Voyager 1 becomes the first human-made object to reach interstellar space

Story: 2013 C.E.  |  Last updated: September 12, 2013

On August 25, 2012 C.E., a small spacecraft launched during the Carter administration quietly crossed one of the most profound boundaries in human history — the edge of the sun’s influence — and drifted into the space between stars. It took scientists nearly a year to confirm it. When they did, the announcement reverberated around the world.

Key findings

• Voyager 1 interstellar space: NASA confirmed in September 2013 C.E. that Voyager 1 had crossed the heliopause — the boundary where the sun’s solar wind gives way to interstellar plasma — making it the first human-made object to enter interstellar space.
• Solar wind density: The critical clue came from electrical activity triggered by solar storms in late 2012 C.E. and early 2013 C.E. The density of charged particles around the spacecraft was roughly 50 times higher than in the solar wind zone — a signature of interstellar space.
• Plutonium-powered mission: Launched on September 5, 1977 C.E., Voyager 1 flew past Jupiter and Saturn before heading outward. Its nuclear battery was expected to power transmissions until approximately 2025 C.E., giving scientists more than four decades of data from humanity’s most distant outpost.

How scientists knew

The moment of crossing wasn’t visible. No alarm sounded. No instrument felt a jolt.

“The spacecraft doesn’t feel anything traveling into interstellar space,” said Ed Stone, Voyager’s longtime project scientist at the California Institute of Technology. “We can only detect the transition because of its instruments.”

The instrument that could have directly detected the transition — designed to measure the solar wind itself — had failed back in 1980 C.E. So scientists pieced together the answer indirectly. When solar storms swept past the spacecraft in October 2012 C.E. and April 2013 C.E., they triggered spikes in electrical and radio wave frequency. Those spikes, analyzed by University of Iowa physicist Donald Gurnett and his team, matched the signature of a much denser plasma environment — one consistent only with interstellar space.

The entry date was extrapolated as August 25, 2012 C.E.

“Nature has finally given us a nice set of solar storms which show us that Voyager is now out in interstellar space,” Stone said at the NASA briefing. The findings were published in the journal Science.

What lies beyond the heliopause

For four decades before the confirmation, scientists had debated where the solar system truly ends. The heliopause — the outer boundary of the heliosphere, where the sun’s solar wind stalls against the interstellar medium — had long been the theoretical answer. Voyager 1 gave them the first empirical one.

The interstellar medium is not empty. It is threaded with the cooled debris of thousands of exploded stars — the raw material of galaxies, the diffuse inheritance of supernovae that predate our sun. Voyager 1 was now swimming in it.

One surprise emerged from the crossing: the Milky Way’s magnetic field appeared to be aligned in nearly the same direction as the sun’s, forming what scientists called a “magnetic highway.” This had not been predicted. It also complicated earlier attempts to use magnetic measurements to locate the boundary, because the alignment blurred what researchers had expected to be a detectable shift.

“We have a lot to learn still,” said Stamatios Krimigis of the Johns Hopkins University Applied Physics Laboratory, who had reported that finding the previous year. He described himself as “absolutely convinced” by the new results.

A spacecraft built in a different era

Voyager 1 was designed and built in the early 1970s C.E., when personal computers did not yet exist and the Apollo program had only recently ended. Its onboard computer has roughly 240,000 times less memory than a modern smartphone. It communicates with Earth using a 23-watt radio transmitter — about the power of a refrigerator light bulb — across more than 11.66 billion miles.

The signals travel at the speed of light and still take more than 17 hours to arrive.

Its twin, Voyager 2, had explored Jupiter, Saturn, Uranus, and Neptune before heading in a different direction. By 2013 C.E., it was some 9.55 billion miles from the sun and still transmitting. Voyager 2 crossed the heliopause in November 2018 C.E., becoming the second human-made object to reach interstellar space — and, unlike its sibling, its plasma instrument was still functioning, delivering the most direct measurements yet.

The comparison between the two crossings gave scientists data no single spacecraft could have provided alone.

Lasting impact

Voyager 1’s crossing settled a question humanity had been asking since the Space Age began: where does our sun’s influence end? The answer has reshaped models of the heliosphere and given plasma physicists their first direct measurements of the local interstellar medium.

Practically, it proved that spacecraft could survive and transmit across interstellar distances — an engineering foundation for thinking about deep-space probes in the distant future. The Golden Record aboard both Voyagers — carrying greetings in 55 languages, music from across human cultures, and images of life on Earth — means humanity’s first interstellar emissaries are also its most deliberate act of self-introduction to the cosmos.

The mission was built by thousands of engineers, scientists, and technicians across NASA’s Jet Propulsion Laboratory and partner institutions. Stone himself led the science team for 50 years. The continuity of that human effort — maintained across generations and political changes — is as remarkable as the hardware.

In a subtler sense, the moment rewired something in how humans understand their place in the universe. The solar system is no longer an abstraction. It has a border. And something we built crossed it.

Blindspots and limits

The phrase “leaving the solar system” requires a footnote. The Oort Cloud — the vast, thinly populated shell of cometary objects thought to surround the sun — extends perhaps a quarter of the way to the nearest star, well beyond the heliopause. By that definition, Voyager 1 won’t leave the solar system for another 30,000 years. What it crossed in 2012 C.E. was the heliosphere’s boundary, not the gravitational reach of the sun itself.

The confirmation also came with acknowledged gaps. The instrument designed to directly detect the crossing had been dead for 32 years. Some scientists initially disputed the 2012 C.E. date, and the 2013 C.E. paper was one of several competing analyses. The magnetic field alignment puzzle — the sun’s and galaxy’s fields running parallel rather than at an angle — remains only partially explained and complicates models of the broader heliospheric structure.

Read more

For more on this story, see: National Geographic — Voyager 1 exits the solar system

For more from Good News for Humankind, see:

• Renewables now make up at least 49% of global power capacity
• Global suicide rate has fallen by 40% since 1995
• The Good News for Humankind archive on space exploration

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