"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."

Preliminary calculations indicate 2002 EM7 has several chances to hit the Earth in the next century, with odds of one in six million to one in a billion, reports New Scientist.

It isn't so rare, says Jim Scotti (University of Arizona), "Simply put, objects the size of the Tunguska impactor pass within the distance that 2002 EM7 did about 25 times every year." Rocks the size of 2002 EM7 come by nearly 100 times a year.