Asteroids, unlike comets, are seldom seen sporting a tail as they orbit the sun, but Spanish astronomers say they've observed one of these rare exceptions. Using a telescope in the Canary Islands, they spotted an asteroid dubbed P/2012 F5 that displayed a trail like that of comets. Its emission of dust or gas may have been caused by internal rupture or collision with another asteroid, a release from the Spanish Foundation for Science and Technology reported Wednesday. "Our models indicate that [the trail] was caused by an impulsive short-lived event lasting just a few hours around the July 1st, 2011, with an uncertainty of 20 days," Fernando Moreno, researcher at the Astrophysics Institute of Andalusia said. Telescope images reveal "a fine and elongated dust structure that coincides exactly with the synchrone [timing] of that day," Moreno said. "It could have arisen from collision with another asteroid or rather a rotational rupture" of material gradually breaking free after partial fragmentation of the asteroid, the researchers said. The said they estimate the asteroid has a radius of between 300 and 450 feet and the dust mass emitted is about half a million tons.