Voyager 2 leaves the solar system

The Voyager 2 probe has reached interstellar space outside of the Sun’s influence— the second man-made object to do so after Voyager 1.

New research from the University of Iowa has indicated that the Voyager 2 spacecraft has reached the interstellar medium (ISM )— the region of space between solar systems in a galaxy. As such, it has moved out of the boundary reached by solar winds streaming out from the Sun and therefore crossed the boundary of the solar system.

This means Voyager 2 has become the second man-made object to move beyond the influence of our Sun, joining Voyager 1 — which crossed the same boundary in 2012.

Voyager 2 has left the solar system. (NASA)

Dan Gurnett, professor emeritus in the UI Department of Physics and Astronomy and an author of the study published in the journal Nature Astronomy — and his colleagues confirm that Voyager 2 will cross into the ISM on November 5th.

The crossing of this barrier is indicated by a definitive rise in plasma density detected by a plasma-wave instrument on the craft.

The sudden jump is caused by Voyager 2 moving from the low-density, hot conditions of solar wind to the cooler, higher-density plasma found in interstellar space. This jump in plasma density was also experienced by Voyager 1 as it passed the same threshold. It indicates that the transition anything but smooth.

“In a historical sense, the old idea that the solar wind will just be gradually whittled away as you go further into interstellar space is simply not true,” says Gurnett who is the principal investigator on the plasma wave instruments aboard both Voyager 2 and its predecessor Voyager 1. “We show with Voyager 2 — and previously with Voyager 1 — that there’s a distinct boundary out there.

“It’s just astonishing how fluids, including plasmas, form boundaries.”

Voyager 1 & 2 launched within weeks of each other in 1977. Both had different missions and different trajectories. Despite this, the two craft crossed what is for all intents and purposes the boundary of the solar system at similar distances from the Sun. Voyager 2 entered the ISM at 119.7 AU, Voyager 1 at around 122.6 AU — both approximately 11 billion miles from the Sun.

Learning more about the Sun’s influence by leaving it

Ironically, by leaving an area where it can be reached by solar winds from the Sun, Voyager 2 is teaching us about the Sun’s heliosphere — the wind-sock shaped area the Sun carves out in denser plasma of the ISM. In fact, the knowledge that both Voyage 1 and Voyager 2 crossed this boundary at similar distances tells us much about the shape of the heliosphere.

Iowa physicists have confirmed the spacecraft Voyager 2 has entered interstellar space, in effect leaving the solar system. Data from Voyager 2 has helped further characterize the structure of the heliosphere, structure of the heliosphere — the wind sock-shaped region created by the sun’s wind as it extends to the boundary of the solar system. (NASA JPL)

“It implies that the heliosphere is symmetric, at least at the two points where the Voyager spacecraft crossed,” says Bill Kurth, University of Iowa research scientist and a co-author on the study. “That says that these two points on the surface are almost at the same distance.”

“There’s almost a spherical front to this,” adds Gurnett. “It’s like a blunt bullet.”

Data collected from the plasma instrument also tells us more about the thickness of the outer region of the heliosphere — referred to as the ‘heliosheath’ by astronomers. As Gurnett explains, the heliosheath is where the solar wind ‘piles up’ against the wind from interstellar space. The researcher says that this is analogous to a snowplough pushing snow along a city street creating snowbanks.

The data collected from Voyager 1 and 2 indicates that the heliosheath varies in thickness — determined from the fact that Voyager 2 travelled an extra 10 AU to reach the heliopause — the boundary where solar winds and interstellar winds are in perfect balance.

Researchers had believed based existing models of the heliosphere that Voyager 2 would reach the heliopause closer to Earth than Voyager 1 did, but this hasn’t been the case.

“It’s kind of like looking at an elephant with a microscope,” Kurth says. “Two people go up to an elephant with a microscope, and they come up with two different measurements. You have no idea what’s going on in between.

“What the models do is try to take information that we have from those two points and what we’ve learned through the flight and put together a global model of the heliosphere that matches those observations.”

Leaving the solar system will mean saying goodbye to Voyager 2

Researchers will eventually lose contact with Voyager 2 just as they did with Voyager 1. The last data was received by Voyager 1 when it was at approximately a distance of 146 AU or 14 billion miles from the Sun.

Currently, the data from the plasma instrument aboard Voyager 2 takes 19 hours to reach Earth its distance from us is so great. And eventually, that distance will be too great to overcome.

But, despite being lost to us forever, the journies of both Voyager 1 and Voyager 2 will continue.

“The two Voyagers will outlast Earth,” Kurth says. “They’re in their own orbits around the galaxy for five billion years or longer. And the probability of them running into anything is almost zero.”

“They might look a little worn by then,” Gurnett adds with a smile.

With both Voyager 1 and Voyager 2 leaving that solar system, albeit seven years apart, it is stunning to think that our influence has outreached that of our Sun’s and out into the galaxy.