When a comet’s not a comet after allPosted: October 14, 2010
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Back in January the Lincoln Near Earth Asteroid Research (LINEAR) survey saw something a bit odd amongst the asteroids in the main asteroid belt (found between Mars and Jupiter). Initially the mystery object, P/2010 A2, was designated as a main-belt comet (a rare object found within this region of the Solar System, unlike the majority of comets which orbit a lot further away) because of its elongated fuzzy appearance. However, two sets of results published in Nature today suggest that this thing is actually the aftermath of a collision between two asteroids that occurred some time in February or March 2009.
A comet generally has a fan shaped tail, topped with a dust-enshrouded nucleus; when the first team looked at P/2010 A2 with the Hubble Space Telescope though they saw that it has a more rectangular shaped tail, beginning in an X-shape:
The second team also saw a distinctly un-comet like structure (shown left) when they imaged the object with the OSIRIS camera onboard the Rosetta spacecraft. This had a really good view as it was approaching the asteroid belt at the time, in preparation for its flyby of the asteroid Lutetia.
Modelling the structures seen in both images by the two teams independently revealed that the main body of P/2010 A2 is about 120 metres across, that it was formed from a collision with a much smaller body, and that all this occurred about a year before we first saw it. Discovering all this isn’t possible from Earth though, as ground based telescopes, such as the one used by LINEAR, can’t see it from the right angle.
This sort of collision between asteroids of this approximate size are only predicted to occur roughly once every 12 years, so its likely that P/2010 A2 will remain unique for a few years yet.
Images credit NASA & ESA
Jewitt, D., Weaver, H., Agarwal, J., Mutchler, M., & Drahus, M. (2010). A recent disruption of the main-belt asteroid P/2010 A2 Nature, 467 (7317), 817-819 DOI: 10.1038/nature09456
Snodgrass, C., Tubiana, C., Vincent, J., Sierks, H., Hviid, S., Moissl, R., Boehnhardt, H., Barbieri, C., Koschny, D., Lamy, P., Rickman, H., Rodrigo, R., Carry, B., Lowry, S., Laird, R., Weissman, P., Fitzsimmons, A., Marchi, S., A’Hearn, M., Angrilli, F., Barucci, A., Bertaux, J., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Fornasier, S., Gutiérrez, P., Ip, W., Keller, H., Knollenberg, J., Kramm, J., Kuehrt, E., Kueppers, M., Lara, L., Lazzarin, M., López-Moreno, J., Marzari, F., Michalik, H., Naletto, G., Sabau, L., Thomas, N., & Wenzel, K. (2010). A collision in 2009 as the origin of the debris trail of asteroid P/2010 A2 Nature, 467 (7317), 814-816 DOI: 10.1038/nature09453