[meteorite-list] Researchers Gain New Insights Into Comet Hartley 2

[Ron Baalke]

Researchers gain new insights into Comet Hartley 2
Planetary Science Institute Press Release

May 16, 2011-- A tumbling comet nucleus with a changing rotational
rate has been observed for the first time, according to a new paper by a
Planetary Science Institute researcher. 

These findings, as well as information gleaned from a recent NASA EPOXI
spacecraft flyby of Comet 103P/Hartley 2, are expected to offer new
insights as researchers strive to better understand comets and the role
they could possibly play in aiding human solar system exploration, said
Nalin H. Samarasinha, senior scientist at PSI and lead author of a paper
titled "Rotation of Comet 103P/Hartley 2 from Structures in the Coma"
that appears in Astrophysical Journal Letters. 

"Understanding the makeup of comets has immediate relevance to planetary
explorations efforts. Small bodies of the solar system such as asteroids
and comets could potentially act as way stations, as well as to supply
needed resources, for the human exploration of the solar system,"
Samarasinha said. "For this purpose, it is necessary to know the
properties and the character of these objects to maximize our investment." 

The research team analyzed images of the rotationally excited, or
tumbling, Hartley 2 comet taken during 20 nights between Sept. 1 and
Dec. 15, 2010 using the 2.1-meter telescope at Kitt Peak National
Observatory near Tucson, Ariz. 

A blue filter that isolates the light emitted by cyanogen (CN) molecules
was used to observe CN features in the coma of the comet, Samarasinha
said. This showed clear variations over time scales ranging from a few
hours to over several days. The coma is the extended "atmosphere" of the
comet that surrounds the solid nucleus that consists of ice and dirt. 

"The rotational state of a comet's nucleus is a basic physical parameter
needed to accurately interpret other observations of the nucleus and
coma. Analysis of these cyanogen features indicates that the nucleus is
spinning down and suggests that it is in a state of a dynamically
excited rotation," he said. "Our observations have clearly shown that
the effective rotation period has increased during the observation window." 

The team is the first group to point this out based on their
observations from early September and early October. 

Hartley 2, a relatively small comet with a 2-kilometer long nucleus, is
highly active for its size, he said. It is experiencing rotational
changes due to torque caused by jets of gases emitting from the icy body. 

Information on the makeup of Hartley 2 gleaned from this research and
the EPOXI flyby, and similar research on additional comets, could offer
the early tools researchers need to determine the best way to deal with
a comet on a collision course with Earth. 

"Although extremely rare, comets can collide with Earth. This could
cause regional or global damage to the environment and to life on Earth.
However, fortunately for the first time, we are on the threshold of our
technical knowhow to mitigate such a hazardous impact," Samarasinha
said. "In order to do that we need to know the material properties of
comets. The most appropriate mitigation strategy for a strong rigid body
is different from that for a weakly bound agglomerate." 

Hartley 2 offered a significant opportunity for research, said co-author
Beatrice E.A. Mueller. 

"This comet had such a great apparition - it came close to Earth and was
observable from the ground over months with great resolution, and was
encountered by the EPOXI spacecraft," said Mueller, PSI Senior Scientist
and Principal Investigator of the NASA Planetary Astronomy Grant to PSI
that funded the study. "Ultimately, one wants to deduce the physical
parameters of the nucleus as well as its structure. This will give
insights into the conditions during the formation of the solar system."

Other authors of the paper are Michael F. A'Hearn, Tony L. Farnham and
Alan Gersch, all of the University of Maryland Department of Astronomy.

 CONTACT:

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

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