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First man-made object may have left solar system—or not

March 20, 2013
Special to World Science  

Thirty-five years af­ter its launch, the Voy­ag­er 1 space­craft may have moved out of the Sun’s in­flu­ence and left the so­lar sys­tem, be­com­ing the first man-made ob­ject to do so, a study says.

But Voy­ag­er proj­ect sci­en­tists say that’s not so, based on the sig­nals they’re read­ing.

The NASA craft has been head­ed to­ward the edge of the he­lio­sphere, a bubble-like re­gion of space dom­i­nat­ed by the Sun and the “so­lar wind” of en­er­get­ic par­t­i­cles it gives off.

Artist's render­ing of Voy­a­ger 1. (Cre­dit: NA­SA)


On Aug. 25, it meas­ured dras­tic changes in rad­ia­t­ion lev­els, more than 11 bil­lion miles from the Sun, ac­cord­ing to the newly pub­lished stu­dy. Anom­a­lous cos­mic rays, which are cos­mic rays trapped in the out­er he­lio­sphere, all but van­ished, the report adds. 

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 find­ings have been ac­cept­ed for pub­lica­t­ion in the jour­nal Geo­phys­i­cal Re­search Let­ters.

“Within just a few days, the he­lio­spheric in­tens­ity of trapped radia­t­ion de­creased, and the cos­mic ray in­tens­ity went up as you would ex­pect if it ex­ited the he­lio­sphere,” said Bill Web­ber, an as­tron­o­mer at New Mex­i­co State Uni­vers­ity in Las Cru­ces and co-author of the report.

But sci­en­tists are de­bat­ing wheth­er Voy­ag­er 1 has reached “in­ter­stel­lar space”—the zone def­i­nitely out­side the so­lar sys­tem—or en­tered a sep­a­rate, un­de­fined re­gion in be­tween, he added. “It’s out­side the nor­mal he­lio­sphere, I would say that…. We’re in a new re­gion. And eve­ry­thing we’re meas­ur­ing is dif­fer­ent and ex­cit­ing.”

Ed­ward Stone, Voy­ag­er proj­ect sci­ent­ist based at the Cal­i­for­nia In­sti­tute of Tech­nol­o­gy in Pas­a­de­na, Calif., said the Voy­ag­er sci­en­tists be­lieve “Voy­ag­er 1 has not yet left the so­lar sys­tem.”

“A change in the di­rec­tion of the mag­net­ic field is the last crit­i­cal in­di­ca­tor of reach­ing in­ter­stel­lar space, and that change of di­rec­tion has not yet been ob­served,” he ex­plained. How­ev­er, last De­cem­ber, “the Voy­ag­er sci­ence team re­ported that Voy­ag­er 1 is with­in a new re­gion called ‘the mag­net­ic high­way’ where en­er­get­ic par­t­i­cles changed dra­mat­ic­ally.”


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Thirty-five years after its launch, the Voyager 1 spacecraft may have travelled past the Sun’s influence and left the solar system, becoming the first man-made object to do so, a study said. But Voyager project scientists say that’s not so, based on the signals they’re reading. The NASA craft has been headed toward the edge of the heliosphere, a bubble-like region of space dominated by the Sun and the “solar wind” of energetic particles it gives off. On August 25, it measured drastic changes in radiation levels, more than 11 billion miles from the Sun, according to the newly published study. Anomalous cosmic rays, which are cosmic rays trapped in the outer heliosphere, all but vanished, dropping to less than 1 percent of previous amounts, the study added. 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 findings have been accepted for publication in the journal Geophysical Research Letters. “Within just a few days, the heliospheric intensity of trapped radiation decreased, and the cosmic ray intensity went up as you would expect if it exited the heliosphere,” said Bill Webber, an astronomer at New Mexico State University in Las Cruces. He calls this transition boundary the “heliocliff.” But scientists are debating whether Voyager 1 has reached “interstellar space”—the zone definitely outside the solar system—or entered a separate, undefined region in between, he added. “It’s outside the normal heliosphere, I would say that…. We’re in a new region. And everything we’re measuring is different and exciting.” On the other hand, Edward Stone, Voyager project scientist based at the California Institute of Technology in Pasadena, Calif., said the Voyager scientists believe “Voyager 1 has not yet left the solar system.” “A change in the direction of the magnetic field is the last critical indicator of reaching interstellar space, and that change of direction has not yet been observed,” he explained. However, last December, “the Voyager science team reported that Voyager 1 is within a new region called ‘the magnetic highway’ where energetic particles changed dramatically.”