Freak space rock spins dusty trail
The Hubble telescope has spotted an asteroid radiating six comet-like tails, making it resemble a "rotating lawn sprinkler".
Other asteroids appear as tiny points of light to astronomers, who are puzzled by the outbursts of dust.
Asteroid P/2013 P5 has been ejecting dust periodically for at least five months and may be in the process of breaking up.
They have outlined details in the journal Astrophysical Journal Letters.
"We were literally dumbfounded when we saw it," said Prof Dave Jewitt, from 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."
Astronomers say it is possible the asteroid's rotation rate increased to the point where its surface started flying apart.
Radiation pressure from the Sun could have sent the space rock spinning, to a point where the asteroid's weak gravity could no longer hold it together.
Astronomers will continue observing P/2013 P5 to see whether the dust leaves the asteroid in the equatorial plane. Because of the physics involved in the spin rate theory, say the astronomers, this would provide strong evidence for a rotational breakup.
They do not believe the tails are the result of an impact with another asteroid because they have not seen a large quantity of dust blasted into space all at once.
Astronomers discovered the object in August, using the Pan-STARRS telescope in Hawaii. At the time, P/2013 P5 looked unusually fuzzy.
The multiple tails were discovered when Hubble was used to take a more detailed image on 10 September.