ESA study reveals twice as many asteroids as previously believed
There may be more asteroids in our solar system than was previously thought, according to the results of the first search performed using the European space agency (ESA) infrared space observatory (ISO). The ISO Deep Asteroid Search (IDAS) indicates that there are between 1.1 million and 1.9 million space rocks larger than 1 kilometre in diameter in the solar system's main asteroid belt, around twice previous estimates. Astronomers believe, however, that it is still too early to revise current assessments of the risk of the Earth being hit by an asteroid. Despite their relative proximity, it can be harder to observe asteroids in our own solar system than distant galaxies. The changing brightness of asteroids and their relative speed - they have been dubbed 'vermin of the sky' because they often appear as trails on long exposure images - means asteroids can prove elusive to astronomers. IDAS, the first ever systematic search for these objects performed using infrared light, focused on the main asteroid belt between Mars and Jupiter where asteroids are too far from Earth to pose any significant threat. As it is impossible to focus on the whole asteroid belt at once, astronomers analysed selected regions and then used a theoretical model to apply the data to the whole belt. Edward Tedesco of the USA's TerraSystems Inc., one of the astronomers involved in the project, said: 'If you consider the average value of 1.5 million asteroids, the ISO result is about twice as high as estimated by two other recent studies in visible light.' The ISO operated from 1995 until May 1998. During this period it made nearly 30,000 scientific observations.