The Interstellar Argument: Has Voyager Really Made It?

Earlier this month, NASA's Jet Propulsion Laboratory (JPL) confirmed that the unmanned spacecraft Voyager1 has slipped into interstellar space - a first for a manmade observational tool. However, researchers are now refuting this claim, saying that we won't truly know if this spacecraft has gone interstellar until late 2015.

NASA concluded that Voyager has truly gone interstellar on July 8, when measurements revealed that, for the third time, electron-reading instruments were reporting a surrounding plasma density 40 times the densities previously seen.

According to traditional knowledge of our galaxy, an object is in "interstellar space" once it passes the influence of any one star. The Voyager had previously been spending its time taking readings while it traveled through the outer-heliosphere of the Sun - the outer ring of the Sun's atmosphere. There, plasma electrons from the Sun freely floated within the bubble of their own influence. However, researchers theorized that where this bubble ends, plasma electrons from distant stars will be found packed against one another, pressed against the hemisphere's barrier. This increased plasma density would then mark the Voyager as truly leaving the influences of the Sun behind it.

"We're excited to analyze these new data. So far, we can say that it confirms we are in interstellar space," Don Gurnett, the principal investigator of the plasma wave instrument on Voyager, said in a statement.

However, now two JPL scientists are arguing that based on their model of the Sun's influence, the Voyager isn't really in interstellar space. Instead, it has simply encountered its first wave of slowed solar winds, which can compress in their reduced speeds. Soon, they argue, a reversal of the solar magnetic field will occur, and when it does, it will be indisputable evidence that Voyager is still within the Sun's broad influence.

"If that happens, I think if anyone still believes Voyager1 is in the interstellar medium, they will really have something to explain," Geord Gloeckler, who authored a study on this new model, said in a release. "It is a signature that can't be missed."

NASA's Voyager project scientist Ed Stone appears unfazed by Gloeckler's claims.

"It is the nature of the scientific process that alternative theories are developed in order to account for new observations," he said in a statement.

He adds that the Voyager team will not ignore the study, and will be paying close attention to all viable models as more data is collected. Gloeckler expects the spacecraft to encounter the magnetic reversal by the end of next year.

"The proof is in the pudding," he said. "This controversy will continue until it is resolved by measurements."

The new study was accepted by the journal Geophysical Research Letters.