The mystery of a comet-like object circling among the main-belt asteroids has deepened, now that astronomers have slewed the Hubble Space Telescope (HST) over for a close-up look.
The release of a Hubble image taken on 29 January shows that this object, called P/2010 A2, is no normal comet. There鈥檚 a strange X-shape feature at its brightest end (I hesitate to call it a 鈥渘ucleus鈥�) that defies easy explanation. 鈥淭his is quite different from the smooth dust envelopes of normal comets,鈥� explains David Jewitt of the University of California at Los Angeles, who led the Hubble effort. The Hubble view also clearly shows a point-like object hovering nearby, about 1600 kilometres from the 鈥淴鈥� and seemingly connected to it by a thread of material.
Comets within the asteroid belt aren鈥檛 unprecedented. comments that four others are known. Most notable among these is 133P/Elst-Pizarro, first spotted as an asteroid in 1979 and then found to have a cometary appearance in 1996.
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Fast-spinning asteroid?
But apart from its long tail of debris, P/2010 A2 doesn鈥檛 look much like a comet, at least in the HST images taken on January 25th and 29th. Moreover, it lacks the emissions that are usually found in a comet鈥檚 coma and tail. 鈥淣o gas yet,鈥� Jewitt told me, 鈥渂ut we are still looking.鈥� Unfortunately, a request to observe this curiosity with the Spitzer Space Telescope was turned down.
The most likely explanation for this object鈥檚 sudden appearance is that a pair of small, unseen asteroids collided, creating the trail of debris first spotted on January 6th by the LINEAR telescope in New Mexico.
So would a smashup involving two main-belt asteroids result in something like this? Perhaps. 鈥淏ill Bottke and I are thinking about what kind of modelling would be useful to do with this object,鈥� notes of the Southwest Research Institute in Boulder, Colorado, 鈥渂ut we have nothing definitive so far鈥�. Bottke notes that while a collision seems plausible, it鈥檚 also possible we are witnessing an asteroid that has been spun up (by gradual interactions with sunlight) to the point that it started shedding mass.
Jewitt says that there鈥檚 no handle yet on whether the 鈥渘ucleus鈥� is tumbling or spinning rapidly. But he says more Hubble sessions are planned in the months ahead.
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