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Collection notes: Moore County meteorite

June 12, 2012
Moore County meteorite
The Moore County meteorite, showing some of the flight markings caused by abrasion from the atmosphere.

It fell with roaring and zooming noises, trailing black smoke and sparklers. It was 21 April, 1913, and the meteorite landed within six feet of three men working a cotton field (for Google Earthlings, at 35.416670° , -79.383330°). They later claimed that it inspired them to give up drinking and swearing. After all, God had sent them that rock from the Rocky Mountains.  Haig Cockman ran to pick it up, a mistake he quickly realized. (Details are in the notes of Harry Davis, then Curator of Geology for the North Carolina State Museum, who later interviewed the men.)

Harry Davis co-authored the formal description of the meteorite, known as Moore County,  in 1936. First author of the paper was E.P. Henderson of the Smithsonian Institution, who realized that the meteorite was a eucrite.

Most meteorites are chondrites: they contain tiny rounded blebs known as chondrules. Chondrites really don’t have a terrestrial counterpart, but eucrites are a form of achondrite, similar to terrestrial basalts.  Since 1936 data has accumulated to relate the eucrites to another kind of meteorite, the diogenites. Diogenites are similar to earthly gabbros, a crystallized version of a basalt. The eucrites and diogenites are together related to howardites, which are made of pieces of the other two. This became known as the HED (howardite, eucrite, diogenite) family of meteorites. HED meteorites come from a parent body that was well on its way to becoming a planet before a collision short-circuited the process.

Vesta elevation - Hubble Space Telescope

Asteroid 4 Vesta. Hubble Space Telescope image, upper left. Interpreted images, upper right. Elevation model showing the impact basin at the south pole at bottom. Blue is lower elevations, and the central cone in the crater is prominent. Courtesy JPL/NASA.

The story heated up in the 1970’s when scientists using optical spectroscopy realized that the oddball HED meteorites had spectra that matched that of an oddball asteroid, 4 Vesta. In 1979, Frank Drake suggested that Vesta was the source of these achondrites. Strong support came from the Hubble Space telescope in 1995, which found a Connecticut- sized crater near the south pole of Vesta.

The interior of the crater was a match for the diogenites, and the crust around the crater was a match for the eucrites.  Here was a fabulous natural laboratory for studying the way that planets form. If we could only take a closer look….

The closer look is going on right now. In 2007, NASA launched the Dawn mission  with the objective of studying the protoplanets Vesta and Ceres. Some of the first results were presented at the American Geophysical Union (AGU) meeting in December. The first good looks at Vesta showed a lot of strange and wonderful features that will inspire years of study, including the giant Rheasilvia impact basin. (AGU meeting abstracts can be searched for Vesta or Dawn.) The journal Science published several Vesta papers in the 11 May 2012 issue. NASA is sharing the data on its Dawn website, including this false-color image of a rotating Vesta. The end of the video shows the giant impact basin at the south polar region.

In the meantime, you can visit the North Carolina Museum of Natural Sciences’ piece of Vesta on the second floor of the main building.

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