from ScienceDaily Website
The Sun-grazing asteroid, Phaethon, has betrayed its true nature by showing a comet-like tail of dust particles blown backwards by radiation pressure from the Sun.
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.
Geminids over Pendleton, Oregon.
(Credit: Thomas W. Earle)
However, astronomers have known for 30
years that the Geminids are not caused by a but by a 5 km diameter
asteroid called (3200) Phaethon.
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
Asteroids and comets derive from entirely different regions of the solar system: