voyager images of saturn

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When Voyager gave us the first close-up pictures of Saturn’s rings

For centuries, astronomers using telescopes spied a ring of material circling the planet’s equator. Pinpricks of light, the planet’s moons, floated nearby. Technical advances led to better views, until scientists could see gaps or divisions in the material ringing Saturn. They also saw oddities on its moons: One seemed to hold a methane atmosphere laced with clouds, while another was two-faced, bright on one half but dark as asphalt on the other.

But it would take Voyager 1 and 2, a pair of visiting spacecraft, to fully reveal the beautiful and intriguing ringed world and its equally fascinating system of moons. The planet hosts a wide array of astronomical processes and structures, and the Voyager probes were the first to show scientists how incredible the Saturn system truly is. The system they uncovered was too intriguing not to revisit, laying the foundation for the groundbreaking Cassini mission decades later.

The twin Voyager spacecraft launched 16 days apart in 1977, beginning their Grand Tour of the outer solar system. They took separate journeys to the ringed planet and its diverse moons. Voyager 1 arrived in November 1980, and afterward used the planet’s gravity to slingshot itself out of the solar system’s plane. Voyager 2 swung through in August 1981, continuing on to Uranus and Neptune.

The pair of probes revealed many unexpected details about the Saturn system, but Voyager 1 was not the first mission to snap an up-close view of the planet. That title belongs to Pioneer 11, which flew by the ringed world in 1979. Its photographs, combined with ground-based detections, helped planetary scientists better plan the Voyagers’ Saturn flyby routes, as well as choose which targets to focus on.

Each closest approach was a quick encounter — after all, the probes were traveling faster than 9 miles per second (15 km/s). But the mission team began collecting detailed observations of each target weeks in advance. And for the two weeks surrounding each nearest encounter of Saturn, all the science teams would converge at the Jet Propulsion Laboratory in Pasadena, California, for an intense observing session.

Remarkable features of the rings  

Before Voyager arrived at Saturn, scientists knew of two empty paths splitting Saturn’s rings: the Cassini Division and the Encke Gap. But based on observations from both Pioneer and ground-based telescopes, “we thought we would find bland, featureless sheets of material separated by gaps,” says Linda Spilker, who studied the rings as part of the Voyager team and is now the Cassini project scientist. Instead, the twin spacecraft revealed the rings are anything but bland.

As Voyager 1 neared closest approach and the resolution improved, the team could make out more details. “It looked like grooves on a phonograph record,” says Spilker of the rings. Hundreds of concentric rings circled Saturn. Scientists saw waves along the edges of gaps between those rings, as well as braided features and spiral structures within the rings — all due to the gravitational influence of small moons embedded in and sitting just outside of the rings. They even saw patterns that looked like propeller wings spiraling out from moonlets, showing how large boulders clear material along gaps in their orbit. Studying the behavior of moonlets in a “debris disk” such as Saturn’s rings has allowed scientists to indirectly study how planets form around stars in protostellar disks. “The rings were just so much more than I had imagined,” adds Spilker.

But it wasn’t just the beautiful images of the photogenic ring system that surprised scientists. When Voyager 2 approached Saturn in August, it observed starlight from Delta Scorpii as the rings passed in between that background star and the spacecraft. Called an occultation, this filtered view allowed researchers to see even finer details in the rings. In fact, they saw the particles in the rings with a resolution 10 to 20 times better than by just photographing the rings directly.

With those data, scientists could estimate the thickness at the edge of each ring: between 33 and 656 feet (10–200m). They saw smaller structures in the rings: clumps, twists, and waves — all due to the gravity of Saturn’s satellites. That occultation using Delta Scorpii was one of the most crucial observations Voyager made at Saturn. And with only one such event, the data was extremely precious, says Spilker.

What a difference a generation of technology design makes: Today, scientists have hundreds of occultation observations from the Cassini spacecraft, which studied the Saturn system from 2004 until September of this year. Cassini’s 13 years of observations provided answers about how the moons and Saturn itself shape the rings.

Before either Voyager arrived at Saturn, most of the planet’s moons were no more than pinpricks of light. Ground-based telescopes couldn’t resolve their surfaces, so scientists had little information about the immense variation these worlds hold.

First up was Titan, the planet’s largest moon. Voyager 1 made its closest approach to the orange sphere in the late hours of November 11, 1980, when it flew less than 310,000 miles (500,000km) from the moon. Scientists hoped to see through the thick atmosphere to learn about the surface, but Titan’s mysteries weren’t so easy to solve. The visible and infrared cameras could not penetrate the clouds. Fortunately, researchers could get a radio signal to the surface and back, and used it to calculate the atmosphere’s density: 1.6 times that of Earth.

During the analysis of the radio data, a hushed rumor spread among the dozens of Voyager scientists stationed at JPL, recalls planetary scientist Carolyn Porco, that liquid nitrogen might exist on the surface of Titan. “It turned out the initial analysis was incorrect,” she says. “But I’ll never forget the indescribable thrill of hearing that rumor. It felt, for a moment, like all of us . . . were crewmates on the starship Enterprise, and we had just come upon the most alien of worlds yet seen. We were indeed planetary explorers.” Porco later explored the Saturnian system as a member of the Cassini team.

What Voyager did reveal of Titan, though — knowledge of its atmosphere’s density and composition, the possibility of hydrocarbons perhaps in liquid form at the surface — made Titan even more intriguing for further study. In fact, says Spilker, “it was really the Voyager flyby of Titan, and what we learned and what we didn’t learn, that led to this strong desire to go back.” And ultimately, it was that flyby that sparked the Cassini mission.

Observations from Earth of a ring around Saturn at the distance of Enceladus’ orbit already hinted that perhaps that small moon somehow feeds the ring. Could there be ice volcanoes on Enceladus, providing the sloshy material that would fill in impact craters? If so, some of that gushing material perhaps could escape the surface and orbit Saturn as part of the E ring. Those first detailed observations from Voyager triggered an ongoing fascination with this small, reflective moon, adds Ingersoll.

Scientists now know from the Cassini mission that an underground water ocean feeds geysers at Enceladus’ south pole. They’ve also discovered likely hydrothermal activity at the ocean floor. On Earth, biological ecosystems thrive in such environments. Could they do the same on Enceladus? That’s a question a future dedicated mission to the small moon might answer.

Scientists didn’t send Voyager to Saturn to study only its rings and moons. The planet and its atmosphere were also a science focus. Like that of its sister giant planet, Jupiter, Saturn’s atmosphere hosts incredible storms and enormous jet streams, and the Voyager twins were the first spacecraft to photograph the details in those cloud tops up close.

And then there are Saturn’s winds themselves. “I remember being amazed at how fast the winds were blowing,” recalls Ingersoll — although how fast isn’t actually known yet. That’s because scientists don’t have a reference against which to measure the wind speeds, explains Ingersoll, who has studied planetary atmospheres for decades. “On Earth, we measure the wind relative to the continents,” explains Ingersoll, and Saturn, of course, doesn’t have any continents. But if scientists could measure how fast the planet’s solid core rotates, that speed would serve as the reference.

To get at that rotation rate for a giant planet, researchers track the planet’s magnetic field, which is produced in the solid core. On Jupiter, the magnetic field’s axis is tilted in relation to the rotation axis, which means as the core rotates, the magnetic field wobbles. “You see the magnetic field wobble back and forth like a . . . top, and so that tells you how fast the interior of the planet is rotating,” says Ingersoll. Unfortunately, Saturn’s magnetic field axis and rotation axis are too similar to produce a measurable wobble on the Voyagers’ instruments. But in its final mission phase, skimming just above the cloud tops, Cassini may finally get close enough to the planet to better track the wobble.

On September 15, Cassini will end its study of Saturn, closing the door on up-close observations of the ringed planet, just like Voyager’s departure in 1981. Both missions have answered long-standing questions about the ringed world and its system, as well as introduced new mysteries for future spacecraft to resolve.

This world holds beautiful rings that mimic some characteristics of disks around young stars, intense atmospheric storms, and a variety of moons — including one with an Earth-like weather system and another with the ingredients of a habitable environment. “The study of Saturn has provided scientists the means to study processes that are at work all across our solar system and scale-invariant across the cosmos,” says Porco. “No other planet can claim as much.”

Because of Voyager 1 and 2, we know why the Saturn system continues to tempt planetary explorers.

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August 1981 – voyagers encountered saturn.

Voyager 2 came within 101,000 kilometers (63,000 miles) of Saturn. Voyager 2 noticed changes in Saturn’s atmosphere since the Voyager 1 encounter and took more detailed images of the planet’s rings. Voyager 2 was downlinking at a rate of 44.8 kilobits per second. After its encounter with Saturn, Voyager 2 headed to Uranus.

› Voyager – The Interstellar Mission › SCaN History of the 1980’s

NASA's Voyager probes have been traveling through space for nearly 46 years. Here are 18 groundbreaking photos from their incredible mission.

• Nearly 46 years after their launch, Voyager 1 and 2 will likely soon reach the end of their scientific mission . 
• NASA recently lost contact with Voyager 2 after sending it a bad command by mistake. 
• Here are 18 pictures the probes took over the course of their forty-plus-year journey. 

The Voyager probes are pioneers of science, making it farther into space than any other manufactured object. But now, they face a terminal problem: their power is running out.

The twin probes were originally sent on a four-year mission to tour the solar system, but they exceeded all expectations and are still going nearly 46 years later. That makes them NASA's longest-lived mission.

Scientists are now doing their best to  keep the probes going for as long as possible. They recently found a clever hack to extend Voyager 2's life for another three years and plan to do the same with Voyager 1.

But these are old machines and NASA is constantly scrambling to fix mistakes. Last year, Voyager 1 started sending garbled data from the outside of the solar system. NASA ultimately figured out one of its computers had gone dead.

Voyager 2 is now in limbo , as the agency revealed Friday it had lost contact with the probe when someone sent a wrong command. It could be the end of Voyager 2's mission if NASA can't fix the mistake, which the agency probably won't be able to do before October.

As the probes are nearing the end of their scientific mission, here are 18 images from Voyager that changed science.

The Voyager probes were designed to visit Jupiter and Saturn.

The Voyager mission included two probes — Voyager 1 and Voyager 2 — which NASA launched in 1977 within a few months of each other.

NASA took advantage of a rare planet alignment to turbocharge their journeys into space.

NASA originally built the probes to last five years, but they have exceeded that lifespan many times .

As of August 20 and September 5, 2023, Voyager 2 and Voyager 1 will have been traveling for 46 years, respectively. 

This is what Voyager 1 saw on its approach to Jupiter.

Voyager 1 and Voyager 2 reached Jupiter in 1979.

As they flew by the planet, they took about 50,000 pictures of Jupiter. These blew away scientists, as the quality of the pictures was much better than those taken from Earth, according to NASA.

These snaps  taught scientists important facts about the planet's atmosphere, magnetic forces, and geology that would have been difficult to decipher otherwise.

The probes discovered two new moons orbiting Jupiter: Thebe and Metis.

They also spotted a thin ring around Jupiter.

The probe captured this picture as it was looking back at the planet backlit by the Sun. 

Voyager 1 discovered volcanoes at the surface of Io, one of Jupiter's moons.

Next stop: Saturn.

In 1980 and 1981, the probes reached Saturn . The flyby gave scientists unprecedented insight into the planet's ring structure, atmosphere, and moons.

Voyager snapped Saturn's rings in more detail than ever before.

And showed every secret that Enceladus, Saturn's moon, had to offer.

Saturn, snapped as the probe flew away, was shown in a new light.

By 1986, Voyager 2 had made it to Uranus.

By 1986, Voyager 1 has finished its grand tour of the solar system, and few out towards space. But Voyager 2 kept on its exploring our nearest planets, passing 50,600 miles away from Uranus in January 1986. 

Voyager 2 discovered two extra rings around Uranus , revealing the planet had at least 11, not 9. 

Voyager 2 also spotted 11 previously unseen moons around Uranus.

Here is a picture of Miranda, Uranus's sixth-biggest moon.

Voyager 2 was the first spacecraft to observe Neptune from a close distance.

In 1989, 12 years after its launch, Voyager 2 passed within 3,000 miles of Neptune. 

Here's Nepture taken by Voyager 2, in all its blue glory.

Voyager 2 took this unflattering pic of Triton's rough face.

It captured Triton, Neptune's moon in unprecedented detail. 

And snapped Triton's southern hemisphere.

As it flew by, Voyager 2 uncovered Neptune's rings.

As its parting gift, Voyager 2 took this beautiful picture of light grazing Neptune's south pole.

This is Voyager 2's last picture. Since it wouldn't come across another planet on its ongoing journey, NASA switched off its cameras after its flyby of Neptune to conserve energy for other instruments. 

Voyager 1 had one last trick up its sleeve.

As its last photographic hurrah in 1990, Voyager 1 took 60 images of the solar system from 4 billion miles away.

It gave us the Earth's longest selfie, dubbed the "pale blue dot."

This remains the longest-range selfie: a portrait of the Earth taken by a human-made probe from 4 billion miles away. 

After this picture, NASA switched off Voyager 1's cameras to save energy. NASA could switch the probes' cameras back on , but it is not a priority for the mission. 

Beyond the solar system

Though the probes are no longer sending pictures, they haven't stopped sending crucial information about space. 

In 2012, Voyager 1 became the first human-made instrument to cross into interstellar space by crossing the boundary between our solar system and the rest of the universe, called the heliopause. 

Voyager 2 was second, crossing that threshold in 2018 . The probe revealed that there was yet another  layer outside of our heliosphere.

The probes keep sending back measurements from interstellar space, like weird hums likely coming from vibrations made by neighboring stars.

Even after their instruments are switched off, the probes' mission continues.

NASA is planning to switch more of the probes' instruments in the hope of extending their life to the 2030s.

But even after all their instruments become quiet, their mission will carry on. As they drift off, they will still be carrying a golden record that carries crucial information about humanity. If intelligent extraterrestrial life exists, they could use that information to reach out to us.

This article was originally published on June 6, 2022, and is being updated with the latest developments about Voyager 1 and 2. 

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Rae Paoletta • Mar 03, 2022

The best space pictures from the Voyager 1 and 2 missions

Launched in 1977, NASA’s Voyager 1 and 2 missions provided an unprecedented glimpse into the outer solar system — a liminal space once left largely to the imagination. The spacecraft provided views of worlds we’d never seen before, and in some cases, haven’t seen much of since.

The Voyager probes were launched about two weeks apart and had different trajectories, like two tour guides at the same museum. Only Voyager 2 visited the ice giants — Uranus and Neptune — for example.

The Voyagers hold a unique position in the pantheon of space history because they’re still making it; even right now, Voyagers 1 and 2 are the only functioning spacecraft in interstellar space. Both hold a Golden Record that contains sights and sounds of Earth in case alien life were to find one of the spacecraft.

As the Voyager missions voyage on, it’s good to look back at how they captured our solar system before leaving it.

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Carl Sagan in 1986: ‘Voyager has become a new kind of intelligent being—part robot, part human’

The renowned scientist reflected on the lesser-known triumphs and lofty ambitions of Voyager in Popular Science's October 1986 issue.

By Bill Gourgey | Published Mar 25, 2024 9:02 AM EDT

One of the worries that kept legendary astronomer Carl Sagan up at night was whether aliens would understand us. In the mid-1970s, Sagan led a committee formed by NASA to assemble a collection of images, recorded greetings, and music to represent Earth. The montage was pressed onto golden albums and dispatched across the cosmos on the backs of Voyagers 1 and 2 .

In a 1986 story Sagan wrote for Popular Science , he noted that “hypothetical aliens are bound to be very different from us—independently evolved on another world,” which meant they likely wouldn’t be able to decipher the golden discs. But he took assurance from an underappreciated dimension of Voyagers’ message: the designs of the vessels themselves.

“We are tool makers,” Sagan wrote. “This is a fundamental aspect, and perhaps the essence, of being human.” What better way to tell alien civilizations that Earthlings are toolmakers than by sending a living room-sized, aluminum-framed probe clear across the Milky Way. 

Although both spacecraft were only designed to swing by Jupiter and Saturn , Voyager 2’s trajectory also hurled it past Uranus and Neptune . Despite numerous mishaps along the way—and because of the elite toolmaker skills of NASA engineers—the probe was in good enough shape to send back close-ups of those distant worlds. In 2012, Voyager 1 became the first interstellar spacecraft , followed soon thereafter by Voyager 2 . “Once out of the solar system,” Sagan wrote, “the surfaces of the spacecraft will remain intact for a billion years or more,” so resilient is their design.

Today, the probes are 12–15 billion miles from Earth , still operable (despite experiencing recent communication difficulties ), and sailing through the relative calm of interstellar space. They are expected to continue to transmit data back to Earth for another year or so , or until their plutonium batteries quit. 

It was early 20th century wireless inventor Guglielmo Marconi who suggested that radio signals never die, they only diminish as they travel across space and time. Even after communications from the Voyager spacecraft cease, perhaps the tiny voices of Earth’s first emissaries, animated by NASA’s master toolmakers nearly half a century ago, will continue to drift through the cosmos for all time, accessible to far-flung civilizations equipped with sensitive enough receivers to listen.

“Voyager’s Triumph” (Carl Sagan, October 1986)

A noted scientist tells the little-known story of the remarkable feats of the Voyager engineers, a dedicated band who repeatedly overcame technical adversity to ensure the success of these historic expeditions to the outer solar system.

Carl Sagan is Director, Laboratory for Planetary Studies, Cornell University, and, since 1970, a member of the Voy­ager Imaging Science Team. His Cosmos: A Special Edition is televised this fall. 

On Jan. 25, 1986, the Voyager 2 robot probe entered the Uranus system and reported a procession of wonders. The encounter lasted only a few hours, but the data faithfully relayed back to Earth have revolu­tionized our knowledge of the aquamarine planet, its more than 15 moons, its pitch black rings, and its belt of trapped high-energy charged particles. Voyager 2 and its compan­ion, Voyager 1, have done this before. At Jupiter, in 1979, they braved a dose of trapped charged particles 1,000 times what it takes to kill a human being [PS, July ’79); and in all that radiation they discovered the rings of the largest planet, the first active volcanoes outside Earth, and a pos­sible underground ocean on an airless world—among a few hundred other major findings. At Saturn, in 1980 and 1981, the two spacecraft survived a pummeling by tiny icy particles as they plummeted through previously un­ known rings; and there they discovered not a few, but thou­ sands of Saturnian rings, icy moons recently melted through unknown causes, and a large world with an ocean of liquid hydrocarbons surmounted by clouds of organic matter IPS, March ’81 l. These spacecraft have returned to Earth four trillion bits of information, the equivalent of about 100,000 encyclopedia volumes. 

Because we are stuck on Earth, we are forced to peer at distant worlds through an ocean of distorting air. It is easy to see why our spacecraft have revolutionized the study of the solar system: We ascend to the stark clarity of the vacuum of space, and there approach our objectives, flying past them or orbiting them or landing on their surfaces. These nearby worlds have much to teach us about our own, and they will be—unless we are so foolish as to destroy ourselves—as familiar to our descendents as the neighboring states are to those who live in America today. 

Voyager and its brethren are prodigies of human inven­tiveness. Just before Voyager 2 was to encounter the Uranus system, the mission design had scheduled a final course correction, a short firing of the on-board propul­sion system to position Voyager correctly as it flew among the moving moons. But the course correction proved un­necessary. The spacecraft was already within 200 kilome­ters of its designed trajectory after a voyage along an arcing path five billion kilometers in length. This is roughly the equivalent of throwing a pin through the eye of a needle 50 kilometers away, or firing your target pistol in New York and hitting the bull’s eye in Dallas.

The lodes of planetary treasure were transmitted back to Earth by the radio antenna aboard Voyager; but Earth is so far away that by the time the signal was gathered in by radiotelescopes on our planet, the received power was only 10-16 watts (fifteen zeros after the decimal point). Comparing this weak signal with the power emitted by an ordinary reading lamp is like comparing the width of an atom with the distance between Earth and the moon. (Incidentally, the first photograph ever taken of Earth and the moon together in space was acquired by one of the Voyager spacecraft.)

We tend to hear much about the splendors returned, and very little about the ships that brought them, or the shipwrights. It has always been that way. Our history books do not tell us much about the builders of the Nina, Pinta, and Santa Maria, or even the principle of the caravel. De­spite ample precedent, it is a clear injustice: The Voyager engineering team and its accomplishments deserve to be much more widely known.

The Voyager spacecraft were designed and assembled, and are operated by the Jet Propulsion Laboratory (JPL) of the National Aeronautics and Space Administration in Pasadena, Calif. The mission was conceived during the late 1960s, first funded in 1972, but was not approved in its present form (which includes encounters at Uranus and Neptune) until after the 1979 Jupiter flyby. The two spacecraft were launched in late summer and early fall 1977 by a non-reusable Titan/Centaur booster configuration at Cape Canaveral, Fla. Weighing about a ton, a Voyager would fill a good-sized living room. Each spacecraft draws about 400 watts of power—considerably less than an average American home—from a generator that converts radioactive plutonium into electricity. The instrument that measures interplanetary magnetic fields is so sensitive that the flow of electricity through the innards of the spacecraft would generate spurious signals. As a result, this instrument is placed at the end of a long boom stretching out from the spacecraft. With other projections, it gives Voyager a slightly porcupine appearance. Two cameras, infrared and ultraviolet spectrometers, and an instrument called the photopolarimeter are on a scan platform; the platform swivels so these instruments can point toward a target world. The spacecraft antenna must know where Earth is if the transmitted data are to be received back home. The spacecraft also needs to know where the sun is and at least one bright star, so it can orient itself in three dimensions and point properly toward any passing world. It does no good to be able to return pictures over billions of miles if you can’t point the camera.

On-orbit repairs

Each spacecraft costs about as much as a single modern strategic bomber. But unlike bombers, Voyager cannot, once launched, be returned to the hangar for repairs.

As a result, the spacecraft’s computers and electronics are designed redundantly. And when Voyager finds itself in trouble, the computers use branched contingency tree logic to work out the appropriate course of action. As the spacecraft journeys increasingly far from Earth, the round-trip light (and radio) travel time also increases, approaching six hours by the time Voyager is at the distance of Uranus.

Thus, in case of an emergency, the spacecraft needs to know how to put itself in a safe standby mode while awaiting instructions from Earth. As the spacecraft ages, more and more failures are expected, both in its mechanical parts and its computer system, although there is as yet no sign of a serious memory deterioration, some robot Alzheimer’s disease. When an unexpected failure occurs, special teams of engineers—some of whom have been with the Voyager program since its inception—are assigned to “work” the problem. They will study the underlying basic science and draw upon their previous experience with the failed subsystems. They may do experiments with identical Voyager spacecraft equipment that was never launched or even manufacture a large number of components of the sort that failed in order to gain some statistical understanding of the failure mode.

In April 1978, almost eight months after launch, an omitted ground command caused Voyager 2’s on-board computer to switch from the prime radio receiver to its backup.

During the next ground transmission to the spacecraft, the receiver refused to lock onto the signal from Earth. A component called a tracking loop capacitor had failed. After seven days in which Voyager 2 was out of contact, its fault protection software commanded the backup receiver to be switched off and the prime receiver to be switched back on. But, mysteriously, the prime receiver failed moments later: It never recovered. Voyager 2 was now fundamentally imperiled. Although the primary receiver had failed, the on-board computer commanded the spacecraft to use it. There was no way for the controllers on Earth to command Voyager to revert to the backup receiver. Even worse, the backup receiver would be unable to receive the commands from Earth because of the failed capacitor. Finally, after a week of command silence, the computer was programmed to switch automatically between receivers.

And during that week’s time the JPL engineers designed an innovative command frequency control procedure to make a few essential commands comprehensible to the damaged backup receiver.

This meant the engineers were able to communicate, at least a little bit, with the spacecraft. Unfortunately the backup receiver now turned giddy, becoming extremely sensitive to the stray heat dumped when various components of the spacecraft were powered up or down. Over the following months the JPL engineers designed and conducted a series of tests that let them thoroughly understand the thermal consequences of most operational modes of the spacecraft on its ability to receive commands from Earth. The backup-receiver problem was entirely circumvented. It was this backup receiver that acquired all the commands from Earth on how to gather data in the Jupiter, Saturn, and Uranus systems. The engineers had saved the mission. (But to be on the safe side, during most of Voyager’s subsequent flight there is in residence in the onboard computers a nominal data-taking sequence for the next planet to be encountered.)

Another heart-wrenching failure occurred just after Voyager 2 emerged from behind Saturn after its closest approach to the planet in August 1981. The scan platform had been moving rapidly in the azimuth direction—quickly pointing here and there among the rings, moons, and the planet itself during the time of closest approach. Suddenly, the platform jammed. A stuck scan platform obviously implies a severe reduction in future pictures and other key data. The scan platform is driven by gear trains called actuators, so first the JPL engineers ran an identical copy of the flight actuator in a simulated mission. The ground actuator failed after 348 revolutions: the actuator on the spacecraft had failed after 352 revolutions. The problem turned out to be a lubrication failure. Plainly, it would be impossible to overtake Voyager with an oil can. The engineers wondered whether it would be possible to restart the failed actuator by alternately heating and cooling it, so that the thermal stresses would cause the components of the actuator to expand and contract at different rates and un-jam the system. After gaining experience with specially manufactured actuators on the ground, the engineers jubilantly found that they were able to use this procedure to start the scan platform up again in space. More than this, they devised techniques to diagnose any imminent actuator failure early enough to work around the problem. Voyager 2’s scan platform worked perfectly in the Uranus system. The engineers had saved the day again.

Ingenious solutions

Voyager 1 and 2 were designed to explore the Jupiter and Saturn systems only. It is true that their trajectories would carry them to Uranus and Neptune, but officially these planets were never contemplated as targets for Voyager exploration: The spacecraft was not supposed to last that long. Because of trajectory requirements in the Saturn system, Voyager 1 was flung on a path that will never encounter any other known world; but Voyager 2 flew to Uranus with brilliant success, and is now on its way to an August 1989 encounter with the Neptune system.

At these immense distances, sunlight is getting progressively dimmer, and the spacecraft’s transmitted radio signals to Earth are getting progressively fainter. These were predictable but still very serious problems that the JPL engineers and scientists also had to solve before the encounter with Uranus.

Because of the low light levels at Uranus, the Voyager television cameras were obliged to take longer time exposures. But the spacecraft was hurtling through the Uranus system so fast (about 35,000 miles per hour) that the image would have been smeared or blurred—an experience shared by many amateur photographers. To overcome this, the entire spacecraft had to be moved during the time exposures to compensate for the motion, like panning in the direction opposite yours while taking a photograph of a street scene from a moving car. This may sound easier than it is: You have to compensate for the most casual of motions. At zero gravity, the mere start and stop of the on-board tape recorder that’s registering the image can jiggle the spacecraft enough to smear the picture. This problem was solved by commanding the spacecraft thrusters, instruments of exquisite sensitivity, to compensate for the tape-recorder jiggle at the start and stop of each sequence by turning the entire spacecraft just a little. To compensate for the low received radio power at Earth, a new and more efficient digital encoding algorithm was designed for the cameras, and the radiotelescopes on Earth were joined together with oth ers to increase their sensitivity. Overall, the imaging system worked, by many criteria, better at Uranus than it did at Saturn or even at Jupiter.

Voyager has become a new kind of intelligent being—part robot, part human. It extends the human senses to far-off worlds.

The ingenuity of the JPL engineers is growing faster than the spacecraft is deteriorating. And Voyager may not be done exploring after its Neptune encounter.

There is, of course, a chance that some vital subsystem will fail tomorrow, but in terms of the radioactive decay of the plutonium power source, the two Voyager spacecraft will be able to return data to Earth until roughly the year 2015. By then they will have traveled more than a hundred times Earth’s distance from the sun, and may have penetrated the heliopause, the place where the interplanetary magnetic field and charged particles are replaced by their interstellar counterparts; the heliopause is one definition of the frontier of the solar system.

Robot-human partnerships

These engineers are heroes of our time. And yet almost no one knows their names. I have attached a table giving the names of a few of the JPL engineers who played central roles in the success of the Voyager missions.

In a society truly concerned for its future, Don Gray, Charlie Kohlhase, or Howard Marderness, would be as well known for their extraordinary abilities and accomplishments as Dwight Gooden, Wayne Gretzky, or Kareem Abdul Jabbar are for theirs.

Voyager has become a new kind of intelligent being-part robot, part human. It extends the human senses to far-off worlds. For simple tasks and short-term problems, it relies on its own intelligence; but for more complex tasks and longer term problems, it turns to another, considerably larger brain—the collective intelligence and experience of the JPL engineers. This trend is sure to grow. The Voyagers embody the technology of the early 1970s; if such spacecraft were to be designed in the near future, they would incorporate stunning improvements in artificial intelligence, in data-processing speed, in the ability to self-diagnose and repair, and in the capacity for the spacecraft to learn from experience. In the many environments too dangerous for people, the future belongs to robot-human partnerships that will recognize Voyager as antecedent and pioneer.

Unlike what seems to be the norm in the so-called defense industry, the Voyager spacecraft came in at cost, on time, and vastly exceeding both their design specifications and the fondest dreams of their builders. These machines do not seek to control, threaten, wound, or destroy; they represent the exploratory part of our nature, set free to roam the solar system and beyond.

Once out of the solar system, the surfaces of the spacecraft will main intact for a billion years or more, as the Voyagers circumnavigate the center of the Milky Way galaxy.

This kind of technology, its findings freely revealed to all humans everywhere, is one of the few activities of the United States admired as much by those who find our policies uncongenial as by those who agree with us on every issue. Unfortunately, the tragedy of the space shuttle Challenger implies agonizing delays in the launch of Voyager’s successor missions, such as the Galileo Jupiter orbiter and entry probe. Without real support from Congress and the White House, and a clear long-term NASA goal, NASA scientists and engineers will be forced to find other work, and the historic American triumphs in solar-system exploration—symbolized by Voyager—will become a thing of the past. Missions to the planets are one of those things—and I mean this for the entire human species—that we do best. We are tool makers—this is a fundamental aspect, and perhaps the essence, of being human.

Greeting the aliens

Both Voyager spacecraft are on escape trajectories from the solar system. The gravitational fields of Jupiter, Saturn, and Uranus have flung them at such high velocities that they are destined ultimately to leave the solar system altogether and wander for ages in the calm, cold blackness of interstellar space—where, it turns out, there is essentially no erosion.

Once out of the solar system, the surfaces of the spacecraft will main intact for a billion years or more, as the Voyagers circumnavigate the center of the Milky Way galaxy. We do not know whether there are other space-faring civilizations in the Milky Way. And if they do exist, we do not know how abundant they are.

But there is at least a chance that some time in the remote future one of the Voyagers will be intercepted by an alien craft. Voyagers 1 and 2 are the fastest spacecraft ever launched by humans; but even so, they are traveling so slowly that it will be tens of thousands of years before they go the distance to the nearest star. And they are not headed toward any of the nearby stars. As a result there could be no danger of Voyager attracting “hostile” aliens to Earth, at least not any time soon.

So, it seemed appropriate to include some message of greeting from Earth At NASA’s request, a committee I chaired designed a phonograph record that was affixed to the outside of each of the Voyager spacecraft. The records contain 116 pictures in digital form, describing our science and technology, our institutions, and ourselves; what will surely be unintelligible greetings in many languages; a sound essay on the evolution of our planet; and an hour and a half of the world’s greatest music. But the hypothetical aliens are bound to be very different from us—independently evolved on another world. Are we really sure they could understand our message? Every time I feel these concerns stirring, though, I reassure myself: Whatever the incomprehensibilities of the Voyager record, any extraterrestrial that finds it will have another standard by which to judge us.

Each Voyager is itself a message. In its exploratory intent, in the lofty ambition of its objectives, and in the brilliance of its design and performance, it speaks eloquently for us.

Bill Gourgey is a Popular Science contributor and unofficial digital archeologist who enjoys excavating PopSci’s vast archives to update noteworthy stories (yes, merry-go-rounds are noteworthy).

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• The Farthest-Away Pictures of Earth Ever Taken

Space travel has created an opportunity for people to not only see other planets, but also to see Earth differently. There is something special about seeing Earth from a photograph in space. Farther away photographs of Earth serve as a reminder of how small the world is. While the pale blue dot photograph of Earth is one of the most famous, there are now many other photographs showing Earth in space. Explore the farthest-away pictures of Earth ever taken.

Earth and the Moon

The image of Earth and moon was taken from 804,000 miles away by NASA's OSIRIS REx spacecraft. From the image, you can still Earth's marble form, a mix of blue and green. The earth and moon are around a quarter million miles apart in this photo. NASA's OSIRIS REx spacecraft traveled to the rubbly asteroid Bennu to gather a sample. The mission was a success, and the spacecraft snapped the image of the moon and Earth on its way into deeper space.

The Pale Blue Dot

One of the most famous photographs ever taken of Earth is the Pale Blue Dot . The photo dates back to February 14th, 1990, by NASA's Voyager 1. Voyager 1 was on its way out of the solar system, past Neptune, at 3.7 billion miles from the sun at the time of the photo. The mission managers commanded Voyager to look towards Earth one last time before it headed any further. As it looked back, Voyager snapped 60 images, including the Pale Blue Dot image. Earth is so small in the photo that it is nearly the size of one pixel.

Earth From Mars

It's rare to get a photograph of Earth from a planet besides the moon. However, NASA's Spirit Rover snapped a historic photo of Earth in 2004. The rover explored the Martian planet for six years and gained fame for capturing the first image of Earth from the surface of a planet that wasn't the moon. In the photograph, you can see the Martian landscape. There are rolling hills below, and Earth faintly appears in the sky.

Earth From Mercury

There is another photo today of what Earth looks like from a planet closer to the sun. While not many spacecrafts visit Mercury , in 2013, NASA's MESSENGER spacecraft did. The spacecraft captured an image of Earth and the moon from 61 million miles away. The goal of the mission was to look for small moons around Mercury, and the photograph was an added bonus. Since the Earth and moon can be dark and hard to see at 61 million miles away, MESSENGER took a long exposure of Earth. This made Earth and the moon appear exceptionally bright and large. However, both are still very small in the picture at less than a pixel in size.

Earth Beyond Saturn

One of the most stunning far-away photos captured of Earth is a photo beyond Saturn . In 2013 NASA's Cassini spacecraft snapped an amazing photo of Earth just beyond the rings of Saturn at a distance of under 900 million miles away. Earth's rich blue color is particularly visible in the photo. Sunlight scattered on the planet's surface gives Earth its beautiful blue sky. The rare image used a special wide-angle camera lens on Cassini's spacecraft. This is a special photo since it is the only wide-angle footprint that has the Earth-moon system in it.

Final Thoughts

Today, there are photos of Earth from millions and billions of miles away. This is an amazing feat, unimaginable a century ago. As space travel and technology continue to advance, humans will figure out how to take photos of Earth further and further away. Seeing these photos is a reminder of how small the planet is in the vastness of the galaxy.

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Life on Enceladus? Europe eyes astrobiology mission to Saturn ocean moon

Such a mission, which would launch in the 2040s for arrival in the 2050s, could be the first to search for life in the Saturn system.

Europe could be heading to the Saturn moon Enceladus in search of life, according to a new report from planetary scientists who are masterminding a future large-class mission to the outer solar system.

The European Space Agency (ESA) is exercising considerable forward-thinking with its "Voyager 2050" program, which describes the scientific goals and missions for the middle of this century. Its overarching theme of "moons of the solar system " was chosen in 2021, and now an expert report has recommended that Enceladus should be the primary target.

Enceladus is a 309-mile-wide (498 kilometers) icy moon of Saturn . In 2006, the Cassini mission discovered that giant plumes of water vapor are spewing out from deep fractures in the surface, nicknamed "tiger stripes," located near Enceladus' south pole. The plumes are the result of Saturn's gravity stretching and squeezing Enceladus' innards like putty, injecting energy into the moon 's interior to keep water liquid in a global ocean and periodically squirting some of that water out through the tiger stripes, like squeezing water out of a bottle.

Related: Saturn's moons: Facts about the weird and wonderful satellites of the ringed planet

ESA convened a 12-person panel of planetary scientists from across Europe and chaired by Zita Martins, who is an astrobiologist at Instituto Superior Técnico in Portugal, to asses the science that could be gained from venturing to Enceladus, its fellow Saturn satellite Titan or the Jupiter ocean moon Europa . Meanwhile, engineers at ESA's Concurrent Design Facility (CDF) explored what kind of mission would be most realistic given current and near-future technologies.

"The search for habitable conditions and for signatures of life in the solar system is challenging from a science and technology point of view, but very exciting," said Martins in a press statement .

From both a scientific and technology point of view, Enceladus came out on top, followed by Titan and then Europa.

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Enceladus has all the ingredients necessary for a potentially habitable environment. Liquid water — check. Organic molecules — check. A source of chemical energy to fuel life — check.

The report suggests that a mission to Enceladus (or Titan) be composed of both an orbiter and a lander. They'd be launched separately on Ariane 6 rockets and then rendezvous in Earth orbit before heading for Saturn. Once there, they'd perform several flybys of Saturn's other moons that could harbor oceans, such as Dione , Mimas and Rhea , before closing in on their target of either Enceladus or Titan.

If Enceladus were chosen, the lander would touch down in the south polar region near the tiger stripes and collect samples of the ocean that have snowed back onto the surface from the plumes. Alternatively, if ESA wished to dispense with the lander for budgetary reasons, the orbiter could fly through the plumes and sample material that way. This has been done previously, with the Cassini spacecraft. Although Cassini did not have the instruments capable of detecting life, it did find organic molecules from the ocean within the plumes. 

A lander as part of a Titan mission would focus on touching down in an empty lakebed that seasonally fills with liquid hydrocarbons such as ethane and methane, and sampling the sediments there. However, getting into low-Titan orbit where an orbiter could also sample the moon's upper atmosphere is challenging because of the significant delta-v (change in velocity) needed, which would require a more complex spacecraft with greater fuel reserves, which in turn increases the mass at launch. 

It's also worth pointing out that NASA is already developing a mission to Titan, namely a quadcopter called Dragonfly that's scheduled to launch in 2028 to explore the skies and surface of the big moon. Also, while Titan certainly possesses the organic chemistry that could assemble life's building blocks, the moon's astrobiological potential has recently been questioned in research that suggested that not enough organic material from the surface would reach its underground ocean.

Related: Titan: Facts about Saturn's largest moon

— Finding life on Saturn's moon Enceladus might be easier than we thought

— Saturn's moon Enceladus has all the ingredients for life in its icy oceans. But is life there?

— This snake robot could hunt alien life on icy moons like Saturn's Enceladus  

Europa Clipper that will blast off in October 2024, will already maximize the science that can be conducted from close flybys of Europa. To significantly further the science that can be done at Europa would require a lander, but estimates place the lifetime of any lander on the irradiated surface of Europa at just 10 days using current radiation shielding technology. Both ESA's scientific and CDF panels concluded that such a mission is not feasible at the current time .

If ESA can pull off an Enceladus mission, it would be a huge, potentially history-making achievement, depending upon what it finds. 

"An investigation into signs of past or present life around Saturn has never been achieved before," said Carole Mundell, who is the director of science at ESA. "It would guarantee ESA leadership in planetary science for decades to come."

The full report can be found on the European Space Agency's website. 

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].

Keith Cooper is a freelance science journalist and editor in the United Kingdom, and has a degree in physics and astrophysics from the University of Manchester. He's the author of "The Contact Paradox: Challenging Our Assumptions in the Search for Extraterrestrial Intelligence" (Bloomsbury Sigma, 2020) and has written articles on astronomy, space, physics and astrobiology for a multitude of magazines and websites.

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• Dr.Zilman About time! Stop wasting millions of dollars on that dead dusty desert of Mars. Reply

Dr.Zilman said: About time! Stop wasting millions of dollars on that dead dusty desert of Mars.

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What's Up - April 2024

What are some skywatching highlights in April 2024? Catch Mars and Saturn rising, and Jupiter hangs out with Comet 12P. Plus NASA has you covered for the total eclipse whether you're headed to totality or watching from afar.

What's Up for April? Some easy-to-spot planets, there's still time to observe comet 12P, and how to enjoy this month's solar eclipse if you're not in the path of totality.

For several days in the first half of April, early risers can watch Mars and Saturn rising together in the morning. Taking a look about half an hour before sunrise, you can find them low in the east, about 10 degrees above the horizon. They're at their closest on April 10th and 11th, but still really close in the sky the whole second week of April.

Now, on the evening of April 10th you can find the Moon with Jupiter in the west. Jupiter's easy to identify as a bright, unflickering light, low in the west following sunset, all month. Being just a couple of days after its "new moon" phase, the Moon shows only 7% of its illuminated surface on this evening, making for a beautiful crescent shining there with the giant planet Jupiter.

This is also a good night to have a look for comet 12P/Pons-Brooks, which has been getting brighter, and is easily observable with binoculars or a small telescope, especially if you can get away from bright city lights. The comet will be just beneath the Moon, and just right of Jupiter, but you'll have to be quick, as it drops below 10 degrees elevation an hour after sunset and then sets an hour later. So you'll want a clear view toward the horizon, and be looking for it as twilight ends. If you want to catch this comet, do it soon, because it will be too close to the Sun in the sky to observable after mid-April, and later when it makes its closest approach to Earth, it will be on its way outward from the Sun and growing fainter.

There's a total solar eclipse on the way, and it's kind of a big deal. We've been really fortunate to have two total eclipses visible across a wide swath of the U.S. recently, first in 2017, and now on April 8th, 2024. The next time such an eclipse will cross the States is 21 years from now. If you live in or near the path of totality, or you're traveling there to experience the eclipse, you're in for an incredible experience.

But what if you're not going to be able to experience totality for this eclipse in person? What can you expect, and how can you still enjoy it? Well for starters, NASA has you covered with a live webcast, from multiple locations, as the Moon's shadow moves across the country. So join us for the total eclipse online, whatever your plans.

If you're anywhere in the continental U.S. outside of totality, you'll still experience a partial solar eclipse. The amount of the Sun to be covered by the Moon at maximum eclipse depends on how far you are from the path of totality.

In observing a partial eclipse, you'll still need to use specialized eye protection, such as eclipse glasses, a pinhole projector, or a telescope with a solar filter. One of the easiest methods is something most of us have in our kitchen – a regular colander. These make excellent pinhole cameras that project the eclipse onto the ground. And barring that, the sun dapples that filter through the tree leaves do something very similar. It's also fun to note the eerie way the sunlight dims during the eclipse, especially in places where the Moon covers 80% or more of the Sun's disk.

NASA has a bunch of eclipse resources to help you get ready for this awe-inspiring celestial event. There's info on safe-viewing, citizen science opportunities, and you'll even find our "eclipse explorer," where you can find eclipse details for your specific zip code.

From wherever you're observing, solar eclipses are remarkable events. So observe safely, and join our live webcast, because it's an event you surely don't want to miss.

Here are the phases of the Moon for April. Stay up to date on NASA's missions exploring the solar system and beyond at science.nasa.gov. I'm Preston Dyches from NASA's Jet Propulsion Laboratory, and that's What's Up for this month.