The path of the small asteroid 2010RF12 around the Sun. On this scale on 9 September 2010 the positions of Earth and the asteroid cannot be separated. Image credit NASA/JPL
Between 7 pm AEST on Wednesday 8 September 2010 and 8 am the next morning two small, newly discovered pieces of space rock are passing between the Earth and the Moon. Such passes by small asteroids are not rare, but it is unusual to have two happening at almost the same time. The two asteroids, 2010RX30 and 2010RF12, were both discovered by the Catalina Sky Survey operated by the University of Arizona on Sunday 5 September 2010.
The asteroid 2010RX30 is believed to be the larger with an estimated width between 10 and 20 metres. It is due to pass at a distance of about 230,000 km above the Earth at about 7:45 pm AEST Wednesday. A large telescope will be needed to see the object even at its closest and it will be low in the sky and setting as seen from Australia.
The asteroid 2010RF12 is estimated at 6 to 14 metres in width. It is due to pass the Earth on Thursday morning at about 7:15 am at a distance of about 77,000 km. This distance is about twice the height at which geosynchronous communication satellites circle the Earth so they should be safe. At the time of closest approach the Sun is already up for the east coast of Australia, but the object should be visible for much of the previous night. Note though it is faint (magnitude 14) so only people with large telescopes, a dark sky and good practical knowledge of the sky would be able to locate and track the object as it races across the sky.
According to NASA’s Jet Propulsion Laboratory there are about 50 million undiscovered asteroids of around 10 metres in width in the vicinity of the Earth’s path around the Sun. Consequently passes near the Earth are not uncommon. Impacts with Earth happen roughly every 10 years or so – such as the impact over Indonesia on 8 October 2009. Fortunately, stony asteroids of that size explode in the atmosphere and are not likely to cause damage on the ground.
The passages of two space rocks close to the Earth is an interesting event, but there is no need to worry or lose sleep because of them.