence that water used to be
  very abundant.

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Evidence of water on Mars
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The Face on Mars
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Life on Mars?

• Even with the water and atmosphere and all of the
  probes that have been to Mars, no life or fossils
  of life have been found.
• Viking robots tested Martian soil for bacteria
  and other life.
• However, the orbiters have not widely surveyed
  the area.
• Particularly, they have not surveyed the area
  near the polar ice caps.

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What do scientists think about Mars today?

• Biologists and chemists agree that no life exists
  on Mars today.
• We will need to explore Mars more to learn if
  life existed there in the past.

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Alternative Biochemistry

• Would we necessarily recognize life if we saw it?
• Could it be different from life as we know it?
• Some scientists think that silicon might replace
  carbon in other lifeforms.
• However, its bonds are weaker.
• Maybe ammonia is used in place of water.

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Alternative Biochemistry

• You would have to have lower temperatures for
  ammonia to remain a liquid.
• Colder temperatures are a problem.
• There would not be enough energy to drive
  biological processes.