Asteroid P/2010 A2 was discovered in 2010 by the Lincoln Near-Earth Asteroid Research project, which was searching for near-Earth objects with the potential to threaten Earth. It is an asteroid roughly 220 m long in the inner part of the Main Asteroid Belt, orbiting every 3.47 years at an average distance of 2.29 AU from the sun (i.e. 2.29 times as far from the Sun as the Earth is). The asteroid had a tail of material following it, and was originally classified as a comet, but follow-up observations by the Hubble Space Telescope and the Rosetta Spacecraft revealed this to be a trail of debris from a collision with another body, probably in February or March 2009. The name P/2010 A2 implies a periodic comet (P) discovered in the first two weeks of 2010 (2010 A - if dicovered in the second two weeks it would have been 2010 B etc.), and that it was the second comet discovered in this period (2). Despite the re-classification of the object, the name has stuck.
Hubble image of P/2010 A2.
On 14 January 2012 a paper appeared on the arXiv database at Cornell University Library, by a team lead by Korean Astronomer Junham Kim detailing the results of a new study of P/2010 A2 using a 105 cm telescope at Ishigakijima Observatory in Japan.
P/2010 A2 is considered to be part to the Flora Family of asteroids, asteroids of the Inner Main Belt, orbiting between 2.17 and 2.33 AU. The origin of the Flora Family of asteroids is uncertain, they may have originated from the break-up of a single, larger body, or they may have different origins and have been herded into a distinct band by the gravitational influence of larger bodies. The Flora family is thought to be the source of the majority of stoney meteorites that fall on Earth, and has been linked to the large object that some scientists believe collided with the Earth at the end of the Cretaceous, bringing about the mass extinction that wiped out the dinosaurs (though attributing origins to strictly hypothetical bodies is not very good science).
The overwhelming majority (92%) of the Flora Family are S or Sq-type asteroids - stoney or stoney with some metal traces. Only two bodies towards the outer edge of the group are considered to be C-type asteroids, made up of a mixture of water ice and hydrated minerals.
By carrying out a spectrographic analysis of both P/2010 A2 and its tail, Kim et al. hoped to be able to place the asteroid in a precise type, important when trying to understand its origin, since an icy meteor might produce a tail similar to a comets when heated by the sun, whereas a stoney asteroid could only have a tail as a result of a collision. In the event they were not able to classify P/2010 A2 very well. The spectrum for the asteroid was not distinct enough for a classification to be obtained, based upon its spectra it could be an S, an Sq or a C-type asteroid. The tail was even less helpful, it could not be clearly assigned to an asteroid type, though it appeared highly atypical for S-type asteroid material.
Based upon its position within the Flora Family and its orbit, which brings it within 2.00 AU of the Sun at its closest, Kim et al. consider it unlikely that P/2010 A2 is an icy object, since it would have long since have been evaporated by the Sun's heat if this was the case. They consider it more likely that it is an S-type asteroid, and that the anomalous spectra of the tail comes from its containing a high proportion of material from inside the original body, that may not have the same colour as material from the outer surface as it is unweathered by conditions that the outer surface material is exposed to.
