The rock, dubbed "Block Island," is approximately 2 feet long and has a blue tint. The rover took a picture of the formation in passing two weeks back, but the Rover team decided that Opportunity should backtrack and do some more tests on the relatively giant space rock.

The tests revealed that the meteorite is made up of iron and nickle, which makes it very similar to the kinds of rocks that have been found on the surface of the Earth. The big discovery isn't the composition of the meteorite, though. It's the size.

NASA says that any rock of this size would certainly break apart if it were to fall on the surface of Mars today. For such a large meteorite to remain intact, the red planet's atmosphere would have to have been much thicker. The NASA team chalks the existence of Mars's thicker atmosphere up to one of two causes: either Mars has vast stores of carbon dioxide ice that filled the atmosphere in a relatively recent warm period, or the meteorite fell billions of years ago.

Whatever the case, the rock also provides scientists with a way to see how Mars's weather and climate have affected a foreign object, letting them piece together a sort of reverse long-term weather forecast for the planet's surface. And if we ever get that manned flight to Mars we are all hoping for, "Block Island" could become one of Mars's popular roadside attractions, like a Martian Chimney Rock.

Meteorite Found on Mars Yields Clues About Planet's Past [via PhysOrg]

Even if Mars has had steadily sub-freezing weather for a long time now, glaciers can provide the kind of cover needed to maintain liquid water. We know from Earthling ice sheets that as you go deeper inside them, the temperature tends to go up. Down near the bottom the crushing pressure of miles of ice piled on top can cause melting. Ponds and lakes can even form.

The researchers — headed by Jay Dickson of Brown University — think the same thing could've happened on Mars:

After examining stunning high-resolution images taken last year by the Mars Reconnaissance Orbiter, the researchers have documented for the first time that ice packs at least 1 kilometer (0.6 miles) thick and perhaps 2.5 kilometers (1.6 miles) thick existed along Mars' mid-latitude belt as recently as 100 million years ago. In addition, the team believes other images tell them that glaciers flowed in localized areas in the last 10 to 100 million years - akin to the day before yesterday in Mars' geological timeline.

This evidence of recent activity means the Martian climate may change again and could bolster speculation about whether the Red Planet can, or did, support life.

"We've gone from seeing Mars as a dead planet for three-plus billion years to one that has been alive in recent times," said Jay Dickson, a research analyst in the Department of Geological Sciences at Brown and lead author of the Geology paper. "[The finding] has changed our perspective from a planet that has been dry and dead to one that is icy and active."

Images from Mars orbiter.
Source: Geology via Science Blog