Space Missions Aim to Shed Light on Comets

Robert S. Boyd
Biloxi Sun Herald
September xx, 2002
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 apiece—peanuts 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.

A trillion or more of these ghostly objects are believed to hang out in the deep cold beyond the fringes of the solar system. Periodically, gravity nudges one of them into a long looping voyage past the planets and around the sun.

Because they are so far away, comets are believed to preserve the original gas and dust left over from the formation of the solar system 4.5 billion years ago. Astronomers regard them as virtual time machines that enable scientists to study the raw materials of our sun, planets, and moons.

Furthermore, scientists believe comets brought huge quantities of water and carbon-based molecules to Earth during the era of heavy bombardment, when our planet was young.

"These missions will help us understand where our oceans came from," Morgan said.

Some theorists speculate that the cometary molecules may even explain how life got started on Earth."We may really be the progeny of comets," Veverka wrote in the journal Science last month.

Copyright 2002 Biloxi (Mississippi) Sun Herald

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