Biloxi Sun Herald
For millions of years, comets have been swooping past Earth and occasionally bashing into us. Now, earthlings are turning the tables on those luminous, mysterious, potentially dangerous visitors from outer space.
No less than four spaceships are on their way, or soon will be, to five or six nearby comets. Starting in January, they will take close-up pictures, collect samples, punch a hole in, and even land on the surface of their assigned targets.
"This is a golden decade for cometary science," said Donald Yeomans, who tracks comets and asteroids at NASA's Jet Propulsion Laboratory in Pasadena, California.
Comets are chunks of rock and ice surrounded by glowing clouds of gas and dust that come from the outer edge of the solar system. Asteroids are fragments of metal or rocks that orbit the sun, largely between Jupiter and Mars.
Two NASA comet missions, Stardust and Contour, have already been launched. A European spaceship, Rosetta, will follow in January, and a third American project, Deep Impact, a year later.
Why this sudden surge of scientific interest in comets, which have intrigued and sometimes terrified people in the past?
One reason, Yeomans pointed out, is home-planet security. We live in a veritable shooting gallery of comets and asteroids that periodically pummel Earth, such as the object that hastened the death of the dinosaurs 65 million years ago.
"These things can run into us," Yeomans said. "If one of them has our name on it, we've got to know what they're made of." Such information could be crucial for any attempt to deflect a comet or asteroid from colliding with Earth.
Basic scientific curiosity is also driving the comet hunt, especially now that modern technology makes it possible to visit comets efficiently and relatively cheaply.
The four missions will cost between $150 million and $325 million apiecepeanuts for space projects. Contour, for example, is budgeted at $159 million, compared with $1.5 billion for a major planetary explorer such as Galileo.
"There's an awful lot of high-class science waiting to be done," said Tom Morgan, who directs the three U.S. comet hunts from NASA headquarters in the Washington, D.C., area.
According to Joseph Veverka, an astronomer at Cornell University in Ithaca, New York, and chief scientist for the Contour mission, comets are among the solar system's biggest mysteries. "We really have more ideas about comets than facts," he said.