Asteroids lurk in the dark

In order to deal with the danger of asteroids hitting the Earth, they must be located ahead of time. But how do you deal with a danger that hides in space? The Wise Space Telescope reveals dark asteroids that have so far disappeared from sight

Yoram Ored, Galileo

Tracking asteroids close to the Earth's orbit around the Sun is of great importance due to the danger that one of them will hit the Earth and cause great damage. Such asteroids have been tracked for many years, but it is not always possible to identify them due to optical circumstances.

Dark asteroids were recently discovered using the WISE space telescope, which had not been discovered until now due to their low light reflection (albedo) and due to their tilted orbit relative to the plane of the Earth's orbit around the Sun.

The WISE Space Telescope (Wide-Field Infrared Survey Explorer), launched by NASA in December 2009. Its purpose is to map the sky using infrared radiation observations.

Wise recently managed to discover 16 asteroids, which, as mentioned, were not discovered before, orbiting the Sun in an orbit close to the orbit in which the Earth orbits the Sun. 55 percent of them reflect less than a tenth of the solar radiation that hits them, in other words they are very dark and difficult to locate using visible light telescopes.

On the other hand, the infra-red radiation emitted by them is precisely because they heat up due to the absorption of the sun's radiation in them. Many of these dark asteroids circle the Sun in orbits tilted relative to the plane of orbit of the planets and most of the asteroids, and thus they may escape the "eyes" of telescopes surveying the asteroid belt.

Astronomers expect the discovery of about 200 near-earth objects by the Wise Space Telescope. However, it is estimated that the number of objects whose mass is large enough to cause damage when impacting the Earth may reach tens of thousands.

The article was published in Galileo magazine, June 2010