![]() It might also smell faintly of sulfur, appear heavily shocked, exhibit significant exposure to cosmic rays, and might even be slightly magnetic. For one thing, they're too reflective - anything coming from Mercury would be much darker, tinted by some yet-to-be-identified compound that's seen widely in Messenger's images. Also known as enstatite achondrites, aubrites are igneous rocks dominated by the iron-free mineral enstatite (Mg 2Si 2O 6).īut aubrites aren't from the innermost planet. This closely matches the composition of another rare meteorite group, the aubrites. Instead, the compositional clues suggest that a Mercurian meteorite would be an igneous rock - or perhaps a fused breccia of different rock types - rich in magnesium and volatile elements (especially sulfur and potassium). These contain very little iron and are similar - but aren't an exact match - to the composition of Mercury's surface. The Cumberland Falls stone, which fell in 1919, is one of only 62 recognized samples of aubrite meteorite. We now know that it's much different than that." After nearly a yearly scrutinizing the planet from orbit, Messenger has confirmed that iron is in short supply at the surface. "At that time," comments geochemist David Blewett (Applied Physics Laboratory), "people were expecting Mercury to have a composition more like a lower-iron version of the lunar highlands. A few years ago, meteoriticists had speculated that the best existing match to Mercury were a rare handful of ancient, basalt-rich stones known as angrites.īut even before Messenger's arrival, ground-based astronomers had concluded that Mercurian surface rocks contained very little iron - strange indeed, given that the innermost planet has an iron core that takes up 80% of its diameter and more than half of its volume! Meteorite collectors would value a Mercurian meteorite above all others, likely fetching $5,000 or more per gram, so they've been on the lookout for one. Gladman conservatively suggests that at least a half dozen stones should be lying around somewhere on terra firma. Their numbers suggest that Mercurian meteorites should be roughly one third as common as those from Mars, for which the count now stands at 60. The dynamicists conclude that 2% to 5% of the debris blasted by impacts off the surface of Mercury at or above escape velocity (2.6 miles per second) should reach Earth within 30 million years. Well, Shoshana, you might still get to hold such a rock someday.Īccording to a 2008 analysis by Brett Gladman and Jaime Coffey (University of British Columbia), chunks of Mercury should be lying somewhere on Earth right now. Dynamicists believe that such high-velocity impacts should have blasted many pieces of the innermost planet into space, some of which should have reached Earth. A dramatic splash of rays surround Mena, a fresh crater on Mercury about 10 miles (15 km) across.
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