In the old days, astronomy was simple – comets had tails and asteroids didn’t. Now, as if to not only disprove such established views, but drive the point home, NASA's Hubble Space Telescope took images in September of an asteroid called P/2013 P5 that has not one, but six comet-like tails.
P/2013 P5 is located in our solar system's asteroid belt and was first discovered in August by astronomers using the Pan-STARRS survey telescope in Hawaii. At that time, it was just a fuzzy image, but when the Hubble was turned on it on September 10, it revealed six distinct tails and looked like a rotating lawn sprinkler.
When Hubble looked again on September 23, the asteroid looked as if it had turned. The tails are very likely dust being ejected from the asteroid and it seems to have been doing so on and off for at least five months. As with a comet, the tails spread out by being blown by solar radiation.
"We were literally dumbfounded when we saw it," says lead investigator David Jewitt of the University of California at Los Angeles (UCLA). "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."
Despite the tails, P/2013 P5 is not a comet. According to Jewitt, the orbit of P/2013 P5 and its small size indicates that it isn’t likely to be a comet, but rather may have been part of a larger asteroid that broke up 200 million years ago in a collision that may have subjected it to temperatures as high as 1,500° F (815° C). If so, the ice that makes up a comet would have boiled away and P/2013 P5 is more likely made of metamorphic rocks.
According to NASA, P/2013 P5 has been ejecting dust periodically for at least five months. Astronomers hypothesize that the 1,400-ft (426-m) asteroid may have recently sped up due to solar radiation rather than a collision with another asteroid because there isn’t any sign of a debris cloud. The asteroid’s spin eventually became so fast that it’s now tearing itself apart and the dust is billowing out like plaster dust from a shattered ceiling.
The NASA team is observing the dust plumes closely to see if they are concentrated on the asteroid’s equator. If so, it would support the spin hypothesis.
NASA says that modeling of the asteroid’s behavior by Jessica Agarwal of the Max Planck Institute for Solar System Research in Lindau, Germany indicates that between 100 and 1,000 tons of dust have erupted from the asteroid over five occasions on April 15, July 18, July 24, August 8, August 26 and September 4.
Jewitt believes that if the rotation hypothesis is correct, P/2013 P5 may not be an isolated incident. "In astronomy, where you find one, you eventually find a whole bunch more," Jewitt says. "This is just an amazing object to us, and almost certainly the first of many more to come."
The NASA team’s results were published in the November 7 issue of the Astrophysical Journal Letters.