By Adrian Berry, Science Correspondent

THE number of asteroids and comets that could be on collision course with Earth is much greater than previously believed.

Using a new kind of computer chip in a 39-inch telescope at the summit of Mount Haleakala in Hawii, astronomers said yesterday that they had found a hitherto unknown comet and four asteroids.

The discovery was disturbing because although the skies had been searched for 25 years for small but potentially dangerous objects of this kind, this was the first time that these particular ones had been spotted, said Dr Eleanor Helin, of the Jet Propulsion Laboratory, in Pasadena, California.

"Since these objects that cross the Earth's orbit have not been seen before, that is strong evidence than many others are near the vicinity of our planet," Dr Helin said. "These discoveries suggest that we could face a surprise encounter with a large, unseen object."

The March run of the camera called NEAT camera - Near Earth Asteroid Tracking - detected 2,400 objects of which only 45 percent had hitherto been known. When the camera is upgraded next month, astronomers expect to detect four times the number of comets and asteroids that at present can be observed.

With its short exposure time and ultra-fast electronics, NEAT is able to achieve wide-sky coverage and detect objects much fainter than was possible with earlier asteroid-hunting telescopes. It detects sunlight shining on small objects 100 times more efficiently than the most sensitive photographic film.

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