AN asteroid capable of devastating an area the size of a sub-continent has about a one in 1000 risk of hitting Earth early next century, NASA said today. The rock, 2004 VD17, is about 500m long and has a mass of nearly a billion tonnes. If it hit Earth it would deliver 10,000 megatonnes of energy, equivalent to all the world's nuclear weapons. Spotted on November 27 2004, VD17 was identified as potentially crossing Earth's orbit, with a one in 3000 risk of collision on May 4, 2102. Further observations and calculations have prompted the risk on that day to...