Thursday, November 7, 2013

Surprising Recent Discoveries of Three Large Near-Earth Objects

via NASA

Don Yeomans and Paul Chodas
NASA/JPL Near-Earth Object Program Office
November 5, 2013

Two surprisingly large Near-Earth Asteroids have been discovered in just the last week or so, as well as a third moderately large asteroid which surprisingly has also gone undetected until now, even though it can pass close enough to the Earth to be classified as "potentially hazardous". Not since 1983 has any near-Earth asteroid been found as large as the approximately 20-kilometer (12-mile) size of the two new large ones. In fact, there are only three other known near-Earth asteroids that are of comparable size or larger than the two new large ones. It is important to note that none of these three new large near-Earth asteroids can come close enough to the Earth to represent a near-term threat to our planet. The first of the new large near-Earth asteroid discoveries is named 2013 UQ4, and it is perhaps the most unusual. This approximately 19-kilometer (12-mile) wide object was spotted by the Catalina Sky Survey on Oct. 23 when the asteroid was 435 million kilometers (270 million miles) away from Earth. Not only is this object unusually large, it follows a very unusual highly inclined, retrograde orbit about the Sun, which means it travels around the Sun in the opposite direction of all the planets and the vast majority of asteroids. The only objects usually found in retrograde orbits are comets, which suggests that 2013 UQ4 may be the remains of an old comet that no longer possesses the near-surface ices required for it to become active while near the Sun. Comets that have exhausted most, or all, of their volatile ices do not spew dust during sweeps through the inner-solar system like their less-seasoned, more hyperactive space kin. Without the telltale comet tails or atmospheres, dead comets look like, and in fact for all practical purposes are, asteroids. (continue reading here

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