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NASA to Study Comets - 2002-06-28


A U.S. spacecraft will soon be on its way for a rendezvous with comets, the big, dirty ice balls that have sped around the farthest reaches of our solar system from its earliest days. Scientists want to discern what these celestial bodies can tell them about the origin of the solar system and of us.

No one knows how comets originated, although a popular theory is that they formed near the outer planets and were ejected to a much greater distance later.

But scientists do know what comets represent. Cornell University astronomer Joseph Veverka says they are best preserved remnants of the material from which our solar system formed four-and-half billion years ago, and therefore are worth examining up close with a U.S. spacecraft named Contour.

"It is the essential next step in the exploration of comets. Comets remain mysterious objects," Mr. Veverka said. "They are indeed the most abundant and least understood bodies in our solar system. Contour's main purpose is to investigate the nature and diversity of comets in unprecedented detail."

The eight-sided Contour spacecraft is just one of a fleet of four U.S. and European satellites destined for comets over the next few years. Colleen Hartman, who directs the U.S. space agency NASA's division of Solar System Exploration said "we are about to enter a golden era of comet investigation."

She also said one of the comet explorers, NASA's Stardust mission, is already on its way. It will gather material from a comet.

"In January 2004, the Stardust spacecraft will fly by comet Wild-2, collecting comet dust to return to Earth in the year 2006," Ms. Hartman said. "This is the first-ever return of pristine comet dust to the Earth."

In addition, the European Space Agency will send up its Rosetta spacecraft next January to drop scientific instruments on a comet to study its composition and chemistry. Then in 2004, NASA will launch the Deep Impact satellite, which will eject a probe to crash into a comet. That will be the first mission to look beneath the surface of one. Contour's role in this effort is to fly within 100 to 300 kilometers of two comets to get the sharpest images yet of a rocky, icy nucleus and study the chemistry of the dust and gas comets release in their long, wispy tails.

Mr. Veverka said the chemical analysis from Contour will try to answer several questions about the role comets may have played in Earth's early history. "Can we demonstrate that much of the water that exists in our lakes, rivers and oceans was actually brought to Earth by comets?," he asked. "Is it plausible that the air that we breathe once was comet stuff? And is it likely that the molecules that led to the origin of life on Earth came from comets?"

In addition to looking back, the comet investigations will help space planners look ahead. NASA astronomer Donald Yeomans says comets may contain resources to help colonize the solar system.

"If we do that, we are going to need raw materials in space to build structures. We are going to need water to sustain life," he said. "You can break the water down into hydrogen and oxygen, which is the most efficient form of rocket fuel. So in some sense, comets may one day be the fueling stations and watering holes for planetary colonization."

The Contour mission is to arrive at the comet Encke in November of next year and at Schwassman-Wachmann-3 two-and-a-half years later.

At a cost of $159 million, it is the sixth in a series of NASA's inexpensive explorations of our solar system.

To reach its targets cheaply, Contour's orbit will take it around the Sun and Earth for at least four annual gravity boosts. These maneuvers will bend its trajectory and help it reach its destinations without using much fuel.

In addition, mission director Robert Farquhar of the Johns Hopkins University Applied Physics Laboratory said Contour will cruise in hibernation mode for up to nine months at a time. "We turn off almost everything on the spacecraft except for the heaters and the receivers," he said. "So that means that we do not have to maintain a large operations team during that time, and we do not have to make use of antennas."

The Contour spacecraft's mission plan is flexible enough to allow controllers to send it to another comet arriving from the outer solar system if one is discovered in time for the probe to catch it.

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