Plowing through the solar system'sunexplored frontier, NASA's Voyager 1 spacecraft has entered a region of stagnant solar wind andmagnetic pressure and is on the precipice of crossing over into interstellarspace, scientists saidMonday.
But estimates for when thenuclear-powered probe will break through are not precise. Ed Stone,Voyager's project scientist, said it could be any time betweena few months and a few years from now.
"I can almost assure you that will be confused when this first happens because this will not be simple," Stone said. "Nature tends to be much more creative thanour own minds."
Moving aroundthe perimeter of the Milky Way galaxy, the sun generates a wind ofcharged particles moving out in all directions. Ahead of the sun, thesolar wind is compressed like the waves in front of a moving ship by asteady flow of plasma emanating from outside the solar system. The solarparticles are mostly diverted down and up, then behind the sun like aship's wake or a comet's tail.
The region of the sun's influence, in which the solar wind is dominant, is called the heliosphere. Theheliopause is the boundary between the heliosphere and interstellar space.
No spacecraft has ever leftthe solar system before, so Voyager 1 is flying through anuncharted void between the influence of the sun and the interstellar wind, which blowswaves of plasma and charged particles at a clip of up to 15 milesper second.
"That transition may not be instantaneous," Stone said. "It maytake us months to get through a rathermessy interface between these twowinds."
The latest data from Voyager 1show the spacecraft is in a region of stagnation, where thestream of charged particles from the sun has slowedand the sun's magnetic field has piled up,researchers said at the American Geophysical Union's fall meeting in SanFrancisco.
"We've been using the flow ofenergetic charged particles at Voyager 1 as a kind of wind sock to estimate the solar wind velocity," said RobDecker, a co-investigator for Voyager's low-energy charged particle instrumentat the Johns Hopkins University Applied Physics Laboratory. "We've found that the wind speeds are low in this region and gust erratically. For the first time, the wind even blows back at us. We are evidently traveling in completely new territory. Scientists had suggestedpreviously that there might be astagnation layer, but we weren't sureit existed until now."
High-energy electronsfrom interstellar space are also leaking into theheliosphere, Stone said.
Voyager 1 is now stationed 11 billion miles from the sun.
"What we're talking about todaywith all these new developments is simply one more chapter in ascientific inquiry that began over 100 years ago,"said Eugene Parker, professor emeritus of physics at the University of Chicago.
Looking for signs that the probe has crossed over the heliopause and left the solarsystem, scientists are closelywatching data from Voyager 1's low-energy charged particle counter and magnetic field, cosmic ray and plasma wave instruments.
The twin Voyager2 probe is about 2 billion miles behind Voyager 1, but it'sexploring the southern hemisphere of the heliosphere. Voyager 1 is flyingup and out relative to the sun.
The spacecraft have enough power to continue scientific investigations until approximately 2020, according to Stone. The probescould remain functionaluntil around 2025.
Stone said heexpects the magnetic field to switch from an east-west to anorth-south orientation. Evidence should also show up from more intenselow-energy galactic cosmic radiation and reduced intensity ofcharged particles originating from the sun.
"I think it's reasonable to think it could only be a matter of months or a matter ofseveral years before we cross this region," Stone said. "But no spacecraft has ever been there before and we continue to find our modelsneed to be improved as we learn more about the complex interaction between the solar wind and the interstellar wind."
Traveling abillion miles every three years, the Voyager probes won'treach the vicinity of another star foranother 40,000 years.
Both missions launched on Titan-Centaurrockets in 1977. Voyager 2 completed a tour of the outer solar system, flyingby Jupiter, Saturn, Uranus and Neptune before heading toward interstellar space.
Voyager 1 studied Jupiterand Saturn in 1979 and 1980.
"To me, it's been constant [discovery]," Parker said. "I hold my breath as to what's going to happen next."
(By Stephen Clark)
(By Stephen Clark)
NOTE: Reading this account of Voyager’spassage from heliosphere throughheliopause to the windless non-aether of interstellar space almost moved me to tears yesterday.
I suppose it’s anexample of the “patheticfallacy” writ pathetically stress-enlarged; I’m constantly feeling myself in astate of similar sea passage, buffeted sometimes by high winds, in irons at others, alternately bored by, dreading and wishing the next transition. I think this iswhat attracted and involved me to such a strong degree with Jules Verne’s Captain Hatteras last summer.
I thought about this falling asleep last night, awake between 2 and 4, and then just beforerising at 6.
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