Published online 14 January 2005 | Nature | doi:10.1038/news050110-19

News

Metal meteorite found on Mars

Odd chunk of iron thought to come from an asteroid.

Opportunity spotted Shield rock (above) on 10 January.Opportunity spotted Shield rock (above) on 10 January.© NASA/JPL

The Mars rover Opportunity may have found an iron meteorite. NASA scientists believe it probably came from the core of a large asteroid, which broke up when it crashed into the red planet.

"It looks like nothing we've ever seen on Mars before," Steve Squyres, who leads NASA's Mars-rover science team at the Jet Propulsion Laboratory in California, told news@nature.com.

Opportunity spotted the odd-looking rock on 10 January, the rover's 345th martian day on the planet.

The rover had previously spent six months inside Endurance crater, studying the layered rock outcrops there. After carefully picking its way out of the crater, Opportunity trundled over to where its protective heat shield had landed after being ejected during the rover's descent.

“It looks like nothing we've ever seen on Mars before.”

Steve Squyres
Jet Propulsion Laboratory, Pasadena

Mission engineers wanted to get a good look at the shield, now in two fragments, to see how it had stood up to the battering on the way down.

"And right there next to the heat shield is a little rock," says Squyres, "which we imaginatively call 'Shield Rock'."

Infrared scans of the rock suggest that it is actually made of metal. "We believe we've found an iron meteorite," says Squyres. He revealed the discovery on 12 January, during a presentation at the American Astronomical Society's conference in San Diego.

"You'd expect there to be meteorites on Mars, but the chance of actually bumping into one is incredible," says Glenn Schneider, an astronomer from the University of Arizona, Tucson.

Historic meteors

Meteorites are chunks of Solar System debris that manage to reach a planet's surface without completely burning up in the atmosphere. Most originate from the break-up of asteroids.

Outer parts of the asteroid usually produce stony meteorites, but iron meteorites, which also contain traces of nickel and other metals, are thought to come from the cores of larger asteroids. When such asteroids formed, the metal stayed molten long enough to accumulate at the core, separating from the less dense minerals that remained in the outer portions of the asteroid.

Meteorites are prized by scientists who use them to work out the age and nature of their parent bodies, which helps to build a picture of what the solar system was like at the time when the asteroids first formed.

Shielding facts

This image, from 22 December 2004, shows remains of the heat shield that protected the spacecraft as it barrelled through the martian atmosphere.This image, from 22 December 2004, shows remains of the heat shield that protected the spacecraft as it barrelled through the martian atmosphere.© NASA/JPL/Cornell

Opportunity will use various instruments over the next few days to determine the rock's exact composition, but its investigation of the heat-shield fragment is going less well.

The rover is hampered by the fact that the shield seems to have turned inside out when it crashed into Mars. The outer thermal protection layer is now relatively inaccessible, but Opportunity has been using its microscopic imager to take a close look at the debris.

"With luck, our observations may help to improve our ability to deliver future vehicles to the surface of other planets," says Jim Erickson, the rover project manager. 

Jet Propulsion Laboratory, Pasadena