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NASA’s Voyager 2 Sends First Data From Interstellar Space After 42-Year Trip

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NASA’s Voyager 2 Sends First Data From Interstellar Space After 42-Year Trip

The Voyager 2 probe signaled its passage into interstellar space with a cascade of data from beyond the planets, where the cold breath of stars envelops the solar system, NASA scientists reported Monday.

It was a moment 42 years in the making.

When the National Aeronautics and Space Administration launched the spindly spacecraft in 1977—one in a pair of star-bound Voyager probes—Jimmy Carter was president, Apple Computer had just been incorporated, and snow fell in Miami for the first time in memory.

The Titan Centaur rocket rises in the sky Aug. 20, 1977, at Cape Canaveral, Fla., carrying the Voyager 2.


Photo:

Jim Bourdier/Associated Press

Originally designed to visit Jupiter and Saturn, the probe was never meant to go so far, the scientists said. By doing so, researchers were able to get rare firsthand reports about the limits of the sun’s protective shield, the heliosphere, which blocks most damaging cosmic rays from interstellar space, gaining knowledge that overturns some long-held assumptions.

In five technical papers about the milestone published in the journal Nature Astronomy, mission scientists and engineers detailed the exotic collision of superheated solar winds and frigid currents of interstellar space in a zone where the sun’s protective bubble of influence fades away.

That solar boundary, called the heliopause, is created by intersecting magnetic fields, streams of cosmic rays from deep space and bursts of charged atomic particles from the sun.

When the hotter but more tenuous material of solar particles plows into the cooler, denser substance of the space between the stars, it creates a bow wave like the prow of a speeding sailboat approximately 11 billion miles from the sun, the scientists said.

“There was a time 50 years or so ago when people thought that the solar wind would get gradually whittled away or dissipated as it propagated into interstellar space,” said physicist Edward Stone, Voyager’s project scientist at the California Institute of Technology. “In fact, there is a very, very sharp boundary there.”


‘There was a time 50 years or so ago when people thought that the solar wind would get gradually whittled away or dissipated as it propagated into interstellar space. In fact, there is a very, very sharp boundary there.’


—Edward Stone, Voyager project scientist

Voyager 2 officially crossed the boundary of the solar bubble on Nov. 5, 2018, recording its passage with all five of its sensors in working order, the scientists said. NASA is confirming the border crossing only now because it took almost a year to receive all the probe’s data. The information was coming from a distance where signals traveling at the speed of light take 16.5 hours to reach researchers on Earth, who then processed it, analyzed it and double-checked their conclusions.

No obvious visual indicators, such as an orbiting planet or an asteroid belt, mark the border. So the scientists decided the probe had broken through into interstellar space because data from the craft’s sensors showed a sharp decrease in the intensity of low-energy solar ions and a simultaneous increase in the intensity of cosmic rays.

“We saw the plasma density jump by a very large amount, by a factor of 20, in this very short boundary out there,” said Voyager plasma wave physicist Donald Gurnett at the University of Iowa.

Voyager 2 was the second spacecraft to go the distance. After several premature reports, NASA scientists in 2013 announced that the Voyager 1 probe had officially crossed into interstellar space on Aug. 25, 2012, becoming the first human artifact to leave the sphere of solar influence. It is the most distant object made by human hands.

Technically, neither craft has left the solar system yet, just the neighborhood encompassed by the sun’s influence.

The farthest known region of the solar system is vast collection of comets and other space debris called the Oort cloud. At its current speed of about a million miles a day, NASA’s Voyager 1 spacecraft won’t enter the Oort cloud for about 300 years and won’t exit the outer edge for 30,000 years or so, space agency scientists said.

Both Voyager probes are powered by plutonium-fueled nuclear generators and are expected to keep their sensors operating for another five years or so, the scientists said.

Even after they lose power, they will continue outward as ambassadors from the life forms of Earth. Each carries a gold-plated disc containing images of humankind and multicultural greetings in 55 languages. Sounds include laughter and a human heartbeat.

Barring any mishap, the Voyager 1 probe is expected to pass within 1.6 light years of a star called Gilese 445 in about 40,000 years, the scientists calculated. In about 296,000 years, Voyager 2, should its journey continue to be uneventful, will pass within 4.3 light years of Sirius—the brightest star in the night sky.

In this Aug. 4, 1977, photo provided by NASA, the ‘Sounds of Earth’ record is mounted on the Voyager 2.


Photo:

NASA/Associated Press

Write to Robert Lee Hotz at sciencejournal@wsj.com

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