Deep Impact closes in on comet target
On July 4, NASA's Deep Impact spacecraft will smash into Comet Tempel 1.
June 22, 2005
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June 21, 2005
***Scroll down to access graphics and PDF versions of Astronomy magazine articles about Deep Impact.***
WAUKESHA, WI — In the early morning hours of July 4, a projectile from NASA's Deep Impact spacecraft will smash into Comet Tempel 1. Professional and amateur astronomers around the world will keep their eyes glued on the comet, seeking to learn more about this relic from the ancient past — and hoping to view some celestial fireworks.
Comets like Tempel 1 consist of ice and dust — they're "dirty snowballs," as American astronomer Fred Whipple once famously described them. They date back to the solar system's origin some 4.5 billion years ago and have spent most of their lives in the deep freeze at the solar system's edge. This makes them time capsules that hold clues as to how the solar system formed and evolved. Yet, most of these clues lie buried beneath a veneer of material altered by exposure to space and sunlight.
Enter Deep Impact. NASA launched the spacecraft January 12, 2005, putting it on a collision course with Tempel 1. Deep Impact actually consists of two spacecraft: an impactor and a larger flyby spacecraft. The impactor will slam into the comet's nucleus, while the flyby craft will study the crater using a suite of instruments. The collision is expected to expose fresh comet material. The two spacecraft will separate about 24 hours before impact — impact is scheduled for 1:52 a.m. EDT July 4 (10:52 p.m. PDT July 3).
The solid copper impactor weighs 816 pounds and will travel 23,000 mph when it hits Tempel 1, creating a blast equivalent to 4.8 tons of TNT. Astronomers speculate the crater could be as small as a house or as big as a football stadium, and anywhere from 2 to 14 stories deep.
Sunlight reflecting off material expelled by the blast should cause the comet to brighten dramatically. Although it likely will remain below naked-eye visibility, the comet will come within easy range of backyard observers using small telescopes. Potentially, freshly excavated ice will convert to gas in sunlight, creating a jet of material that could keep the comet brighter than normal for weeks or even months. In addition to observations made by the flyby spacecraft, professional astronomers will be viewing the impact and its aftermath with many of Earth's biggest telescopes, as well as with the Hubble Space Telescope.
Fast facts about Deep Impact and Comet Tempel 1:
Length of spacecraft's voyage — 173 days and 268 million milesTime of impact — 1:52 a.m. EDT July 4Speed at impact — 23,000 mphSize of impactor — 39 inches in diameterWeight of impactor — 816 poundsComposition of impactor — 97 percent copper and 3 percent beryllium (Copper was chosen because it reacts slowly with other elements and thus won't affect observations of the comet's composition.) Flyby distance — approximately 310 milesComet's distance from Earth at impact — 83 million milesComet's diameter — roughly 6 milesComet's period — revolves around the Sun in 5.5 yearsWilhelm Tempel discovered Comet Tempel 1 April 3, 1867, from Marseilles, France.
|Extensive Astronomy magazine coverage of Deep Impact|
***Both of these articles and supplemental graphics are AVAILABLE FOR DOWNLOAD.***
Check out Astronomy magazine's June 2005 issue for "Fireworks on the Fourth." This 3-page article previews the much-anticipated collision and provides a map of the comet's location in the sky.
|In the 2005 edition of Astronomy magazine's annual Explore the Universe, you'll find "Deep Impact delivers a hit." This 6-page feature includes an illustration of Deep Impact's collision course with Tempel 1 and provides a comprehensive overview of the historic mission.|
|Be sure to follow Astronomy and Astronomy.com to keep abreast of the latest findings from the Deep Impact mission. |
The Deep Impact spacecraft looks on as an 816-pound projectile slams into Comet Tempel 1 July 4. Astronomers don't know for sure what effect the impact will have - that's why they're performing the experiment, after all - but the comet should brighten as fresh ice is exposed to sunlight.
Photo by NASA/JPL/UMD Artwork by Pat Rawlings
Comet Tempel 1 will be difficult to see without a telescope. The comet will be in Virgo the Maiden before and after its July 4 encounter with Deep Impact. Note the positions of Jupiter and Spica, two bright objects that will help you locate the field of Tempel 1. This chart presents a normal view, with north up and east to the left.
Photo by Astronomy: Roen Kelly
Key positions of Tempel 1, Deep Impact, Earth, and orbits of planets out to Jupiter appear in this diagram. Deep Impact's travel time to Tempel 1 is approximately 6 months.
Photo by Astronomy: Roen Kelly
Gas and dust ejected from Comet Tempel 1 glowed softly as the comet made its closest approach to Earth in April. About 100 times too faint to see with the naked eye, Tempel 1 nevertheless appeared conspicuous through the 84-inch telescope at Kitt Peak National Observatory in Arizona.
Photo by Tony Farnham and Matthew Knight (University of Maryland)