QUESTION: 
Why does the Martian atmosphere have so much Carbon Dioxide? When Mars was
formed, what kind of atmosphere do you think it had? What do you think is
the most interesting Martian atmosphere fact?

ANSWER from Bob Haberle on May 11, 1999:
The Martian atmosphere has about 50 times the amount of carbon dioxide in
the earth's atmosphere. So you are right; it does have alot of carbon
dioxide. On both planets, carbon dioxide gets into the atmosphere from
erupting volcanoes. But on earth, it gets taken out of the atmosphere when
it rains. Eventually it is used to make rocks. On Mars, there is no rain. So
it doesn't get removed very efficiently.

When Mars was formed, its atmosphere was probably mostly carbon dioxide and
water vapor. The atmosphere was probably much thicker than it is today, but
we can't be sure. There might also have been trace amounts of gases like
methane, ammonia, and sulfur dioxide. But again, we can't be sure. It was
sooooo long ago - almost 4 and a half BILLION years!

Even the today's martian atmosphere is thin (surface pressure is only 7 mb
compared to earth's 1013 mb), it is capable of generating global scale dust
storms. These storms are so intense that you can't see the surface for
weeks. Wow! How does it do that?