[meteorite-list] NASA's Deep Impact Produced Deep Results

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 20 Sep 2013 10:36:29 -0700 (PDT)
Message-ID: <201309201736.r8KHaTP5000779_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.php?release=2013-286

NASA's Deep Impact Produced Deep Results
Jet Propulsion Laboratory
September 20, 2013

Launched on a clear winter day in January 2005, NASA's Deep Impact
spacecraft spanned 268 million miles (431 million kilometers) of deep
space in 172 days, then reached out and touched comet Tempel 1. The
collision between the coffee table-sized impactor and city-sized comet
occurred on July 4, 2005, at 1:52 a.m. EDT. This hyper-speed collision
between spaceborne iceberg and copper-fortified, rocket-powered probe
was the first of its kind. It was a boon to not only comet science, but
to the study of the evolution of our solar system.

The mission of Deep Impact was supposed to conclude within weeks of this
July 4 cometary smackdown. Then, NASA approved a mission extension,
re-enlisting the Deep Impact spacecraft for two distinct celestial
targets of opportunity. EPOXI, as the mission was renamed, was 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 Deep Impact spacecraft, history's most traveled deep-space comet
hunter, provided many significant results for the science community.
Here are the top five, according to the mission's principal
investigator, Michael A'Hearn of the University of Maryland, College Park.

Studies of imagery showed that that the luminous flash created within a
fraction of a second after Deep Impact's impactor was atomized by comet
Tempel 1 was much fainter than expected. Comparison with experimental
impacts at the Vertical Gun Range at NASA Ames Research Center in
Moffett Field, Calif., showed that such a faint flash was consistent
only with a surface layer (depth a few times the diameter of the
impactor) that was more than 75 percent empty space. This surprisingly
high porosity was in contrast with theories that predicted comets were
armored with a stronger, solid crust that impeded outgassing.

Observations of comet Tempel 1 by Deep Impact's spectrometer instrument
showed that water was arising primarily at longitudes near noon and
peaking near the equator, whereas most of the carbon dioxide was arising
from far southern latitudes, not too far from comet Tempel 1's south
pole. This could be due to seasonal effects (southern hemisphere just
going into winter darkness) or due to differences in the chemical
composition in different parts of the nucleus. During the mission
extension, the EPOXI observations of comet Hartley 2 showed that the
comet's smooth waist was emitting pure water, while the small end was
emitting excess carbon dioxide, regardless of time of day. This was a
clear sign that chemical diversity was the important factor in a comet's
chemical makeup.

For many years we have known that a handful of comets (fewer than 10
percent) produced more water vapor than should be possible by
sublimation of nucleus of water ice, in which the sizes of the nuclei
are known. The flyby of comet Hartley 2 showed a large number of icy
grains in the coma are driven out of the nucleus by the outgassing of
carbon dioxide. These icy grains are plausibly the source of much of the
water coming from the comet.

Observations of Hartley 2 by the Deep Impact spacecraft showed the
importance of carbon-dioxide ice relative to carbon-monoxide ice in
comets, and led to reexamination of all previous observations of these
two ices in comets. The relative abundances in short-period and
long-period comets imply that the short-period comets formed under
warmer conditions than did the long-period comets. Thus, the
short-period comets must have formed closer to the sun than their
longer-period brethren. This is contrary to popular belief in the
astronomical community (for many decades) that the short-period comets
formed in the Kuiper belt beyond Neptune, while the long-period comets
formed in the vicinity of the giant planets. The new model fits well
with measurements by other astronomers of heavy water in Hartley 2, and
with the newest dynamical studies of planetary migration.

The excavation of a crater on Tempel 1 was the trigger that allowed the
proposal for the Stardust NExT mission to succeed. In addition to
searching for the crater formed by Deep Impact, a key goal of that
Stardust-NExT mission was to measure changes in the surface of the comet
over an orbital period. This second set of measurements of Tempel 1
surface features showed that much of the evolution was in discrete,
large areas, i.e., there was not a small, uniform erosion of the all
parts of the surface, but rather large changes in a few places. Thus,
comets evolve in a manner anaologous to erosion - most erosion takes
place in discrete events (floods that make large, local changes) rather
than as a slow, continuous process.

JPL, a division of the California Institute of Technology in Pasadena,
manages the Deep Impact mission for NASA's Science Mission Directorate,
Washington. The mission is 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 Deep Impact. The spacecraft was built for NASA by Ball
Aerospace & Technologies Corp., Boulder, Colo.

For more information about Deep Impact, visit:

http://solarsystem.nasa.gov/deepimpact .

Dwayne Brown 202-358-1726
Headquarters,
Dwayne.c.brown at nasa.gov

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

2013-286
Received on Fri 20 Sep 2013 01:36:29 PM PDT