Two moons for one asteroid

Radar observations of 1994 CC show that this asteroid which flew by the Earth in June 2009 is part of a triple system.

 

Radar observations of asteroid (136617) 1994 CC made with one of the Goldstone radio telescopes on 12 June 2009 at 17 minute intervals. The main 700 m wide object has two moons, each approx. 50 metres in diameter (arrows). Credit: NASA/JPL/GSSR

Certain asteroids follow orbits which bring them more or less regularly close to our planet. They are known as NEA, Near Earth Asteroids, as they can come close to, or cross, the Earth’s orbit. They are obviously monitored, notably by automatic telescopes that scan the sky, scrutinizing their trajectory as well as tacking down new ones. And when certain come sufficiently close, astronomers do not fail to observe them in the hope of learning just that bit more.

Two small moons
Although it is classified as an NEA, 1994 CC does not present any immediate danger. In June 2009 it flew “close” to our planet but only in the astronomical sense as the distance between us was, in fact, a comfortable 2.52 million kilometres (more than 6 times the Earth-Moon distance). Moreover, this 700 m diameter rock is to fly past us again in 2074, but it will still be two and a half million kilometres away. However, good use was made of the rendezvous on 12 June for studying the asteroid by means of radar waves from the Goldstone observatory in California.

Goldstone observatory, equipped with several radio telescopes, is located in California’s Mojave Desert. Credit: NASA

And surprise, it was seen to be a triple system: the main 700 m wide asteroid is actually accompanied by two small moons, each approx. 50 m in diameter. The discovery was made by two scientists from NASA’s Jet Propulsion Laboratory (JPL). The famous institution, which is also responsible for numerous robotic missions on behalf of the American agency, states that out of the hundreds of NEA asteroids that it observes by radar, only 1% are part of triple systems, thus highlighting the importance of the 1994 CC study. JPL are to continue analysing the data.

Consult our feature entitled “Asteroids: from science to exploitation” to find out more about this subject.

Published on 10 August 2009