Pioneer 10 gets new lease on life in outer solar system

Artist's concept of Pioneer as it passed Saturn

March 2, 2000
Web posted at: 6:14 p.m. EST (2314 GMT)

In this story: An impressive list of firsts The edge of the solar system Passing the baton to Voyager 1 RELATED STORIES, SITES

By Richard Stenger
CNN Interactive Staff Writer

MOFFETT FIELD, California (CNN) -- Pioneer 10 weathered boulders in the asteroid belt, intense radiation near Jupiter and a flyby with a mysterious object beyond Pluto. But the mission seemed doomed to perish from an Earthly threat, until chaos theory intervened.

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Pioneer looks at Jupiter
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Star gazing

Launched on March 2 in 1972, Pioneer still performs valuable scientific observations, but almost died for lack of funding a few years ago. That was until scientists studying chaos theory became interested in its weak signals, which take about 10 hours to reach Earth, traveling at the speed of light.

The faint radio transmissions are being read for advanced concept support of chaos theory, according to Pioneer 10 mission leader Larry Lasher, who called the new project a "white knight."

Pioneer has racked up impressive achievements during a 28-year voyage that has taken it almost 7 billion miles, about twice the distance of Pluto from the sun. It was the first spacecraft to pass beyond Pluto's orbit and the first to make direct observations and take close-up pictures of Jupiter.

Pioneer 10 charted Jupiter's intense radiation belts and verified that the jovian planet is mostly liquid.

But many astronomers consider Pioneer 10's unprecedented passage through the asteroid belt between Mars and Jupiter as its crowning accomplishment.

No one knew if a spacecraft could navigate the cosmic mine field, filled with speeding boulders, some the size of Alaska. Pioneer 10 made the crossing virtually untouched, opening the way for later spacecraft to voyage beyond Mars.

Pioneer 10 is now about 75 astronomical units away from the sun, or 75 times the distance of the Earth from the sun.

Scientists still can receive data from a low-watt telescope, but the craft, its nuclear-powered battery supply dwindling, dare not turn on its instruments for fear of a power outage, said Lasher, who works for NASA's Ames research center in Moffett Field, California.

The craft recently performed a maneuver to improve the reception of its signal on Earth, but had to turn off its transmitter and fly blindly for 90 minutes to do so.

When Pioneer was 5.2 billion miles away, it was knocked off course by a mysterious gravitation tug. Astronomers think the cause was a Kuiper Belt Object. KBOs are asteroid-sized bodies, similar in make up as Pluto, that circle the sun far beyond Pluto.

Voyager

Pioneer faces another great challenge: searching for the edge of the solar system. It could close in soon on the outer reaches of the heliosphere, an elliptical field of solar wind that radiates from the sun. At the edge, where the solar system meets outer space, the interstellar ray flux stops the solar winds in their tracks.

"We're hoping we are at the point where we can make that determination soon," said Lasher, who estimates the boundary at a distance of 75 to 125 AUs.

"We think that it's pretty close, but our hopes are dashed all the time," he said.

Scientists once thought the heliosphere extended out only as far as Jupiter, a theory dashed by Pioneer and other veteran travelers into the outer solar system -- Voyager 1 and 2.

Launched in 1977, the Voyagers have similar records of achievement as Pioneer 10. Both Voyagers flew by Saturn and Jupiter. Voyager 2 also passed near Uranus and Neptune.

But they have taken far different paths. The Voyagers are heading in the opposite direction than Pioneer, in relation to the sun.

The Voyagers, both well beyond Pluto, could have better luck in their search for the edge of the heliosphere. In 1998, Pioneer "passed the baton," Lasher said, to the faster Voyager I as the most distant manmade object in the solar system.

Pioneer should stop sending transmissions in the coming years.

But having used planetary gravitational assists to reach escape velocity from the solar system, it will continue to drift into interstellar space for millions of years. It is headed at 27,380 mph for the red star Aldebaran, which makes the eye of Taurus, the Bull. Pioneer will need more 2 million years to reach it.

It will probably still be chugging through the galaxy 5 billion years from now when the sun expands into a red giant and obliterates Earth.

Should other sentient life forms find Pioneer, however, they may learn about humans. The ship carries a plaque, designed in part by the late Dr. Carl Sagan, engraved with pictures, solar maps and elemental symbols to describe civilization on Earth.

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NASA
Pioneer Project Site
Voyager Project Site

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