Comet Tempel 1 and the Deep Impact Spacecraft

Comets are often called "dirty snowballs" because they are comprised of ice, dust, and gases. They orbit the sun and cast off the dust particles that hurtle through Earth's atmosphere in the form of meteor showers. That accounts for the outside of the comet, but what is inside a comet? Scientists want to know. That is why Comet Tempel is about to meet the Deep Impact spacecraft in a head on crash on July 4th.

Comet Tempel 1 measures about 10 miles by 4 miles. There are two parts to the Deep Impact spacecraft. The larger part, called the flyby, is about the size of a car. It will release the smaller part, called the smart impactor, the day before the crash. The smart impactor is about the dimensions of a coffee table - although it weighs 820 lbs. It got its name because it will maneuver itself into the path of the comet where the two will collide. You might think that a spacecraft the size of a coffee table couldn't make much of a dent in a huge comet. But wait! Comet Tempel 1 will crash into the smart impactor at a speed of 23,000 mph (36,000 kph). At that speed, the crash will create a crater two to 14 stories deep.

Scientists expect the impact to eject the insides of the comet out into a plume of dust and gases. Instruments on the flyby craft will measure the makeup of the comet innards. After the impact, the flyby will have about 15 minutes to look into the crater and gather data before the crater moves out of view.

Why do scientists want this information? Understanding a comet's composition could help them figure out how to deal with a comet if ever one was heading toward Earth. Also, there may be material inside a comet that could be used by astronauts in the future. NASA plans to return astronauts to the moon and eventually send them to Mars. It would be terrific for future space travelers if comet data reveals that the water inside can be broken down into hydrogen for fuel, oxygen to breathe and just plain old water to drink. Learning about the stuff of comets may even provide some clues as to how the Universe was formed!

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