Washington: The Sun-grazing asteroid, Phaethon, has a comet-like tail of dust particles that is blown backwards by Sun`s radiation pressure.
Unlike a comet, however, Phaethon`s tail doesn`t arise through the vaporization of an icy nucleus. During its closest approach to the Sun, researchers believe that Phaethon becomes so hot that rocks on the surface crack and crumble to dust under the extreme heat.
The Geminids, which grace the night sky annually in December, are one of the best known and most spectacular of the dozens of meteor showers. However, astronomers have known for 30 years that the Geminids are not caused by a comet but by a 5 km diameter asteroid called (3200) Phaethon.
David Jewitt and colleague, Jing Li, found Phaethon to be anomalously bright when closest to the Sun. The key to success was their use of NASA`s STEREO Sun-observing spacecraft. Phaethon at perihelion appears only 8 degrees (16 solar diameters) from the Sun, making observations with normal telescopes impossible.
Now, in further STEREO observations from 2009 and 2012, Jewitt, Li and Jessica Agarwal have spotted a comet-like tail extending from Phaethon.
The team believes that thermal fracture and desiccation fracture (formed like mud cracks in a dry lake bed) may be launching small dust particles that are then picked up by sunlight and pushed into the tail.
While this is the first time that thermal disintegration has been found to play an important role in the solar system, astronomers have already detected unexpected amounts of hot dust around some nearby stars that might have been similarly-produced.
"By the shape of its orbit, Phaethon is definitely an asteroid. But by ejecting dust it behaves like a ` rock comet`," said Jewitt.