NASA is looking for a direct strike on a giant comet

A picture imagines the "impactor" heading from the spacecraft toward the comet.
Courtesy NASA / Jet Propulsion Laboratory

You peek over the edge of your snow fort. Somewhere out there your best friend is sneaking around with a snowball. But where?

Smack! A big wet clump of snow lands on your back. It feels like it's about 10 miles wide. Cold water dribbles down your neck, but you're grinning. You spin around, snowball in hand. It's time to strike back.

A NASA mission named Deep Impact has the same idea. But NASA is not after your best friend. NASA is after a comet.

A long time ago -- about 4 billion years -- comets hit Earth almost every day. It was like a big snowball fight. In fact, astronomers call comets "dirty snowballs" because they are made of fluffy ice mixed with some rock and dirt. They are a lot like that snowball your best friend made, except that comets really can be 10 miles wide.

In 2004, the Deep Impact spacecraft will chase Comet Tempel 1. When it catches up, one part of the spacecraft, called the "impactor," will separate from the other part, called the "flyby spacecraft" and maneuver right into the comet's path. An on-board camera will take pictures and send them back to Earth.

The impactor will be going 23,000 mph when it hits the comet, creating a big crater and sending tiny bits of the comet into space. We will see the comet getting closer and closer until the camera is vaporized. Cameras on the flyby spacecraft will also take pictures of the comet bits flying through space. By studying these pictures scientists expect to learn a lot more about comets. Just call it an educational snowball fight -- and maybe the most fun space mission ever!

You can find out more about Deep Impact and watch an animation of the comet impact at spaceplace.nasa.gov/deepimpact/deepimpact.htm.

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