Probe Approaches 'Final Frontier'
NASA's Voyager I spacecraft has entered the final frontier of our solar system and is cruising its way to a vast area marking the beginning of interstellar space.
The spacecraft, launched 28 years ago, is 8.7 billion miles from the sun in a region called the heliosheath, located just beyond the termination shock, or precursor of the boundary that marks the beginning of interstellar space.
"Voyager I has entered the final lap on its race to the edge of the interstellar space," said Edward Stone, project scientist at the California Institute of Technology in Pasadena, which manages NASA's Jet Propulsion Laboratory.
The findings were presented Tuesday at the American Geophysical Union meeting in New Orleans.
Voyager I, which is now 94 astronomical units (8.7 billion miles), still has a decade to go before reaching the heliopause, which marks the beginning of interstellar space and the end of our solar system. Beyond, it's the interstellar medium, made up of the particles cast off by dying stars.
Voyager I has crossed a boundary called the "termination shock," said University of Iowa space physicist Don Gurnett, principal investigator for the plasma wave instrument on the craft.
Evidence for the crossing, which occurred December 16, 2004, included steadiness in the strength of energetic particle beams, a near reversal of the direction of these beams and a jump in the magnetic field strength. An electron beam generated by the termination shock created the electron plasma oscillations observed by Gurnett's team.
"We saw a burst of plasma oscillations before we went through the termination shock," Gurnett said in a press release before presenting his findings at the AGU meeting.
The heliosheath, the region where termination shock occurs, is where the solar wind slows from supersonic to subsonic speed as it approaches the gas generated by stars beyond our sun, said fellow University of Iowa researcher Bill Kurth.
"The solar wind creates a bubble (the heliosphere) around the sun, and near the edges of the bubble is a place where the solar wind piles up as it encounters the interstellar wind," says Ed Stone, Voyager project chief scientist and professor of physics at the California Institute of Technology.
"We think the sun is currently in a phase where the heliosphere is shrinking," Stone said. "If so, Voyager would continue to be in this thicker and hotter region until it reaches the heliopause, the outer edge of the bubble. This is a wonderful opportunity to reach interstellar space, and we hope we can keep the spacecraft operating through the year 2020."