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Rocks from another world

Pieces of Mars that fall to Earth as meteorites gave us our first samples of the surface of another planet.

The martian landscape looks strikingly similar to the deserts of Earth. But billions of years ago, water flowed in abundance on Mars, carving huge canyons bigger than any on Earth, and immense volcanoes have gushed forth mountains of lava since that time.

Today, dust storms swirl over a barren surface scarred by impact craters-one or more of which may mark the site of impacts that dislodged the meteorites displayed here. But large amounts of water still lie frozen just beneath the Martian surface, raising hopes that some form of life might have arisen on Mars.

In 1996, one Martian meteorite caused a stir when some thought it contained evidence of ancient microbes. Most experts remain unconvinced, but all Martian meteorites do show the effects of a watery climate. The presence of water makes Mars a great place to start the search for life beyond Earth.

How do we know: Tracing meteorites to Mars

Conclusive evidence that these meteorites are from Mars came in the form of gases trapped inside the rocks. These gases were a perfect match for the Martian atmosphere, as measured by NASA's Viking probes that landed on Mars in the 1970s. Some of the Martian atmosphere became trapped in the rock when it was shocked by an impact-probably the impact that launched the rocks on their way toward Earth.

 Most meteorites are pieces of asteroids, which solidified into cold, hard rock some 4.4 billion years ago. So experts took notice when volcanic meteorites were found that had crystallized within the past 1.3 billion years. Only a large planet could have remained volcanically active up to such recent times. The meteorites also showed evidence of an atmosphere, liquid water and chemical and geological processes that could only take place on a planet. Evidence of water pointed specifically to Mars.

For Educators

Topic: Astronomy

Subtopic: Planets

Keywords: Meteorites, Astrophysics, Mars (Planet)--Atmosphere, Astrogeology, Life on other planets, Mars (Planet)--Geology, Mars (Planet)--Surface

Audience: General