A rare, golf-ball-sized lunar meteorite, called MIL 05035, reveals more about the Moon than samples taken directly from the lunar surface.
Credit: Case Western Reserve University
SYDNEY: A rare, golf-ball-sized lunar meteorite recently discovered in the snow fields of Antarctica can tell us more about the Moon than samples taken directly from the lunar surface, according to researchers.
The meteorite, known as MIL 05035, is similar in bulk and composition to basaltic lavas that fill the lunar maria, an expansive part of the Moon's surface not sampled by the U.S. Apollo program. Only one other meteorite of this type has ever been found.
"If you look at a map where the U.S. Apollo and Soviet Luna missions went, they only covered something like 17 per cent of the Moon and those were all near-side, near-equatorial sites," said Timothy McCoy of the Smithsonian Institution's National Museum of Natural History in Washington. "As it turns out, this region is geochemically different from the rest of the Moon."
Lunar meteorites found on the Earth seem to be more representative of the Moon as a whole, he said. "They can give us an idea of the variety of rocks that we should expect over a broader swathe of the Moon."
MIL 05035 was discovered on an icefield in the Transantarctic Mountains, roughly 750 km from the South Pole. A black rock, slightly larger than a golfball and weighing 142.2 g, the meteorite's chemical composition suggests it has been subjected to extreme shock, probably due to impact events. Large crystals suggest it formed by slow cooling deep within the Moon's crust.
While over 200 meteorites were found in Antarctica by a field party from the U.S. Antarctic Search for Meteorites program (ANSMET) during their 2005-2006 mission, MIL 05035 is remarkably unusual. Only one other meteorite, Asuka 881757, bears a close resemblance. It was also found in Antarctica and is one of the oldest known samples of lunar basalt.
"We discover rare types on a fairly regular basis, but it is always quite exciting," said McCoy. "To put this in perspective, we described 850 meteorites for the last issue of the Antarctic Meteorite Newsletter and only two or three of them would be considered of this type of rarity."
According to McCoy, such discoveries influence any future plans the U.S. space agency NASA might have for returning to the Moon. "It might inspire us to look for certain types of rocks or to travel to certain locales," he said.
"After the early lunar landings, we gained a much better appreciation of the impact history of the Moon … and rocks like MIL 05035 tell us that we are only beginning to fully understand this history. Going to particularly ancient craters, such as the enormous South Pole-Aitken basin, might help us further understand this history."
In the meantime, exploration will be left to the agents of ANSMET, who spend six weeks of every year living in tents on the ice, searching Antarctica for meteorites.
