They're not exactly prime real estate, but Martians may have called them home. The craterlike features in this image, taken by NASA's Mars Reconnaissance Orbiter, are not from comet or asteroid impacts. They're small volcanic cones about 250 meters wide, thousands of which dot a northern lowlands region of the red planet called Acidalia Planitia. Scientists analyzing the cones have concluded that their centers are filled with sediments that once harbored water. The muddy layers were ejected from deep under the surface possibly billions of years ago. If so, the team reports  in this month's issue of the journal Icarus, the mud could have contained enough organic materials to support primitive forms of life. Even if the sediments turn out to be lifeless, they could reveal more about the planet's chemical and geological history.
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