BEYOND THE ORBIT OF PLUTO (WHTM) — On this day the deep space probe Voyager 2 entered the area of deep space called the “solar wind termination shock.” It’s an area where the solar wind, (the enormous bubble of charged particles ejected into space by the sun) abruptly slows when it hits gases and magnetic fields from interstellar space.

NASA launched Voyager 1 and Voyager 2 In 1997. The launches were designed to take advantage of a rare lineup of Jupiter, Saturn, Uranus, and Neptune which only happens about every 175 years. This arrangement, combined with a carefully chosen flight path, would allow the Voyagers to use the gravity of each planet to “slingshot” them to the next, allowing them to make the journey without a huge propulsion system.

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The only problem, nobody was sure they could build a spacecraft that could last long enough to complete the mission. So Voyager 1’s mission called for it to explore Jupiter and Saturn, and then go…out there, thataway.

Voyager 2’s flight path was designed to pass Jupiter and Saturn, with trips to Neptune and Uranus as an option.

NASA exercised the option. Voyager 2 passed Uranus on January 24, 1986, and Neptune on August 25, 1989. Then, like Voyager 1, it was on its way to interstellar space. Both spacecraft continued to send back data to Earth.

The two spacecraft were traveling in different directions. Both were still in the area where the solar wind held sway, a region scientists call the heliosphere. Voyager 1 began its departure from the Heliosphere when it hit the termination shock on December 15, 2004 (This date is a bit “soft” because the craft’s solar wind detector had failed, and the time had to be inferred from readings by other instruments.) After passing through the termination shock, and through the boundary layer called the heliosheath, the craft was now out of the heliosphere, and in a region called the heliopause, where the effects of interstellar particles overpower those of the solar wind.

Then it was Voyager 2’s turn. It entered the termination shock on August 30, 2007. Its Plasma Science instrument was working, and it registered at least five shock crossings in a few days. (the termination shock boundary moves back and forth depending on the energies hitting it.) It also entered the termination shock almost 1 billion miles closer to the sun than Voyager 1, which indicated that part of the heliosphere was being pushed inward by the interstellar magnetic field. This was one of the first confirmations the heliosphere is not a simple, symmetrical bubble.

Voyager 1 left the heliopause on August 25, 2012, and Voyager 2 left the heliopause on November 5, 2018. They are now considered to be in interstellar space, but a part of the Solar System is still ahead of them. This is the Oort Cloud, a spherical shell of objects (small planets, potential comets, and the like) far beyond the outermost planets and, in fact, the boundaries of the heliosphere. How far away is it? Well, it’s estimated it will take about 300 years for the Voyager craft to reach the Oort cloud and about 30,000 years to go all the way through it.

But long before that, the Voyager spacecraft will have ceased to function. It’s estimated that somewhere between 2025 and 2036, they will use up the last of their power, and no more data will be coming from them.

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But for now, they’re still in touch with the home sod, still sending us data. And who knows? Maybe they’ll make it to 2027. That would truly be a 50th anniversary to celebrate.