Its discovery is important in understanding the behavior of a double system, in case such a system approaches the Earth and endangers it
A rare event has given astronomers a good look at a double asteroid system. On July 14, the asteroid 2008 BT18 passed at a distance of about 1.5 million km from the Earth. It shone as a star at magnitude 13. Before July 7, astronomers believed that BT18 was another near-Earth asteroid, but an observation made by the Arecibo Radio Observatory using a delayed Doppler imaging device revealed that it was a double system. Although double asteroids are common in the solar system, this was a rare opportunity for a ground-based telescope to capture such a clear view of a double asteroid.
Double impact craters found on Earth indicate that our planet has been hit by double asteroids in the past. Although BT18 does not pose a threat to Earth, astronomers want to learn more about binary asteroids to understand how they form and how they can be diverted from Earth-friendly orbits, should such a pair approach and endanger Earth.
About 16% of the asteroids in the solar system are considered double asteroids, so the event served as a great opportunity for Arecibo to photograph one of these and it can also be observed by amateur telescopes as a star at magnitude 13. The Arecibo Observatory has so far discovered 53% of all double asteroids close to Earth, so it is an important component of observations on these objects. In the coming days it will still be possible to see it crossing the constellation Canis Major towards the south.
