- The Washington Times - Monday, January 10, 2005

NASA is preparing to launch a spacecraft tomorrow that is expected to smash into a comet, piercing the celestial body’s outer surface and giving scientists a look at its inner structure for the first time.

Although other spacecraft have studied comets up close and chemically analyzed their tails, Deep Impact will be the first spacecraft to touch a comet. It will strike comet Tempel 1 traveling at a speed of more than 22,000 mph with the same amount of energy as 4 tons of TNT.

“The impactor will penetrate the comet’s surface, blowing away material from the surface and revealing the mysteries of the interior of the nucleus,” said Andy Dantzler, acting director of the solar system division at NASA.

Deep Impact is a two-part spacecraft — a parent “flyby” spacecraft and a washing machine-size impactor. The two parts separate, and the impactor is aimed at the comet’s nucleus.

The 820-pound impactor will smash into the comet’s surface sending up a giant cloud of dust, water and debris. The front of the probe has a hammerhead, made of 317 pounds of copper. Copper was chosen because it won’t react chemically with the water within the nucleus. It’s possible that the impact could split the nucleus into multiple pieces.

There’s no detailed information on the interiors of comets. Some scientists estimate that the crust could be 3 feet deep; others say it could be more than 30 feet. How much dust will result from the impact depends on the strength of the comet’s surface. Scientists estimate that the impactor will create a 80-foot-deep, 330-foot-wide crater.

“What we’re interested in is the source of the dust and gases [in a comet’s tail], which is a small core of ices, organic compounds and dust, which is called the nucleus, which is typically a couple of miles in diameter,” said Tom Morgan, Deep Impact program scientist at NASA. “These objects are of interest to us because they are literally the leftover building blocks of our solar system.”

The impactor, during its last seconds, will radio the closest pictures of the comet before its lens is sandblasted by dust from the surface. The flyby spacecraft’s cameras and chemical analysis instruments will monitor the probe as it smashes into the comet’s surface.

Just as important is the view from Earth. Astronomical spacecraft such as the Hubble, Chandra and Spitzer telescopes, will observe the results from the impact, as will dozens of telescopes from the Earth’s surface.

The collision will happen, appropriately enough, on the Fourth of July.

“We expect to provide some great fireworks for all our observatories,” said NASA program manager Rick Grammier.

The encounter only will be visible above the horizon in the west and over the Pacific — from New Zealand to Arizona. Scientists expect the results to be spectacular, lasting for days so observers around the world can participate, including amateur astronomers.

All together, the spacecraft, launch vehicle and operations will cost taxpayers $330 million.

The target, comet Tempel 1, was discovered in 1867. It orbits the sun every 5.6 years, and its closest possible approach to the Earth is a comfortable 53 million miles.

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