Asteroid 3200 Phaethon is a 5 km body with a highly eccentric orbit similar to that of a comet, which takes it closer to the Sun than any other named Asteroid. It appears to be the parent body of the Geminid Meteors, which share essentially the same orbit as it, as well as a group of larger bodies known as the Phaethon-Geminid Complex. Such meteor showers typically form from the tail of a comet; as the comet approaches its perihelion (the closest point in its orbit to the Sun), ice at the surface sublimates away (turns directly from a solid to a gas - liquids do not form in a vacuum), releasing particles of silica trapped in the ice, which continue to follow essentially the same path as the comet, creating a meteor shower every time the Earth passes through this stream. However, 3200 Phaethon, which has a 1.43 year orbital period in which it reaches 0.14 AU from the Sun (14% of the distance between the Earth and the Sun, or less than half the distance at which Mercury orbits) is thought to regularly suffer surface temperatures in excess of 1000K, making it highly unlikely that it has ice on its surface, which calls its potential role as the parent body to the Geminid Meteors into question.
In a paper published on the arXiv online database at Cornell University Library on 17 June 2013, David Jewitt of the Department of Earth and Space Sciences and Department of Physics and Astronomy at the University of California Los Angeles, Jing Li of the Department of Earth and Space Sciences at the University of California Los Angeles, and Jessica Agarwal of the Max Planck Institute for Solar System Research, describe the results of a study of 3200 Phaeton using the NASA STEREO Spacecraft.
Jewitt et al. observed two successive perihelions of 3200 Phaeton, in June 2009 and May 2012. On both occasions they were able to observe a faint comet-like dust tail emerging from the body, even though it was apparently reaching temperatures that would rapidly destroy an icy comet. This tail grew rapidly, reaching a length of over 250 000 km within a day of first appearing, and appeared to represent material being lost from the parent body at a rate of about 3 kg per second.
Composite images of 3200 Phaethon in 2009 compared with the projected sun- comet line (white). The Sun is to the upper right in each panel. Insets are 49000 square and show eld stars near to Phaethon to demonstrate the point spread function of the data. Each panel has North to the top, East to the left and shows the median of 30 images taken over a 1 day period. Jewitt et al. (2013).
Same as above, but for data from 2012. Jewitt et al. (2013).
Jewitt et al. suggest that at it's perihelion 3200 Phaethon is being heated to such a degree that hydrated minerals at its surface could be thermally fractured and desiccated, leading to the ejection of dust particles.
See also The Perseid Meteors, The perihelion of Comet 103P/Hartley 2, Astroid 2006 BL8 to pass the Earth at 502 000 km, The ejecta of Main-Belt Comet P/2012 T1 (PANSTARRS) and Asteroid 2013 NH4 passes by the Earth.
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