Humanity has gone interstellar again. For the second time this decade, NASA has successfully sent a probe past the threshold of the heliopause, establishing humanity as an interstellar presence. The Voyager 2 probe now joins its sibling, Voyager 1, in having crossed the barrier.
Launched in 1977, Voyager 2 has covered over 11 billion miles (18 billion kilometers) on its journey into the void. To leave, Voyager 2 would have to leave what’s known as the heliopause— “where the tenuous, hot solar wind meets the cold, dense interstellar medium,” NASA says in a press release. Solar wind is in actuality plasma flowing from the sun, and the heliopause is the last segment of a bubble encompassing the entire solar system known as the heliosphere.
The sun’s plasma envelops all eight planets as well as smaller bodies like Pluto. As scientific experience with Voyager 1 in 2012 showed, leaving the heliopause would make for a drastic reduction in solar wind detected by the probe. Unlike its sibling, Voyager 2 still has a functioning Plasma Science Experiment (PLS)— an instrument that has been able to detect the drop-off with accuracy.
Voyager 2 has been traveling through the heliosphere for the last 11 years. Starting in October, scientists believed that it would be entering interstellar space somewhat soon.
There are now 2 human-made objects in interstellar space! @NASAVoyager 2 has joined Voyager 1 in the area between the stars. This is the 1st time we’ve crossed into this area with a working direct plasma sensor, which is no longer detecting the solar wind! https://t.co/UdqupR3Gj5 pic.twitter.com/TJ5MHlRSqQ
— Thomas Zurbuchen (@Dr_ThomasZ) December 10, 2018
Documents from NASA describing the PLS date back to the 1980s and note that it has “provided a wealth of data on the plasma ions and electrons in the interplanetary medium and the magnetospheres of the giant planets Jupiter and Saturn.” The breakthrough in the heliopause allows the PLS to get back to what it was doing decades ago—provide groundbreaking scientific research on the unknown.
“There is still a lot to learn about the region of interstellar space immediately beyond the heliopause,” says Ed Stone, Voyager project scientist based at Caltech in Pasadena, California, in the press statement. Stone has been involved in Voyager since its origins in 1972, its first project manager.
“Voyager has a very special place for us in our heliophysics fleet,” says Nicola Fox, director of the Heliophysics Division at NASA Headquarters. “Our studies start at the Sun and extend out to everything the solar wind touches. To have the Voyagers sending back information about the edge of the Sun’s influence gives us an unprecedented glimpse of truly uncharted territory.”
On a technical level, neither Voyagers have left the solar system. Passing through the heliopause still means that the Oort Cloud lies beyond. Beyond Pluto and the Kuiper Belt, the little-known Oort Cloud is a spherical shell around the solar system that still feels influence from the sun’s gravity, though it is technically still considered interstellar space. Possibly containing over a trillion icy bodies, no spacecraft have ever been sent to investigate.
Adding the Oort Cloud to Voyager 2’s range of study would hardly be out of character for the spacecraft, which grabbed the world’s attention in the late ’70s and early ’80s with its stunning encounters with Jupiter, Saturn, Uranus, Neptune, and moons including Io, Europa, and Titan. Launched 16 days before Voyager 1, the secondary spacecraft saw its historic mission expand from two planets to four.
Now, 41 years later, Voyager 2 stands as NASA’s single longest-running mission.
“I think we’re all happy and relieved that the Voyager probes have both operated long enough to make it past this milestone,” says Suzanne Dodd, Voyager‘s current project manager at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “This is what we’ve all been waiting for. Now we’re looking forward to what we’ll be able to learn from having both probes outside the heliopause.”
Originally posted on Popular Mehanics