Mankind's most distant probe prepares to leave the Solar System

After more than 30 years spent careening away from Earth, Voyager 1 is on the cusp of entering interstellar space.

"2nd Voyager Spacecraft Lifts Off Smoothly, Speeds Toward Jupiter" was the headline chosen by the New York Times to document the 1977 launch of the Voyager 1 spacecraft, which, despite its name, launched soon after its counterpart, Voyager 2. The craft weighed just 1,592 lbs on Earth--less than a small car--and launched without incident. It's mission, according to an article in the same paper, was as follows: "To fly to Jupiter, Saturn, Uranus and possibly Neptune."

It took nearly two years for the Voyager 1 to reach its first gas giant, and the images it returned from Jupiter were among the most iconic in NASA's history. The probe's later work--a swing by Saturn, which helped accelerate the Voyager 1 past its sister craft, and the first "family portrait" of the entire Solar System. But that Saturn fly-by took place took place in 1980, and those early assessments of our solar system from its outer reaches took place in 1990. At that point, Voyager's planned lifespan had already been exceeded. A full 20 years later, the craft is far and away the furthest human creation from Earth--and it's still going.

As of publication, Voyager 1 is 10,818,595,504 miles from its home planet. Radio commands to the probe take 16 hours to reach it, and just as long to be returned. The craft, which has been consistently returning data throughout its life, is nearing its first major milestone in years. Soon, NASA claims, Voyager 1 will leave the Solar System:

Now hurtling toward interstellar space some 17.4 billion kilometers (10.8 billion miles) from the sun, Voyager 1 has crossed into an area where the velocity of the hot ionized gas, or plasma, emanating directly outward from the sun has slowed to zero. Scientists suspect the solar wind has been turned sideways by the pressure from the interstellar wind in the region between stars.

NASA had suspected that Voyager 1 had reached this stage in June, but took a few more months' worth of readings to be sure. The agency has now confirmed that the craft has entered the outer reaches of the bubble in space created and affected by the Sun, called the heliosheath. When it crosses through the heliosheath, which NASA currently estimates will happen in about four years, it will be the first man-made object to leave the solar system, crossing into interstellar space.

Voyager 1 still has quite a long useful life ahead of it, at least in theory. Though some of its instruments have already been shut down to conserve power, it is expected to remain at least partially operational for at least another ten years, meaning that the probe will likely be able to transmit the first directly collected data from outside of the Solar System, albeit with instruments that haven't been considered state-of-the-art since Carter was President.

Even after its plutonium power source blinks out for good, the Voyager 1 will continue its tertiary mission: to extend a hand from Earth to the rest of the galaxy. The probe is carrying one of two Voyager Golden Disks, 12-inch gold-plated copper records containing sounds and images selected to represent mankind to, well, anyone who might find them. (For a fascinating account of the creation of the Golden Disks, check out this Radiolab episode.)

Image courtesy of NASA

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