From the June 2012 issue

Twin rovers’ meteorite encounters

Earth isn’t the only planet that features rocks from space.
By | Published: June 25, 2012
Block Island, an iron-nickel meteorite that Opportunity spotted, is about 2 feet across. The rover imaged the rock on sol 1,959 (July 28, 2009). Credit: NASA/JPL-Caltech
Both of NASA’s Mars Exploration Rovers, Sprit and Opportunity, have encountered “strangers” — rocks that did not break off a local outcrop, but came from someplace else. Most of these are meteorites, the first ones ever found on another planet.

Opportunity has found the most meteorites because stray rocks stand out clearly on the smooth plains of Meridiani. Also, Meridiani’s bedrock erodes easily, so meteorites and other durable rocks (such as those from distant craters) naturally end up sitting atop the ground surface. Unfortunately, none of the meteorites provides any clue about how long ago it fell. Here’s a list of the meteorites that the rovers have found on Mars.

• Bounce Rock (Opportunity, sol 36): Rich in the igneous mineral pyroxene, probably ejected debris from a distant impact; has a composition similar to a meteorite that reached Earth from Mars

• Barberton (Opportunity, sol 121): Stony-iron meteorite

• Heat Shield Rock (Opportunity, sol 339): First meteorite ever found on another planet; complex iron meteorite

• Santa Catarina (Opportunity, sol 1,034): Stony-iron meteorite

• Joacaba (Opportunity, sol 1,046): Stony-iron meteorite

• Mafra (Opportunity, sol 1,151): Stony-iron meteorite

• Paloma (Opportunity, sol 1,190): Stony-iron meteorite

• Santorini (Opportunity, sol 1,713): Stony-iron meteorite

• Kasos (Opportunity, sol 1,889): Stony-iron meteorite

• Block Island (Opportunity, sol 1,961): Complex iron meteorite; deeply hollowed out due to chemical erosion

• Shelter Island (Opportunity, sol 2,022): Complex iron meteorite
• Mackinac Island (Opportunity, sol 2,034): Nickel-iron meteorite

• Oileán Ruaidh (Opportunity, sol 2,368): Nickel-iron meteorite

• Ireland (Opportunity, sol 2,374): Nickel-iron meteorite

• Bingag Cave (Opportunity, sol 2,642): Nickel-iron meteorite

• Dia Island (Opportunity, sol 2,642): Nickel-iron meteorite

• Zhong Shan (Spirit, sol 858): Nickel-iron meteorite; found next to Allan Hills

• Allan Hills (Spirit, sol 858): Nickel-iron meteorite; found next to Zhong Shan