Space.com: Princeton astronomer Charles H. Young (1834-1908) used to tell his students that small asteroids were hardly more than “mountains broken loose,” compared to the solar system’s larger asteroids which are entire worlds unto themselves. This is probably an appropriate characterization of the asteroid 3200 Phaethon, which is an irregular chunk of rock about 3 miles (5 kilometers) wide — compared to the system’s largest asteroids which can have diameters more than 100 times that. 3200 Phaethon would be a quite insignificant member of the solar system were it not for the object’s remarkable orbit, which will carry it to within 6.4 million miles (10.3 million km) of Earth on Dec. 16.
Since the asteroid’s discovery on Oct. 11, 1983, by NASA’s Infrared Astronomical Satellite (IRAS), this pocket space rock — catalogued as 1983 TB — has gone around the sun nearly 24 times. It follows a 523-day ellipse that takes the object deep within Mercury’s orbit during close approach to the sun and outside the orbit of Mars at furthest approach from the star. Phaethon is the third largest near-Earth asteroid classified as “potentially hazardous” by NASA, and as such, astronomers always keep a close watch on the rock’s path when it closely approaches our planet.
We can also say that 3200 Phaethon may be “the mother of all Geminids.” Meteor showers are created when the Earth flies through a path of debris left behind by a comet. 3200 Phaethon’s orbit nearly coincides with the well-defined path of the Geminid meteor shower, suggesting that this asteroid might be the remnant of a comet that released a trail of debris behind it, creating the path that is now responsible for the annual shower. Interestingly, at the same time that the Geminids take center stage on Dec. 14, astronomers will also be concentrating on the object that may have given rise to the meteors a timeless interval ago. more here