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.