Deep Impact: The Day of the Comet

Deep Impact

by Bonnie J. Walters
NASA/JPL Solar System Ambassador

NASA's Deep Impact mission is essentially trying to "hit a bullet with a second bullet while a third bullet takes in data!" Deep Impact will encounter Comet 9P/Tempel 1 on July 4th 1:52 a.m., EDT. Its mission: to send an impactor to blast a hole into a comet. The goal: to find out what the guts of a comet look like. Deep Impact consists of a subcompact-car-sized flyby spacecraft, which will image the event, and an 820 pound copper impactor, about the size of a washing machine. The dual spacecraft carry three imaging instruments, two on the flyby and one on the impactor. The events are going to unravel as follows:

Mission Events
(Earth-receive time - in EDT)

July 3, 2:07 a.m: Impactor released into comet's path
July 4, 12:22 a.m.: 1st impactor targeting maneuver
July 4, 1:17 a.m.: 2nd impactor targeting maneuver
July 4, 1:39 a.m.: 3rd impactor targeting maneuver
July 4, 1:52 a.m.: (+ or - 3 min.): Impact with Tempel 1
July 4, 2:05 a.m.: Flyby goes into shield mode
July 4, 2:06 a.m.: Flyby's closest approach to Tempel 1

Animation of Impact. Credit: NASA The speeds with which these events will occur are truly staggering. Tempel 1 is a matte black elongated comet moving at the rate of 23,000 miles per hour or 6.3 miles per second! It reflects only 4% of the sunlight reaching it. The Spitzer and Hubble telescopes refined 9P/Tempel 1's measurements to approximately 14 by 4 kilometers (8.7 by 2.5 miles) or about half the size of Manhattan Island in New York. The impactor will essentially drift in front of the comet. It has autonomous navigation and will be doing its own course corrections starting two hours before impact. The crater it produces can be anywhere from the size of a large house to a football stadium and two to fourteen stories deep. Even though it has a short 24 hour lifespan, the impactor will provide unprecedented data on the innards of a comet.

The Hubble and Spitzer telescopes and the Chandra X-ray Observatory will be recording the event as will 30 large ground based telescopes and thousands of amateur astronomers. Where is this comet in the night sky and what could you expect to see? David Levy has written a beautiful article describing the event at: http://spaceweather.com/glossary/deepimpact.htm - included is a detailed star map for the comet.

So do we need to worry about changing this comet's course? Apparently not. "In the world of science, this is the astronomical equivalent of a 767 airliner running into a mosquito," said Dr. Don Yeomans, a Deep Impact mission scientist at JPL. Check out the Deep Impact sites below. There are wonderful interactive animations of the event. Watch NASA TV as the fireworks begin. So hold on to your hats and watch this incredible event unfurl before your very eyes!

Deep Impact Home: http://deepimpact.jpl.nasa.gov/home/index.html
NASA’s Deep Impact Site: http://www.nasa.gov/mission_pages/deepimpact/main/index.html
NASA TV: http://www.nasa.gov/multimedia/nasatv/index.html and http://science.ksc.nasa.gov/shuttle/countdown/video/video.html

Send your questions about Deep Impact and comets to: Imagiverse - Ask The Expert

- 2 July 2005

Last Updated:
3 July 2005