News item from SPA
New observations by the Wide-field Infrared Survey Explorer (WISE) indicate that there are significantly fewer near-Earth asteroids in the mid-size range than previously thought.
WISE scanned the entire celestial sky twice in infrared light between 2010 January and 2011 February. It observed more than 100,000 asteroids in the main belt between Mars and Jupiter, in addition to at least 585 'near-Earth' ones.
It observed in the infrared, detecting objects by their heat rather than by reflected light, and is supposed to have taken a more accurate census of the asteroid population than previous visible-light surveys which were affected by the differing albedos of asteroids.
The WISE data suggest that more than 90% of the largest near-Earth asteroids (1 km or larger), which would have global consequences if they were to strike the Earth, have been found.
It is believed that all near-Earth asteroids as much as 10 kilometres across, as big as the one that is thought to have wiped out the dinosaurs, are now known.
The new estimate for the number of mid-sized near-Earth asteroids, about 20,000, is lower than the 35,000 previously suggested. However, the majority of mid-size asteroids remains to be discovered.