[meteorite-list] Changes in Comet Rotation May be Predicted With Greater Accuracy

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 4 Sep 2013 10:03:09 -0700 (PDT)
Message-ID: <201309041703.r84H39WS005798_at_zagami.jpl.nasa.gov>

NEWS RELEASE FROM THE PLANETARY SCIENCE INSTITUTE


FROM:
Alan Fischer
Public Information Officer
Planetary Science Institute
520-382-0411
520-622-6300
fischer at psi.edu

Changes in Comet Rotation May be Predicted With Greater Accuracy

Sept. 4, 2013, Tucson, Ariz. -- Planetary Science Institute researchers
have discovered a way to predict the changes in the rotational states of
comets that could help scientists learn more about the approaching Comet
C/2012 S1 (ISON), which will pass by the Sun on Thanksgiving Day and has
attracted worldwide interest because it may become sufficiently bright to
be seen by the naked eye.

PSI 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 according to a paper published in the
Astrophysical Journal Letters.

"You get more change if there is more solar energy and less change if it
is spinning more rapidly to begin with or if it is a larger comet. Larger,
rapidly rotating comets are not going to change their spin status very
much," Samarasinha said. "We expected that the fraction of the surface of
the comet that is active would also be a controlling factor, but that
proved not to be the case."

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.

"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," Samarasinha said.

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 spin-up of ISON could result in increased shedding of material from the
nucleus as it is subjected to solar tides and intense heating during its
close passage by the Sun.

"While these mass sheddings may result in interesting events for
astronomers, we hope the nucleus of comet ISON is sufficiently large to
avoid complete disruption - an outcome common to many sungrazing comets,"
Mueller said.

CONTACT:
Nalin Samarasinha
Senior Scientist
520 547-3952
nalin at psi.edu

PSI INFORMATION:
Mark V. Sykes
Director
520-622-6300
sykes at psi.edu

PSI HOMEPAGE:
http://www.psi.edu

PSI PRESS RELEASES:
http://www.psi.edu/news/press-releases

THE PLANETARY SCIENCE INSTITUTE:

The Planetary Science Institute is a private, nonprofit 501(c)(3)
corporation dedicated to solar system exploration. It is headquartered in
Tucson, Arizona, where it was founded in 1972.

PSI scientists are involved in numerous NASA and international missions,
the study of Mars and other planets, the Moon, asteroids, comets,
interplanetary dust, impact physics, the origin of the solar system,
extra-solar planet formation, dynamics, the rise of life, and other areas
of research. They conduct fieldwork in North America, Australia and Africa.
They also are actively involved in science education and public outreach
through school programs, children's books, popular science books and art.

PSI scientists are based in 18 states and the District of Columbia,
Australia, Canada, Ireland, Latvia, Russia, South Africa, Switzerland and
the United Kingdom.
                                                                      
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Received on Wed 04 Sep 2013 01:03:09 PM PDT