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Asteroid, invisible



HEALTH & SCIENCE

||| NEW SCIENTIST - One of the largest asteroids known to have
approached the Earth zipped past about 450,000 kilometres away on March
8 - but nobody recorded it until four days later. The object, now called

2002 EM7, was hard to spot because it was moving outward from the
innermost point of its orbit, 87 million km from the Sun. When it passed

closest to the Earth - just 1.5 times the distance to the Moon - it was
too close to the Sun to be visible. Asteroids approaching from this
blind spot cannot be seen by astronomers. If a previously unknown object

passed through this zone on a collision course with Earth, it would not
be identified until it was too late for any intervention. Astronomers
have made numerous calls in recent years for more funds to catalogue
near-Earth objects and refine their orbits. This would reduce the number

of unknown objects that could catch us unaware, and give early warning
of potential future collisions. . .

Invisible to the unaided eye, 2002 EM7 is too small to be classed as a
"potentially hazardous asteroid." But it is probably between 50 to 100
metres across, making it larger than the object that exploded in 1908
over the Tunguska region of Siberia, flattening trees over 2000 square
kilometres. The approach puts it among the 10 closest known approaches
by minor planets, says Brian Marsden of Harvard-Smithsonian. More
ominously, only one of the 10 closest objects was larger. This was 1996
JA1, which passed only slightly closer to the Earth on 19 May 1996.

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http://www.newscientist.com/news/news.jsp?id=ns99992052