In response to international concerns about potential asteroid impacts on Earth, Nasa has implemented a new web-based monitoring system that will automatically update the orbits on a daily basis.
The Sentry system is also designed to forecast close approaches of near-Earth asteroids up to 100 years into the future.
The purpose of the programme, which has been under development for two years, is to co-ordinate Nasa-sponsored attempts to detect, track and characterise asteroids and comets that could approach Earth.
Sentry will focus on locating by 2008 at least 90 per cent of the estimated 1,000 asteroids and comets in our vicinity which are larger than 1km in diameter. About 500 of these have been found so far.
As of 21 March, 1,861 near-Earth objects have been discovered, 575 of which are asteroids with a diameter of 1km or larger. A total of 412 of these have been classified as potentially hazardous.
Donald Yeomans, manager of Nasa's near-Earth asteroids programme, explained that objects normally appear on the Risks Page because their orbits can bring them close to that of Earth's and the limited number of available observations do not yet allow their trajectories to be well-enough defined.
Sentry's online Risks Page, available here, includes 36 such asteroids at 21 March. Nasa researchers said the objects will disappear from the list when there are no longer any potential impact indications.
The system complements another online database, NEODyS Clomon, which runs in Italy. Personnel from both Sentry and NEODyS are in constant communication and crosscheck each other's results.
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