[meteorite-list] Ground-based and Spacecraft Flyby Observations to Offer Insight on Comet Nucleus

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 2 Nov 2010 17:34:56 -0700 (PDT)
Message-ID: <201011030034.oA30Yu7U014909_at_zagami.jpl.nasa.gov>

NEWS RELEASE FROM THE PLANETARY SCIENCE INSTITUTE

SENT:
Nov. 2, 2010

FROM:
Alan Fischer
Public Information Office
Planetary Science Institute
520-622-6300
520-885-5648
fischer at psi.edu

Ground-based and Spacecraft Flyby Observations to Offer Insight on
Comet Nucleus

Nov. 2, 2010 -- Recent ground-based telescope observations by
Planetary Science Institute researchers have offered new insights into
the nucleus of a comet that will be the target of a NASA spacecraft
flyby this week.

Analysis of images of a jet of cyanide gas emerging from comet Hartley 2
will be combined with data derived from a spacecraft flyby scheduled for
Thursday morning to offer researchers a clearer view of the comet's
nucleus, said Beatrice Mueller, senior scientist at PSI.

NASA's EPOXI project will see a spacecraft pass within 700 km of
Hartley 2's nucleus Thursday. The craft will image the comet as the two
move past each other at a relative velocity of more than 12 km per
second, or 27,000 mph.

While EPOXI offers great scientific opportunities because of its
closeness to Hartley 2, the quick nature of the flyby encounter means
not all details will be revealed, Mueller said.

Numerous nights of observation from Earth can offer data that a quick
encounter with a passing spacecraft would be unable to gather, she said.

"You cannot get a complete picture, or as complete a picture. The
spacecraft will only be able to image part of the comet. It flies by
pretty fast. It only sees part of the nucleus, so they get a tiny little
snapshot," she said. "But it is important. A flyby is really exciting.
You do not get this resolution from the ground. You can get really close
and get really good details."

Utilizing images taken from September to October using a 2.1-meter
telescope at Kitt Peak National Observatory near Tucson, Mueller and
Nalin Samarasinha, senior scientist at PSI, were able to analyze
activity in the comet's coma and study the cyanide (CN) jet that was
revealed after images were enhanced by Samarasinha to carefully remove
background contribution and focus on the CN jet activity.

"We would like to put the spacecraft images into context with what we
see from the ground. So we should be able to tell where on the nucleus a
jet originates. The spacecraft sees less area due to the high resolution
and proximity, and cannot see the other side of the comet and get a full
view of what is going on with the nucleus," she said. "If I only see the
back of your head, I would not know there are the eyes and the nose.
It's kind of the same thing."

Samarasinha likened the CN jet to a garden hose gushing water, which
places a torque on the comet's nucleus and causes it to change its spin.

Visit
 http://www.psi.edu/news/releases/comet%20Hartley%202%20Cn%20gas%20image.jpg
to see a jet of CN gas, shown red, emerging from the nucleus of comet
Hartley 2 in an enhanced color image 23,000 miles across taken recently
by PSI researchers.

Earth-based telescope observations have indeed detected a changing
rotations period for Hartley 2, he said.

"That is a physical property which would help to interpret other
observations, from the ground as wall as from the spacecraft," he said.
"This kind of observations put some of the spacecraft observations in
context. You have to have the whole, big picture."

Observations and analysis by Mueller and Samarasinha were funded by a
grant from the NASA Planetary Astronomy Program to PSI.

The principal investigator of the observing proposal was University of
Maryland professor and EPOXI principal investigator Michael F. A'Hearn.

EPOXI is an extended mission that utilizes the already "in-flight" Deep
Impact spacecraft to explore distinct celestial targets of opportunity.
The term EPOXI is a combination of the names for the two extended
mission components: the Extrasolar Planet Observations and
Characterization (EPOCh), and the Hartley 2 flyby, called the Deep
Impact eXtended Investigation (DIXI). For more information about EPOXI,
visit: http://www.nasa.gov/epoxi and http://epoxi.umd.edu
<http://epoxi.umd.edu/>.

 
CONTACTS:

Beatrice Mueller
Senior Scientist
520-547-3950
mueller at psi.edu

Nalin Samarasinha
Senior Scientist
520-547-3952
nalin at psi.edu
Received on Tue 02 Nov 2010 08:34:56 PM PDT