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Image: Mars rock
This approximately true-color view of Marquette Island comes from combining three exposures that Opportunity's panoramic camera (Pancam) took through different filters during the rover's 2,117th Martian day, or sol, on Mars (Jan. 6, 2010). 
updated 1/25/2010 1:13:18 PM ET 2010-01-25T18:13:18

NASA's Opportunity rover has discovered a peculiar rock on Mars that scientists think originated deep within the red planet.

The stone could reveal new secrets about the makeup of Mars' interior.

Dubbed "Marquette Island," the rock is a dark boulder not much bigger than a basketball that sits on a rippled Martian plain.

"Marquette Island is different in composition and character from any known rock on Mars or meteorite from Mars," said Opportunity principal investigator Steve Squyres of Cornell University in Ithaca, N.Y. "It is one of the coolest things Opportunity has found in a very long time."

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Opportunity and its twin rover, Spirit, landed on Mars in 2004, and have drastically outlived their original 90-day mission plan. While Spirit is currently stuck in a sand trap with two broken wheels, Opportunity is still roving free.

In all of its 11 miles worth of traveling, Opportunity has found only one other rock of comparable size to Marquette Island and scientists think it was ejected from a distant crater. Called "Bounce Rock," that stone closely matched the composition of a meteorite that landed on Earth, but was thought to have originated on Mars.

The coarse-grained texture and basalt composition of Marquette Island indicates that it cooled slowly from molten rock, allowing crystals time to grow. That means that it likely originated deep in the crust, not at the surface where it would cool quicker and have finer-grained texture, scientists say.


In contrast, most Martian basalt rocks that Spirit and Opportunity have encountered have different textures and composition.

At first, scientists thought Marquette Island could be a meteorite, but it appears to have a much lower nickel content than other meteorites Opportunity has found. And Marquette Island's interior contains more magnesium than typical Martian basalt rocks.



This was the 38th rock target Opportunity has ground into, and one of the hardest. The tool was designed to grind into only one Martian rock, and this rock may not be its last.


While Marquette Island is intriguing, Opportunity couldn't stop too long to investigate — it left the site Jan. 12. The rover is mid-way on a journey toward a much larger crater, Endeavour, that scientists think will offer a host of scientific prospects.


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