Details of Approaching Comet ISON Begin to Emerge
Scientists are unraveling more information on the potentially super-bright Comet C/2012 S1 (ISON) as it continues on its journey toward the Sun. ISON will skim 730,000 miles above the Sun's surface on Nov. 28 and has the potential to be readily visible from Earth starting in early December.
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"We measured the rotational pole of the nucleus. The pole indicates that only one side of the comet is being heated by the Sun on its way in until approximately one week before it reaches it closest point to the Sun," said Planetary Science Institute research scientist Jian-Yang Li, who led a team that imaged the comet.
"Since the surface on the dark side of the comet should still retain a large fraction of very volatile materials, the sudden exposure to the strong sunlight when it gets closer to the Sun than Mercury could trigger huge outbursts of material," Li said.
Li presented the findings today at the American Astronomical Society's Division for Planetary Sciences 45th annual meeting in Denver.
Comet ISON was imaged with the Hubble Space Telescope using the Wide Field Camera 3 on April 10.
We measured the color of the coma, and found that the outer part of the coma is slightly redder than the inner part," Li said. "This color change is unusual in comets, and seems to imply that the inner part contains some water ice grains, which sublimate as they move away from the nucleus."
Comet ISON was discovered in September 2012 when it was farther away from the Sun than Jupiter, and was already active at such a great distance. This is distinct from most other sungrazers -- comets that pass extremely close to the Sun -- that are only discovered and remain visible for at most several days nearest the Sun. -- © Planetary Science Institute