Fewer asteroids near Earth than previously thought

Sep 29, 2011, 22:19 GMT

Washington - The number of medium-sized asteroids near Earth is significantly lower than previously thought, according to a survey by a satellite-mounted infrared telescope released Thursday.

Data collected by NASA in a programme scanning space also indicate that researchers have now found 90 per cent of the largest asteroids in Earth's vicinity. Orbiting the sun near Earth are 981 large asteroids, defined by a diameter greater than 1,000 metres, none of which are likely to pose a danger to the planet within the next century, the survey showed.

'That can really reduce our risk for an impact by a really big one,' said scientist Amy Mainzer, who heads the asteroid-hunting effort at the US space agency's Jet Propulsion Laboratory.

Scientists estimate there are some 19,500 medium-sized asteroids - between 100 and 1,000 metres across - not the 35,000 previously believed.

Many of the medium-sized asteroids remain to be discovered and could still be very destructive if they were to hit Earth, the researchers said. An object 100 metres in diametre could devastate a major city.

The survey of asteroids was conducted by infrared instruments aboard a NASA satellite, which made it possible to survey both light and dark objects in the solar system.