Six Tails of An Asteroid

Hubble P5 Image
Image Credit: NASA, ESA, and D. Jewitt (UCLA)
P/2013 P5, the six-tailed asteroid.

Astronomers have discovered an asteroid with not one, but six streaming tails. This has never been seen before, and intrigued scientists are trying to figure out why this one is so special.

Most asteroids only appear as a single modest point of light, and they’re not even supposed to have tails. That luxury is usually reserved for icy comets who come too close to the sun. But this six-tailed asteroid, dubbed P/2013 P5 (P5 for short), has so many tails that it looks more like a badminton birdie. “We were literally dumbfounded when we saw it,” said lead investigator David Jewitt of the University of California at Los Angeles.

The inner solar system. P/2013 P5 is located in the main asteroid belt of our solar system, shown above in white.

Scientists think P5 is a fragment of a larger asteroid that broke apart in a collision. It was first spotted by the Pan-STARRS survey telescope in Hawaii on Aug. 18th. Nothing about it seemed special at the time, though it did seem unusually fuzzy-looking in the images taken. But when astronomers revisited the asteroid with NASA’s Hubble Space Telescope on Sept. 10th, the more detailed images clearly showed P5’s six tails. And as if that wasn’t amazing enough, when they returned just 13 days later for another look, P5’s tail composition had changed so drastically that it looked as if its entire structure had flipped around. “We were completely knocked out,” Jewitt said.

The cause of P5’s extra tails may stem from the sun. Sometimes photons in sunlight contain momentum that can actually be transferred to matter. This transferred momentum, or radiation pressure, is usually very small, but Jewitt thinks that in P5’s case it may have been enough to cause the asteroid’s rotation to speed up. Once this happened, P5’s weak gravity couldn’t hold itself together anymore and dust started to slide towards its equator and fly off, like when a ballerina’s tutu flies out from her waist as she pirouettes. As the dust flew off, radiation pressure pulled it into six delicate tails.

Image credit: NASA, ESA, and Z. Levay (STScI/AURA)
P5 and its six tails in relation to the sun.

P5’s six tails are intriguing, but the asteroid didn’t generate all of those tails at once; it’s been working on them since April, according to team member Jessica Agarwal of the Max Planck Institute for Solar System Research in Lindau, Germany. Since the initial discovery, Agarwal has been able to show through modeling that P5’s tails could have been created by a series of spontaneous dust-ejections on April 15th, July 18th, July 24th, Aug. 8th, Aug. 26th and Sept. 4th.

Jewitt and his team have published their research paper online in the Nov. 7 issue of the Astrophysical Journal Letters, and astronomers are planning further research into P5’s true spin rate and the rotational breakup theory.


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