what has voyager 2 discovered in interstellar space

First to visit all four giant planets

Voyager 2 is the only spacecraft to visit Uranus and Neptune. The probe is now in interstellar space, the region outside the heliopause, or the bubble of energetic particles and magnetic fields from the Sun.

Mission Type

What is Voyager 2?

NASA's Voyager 2 is the second spacecraft to enter interstellar space. On Dec. 10, 2018, the spacecraft joined its twin – Voyager 1 – as the only human-made objects to enter the space between the stars.

• Voyager 2 is the only spacecraft to study all four of the solar system's giant planets at close range.
• Voyager 2 discovered a 14th moon at Jupiter.
• Voyager 2 was the first human-made object to fly past Uranus.
• At Uranus, Voyager 2 discovered 10 new moons and two new rings.
• Voyager 2 was the first human-made object to fly by Neptune.
• At Neptune, Voyager 2 discovered five moons, four rings, and a "Great Dark Spot."

In Depth: Voyager 2

The two-spacecraft Voyager missions were designed to replace original plans for a “Grand Tour” of the planets that would have used four highly complex spacecraft to explore the five outer planets during the late 1970s.

NASA canceled the plan in January 1972 largely due to anticipated costs (projected at $1 billion) and instead proposed to launch only two spacecraft in 1977 to Jupiter and Saturn. The two spacecraft were designed to explore the two gas giants in more detail than the two Pioneers (Pioneers 10 and 11) that preceded them.

In 1974, mission planners proposed a mission in which, if the first Voyager was successful, the second one could be redirected to Uranus and then Neptune using gravity assist maneuvers.

Each of the two spacecraft was equipped with a slow-scan color TV camera to take images of the planets and their moons and each also carried an extensive suite of instruments to record magnetic, atmospheric, lunar, and other data about the planetary systems.

The design of the two spacecraft was based on the older Mariners, and they were known as Mariner 11 and Mariner 12 until March 7, 1977, when NASA Administrator James C. Fletcher (1919-1991) announced that they would be renamed Voyager.

Power was provided by three plutonium oxide radioisotope thermoelectric generators (RTGs) mounted at the end of a boom.

Voyager 2 at Jupiter

Voyager 2 began transmitting images of Jupiter April 24, 1979, for time-lapse movies of atmospheric circulation. Unlike Voyager 1, Voyager 2 made close passes to the Jovian moons on its way into the system, with scientists especially interested in more information from Europa and Io (which necessitated a 10 hour-long “volcano watch”).

During its encounter, it relayed back spectacular photos of the entire Jovian system, including its moons Callisto, Ganymede, Europa (at a range of about 127,830 miles or 205,720 kilometers, much closer than Voyager 1), Io, and Amalthea, all of which had already been surveyed by Voyager 1.

Voyager 2’s closest encounter to Jupiter was at 22:29 UT July 9, 1979, at a range of about 400,785 miles (645,000 kilometers). It transmitted new data on the planet’s clouds, its newly discovered four moons, and ring system as well as 17,000 new pictures.

When the earlier Pioneers flew by Jupiter, they detected few atmospheric changes from one encounter to the second, but Voyager 2 detected many significant changes, including a drift in the Great Red Spot as well as changes in its shape and color.

With the combined cameras of the two Voyagers, at least 80% of the surfaces of Ganymede and Callisto were mapped out to a resolution of about 3 miles (5 kilometers).

Voyager 2 at Saturn

Following a course correction two hours after its closest approach to Jupiter, Voyager 2 sped to Saturn, its trajectory determined to a large degree by a decision made in January 1981, to try to send the spacecraft to Uranus and Neptune later in the decade.

Its encounter with the sixth planet began Aug. 22, 1981, two years after leaving the Jovian system, with imaging of the moon Iapetus. Once again, Voyager 2 repeated the photographic mission of its predecessor, although it actually flew about 14,290 miles (23,000 kilometers) closer to Saturn. The closest encounter to Saturn was at 01:21 UT Aug. 26, 1981, at a range of about 63,000 miles (101,000 kilometers).

The spacecraft provided more detailed images of the ring “spokes” and kinks, and also the F-ring and its shepherding moons, all found by Voyager 1. Voyager 2’s data suggested that Saturn’s A-ring was perhaps only about 980 feet (300 meters) thick.

As it flew behind and up past Saturn, the probe passed through the plane of Saturn’s rings at a speed of 8 miles per second (13 kilometers per second). For several minutes during this phase, the spacecraft was hit by thousands of micron-sized dust grains that created “puff” plasma as they were vaporized. Because the vehicle’s attitude was repeatedly shifted by the particles, attitude control jets automatically fired many times to stabilize the vehicle.

During the encounter, Voyager 2 also photographed the Saturn moons Hyperion (the “hamburger moon”), Enceladus, Tethys, and Phoebe as well as the more recently discovered Helene, Telesto and Calypso.

Voyager 2 at Uranus

Although Voyager 2 had fulfilled its primary mission goals with the two planetary encounters, mission planners directed the veteran spacecraft to Uranus—a journey that would take about 4.5 years.

In fact, its encounter with Jupiter was optimized in part to ensure that future planetary flybys would be possible.

The Uranus encounter’s geometry was also defined by the possibility of a future encounter with Neptune: Voyager 2 had only 5.5 hours of close study during its flyby.

Voyager 2 was the first human-made object to fly past the planet Uranus.

Long-range observations of the planet began Nov. 4, 1985, when signals took approximately 2.5 hours to reach Earth. Light conditions were 400 times less than terrestrial conditions. Closest approach to Uranus took place at 17:59 UT Jan. 24, 1986, at a range of about 50,640 miles (81,500 kilometers).

During its flyby, Voyager 2 discovered 10 new moons (given such names as Puck, Portia, Juliet, Cressida, Rosalind, Belinda, Desdemona, Cordelia, Ophelia, and Bianca -- obvious allusions to Shakespeare), two new rings in addition to the “older” nine rings, and a magnetic field tilted at 55 degrees off-axis and off-center.

The spacecraft found wind speeds in Uranus’ atmosphere as high as 450 miles per hour (724 kilometers per hour) and found evidence of a boiling ocean of water some 497 miles (800 kilometers) below the top cloud surface. Its rings were found to be extremely variable in thickness and opacity.

Voyager 2 also returned spectacular photos of Miranda, Oberon, Ariel, Umbriel, and Titania, five of Uranus’ larger moons. In flying by Miranda at a range of only 17,560 miles (28,260 kilometers), the spacecraft came closest to any object so far in its nearly decade-long travels. Images of the moon showed a strange object whose surface was a mishmash of peculiar features that seemed to have no rhyme or reason. Uranus itself appeared generally featureless.

The spectacular news of the Uranus encounter was interrupted the same week by the tragic Challenger accident that killed seven astronauts during their space shuttle launch Jan. 28, 1986.

Voyager 2 at Neptune

Following the Uranus encounter, the spacecraft performed a single midcourse correction Feb. 14, 1986—the largest ever made by Voyager 2—to set it on a precise course to Neptune.

Voyager 2’s encounter with Neptune capped a 4.3 billion-mile (7 billion-kilometer) journey when, on Aug. 25, 1989, at 03:56 UT, it flew about 2,980 miles (4,800 kilometers) over the cloud tops of the giant planet, the closest of its four flybys. It was the first human-made object to fly by the planet. Its 10 instruments were still in working order at the time.

During the encounter, the spacecraft discovered six new moons (Proteus, Larissa, Despina, Galatea, Thalassa, and Naiad) and four new rings.

The planet itself was found to be more active than previously believed, with 680-mile (1,100-kilometer) per hour winds. Hydrogen was found to be the most common atmospheric element, although the abundant methane gave the planet its blue appearance.

Images revealed details of the three major features in the planetary clouds—the Lesser Dark Spot, the Great Dark Spot, and Scooter.

Voyager photographed two-thirds of Neptune’s largest moon Triton, revealing the coldest known planetary body in the solar system and a nitrogen ice “volcano” on its surface. Spectacular images of its southern hemisphere showed a strange, pitted cantaloupe-type terrain.

The flyby of Neptune concluded Voyager 2’s planetary encounters, which spanned an amazing 12 years in deep space, virtually accomplishing the originally planned “Grand Tour” of the solar system, at least in terms of targets reached if not in science accomplished.

Voyager 2's Interstellar Mission

Once past the Neptune system, Voyager 2 followed a course below the ecliptic plane and out of the solar system. Approximately 35 million miles (56 million kilometers) past the encounter, Voyager 2’s instruments were put in low power mode to conserve energy.

After the Neptune encounter, NASA formally renamed the entire project the Voyager Interstellar Mission (VIM).

Of the four spacecraft sent out to beyond the environs of the solar system in the 1970s, three of them -- Voyagers 1 and 2 and Pioneer 11 -- were all heading in the direction of the solar apex, i.e., the apparent direction of the Sun’s travel in the Milky Way galaxy, and thus would be expected to reach the heliopause earlier than Pioneer 10 which was headed in the direction of the heliospheric tail.

In November 1998, 21 years after launch, nonessential instruments were permanently turned off, leaving seven instruments still operating.

At 9.6 miles per second (15.4 kilometers per second) relative to the Sun, it will take about 19,390 years for Voyager 2 to traverse a single light year.

Asif Siddiqi

Beyond Earth: A Chronicle of Deep Space Exploration

Through the turn of the century, NASA's Jet Propulsion Laboratory (JPL) continued to receive ultraviolet and particle fields data. For example, on Jan. 12, 2001, an immense shock wave that had blasted out of the outer heliosphere on July 14, 2000, finally reached Voyager 2. During its six-month journey, the shock wave had plowed through the solar wind, sweeping up and accelerating charged particles. The spacecraft provided important information on high-energy shock-energized ions.

On Aug. 30, 2007, Voyager 2 passed the termination shock and then entered the heliosheath. By Nov. 5, 2017, the spacecraft was 116.167 AU (about 10.8 billion miles or about 17.378 billion kilometers) from Earth, moving at a velocity of 9.6 miles per second (15.4 kilometers per second) relative to the Sun, heading in the direction of the constellation Telescopium. At this velocity, it would take about 19,390 years to traverse a single light-year.

On July 8, 2019, Voyager 2 successfully fired up its trajectory correction maneuver thrusters and will be using them to control the pointing of the spacecraft for the foreseeable future. Voyager 2 last used those thrusters during its encounter with Neptune in 1989.

The spacecraft's aging attitude control thrusters have been experiencing degradation that required them to fire an increasing and untenable number of pulses to keep the spacecraft's antenna pointed at Earth. Voyager 1 had switched to its trajectory correction maneuver thrusters for the same reason in January 2018.

To ensure that both vintage robots continue to return the best scientific data possible from the frontiers of space, mission engineers are implementing a new plan to manage them. The plan involves making difficult choices, particularly about instruments and thrusters.

National Space Science Data Center: Voyager 2

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An illustration shows the position of NASA's Voyager 1 and Voyager 2 probes outside of the heliosphere, a protective bubble created by the sun that extends well past the orbit of Pluto.

Interstellar space even weirder than expected, NASA probe reveals

The spacecraft is just the second ever to venture beyond the boundary that separates us from the rest of the galaxy.

In the blackness of space billions of miles from home, NASA’s Voyager 2 marked a milestone of exploration, becoming just the second spacecraft ever to enter interstellar space in November 2018. Now, a day before the anniversary of that celestial exit, scientists have revealed what Voyager 2 saw as it crossed the threshold—and it’s giving humans new insight into some of the big mysteries of our solar system.

The findings, spread across five studies published today in Nature Astronomy , mark the first time that a spacecraft has directly sampled the electrically charged hazes, or plasmas, that fill both interstellar space and the solar system’s farthest outskirts. It’s another first for the spacecraft, which was launched in 1977 and performed the first—and only—flybys of the ice giant planets Uranus and Neptune. ( Find out more about the Voyager probes’ “grand tour”—and why it almost didn’t happen .)

See pictures from Voyager 2's solar system tour

Voyager 2’s charge into interstellar space follows that of sibling Voyager 1, which accomplished the same feat in 2012. The two spacecrafts’ data have many features in common, such as the overall density of the particles they’ve encountered in interstellar space. But intriguingly, the twin craft also saw some key differences on their way out—raising new questions about our sun’s movement through the galaxy.

“This has really been a wonderful journey,” Voyager project scientist Ed Stone , a physicist at Caltech, said in a press briefing last week.

“It’s just really exciting that humankind is interstellar,” adds physicist Jamie Rankin , a postdoctoral researcher at Princeton University who wasn’t involved with the studies. “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.”

Inside the bubble

To make sense of Voyager 2’s latest findings, it helps to know that the sun isn’t a quietly burning ball of light. Our star is a raging nuclear furnace hurtling through the galaxy at about 450,000 miles an hour as it orbits the galactic center.

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The sun is also rent through with twisted, braided magnetic fields and, as a result, its surface constantly throws off a breeze of electrically charged particles called the solar wind. This gust rushes out in all directions, carrying the sun’s magnetic field with it. Eventually, the solar wind smashes into the interstellar medium, the debris from ancient stellar explosions that lurks in the spaces between stars.

Like oil and water, the solar wind and the interstellar medium don’t perfectly mix, so the solar wind forms a bubble within the interstellar medium called the heliosphere. Based on Voyager data, this bubble extends about 11 billion miles from the sun at its leading edge, surrounding the sun, all eight planets, and much of the outer objects orbiting our star. Good thing, too: The protective heliosphere shields everything inside it, including our fragile DNA, from most of the galaxy’s highest-energy radiation.

The heliosphere’s outermost edge, called the heliopause, marks the start of interstellar space. Understanding this threshold has implications for our picture of the sun’s journey through the galaxy, which in turn can tell us more about the situations of other stars scattered across the cosmos.

“We are trying to understand the nature of that boundary, where these two winds collide and mix,” Stone said during the briefing. “How do they mix, and how much spillage is there from inside to outside the bubble, and from outside the bubble to inside?”

Scientists got their first good look at the heliopause on August 25, 2012, when Voyager 1 first entered interstellar space. What they began to see left them scratching their heads. For instance, researchers now know that the interstellar magnetic field is about two to three times stronger than expected, which means, in turn, that interstellar particles exert up to ten times as much pressure on our heliosphere than previously thought.

“It is our first platform to actually experience the interstellar medium, so it is quite literally a pathfinder for us,” says heliophysicist Patrick Koehn , a program scientist at NASA headquarters.

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Leaky boundary.

But for all that Voyager 1 upended expectations, its revelations were incomplete. Back in 1980, its instrument that measured the temperature of plasmas stopped working. Voyager 2’s plasma instrument is still working just fine, though, so when it crossed the heliopause on November 5, 2018, scientists could get a much better look at this border.

For the first time, researchers could see that as an object gets within 140 million miles of the heliopause, the plasma surrounding it slows, heats up, and gets more dense. And on the other side of the boundary, the interstellar medium is at least 54,000 degrees Fahrenheit, which is hotter than expected. However, this plasma is so thin and diffuse, the average temperature around the Voyager probes remains extremely cold.

In addition, Voyager 2 confirmed that the heliopause is one leaky border—and the leaks go both ways. Before Voyager 1 passed through the heliopause, it zoomed through tendrils of interstellar particles that had punched into the heliopause like tree roots through rock. Voyager 2, however, saw a trickle of low-energy particles that extended more than a hundred million miles beyond the heliopause.

Another mystery appeared as Voyager 1 came within 800 million miles of the heliopause, where it entered a limbo-like area in which the outbound solar wind slowed to a crawl. Before it crossed the heliopause, Voyager 2 saw the solar wind form an altogether different kind of layer that, oddly, was nearly the same width as the stagnant one seen by Voyager 1.

“That is very, very weird,” Koehn says. “It really shows us that we need more data.”

Interstellar sequel?

Solving these puzzles will require a better view of the heliosphere as a whole. Voyager 1 exited near the heliosphere’s leading edge, where it collides with the interstellar medium, and Voyager 2 exited along its left flank. We have no data on the heliosphere’s wake, so its overall shape remains a mystery. The interstellar medium’s pressure might keep the heliosphere roughly spherical, but it’s also possible that it has a tail like a comet—or that it is shaped like a croissant .

But while other spacecraft are currently outward bound, they won’t be able to return data from the heliopause. NASA’s New Horizons spacecraft is zooming out of the solar system at more than 31,000 miles an hour , and when it runs out of power in the 2030s, it’ll fall silent more than a billion miles short of the heliosphere’s outer edge. That’s why Voyager scientists and others are calling for a follow-up interstellar probe . The goal: a 50-year, multi-generation mission that explores the outer solar system on its way into unexplored regions beyond the solar wind.

“Here's an entire bubble, [and] we only crossed it with two points,” study coauthor Stamatios Krimigis , the emeritus head of the Johns Hopkins University Applied Physics Laboratory's space department, said at the briefing. “Two examples are not enough.”

A new generation of scientists is eager to run with the baton—including Rankin, who did her Ph.D. at Caltech with Voyager 1’s interstellar data with Stone as her adviser.

“It was amazing to work on this cutting-edge data from spacecraft that were launched before I was born and still doing amazing science,” she says. “I’m just really thankful for all the people who have spent so much time on Voyager.”

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We Finally Know What Happened When Voyager 2 Reached Interstellar Space

A few big takeaways from the craft's incredible journey.

• The spacecraft reached the interstellar boundary between our solar system and interstellar space in 2018. Voyager 1 reached the boundary in 2012.
• Both spacecraft were launched in 1977, and have far surpassed scientists' expectations.

Scientists have finally analyzed data from Voyager 2’s journey to interstellar space and discovered a number of surprising differences—plus a few strange similarities.

Voyager 1 and 2 launched in August and October of 1977, respectively, and set out to explore the far reaches of the solar system and beyond. The spacecraft have revealed a vast amount of insight into distant planets and snapped pictures of previously undiscovered moons. Still, more than 40 years after their launch, they continue to provide scientists with an unparalleled look at the universe.

In 2012, Voyager 1 became the first spacecraft to reach interstellar space. Last year, Voyager 2 joined its companion in the interstellar medium, reaching the boundary set 119 times the Earth–sun distance away from Earth. The transition from our solar system to interstellar space, the researchers say, may take less than a day to cross. The data from Voyager 2’s crossing was published November 4 in a series of five papers in Nature Astronomy .

The heliopause is the theoretical boundary at which the sun’s solar wind meets interstellar winds, which are shot out from supernovae that have exploded millions of years ago. Additionally, galactic cosmic rays try to flow into our solar system, but only 30 percent of these rays actually reach Earth. Voyager 1 and 2 were also able to study changes in the magnetic fields within and outside of our solar system.

The two spacecraft reached interstellar space during different periods of solar activity, meaning conditions along the boundary were markedly different. Voyager 1 reached the interstellar boundary during the sun’s solar minimum, whereas Voyager 2 reached the boundary during the solar maximum, a period of heightened activity. Additionally, unlike its quicker counterpart, Voyager 2’s mission has largely taken place in Earth’s southern hemisphere.

The researchers also discovered that solar material was “leaking” out into the interstellar medium. “That was very different than what happened with Voyager 1, where hardly any material was leaking out,” said Tom Krimigis of John’s Hopkins’s Applied Physics Laboratory in an October 31 press conference.

In the case of Voyager 1, the team saw the opposite, where interstellar particles leaked into our solar system. The team hopes to reconvene to take a closer look at their data in the near future to understand how and why these particles slip out of the grasp of our solar system.

Another perplexing discovery? The direction of the magnetic fields both inside and outside of the heliopause is aligned, as was the case with Voyager 1. Leonard Burlaga of NASA Goddard Space Flight Center said scientists can dismiss the alignment of the magnetic fields once, but twice would be a remarkable coincidence. The strength of the magnetic field was stronger in interstellar space, the Voyager 2 found.

The scientists also discovered that the heliopause itself is much thinner and smoother than expected, and that the interstellar medium tucked close to the boundary layer, where solar and interstellar winds meet, is much hotter and unpredictable than expected. This newest research also revealed that the boundary layer itself may be more complex than initially thought, with multiple layers of different temperature, density, and speed.

Voyager 1 and 2 have roughly five years before they'll lose the use of their scientific instruments, said Ed Stone of the California Institute of Technology during the press conference. "When the two voyagers were launched, the space age was only 20 years old, Stone said. "So it was hard to know at that time that anything could last over 40 years."

There's still a lot left to explore, and the data dump has sparked a desire to explore faster, farther, and deeper into interstellar space.

Jennifer Leman is a science journalist and senior features editor at Popular Mechanics, Runner's World, and Bicycling. A graduate of the Science Communication Program at UC Santa Cruz, her work has appeared in The Atlantic, Scientific American, Science News and Nature. Her favorite stories illuminate Earth's many wonders and hazards.

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• Published: 04 November 2019

Cosmic ray measurements from Voyager 2 as it crossed into interstellar space

• Edward C. Stone   ORCID: orcid.org/0000-0002-2010-5462 1 ,
• Alan C. Cummings   ORCID: orcid.org/0000-0002-3840-7696 1 ,
• Bryant C. Heikkila 2 &
• Nand Lal 2  

Nature Astronomy volume  3 ,  pages 1013–1018 ( 2019 ) Cite this article

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The interaction of the interstellar and solar winds is complex, as revealed by differences in intensities and anisotropies of low-energy ions (>0.5 MeV per nucleon) originating inside the heliosphere and those of higher-energy Galactic cosmic rays (>70 MeV per nucleon) originating outside, in the Milky Way. On 5 November 2018, Voyager 2 observed a sharp decrease in the intensity of low-energy ions and a simultaneous increase in the intensity of cosmic rays, indicating that Voyager 2 had crossed the heliopause at 119 au and entered interstellar space about six years after Voyager 1. Unlike Voyager 1, which found that two interstellar flux tubes had invaded the heliosheath and served as precursors to the heliopause, Voyager 2 found no similar precursors. However, just beyond the heliopause Voyager 2 discovered a boundary layer, in which low-energy particles streamed outward along the magnetic field and cosmic ray intensities were only 90% of those further out.

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Insights from LHAASO and IceCube into the origin of the Galactic diffuse teraelectronvolt–petaelectronvolt emission

Data availability.

Most of the CRS data can be obtained by clicking on the DATA link at https://voyager.gsfc.nasa.gov/ and following other links to obtain rate and flux data. All data that were used in the figures can be provided by the corresponding author on request.

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Acknowledgements

We thank L. Burlaga for providing magnetic field data before publication. A.C.C. acknowledges support from the International Space Sciences Institute in Bern, Switzerland, to participate in the international team The Physics of the Very Local Interstellar Medium in the autumn of 2018. This work was supported by NASA under grant NNN12AA01C.

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All authors contributed to the production of this manuscript. A.C.C. and E.C.S. wrote the text. A.C.C., B.C.H. and N.L. performed the data analysis and A.C.C. and B.C.H. prepared the figures. All authors participated in reviewing and commenting on the paper and on the editor’s and referees’ comments.

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Stone, E.C., Cummings, A.C., Heikkila, B.C. et al. Cosmic ray measurements from Voyager 2 as it crossed into interstellar space. Nat Astron 3 , 1013–1018 (2019). https://doi.org/10.1038/s41550-019-0928-3

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NASA’s Voyager 2 Discovers New Details About Interstellar Space

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About one year ago, the U.S. space agency NASA’s Voyager 2 spacecraft left our solar system. Several reports recently released in Nature Astronomy describe the spacecraft’s main scientific findings.

NASA says Voyager 2’s mission led to new discoveries about the border that divides our solar system from interstellar space . “Interstellar” means “between stars.” But scientists define interstellar space as the place where the sun's continual flow of material and magnetic field stop affecting its surroundings.

Interstellar space is estimated to be about 18 billion kilometers from Earth.

What did the spacecraft find?

Project researchers say Voyager 2’s scientific instruments discovered unexpected differences in the density of plasma, a collection of charged particles existing in the solar system.

NASA also says the new research reports confirmed that both Voyager 1 and Voyager 2 appear to be in a transitional area just beyond the heliosphere. The heliosphere is a protective bubble that protects our solar system . It is created by solar wind formed from charged particles. The border of the solar system - the place where solar wind ends and interstellar space begins - is called the heliopause.

The team reported that data from Voyager 2 suggests that the heliopause appears to be much thinner than expected.

Edward Stone is a physicist with the California Institute of Technology and a project leader for the Voyager program. Stone told reporters the findings represent “a very exciting time for us.”

He said in a statement the Voyager 2 mission was providing details about how the sun interacts with the materials that fill most of the space between stars in the Milky Way galaxy .

Researchers said Voyager 2 also confirmed the existence of a “magnetic barrier” at the outer edge of the heliosphere that had been predicted by theory and observed by Voyager 1.

"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," Stone said.

Leonard Burlaga is a scientist at NASA’s Goddard Space Flight Center and a lead researcher on one of the reports. He told the French news agency AFP there were some surprises. " Contrary to all expectations and predictions, the magnetic field direction did not change when Voyager 2 crossed the heliopause," he said.

The spacecraft also collected information on incoming cosmic rays - particles that hit Earth from anywhere beyond its atmosphere. The data showed that the rays grew stronger as the Voyager explorers neared the heliopause.​

Origins of the Voyager spacecraft

Voyager 2 was one of two explorers launched by NASA back in the summer of 1977. The other was Voyager 1. Both spacecraft were first designed to carry out fly-by studies of Jupiter and Saturn.

Later, Voyager 2 completed the first-ever close observations of Uranus and Neptune. The fly-by trips involving the four planets became known as the Voyager “Grand Tour.”

The two spacecraft then began a new mission to explore areas at the edge of the sun’s influence.

The two Voyagers – first built to last only five years – have long outlasted their operational lifetimes. But after 42 years in action, both are expected to run out of power and go silent within five years.

However, that does not mean that they will disappear. Bill Kurth, a researcher at the University of Iowa and co-writer of one of the research reports, said he expects the space explorers to outlast Earth. "They are in their own orbits around the galaxy for five billion years or longer,” he said. “And the probability of them running into anything is almost zero."

I’m Bryan Lynn.

Bryan Lynn wrote this story for VOA Learning English, based on reports from NASA, Reuters and Agence France-Presse. Kelly Jean Kelly was the editor.

Are you interested in research related to interstellar space and beyond? Write to us in the Comments section, and visit our Facebook page .

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mission – n. an important task, usually involving travel

bubble – n. an enclosed or isolated space

transitional – adj. changing from one system or method to another

characteristic – adj. typical of someone or something

specific – adj. a particular thing and not something general

contrary – adj. opposite or very different

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The Fate of Voyager: Where Will NASA’s Iconic Space Probe Be in a Billion Years?

Within a billion years, NASA’s Voyager 1 probe will have made it to the opposite side of the Milky Way disk relative to the Sun. By the time it arrives, the Sun will have boiled off all the oceans on Earth, making it inhabitable. As a result, NASA might not be around to celebrate this remarkable milestone in the journey of one of its most iconic spacecraft.

Last month, I asked my brilliant undergraduate student at Harvard, Shokhruz Kakharov where the Voyager 1 spacecraft will be in a billion years. By using a detailed model for the mass distribution of the Milky Way galaxy, Shokhruz was able to plot the future orbit of Voyager relative to the Sun over billions of years. The results will be featured in a forthcoming peer-reviewed paper.

This may all sound academic and not anchored “down to Earth,” as the adults in the room often pretend to be. But the reason for my question was down to Earth. In fact, I wondered about this question because most stars formed billions of years before the Sun. Therefore, if Voyager’s-like rocketry was used on exoplanets more than a billion years ago, then the corresponding space probes might have reached the Solar system by now from anywhere within the Milky Way disk. We can observe these interstellar objects with our telescopes as they pass near Earth.

In particular, pairing an Earth-based telescope with the space-based Webb telescope, a million miles away, will allow us to localize precisely the trajectory of the objects and detect any non-gravitational acceleration that they display. It would also be extremely sensitive to the detection of trailing gases either as a result of cometary evaporation of natural ices or exhaust gases out of an engine. But even with no surrounding gas, the Webb telescope can measure the surface temperature and size of the objects based on the infrared flux that they emit. This would allow us to determine their reflectance of sunlight within the Earth-Sun separation as long as they are much bigger than Voyager.

However, on the size scale of Voyager, there is not enough sunlight reflected for our telescopes to detect these objects unless they arrive near Earth. Better still – if they were to collide with Earth, they would show up as interstellar meteors of unusual material strength and composition. Our next expedition to the site of the interstellar meteor, IM1, which collided with Earth on January 8, 2014 , and exhibited unusual material strength and composition , aims to find large pieces of that object and infer its origin.

Shokhruz and I calculated the Galactic orbits of all 5 probes launched so far by NASA to interstellar space, namely: Voyager 1, Voyager 2, Pioneer 10, Pioneer 11 and New Horizons . We also calculated the past trajectories of the two interstellar meteors, IM1 and IM2 , as well as the interstellar object `Oumuamua and the interstellar comet Borisov .

The fundamental question of whether any of the interstellar objects detected near Earth is artificial in origin will be better answered as more of them are discovered. The most promising path for increasing the current sample of interstellar objects is with the Rubin Observatory in Chile which within a year will survey the Southern sky every 4 days with a 3.2-billion-pixel camera that just arrived a week ago at the observatory . With its unprecedented sensitivity, the Rubin Observatory might find an interstellar object every few months. With my postdoc, Richard Cloete, we are developing the software needed to analyze the Rubin data. By tracing the orbits of interstellar objects and observing them with other telescopes, we hope to identify their likely origin and figure out the nature of the environment that gave birth to them.

For the same reasons that humans might not be around on Earth when Voyager arrives at the opposite side of the Milky Way, the senders of any interstellar probes may not be around on their exoplanet because of the evolution of their older star when we receive these packages in our mailbox near Earth. Even if these technological objects stopped functioning a long while ago, their existence would imply that there used to be other intelligent residents of the Milky Way. Their trash is our treasure. Learning about their state of mind from what they left behind is equivalent to studying ancient civilizations on Earth that do not exist anymore based on the relics we recover in archaeological sites.

In a recent public appearance, I was asked what I envision for humanity’s future. I explained that humans arrogantly believe that they are important actors on the cosmic stage. But the truth is that even on the provincial stage of Earth, life survived huge catastrophes long before humans came to the scene, including a global warming event 252 million years ago that wiped out 96% of all marine species.

Complete Transcript of Congress’s Historic Hearing on Unidentified Aerial Phenomena

This gives hope that, in the grand scheme of things, life on Earth will also survive the environmental catastrophes triggered by humans. Another way to put it is that microbes are more resilient than humans. In a billion years, human existence might be a minor footnote on the cosmic playbook. To get a more balanced perspective, we must search for other actors on the cosmic stage and learn from them.  And if none of them survived, we can study their history based on the artifacts they left behind.

We are not in a position to claim a major role in cosmic history. But the good news is that we can figure out what happened on the cosmic stage and find pleasure in the fact that our own Voyager will reach the other side of the Milky Way relative to the Sun in a billion years. Isn’t this accomplishment breathtaking?

Yes, we are short-lived, meter-scale creatures with major physical limitations, but we are so ambitious and fearless that we can send our message in a bottle to the other side of the Milky Way, 50 thousand light-years away, within a billion years.

Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s – Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011-2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “ Extraterrestrial: The First Sign of Intelligent Life Beyond Earth ” and a co-author of the textbook “ Life in the Cosmos ”, both published in 2021. His new book, titled “ Interstellar ,” was published in August 2023.

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Voyager 1, First Craft in Interstellar Space, May Have Gone Dark

The 46-year-old probe, which flew by Jupiter and Saturn in its youth and inspired earthlings with images of the planet as a “Pale Blue Dot,” hasn’t sent usable data from interstellar space in months.

By Orlando Mayorquin

When Voyager 1 launched in 1977, scientists hoped it could do what it was built to do and take up-close images of Jupiter and Saturn. It did that — and much more.

Voyager 1 discovered active volcanoes, moons and planetary rings, proving along the way that Earth and all of humanity could be squished into a single pixel in a photograph, a “ pale blue dot, ” as the astronomer Carl Sagan called it. It stretched a four-year mission into the present day, embarking on the deepest journey ever into space.

Now, it may have bid its final farewell to that faraway dot.

Voyager 1 , the farthest man-made object in space, hasn’t sent coherent data to Earth since November. NASA has been trying to diagnose what the Voyager mission’s project manager, Suzanne Dodd, called the “most serious issue” the robotic probe has faced since she took the job in 2010.

The spacecraft encountered a glitch in one of its computers that has eliminated its ability to send engineering and science data back to Earth.

The loss of Voyager 1 would cap decades of scientific breakthroughs and signal the beginning of the end for a mission that has given shape to humanity’s most distant ambition and inspired generations to look to the skies.

“Scientifically, it’s a big loss,” Ms. Dodd said. “I think — emotionally — it’s maybe even a bigger loss.”

Voyager 1 is one half of the Voyager mission. It has a twin spacecraft, Voyager 2.

Launched in 1977, they were primarily built for a four-year trip to Jupiter and Saturn , expanding on earlier flybys by the Pioneer 10 and 11 probes.

The Voyager mission capitalized on a rare alignment of the outer planets — once every 175 years — allowing the probes to visit all four.

Using the gravity of each planet, the Voyager spacecraft could swing onto the next, according to NASA .

The mission to Jupiter and Saturn was a success.

The 1980s flybys yielded several new discoveries, including new insights about the so-called great red spot on Jupiter, the rings around Saturn and the many moons of each planet.

Voyager 2 also explored Uranus and Neptune , becoming in 1989 the only spacecraft to explore all four outer planets.

Voyager 1, meanwhile, had set a course for deep space, using its camera to photograph the planets it was leaving behind along the way. Voyager 2 would later begin its own trek into deep space.

“Anybody who is interested in space is interested in the things Voyager discovered about the outer planets and their moons,” said Kate Howells, the public education specialist at the Planetary Society, an organization co-founded by Dr. Sagan to promote space exploration.

“But I think the pale blue dot was one of those things that was sort of more poetic and touching,” she added.

On Valentine’s Day 1990, Voyager 1, darting 3.7 billion miles away from the sun toward the outer reaches of the solar system, turned around and snapped a photo of Earth that Dr. Sagan and others understood to be a humbling self-portrait of humanity.

“It’s known the world over, and it does connect humanity to the stars,” Ms. Dodd said of the mission.

She added: “I’ve had many, many many people come up to me and say: ‘Wow, I love Voyager. It’s what got me excited about space. It’s what got me thinking about our place here on Earth and what that means.’”

Ms. Howells, 35, counts herself among those people.

About 10 years ago, to celebrate the beginning of her space career, Ms. Howells spent her first paycheck from the Planetary Society to get a Voyager tattoo.

Though spacecraft “all kind of look the same,” she said, more people recognize the tattoo than she anticipated.

“I think that speaks to how famous Voyager is,” she said.

The Voyagers made their mark on popular culture , inspiring a highly intelligent “Voyager 6” in “Star Trek: The Motion Picture” and references on “The X Files” and “The West Wing.”

Even as more advanced probes were launched from Earth, Voyager 1 continued to reliably enrich our understanding of space.

In 2012, it became the first man-made object to exit the heliosphere, the space around the solar system directly influenced by the sun. There is a technical debate among scientists around whether Voyager 1 has actually left the solar system, but, nonetheless, it became interstellar — traversing the space between stars.

That charted a new path for heliophysics, which looks at how the sun influences the space around it. In 2018, Voyager 2 followed its twin between the stars.

Before Voyager 1, scientific data on the sun’s gases and material came only from within the heliosphere’s confines, according to Dr. Jamie Rankin, Voyager’s deputy project scientist.

“And so now we can for the first time kind of connect the inside-out view from the outside-in,” Dr. Rankin said, “That’s a big part of it,” she added. “But the other half is simply that a lot of this material can’t be measured any other way than sending a spacecraft out there.”

Voyager 1 and 2 are the only such spacecraft. Before it went offline, Voyager 1 had been studying an anomalous disturbance in the magnetic field and plasma particles in interstellar space.

“Nothing else is getting launched to go out there,” Ms. Dodd said. “So that’s why we’re spending the time and being careful about trying to recover this spacecraft — because the science is so valuable.”

But recovery means getting under the hood of an aging spacecraft more than 15 billion miles away, equipped with the technology of yesteryear. It takes 45 hours to exchange information with the craft.

It has been repeated over the years that a smartphone has hundreds of thousands of times Voyager 1’s memory — and that the radio transmitter emits as many watts as a refrigerator lightbulb.

“There was one analogy given that is it’s like trying to figure out where your cursor is on your laptop screen when your laptop screen doesn’t work,” Ms. Dodd said.

Her team is still holding out hope, she said, especially as the tantalizing 50th launch anniversary in 2027 approaches. Voyager 1 has survived glitches before, though none as serious.

Voyager 2 is still operational, but aging. It has faced its own technical difficulties too.

NASA had already estimated that the nuclear-powered generators of both spacecrafts would likely die around 2025.

Even if the Voyager interstellar mission is near its end, the voyage still has far to go.

Voyager 1 and its twin, each 40,000 years away from the next closest star, will arguably remain on an indefinite mission.

“If Voyager should sometime in its distant future encounter beings from some other civilization in space, it bears a message,” Dr. Sagan said in a 1980 interview .

Each spacecraft carries a gold-plated phonograph record loaded with an array of sound recordings and images representing humanity’s richness, its diverse cultures and life on Earth.

“A gift across the cosmic ocean from one island of civilization to another,” Dr. Sagan said.

Orlando Mayorquin is a general assignment and breaking news reporter based in New York. More about Orlando Mayorquin

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Things are finally looking up for the Voyager 1 interstellar spacecraft

Two of the four science instruments aboard the Voyager 1 spacecraft are now returning usable data after months of transmitting only gibberish, NASA scientists have announced.

I was once sitting with my father while Googling how far away various things in the solar system are from Earth. He was looking for exact numbers, and very obviously grew more invested with each new figure I shouted out. I was thrilled. The moon? On average, 238,855 miles (384,400 kilometers) away. The James Webb Space Telescope ? Bump that up to about a million miles (1,609,344 km) away. The sun? 93 million miles (149,668,992 km) away.  Neptune ? 2.8  billion  miles (4.5 billion km) away. "Well, wait until you hear about Voyager 1," I eventually said, assuming he was aware of what was coming. He was not.

"NASA's  Voyager 1  interstellar spacecraft actually isn't even in the solar system anymore," I announced. "Nope, it's more than 15 billion miles (24 billion km)  away from us  — and it's getting even farther as we speak." I can't quite remember his response, but I do indeed recall an expression of sheer disbelief. There were immediate inquiries about how that's even physically possible. There were bewildered laughs, different ways of saying "wow," and mostly, there was a contagious sense of awe. And just like that, a new Voyager 1 fan was born.

It is easy to see why Voyager 1 is among the most beloved robotic space explorers we have — and it is thus easy to understand why so many people felt a pang to their hearts several months ago, when Voyager 1 stopped talking to us.

Related:  After months of sending gibberish to NASA, Voyager 1 is finally making sense again

For reasons unknown at the time, this spacecraft began sending back gibberish in place of the neatly organized and data-rich 0's and 1's it had been providing since its  launch in 1977 . It was this classic computer language which allowed Voyager 1 to converse with its creators while earning the title of "farthest human made object." It's how the spacecraft relayed vital insight that led to the discovery of new Jovian moons and, thanks to this sort of binary podcast, scientists incredibly identified a new ring of Saturn and created the solar system's first and only "family portrait." This code, in essence, is crucial to Voyager 1's very being.

Plus, to make matters worse, the issue behind the glitch turned out to be associated with the craft's Flight Data System, which is literally the system that transmits information about Voyager 1's health so scientists can correct any issues that arise. Issues like this one. Furthermore, because of the spacecraft's immense distance from its operators on Earth, it takes about 22.5 hours for a transmission to reach the spacecraft, and then 22.5 hours to receive a transmission back. Alas, things weren't looking good for a while — for about five months, to be precise.

But then, on April 20, Voyager 1  finally phoned home  with legible 0's and legible 1's.

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"The team had gathered early on a weekend morning to see whether telemetry would return," Bob Rasmussen, a member of the Voyager flight team, told Space.com. "It was nice to have everyone assembled in one place like this to share in the moment of learning that our efforts had been successful. Our cheer was both for the intrepid spacecraft and for the comradery that enabled its recovery."

And  then,  on May 22 , Voyager scientists released the welcome announcement that the spacecraft has successfully resumed returning science data from two of its four instruments, the plasma wave subsystem and magnetometer instrument. They're now working on getting the other two, the cosmic ray subsystem and low energy charged particle instrument, back online as well. Though there technically are six other instruments onboard Voyager, those had been out of commission for some time.

The comeback

Rasmussen was actually a member of the Voyager team in the 1970s, having worked on the project as a computer engineer before leaving for other missions including  Cassini , which launched the spacecraft that taught us almost everything we currently know about Saturn. In 2022, however, he returned to Voyager because of a separate dilemma with the mission — and has remained on the team ever since.

"There are many of the original people who were there when Voyager launched, or even before, who were part of both the flight team and the science team," Linda Spilker, a planetary scientist at NASA's Jet Propulsion Laboratory , who also worked on the Voyager mission, told Space.com in the This Week from Space podcast on the TWiT network. "It's a real tribute to Voyager — the longevity not only of the spacecraft, but of the people on the team."

To get Voyager 1 back online, in rather cinematic fashion, the team devised a complex workaround that prompted the FDS to send a copy of its memory back to Earth. Within that memory readout, operators managed to discover the crux of the problem — a corrupted code spanning a single chip — which was then remedied through another (honestly,  super interesting ) process to modify the code. On the day Voyager 1 finally spoke again, "you could have heard a pin drop in the room," Spilker said. "It was very silent. Everybody's looking at the screen, waiting and watching." 

Of course, Spilker also brought in some peanuts for the team to munch on — but not just any peanuts. Lucky peanuts. 

It's a longstanding tradition at JPL to have a peanut feast before major mission events like launches, milestones and, well, the possible resurrection of Voyager 1. It  began  in the 1960s, when the agency was trying to launch the Ranger 7 mission that was meant to take pictures of and collect data about the moon's surface. Rangers 1 through 6 had all failed, so Ranger 7 was a big deal. As such, the mission's trajectory engineer, Dick Wallace, brought lots of peanuts for the team to nibble on and relax. Sure enough, Ranger 7 was a success and, as Wallace once said, "the rest is history." 

Voyager 1 needed some of those positive snacky vibes. 

"It'd been five months since we'd had any information," Spilker explained. So, in this room of silence besides peanut-eating-noises, Voyager 1 operators sat at their respective system screens, waiting. 

"All of a sudden it started to populate — the data," Spilker said. That's when the programmers who had been staring at those screens in anticipation leapt out of their seats and began to cheer: "They were the happiest people in the room, I think, and there was just a sense of joy that we had Voyager 1 back."

Eventually, Rasmussen says the team was able to conclude that the failure probably occurred due to a combination of aging and radiation damage by which energetic particles in space bombarded the craft. This is also why he believes it wouldn't be terribly surprising to see a similar failure occur in the future, seeing as Voyager 1 is still roaming beyond the distant boundaries of our stellar neighborhood just like its spacecraft twin,  Voyager 2 .

To be sure, the spacecraft isn't fully fixed yet — but it's lovely to know things are finally looking up, especially with the recent news that some of its science instruments are back on track. And, at the very least, Rasmussen assures that nothing the team has learned so far has been alarming. "We're confident that we understand the problem well," he said, "and we remain optimistic about getting everything back to normal — but we also expect this won't be the last."

In fact, as Rasmussen explains, Voyager 1 operators first became optimistic about the situation just after the root cause of the glitch had been determined with certainty. He also emphasizes that the team's spirits were never down. "We knew from indirect evidence that we had a spacecraft that was mostly healthy," he said. "Saying goodbye was not on our minds."

"Rather," he continued, "we wanted to push toward a solution as quickly as possible so other matters on board that had been neglected for months could be addressed. We're now calmly moving toward that goal."

The future of Voyager's voyage

It can't be ignored that, over the last few months, there has been an air of anxiety and fear across the public sphere that Voyager 1 was slowly moving toward sending us its final 0 and final 1. Headlines all over the internet, one written by  myself included , have carried clear, negative weight. I think it's because even if Voyager 2 could technically carry the interstellar torch post-Voyager 1, the prospect of losing Voyager 1 felt like the prospect of losing a piece of history. 

"We've crossed this boundary called the heliopause," Spilker explained of the Voyagers. "Voyager 1 crossed this boundary in 2012; Voyager 2 crossed it in 2018 — and, since that time, were the first spacecraft ever to make direct measurements of the interstellar medium." That medium basically refers to material that fills the space between stars. In this case, that's the space between other stars and our sun, which, though we don't always think of it as one, is simply another star in the universe. A drop in the cosmic ocean.

"JPL started building the two Voyager spacecraft in 1972," Spilker explained. "For context, that was only three years after we had the first human walk on the moon — and the reason we started that early is that we had this rare alignment of the planets that happens once every  176 years ." It was this alignment that could promise the spacecraft checkpoints across the solar system, including at Jupiter, Saturn, Uranus and Neptune. Those checkpoints were important for the Voyagers in particular. Alongside planetary visits come gravity assists, and gravity assists can help fling stuff within the solar system — and, now we know, beyond.

As the first humanmade object to leave the solar system, as a relic of America's early space program, and as a testament to how robust even decades-old technology can be, Voyager 1 has carved out the kind of legacy usually reserved for remarkable things lost to time.

"Our scientists are eager to see what they’ve been missing," Rasmussen remarked. "Everyone on the team is self-motivated by their commitment to this unique and important project. That's where the real pressure comes from." 

Still, in terms of energy, the team's approach has been clinical and determined. 

— NASA's Voyager 1 sends readable message to Earth after 4 nail-biting months of gibberish

— NASA engineers discover why Voyager 1 is sending a stream of gibberish from outside our solar system

— NASA's Voyager 1 probe hasn't 'spoken' in 3 months and needs a 'miracle' to save it

"No one was ever especially excited or depressed," he said. "We're confident that we can get back to business as usual soon, but we also know that we're dealing with an aging spacecraft that is bound to have trouble again in the future. That's just a fact of life on this mission, so not worth getting worked up about."

Nonetheless, I imagine it's always a delight for Voyager 1's engineers to remember this robotic explorer occupies curious minds around the globe. (Including my dad's mind now, thanks to me and Google.)

As Rasmussen puts it: "It's wonderful to know how much the world appreciates this mission."

Originally posted on Space.com .

Monisha Ravisetti is Space.com's Astronomy Editor. She covers black holes, star explosions, gravitational waves, exoplanet discoveries and other enigmas hidden across the fabric of space and time. Previously, she was a science writer at CNET, and before that, reported for The Academic Times. Prior to becoming a writer, she was an immunology researcher at Weill Cornell Medical Center in New York. She graduated from New York University in 2018 with a B.A. in philosophy, physics and chemistry. She spends too much time playing online chess. Her favorite planet is Earth.

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May 30, 2024

Voyager 1’s Revival Offers Inspiration for Everyone on Earth

Instruments may fail, but humanity’s most distant sentinel will keep exploring, and inspiring us all

By Saswato R. Das

Artist's rendering of a Voyager spacecraft in deep space.

Dotted Zebra/Alamy Stock Photo

Amid April’s litany of bad news—war in Gaza, protests on American campuses, an impasse in Ukraine—a little uplift came for science buffs.

NASA has reestablished touch with Voyager 1 , the most distant thing built by our species, now hurtling through interstellar space far beyond the orbit of Pluto. The extraordinarily durable spacecraft had stopped transmitting data in November, but NASA engineers managed a very clever work-around, and it is sending data again. Now more than 15 billion miles away, Voyager 1 is the farthest human object, and continues to speed away from us at approximately 38,000 miles per hour.

Like an old car that continues to run, or an uncle blessed with an uncommonly long life, the robotic spacecraft is a super ager that goes on and on—and, in doing so, has captivated space buffs everywhere.

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Launched on September 5, 1977, the one-ton Voyager 1 was meant to chart the outer solar system, in particular the gas giant planets Jupiter and Saturn, and Saturn’s moon, Titan. Its twin, Voyager 2 , launched the same year, followed a different trajectory with a slightly different mission to explore the outer planets before heading to the solar system’s edge.

Those were NASA’s glory days. A few years earlier, NASA had successfully landed men on the moon—and won the space race for the U.S. NASA’s engineers were the envy of the world.

To get to Jupiter and Saturn, both Voyagers had to traverse the asteroid belt, which is full of rocks and debris orbiting the sun. They had to survive cosmic rays, intense radiation from Jupiter and other perils of space. But the two spacecraft made it without a hitch.

President Jimmy Carter held office when Voyager 1 was launched from Cape Canaveral; Elvis Presley had died just three weeks before; gas was about 60 cents a gallon; and, like now, the Middle East was in crisis, with Israeli Prime Minister Menachem Begin and Egyptian President Anwar Sadat trying to find peace.

Voyager 1 sent back spectacular photos of Jupiter and its giant red spot. It showed how dynamic the Jovian atmosphere was, with clouds and storms. It also took pictures of Jupiter’s moon Io, with its volcanoes, and Saturn’s moon Titan , which astronomers think has an atmosphere similar to the primordial Earth’s. The spacecraft discovered a thin ring around Jupiter and two new Jovian moons, which were named Thebe and Metis. On reaching Saturn, it discovered five new moons as well as a new ring.

And then Voyager 1 continued on its journey and sent images back from the edge of the solar system. Many of us remember the Pale Blue Dot , a haunting picture of the Earth it took on Feb 14, 1990, when it was a distance of 3.7 billion miles from the sun. The astronomer Carl Sagan wrote:

“There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we've ever known.”

By then Voyager 1 had long outlived its planetary mission but kept faithfully calling home as it traveled beyond the solar system into the realm of the stars. By 2012 Voyager 1 had reached the heliosphere , the farthest edge of the solar system. There, it penetrated the heliopause, where the solar wind ends, stopped by particles coming from the interstellar medium, the vast space between the stars. (Astronomers know that the space between the stars is not totally empty but permeated by a rarefied gas .)

From Voyager 1, scientists learned that the heliopause is quite dynamic and first measured the magnetic field of the Milky Way beyond the solar system. And its instruments kept sending data as it traveled through the interstellar medium.

On hearing that Voyager 1 had gone dark, I had checked in with Louis Lanzerotti , a former Bell Labs planetary scientist who did the calibrations for the Voyager 1 spacecraft and was a principal investigator on many experiments. He told me that a NASA manager in the 1970s had doubted that the spacecraft’s mechanical scan platform, which pointed instruments at targets, and very thin solid state detectors, which took those edge of the solar system readings, on the spacecraft would survive. They not only survived but worked flawlessly for all this time, Lanzerotti said, providing excellent data for decades. He was overjoyed on hearing the news that Voyager 1 was still alive.

Voyager 1 instruments have power until 2025 . After that, they will shut off, one by one. But there is nothing to stop the spacecraft as it speeds away from us in the vast emptiness of space.

Thousands of years from now, maybe when the human race has left this planet, Voyager 1, the tiny little spacecraft that could, will still continue its inexorable journey to the stars.

This is an opinion and analysis article, and the views expressed by the author or authors are not necessarily those of Scientific American.

Scientists call the region of space influenced by the Sun the heliosphere – but without an interstellar probe, they don’t know much about its shape

T he Sun warms the Earth, making it habitable for people and animals. But that’s not all it does, and it affects a much larger area of space. The heliosphere , the area of space influenced by the Sun, is over a hundred times larger than the distance from the Sun to the Earth.

The Sun is a star that constantly emits a steady stream of plasma – highly energized ionized gas – called the solar wind. In addition to the constant solar wind , the Sun also occasionally releases eruptions of plasma called coronal mass ejections , which can contribute to the aurora , and bursts of light and energy, called flares .

The plasma coming off the Sun expands through space, along with the Sun’s magnetic field. Together they form the heliosphere within the surrounding local interstellar medium – the plasma, neutral particles and dust that fill the space between stars and their respective astrospheres. Heliophysicists like me want to understand the heliosphere and how it interacts with the interstellar medium.

The eight known planets in the solar system, the asteroid belt between Mars and Jupiter, and the Kuiper Belt – the band of celestial objects beyond Neptune that includes the planetoid Pluto – all reside within the heliosphere. The heliosphere is so large that objects in the Kuiper Belt orbit closer to the Sun than to the closest boundary of the heliosphere .

Heliosphere protection

As distant stars explode, they expel large amounts of radiation into interstellar space in the form of highly energized particles known as cosmic rays . These cosmic rays can be dangerous for living organisms and can damage electronic devices and spacecraft.

Earth’s atmosphere protects life on the planet from the effects of cosmic radiation, but, even before that, the heliosphere itself acts as a cosmic shield from most interstellar radiation.

In addition to cosmic radiation, neutral particles and dust stream steadily into the heliosphere from the local interstellar medium. These particles can affect the space around Earth and may even alter how the solar wind reaches the Earth .

Supernovae and the interstellar medium may have also influenced the origins of life and the evolution of humans on Earth. Some researchers predict that millions of years ago, the heliosphere came into contact with a cold, dense particle cloud in the interstellar medium that caused the heliosphere to shrink , exposing the Earth to the local interstellar medium.

An unknown shape

But scientists don’t really know what the heliosphere’s shape is. Models range in shape from spherical to cometlike to croissant-shaped. These predictions vary in size by hundreds to thousands of times the distance from the Sun to the Earth.

Scientists have, however, defined the direction that the Sun is moving as the “nose” direction and the opposing direction as the “tail” direction. The nose direction should have the shortest distance to the heliopause – the boundary between the heliosphere and the local interstellar medium.

No probe has ever gotten a good look at the heliosphere from the outside or properly sampled the local interstellar medium. Doing so could tell scientists more about the heliosphere’s shape and its interaction with the local interstellar medium, the space environment beyond the heliosphere.

Crossing the heliopause with Voyager

In 1977, NASA launched the Voyager mission : Its two spacecraft flew past Jupiter, Saturn, Uranus and Neptune in the outer solar system. Scientists have determined that after observing these gas giants, the probes separately crossed the heliopause and into interstellar space in 2012 and 2018, respectively.

While Voyager 1 and 2 are the only probes to have ever potentially crossed the heliopause, they are well beyond their intended mission lifetimes. They can no longer return the necessary data as their instruments slowly fail or power down.

These spacecraft were designed to study planets, not the interstellar medium. This means they don’t have the right instruments to take all the measurements of the interstellar medium or the heliosphere that scientists need.

That’s where a potential interstellar probe mission could come in. A probe designed to fly beyond the heliopause would help scientists understand the heliosphere by observing it from the outside.

An interstellar probe

Since the heliosphere is so large, it would take a probe decades to reach the boundary , even using a gravity assist from a massive planet like Jupiter.

The Voyager spacecraft will no longer be able to provide data from interstellar space long before an interstellar probe exits the heliosphere. And once the probe is launched, depending on the trajectory, it will take about 50 or more years to reach the interstellar medium. This means that the longer NASA waits to launch a probe, the longer scientists will be left with no missions operating in the outer heliosphere or the local interstellar medium.

NASA is considering developing an interstellar probe . This probe would take measurements of the plasma and magnetic fields in the interstellar medium and image the heliosphere from the outside. To prepare, NASA asked for input from more than 1,000 scientists on a mission concept.

The initial report recommended the probe travel on a trajectory that is about 45 degrees away from the heliosphere’s nose direction. This trajectory would retrace part of Voyager’s path, while reaching some new regions of space. This way, scientists could study new regions and revisit some partly known regions of space.

This path would give the probe only a partly angled view of the heliosphere, and it wouldn’t be able to see the heliotail, the region scientists know the least about.

In the heliotail, scientists predict that the plasma that makes up the heliosphere mixes with the plasma that makes up the interstellar medium. This happens through a process called magnetic reconnection , which allows charged particles to stream from the local interstellar medium into the heliosphere. Just like the neutral particles entering through the nose, these particles affect the space environment within the heliosphere.

In this case, however, the particles have a charge and can interact with solar and planetary magnetic fields. While these interactions occur at the boundaries of the heliosphere, very far from Earth, they affect the makeup of the heliosphere’s interior.

In a new study published in Frontiers in Astronomy and Space Sciences, my colleagues and I evaluated six potential launch directions ranging from the nose to the tail. We found that rather than exiting close to the nose direction, a trajectory intersecting the heliosphere’s flank toward the tail direction would give the best perspective on the heliosphere’s shape.

A trajectory along this direction would present scientists with a unique opportunity to study a completely new region of space within the heliosphere. When the probe exits the heliosphere into interstellar space, it would get a view of the heliosphere from the outside at an angle that would give scientists a more detailed idea of its shape – especially in the disputed tail region.

In the end, whichever direction an interstellar probe launches, the science it returns will be invaluable and quite literally astronomical.

This article is republished from The Conversation , >, a nonprofit, independent news organization bringing you facts and analysis to help you make sense of our complex world.

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Sarah A. Spitzer works as a research fellow for the University of Michigan department of Climate and Space Sciences and Engineering. She receives funding from the the University of Michigan and from grants supported by organizations such as NASA. She is affiliated with the University of Michigan and the Interstellar Probe Study Team.

Voyager 1 discovers faint plasma 'hum' in interstellar space

Four and a half decades after launch and over 14 billion miles from Earth, Voyager 1 still makes new discoveries. The spacecraft has picked up the signature of interstellar space itself, a faint plasma "hum" scientists compared to gentle rain. 

Plasma has been part of Voyager 1's mission from its launch — the spacecraft discovered lightning strikes in Jupiter's atmosphere and studied how the solar wind tapered off in the outer solar system.

And since 2012, scientists have turned the spacecraft's instruments upon a completely unexplored part of distant space. That's when Voyager 1 crossed the heliopause , where the solar wind — the constant stream of charged particles that flows off the sun — is no longer strong enough to hold back the interstellar medium that surrounds our little neighborhood. Since 2012, as Voyager 1 has drifted ever farther from the sun, the spacecraft has measured the plasma around it.

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This part of the interstellar medium is, mostly, quiet. "It's very faint and monotone, because it is in a narrow frequency bandwidth," Stella Koch Ocker, a doctoral student at Cornell University who led the new research, said in a statement . "We're detecting the faint, persistent hum of interstellar gas."

But every few years, the solar wind pushes back. Voyager 1 picks up those events as shockwaves. "In the case of a solar outburst, it's like detecting a lightning burst in a thunderstorm," senior author James Cordes, an astronomer at Cornell, said in the same statement. "Then it's back to a gentle rain." 

For a time, scientists thought those shocks were the only way that Voyager 1 could measure the density of plasma out there.

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Related: What spacecraft will enter interstellar space next?

But now that scientists have heard this unexpected hum, they can track the interstellar medium between shocks, which can help them understand much more about a largely undiscovered expanse of space. Ocker believes there's much more low-level activity in the interstellar medium than scientists previously thought.

"Now we know we don't need a fortuitous event related to the sun to measure interstellar plasma," Shami Chatterjee, a Cornell astronomer, said in the same statement. "Regardless of what the sun is doing, Voyager is sending back detail. The craft is saying, 'Here's the density I'm swimming through right now. And here it is now. And here it is now. And here it is now.' Voyager is quite distant and will be doing this continuously."

Voyager 1 and its twin, Voyager 2, will sail away to the stars for time immemorial . But for scientists here on Earth, the spacecraft's days are numbered. Sometime within this decade, the spacecraft's plutonium power sources will finally run dry. 

In the meantime, scientists are savoring every last bit of data that trickles back. "It's the engineering gift to science that keeps on giving," Ocker said.

Follow us on Twitter @Spacedotcom and on Facebook.

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Rahul Rao is a graduate of New York University's SHERP and a freelance science writer, regularly covering physics, space, and infrastructure. His work has appeared in Gizmodo, Popular Science, Inverse, IEEE Spectrum, and Continuum. He enjoys riding trains for fun, and he has seen every surviving episode of Doctor Who. He holds a masters degree in science writing from New York University's Science, Health and Environmental Reporting Program (SHERP) and earned a bachelors degree from Vanderbilt University, where he studied English and physics. 

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