for National Geographic News
As principal investigator of NASA's Deep Impact mission, Michael A'Hearn will be in charge of shooting a projectile into the surface of a frozen ball of ice and rock, comet Tempel 1, creating a crater the size of a football stadium.
So does he feel like a kid in a sandbox?
"Yeah, there's something to that," A'Hearn chuckled.
But A'Hearn and his team are not shooting up celestial objects just for fun. Instead, by impacting a copper projectile about the size of a trash can into Tempel 1, scientists hope to find out what the comet is made of.
That's important because comets were instrumental in the formation of the solar system. Many scientists consider comets to be the source of most of the water and organic material that was once delivered to all terrestrial planets.
"The goal is to learn more about how the solar system was formed," said A'Hearn, an astronomy professor at University of Maryland in College Park.
It is the first space mission to probe beneath a comet's surface to reveal secrets of its interior. The experiment could also help scientists devise ways to deflect rogue comets if they threaten to collide with Earth in the future.
To build public support, NASA is inviting space enthusiasts to its Web site (Deep Impact Home Page) to add their names to a CD that will be carried by the projectile onto the comet. The submission deadline is January 31, 2004.
Planning for the Deep Impact mission began in 1999. It culminates on July 4, 2005, when a "fly-by" spacecraft will release a smaller "impactor" spacecraft, which will smash into comet Tempel 1 at 37,000 kilometers (22,000 miles) per hour.
Since the fly-by spacecraft is traveling at almost the same high speed after slowing down slightly, scientists have only an 800-second window to make their observations before launching the projectile, which is equipped with a camera and has autonomous navigation.
"It's a one shot-deal," said A'Hearn.
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