domingo, 24 de novembro de 2013

Visitor from planet Mercury at the Peabody Museum of Natural History

On the second floor of the Yale Peabody Museum of Natural History is a strange visitor from another planet.

No bigger than a small child's fist, the greenish rock was likely blasted off the surface of the planet Mercury 24 million years ago, and after traveling through the eons, fell on the Sahara Desert in Morocco, where it was eventually found by a desert traveler and later sold to a German collector.

The discovery was announced by Prof. Tony Irving of the University of Washington's Dept. of Earth & Space Sciences. He said that the origin of the rock was determined by its magnetic qualities, which match those of Mercury.

The Peabody is where the Mercury meteorite is getting its first public showing.

"Once we determined that it was extraterrestrial, the next question was `Where was it from?' " he said. "Of all the places where it may have come from -- Mars, the Moon, the asteroid belt -- it most closely resembles what we know about Mercury."

It's the first object believed to have come from Mercury. Meteors have been found that came from Mars and the Moon, but this is the first that likely came from the innermost planet.

The thought isn't that far-fetched, Irving said. For starters, Mercury is the smallest planet in the Solar System, with a little more than one-third the gravity of Earth. It also bears the scars of countless impact events, many sufficiently large to launch projectiles out to Earth's orbit and beyond. It also has almost no atmosphere.

Irving said that it has a number of qualities that point to a Mercurian origin: It has "native" or non-oxidized iron in small amounts. That, in and of itself, points to an extraterrestrial origin, Irving said.

But most significantly, it has the same magnetic qualities as what has been seen on Mercury. The ongoing NASA Messenger mission has measured the magnetic field of Mercury in detail, and the magnetic signatures of the object and Mercury seem to match.

The greenish rock has, in fact, the lowest magnetic intensity ever measured in any meteorite -- a magnetism that matches Mercury's modern field almost exactly, Irving says.

"This object does not have a counterpart with any rock that we know about," saidIrving, who has studied the rock with his colleagues since the spring of 2012.

The green coating is caused by the presence of chromium, combined with the heat of entering the Earth's atmosphere. The orange flecks were caused by terrestrial contamination, Irving said.

The meteor was one of about 35 space rocks found in the same locale, and all believed to be from a much larger meteor that crashed into what is now Morocco several thousand years ago.

Unfortunately for the researchers, all but one were tested with powerful magnets by the desert wanderers who found them. They do this to determine in the field if the rocks they find are indeed meteorites. This is not an issue for most space rocks, but for those that come from other planets, it makes exacting magnetic research impossible.

"To some people, not having an absolute answer is annoying," Irving said, "But, you're just going to have to live with that. The problem, of course, is that meteorites don't come with an address."

Irving said that it's not out of the question that the object is from somewhere else.

"But, if it is, that somewhere else is a really interesting place," he said.


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