Voyager At Edge Of Solar System
Wednesday, May 25, 2005
After a storied, 28-year odyssey, NASA's venerable Voyager 1 spacecraft appears to have reached the edge of the solar system, a turbulent zone of near-nothingness where the solar wind begins to give way to interstellar space in a cosmic cataclysm known as "termination shock," scientists said yesterday.
"This is an historic step in Voyager's race," said California Institute of Technology physicist Edward C. Stone, the mission's chief scientist since Voyager 1 and its twin, Voyager 2, were launched in the summer of 1977. "We have a totally new region of space to explore, and it's a once-in-a-lifetime opportunity."
Stone said project scientists, working from models of a phenomenon never before directly observed, finally agreed that data from Voyager 1's tiny 80-kilobyte computer memory showed that the spacecraft had passed through termination shock to the "heliosheath," a frontier of unknown thickness that defines the border with interstellar space.
Stamatios M. Krimigis, another longtime Voyager scientist, said in an interview that the spacecraft might remain in the heliosheath for perhaps 10 years but should easily survive, going dark when its plutonium power source expires around 2020.
Of far greater concern to scientists is the possibility that NASA could kill the $4.2 million-a-year project to free up money for President Bush's initiative to send humans back to the moon and eventually to Mars.
NASA has put Voyager's fate on hold while independent reviewers evaluate the mission, with a decision expected in February. "We're very excited," Krimigis said of the latest findings. "We hope NASA will reconsider, and we're confident they will."
Stone presented the Voyager data during a telephone news conference at the 2005 Joint Assembly in New Orleans -- a joint meeting of the American Geophysical Union, the North American Benthological Society, the Society of Exploration Geophysicists and the Solar Physics Division of the American Astronomical Society.
NASA also updated the progress of the rovers Spirit and Opportunity, which have been exploring Mars since the beginning of last year. Spirit is examining layered rock outcrops in the Gusev Crater, and Opportunity is carefully driving itself out of a dune, where it has been stuck for a month.
Both the Mars rovers and Voyager are NASA "extended missions" that have continued to deliver valuable science long after fulfilling their original goals. The rovers are in good shape after an extra year, despite Opportunity's distress, said Project Manager James K. Erickson, and will continue to run "basically until they wear out."
Voyager's "design mission" to Jupiter and Saturn lasted five years, then simply kept on going. Voyager 2 flew by Uranus and Neptune to complete a "grand tour" of the major planets and is now about 7 billion miles from the sun, traveling 63,000 mph.
Voyager 1 broke away from the tour at Saturn and headed for interstellar space. When it entered the heliosheath, it was 8.7 billion miles away -- the farthest any manmade object has traveled. Its speed is 46,000 mph.
Krimigis said the solar wind, made up of fast-moving electrons, protons and other charged particles, has a magnetic field that prevents the interstellar wind from breaching the solar envelope -- known as the "heliosphere" -- as the solar system travels through space.
The heliosheath is the heliosphere's outer frontier, a zone where the solar wind begins to dissipate. This process begins at termination shock and is marked by a sudden drop in the speed of the solar wind and a corresponding build-up in heat and the strength of the magnetic field. The effect is like traffic piling up on a freeway during rush hour.
Scientists first detected these symptoms in 2002, but they receded, then returned more strongly, only to recede again. It is a script not foreseen by the computer models.
"We've gone back and forth since then," Krimigis said. "But this time I guess we all agree." This is because the magnetic field jumped by a factor of 2.5 to 4 around Dec. 15 -- and has remained fluctuating at a high level since then, Krimigis said. Scientists estimated that the speed of the solar wind dropped from 1.5 million mph to near zero.
Stone stressed, however, that this clash of cosmic forces has little effect on Voyager, since the amount of matter in the heliosheath is so meager.
"The spacecraft knows nothing about what is going on," Stone said. "It is just sending us the data."