Heat Shield Rock

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Heat shield, with Heat Shield Rock just above and to the left in the background (click to enlarge)

Heat Shield Rock is a basketball-sized iron-nickel meteorite found on Mars by the Mars rover Opportunity in January 2005. The meteorite was formally named Meridiani Planum by the Meteoritical Society in October, 2005 (meteorites are always named after the place where they were found).

Opportunity encountered the meteorite entirely by chance, in the vicinity of its own discarded heat shield (hence the name). Opportunity had been sent to examine the heat shield after exiting Endurance crater. This was the first meteorite of any kind identified on another solar system body — none were found on the Moon.

Readings from Opportunity's spectrometers were used to identify the composition of the rock and confirm its identity as a meteorite. No attempt was made to drill into the meteorite, because testing on iron meteorites on Earth showed that the rover's drilling tools would be abraded and damaged. The drilling tool was designed to drill into ordinary rock, not into iron-nickel alloy.

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Meridiani Planum, the part of Mars where this meteorite was found, is suspected to have once been covered by a layer of material with a thickness of as much as 1 km which has been subsequently eroded. This means that on impact this meteorite might have created a crater, but evidence of that crater may have been subsequently erased by millions, or even billions, of years of erosion. In any case, the meteorite does not show much sign of rust despite Mars's oxidizing environment, so it either fell recently or was buried until recently. It also shows little sign of weathering.

Note that the term "Martian meteorite" usually refers to something entirely different: meteorites on Earth which are believed to have originated from Mars, a famous example being ALH84001.