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Voyager Goes Where No Other Spacecraft Has Gone Before - 2003-11-05


The spacecraft Voyager 1 is still sending data back to NASA, the U.S. government space agency, after more than 26 years in space. It is now the most distant man-made object in space, traveling billions of kilometers from earth and perhaps reaching the outer edges of our solar system. Two teams of American scientists are reporting two different scenarios of the Voyager's latest adventures, although both teams agree that the spacecraft is in uncharted territory.

Space scientists believe the unmanned spacecraft, Voyager 1, is on the verge of reaching the outside of our solar system, beyond the sun's influence. Or perhaps, as at least one prominent professor says, it's already there. Just what kind of threshold Voyager has crossed is under debate. However, there is no question as to where it's headed. As Project Scientist Edward Stone explains, Voyager is going where no other spacecraft has gone before.

"This is a very exciting time," he said. "Voyager is beginning to explore the final frontier of the solar system. Our heliosphere is like a ship, plowing through these clouds of inter-stellar material. But for the last forty years of solar exploration, we have been inside of this bubble, in the supersonic solar wind blowing at a million miles per hour. But last year, in the middle of last year, we got the first signs of this final frontier."

There is no conclusion on whether or not Voyager has actually passed the so-called "Termination Shock," where the spacecraft would encounter a dramatic drop in solar wind speed and an increase in interstellar plasma or particles. But according to the head of the space department at Johns Hopkins University, Stamatios (Tom) Krimigis, that has already happened. He says Voyager 1 crossed the threshold last year.

"There was a huge increase, about 100 times as much radiation intensity, beginning early in August and then it abruptly dropped about the beginning of February," he said.

Mr. Krimigis is the leader of a team of scientists whose findings are published in this week's issue of the journal Nature.

On the other side of the debate is Frank McDonald of the University of Maryland whose teams' findings will also be published in Nature. He says the Voyager has been on an amazing ride, traveling 13.4 billion kilometers, but he does not believe it has reached the region of the "termination shock."

"We've learned many new things about cosmic rays, new cosmic ray components, the change with radial distance, the change in solar cycle. So the data is constantly evolving over that period," he said. "So we haven't been just sitting there waiting to get to the termination shock. Half the fun is getting there."

Mr. McDonald says he agrees with the observations of the Krimigis team, but his researchers interpret them differently. He says the Voyager is in the neighborhood of termination shock, just not over it.

Both teams of scientists note the drop in solar wind, which is believed to be one of the indicators of reaching the end of the solar system, but they give different explanations for the phenomenon. Keith Cowing of explains the discrepancy this way:

"I guess it's this old zen saying that what you observe is based on your experience, and what you experience is based on your observations. So, if you expect to see something sometimes, you can make data fit that picture," he said.

Mr. Cowing goes on to say that scientists have created this boundary where they believe the solar system ends, and interstellar space begins. "And what they're seeing is they've reached this point that they thought they've crossed this line," he said, "then they come back again and they're seeing some readings representative of interstellar influences but they're still seeing readings that represent what they would expect if the sun were still controlling the show, so as one scientist said, its nature doesn't seem to be cooperating with our models."

But whether or not Voyager 1 has reached the edge of the solar system, or still has a way to go, is not necessarily the main lesson from the team's findings. Mr. Cowing says scientists are gathering data from truly unknown territory and are scratching their heads over numbers being sent from a spacecraft that should have died 20 years ago.