Earth volcanoes craters mountains riverbeds

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Earthvolcanoescratersmountainsriverbeds
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Venusvolcanoesfew craters
Radar view of a twin-peaked volcano
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Marssome cratersvolcanoesriverbeds?
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Mercurycraterssmooth plains,cliffs
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Mooncraterssmooth plains
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7.3 Mars A Victim of Planetary Freeze-drying

• Our Goals for Learning
• What geological features tell us that water once
  flowed on Mars?
• Why did Mars change?

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Mars vs. Earth

• 50 Earths radius, 10 Earths mass
• 1.5 A.U from the Sun
• Axis tilt about the same as Earth.
• Similar rotation period.
• Orbit is more elliptical than Earths seasons
  more extreme in the south than the north.
• Thin CO2 atmosphere little greenhouse

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Main Difference seems to be

• Mars is SMALLER!

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What geological features tell us water once
flowed on Mars?
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Eroded crater
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Volcanoesas recent as 180 million years ago
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Past tectonic activity
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• 2004 Opportunity Rover provided strong evidence
  for abundant liquid water on Mars in the distant
  past.
• How could Mars have been warmer and wetter in the
  past?

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Today, most water lies frozen underground (blue
regions) Some scientists believe accumulated
snowpack melts to carve gullies even today
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Why did Mars change?
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Would terraforming Mars work?

• Yes
• No

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What have we learned?

• What geological features tell us that water
  once flowed on Mars?
• Dry river channels, rock-strewn floodplains, and
  eroded craters all show that water once flowed on
  Mars, though any periods of rainfall seem to have
  ended at least 3 billion years ago. Mars today
  still has water ice underground and in its polar
  caps, and could possibly have pockets of
  underground liquid water.

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What have we learned?

• Why did Mars change?
• Marss atmosphere must once have been much
  thicker with a much stronger greenhouse effect,
  so change must have occurred due to loss of
  atmospheric gas. Much of the lost gas probably
  was stripped away by the solar wind, which was
  able to reach the atmosphere as Mars cooled and
  lost its magnetic field and protective
  magnetosphere. Water was probably also lost
  because ultraviolet light could break apart water
  molecules in the atmosphere, and the lightweight
  hydrogen then escaped to space.