2102 space rock to give Earth its closest shave, say watchers

SPACE: A space rock capable of sub-continent scale devastation has about a one in 1,000 risk of colliding with Earth early next century, the highest of any known asteroid, watchers said on Thursday.

The rock, 2004 VD17, is about 500 metres (yards) long and has a mass of nearly a billion tonnes, which - if it were to impact - would deliver 10,000 megatonnes of energy, equivalent to all the world's nuclear weapons.

Spotted on November 27 2004, VD 17 was swiftly identified as rock that potentially crossed Earth's orbit, with a 1 in 3,000 risk of collision on May 4 2102.

Further observations and calculations have prompted the risk on that day to be upgraded to "a bit less than 1 in 1,000," said NASA Near-Earth Object (NEO) expert David Morrison in an emailed circular.

"The risk of an impact within the next century (is) higher than that of any other known asteroid," he said, stressing however that the likelihood of a hit was small.

"Fortunately, it is nearly a century before the close pass from VD 17. This should provide ample time to refine the orbit and, most probably, determine that the asteroid will miss the Earth."

VD 17, which was previously categorised as a grade green ("merits careful watching") on the Torino scale of NEO hazards, has been upgraded to grade yellow, "meriting attention."

There are two more grades beyond this, orange ("close encounter") and red ("collision is certain"), involving objects capable of inflicting regional or global devastation.

The asteroid's closest proximity to Earth on the 2102 flyby was not given by Morrison or the hazard list maintained by NASA and the US Jet Propulsion Laboratory (JPL).

Further observations, however, downgraded Apophis' risk to a one in 5,000 chance of collision, making it a grade green risk.

Apophis, measuring 300 metres (1,000 feet) across and with a mass of less than 100 million tonnes, will fly by Earth at a distance of 36,350 km (22,600 miles) from the Earth's surface on April 13, 2029, slightly higher than the altitude of geosynchronous satellites, according to the website of the International Astronomical Union's Minor Planet Center.

PARIS, Friday AFP