Deep Impact: Early Results
"Although the collision of the comet and the impactor was not spectacular
from the public's point of view, it is extremely interesting scientifically," stated
IfA astronomer and Deep Impact Science Team member Karen Meech. In a talk
to visiting science teachers and IfA staff at IfA Manoa on July 19, Meech
discussed the early scientific results from the July 3 impact with Comet
She reviewed the goals of the mission: to investigate the interior of
a comet, which holds primitive debris left over from the first 100 million
years of our solar system's existence, and to learn more about crater
The early results show that most of the material ejected by the comet
was a very fine and very opaque dust. So far, the spectra taken after impact
have revealed water, carbon dioxide, carbon monoxide, and a variety of
hydrocarbons. Scientists are intrigued that materials detected in a pre-impact
outburst have not yet been found in the post-impact data.
Five minutes before impact.
Sixty-seven seconds after impact.
The opacity of the ejected material has made it difficult for scientists
to see the crater, but at this point, it appears that the crater created
by the impactor was on the high end of predictions, that is, about the
size of a football field. Scientists had several theories about crater
formation, with the most likely being that it is controlled by gravity.
Early results seem to confirm this.
Deep Impact, NASA's eighth Discovery mission, represented a worldwide
collaboration of major proportions, making Comet Tempel 1 the most intensively
studied comet in history. In addition to the science team members, led
by Principal Investigator Michael A'Hearn (University of Maryland),
there were 130 registered observers at 70 major observatories who were
able to communicate with each other in real-time during the impact event.
The timing of the impact was optimized for observing from Hawaii, and Meech
was the member of the Deep Impact team who coordinated all of the Earth-based
observations. When asked who observed the comet, she replied, "Everybody
on Earth with a large telescope. I am even getting data from people who
were not registered observers."
In addition to the ground-based observations, many space observatories
studied Tempel 1 at various wavelengths. They included the Hubble
Space Telescope (optical), the Spitzer
Space Telescope (infrared), the
Chandra X-ray Observatory, XMM (also X-rays), and the Swift
Gamma-Ray Burst Explorer (optical light, ultraviolet, X-rays, and gamma rays). Two radio
observatories in space, the Submillimeter
Wave Astronomy Satellite and
Odin, looked for water in the comet. Even the Rosetta
is on a 10-year mission to land on Comet 67 P/Churyumov-Gerasimenko in
2014, observed Comet Tempel 1 between late June and mid-July from its position
beyond Tempel 1's orbit.
Comet Tempel 1 90 seconds before impact.
The image was taken by the targeting sensor on Deep Impact's impactor.
A camera on the impactor itself took some great close-up images as it
approached Comet Tempel 1. The final image before impact
taken from a distance of 19 miles from the surface shows features less
than 13 feet across. The bright flash resulting from the vaporization of
the impactor when it collided with the comet was not reported as an obvious
sudden increase as seen from Earth, but the two cameras on the flyby portion
of the Deep Impact spacecraft did record the event. After impact, the comet's
brightness increased steadily for about an hour before leveling off. It
maintained that level of brightness for about a day, but within two to
three days after impact, its brightness returned to pre-impact levels.
Scientists had hoped that the impact would create a long-lasting jet of
material from deep inside the comet, but that did not happen.
In early August, the Deep Impact Science Team
held its initial post-impact meeting in Hilo to analyze their data and discuss
what they have learned. Many will present papers at the Asteroid, Comets,
and Meteors meeting in Rio de Janeiro in August and at the annual meeting
of the Division for Planetary Science of the American Astronomical Society
in Cambridge, England, in September. The journal Science will feature Deep
Impact in a special issue this fall. More detailed papers will appear in
astronomy journals. We will update you on further scientific finds from
this mission in later issues of this newsletter and in public talks.
What will happen to the Deep Impact spacecraft now that is has completed
its primary mission? The science team has hopes of sending it to study
another comet. NASA, citing budgetary constraints, had initially rejected
this proposal. But the success of Deep Impact and the intense public interest
in it has persuaded NASA to allow the Deep Impact team to make a formal
proposal for an extended mission.