Asteroid P/2013 P5

Hubble looks at a six-tailed asteroid. Credit: NASA, ESA, D. Jewitt (University of California, Los Angeles), J. Agarwal (Max Planck Institute for Solar System Research), H. Weaver (Johns Hopkins University Applied Physics Laboratory), M. Mutchler (STScI), and S. Larson (University of Arizona)

Hubble looks at a six-tailed asteroid. Credit: NASA, ESA, D. Jewitt (University of California, Los Angeles), J. Agarwal (Max Planck Institute for Solar System Research), H. Weaver (Johns Hopkins University Applied Physics Laboratory), M. Mutchler (STScI), and S. Larson (University of Arizona)

How cool is this? It’s an asteroid with an identity crisis. Just like the press release (linked below) says, an asteroid normally appears as a point of light. Not P/2013 P5, this thing is very comet-like in that it has a tail. In fact it has six tails!?

Six Tails? Wait, comets are ice and asteroids are rock. How does that happen?

Careful modeling by team member Jessica Agarwal of the Max Planck Institute for Solar System Research in Lindau, Germany, showed that the tails could have been formed by a series of impulsive dust-ejection events. She calculated that the first ejection event occurred on April 15 and the last one on Sept. 4. The rest sequentially erupted on July 18, July 24, Aug. 8, and Aug. 26. Radiation pressure from the Sun smears out the dust into streamers.

The asteroid could possibly have been spun up if the pressure of sunlight exerted a torque on the body. If the asteroid’s spin rate became fast enough, Jewitt said, the asteroid’s weak gravity would no longer be able to hold it together. Dust might avalanche downslope 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 1,000 tons of dust, has been lost. The 700-foot-radius nucleus is thousands of times more massive.

Follow-on observations may show if the dust leaves the asteroid in the equatorial plane, and this would be pretty strong evidence for a rotational breakup. Astronomers will also try to measure the asteroid’s true spin rate.

Here’s the full press release and links to larger images.