"A Matter of Time": APPOLLO ASTEROID

Tuesday, November 5, 2013

APPOLLO ASTEROID

It is categorized as an Apollo asteroid (because its semi-major axis is greater than that of the Earth's and its perihelion is less than 1.017 astronomical units. It is also suspected to be a member of the Pallas family of asteroids.^[3]

Phaethon's most remarkable distinction is that it approaches the Sun closer than any other named asteroid: its perihelion is only 0.140 AU — less than half of 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.

[edit]Physical characteristics and meteor shower

Phaethon's orbit looks more like that of a comet than an asteroid. However, it has never been observed to exhibit a coma, gas jet, ordust tail, typical features of comets. Despite this, shortly after its discovery, Fred Whipple observed that the "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".^[4] In other words, Phaethon is the long-sought parent body of the Geminids meteor shower of mid-December. Phaethon has been referred to as a "rock comet".^[5]

Phaethon's composition fits the notion of its cometary origin; it is classified as a B-type asteroid because it is composed of dark material. Since Phaethon, several other objects showing mixed cometary and asteroidal features have been discovered, such as133P/Elst–Pizarro.

[edit]Recent close approaches

Phaethon approached to 18.1 Gm of Earth 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).^[6]

When Phaethon came to perihelion in July 2009, it was brighter than expected.^[7]^[8] As Phaethon approached perihelion in June 2009, the STEREO-A spacecraft detected an unexpected brightening, by a factor of two.^[5]