Original URL: http://www.theregister.co.uk/2013/03/20/voyager_exits_heliopause/
Voyager goes off a (helio) cliff
Tiny traveller still telling tales
Posted in SPB, 20th March 2013 23:47 GMT
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Probably the most-loved survivor of 1970s space optimism, Voyager, has sent back signals indicating that it's left the heliosphere.
Scientists are now discussing whether they should consider the 35-year-old probe to be in interstellar space, or to have entered a new region of space that hasn't been previously described.
The signals analysed by scientists, to be published by the American Geophysical Union, showed a precipitous fall in solar radiation detected by Voyager in August last year, when it was more than 11 billion miles – nearly 18 billion kilometres – from the Sun.
“Anomalous cosmic rays, which are cosmic rays trapped in the outer heliosphere, all but vanished, dropping to less than 1 percent of previous amounts. At the same time, galactic cosmic rays – cosmic radiation from outside of the solar system – spiked to levels not seen since Voyager's launch, with intensities as much as twice previous levels,” the AGU announcement states [1].
The transition from radiation trapped in the heliosphere (as the AGU says, rather like a bubble) to galactic radiation was so sudden, New Mexico State University emeritus professor of astronomy Bill Webber calls the transition boundary the “heliocliff”.
Whether Voyager is truly in interstellar space or in a new, undefined region, Webber says, “everything we're measuring is different and exciting.”
The research paper describing Voyager's exit from the heliopause is here [2]. ®