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Question
Why is Mars considered to be the most likely candidate for life elsewhere in the solar system, and not Europa?
Briefly, Mars is often considered the most likely candidate for life because it had very Earth-like surface conditions 4 billion years ago, when life began on Earth. Thus if it happened here, it is likely to have happened there also. Europa, in contrast, has never had a warm surface, so the likelihood of life there depends on whether life could have begun in the dark ocean depths. See also answers to other questions about Mars and Europa in elsewhere in the NAI Q&A files.
David Morrison
NAI Senior Scientist
March 31, 2003
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