Volume: 03, Issue: 13 06/29/2005 
Artist Pat Rawlings gives us a look at the moment of impact and the forming of the crater. Image courtesy NASA/JPL/UMD.
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Artist's concept of Deep Impact impactor approaching comet Tempel 1. Image courtesy NASA/JPL/Maas Digital.
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The Hubble image at left is a view of comet Tempel 1 before the outburst. The photo at right reveals the dust jet. Image courtesy NASA/ESA/P. Feldman/H. Weaver.
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Other Articles in This Issue:
Researchers Brace for Violent Hurricane Season
Cassini Reveals Lake-Like Feature on Titan
Hubble Chases Unruly Planet
Learn From Women in Space Fields

Deep Impact on Course for Independence Day Collision

Fireworks won’t be the only thing lighting up the sky this Independence Day. In the early morning hours of July 4, 2005, NASA’s Deep Impact spacecraft will smash into comet Tempel 1 at a speed of about 23,000 miles per hour.

The Deep Impact mission, launched Jan. 12, 2005, will explore the comet's interior by creating an impact crater. The Deep Impact spacecraft will deploy a 39-inch-wide impactor into the path of the comet, which is about half the size of Manhattan. The impactor will collide with the comet, and the flyby craft will pass approximately 310 miles below. Another spacecraft will then look deep inside the comet during a fly-by immediately afterward, allowing the crust and the interior of a comet to be studied for the first time.

Dramatic images of the impactor spacecraft’s final approach -- and possibly of the impact itself and the crater -- will be sent to Earth in near-real time by both spacecraft. Several observatories in orbit around Earth, as well as countless Earth-bound telescopes, will work in concert for an unprecedented global observation campaign to collect a maximum amount of additional data and information on this event. NASA’s Spitzer Space Telescope and Hubble Space Telescope will observe the event, as well as the European Space Agency’s (ESA) Rosetta comet chaser, XMM/Newton Observatory, and OGS telescope. The European Southern Observatory (ESO) will also direct all seven powerful telescopes it operates toward the event.

"The last 24 hours of the impactor's life should provide the most spectacular data in the history of cometary science," said Deep Impact Principal Investigator Dr. Michael A'Hearn of the University of Maryland. "With the information we receive after the impact, it will be a whole new ballgame. We know so little about the structure of cometary nuclei that almost every moment we expect to learn something new."

Deep Impact has already observed a massive, short-lived outburst of ice or other particles from Tempel 1 that temporarily expanded the size and reflectivity of the cloud of dust and gas (coma) that surrounds the comet nucleus. The outburst was detected as a dramatic brightening of the comet on June 22. It is the second of two such events observed in the past two weeks. A smaller outburst also was seen on June 14 by Deep Impact, the Hubble Space Telescope, and ground-based observers.

"Outbursts such as this may be a very common phenomenon on many comets, but they are rarely observed in sufficient detail to understand them because it is normally so difficult to obtain enough time on telescopes to discover such phenomena," A'Hearn said. "We likely would have missed this exciting event, except that we are now getting almost continuous coverage of the comet with the spacecraft's imaging and spectroscopy instruments."

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