New method that predicts changes in comets` rotational states identified
Washington: Researchers have discovered a new method that can help them predict the changes in the rotational states of comets.
The new way will also help them learn more about the approaching Comet C/2012 S1 (ISON), which will pass by the Sun on Thanksgiving Day.
Planetary Science Institute senior scientists Nalin H. Samarasinha and Beatrice E. A. Mueller have determined such changes are a function of a comet`s size, period and solar energy it receives, but surprisingly not a function of the fraction of a comet`s surface that is active.
Rotational changes occur due to reaction torques on the nucleus caused by outgassing as a comet approaches the Sun. By investigating the changes in the rotational periods of four comets-Encke, Tempel 1, Tempel 2, and Hartley 2, where the second and the fourth comets had close flybys by NASA spacecraft - Samarasinha and Mueller discovered a simple relationship using their size, rotational period and amount of sunlight received that reproduced the magnitude of those changes.
Samarasinha said that rotational periods and their changes are important not only for investigating the physical evolution of comets but also for detailed planning of future space missions to comets.
Applying their method to Comet ISON, Samarasinha and Mueller conclude it will spin-up and will become a tumbling object as it gets close to the Sun. Comet ISON will come to within 740,000 miles from the "surface" of the Sun-about three times the distance between the Earth and the Moon.
The study has been published in the Astrophysical Journal Letters.
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