3200 Phaethon

Simon F. Green and John K. Davies, while searching Infrared Astronomical Satellite (IRAS) data for moving objects, discovered 3200 Phaethon (1983 TB) in images from October 11, 1983. It was announced on October 14 in IAUC 3878 along with optical confirmation by Charles T. Kowal, who reported it to be asteroidal in appearance. It was the first asteroid to be discovered by a spacecraft. It measures 5.10 km in diameter.

Phaethon's most remarkable distinction is that it approaches the Sun closer than any other numbered asteroid; its perihelion is only 0.140 AU — less than half Mercury's perihelion distance. It is a Mercury-, Venus-, Earth- and Mars-crosser. The surface temperature at perihelion could reach ~1025 K, or 1400 F. For this reason, it was named after the Greek myth of Phaëton, son of the sun god Helios.

Phaethon's attributes can be argued as being cometary, except that Phaethon has never been observed exhibiting a coma, gas jets, or dust trail. However IAUC 3881 soon after discovery of 3200 Phaethon reported Fred Whipple's observation that "orbital elements of 1983 TB shown on IAUC 3879 are virtually coincident with the mean orbital elements of 19 Geminid meteors photographed with the super-Schmidt meteor cameras". Phaethon thus turned out to be the long-sought parent body of the Geminids meteor shower of mid-December. It is classified as an Apollo asteroid because of its orbital qualities, also much in common with comets and is also classified as a B-type asteroid because it is composed of dark material; this too fits well with a cometary origin. There are several asteroid/comet mixed type objects now known, such as 133P/Elst-Pizarro.

Phaethon approached to 18.1 Gm on December 10,2007. It will draw nearer in 2017, 2050, 2060, and closer still on December 14, 2093, passing within 0.0198 AU (3.0  Gm).

External links

• Phaethon's orbit in 3D (java required)