On July 27, NASA announced the discovery of the first Trojan asteroid, designated 2010 TK7, which shares the Earth's orbit. It was initially spotted by the Wide-field Infrared Survey Explorer (WISE) mission on 2010 Oct 01 at a solar elongation close to 90 degrees and the near-Earth object was flagged on the NEO Confirmation Page shortly afterwards. Using the Faulkes Telescope South located at Siding Spring , amateur astronomer Sergio Foglia observed the NEOCP object (see Figure) and reported astrometry on October 6. However, since the final observing arc spanned a total of only 6 days, its special nature was not evident at that time. Martin Connors of Athabasca University in Canada and colleagues used observations made in late April this year with the 3.6-m CFHT on Mauna Kea to identify 2010 TK7 as a Trojan object; one which currently circulates around the L4 Lagrangian point thereby leading the Earth in its orbit around the Sun. For more information see the NASA JPL webpages and NASA videos.
Such objects typically remain gravitationally trapped for relatively short periods (1,000-100,000 years) and eventually switch to one or other Lagrangian point or are even ejected altogether thereby losing their unusual Trojan status. They are of particular interest in that they are potentially useful as a spacecraft destination in that they can be energetically less costly to reach than our Moon - even as a possible site for a future space observatory. It is likely that there are a number of natural objects which are loosely bound to each of the Earth's Lagrangian points, where they occupy relatively shallow gravity wells. However, astronomers have searched for Earth Trojans for some years now without success and so those that do exist are all likely to be less than 1 km in size. 2010 TK7 is estimated to be 150-500 metres across depending on its albedo (assumed range: 0.04-0.25). However, although it orbits the Sun almost exactly once per year, the orbit is at present rather too inclined (I = 21 degrees) and has too large an eccentricity (e = 0.19) for it to be a convenient target for a visitation by a spacecraft in the near future.
Follow-up observations are required to better define the exact shape of this Earth Trojan's orbit. It is currently magnitude 22 but will be more favourably situated in Oct/Nov 2011 when it attains a V magnitude of 21.
The observations are being made as part of IASC collaboration, and the observations were made using observing time given to Faulkes Telescope Project by LCOGT.
Many thanks to Richard Miles from BAA for sending us this report.
*** Updated report from one of the observers, Luca Buzzi on his blog ***
