Dec. 10 (UPI) -- Following in the footsteps of its older sibling, Voyager 2 has left the heliosphere and entered interstellar space. It's now 11 billion miles from Earth.
The probe actually left the solar system over a month ago, but it takes a long time for data to travel from the edge of solar system to Earth. The newest data retrieved and analyzed by scientists working on the Voyager mission showed the probe had crossed into interstellar space.
Readings by the probe's PLS instrument offered the most conclusive proof of Voyager 2's feat.
As the sun moves through the Milky Way galaxy, its solar winds carve out a bubble-like space known as the heliosphere. Plasma pulses through this bubble, and PLS can measure the plasma's electric current, revealing the speed, density, temperature, pressure and flux of the solar wind.
On Nov. 5, PLS registered a precipitous decline in the speed of solar wind particles.
The probe's cosmic ray subsystem, which measures charged particles, as well as its magnetometer, measured drop-offs in activity.
Voyager 2's predecessor, Voyager 1, crossed the edge of the solar system in 2012.
"I think we're all happy and relieved that the Voyager probes have both operated long enough to make it past this milestone," Suzanne Dodd, Voyager project manager at NASA's Jet Propulsion Laboratory said in a news release. "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."
Both Voyager probes were launched in 1977. During their epic journeys through the solar system, the two spacecraft studied a variety of planetary bodies. Voyager 1 conducted flybys of Jupiter and Saturn, while Voyager 2 executed close encounters with Jupiter, Saturn, Uranus and Neptune.
Earlier this year, the New Horizons probe spotted the wall of hydrogen that separates the heliosphere from interstellar space. Eventually, New Horizons will join the two Voyager probes in interstellar space.