where is the voyager spacecraft now

The remarkable twin Voyager spacecraft continue to explore the outer reaches of the solar system decades after they completed their surveys of the Outer Planets.  Launched in 1977 (September 5 for Voyager 1 (V1) and August 20 for Voyager 2 (V2), whose trajectory took it past Jupiter after Voyager 1), the spacecraft pair made many fundamental discoveries as they flew past Jupiter (March 1979 for V1, July 1979 for V2) and Saturn (November 1980 for V1, August 1981 for V2).  The path of Voyager 2 past Saturn was targeted so that it continued within the plane of the solar system, allowing it to become the first spacecraft to visit Uranus (January 1986) and Neptune (August 1989).  Following the Neptune encounter, both spacecraft started a new phase of exploration under the intriguing title of the Voyager Interstellar Mission.

Five instruments continue to collect important measurements of magnetic fields, plasmas, and charged particles as both spacecraft explore different portions of the solar system beyond the orbits of the planets.  Voyager 1 is now more than 118 astronomical units (one AU is equal to the average orbital distance of Earth from the Sun) distant from the sun, traveling at a speed (relative to the sun) of 17.1 kilometers per second (10.6 miles per second).  Voyager 2 is now more than 96 AU from the sun, traveling at a speed of 15.5 kilometers per second (9.6 miles per second).  Both spacecraft are moving considerably faster than Pioneers 10 and 11, two earlier spacecraft that became the first robotic visitors to fly past Jupiter and Saturn in the mid-70s.

This processed color image of Jupiter was produced in 1990 by the U.S. Geological Survey from a Voyager image captured in 1979. The colors have been enhanced to bring out detail. Zones of light-colored, ascending clouds alternate with bands of dark, descending clouds. The clouds travel around the planet in alternating eastward and westward belts at speeds of up to 540 kilometers per hour. Tremendous storms as big as Earthly continents surge around the planet. The Great Red Spot (oval shape toward the lower-left) is an enormous anticyclonic storm that drifts along its belt, eventually circling the entire planet.

As seen in the night sky at Earth, Voyager 1 is within the confines of the constellation Ophiuchus, only slightly above the celestial equator; no telescope can see it, but radio contact is expected to be maintained for at least the next ten years.  Voyager 2 is within the bounds of the constellation Telescopium (which somehow sounds quite appropriate) in the far southern night sky.

Both spacecraft have already passed something called the Termination Shock † (December 2004 for V1, August 2007 for V2), where the solar wind slows as it starts to interact with the particles and fields present between the stars.  It is expected that both spacecraft will encounter the Heliopause, where the solar wind ceases as true interstellar space begins, from 10 to 20 years after crossing the Termination Shock.  Theories exist for what should be present in interstellar space, but the Voyagers will become the first man-made objects to go beyond the influences of the Sun, hopefully returning the first measurements of what it is like out there.  Each spacecraft is carrying a metal record with encoded sounds and sights from Earth, along with the needle needed to read the recordings, and simplified instructions for where the spacecraft came from, in case they are eventually discovered by intelligent extra-terrestrials.

Keep track of the Voyager spacecraft on the official  Voyager Interstellar Mission website or follow  @NASAVoyager2 on Twitter.    † The sun ejects a continuous stream of charged particles (electrons, protons, etc) that is collectively termed the solar wind.  The particles are traveling extremely fast and are dense enough to form a very tenuous atmosphere; the heliosphere represents the volume of space where the effects of the solar wind dominate over those of particles in interstellar space.  The solar wind particles are moving very much faster than the local speed of sound represented by their low volume density.  When the particles begin to interact with interstellar particles and fields (the interaction can be either physically running into other particles or experiencing an electromagnetic force resulting from a charged particle moving within a magnetic field), then they start to slow down.  The point at which they become subsonic (rather than their normal hypersonic speed) is the Termination Shock.

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Voyagers Continues to Returns Data from The Edges of the Milky Way

More than two years after Voyager 2 looked Neptune's Great Dark Spot in the eye and darted past the frozen surface of its moon Triton, both Voyager spacecraft are continuing to return data about interplanetary space and some of our stellar neighbors near the edges of the Milky Way.

After the Voyager spacecraft flew by the four giant outer planets -- Jupiter, Saturn, Uranus and Neptune -- their mission might have been over. But, in fact, these 14-year-old twins are just beginning a new phase of their journey, called the Voyager Interstellar Mission (VIM).

As the Voyagers cruise gracefully in the solar wind, their fields, particles and waves instruments are studying the space around them while searching for the elusive heliopause -- the outer edge of our solar system.

The heliopause is the outermost boundary of the solar wind, where the interstellar medium restricts the outward flow of the solar wind and confines it within a magnetic bubble called the heliosphere. The solar wind is made up of electrically charged atomic particles, composed primarily of ionized hydrogen, that stream outward from the Sun. "The termination shock is the first signal that we are approaching the heliopause. It's the area where the solar wind starts slowing down," said Voyager Project Scientist and JPL's Director, Dr. Edward C. Stone. Mission scientists now anticipate that the spacecraft may cross the termination shock by the end of the century. Exactly where the heliopause is remains a mystery. Its long been thought to be located some 75 to 150 astronomical units (AU) from the Sun. (One AU is equal to 150 million kilometers (93 million miles), or the distance from the Earth to the Sun.) Any speculation about where the heliopause is or what it is like, has come only from computer models and theories. "Voyager 1 is likely to return the first direct evidence from the heliopause and what lies beyond it," Stone said.

Yet the Voyagers are not sitting idly by as they wait to cross over into interstellar space. Both spacecraft are involved in an extensive program of ultraviolet astronomy that allows them to study active galaxies, quasars and white dwarf stars, in ways unlike any other spacecraft or telescope in existence.

Voyager's ultraviolet spectrometers are the only way scientists can currently observe celestial objects in a unique region in the short end of the ultraviolet portion of the electromagnetic spectrum. "Voyager's instruments allow it to observe things at wavelengths that are for the most part unavailable to other spacecraft," said Dr. Jay Holberg, a member of Voyager's ultraviolet subsystem team.

The Voyagers have become space-based ultraviolet observatories and their unique location in the universe gives astronomers the best vantage point they have ever had for looking at celestial objects that emit ultraviolet radiation. "The light that Voyager is sensitive to has to be observed in outer space," said Holberg.

Voyager's ultraviolet instruments are best suited to study the two extreme phases of a star's life -- its birth and its death. Thus the Voyagers are currently gathering data on early blue stars as well as other white dwarf stars nearing the end of their lifetime. "Voyager is helping us get a better handle on exactly how much energy these hot stars emit," Holberg said.

Now that Voyager's primary mission of exploring the outer planets is over, there are fewer constraints on the science team when it comes to programming the spacecrafts' observations. "We can sit on these things for very long periods of time and watch these stars go through their phases," Holberg said.

Stars can be very active, but also unpredictable. "We don't know when a star will do something. If we want to sit there and wait, we can do it in the hopes that the star will go through an outburst and Voyager will be there to observe it," he continued. Voyager can now stare at an object for days and even weeks at a time to thoroughly map it and the region around it.

Since the beginning of the interstellar mission, the Voyager project has been conducting a guest observer program which allows astronomers from around the world to make proposals and apply for time to use the Voyager ultraviolet spectrometer in much the same way that astronomers apply for time at ground-based observatories. This program enables scientists to make simultaneous observations of the same object using Voyager and ground-based telescopes.

The cameras on the spacecraft have been turned off and the ultraviolet instrument is the only experiment on the scan platform that is still functioning. Voyager scientists expect to continue to receive data from the ultraviolet spectrometers at least until the year 2000. At that time, there will not be enough electrical power for the heaters to keep the ultraviolet instrument warm enough to operate.

Yet there are several other fields and particle instruments that can continue to send back data as long as the spacecraft stay alive. They include: the cosmic ray subsystem, the low-energy charged particle instrument, the magnetometer, the plasma subsystem, the plasma wave subsystem and the planetary radio astronomy instrument. Barring any catastrophic events, JPL should be able to retrieve this information for at least the next 20 and perhaps even the next 30 years.

"In exploring the four outer planets, Voyager has already had an epic journey of discovery. Even so, their journey is less than half over with more discoveries awaiting the first contact with interstellar space," Stone said. "The Voyagers revealed how limited our imaginations really were about our solar system, and I expect that as they continue toward interstellar space, they will again surprise us with unimagined discoveries of this never-before-visited place which awaits us beyond our planetary neighborhood."

Voyager 1 is now 7 billion kilometers (4.3 billion miles) from Earth, traveling at a heliocentric velocity of 63,800 km/hr (39,700 mph). Voyager 2, traveling in the opposite direction from its twin, is 5.3 billion kilometers (3.3 billion miles) from Earth with a heliocentric velocity of 59,200 km/hr (36,800 mph).

The Voyager Interstellar Mission is managed by JPL and sponsored by NASA's Office of Space Science and Applications, Washington, DC.

Voyager 1 enters interstellar space in an illustration. The NASA spacecraft officially crossed into the space between the stars in 2012.

Both of NASA's Voyager spacecraft are now interstellar. Where to next?

Launched in 1977, the twin probes will likely outlive the sun. Find out what star systems they’ll meet as they head deeper into the galaxy.

NASA’s twin Voyager spacecraft have been traveling the interstellar road for more than 40 years, sweeping past the giant planets of the outer solar system before heading to the very fringes of our sun’s domain. Now, one probe has achieved a milestone in exploration: On December 10, NASA announced that Voyager 2 has entered interstellar space , six years after Voyager 1 first crossed the threshold. The twins are the only two spacecraft ever to venture so far from home.

To confirm Voyager 2's exit, scientists analyzed data from the spacecraft's Plasma Science Experiment , which measured the heliopause—the boundary between the sun's protective plasma bubble and interstellar space. On November 5, the instrument recorded a steep decline in particles from the sun's plasma. At the same time, Voyager 2 saw more high-energy particles from elsewhere in the galaxy, confirming that the probe had left our cosmic cul-de-sac.

"Working on Voyager makes me feel like an explorer, because everything we're seeing is new," MIT researcher John Richardson, the principal investigator for the plasma experiment, said in a statement . "Even though Voyager 1 crossed the heliopause in 2012, it did so at a different place and a different time, and without the PLS data. So we're still seeing things that no one has seen before."

But even at more than 11 billion miles from the sun, the Voyagers’ story is just beginning. On their current paths, both probes will still be heading outward across the galaxy eons after they escape the gravitational tug of the sun, and perhaps long after our star dies in four or five billion years. Should the spacecraft ever be intercepted by an alien civilization, two golden records bearing the sights and sounds of planet Earth could play the last whispers of a long-dead planet.

Assuming they stay on course, it’s going to be a lonely trip for the Voyagers, because even though our Earthly skies appear to glitter with countless pinpricks of light, space is mostly empty. Distances between the stars are so vast that even when our galaxy smashes into the one next door , not much will happen in the way of stellar collisions.

Still, according to astronomers’ predictions, their cosmic treks will bring the Voyagers close to several starry milestones and a dust cloud or three over the next hundred thousand or so years. Here are some of the known cosmic landmarks the Voyagers could meet in their relatively near futures.

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Launched from Cape Canaveral, Florida, on August 20, 1977, the dairy cow-size Voyager 2 began its odyssey with a grand tour of the outer solar system, making vital discoveries at Jupiter and Saturn and returning some of the best views yet of Uranus and Neptune.

The probe is now dipping below the plane of the solar system at roughly 34,500 miles an hour and heading celestially south, toward the constellation Sagittarius. On November 5, 2018, it crossed the heliopause, exiting the sun’s protective plasma bubble.

Voyager 2 may be freshly interstellar, but it won’t be anywhere near another star until 40,000 years from now, when it will pass within 1.7 light-years of the small red dwarf star Ross 248. At that point, Ross 248 will be the closest star to our sun, briefly eclipsing the Alpha Centauri system’s claim to fame as its path through the galaxy brings it just 3.02 light-years away.

About 61,000 years from now, Voyager 2 will pass beyond the Oort Cloud—a large, diffuse swarm of icy objects that is thought to extend as far as 200,000 times farther from the sun than Earth, says Wesleyan University’s Seth Redfield .

Voyager 2 may be freshly interstellar, but it won’t be anywhere near another star until 40,000 years from now.

Most scientists think the Oort cloud is the source of comets that take thousands of years to complete one orbit around the sun. It could also be the true boundary of the solar system, if you consider that to be the point where the sun’s gravitational influence drops off.

“The outer edge of the Oort Cloud is approximately where that is,” says Redfield, who has used the Hubble Space Telescope to study the Voyagers’ paths in detail for the next hundred thousand years, and more crudely for the next several million.

Next, in the year 298,000 Voyager 2 will swing within about four light-years of Sirius, the brightest star in Earth’s sky. It’ll then brush by two stars, delta Pav and GJ 754, about a hundred thousand years later.

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Voyager 1 followed its twin into the sky on September 5, 1977. It rendezvoused with Jupiter and Saturn in 1979 and 1980, returning some spectacular views of volcanoes erupting on the Jovian moon Io, then continued outward.

On February 14, 1990, it swiveled to capture the solar system retreating from its view, including a series of images that revealed our pale blue planet looking like “a mote of dust suspended in a sunbeam,” according to Carl Sagan.

Now traveling more than 35,000 miles an hour in the direction of the constellation Ophiuchus, Voyager 1 is the fastest human-made object in space. In 2013, it became the first spacecraft to leave the heliosphere and cross into interstellar space.

In the year 40,272, the spacecraft will sail within 1.7 light-years of the star Gliese 445 in the constellation Camelopardalis.

In 56,000 years, Voyager 1 will exit the Oort cloud, then brush by the stars GJ 686 and GJ 678 in 570,000 years.

Wandering Wonders

Beyond that, both spacecraft will continue on their journeys outward, passing through scattered dust clouds on their way through the local bubble, a cavern of relatively empty space blown by tempestuous dying stars. They’ll exit this bubble in 5.7 and 6.3 million years, respectively.

From there, things get murky. The peculiar motions of stars and dust clouds orbiting the galactic center aren’t well known yet, and the spacecraft could be slowed by sailing through dust clouds. Plus, gravitational encounters with things like wandering, starless planets could bounce the probes around like billiard balls.

“There may be a whole population of rogue planets out in interstellar space,” Redfield says. “A mildly close encounter with one of those could change the itinerary of the Voyagers.”

Ultimately, like the stars in the Milky Way, the Voyagers will march to the galaxy’s tune and orbit its core for the rest of their lives.

“All the stars in the solar neighborhood are in an orbit around the center of the Milky Way, with orbital periods of 225 to 250 million years,” says Voyager project scientist Ed Stone . “The Voyagers will also be in such independent orbits, completing an orbit every 225 million years for billions of years until a collision with another galaxy disrupts this orderly flow.”

That might occur in four billion years, when the neighboring Andromeda galaxy smashes into the Milky Way and rearranges our skies in spectacular ways.

How the Voyagers’ ultimate demise occurs—whether it’s death by a thousand micrometeorite impacts, or one large improbable collision—remains a mystery. It’s even possible the Voyagers will outlive the solar system, surviving long after the sun’s death sculpts our neighborhood into a dramatically different place.

“The universe tends to do a great job of preserving its occupants,” Redfield says. After all, “the objects in our solar system, even small objects, have been around for 4.5 billion years.”

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July 1, 2022

21 min read

Record-Breaking Voyager Spacecraft Begin to Power Down

The pioneering probes are still running after nearly 45 years in space, but they will soon lose some of their instruments

By Tim Folger

NASA/JPL-Caltech

I f the stars hadn't aligned, two of the most remarkable spacecraft ever launched never would have gotten off the ground. In this case, the stars were actually planets—the four largest in the solar system. Some 60 years ago they were slowly wheeling into an array that had last occurred during the presidency of Thomas Jefferson in the early years of the 19th century. For a while the rare planetary set piece unfolded largely unnoticed. The first person to call attention to it was an aeronautics doctoral student at the California Institute of Technology named Gary Flandro.

It was 1965, and the era of space exploration was barely underway—the Soviet Union had launched Sputnik 1, the first artificial satellite, only eight years earlier. Flandro, who was working part-time at NASA's Jet Propulsion Laboratory in Pasadena, Calif., had been tasked with finding the most efficient way to send a space probe to Jupiter or perhaps even out to Saturn, Uranus or Neptune. Using a favorite precision tool of 20th-century engineers—a pencil—he charted the orbital paths of those giant planets and discovered something intriguing: in the late 1970s and early 1980s, all four would be strung like pearls on a celestial necklace in a long arc with Earth.

This coincidence meant that a space vehicle could get a speed boost from the gravitational pull of each giant planet it passed, as if being tugged along by an invisible cord that snapped at the last second, flinging the probe on its way. Flandro calculated that the repeated gravity assists, as they are called, would cut the flight time between Earth and Neptune from 30 years to 12. There was just one catch: the alignment happened only once every 176 years. To reach the planets while the lineup lasted, a spacecraft would have to be launched by the mid-1970s.

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READY FOR LAUNCH: Voyager 2 undergoes testing at NASA’s Jet Propulsion Laboratory before its flight ( left ). The spacecraft lifted off on August 20, 1977. Credit: NASA/JPL-Caltech

As it turned out, NASA would build two space vehicles to take advantage of that once-in-more-than-a-lifetime opportunity. Voyager 1 and Voyager 2, identical in every detail, were launched within 15 days of each other in the summer of 1977. After nearly 45 years in space, they are still functioning, sending data back to Earth every day from beyond the solar system's most distant known planets. They have traveled farther and lasted longer than any other spacecraft in history. And they have crossed into interstellar space, according to our best understanding of the boundary between the sun's sphere of influence and the rest of the galaxy. They are the first human-made objects to do so, a distinction they will hold for at least another few decades. Not a bad record, all in all, considering that the Voyager missions were originally planned to last just four years.

Early in their travels, four decades ago, the Voyagers gave astonished researchers the first close-up views of the moons of Jupiter and Saturn, revealing the existence of active volcanoes and fissured ice fields on worlds astronomers had thought would be as inert and crater-pocked as our own moon. In 1986 Voyager 2 became the first spacecraft to fly past Uranus; three years later it passed Neptune. So far it is the only spacecraft to have made such journeys. Now, as pioneering interstellar probes more than 12 billion miles from Earth, they're simultaneously delighting and confounding theorists with a series of unexpected discoveries about that uncharted region.

Their remarkable odyssey is finally winding down. Over the past three years NASA has shut down heaters and other nonessential components, eking out the spacecrafts' remaining energy stores to extend their unprecedented journeys to about 2030. For the Voyagers' scientists, many of whom have worked on the mission since its inception, it is a bittersweet time. They are now confronting the end of a project that far exceeded all their expectations.*

“We're at 44 and a half years,” says Ralph McNutt, a physicist at the Johns Hopkins University Applied Physics Laboratory (APL), who has devoted much of his career to the Voyagers. “So we've done 10 times the warranty on the darn things.”

The stars may have been cooperating, but at first, Congress wasn't. After Flandro's report, NASA drew up plans for a so-called Grand Tour that would send as many as five probes to the four giant planets and Pluto. It was ambitious. It was expensive. Congress turned it down. “There was this really grand vision,” says Linda Spilker, a JPL planetary scientist who started working on the Voyager missions in 1977, a few months before their launch. “Because of cost, it was whittled back.”

Congress eventually approved a scaled-down version of the Grand Tour, initially called Mariner Jupiter-Saturn 1977, or MJS 77. Two spacecraft were to be sent to just two planets. Nevertheless, NASA's engineers went about designing, somewhat surreptitiously, vehicles capable of withstanding the rigors of a much longer mission. They hoped that once the twin probes proved themselves, their itinerary would be extended to Uranus, Neptune, and beyond.

“Four years—that was the prime mission,” says Suzanne Dodd, who, after a 20-year hiatus from the Voyager team, returned in 2010 as the project manager. “But if an engineer had a choice to put in a part that was 10 percent more expensive but wasn't something that was needed for a four-year mission, they just went ahead and did that. And they wouldn't necessarily tell management.” The fact that the scientists were able to build two spacecraft, and that both are still working, is even more remarkable, she adds.

In terms of both engineering and deep-space navigation, this was new territory. The motto “Failure is not an option” hadn't yet been coined, and at that time it would not have been apt. In the early 1960s NASA had attempted to send a series of spacecraft to the moon to survey future landing sites for crewed missions. After 12 failures, one such effort finally succeeded.

GOLDEN RECORD: Each Voyager carries a golden record ( left ) of sounds and images from Earth in case the spacecraft are intercepted by an extraterrestrial civilization. Engineers put the cap on Voyager 1’s record before its launch ( right ). Credit: NASA/JPL-Caltech

“In those days we always launched two spacecraft” because the failure rate was so high, said Donald Gurnett, only partly in jest. Gurnett, a physicist at the University of Iowa and one of the original scientists on the Voyager team, was a veteran of 40 other space missions. He spoke with me a few weeks before his death in January. (In an obituary, his daughter Christina said his only regret was that “he would not be around to see the next 10 years of data returning from Voyager.”)

When the Voyagers were being built, only one spacecraft had used a gravity assist to reach another planet—the Mariner 10 probe got one from Venus while en route to Mercury. But the Voyagers would be attempting multiple assists with margins of error measured in tens of minutes. Jupiter, their first stop, was about 10 times farther from Earth than Mercury. Moreover, the Voyagers would have to travel through the asteroid belt along the way. Before Voyager there had been a big debate about whether spacecraft could get through the asteroid belt “without being torn to pieces,” McNutt says. But in the early 1970s Pioneer 10 and 11 flew through it unscathed—the belt turned out to be mostly empty space—paving the way for Voyager, he says.

To handle all these challenges, the Voyagers, each about the size of an old Volkswagen Beetle, needed some onboard intelligence. So NASA's engineers equipped the vehicles' computers with 69 kilobytes of memory, less than a hundred thousandth the capacity of a typical smartphone. In fact, the smartphone comparison is not quite right. “The Voyager computers have less memory than the key fob that opens your car door,” Spilker says. All the data collected by the spacecraft instruments would be stored on eight-track tape recorders and then sent back to Earth by a 23-watt transmitter—about the power level of a refrigerator light bulb. To compensate for the weak transmitter, both Voyagers carry 12-foot-wide dish antennas to send and receive signals.

“It felt then like we were right on top of the technology,” says Alan Cummings, a physicist at Caltech and another Voyager OG. “I'll tell you, what was amazing is how quickly that whole thing happened.” Within four years the MJS 77 team had built three spacecraft, including one full-scale functioning test model. The spacecraft were rechristened Voyager 1 and 2 a few months before launch.

Although many scientists have worked on the Voyagers over the decades, Cummings can make a unique claim. “I was the last person to touch the spacecraft before they launched,” he says. Cummings was responsible for two detectors designed to measure the flux of electrons and other charged particles when the Voyagers encountered the giant planets. Particles would pass through a small “window” in each detector that consisted of aluminum foil just three microns thick. Cummings worried that technicians working on the spacecraft might have accidentally dented or poked holes in the windows. “So they needed to be inspected right before launch,” he says. “Indeed, I found that one of them was a little bit loose.”

Credit: Graphic by Matthew Twombly and Juan Velasco (5W Infographic); Consultants: John Richardson (principal investigator, Voyager Plasma Science, Massachusetts Institute of Technology, Center for Space Research) and Merav Opher (professor, Department of Astronomy, Boston University)

Voyager 1 reached Jupiter in March 1979, 546 days after its launch. Voyager 2, following a different trajectory, arrived in July of that year. Both spacecraft were designed to be stable platforms for their vidicon cameras, which used red, green and blue filters to produce full-color images. They hardly spin at all as they speed through space—their rotational motion is more than 15 times slower than the crawl of a clock's hour hand, minimizing the risk of blurred images. Standing-room crowds at JPL watched as the spacecraft started transmitting the first pictures of Jupiter while still about three or four months away from the planet.

“In all of the main conference rooms and in the hallways, they had these TV monitors set up,” Spilker says. “So as the data came down line by line, each picture would appear on a monitor. The growing anticipation and the expectation of what we were going to see when we got up really, really close—that was tremendously exciting.”

Cummings vividly recalls the day he caught his first glimpse of Jupiter's third-largest moon, Io. “I was going over to a building on the Caltech campus where they were showing a livestream [of Voyager's images],” he says. “I walk in, and there's this big picture of Io, and it's all orange and black. I thought, okay, the Caltech students had pulled a prank, and it's a picture of a poorly made pizza.”

Io's colorful appearance was completely unexpected. Before the Voyagers proved otherwise, the assumption had been that all moons in the solar system would be more or less alike—drab and cratered. No one anticipated the wild diversity of moonscapes the Voyagers would discover around Jupiter and Saturn.

The first hint that there might be more kinds of moons in the heavens than astronomers had dreamed of came while the Voyagers were still about a million miles from Jupiter. One of their instruments—the Low-Energy Charged Particle [LECP] detector system—picked up some unusual signals. “We started seeing oxygen and sulfur ions hitting the detector,” says Stamatios Krimigis, who designed the LECP and is now emeritus head of the space department at Johns Hopkins APL. The density of oxygen and sulfur ions had shot up by three orders of magnitude compared with the levels measured up to that point. At first, his team thought the instrument had malfunctioned. “We scrutinized the data,” Krimigis says, “but there was nothing wrong.”

The Voyagers' cameras soon solved the mystery: Io had active volcanoes. The small world—it is slightly larger than Earth's moon—is now known to be the most volcanically active body in the solar system. “The only active volcanoes we knew of at the time were on Earth,” says Edward Stone, who has been the project scientist for the Voyager missions since 1972. “And here suddenly was a moon that had 10 times as much volcanic activity as Earth.” Io's colors—and the anomalous ions hitting Krimigis's detector—came from elements blasted from the moon's volcanoes. The largest of Io's volcanoes, known as Pele, has blown out plumes 30 times the height of Mount Everest; debris from Pele covers an area about the size of France.

The twin spacecraft took a grand tour through the giant planets of the solar system, passing by Jupiter ( 1 , 2 ) and Saturn ( 5 , 6 ) and taking the first close-up views of those planets’ moons. Jupiter’s satellite Europa ( 3 ), for instance, turned out to be covered with ice, and its moon Io ( 4 ) was littered with volcanoes—discoveries that came as a surprise to scientists who had assumed the moons would be gray and crater-pocked like Earth’s. Voyager 2 went on to fly by Uranus ( 7 ) and Neptune ( 8 ), and it is still the only probe to have visited there. Credit: NASA/JPL ( 1 , 2 , 4 , 5 , 6 , 8 ); NASA/JPL/USGS (3); NASA/JPL-Caltech ( 7 )

Altogether, the Voyagers took more than 33,000 photographs of Jupiter and its satellites. It felt like every image brought a new discovery: Jupiter had rings; Europa, one of Jupiter's 53 named moons, was covered with a cracked icy crust now estimated to be more than 60 miles thick. As the spacecraft left the Jupiter system, they got a farewell kick of 35,700 miles per hour from a gravity assist. Without it they would not have been able to overcome the gravitational pull of the sun and reach interstellar space.

At Saturn, the Voyagers parted company. Voyager 1 hurtled through Saturn's rings (taking thousands of hits from dust grains), flew past Titan, a moon shrouded in orange smog, and then headed “north” out of the plane of the planets. Voyager 2 continued alone to Uranus and Neptune. In 1986 Voyager 2 found 10 new moons around Uranus and added the planet to the growing list of ringed worlds. Just four days after Voyager 2's closest approach to Uranus, however, its discoveries were overshadowed when the space shuttle Challenger exploded shortly after launch. All seven of Challenger 's crew members were killed, including Christa McAuliffe, a high school teacher from New Hampshire who would have been the first civilian to travel into space.

Three years later, passing about 2,980 miles above Neptune's azure methane atmosphere, Voyager 2 measured the highest wind speeds of any planet in the solar system: up to 1,000 mph. Neptune's largest moon, Triton, was found to be one of the coldest places in the solar system, with a surface temperature of −391 degrees Fahrenheit (−235 degrees Celsius). Ice volcanoes on the moon spewed nitrogen gas and powdery particles five miles into its atmosphere.

Voyager 2's images of Neptune and its moons would have been the last taken by either of the spacecraft had it not been for astronomer Carl Sagan, who was a member of the mission's imaging team. With the Grand Tour officially completed, NASA planned to turn off the cameras on both probes. Although the mission had been extended with the hope that the Voyagers would make it to interstellar space—it had been officially renamed the Voyager Interstellar Mission—there would be no photo ops after Neptune, only the endless void and impossibly distant stars.

ERUPTION: The discovery of the volcano Pele, shown in this photograph from Voyager 1, confirmed that Jupiter’s moon hosts active volcanism. Credit: NASA/JPL/USGS

Sagan urged NASA officials to have Voyager 1 transmit one last series of images. So, on Valentine's Day in 1990, the probe aimed its cameras back toward the inner solar system and took 60 final shots. The most haunting of them all, made famous by Sagan as the “Pale Blue Dot,” captured Earth from a distance of 3.8 billion miles. It remains the most distant portrait of our planet ever taken. Veiled by wan sunlight that reflected off the camera's optics, Earth is barely visible in the image. It doesn't occupy even a full pixel.

Sagan, who died in 1996, “worked really hard to convince NASA that it was worth looking back at ourselves,” Spilker says, “and seeing just how tiny that pale blue dot was.”

Both Voyagers are now so far from Earth that a one-way radio signal traveling at the speed of light takes almost 22 hours to reach Voyager 1 and just over 18 to catch up with Voyager 2. Every day they move away by another three to four light-seconds. Their only link to Earth is NASA's Deep Space Network, a trio of tracking complexes spaced around the globe that enables uninterrupted communication with spacecraft as Earth rotates. As the Voyagers recede from us in space and time, their signals are becoming ever fainter. “Earth is a noisy place,” says Glen Nagle, outreach and communications manager at the Deep Space Network's facility in Canberra, Australia. “Radios, televisions, cell phones—everything makes noise. And so it gets harder and harder to hear these tiny whispers from the spacecraft.”

Faint as they are, those whispers have upended astronomers' expectations of what the Voyagers would find as they entered the interstellar phase of the mission. Stone and other Voyager scientists I spoke with cautioned me not to conflate the boundary of interstellar space with that of the solar system. The solar system includes the distant Oort cloud, a spherical collection of cometlike bodies bound by the sun's gravity that may stretch halfway to the closest star. The Voyagers won't reach its near edge for at least another 300 years. But interstellar space lies much closer at hand. It begins where a phenomenon called the solar wind ends.

Like all stars, the sun emits a constant flow of charged particles and magnetic fields—the solar wind. Moving at hypersonic speeds, the wind blows out from the sun like an inflating balloon, forming what astronomers call the heliosphere. As the solar wind billows into space, it pulls the sun's magnetic field along for the ride. Eventually pressure from interstellar matter checks the heliosphere's expansion, creating a boundary—preceded by an enormous shock front, the “termination shock”—with interstellar space. Before the Voyagers' journeys, estimates of the distance to that boundary with interstellar space, known as the heliopause, varied wildly.

“Frankly, some of them were just guesses,” according to Gurnett. One early guesstimate located the heliopause as close as Jupiter. Gurnett's own calculations, made in 1993, set the distance at anywhere from 116 to 177 astronomical units, or AU—about 25 times more distant. (One AU is the distance between Earth and the sun, equal to 93 million miles.) Those numbers, he says, were not very popular with his colleagues. By 1993 Voyager 1 already had 50 AU on its odometer. “If [the heliopause] was at 120 AU, that meant we had another 70 AU to go.” If Gurnett was right, the Voyagers, clipping along at about 3.5 AU a year, wouldn't exit the heliosphere for at least another two decades.

That prediction raised troubling questions: would the Voyagers—or the support of Congress—last that long? The mission's funding had been extended on the expectation that the spacecraft would cross the heliopause at about 50 AU. But the spacecraft left that milestone behind without finding any of the anticipated signs of interstellar transit. Astronomers had expected the Voyagers to detect a sudden surge in galactic cosmic rays—high-energy particles sprayed like shrapnel at nearly the speed of light from supernovae and other deep-space cataclysms. The vast magnetic cocoon formed by the heliosphere deflects most low-energy cosmic rays before they can reach the inner solar system. “[It] shields us from at least 75 percent of what's out there,” Stone says.

The Voyager ground team was also waiting for the spacecraft to register a shift in the prevailing magnetic field. The interstellar magnetic field, thought to be generated by nearby stars and vast clouds of ionized gases, would presumably have a different orientation from the magnetic field of the heliosphere. But the Voyagers had detected no such change.

Gurnett's 1993 estimates were prescient. Almost 20 years passed before one of the Voyagers finally made it to the heliopause. During that time the mission narrowly survived threats to its funding, and the Voyager team shrank from hundreds of scientists and engineers to a few dozen close-knit lifers. Most of them remain on the job today. “When you have such a long-lived mission, you start to regard people like family,” Spilker says. “We had our kids around the same time. We'd take vacations together. We're spanning multiple generations now, and some of the younger people on Voyager were not even born [when the spacecraft] launched.”

The tenacity and commitment of that band of brothers and sisters were rewarded on August 25, 2012, when Voyager 1 finally crossed the heliopause. But some of the data it returned were baffling. “We delayed announcing that we had reached interstellar space because we couldn't come to an agreement on the fact,” Cummings says. “There was lots of debate for about a year.”

Although Voyager 1 had indeed found the expected jump in plasma density—its plasma-wave detector, an instrument designed by Gurnett, inferred an 80-fold increase—there was no sign of a change in the direction of the ambient magnetic field. If the vehicle had crossed from an area permeated by the sun's magnetic field to a region where the magnetic field derived from other stars, shouldn't that switch have been noticeable? “That was a shocker,” Cummings says. “And that still bothers me. But a lot of people are coming to grips with it.”

When Voyager 2 reached the interstellar shoreline in November 2018, it, too, failed to detect a magnetic field shift. And the spacecraft added yet another puzzle: it encountered the heliopause at 120 AU from Earth—the same distance marked by its twin six years earlier. That did not jibe with any theoretical models, all of which said the heliosphere should expand and contract in sync with the sun's 11-year cycle. During that period the solar wind ebbs and surges. Voyager 2 arrived when the solar wind was peaking, which, if the models were correct, should have pushed the heliopause farther out than 120 AU. “It was unexpected by all the theorists,” Krimigis says. “I think the modeling, in terms of the findings of the Voyagers, has been found wanting.”

Now that the Voyagers are giving theorists some real field data, their models of the interaction between the heliosphere and the interstellar environment are becoming more complex. “The sort of general picture is that [our sun] emerged from a hot, ionized region” and entered a spotty, partly ionized area in the galaxy, says Gary Zank, an astrophysicist at the University of Alabama in Huntsville. The hot region likely formed in the aftermath of a supernova—some nearby ancient star, or perhaps a few, exploded at the end of its life and heated up the space, stripping electrons off their atoms in the process. The boundary around that region can be thought of as “kind of like the seashore, with all the water and the waves swirling and mixed up. We're in that kind of turbulent region ... magnetic fields get twisted up, turned around. It's not like the smooth magnetic fields that theorists usually like to draw,” although the amount of turbulence seen can differ depending on the type of observation. The Voyagers' data show little field variation at large scales but many small-scale fluctuations around the heliopause, caused by the heliosphere's influence on the interstellar medium. At some point, it is thought, the spacecraft will leave those roiling shoals behind and at last encounter the unalloyed interstellar magnetic field.

Or maybe that picture is completely wrong. A few researchers believe that the Voyagers have not yet left the heliosphere. “There is no reason for the magnetic fields in the heliosphere and the interstellar medium to have exactly the same orientation,” says Len A. Fisk, a space plasma scientist at the University of Michigan and a former NASA administrator. For the past several years Fisk and George Gloeckler, a colleague at Michigan and a longtime Voyager mission scientist, have been working on a model of the heliosphere that pushes its edge out by another 40 AU.

Most people working in the field, however, have been convinced by the dramatic uptick in galactic cosmic rays and plasma density the Voyagers measured. “Given that,” Cummings says, “it's very difficult to argue that we're not really in interstellar space. But then again, it's not like everything fits. That's why we need an interstellar probe.”

McNutt has been pushing for such a mission for decades. He and his colleagues at Johns Hopkins recently completed a nearly 500-page report outlining plans for an interstellar probe that would launch in 2036 and potentially could reach the heliosphere within 15 years, shaving 20 years off Voyager 1's flight time. And unlike the Voyager missions, the interstellar probe would be designed specifically to study the outer edge of the heliosphere and its environs. Within the next two years the National Academies of Sciences, Engineering, and Medicine will decide whether the mission should be one of NASA's priorities for the next decade.

An interstellar probe could answer one of the most fundamental questions about the heliosphere. “If I'm looking from the outside, what the devil does this structure look like?” McNutt asks. “We really don't know. It's like trying to understand what a goldfish bowl looks like from the point of view of the goldfish. We [need to] be able to see the bowl from the outside.” In some models, as the heliosphere cruises along at 450,000 mph, interstellar matter flows smoothly past it, like water around the bow of a ship, resulting in an overall cometlike shape. One recent computer model, developed by astronomer Merav Opher and her colleagues at Boston University, predicts that more turbulent dynamics give the heliosphere a shape like a cosmic croissant.

“You can start multiple fights at any good science conference about that,” McNutt says, “but it's going to take getting out there and actually making some measurements to be able to see what's going on. It would be nice to know what the neighborhood looks like.”

Some things outlive their purpose—answering machines, VCRs, pennies. Not the Voyagers—they transcended theirs, using 50-year-old technology. “The amount of software on these instruments is slim to none,” Krimigis says. “There are no microprocessors—they didn't exist!” The Voyagers' designers could not rely on thousands of lines of code to help operate the spacecraft. “On the whole,” Krimigis says, “I think the mission lasted so long because almost everything was hardwired. Today's engineers don't know how to do this. I don't know if it's even possible to build such a simple spacecraft [now]. Voyager is the last of its kind.”

It won't be easy to say goodbye to these trailblazing vehicles. “It's hard to see it come to an end,” Cummings says. “But we did achieve something really amazing. It could have been that we never got to the heliopause, but we did.”

Voyager 2 now has five remaining functioning instruments, and Voyager 1 has four. All are powered by a device that converts heat from the radioactive decay of plutonium into electricity. But with the power output decreasing by about four watts a year, NASA has been forced into triage mode. Two years ago the mission's engineers turned off the heater for the cosmic-ray detector, which had been crucial in determining the heliopause transit. Everyone expected the instrument to die.

“The temperature dropped like 60 or 70 degrees C, well outside any tested operating limits,” Spilker says, “and the instrument kept working. It was incredible.”

The last two Voyager instruments to turn off will probably be a magnetometer and the plasma science instrument. They are contained in the body of the spacecraft, where they are warmed by heat emitted from computers. The other instruments are suspended on a 43-foot-long fiberglass boom. “And so when you turn the heaters off,” Dodd says, “those instruments get very, very cold.”

How much longer might the Voyagers last? “If everything goes really well, maybe we can get the missions extended into the 2030s,” Spilker says. “It just depends on the power. That's the limiting point.”

TINY SPECK: Among Voyager 1’s last photographs was this shot of Earth seen from 3.8 billion miles away, dubbed the “Pale Blue Dot” by Voyager scientist Carl Sagan. Credit: NASA/JPL-Caltech

Even after the Voyagers are completely muted, their journeys will continue. In another 16,700 years, Voyager 1 will pass our nearest neighboring star, Proxima Centauri, followed 3,600 years later by Voyager 2. Then they will continue to circle the galaxy for millions of years. They will still be out there, more or less intact, eons after our sun has collapsed and the heliosphere is no more, not to mention one Pale Blue Dot. At some point in their travels, they may manage to convey a final message. It won't be transmitted by radio, and if it's received, the recipients won't be human.

The message is carried on another kind of vintage technology: two records. Not your standard plastic version, though. These are made of copper, coated with gold and sealed in an aluminum cover. Encoded in the grooves of the Golden Records , as they are called, are images and sounds meant to give some sense of the world the Voyagers came from. There are pictures of children, dolphins, dancers and sunsets; the sounds of crickets, falling rain and a mother kissing her child; and 90 minutes of music, including Bach's Brandenburg Concerto No. 2 and Chuck Berry's “Johnny B. Goode.”

And there is a message from Jimmy Carter, who was the U.S. president when the Voyagers were launched. “We cast this message into the cosmos,” it reads in part. “We hope someday, having solved the problems we face, to join a community of galactic civilizations. This record represents our hope and our determination, and our good will in a vast and awesome universe.”

*Editor’ Note (6/22/22): This paragraph was edited after posting to correct the description of when NASA began shutting down nonessential components of the Voyager spacecraft.

Tim Folger is a freelance journalist who writes for National Geographic , Discover , and other national publications.

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March 18, 2024

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As Voyager 1's mission draws to a close, one planetary scientist reflects on its legacy

by Daniel Strain, University of Colorado at Boulder

For nearly 50 years, NASA's Voyager 1 mission has competed for the title of deep space's little engine that could. Launched in 1977 along with its twin, Voyager 2, the spacecraft is now soaring more than 15 billion miles from Earth.

On their journeys through the solar system , the Voyager spacecraft beamed startling images back to Earth—of Jupiter and Saturn, then Uranus and Neptune and their moons. Voyager 1's most famous shot may be what famed astronomer Carl Sagan called the "pale blue dot," a lonely image of Earth taken from 6 billion miles away in 1990.

But Voyager 1's trek could now be drawing to a close. Since December, the spacecraft--which weighs less than most cars--has been sending nonsensical messages back to Earth, and engineers are struggling to fix the problem. Voyager 2 remains operational.

Fran Bagenal is a planetary scientist at the Laboratory for Atmospheric and Space Physics (LASP) at CU Boulder. She started working on the Voyager mission during a summer student job in the late 1970s and has followed the two spacecraft closely since.

To celebrate Voyager 1, Bagenal reflects on the mission's legacy—and which planet she wants to visit again.

Many are impressed that the spacecraft has kept going for this long. Do you agree?

Voyager 1's computer was put together in the 1970s, and there are very few people around who still use those computing languages. The communication rate is 40 bits per second. Not megabits. Not kilobits. Forty bits per second. Moreover, the round-trip communication time is 45 hours. It's amazing that they're still communicating with it at all.

What was it like working on Voyager during the mission's early days?

At the very beginning, we used computer punch cards. The data was on magnetic tapes, and we would print out line-plots on reels of paper. It was very primitive.

But planet by planet, with each flyby, the technology got a lot more sophisticated. By the time we got to Neptune in 1989, we were doing our science on much more efficient computers, and NASA presented its results live across the globe over an early version of the internet.

Think about it—going from punch cards to the internet in 12 years.

How did the Voyager spacecraft shape our understanding of the solar system?

First of all, the pictures were jaw-dropping. They were the first high-quality, close-up pictures of the four gas giant planets and their moons. The Voyagers really revolutionized our thinking by going from one planet to the other and comparing them.

Jupiter and Saturn's ammonia white and orange clouds, for example, were violently swept around by strong winds, while Uranus and Neptune's milder weather systems were hidden and colored blue by atmospheric methane. But the most dramatic discoveries were the multiple distinct worlds of the different moons, from Jupiter's cratered Callisto and volcanic Io to Saturn's cloudy Titan to plumes erupting on Triton, a moon of Neptune.

The Jupiter and Saturn systems have since been explored in greater detail by orbiting missions—Galileo and Juno at Jupiter, Cassini at Saturn.

Voyager 2 is the only spacecraft that has visited Uranus and Neptune. Do we need to return?

My vote is to return to Uranus—the only planet in our solar system that's tipped on its side.

We didn't know before Voyager whether Uranus had a magnetic field. When we arrived, we found that Uranus has a magnetic field that's severely tilted with respect to the planet's rotation. That's a weird magnetic field.

Jupiter, Saturn and Neptune all emit a lot of heat from the inside. They glow in the infrared, emitting two and a half times more energy than they receive from the sun. These things are hot.

Uranus isn't the same. It doesn't have this internal heat source. So maybe, just maybe, at the end of the formation of the solar system billions of years ago, some big object hit Uranus, tipped it on its side, stirred it up and dissipated the heat. Perhaps, this led to an irregular magnetic field .

These are the sorts of questions that were raised by Voyager 30 years ago. Now we need to go back.

Culturally, Voyager 1's most lasting impact may be the 'pale blue dot.' Why?

I have huge respect for Carl Sagan. I met him when I was 16, a high school student in England, and I shook his hand.

He pointed to the Voyager image and said, "Here we are. We're leaving the solar system. We're looking back, and there's this pale blue dot. That's us. It's all our friends. It's all our relatives. It's where we live and die."

This was the time we were just beginning to say, "Wait a minute. What are we doing to our planet Earth?" He was awakening or reinforcing this need to think about what humans are doing to Earth. It also evoked why we need to go exploring space: to think about where we are and how we fit into the solar system.

How are you feeling now that Voyager 1's mission may be coming to an end?

It's amazing. No one thought they would go this far. But with just a few instruments working, how much longer can we keep going? I think it will soon be time to say, "Right, jolly good. Extraordinary job. Well done."

Provided by University of Colorado at Boulder

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NASA's Voyager 1 spacecraft is talking nonsense. Its friends on Earth are worried

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This artist's impression shows one of the Voyager spacecraft moving through the darkness of space. NASA/JPL-Caltech hide caption

This artist's impression shows one of the Voyager spacecraft moving through the darkness of space.

The last time Stamatios "Tom" Krimigis saw the Voyager 1 space probe in person, it was the summer of 1977, just before it launched from Cape Canaveral, Florida.

Now Voyager 1 is over 15 billion miles away, beyond what many consider to be the edge of the solar system. Yet the on-board instrument Krimigis is in charge of is still going strong.

"I am the most surprised person in the world," says Krimigis — after all, the spacecraft's original mission to Jupiter and Saturn was only supposed to last about four years.

These days, though, he's also feeling another emotion when he thinks of Voyager 1.

"Frankly, I'm very worried," he says.

Ever since mid-November, the Voyager 1 spacecraft has been sending messages back to Earth that don't make any sense. It's as if the aging spacecraft has suffered some kind of stroke that's interfering with its ability to speak.

"It basically stopped talking to us in a coherent manner," says Suzanne Dodd of NASA's Jet Propulsion Laboratory, who has been the project manager for the Voyager interstellar mission since 2010. "It's a serious problem."

Instead of sending messages home in binary code, Voyager 1 is now just sending back alternating 1s and 0s. Dodd's team has tried the usual tricks to reset things — with no luck.

It looks like there's a problem with the onboard computer that takes data and packages it up to send back home. All of this computer technology is primitive compared to, say, the key fob that unlocks your car, says Dodd.

"The button you press to open the door of your car, that has more compute power than the Voyager spacecrafts do," she says. "It's remarkable that they keep flying, and that they've flown for 46-plus years."

Each of the Voyager probes carries an American flag and a copy of a golden record that can play greetings in many languages. NASA/JPL-Caltech hide caption

Each of the Voyager probes carries an American flag and a copy of a golden record that can play greetings in many languages.

Voyager 1 and its twin, Voyager 2, have outlasted many of those who designed and built them. So to try to fix Voyager 1's current woes, the dozen or so people on Dodd's team have had to pore over yellowed documents and old mimeographs.

"They're doing a lot of work to try and get into the heads of the original developers and figure out why they designed something the way they did and what we could possibly try that might give us some answers to what's going wrong with the spacecraft," says Dodd.

She says that they do have a list of possible fixes. As time goes on, they'll likely start sending commands to Voyager 1 that are more bold and risky.

"The things that we will do going forward are probably more challenging in the sense that you can't tell exactly if it's going to execute correctly — or if you're going to maybe do something you didn't want to do, inadvertently," says Dodd.

Linda Spilker , who serves as the Voyager mission's project scientist at NASA's Jet Propulsion Laboratory, says that when she comes to work she sees "all of these circuit diagrams up on the wall with sticky notes attached. And these people are just having a great time trying to troubleshoot, you know, the 60's and 70's technology."

"I'm cautiously optimistic," she says. "There's a lot of creativity there."

Still, this is a painstaking process that could take weeks, or even months. Voyager 1 is so distant, it takes almost a whole day for a signal to travel out there, and then a whole day for its response to return.

"We'll keep trying," says Dodd, "and it won't be quick."

In the meantime, Voyager's 1 discombobulation is a bummer for researchers like Stella Ocker , an astronomer with Caltech and the Carnegie Observatories

"We haven't been getting science data since this anomaly started," says Ocker, "and what that means is that we don't know what the environment that the spacecraft is traveling through looks like."

After 35 Years, Voyager Nears Edge Of Solar System

That interstellar environment isn't just empty darkness, she says. It contains stuff like gas, dust, and cosmic rays. Only the twin Voyager probes are far out enough to sample this cosmic stew.

"The science that I'm really interested in doing is actually only possible with Voyager 1," says Ocker, because Voyager 2 — despite being generally healthy for its advanced age — can't take the particular measurements she needs for her research.

Even if NASA's experts and consultants somehow come up with a miraculous plan that can get Voyager 1 back to normal, its time is running out.

The two Voyager probes are powered by plutonium, but that power system will eventually run out of juice. Mission managers have turned off heaters and taken other measures to conserve power and extend the Voyager probes' lifespan.

"My motto for a long time was 50 years or bust," says Krimigis with a laugh, "but we're sort of approaching that."

In a couple of years, the ebbing power supply will force managers to start turning off science instruments, one by one. The very last instrument might keep going until around 2030 or so.

When the power runs out and the probes are lifeless, Krimigis says both of these legendary space probes will basically become "space junk."

"It pains me to say that," he says. While Krimigis has participated in space missions to every planet, he says the Voyager program has a special place in his heart.

Spilker points out that each spacecraft will keep moving outward, carrying its copy of a golden record that has recorded greetings in many languages, along with the sounds of Earth.

"The science mission will end. But a part of Voyager and a part of us will continue on in the space between the stars," says Spilker, noting that the golden records "may even outlast humanity as we know it."

Krimigis, though, doubts that any alien will ever stumble across a Voyager probe and have a listen.

"Space is empty," he says, "and the probability of Voyager ever running into a planet is probably slim to none."

It will take about 40,000 years for Voyager 1 to approach another star; it will come within 1.7 light years of what NASA calls "an obscure star in the constellation Ursa Minor" — also known as the Little Dipper.

If NASA greenlights this interstellar mission, it could last 100 years

Knowing that the Voyager probes are running out of time, scientists have been drawing up plans for a new mission that, if funded and launched by NASA, would send another probe even farther out into the space between stars.

"If it happens, it would launch in the 2030s," says Ocker, "and it would reach twice as far as Voyager 1 in just 50 years."

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NASA finds clue while solving Voyager 1's communication breakdown case

An outlier signal has brought ground control closer to decoding the troubling problem.

NASA engineers are a step closer to solving the communication problem that left the Voyager 1 spacecraft, which presently sits outside the solar system, unable to send usable data back to Earth.

In 2012, Voyager 1 became the first human-made object to leave the solar system and enter interstellar space . For 11 years following this achievement, the spacecraft dutifully sent data to ground control. This was data that detailed how space works beyond the influence of the sun. In Nov. 2023, however, Voyager 1's communications with ground operators stopped making sense. 

To be clear, however, Voyager 2 , which followed its spacecraft sibling out of the solar system in 2018, is still operational and communicating with Earth.

"Effectively, the call between the spacecraft and the Earth was still connected, but Voyager's 'voice' was replaced with a monotonous dial tone," Voyager 1's engineering team previously told Space.com .

The source of the issue appears to be one of Voyager 1's three onboard computers: The flight data subsystem (FDS). This computer, NASA says , is responsible for packaging science and engineering data before it's sent to Earth by the spacecraft's telemetry modulation unit.

Related: NASA's Voyager 1 glitch has scientists sad yet hopeful: 'Voyager 2 is still going strong'

The positive step towards solving communications issues between ground control and Voyager 1 came on March 3 when the Voyager mission team detected activity from one section of the FDS that was different from the rest of the computer’s garbled data stream.

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Voyager 1's messaging to Earth comes in the form of 1s and 0s, a computer language called binary code — but since the end of last year, this code has carried no meaning. Even the newly detected signal is still not in the correct format Voyager 1 should be using when FDS is functioning as designed, meaning the operating team was initially not quite sure what to make of it.

This changed, however, when an engineer at NASA's Deep Space Network , which is tasked with operating radio antennas that communicate with Voyager 1 and its interstellar sibling Voyager 2, as well as other NASA spacecraft closer to home, got a look at the code. The unnamed engineer was able to decode the outlier signal, discovering that it contained a readout of the FDS' entire memory.

Encoded with the FDS memory are performance instructions and code values that can change either if the spacecraft's status changes or if commanded to do so. Science and engineering data to be sent back to Earth are also locked up in the memory. 

The team will now compare this new signal, which occurred because of a prompt, or "poke," from mission control, to data that was sent back to Earth just before Voyager 1 started spouting binary nonsense. Finding discrepancies between regular Voyager 1 data and this poke-prompted signal will help the crew hunt for the source of the issue. The idea of the poke was to prompt FDS to try using different sequences in its software package and determine if the communication issue could be resolved by navigating around a corrupted or damaged section.

—  Voyager 2: An iconic spacecraft that's still exploring 45 years on

—  NASA's interstellar Voyager probes get software updates beamed from 12 billion miles away

—  NASA Voyager 2 spacecraft extends its interstellar science mission for 3 more years

Voyager 1 is currently around 15 billion miles (24 billion kilometers) from Earth, meaning that solving communication issues can be a painstaking process. It takes 22.5 hours to receive a radio signal from Voyager 1, then another 22.5 hours to receive a response via the Deep Space Network's antennas.

That means the results of NASA's poke were received on March 3, and on March 7 engineers started working to decode this signal. Three days later they determined the signal contains an FDS memory readout.

NASA scientists and engineers will continue to analyze this readout to restore communication with the pioneering space mission that extended humanity's reach beyond the solar system.

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].

Robert Lea is a science journalist in the U.K. whose articles have been published in Physics World, New Scientist, Astronomy Magazine, All About Space, Newsweek and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.’s Open University. Follow him on Twitter @sciencef1rst.

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Hubble Provides Interstellar Road Map for Voyagers’ Galactic Trek

NASA’s two Voyager spacecraft are hurtling through unexplored territory on their road trip beyond our solar system. Along the way, they are measuring the interstellar medium, the mysterious environment between stars. NASA’s Hubble Space Telescope is providing the road map – by measuring the material along the probes’ future trajectories. Even after the Voyagers run out of electrical power and are unable to send back new data, which may happen in about a decade, astronomers can use Hubble observations to characterize the environment through which these silent ambassadors will glide.

A preliminary analysis of the Hubble observations reveals a rich, complex interstellar ecology, containing multiple clouds of hydrogen laced with other elements. Hubble data, combined with the Voyagers, have also provided new insights into how our sun travels through interstellar space.

“This is a great opportunity to compare data from in situ measurements of the space environment by the Voyager spacecraft and telescopic measurements by Hubble,” said study leader Seth Redfield of Wesleyan University in Middletown, Connecticut. “The Voyagers are sampling tiny regions as they plow through space at roughly 38,000 miles per hour. But we have no idea if these small areas are typical or rare. The Hubble observations give us a broader view because the telescope is looking along a longer and wider path. So Hubble gives context to what each Voyager is passing through.”

The astronomers hope that the Hubble observations will help them characterize the physical properties of the local interstellar medium. “Ideally, synthesizing these insights with in situ measurements from Voyager would provide an unprecedented overview of the local interstellar environment,” said Hubble team member Julia Zachary of Wesleyan University.

The team’s results will be presented Jan. 6 at the winter meeting of the American Astronomical Society in Grapevine, Texas.

NASA launched the twin Voyager 1 and 2 spacecraft in 1977. Both explored the outer planets Jupiter and Saturn. Voyager 2 went on to visit Uranus and Neptune.

The pioneering Voyager spacecraft are currently exploring the outermost edge of the sun’s domain . Voyager 1 is now zooming through interstellar space, the region between the stars that is filled with gas, dust, and material recycled from dying stars.

Voyager 1 is 13 billion miles from Earth, making it the farthest human-made object ever built. In about 40,000 years, after the spacecraft will no longer be operational and will not be able to gather new data, it will pass within 1.6 light-years of the star Gliese 445, in the constellation Camelopardalis. Its twin, Voyager 2, is 10.5 billion miles from Earth, and will pass 1.7 light-years from the star Ross 248 in about 40,000 years.

For the next 10 years, the Voyagers will be making measurements of interstellar material, magnetic fields and cosmic rays along their trajectories. Hubble complements the Voyagers’ observations by gazing at two sight lines along each spacecraft’s path to map interstellar structure along their star-bound routes. Each sight line stretches several light-years to nearby stars. Sampling the light from those stars, Hubble’s Space Telescope Imaging Spectrograph measures how interstellar material absorbs some of the starlight, leaving telltale spectral fingerprints.

Hubble found that Voyager 2 will move out of the interstellar cloud that surrounds the solar system in a couple thousand years. The astronomers, based on Hubble data, predict that the spacecraft will spend 90,000 years in a second cloud and pass into a third interstellar cloud.

An inventory of the clouds’ composition reveals slight variations in the abundances of the chemical elements contained in the structures. “These variations could mean the clouds formed in different ways, or from different areas, and then came together,” Redfield said.

An initial look at the Hubble data also suggests that the sun is passing through clumpier material in nearby space, which may affect the heliosphere, the large bubble containing our solar system that is produced by our sun’s powerful solar wind. At its boundary, called the heliopause, the solar wind pushes outward against the interstellar medium. Hubble and Voyager 1 made measurements of the interstellar environment beyond this boundary, where the wind comes from stars other than our sun.

“I’m really intrigued by the interaction between stars and the interstellar environment,” Redfield said. “These kinds of interactions are happening around most stars, and it is a dynamic process.”

The heliosphere is compressed when the sun moves through dense material, but it expands back out when the star passes through low-density matter. This expansion and contraction is caused by the interaction between the outward pressure of the stellar wind, composed of a stream of charged particles, and the pressure of the interstellar material surrounding a star.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C. The Voyagers were built by JPL, which continues to operate both spacecraft. JPL is a division of Caltech.

For images and more information about the local interstellar medium and Hubble, visit: http://www.nasa.gov/hubble

For more information about the Voyager mission, visit: www.nasa.gov/voyager

For additional information, contact:

Felicia Chou NASA Headquarters, Washington, D.C. 202-358-0257 [email protected]

Donna Weaver / Ray Villard Space Telescope Science Institute, Baltimore, Maryland 410-338-4493 / 410-338-4514 [email protected]  /  [email protected]

Elizabeth Landau Jet Propulsion Laboratory, Pasadena, Calif. 818-354-6425 [email protected]

Seth Redfield Wesleyan University, Middletown, Connecticut 860-685-3669 [email protected]

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• Goddard Space Flight Center
• Hubble Space Telescope

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Ailing voyager 1 spacecraft offers glimmer of hope to nasa.

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A NASA image of one of the Voyager space probes. Voyager 1 and its identical sister craft Voyager 2 ... [+] were launched in 1977 to study the outer Solar System and eventually interstellar space. (Photo by NASA/Hulton Archive/Getty Images)

NASA’s pioneering Voyager 1 spacecraft is adventuring beyond our solar system, but all is not well with the elderly machine. Voyager 1 has essentially been speaking gibberish since November and NASA has been involved in a long-distance troubleshooting operation ever since. A new development is giving scientists and engineers some reason for hope.

Voyager 1 launched in 1977 on a mission to study the outer solar system. It just kept on going and eventually crossed into interstellar space in 2012. It’s had a remarkable life, but NASA intends to maintain contact with the probe and continue to gather data from a part of the universe never before visited by an Earth spacecraft. The recent data issue put a pause on Voyager 1’s science work.

The culprit seems to be the flight data subsystem, which gathers data from the spacecraft’s science instruments and also monitors the probe’s health. The FDS is supposed to talk to a telemetry modulation unit that sends the data back to Earth. The data has been unintelligible and unusable, but on March 3, something changed. “The Voyager mission team saw activity from one section of the FDS that differed from the rest of the computer’s unreadable data stream,” NASA said in an update on March 13.

The new signal was confusing, but at least it was different. An engineer working with NASA’s Deep Space Network—the communications and tracking network that talks to Voyager 1—decoded the signal and discovered a readout of the FDS memory. “The FDS memory includes its code, or instructions for what to do, as well as variables, or values used in the code that can change based on commands or the spacecraft’s status,” said NASA. “It also contains science or engineering data for downlink.”

The Voyager 1 team is now engaged in a sleuthing exercise that will compare the readout with previous information from before the glitch. This might help NASA finally diagnose the problem and come up with a fix. The new signal wasn’t just random. NASA sent a command known as a “poke” to the spacecraft on March 1 to prompt the FDS to flex its software and find a workaround to whatever is causing the problem.

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It’s complicated enough to fix a spacecraft when it’s near Earth, but Voyager 1 is 15 billion miles away. A radio signal must travel 22.5 hours to reach the probe and then it takes another 22.5 hours to receive a response. That’s like troubleshooting while swimming in molasses. NASA is also dealing with decades-old hardware, software and documentation. “The team is analyzing the readout,” said NASA. “Using that information to devise a potential solution and attempt to put it into action will take time.”

Voyager 1 and its twin Voyager 2 launched when disco reigned and Star Wars was just getting started. The spacecraft were built to last five years, but have now been in operation for over 46 years. NASA has turned off some of Voyager 1’s science instruments over time, but the spacecraft still has life left in it if the team can work through the data issue. It’s too soon to count the space pioneer out.

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NASA optimistic about resolving Voyager 1 computer problem

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WASHINGTON — A NASA official says he is optimistic that a problem with the Voyager 1 spacecraft that has kept it from transmitting intelligible data for months can be resolved.

Speaking at a March 20 meeting of the National Academies’ Committee on Solar and Space Physics, Joseph Westlake, director of NASA’s heliophysics division, said it appeared possible to fix the computer problem on the nearly 50-year-old spacecraft that has disrupted operations since last November.

“I feel like we’re on a path now to resolution,” he said. “They’re on the right path and I think we’re going to get to a point where Voyager 1 is going to continue, alive and kicking in space.”

Spacecraft controllers first noticed a problem with the spacecraft in November, when the data transmitted by the spacecraft was unusable. Engineers concluded that the problem was with an onboard computer called the flight data system (FDS), which collects data from the spacecraft’s instruments and other spacecraft telemetry.

Several factors have hampered efforts to correct the problem. Voyager 1, launched in 1977, is now more than 24 billion kilometers from Earth, which means it takes 22.5 hours for signals to travel between Earth and the spacecraft. None of the people who developed the FDS in the early to mid 1970s are available to assist now, so the project has had to turn to documentation to help identify the problem.

NASA announced March 13 progress in fixing the FDS when a command called a “poke” was transmitted to Voyager, and the spacecraft responded by sending back a readout of its memory. The agency said at the time it will compare that readout to one transmitted before the problem to help identify the issue.

Westlake said at the committee meeting that the problem appears to be a corrupted memory unit on the spacecraft. “It’s a part failure on one of the memories and they’re looking for a way to move a couple hundred words of software from one region to another in the flight computer,” he said. A word is two bytes.

He did not estimate how long it would take to make those software changes. NASA, in its latest statement about the spacecraft, said that using the FDS memory readout “to devise a potential solution and attempt to put it into action will take time.”

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science... More by Jeff Foust

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• The Contents
• The Making of
• Where Are They Now
• Frequently Asked Questions
• Q & A with Ed Stone

golden record

Where are they now.

• frequently asked questions
• Q&A with Ed Stone

The Voyager Planetary Mission

The twin spacecraft Voyager 1 and Voyager 2 were launched by NASA in separate months in the summer of 1977 from Cape Canaveral, Florida. As originally designed, the Voyagers were to conduct closeup studies of Jupiter and Saturn, Saturn's rings, and the larger moons of the two planets.

To accomplish their two-planet mission, the spacecraft were built to last five years. But as the mission went on, and with the successful achievement of all its objectives, the additional flybys of the two outermost giant planets, Uranus and Neptune, proved possible -- and irresistible to mission scientists and engineers at the Voyagers' home at the Jet Propulsion Laboratory in Pasadena, California.

As the spacecraft flew across the solar system, remote-control reprogramming was used to endow the Voyagers with greater capabilities than they possessed when they left the Earth. Their two-planet mission became four. Their five-year lifetimes stretched to 12 and more.

Eventually, between them, Voyager 1 and 2 would explore all the giant outer planets of our solar system, 48 of their moons, and the unique systems of rings and magnetic fields those planets possess.

Had the Voyager mission ended after the Jupiter and Saturn flybys alone, it still would have provided the material to rewrite astronomy textbooks. But having doubled their already ambitious itineraries, the Voyagers returned to Earth information over the years that has revolutionized the science of planetary astronomy, helping to resolve key questions while raising intriguing new ones about the origin and evolution of the planets in our solar system.

History of the Voyager Mission

The Voyager mission was designed to take advantage of a rare geometric arrangement of the outer planets in the late 1970s and the 1980s which allowed for a four-planet tour for a minimum of propellant and trip time. This layout of Jupiter, Saturn, Uranus and Neptune, which occurs about every 175 years, allows a spacecraft on a particular flight path to swing from one planet to the next without the need for large onboard propulsion systems. The flyby of each planet bends the spacecraft's flight path and increases its velocity enough to deliver it to the next destination. Using this "gravity assist" technique, first demonstrated with NASA's Mariner 10 Venus/Mercury mission in 1973-74, the flight time to Neptune was reduced from 30 years to 12.

While the four-planet mission was known to be possible, it was deemed to be too expensive to build a spacecraft that could go the distance, carry the instruments needed and last long enough to accomplish such a long mission. Thus, the Voyagers were funded to conduct intensive flyby studies of Jupiter and Saturn only. More than 10,000 trajectories were studied before choosing the two that would allow close flybys of Jupiter and its large moon Io, and Saturn and its large moon Titan; the chosen flight path for Voyager 2 also preserved the option to continue on to Uranus and Neptune.

From the NASA Kennedy Space Center at Cape Canaveral, Florida, Voyager 2 was launched first, on August 20, 1977; Voyager 1 was launched on a faster, shorter trajectory on September 5, 1977. Both spacecraft were delivered to space aboard Titan-Centaur expendable rockets.

The prime Voyager mission to Jupiter and Saturn brought Voyager 1 to Jupiter on March 5, 1979, and Saturn on November 12, 1980, followed by Voyager 2 to Jupiter on July 9, 1979, and Saturn on August 25, 1981.

Voyager 1's trajectory, designed to send the spacecraft closely past the large moon Titan and behind Saturn's rings, bent the spacecraft's path inexorably northward out of the ecliptic plane -- the plane in which most of the planets orbit the Sun. Voyager 2 was aimed to fly by Saturn at a point that would automatically send the spacecraft in the direction of Uranus.

After Voyager 2's successful Saturn encounter, it was shown that Voyager 2 would likely be able to fly on to Uranus with all instruments operating. NASA provided additional funding to continue operating the two spacecraft and authorized JPL to conduct a Uranus flyby. Subsequently, NASA also authorized the Neptune leg of the mission, which was renamed the Voyager Neptune Interstellar Mission.

Voyager 2 encountered Uranus on January 24, 1986, returning detailed photos and other data on the planet, its moons, magnetic field and dark rings. Voyager 1, meanwhile, continues to press outward, conducting studies of interplanetary space. Eventually, its instruments may be the first of any spacecraft to sense the heliopause -- the boundary between the end of the Sun's magnetic influence and the beginning of interstellar space. (Voyager 1 entered Interstellar Space on August 25, 2012.)

Following Voyager 2's closest approach to Neptune on August 25, 1989, the spacecraft flew southward, below the ecliptic plane and onto a course that will take it, too, to interstellar space. Reflecting the Voyagers' new transplanetary destinations, the project is now known as the Voyager Interstellar Mission.

Voyager 1 is now leaving the solar system, rising above the ecliptic plane at an angle of about 35 degrees at a rate of about 520 million kilometers (about 320 million miles) a year. Voyager 2 is also headed out of the solar system, diving below the ecliptic plane at an angle of about 48 degrees and a rate of about 470 million kilometers (about 290 million miles) a year.

Both spacecraft will continue to study ultraviolet sources among the stars, and the fields and particles instruments aboard the Voyagers will continue to search for the boundary between the Sun's influence and interstellar space. The Voyagers are expected to return valuable data for two or three more decades. Communications will be maintained until the Voyagers' nuclear power sources can no longer supply enough electrical energy to power critical subsystems.

The cost of the Voyager 1 and 2 missions -- including launch, mission operations from launch through the Neptune encounter and the spacecraft's nuclear batteries (provided by the Department of Energy) -- is $865 million. NASA budgeted an additional $30 million to fund the Voyager Interstellar Mission for two years following the Neptune encounter.

Voyagers 1 and 2 are identical spacecraft. Each is equipped with instruments to conduct 10 different experiments. The instruments include television cameras, infrared and ultraviolet sensors, magnetometers, plasma detectors, and cosmic-ray and charged-particle sensors. In addition, the spacecraft radio is used to conduct experiments.

The Voyagers travel too far from the Sun to use solar panels; instead, they were equipped with power sources called radioisotope thermoelectric generators (RTGs). These devices, used on other deep space missions, convert the heat produced from the natural radioactive decay of plutonium into electricity to power the spacecraft instruments, computers, radio and other systems.

The spacecraft are controlled and their data returned through the Deep Space Network (DSN), a global spacecraft tracking system operated by JPL for NASA. DSN antenna complexes are located in California's Mojave Desert; near Madrid, Spain; and in Tidbinbilla, near Canberra, Australia.

The Voyager project manager for the Interstellar Mission is George P. Textor of JPL. The Voyager project scientist is Dr. Edward C. Stone of the California Institute of Technology. The assistant project scientist for the Jupiter flyby was Dr. Arthur L. Lane, followed by Dr. Ellis D. Miner for the Saturn, Uranus and Neptune encounters. Both are with JPL.

JUPITER Voyager 1 made its closest approach to Jupiter on March 5, 1979, and Voyager 2 followed with its closest approach occurring on July 9, 1979. The first spacecraft flew within 277,400 kilometers (172,368 miles) of the planet's cloud tops, and Voyager 2 came within 650,180 kilometers (404,003 miles).

Jupiter is the largest planet in the solar system, composed mainly of hydrogen and helium, with small amounts of methane, ammonia, water vapor, traces of other compounds and a core of melted rock and ice. Colorful latitudinal bands and atmospheric clouds and storms illustrate Jupiter's dynamic weather system. The giant planet is now known to possess 16 moons. The planet completes one orbit of the Sun each 11.8 years and its day is 9 hours, 55 minutes.

Although astronomers had studied Jupiter through telescopes on Earth for centuries, scientists were surprised by many of the Voyager findings.

The Great Red Spot was revealed as a complex storm moving in a counterclockwise direction. An array of other smaller storms and eddies were found throughout the banded clouds.

Discovery of active volcanism on the satellite Io was easily the greatest unexpected discovery at Jupiter. It was the first time active volcanoes had been seen on another body in the solar system. Together, the Voyagers observed the eruption of nine volcanoes on Io, and there is evidence that other eruptions occurred between the Voyager encounters.

Plumes from the volcanoes extend to more than 300 kilometers (190 miles) above the surface. The Voyagers observed material ejected at velocities up to a kilometer per second.

Io's volcanoes are apparently due to heating of the satellite by tidal pumping. Io is perturbed in its orbit by Europa and Ganymede, two other large satellites nearby, then pulled back again into its regular orbit by Jupiter. This tug-of-war results in tidal bulging as great as 100 meters (330 feet) on Io's surface, compared with typical tidal bulges on Earth of one meter (three feet).

It appears that volcanism on Io affects the entire jovian system, in that it is the primary source of matter that pervades Jupiter's magnetosphere -- the region of space surrounding the planet influenced by the jovian magnetic field. Sulfur, oxygen and sodium, apparently erupted by Io's many volcanoes and sputtered off the surface by impact of high-energy particles, were detected as far away as the outer edge of the magnetosphere millions of miles from the planet itself.

Europa displayed a large number of intersecting linear features in the low-resolution photos from Voyager 1. At first, scientists believed the features might be deep cracks, caused by crustal rifting or tectonic processes. The closer high-resolution photos from Voyager 2, however, left scientists puzzled: The features were so lacking in topographic relief that as one scientist described them, they "might have been painted on with a felt marker." There is a possibility that Europa may be internally active due to tidal heating at a level one-tenth or less than that of Io. Europa is thought to have a thin crust (less than 30 kilometers or 18 miles thick) of water ice, possibly floating on a 50-kilometer-deep (30-mile) ocean.

Ganymede turned out to be the largest moon in the solar system, with a diameter measuring 5,276 kilometers (3,280 miles). It showed two distinct types of terrain -- cratered and grooved -- suggesting to scientists that Ganymede's entire icy crust has been under tension from global tectonic processes.

Callisto has a very old, heavily cratered crust showing remnant rings of enormous impact craters. The largest craters have apparently been erased by the flow of the icy crust over geologic time. Almost no topographic relief is apparent in the ghost remnants of the immense impact basins, identifiable only by their light color and the surrounding subdued rings of concentric ridges.

A faint, dusty ring of material was found around Jupiter. Its outer edge is 129,000 kilometers (80,000 miles) from the center of the planet, and it extends inward about 30,000 kilometers (18,000 miles).

Two new, small satellites, Adrastea and Metis, were found orbiting just outside the ring. A third new satellite, Thebe, was discovered between the orbits of Amalthea and Io.

Jupiter's rings and moons exist within an intense radiation belt of electrons and ions trapped in the planet's magnetic field. These particles and fields comprise the jovian magnetosphere, or magnetic environment, which extends three to seven million kilometers toward the Sun, and stretches in a windsock shape at least as far as Saturn's orbit -- a distance of 750 million kilometers (460 million miles).

As the magnetosphere rotates with Jupiter, it sweeps past Io and strips away about 1,000 kilograms (one ton) of material per second. The material forms a torus, a doughnut-shaped cloud of ions that glow in the ultraviolet. Some of the torus's heavy ions migrate outward, and their pressure inflates the Jovian magnetosphere, while the more energetic sulfur and oxygen ions fall along the magnetic field into the planet's atmosphere, resulting in auroras.

Io acts as an electrical generator as it moves through Jupiter's magnetic field, developing 400,000 volts across its diameter and generating an electric current of 3 million amperes that flows along the magnetic field to the planet's ionosphere.

SATURN The Voyager 1 and 2 Saturn flybys occurred nine months apart, with the closest approaches falling on November 12 and August 25, 1981. Voyager 1 flew within 64,200 kilometers (40,000 miles) of the cloud tops, while Voyager 2 came within 41,000 kilometers (26,000 miles).

Saturn is the second largest planet in the solar system. It takes 29.5 Earth years to complete one orbit of the Sun, and its day was clocked at 10 hours, 39 minutes. Saturn is known to have at least 17 moons and a complex ring system. Like Jupiter, Saturn is mostly hydrogen and helium. Its hazy yellow hue was found to be marked by broad atmospheric banding similar to but much fainter than that found on Jupiter. Close scrutiny by Voyager's imaging systems revealed long-lived ovals and other atmospheric features generally smaller than those on Jupiter.

Perhaps the greatest surprises and the most puzzles were found by the Voyagers in Saturn's rings. It is thought that the rings formed from larger moons that were shattered by impacts of comets and meteoroids. The resulting dust and boulder- to house-size particles have accumulated in a broad plane around the planet varying in density.

The irregular shapes of Saturn's eight smallest moons indicates that they too are fragments of larger bodies. Unexpected structure such as kinks and spokes were found in addition to thin rings and broad, diffuse rings not observed from Earth. Much of the elaborate structure of some of the rings is due to the gravitational effects of nearby satellites. This phenomenon is most obviously demonstrated by the relationship between the F-ring and two small moons that "shepherd" the ring material. The variation in the separation of the moons from the ring may the ring's kinked appearance. Shepherding moons were also found by Voyager 2 at Uranus.

Radial, spoke-like features in the broad B-ring were found by the Voyagers. The features are believed to be composed of fine, dust-size particles. The spokes were observed to form and dissipate in time-lapse images taken by the Voyagers. While electrostatic charging may create spokes by levitating dust particles above the ring, the exact cause of the formation of the spokes is not well understood.

Winds blow at extremely high speeds on Saturn -- up to 1,800 kilometers per hour (1,100 miles per hour). Their primarily easterly direction indicates that the winds are not confined to the top cloud layer but must extend at least 2,000 kilometers (1,200 miles) downward into the atmosphere. The characteristic temperature of the atmosphere is 95 kelvins.

Saturn holds a wide assortment of satellites in its orbit, ranging from Phoebe, a small moon that travels in a retrograde orbit and is probably a captured asteroid, to Titan, the planet-sized moon with a thick nitrogen-methane atmosphere. Titan's surface temperature and pressure are 94 kelvins (-292 Fahrenheit) and 1.5 atmospheres. Photochemistry converts some atmospheric methane to other organic molecules, such as ethane, that is thought to accumulate in lakes or oceans. Other more complex hydrocarbons form the haze particles that eventually fall to the surface, coating it with a thick layer of organic matter. The chemistry in Titan's atmosphere may strongly resemble that which occurred on Earth before life evolved.

The most active surface of any moon seen in the Saturn system was that of Enceladus. The bright surface of this moon, marked by faults and valleys, showed evidence of tectonically induced change. Voyager 1 found the moon Mimas scarred with a crater so huge that the impact that caused it nearly broke the satellite apart.

Saturn's magnetic field is smaller than Jupiter's, extending only one or two million kilometers. The axis of the field is almost perfectly aligned with the rotation axis of the planet.

URANUS In its first solo planetary flyby, Voyager 2 made its closest approach to Uranus on January 24, 1986, coming within 81,500 kilometers (50,600 miles) of the planet's cloud tops.

Uranus is the third largest planet in the solar system. It orbits the Sun at a distance of about 2.8 billion kilometers (1.7 billion miles) and completes one orbit every 84 years. The length of a day on Uranus as measured by Voyager 2 is 17 hours, 14 minutes.

Uranus is distinguished by the fact that it is tipped on its side. Its unusual position is thought to be the result of a collision with a planet-sized body early in the solar system's history. Given its odd orientation, with its polar regions exposed to sunlight or darkness for long periods, scientists were not sure what to expect at Uranus.

Voyager 2 found that one of the most striking influences of this sideways position is its effect on the tail of the magnetic field, which is itself tilted 60 degrees from the planet's axis of rotation. The magnetotail was shown to be twisted by the planet's rotation into a long corkscrew shape behind the planet.

The presence of a magnetic field at Uranus was not known until Voyager's arrival. The intensity of the field is roughly comparable to that of Earth's, though it varies much more from point to point because of its large offset from the center of Uranus. The peculiar orientation of the magnetic field suggests that the field is generated at an intermediate depth in the interior where the pressure is high enough for water to become electrically conducting.

Radiation belts at Uranus were found to be of an intensity similar to those at Saturn. The intensity of radiation within the belts is such that irradiation would quickly darken (within 100,000 years) any methane trapped in the icy surfaces of the inner moons and ring particles. This may have contributed to the darkened surfaces of the moons and ring particles, which are almost uniformly gray in color.

A high layer of haze was detected around the sunlit pole, which also was found to radiate large amounts of ultraviolet light, a phenomenon dubbed "dayglow." The average temperature is about 60 kelvins (-350 degrees Fahrenheit). Surprisingly, the illuminated and dark poles, and most of the planet, show nearly the same temperature at the cloud tops.

Voyager found 10 new moons, bringing the total number to 15. Most of the new moons are small, with the largest measuring about 150 kilometers (about 90 miles) in diameter.

The moon Miranda, innermost of the five large moons, was revealed to be one of the strangest bodies yet seen in the solar system. Detailed images from Voyager's flyby of the moon showed huge fault canyons as deep as 20 kilometers (12 miles), terraced layers, and a mixture of old and young surfaces. One theory holds that Miranda may be a reaggregration of material from an earlier time when the moon was fractured by an violent impact.

The five large moons appear to be ice-rock conglomerates like the satellites of Saturn. Titania is marked by huge fault systems and canyons indicating some degree of geologic, probably tectonic, activity in its history. Ariel has the brightest and possibly youngest surface of all the Uranian moons and also appears to have undergone geologic activity that led to many fault valleys and what seem to be extensive flows of icy material. Little geologic activity has occurred on Umbriel or Oberon, judging by their old and dark surfaces.

All nine previously known rings were studied by the spacecraft and showed the Uranian rings to be distinctly different from those at Jupiter and Saturn. The ring system may be relatively young and did not form at the same time as Uranus. Particles that make up the rings may be remnants of a moon that was broken by a high-velocity impact or torn up by gravitational effects.

NEPTUNE When Voyager flew within 5,000 kilometers (3,000 miles) of Neptune on August 25, 1989, the planet was the most distant member of the solar system from the Sun. (Pluto once again will become most distant in 1999.)

Neptune orbits the Sun every 165 years. It is the smallest of our solar system's gas giants. Neptune is now known to have eight moons, six of which were found by Voyager. The length of a Neptunian day has been determined to be 16 hours, 6.7 minutes.

Even though Neptune receives only three percent as much sunlight as Jupiter does, it is a dynamic planet and surprisingly showed several large, dark spots reminiscent of Jupiter's hurricane-like storms. The largest spot, dubbed the Great Dark Spot, is about the size of Earth and is similar to the Great Red Spot on Jupiter. A small, irregularly shaped, eastward-moving cloud was observed "scooting" around Neptune every 16 hours or so; this "scooter," as Voyager scientists called it, could be a cloud plume rising above a deeper cloud deck.

Long, bright clouds, similar to cirrus clouds on Earth, were seen high in Neptune's atmosphere. At low northern latitudes, Voyager captured images of cloud streaks casting their shadows on cloud decks below.

The strongest winds on any planet were measured on Neptune. Most of the winds there blow westward, or opposite to the rotation of the planet. Near the Great Dark Spot, winds blow up to 2,000 kilometers (1,200 miles) an hour.

The magnetic field of Neptune, like that of Uranus, turned out to be highly tilted -- 47 degrees from the rotation axis and offset at least 0.55 radii (about 13,500 kilometers or 8,500 miles) from the physical center. Comparing the magnetic fields of the two planets, scientists think the extreme orientation may be characteristic of flows in the interiors of both Uranus and Neptune -- and not the result in Uranus's case of that planet's sideways orientation, or of any possible field reversals at either planet. Voyager's studies of radio waves caused by the magnetic field revealed the length of a Neptunian day. The spacecraft also detected auroras, but much weaker than those on Earth and other planets.

Triton, the largest of the moons of Neptune, was shown to be not only the most intriguing satellite of the Neptunian system, but one of the most interesting in all the solar system. It shows evidence of a remarkable geologic history, and Voyager 2 images showed active geyser-like eruptions spewing invisible nitrogen gas and dark dust particles several kilometers into the tenuous atmosphere. Triton's relatively high density and retrograde orbit offer strong evidence that Triton is not an original member of Neptune's family but is a captured object. If that is the case, tidal heating could have melted Triton in its originally eccentric orbit, and the moon might even have been liquid for as long as one billion years after its capture by Neptune.

An extremely thin atmosphere extends about 800 kilometer (500 miles) above Triton's surface. Nitrogen ice particles may form thin clouds a few kilometers above the surface. The atmospheric pressure at the surface is about 14 microbars, 1/70,000th the surface pressure on Earth. The surface temperature is about 38 kelvins (-391 degrees Fahrenheit) the coldest temperature of any body known in the solar system.

The new moons found at Neptune by Voyager are all small and remain close to Neptune's equatorial plane. Names for the new moons were selected from mythology's water deities by the International Astronomical Union, they are: Naiad, Thalassa, Despina, Galatea, Larissa, Proteus.

Voyager 2 solved many of the questions scientists had about Neptune's rings. Searches for "ring arcs," or partial rings, showed that Neptune's rings actually are complete, but are so diffuse and the material in them so fine that they could not be fully resolved from Earth. From the outermost in, the rings have been designated Adams, Plateau, Le Verrier and Galle.

Interstellar Mission

The spacecraft are continuing to return data about interplanetary space and some of our stellar neighbors near the edges of the Milky Way.

As the Voyagers cruise gracefully in the solar wind, their fields, particles and waves instruments are studying the space around them. In May 1993, scientists concluded that the plasma wave experiment was picking up radio emissions that originate at the heliopause -- the outer edge of our solar system.

The heliopause is the outermost boundary of the solar wind, where the interstellar medium restricts the outward flow of the solar wind and confines it within a magnetic bubble called the heliosphere. The solar wind is made up of electrically charged atomic particles, composed primarily of ionized hydrogen, that stream outward from the Sun.

Exactly where the heliopause is has been one of the great unanswered questions in space physics. By studying the radio emissions, scientists now theorize the heliopause exists some 90 to 120 astronomical units (AU) from the Sun. (One AU is equal to 150 million kilometers (93 million miles), or the distance from the Earth to the Sun.

The Voyagers have also become space-based ultraviolet observatories and their unique location in the universe gives astronomers the best vantage point they have ever had for looking at celestial objects that emit ultraviolet radiation.

The Ultraviolet Spectrometer (UVS) is the only experiment on the scan platform that is still functioning. The scan platform is parked at a fixed position and is not being articulated. The Infrared Spectrometer and Radiometer (IRIS) heater was turned off to save power on Voyager 1 on December 7, 2011. On January 21, 2014 the Scan Platform Supplemental Heater was also turned off to conserve power. The IRIS heater and the Scan Platform Heater were used to keep UVS warm. The UVS temperature has dropped to below the measurement limits of the sensor; however, UVS is still operating. The scientist expect to continue to receive data from the UVS until 2016, at which time the instrument will be turned off to save power.

Yet there are several other fields and particle instruments that can continue to send back data as long as the spacecraft stay alive. They include: the cosmic ray subsystem, the low-energy charge particle instrument, the magnetometer, the plasma subsystem, the plasma wave subsystem and the planetary radio astronomy instrument. Barring any catastrophic events, JPL should be able to retrieve this information for at least the next 20 and perhaps even the next 30 years.