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Andrew Alden

A New Candidate for a Mercurian Meteorite

By March 31, 2013

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One of the hundreds of items on my list of things to look out for is "news about meteorites from Mercury." A few years ago meteoriticists were excited about the angrite class of meteorite, which was the last time the topic came up. It turns out that the experts thought better of the idea. However, this year at the 2013 Lunar and Planetary Science Conference a new rock, there was a presentation about the spectacularly green stone NWA 7325, "a 345 gram dark green, igneous achondrite with partial chartreuse-colored fusion crust" made of a remarkable blend of plagioclase, chromian diopside and olivine. Anthony Irving of the University of Washington stated that it has every sign of coming from a large, differentiated rocky body—a planet—but doesn't match any of the candidates we know about. It matches the data we have from Mercury, though.

There are any number of breathless stories that make this sound like revolutionary proof, but it's not. An early version of the story by the Planetary Society's Emily Lakdawalla gives the most authentic flavor of this story: it's a strong, tantalizing possibility that has not been fully reviewed in the formal publication process. For one thing, Irving's group had nothing to say about Venus or Theia as a source. Even the Moon is not fully ruled out. Stay tuned, but it may be a while before the next news.

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