- The Washington Times - Tuesday, January 11, 2005

Think of it as the astronomical equivalent of a mosquito running into a 767 airliner. That’s how NASA scientists are describing the planned July 4 collision between a 1-by-1-meter copper probe and the 5-mile-long Tempel 1 comet. Today NASA plans to launch its Deep Impact spacecraft from Cape Canaveral, Fla., to begin its six-month, 268-million-mile mission to intercept Tempel. On July 3, the spacecraft will jettison its 820-pound probe directly in the path of the comet’s trajectory. The next day, the comet and probe will meet at a speed of about 23,000 mph, or 6.3 miles per second — an event that scientists hope will be visible on Earth and provide professional and amateur astronomers a celestial fireworks show just in time for the Fourth of July.

Of course there are scientific reasons behind the Deep Impact mission. Upon impact, the probe will break apart, releasing debris from the comet and boring a crater into its surface. Scientists suspect the crater could be anywhere from the size of a two-story house to the size of the Roman Coliseum. But that’s the point of Deep Impact: They simply don’t know. They suspect that at least the outer crust of a comet’s surface is comprised mostly of ice. What’s inside is anyone’s guess, and discovering that could have far-reaching scientific benefits for us on Earth.

Deep Impact is the eighth mission in NASA’s Discovery Program, which aims at launching many small, relatively low-cost missions with highly focused scientific goals. One of these goals is to better understand the origin of our solar system. Comets are thought to be comprised of the left-over dust and gas that once formed the sun and its orbiting planets. Another, perhaps more practical, goal, according to Joseph Veverka, professor of astronomy at Cornell University and a member of Deep Impact’s science team, is to understand comets and asteroids to prepare for the day when one might threaten earth. “Unfortunately, we don’t know what [comets] are made of and how hard they are,” he said. Knowing such useful information would help decide how humans could deflect a comet or asteroid destined for Earth.

Since 1998, NASA has dramatically increased its efforts to locate near-earth objects (NEOs), or those comets and asteroids that will come within 28 million miles of Earth’s orbit. So far, NASA has located about 65 percent of the estimated 1,100 NEOs thought to be in the solar system. NASA’s goal is to locate 90 percent of NEOs by 2008. The next step will be what to do if one is found to threaten Earth. For that, a successful Deep Impact mission would be most helpful.

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