Image credit: MSSS/JPL-Caltech/NASA

The Curiosity rover surprised NASA engineers with its first Martian rock to examine. Scientists expected to find a rock similar to the ones seen on previous missions to Mars. But instead, they found a rock with a composition seen in many rocks on Earth.

"This rock is a close match in chemical composition to an unusual but well-known type of igneous rock found in many volcanic provinces on Earth," Edward Stolper of the California Institute of Technology in Pasadena said in a NASA statement today. "With only one Martian rock of this type, it is difficult to know whether the same processes were involved, but it is a reasonable place to start thinking about its origin."

According to NASA, rocks on Earth with a similar composition usually come from processes in the planet's mantle and result from crystallization of water-rich magma at an elevated pressure.

"We thought that it would be a basaltic rock because we've found a lot of these volcanic rocks in past missions," said APXS Principal Investigator Ralf Gellert of the University of Guelph in Ontario, Canada. "Volcanic rocks have a huge variety. But we were very surprised because the composition is not what we saw before. It was different, we were very surprised. There were way more elements that are representative of feldspar elements, low magnesium iron and nickel."

As NASA said in a statement, rock compositions are important because they "tell stories about unseen environments and planetary processes."

"The rock possibly tells you something about Martain crust," Gellert said. "Maybe even how these rocks on the Martian surface formed. While we were surprised to find this kind of rock, it's not really that surprising because there are many types of different volcanic rocks. And this is only one rock."

The analysis of the rock will help Curiosity examine other rocks in the future.

"It's the very first rock, it's a baby step," Gellert said. "The arm is a gateway for all of the detailed instruments that were not used at all until now, like the drill and the scoop. We're taking our first baby steps with a complicated machine. We want to get used to taking and investigating samples with the arm. It was an exercise for the engineers who do the deployment so that later on, we will have the experience when we're driving through the landscape and see a rock that interests us. Then we can just drive there and take the sample."

The rock is around the size of a football and is shaped like a pyramid. It has been nicknamed "Jake Matijevic," after a mission engineer who recently died.

"Jake Matijevic was first of all a gentleman," Gellert said. "He had done a lot of work for all the Martian rovers that were starting with Pathfinder. He passed away a couple of weeks after Curiosity's landing so the rock was named after him."