Thursday, March 13, 2008

Antarctic Meteorites Baffle Scientists

via National Geographic, scientists are struggling to identify the source of a pair of meteorites recovered from the Graves Nunataks region of Antarctica in 2006. First thought to have originated from the planet Venus, the rocks origin have continued to puzzle researchers. The Venusian theory been put to rest as the samples have been proven to be far older than the Venusian surface. The rocks are superficially similar to lunar rocks recoverd by Apollo 16 astronauts, but contain a much higher percentage of sodium.

"The identity of the meteorites' source remains exciting and mysterious, said Allan Treiman, a scientist with the Lunar and Planetary Institute in Houston who led one of the recent investigations of the rocks.

"From what has been reported so far, it's pretty clear that the meteorite is not from the Earth, or the moon, or Venus, or any of the common sources of meteorites," he said. "It's much harder to know where it is from."

The second team conducting analysis of the rocks initially believed them to originate either on the Earth or the Moon due to the composition of an oxygen isotope analysis, but other observations torpedoed that theory as well. Another researcher from the Carnegie Institute, Doug Ramble, beleives he has identified the meteors as the extremely rare brachinite type. These rocks are believed to have originated from early planetoids that orbited between the planets Mars and Jupiter in the early formative years of the solar system.

However, other researchers say that they don't fit neatly into this category either, nor do they exactly fit the more common chondrite type that originates from the asteroid belt, although they do have similiarities to both of these types of meteor. The meteors have a couple of rather unique characteristics that greatly complicate their analysis. One is that they have undergone a partial melting, which is not a chondrite characteristic, and the second is they contain unusually high levels of the mineral feldspar, which is not common of rocks originating between Mars and Jupiter. The melting appears to indicate an origin from a dwarf planet or very large asteroid, but it still uncertain what kind of geologic activity would create such unique characteristics.

Identification of these rocks' origin would greatly aid our understanding of the early formative years of the solar system and how asteroids and planetary bodies form.

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