A group of scientists using NASA’s Hubble Space Telescope has discovered a unique multi-tailed object, labeled P/2013 P5, in the main asteroid belt.
P/2013 P5 is about 790 feet (240 m) in diameter. It has six comet-like tails of dust radiating from it like spokes on a wheel.
P/2013 P5 was first seen as an unusual object with the Pan-STARRS survey telescope in Hawaii.
Its multiple tails were discovered in Hubble images taken on September 10, 2013. When Hubble returned to the object on September 23, its appearance had totally changed. P/2013 P5 looked as if the entire structure had swung around.
“It’s hard to believe we’re looking at an asteroid. We were dumbfounded when we saw it. Amazingly, its tail structures change dramatically in just 13 days as it belches out dust,” said Prof David Jewitt from the University of California, Los Angeles, who is a lead author of the article published in the Astrophysical Journal Letters (full paper).
One interpretation is that the P/2013 P5′s rotation rate increased to the point where its surface started flying apart, ejecting dust in episodic eruptions. The astronomers have ruled out a recent asteroid impact scenario because a large quantity of dust would have been blasted into space all at once.
“This object has ejected dust for at least five months,” Prof Jewitt said.
Careful modeling showed that the P/2013 P5′s tails could have been formed by a series of impulsive dust-ejection events. Radiation pressure from the Sun smears out the dust into streamers.
“Given our observations and modeling, we infer that P/2013 P5 might be losing dust as it rotates at high speed,” said co-author Dr Jessica Agarwal of the Max Planck Institute for Solar System Research.
“The Sun then drags this dust into the distinct tails we’re seeing.”
The asteroid could possibly have been spun up to a high speed as pressure from the Sun’s light exerted a torque on the body.
“If the asteroid’s spin rate became fast enough, the asteroid’s weak gravity would no longer be able to hold it together. Dust might avalanche down towards the equator, and maybe shatter and fall off, eventually drifting into space to make a tail. So far, only a small fraction of the main mass, perhaps 100 to 1000 tones of dust, has been lost. The asteroid is thousands of times more massive,” Prof Jewitt said.
“Follow-up observations may reveal whether the dust leaves the asteroid in the equatorial plane. If so, that would indicate a rotational breakup.”
“The object may be a piece from an asteroid collision that occurred roughly 200 million years ago. The resulting collision fragments, known as the Flora asteroid family, are still following similar orbits. Meteorites from these bodies show evidence of having been heated to as much as 1,500 degrees Fahrenheit,” Prof Jewitt said.
Bibliographic information: David Jewitt et al. 2013. The Extraordinary Multi-tailed Main-belt Comet P/2013 P5. ApJ 778, L21; doi: 10.1088/2041-8205/778/1/L21