Comets are icy and sometimes have tails. Asteroids are rocky or metallic and typically don’t have tails. But this asteroid has six tails and rotates like a lawn sprinkler.

Astronomers using NASA’s Hubble Space Telescope have identified what they can only describe as a never-before-seen “weird and freakish object” in the asteroid belt that looks like a rotating lawn sprinkler.

Normal asteroids should appear simply as tiny points of light. But this asteroid, designated P/2013 P5, has six comet-like tails of dust radiating from it like spokes on a wheel.

Because nothing like this has ever been seen before, astronomers are scratching their heads to find an adequate explanation for its out-of-this-world appearance.
“We were literally dumbfounded when we saw it,” said lead investigator David Jewitt of the University of California at Los Angeles. “Even more amazing, its tail structures change dramatically in just 13 days as it belches out dust. That also caught us by surprise. It’s hard to believe we’re looking at an asteroid.”

One interpretation is that the asteroid’s rotation rate increased to the point where its surface started flying apart, ejecting dust in episodic eruptions starting last spring. The team rules out a recent asteroid impact scenario because a lot of dust would be blasted into space all at once, whereas P5 has ejected dust for at least five months.

The asteroid was discovered as an unusually fuzzy-looking object with the Pan-STARRS survey telescope in Hawaii. The multiple tails were discovered in Hubble images taken on Sept. 10, 2013.

When Hubble returned to the asteroid on Sept. 23, its appearance had totally changed. It looked as if the entire structure had swung around. “We were completely knocked out,” Jewitt said.

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. ....