AMY J. BARRY, Special to The Day
Published December 10. 2013 4:00AM
Fragments of a brilliant green rock found in the Sahara desert could very well be the first known meteorite to travel to earth from Mercury, and it's making its public debut at the Yale Peabody Museum of Natural History exhibition, "From Mercury to Earth: A Meteorite Like No Other."
But, even if it doesn't turn out to be Mercury-native, the less than quarter pound meteorite - the largest fragment of a meteorite known as NWA 7325 discovered among 35 green stones in 2012 in Morocco - is extraterrestrial beyond a shadow of a scientific doubt. It is a rare find and presents a rare opportunity for humans to get a close-up look at such a prime specimen.
To put it in perspective, out of almost 47,000 known meteorites, only 67 are from Mars and 177 from Earth's moon. This is the first meteorite believed to have fallen from one of the other six planets.
"We can't tell you with absolute certainty it's from Mercury - it could also be from some really interesting place we don't know about (yet)," admits Dr. Anthony J. Irving, researcher at University of Washington in Seattle and specialist in meteorites of planetary origin. "But either way, it's a mystery, an enigma, and the answer would be an intriguing piece of knowledge."
Stefan Nicolescu, collections manager of the Peabody Division of Mineralogy & Meteoritics, who oversees 40,0000 or more specimens at the Peabody, was instrumental in making the exhibit happen.
Irving and his team's chemical analyses produced strong evidence the meteorite is from Mercury, due to its high magnesium and chromium content and low amount of iron - which concurs with what's been observed at the surface of Mercury by NASA's MESSENGER spacecraft. Its magnetic field is also a perfect match with what is known of Mercury's magnetism.
"We decided to be pretty closed-lipped about what we were doing, and we made sure we had everything done we could think of to believe it was from Mercury before the first public mention of it was presented last March in Houston," Irving says.
The exquisite specimen has a lustrous olive-green crust that was formed as the surface melted while passing through the earth's atmosphere - NWA 7325 is the brightest colored meteorite to have ever been discovered.
"The chromium effect creates a lot of the green color that makes it such a beautiful meteorite - it doesn't have a counterpart anywhere," Irving observes.
It could be as astonishingly old as 4.56 billion years, according to some scientists. Martian meteorites have been known to be even older. It is believed that the meteorite was exposed in space for 25.5 million years.
"It has a peculiar fusion outside crust that melted, and inside, fortunately, it stayed very cold for thousands of years longer," explains Irving.
"One thing that told me this was extraterrestrial rock was that it contains native iron, so we know it's not from here - it would be rusted. There's not that much oxygen in rocks on the Moon or Mars, Earth, Venus - it's very low in iron."
The color is also what made the rocks jump out on the desert. Irving and Nicolescu say it isn't more common for meteorites to fall in the North West African countries, it's just that the Nomadic lifestyle takes more people through the desert with their families and livestock, and therefore, more unusual specimens tend to be discovered in these less populated places.
"It's very fortuitous for us," Irving says. "The nomadic people are very astute about objects with value. They deserve credit for seeing the value in what they find and learning very quickly that things they find for free would have financial value. There's a market for these materials."
"These (specimens) are relatively easy to spot," Nicolescu adds. "The nomads self-train themselves to recognize them."
The Peabody exhibit also explains the composition of Mercury: the orbit, atmosphere, geography and surface gravity. It is the smallest, innermost of the planets in our solar system.
Scientific debate and inquiry will be ongoing during the nine-month tenure of the exhibit. Scientists locally and around the globe will be studying this NWA 7325 specimen to determine it's specific origin. Public forums will be scheduled as more information becomes available and will be posted on the museum website, www.peabody.yale.edu.