Found on a Martian Field: A Whomping Big Meteorite

By Eliza Strickland | August 4, 2009 3:31 pm

Martian meteoriteThe Mars rover Opportunity, an interloper on the Martian soil, has discovered another piece of metal that isn’t native to the planet: a boulder-sized iron meteorite that spun out of the sky and crashed into the planet sometime in the distant past. While the rock isn’t the first iron meteorite spotted on Mars (the two Mars rovers’ previous discoveries make this the fourth), it is the largest, measuring about 2 feet wide and 1 foot high. Researchers hope that studying the mega-meteorite will provide clues to the atmosphere and landscape that it encountered when it arrived on Mars.

Opportunity spotted the out-of-place object on July 18 and snapped a picture of it, but the rover was on its way towards a distant crater and didn’t stop. When NASA scientists saw the photographs, however, they ordered the rover to reverse course and head for the rock. “When you’re driving around on relatively smooth, flat, boring plains for a long time, anything that looks like a decent-sized rock says, ‘Come get me!'” says team member Albert Yen, a planetary scientist at NASA’s Jet Propulsion Laboratory [New Scientist].

Researchers have since used the rover’s alpha particle X-ray spectrometer to study the boulder’s composition, and say that the mix of iron and nickel confirms its meteorite status. Now named Block Island, it will be studied further to determine how much weathering the rock has undergone. Since the meteorite contains iron, any signs of rust on the rock could shed light on the history of water on Mars…. The meteorite may have fallen to Mars in the past 3.5 billion years or so, a period during which the rock likely came into contact with only trace amounts of water in the atmosphere or upper layers of soil. Alternatively, it could have crashed to the surface during the first billion years of the planet’s history [New Scientist], when the area may have been routinely flooded by transitory lakes. Researchers say that using the size of the meteorite in models could also shine light on the Red Planet’s atmosphere at the time of the impact [Nature, blog].

Meteorite expert Alex Bevan says that Block Island was almost certainly jostled free from the asteroid belt, a ring of rubble circling the sun between Mars and Jupiter. “It would be very interesting to compare that one with meteorites we find on Earth, to see if they are of the same type” [Sydney Morning Herald], he says.

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Image: NASA / JPL-Caltech


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