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Voyager 1 Is an Interstellar Craft

the_sun_flareHard to over-emphasize just how historic this is: it has been confirmed that Voyager 1 has pierced the heliosphere and entered into interstellar space. Back in June I posted about a “mysterious region” at the edge of our solar system, which had scientists a little confused about Voyager’s location. Evidently, that confusion has been cleared away.

From the University of Iowa’s IowaNow website:

“On April 9, the Voyager 1 Plasma Wave instrument, built at the UI in the mid-1970s, began detecting locally generated waves, called electron plasma oscillations, at a frequency that corresponds to an electron density about 40 times greater than the density inside the heliosphere—the region of the sun’s influence,” says Gurnett. “The increased electron density is very close to the value scientists expected to find in the interstellar medium.

“This is the first solid evidence that Voyager 1 has crossed the heliopause, the boundary between the heliosphere, and interstellar space,” says Gurnett, principal investigator for the plasma wave instrument.

At age 36, Voyager 1 is the most distant human-made object at more than 11.6 billion miles from the sun, or about 125 astronomical units.

“At that distance it takes more than 17 hours for a radio signal to travel from the spacecraft to one of NASA’s Deep Space Network antennas. The signal strength is so incredibly weak that it takes both a 230-foot and a 110-foot-diameter antenna to receive our highest resolution data,” Gurnett says.

That makes Voyager 1 the first human-made spacecraft to enter interstellar space. Though we can’t see or feel what that’s like, an instrument on the probe captured the sound of vibrating plasma there, and sent it back to Earth. You can listen to that here (or at the bottom of this post).

National Geographic explains how scientists know Voyager 1 crossed over in a little more detail:

Knowing exactly where the solar wind ends and where interstellar space begins has been an open question among space scientists for more than four decades, says Stone.

Since an instrument for directly detecting that transition died in 1980, the researchers have had to rely on indirect measures of magnetic and electrical activity from other instruments aboard Voyager 1 to find an answer.

One key to identifying this boundary is the difference in the density of charged particles between the solar wind and interstellar space, as it is about 50 times greater in the latter region.

Looking at a pair of solar storms that caught up to the spacecraft last October and then again last April, Gurnett’s team reported that measured changes in electrical activity around Voyager correspond to interstellar space.

As the storms passed the spacecraft, they triggered spikes in electrical and radio waves that uniquely corresponded in frequency to the spacecraft having entered the more densely charged interstellar space.

Based on that increase, the team extrapolated the entry date for Voyager 1 into interstellar space as August 25, 2012.

Voyager still has some life left in it too. The probe is not expected to completely lose power until 2025, though instruments on board will likely fail before that time. Remember, Voyager 1 was designed in the early ’70s and was launched on September 5th, 1977. As Suzanne Dodd—the Voyager project manager—points out, your average smartphone has approximately 250,000 times more memory than Voyager 1 does, which makes its continuing operation seem all that more miraculous. Also makes me wonder what we’re doing with all that extra memory in our pockets.