May 03, 2013

Tucson collector gives ASU one of rarest meteorites ever found

Posted: May 03, 2013
mercury meteorite
Melissa Morris (assistant director of ASU’s Center for Meteorite Studies), meteorite collector Fredric Stephan, and Laurence Garvie (collection manager of ASU’s Center for Meteorite Studies) hold samples of the center’s newest acquisition: A meteorite that has been suggested to hail from planet Mercury.
Photo by: Andy DeLisle
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hermian
Here is an up close image of one of the Center for Meteorite Studies' samples of NWA 7325. The piece is 2 centimeters wide. Each tick mark on the ruler is 1 millimeter.
Photo by: Laurence Garvie

Greenish rock found in Morocco may be first from planet Mercury

Arizona State University’s Center for Meteorite Studies recently received pieces of one of the rarest meteorites ever found. Aside from its peculiar green color, what makes this space rock so special is where it could come from: It may be the first known visitor from planet Mercury.

Last year, a group of 35 of these unusual space rocks was found in Morocco. Analysis suggests that the meteorite, called NWA 7325, came from Mercury, and not an asteroid or Mars. With its uncharacteristically chartreuse-green fusion crust and curious chemical composition, it does not resemble any other space rock documented by scientists.

Meteorite enthusiast Fredric Stephan donated two pieces of the green rock, totaling 10 grams. CMS now holds 10 grams of the 345 grams found.

“This unusual and precious donation is really an exciting sample and a wonderful addition to the center’s meteorite collection," said Laurence Garvie, who curates the Center for Meteorite Studies’ collection of more than 1,800 separate meteorites. "Scientists have numerous meteorites for study, more than 50,000, but every so often something new comes along that gives us new insights into our solar system. More than anything, this sample will force us to look at what would really be the defining properties of a Hermian meteorite.”

Although it has been hailed as the first meteorite from the solar system’s innermost planet, its origin is not certain.

“It is difficult, though modeling shows not impossible, to get a sample ejected from Mercury out to our orbit. Basically, Mercury is so close to the sun, it swallows up most rocks ejected from the surface by impacts,” explains Garvie.

However, based on its composition and low remnant magnetism, it is possible that it originated from the closest planet to the sun. NWA 7325 contains little iron but considerable amounts of magnesium, aluminum and calcium silicates – in line with data sent back from NASA’s MESSENGER spacecraft currently in orbit around Mercury.

Although scientists can’t say for sure where the meteorite comes from, they can say it is exceptional and very old, with an estimated age close to ~4.56 billion years. And even if this meteorite turns out not to be from Mercury, it still has properties that scientists have not observed before in a sample, and is, therefore, extremely interesting.

“CMS has a long tradition of working with private meteorite collectors for the benefit of planetary science. We are especially grateful to Fredric for his generosity in making this important contribution along with the many other valuable specimens he has donated to the center,” says Meenakshi Wadhwa, director of CMS and a professor in the School of Earth and Space Exploration.

Members of the public are invited to see this unusual sample that is now on exhibit on the second floor of ASU’s Interdisciplinary Science and Technology Building IV.

Nikki Cassis, ncassis@asu.edu
602-710-7169
School of Earth and Space Exploration