By Jonathan Leake in London

NASA is drawing up a shortlist of ideas, to be unveiled early next year, for diverting a 40 million tonne asteroid on course to pass dangerously close to Earth.

Fears that the planet may be in danger from being struck by asteroids were heightened by the discovery of one orbiting the sun that, on its present path, will pass within 35,405km - a hair's breadth in astronomical terms - in April 2029.

NASA's plan is to engineer a minor shift in the asteroid's trajectory that would make it miss Earth by a wider margin on this and all subsequent passes.

Under one possible plan, a robotic craft would be sent to the asteroid to attempt to alter its course. One option might be to install a propulsion system on the surface to nudge it onto a new course.

The schemes will be presented and discussed at the annual meeting of the American Association for the Advancement of Science.

The studies follow the discovery of hundreds of small asteroids orbiting the sun that repeatedly cross Earth's orbit, raising the possibility of a devastating collision.

The one causing most concern is a rock of more than 304m called Apophis, the Greek name for the Egyptian god Apep, known as "the destroyer". It will come so close to Earth it will pass under many satellites and may destroy some.

Astronomers fear that although 2029 should pass without incident, coming so close to Earth might change Apophis's 323-day orbit around the sun - during which it crosses the planet's path twice - creating an even bigger risk in the future. A second close encounter is predicted for 2036.

http://www.news.com.au/story/0,23599,20973995-401,00.html