Mars is just about lost from sight right now. It's quite low in the western sky as darkness begins to fall. You can still find it, though, because it lines up with a couple of bright companions: the Moon and the planet Venus. Venus is the "evening star," to the lower right of the Moon. Mars is about the same distance to the upper right of Venus. It's fairly bright, but it can be tough to spot through the twilight.
Although Mars is a desert world today, that hasn't always been the case. Billions of years ago, it was much warmer and wetter. Some of its water was highly acidic -- not a comfortable environment for life. But some of it was a lot less so.
The Spirit rover discovered evidence of this cozier water five years ago when it examined layers of rock in the Columbia Hills. Scientists spent years carefully analyzing the rover's observations. And they found that the rock included layers of carbonate -- a mineral that forms only in water that's not acidic. The discovery suggests that the area could once have been much more hospitable.
Scientists have been searching for carbonate on Mars for years. It should have formed when carbon dioxide in the early Martian atmosphere mixed with water at the surface. But observations by spacecraft in orbit around Mars have found little evidence of it. Its discovery in the Columbia Hills renews hope of finding it elsewhere on the planet -- and hope that Mars was once a comfortable home for life.
Script by Damond Benningfield, Copyright 2010
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