Voyager 2 Has Left the Bubble
Here's one of those "Who's-buried-in-Grant's-Tomb" type questions for your next trivia challenge: Which space probe was launched first — Voyager 1 or Voyager 2?
The answer, of course, is Voyager 2, which NASA launched on 20 August, 1977. The probe's twin, Voyager 1, was launched 16 days later on 5 September. The probes were named for the order in which they were expected to arrive at Jupiter, not the order in which they were launched.
"We launched two space craft," Voyager project scientist Ed Stone explained in a 2018 NASA video. "They're basically the same, but they were on different paths. Voyager 2 was the one that was chosen to do the Grand Tour, that is to fly by Jupiter, and then Saturn, then Uranus, and then Neptune. And then, after 1989, we began what is now called the Voyager Interstellar Mission. We were on a path, we hoped to get to reach interstellar space while we still had power on the spacecraft to transmit the data back."
A year ago this month, Voyager 2 became the second spacecraft to leave the heliosphere — a vast bubble of plasma and particles generated by the Sun and stirred by solar winds. Scientists are just now receiving that related data. Voyager 1 crossed this point in 2012, but Voyager 2 is the first spacecraft to sample the electrically charged plasmas that fill both interstellar space and the solar system's farthest outskirts.
"It's just really exciting that humankind is interstellar," said physicist Jamie Rankin in an interview with National Geographic. "We have been interstellar travelers since Voyager 1 crossed, but now, Voyager 2's cross is even more exciting, because we can now compare two very different locations ... in the interstellar medium."
In a NASA press release, Ed Stone notes that the Voyager probes are revealing how the Sun interacts with the matter that fills most of the space between stars in the Milky Way galaxy. "Without this new data from Voyager 2, we wouldn't know if what we were seeing with Voyager 1 was characteristic of the entire heliosphere or specific just to the location and time when it crossed," says Stone.
Suzanne Dodd, Voyager project manager at NASA's Jet Propulsion Laboratory, points out that the Voyager probes were launched almost two human generations ago. "You think about what the technology was back then: your smartphone has 200,000 times more memory than what the Voyager space craft have. So, it's just exciting that we've been able to get [them] into interstellar space. 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 [the edge of the heliosphere]."
That both probes are still sharing science from billions of miles away is a testament to the space technology of the late 1970s. However, some scientists estimate that within five years or so, both Voyagers will run out of the decaying plutonium that fuels their RTG power generators. At that point, the two will continue to fly outward, still carrying a gold audio-visual disk containing greetings from the people of Earth. This "Golden Record" includes a collection of 115 images and a variety of natural Earth sounds such as ocean surf, wind, thunder, birds, whales, and other animals. Musical selections from different cultures, eras, and artists — including Louis Armstrong, Beethoven, Stravinsky, and Blind Willie Johnson — are also included, along with spoken greetings in 55 languages. Hand-etched on the surface of each is the inscription: "To the makers of music — all worlds, all times."
Unless the Voyager probes are destroyed in a collision with another object or are picked up by space explorers from another world, they will, in theory, keep flying until they reach the end of the universe.
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