Comet "Deep Impact" To Be Webcast From Space Tonight; We Provide Link

The mission is intended to provide humankind's first look inside a comet. NASA says the impact at 23,000 mph is expected to produce a crater ranging in size from a house to a football stadium, 2-14 stories deep, ejecting ice and dust debris and revealing fresh material underneath.

Comets are time capsules that hold clues about the formation and evolution of the solar system. They are composed of ice, gas and dust, primitive debris from the solar system's distant and coldest regions that formed 4.5 billion years ago. Deep Impact, a NASA Discovery Mission, is the first space mission to probe beneath the surface of a comet and reveal the secrets of its interior.

On July 4, 2005 [July 3 10:52 p.m. Pacific Time], the Deep Impact spacecraft arrives at Comet Tempel 1 to impact it with a 370-kg (~820-lbs) mass. On impact, the crater produced is expected to range in size from that of a house to that of a football stadium, and two to fourteen stories deep. Ice and dust debris is ejected from the crater revealing fresh material beneath. Sunlight reflecting off the ejected material provides a dramatic brightening that fades slowly as the debris dissipates into space or falls back onto the comet. Images from cameras and a spectrometer are sent to Earth covering the approach, the impact and its aftermath. The effects of the collision with the comet will also be observable from certain locations on Earth and in some cases with smaller telescopes. The data is analyzed and combined with that of other NASA and international comet missions. Results from these missions will lead to a better understanding of both the solar system's formation and implications of comets colliding with Earth.

...The impactor is a battery-powered spacecraft that operates independently of the flyby spacecraft for just one day. It is called a "smart" impactor because, after its release, it takes over its own navigation and maneuvers into the path of the comet. A camera on the impactor captures and relays images of the comet's nucleus just seconds before collision. The impact is not forceful enough to make an appreciable change in the comet's orbital path around the Sun.

After release of the impactor, the flyby spacecraft maneuvers to a new path that, at closest approach passes 500 km (300 miles) from the comet. The flyby spacecraft observes and records the impact, the ejected material blasted from the crater, and the structure and composition of the crater's interior. After its shields protect it from the comet’s dust tail passing overhead, the flyby spacecraft turns to look at the comet again. The flyby spacecraft takes additional data from the other side of the nucleus and observes changes in the comet's activity. While the flyby spacecraft and impactor do their jobs, professional and amateur astronomers at both large and small telescopes on Earth observe the impact and its aftermath, and results are broadcast over the Internet.

...Comet Tempel 1 was discovered in 1867 by Ernst Tempel. The comet has made many passages through the inner solar system orbiting the Sun every 5.5 years. This makes Tempel 1 a good target to study evolutionary change in the mantle, or upper crust...

The flyby spacecraft carries a set of instruments and the smart impactor. Two instruments on the flyby spacecraft observe the impact, crater and debris with optical imaging and infrared spectral mapping. The flyby spacecraft uses an X-band radio antenna (transmission at about eight gigahertz) to communicate to Earth as it also listens to the impactor on a different frequency.