On 27 February 2009 the Near-Earth Asteroid Research survey at Siding Spring discovered a small asteroid, about 50 metres in diameter, which proceeded to skim past the Earth at a distance of only 60,000 kilometres.
As this asteroid was about the same size as that which devastated the Tunguska region in Siberia in 1908, flattening around 5,000 square kilometres of forest the fact that it did not hit our planet was extremely fortuitous.
However, it has recently been revealed that a second discovery was made from the ASNSW’s dark sky observing site at Wiruna a few hours later that night by an expert team of Astro-Imagers headed by Mike Bourbon-Jones, at a time when Siding Spring was clouded out.
This team had been field testing new image acquisition software and in one of the images being processed, they happened upon a second asteroid of similar size following on some hours behind that which was discovered at Siding Spring, perhaps part of a swarm, and which passed slightly closer to our planet than the first one.
Fortunately the image was being processed while the new asteroid was still overhead, so that the team's technical officer, Mike Sunsurfski was able to quickly reconfigure the adjacent society radio telescope into radar mode, fit the Speckle-Doppler Quad-Core Receiver, and collect valuable data on the velocity and orbit of the newly discovered object.
Computer analysis of the data revealed that rather than continuing past our planet and back into the outer solar system, the asteroid had arrived at a time when the alignment between the Earth and Moon had contributed to the asteroid being subjected to a continuous “slingshot effect” between the Earth and the Moon.
When passing by the Earth, it was flung into a curious “Figure-8” orbit which took it around the far side of the Moon and then back towards Earth where it passed behind our planet and then headed back out towards the Moon again.
As the precise stability of the orbit had not been determined the discovery was not immediately made public to avoid a panic, however following daytime adjustments to the Speckle-Doppler Quad-Core Receiver, refined calculations have largely dispelled early fears.
Estimates now suggest that although the orbit may not be entirely stable, the highest chance of an impact would be with the Moon rather than the Earth, and would not be until 2015 at the earliest.
There was a relatively small (< 10%) chance of an impact with planet Earth during April 2014 either in Australia's Simpson Desert region or in a region known as Canberra within the Australian Capital Territory - fortunately neither location represent a significant part of the planet worthy of concern.
ASNSW Astro-Imagers have managed to take a number of photos of the asteroid transiting the Moon, one of which is reproduced below.
Having been given naming rights by the International Astronomical Union the team consulted and named the new object “Apotheosis”.
The discovery has inspired the Astro-Imagers to set up a routine Near-Earth Asteroid Search Program to search for asteroids each new moon weekend at Wiruna, with Monte Willsin nominated to act as Asteroid Team Leader.