Dying asteroid is a six-tailed beast

This freakish asteroid may be spinning in its grave. Unlike its rocky siblings, asteroid P/2013 P5 has a record six tails of dust streaming from its body. It also whirls about on its axis, spewing material like a rotating lawn sprinkler. This suggests the oddball object is spinning so fast it is falling apart, which could help us better understand the life cycles of asteroids.

Until recently, comets were the only space rocks thought to have tails. Born in the frigid outer reaches of the solar system, comets are made from ice and dust. Their famous tails form when they swing close enough to the sun that the ice turns directly to gas, creating haloes of material that get swept back in one direction by radiation pressure from the sun.

Most asteroids occupy a belt between the orbits of Mars and Jupiter and are made primarily of rock without much ice. Since 2006, though, David Jewitt of the University of California, Los Angeles, and colleagues have found a number of asteroids in this belt masquerading as comets.

"These are bodies that are asteroids as determined by their orbit – they're sitting there in the asteroid belt, completely different from the orbits of comets, so there's no confusing them," says Jewitt. "But they look like comets. They're rocks and, weirdly, they're ejecting dust. The question is why."

Telltale spin

P/2013 P5 was first observed by a telescope in Hawaii on 18 August as a fuzzy-looking object in the asteroid belt. When Jewitt's team pointed the Hubble Space Telescope at it on 10 September, the fuzz resolved into six distinct tails. "That must be a record," says Jewitt. "I don't even know of regular comets that do that."

In most previous cases, tailed asteroids had survived a collision with another space rock, and the tails were clouds of dust kicked up by the impact. Others had some remnant ice trapped beneath their rocky surface that escaped to space, forming faint tails. But P/2013 P5 is too close to the sun for any ice to survive, and the odds of all six tails being the result of separate impacts are vanishingly small.

"Space is big, and collisions are rare. You can fly right through the asteroid belt and never see an asteroid, never get close enough to one to take a picture of it, never even get hit by a piece of dust," says Jewitt. "It's not an impact, I would bet a huge amount of money on that."

A clue to the tails' origins came almost two weeks later, when the team again observed the asteroid with Hubble. The tails were all in different positions, as if the entire structure had spun like a wheel. "That freaked us out big time," says Jewitt. "But we can explain it if the dust was emitted on six separate occasions."