An asteroid will skim past the Earth today in the cosmic equivalent of a near miss. The 30-40 meter wide lump of space rock from beyond Mars will shoot by at a distance of only 40,000 miles – less than a sixth the distance of the Moon and around twice the height of communications satellites.
It was only discovered on Friday, 27 February, by Robert McNaught as a faint 19th magnitude speck on a photograph of the sky he took at Australia’s Siding Spring Observatory in New South Wales. It was then one and a half million miles away but closing in rapidly.
The asteroid was labelled 2009 DD45 by astronomers. Closest approach occurs during daylight over Britain at 1.44pm UK time when it will be crossing the sky at a rate of half a degree – the Moon’s apparent diameter – a minute.
It will be close enough to be seen in amateur astronomers’ backyard telescopes from countries in darkness, such as Australia and New Zealand, as a tenth magnitude “star” passing through the constellation of Virgo.
Though there is no danger of a collision, the close approach is a reminder of the need to keep monitoring space for potential impactors. An asteroid the size of DD45 could cause devastation and loss of life if it struck or exploded over a town or city. Close encounters with Earth-crossing asteroids, or Near Earth Objects, turn our region of space into a cosmic shooting gallery.
More than a thousand potentially hazardous asteroids are known to cross our orbit and early 900 are known that are around 500 ft wide. Last October one labelled 2008 TC3 struck a remote part of Sudan only hours after it was first spotted.
In 1908, an asteroid or small comet similar in size to 2009 DD45 exploded over Tunguska, a remote region of Siberia, with the force of up to 15 million tons of TNT, flattening trees for more than 1,000 square miles around.
An impact with an asteroid called Apophis in 2036 has still not been ruled out, although the chances are slim.
Picture: A larger asteroid called Gaspra, photographed by the Galileo spaceprobe in 1991.