Moon and Mars
 Layers of rock that may have formed at the bottom of wet or damp ground highlight this view from the Opportunity rover on Mars. Scientists are debating just how much water was present in the far distant past in this region, known as Meridiani Planum. Small sand dunes sit atop the rocks. [Credit: NASA/JPL/Cornell]
Mars is the most intensely studied planet other than our own. But it's revealing its secrets at a slow pace -- even at the spots where landers and rovers have studied the planet in detail.
Consider Meridiani Planum, where the Opportunity rover has been poking around for the last two years.
The rover spent months inside a crater, studying layers of ancient rock. Scientists initially reported that the layers formed as minerals fell to the bottom of a lake or sea. With so much water, the site was considered a good place to hunt for signs of ancient life.
But more detailed study suggests that Meridiani Planum may not have been quite such a good spot for life. Scientists with the rover mission found that the environment contained a lot of acid. Bacteria live in similar environments on Earth, but they probably adapted to them over time -- something that Martian microbes would not have had.
Other scientists concluded that the region was actually pretty dry. They say the layers of rock came not from water, but from volcanoes.
No one is ruling out the possibility that life once existed at Meridiani Planum -- only suggesting that it's less likely. But we'll need to study the region much more closely to know for sure. More about Mars tomorrow.
Script by Damond Benningfield, Copyright 2006
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