[meteorite-list] Science Paper Details NASA Epoxi Flyby of Hyper Comet

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 16 Jun 2011 16:10:56 -0700 (PDT)
Message-ID: <201106162310.p5GNAuTv004420_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2011-185
  
Science Paper Details NASA Epoxi Flyby of Hyper Comet
Jet Propulsion Laboratory
June 16, 2011

PASADENA, Calif. - Comet Hartley 2's hyperactive state, as studied by
NASA's EPOXI mission, is detailed in a new paper published in this
week's issue of the journal Science.

After visiting a comet and imaging distant stars for hints of extrasolar
planets, you could say the spacecraft used for EPOXI had seen its fair
share of celestial wonders. But after about 3.2 billion miles (5.1
billion kilometers) of deep space travel, one final wonder awaited the
mission's project and science teams. On Nov. 4, 2010, the EPOXI mission
spacecraft flew past a weird little comet called Hartley 2.

"From all the imaging we took during approach, we knew the comet was a
little skittish even before flyby," said EPOXI Project Manager Tim
Larson of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It was
moving around the sky like a knuckleball and gave my navigators fits,
and these new results show this little comet is downright hyperactive."

The EPOXI mission found that the strong activity in water release and
carbon dioxide-powered jets did not occur equally in the different
regions of the comet. During the spacecraft's flyby of the comet ??? with
closest approach of 431 miles (694 kilometers) ??? carbon-dioxide-driven
jets were seen at the ends of the comet, with most occurring at the
small end. In the middle region, or waist of the comet, water was
released as vapor with very little carbon dioxide or ice. The latter
findings indicate that material in the waist likely came off the ends of
the comet and was redeposited.

"Hartley 2 is a hyperactive little comet, spewing out more water than
most other comets its size," said Mike A'Hearn, principal investigator
of EPOXI from the University of Maryland, College Park. "When warmed by
the sun, dry ice -- frozen carbon dioxide -- deep in the comet's body
turns to gas jetting off the comet and dragging water ice with it."

Although Hartley 2 is the only such hyperactive comet visited by a
spacecraft, scientists know of at least a dozen other comets that also
are relatively high in activity for their size and which are probably
driven by carbon dioxide or carbon monoxide.

"These could represent a separate class of hyperactive comets," said
A'Hearn. "Or they could be a continuum in comet activity extending from
Hartley 2-like comets all the way to the much less active, 'normal'
comets that we are more used to seeing."

The study provides several new twists in the unfolding story of this
small cometary dynamo, including: (1) Hartley 2 has an 'excited state of
rotation' because it spins around one axis, but also tumbles around a
different axis; and (2) on its larger, rougher ends, the comet's surface
is dotted with glittering blocks that can reach approximately 165 feet
(50 meters) high and 260 feet (80 meters) wide. The block-like, shiny
objects, some as big as one block long and 16 stories tall, appear to be
two to three times more reflective than the surface average.

EPOXI was an extended mission that utilized the already "in-flight" Deep
Impact spacecraft to explore distinct celestial targets of opportunity.
The name EPOXI itself is a combination of the names for the two extended
mission components: the extrasolar planet observations, called
Extrasolar Planet Observations and Characterization (EPOCh), and the
flyby of comet Hartley 2, called the Deep Impact Extended Investigation
(DIXI). The spacecraft retained the name "Deep Impact." During its
approach, encounter and departure from comet Hartley 2, the spacecraft
beamed back more than 117,000 images and spectra.

JPL managed the EPOXI and Deep Impact missions for NASA's Science
Mission Directorate, Washington. The EPOXI mission was part of the
Discovery Program managed at NASA's Marshall Space Flight Center in
Huntsville, Ala. The University of Maryland, College Park, is home to
Michael A'Hearn, principal investigator for EPOXI. Drake Deming of
NASA's Goddard Space Flight Center, Greenbelt, Md., is the science lead
for the EPOXI mission's extrasolar planet observations. The spacecraft
was built for NASA by Ball Aerospace & Technologies Corp., Boulder, Colo.

DC Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif
agle at jpl.nasa.gov

2011-185
Received on Thu 16 Jun 2011 07:10:56 PM PDT