Voyager 1 Explores Saturn

Voyager 1 Explores Saturn

On November 12, 1980, Voyager 1 edged within 78,000 miles of Saturn, the second-largest planet in the solar system. Cameras beamed pictures 950 million miles back to California, revealing interesting new information about Saturn's rings. A news report details the discovery.


Voyager 1 Explores Saturn - HISTORY

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.

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

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.

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.

Voyager Operations

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, 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

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 (30-mile) deep 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. The torus's heavy ions migrate outward, and their pressure inflates the jovian 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

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

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

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, and 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

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 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 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 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.

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Voyager 1: 'The little spacecraft that could'

Scientists may dispute the exact location of Voyager 1, but the spacecraft remains one of NASA's greatest success stories. Take a look at some of the amazing images the probe has provided its Earthbound audience.

Jupiter, its Great Red Spot and three of its four largest satellites are visible in this photo taken February 5, 1979, by Voyager 1.

A dramatic view of Jupiter's Great Red Spot and its surroundings was obtained by Voyager 1 on February 25, 1979.

This image of Jupiter was assembled from three black and white negatives from different color filters and recombined to produce the color image.

Voyager 1 captured the first evidence of a ring around the planet Jupiter. The multiple exposure of the extremely thin faint ring appears as a broad light band crossing the center of the picture. The background stars look like broken hairpins because of spacecraft motion during the 11-minute exposure. The black dots are geometric calibration points in the camera.

This mosaic image of Jupiter's moon "Io" shows a variety of features that appear linked to the intense volcanic activity. The circular, doughnut-shaped feature in the center has been identified as a known erupting volcano.

Another image of "Io" shows an active plume of a volcano dubbed "Loki."

This August 1998 NASA file image shows a true color photo of Saturn assembled from the Voyager 2 spacecraft.

A mosaic image of Saturn's rings, taken by NASA's Voyager 1 on November 6, 1980, shows approximately 95 individual concentric features in the rings. The ring structure was once thought to be produced by the gravitational interaction between Saturn's satellites and the orbit of ring particles, but has now been found to be too complex for this explanation alone.

This image of Rhea, the largest airless satellite of Saturn, was acquired by the Voyager 1 spacecraft on November 11, 1980.

The cratered surface of Saturn's moon "Mimas" is seen in this image taken by Voyager 1 on November 12, 1980. Impact craters made by the infall of cosmic debris are shown the largest is more than 100 kilometers (62 miles) in diameter and displays a prominent central peak.

Uranus' outermost and largest moon, Oberon, is seen in this Voyager 2 image, obtained January 22, 1986.

This image of Earth, dubbed "Pale Blue Dot," is a part of the first "portrait" of the solar system taken by Voyager 1. The spacecraft acquired a total of 60 frames for a mosaic of the solar system from a distance of more than 4 billion miles from Earth. Earth lies right in the center of one of the scattered light rays, which are the result of taking the image so close to the sun.

This image of Jupiter's moon "Callisto" was captured from a distance of 350,000 kilometers. The large "bull's-eye" at the top of the image is believed to be an impact basin formed early in Callisto's history. The bright center of the basin is about 600 kilometers across and the outer ring is about 2,600 kilometers across.

A gold record in its cover was attached to the Voyager 1 space probe prior to launch. The record, entitled "The Sounds Of Earth" contains a selection of recordings of life and culture on Earth. The cover also contains instructions for any extraterrestrial being wishing to play the record.

  • Launched in 1977, Voyager 1 was part of a twin-spacecraft mission on a multi-planet tour
  • A rare planetary alignment let the mission travel past Jupiter, Saturn, Uranus, Neptune
  • The two Voyagers have provided unparalleled insight into our solar system
  • NASA announced Voyager 1 had left heliosphere last year, but some dispute that

The Art of Movement is a monthly show that highlights the most significant innovations in science and technology that are helping shape our modern world.

(CNN) -- Hurtling across the Milky Way like an eternal explorer -- the Voyager 1 spacecraft continues to nonchalantly reveal the mysteries of the solar system to a captivated Earthbound audience.

Active volcanoes, methane rain, icy geysers and intricate details about Saturn's rings -- the list of revelations attributed to the mission reads like fantastical sci-fi novel but it has revolutionized planetary astronomy.

Thirty-seven years after it launched, Voyager 1 is still out in the vast expanse of space, periodically relaying new data back home. But in 2013, NASA made the groundbreaking announcement that Voyager 1 had left the heliosphere -- a magnetic boundary "bubble," if you will, which scientists use to explain the separation of our solar system from the rest of the galaxy.

"That means Voyager has traveled outside the bubble of our sun," explains Voyager project manager Suzy Dodd. "The data Voyager 1 sends us now is data from other stars and from super nova eruptions and the remnant of stars that have exploded over the course of history."

It's an incredible achievement for a probe built for an initial five-year mission. But now, not for the first time since the extraordinary statement, doubts have been cast on whether the craft has actually made the historic crossing.

While measurements allowed NASA to feel confident enough to confirm Voyager 1 had entered interstellar space, two University of Michigan scientists who have worked on the Voyager missions remain skeptical.

Reliving the moon landing Solar flares caught on camera Zero gravity training with NASA Maneuvering NASA's Curiosity rover

"This controversy will continue until it is resolved by measurements," said George Gloeckler, a University of Michigan professor of atmospheric, oceanic and space sciences, and lead author of a new study, in an American Geophysical Union press release.

To that end, Gloeckler and fellow University of Michigan professor and study co-author Len Fisk, predict that when Voyager does cross the threshold into interstellar space, the probe will identify a reversal in the magnetic field, which will be relayed back to scientists on Earth, conclusively determining the spacecraft's location. They expect this magnetic field shift to occur in the next two years, and if it doesn't, this would confirm that Voyager 1 has already left the heliosphere.

But while we may not know the exact location of Voyager 1, we do know that it's one of the most successful spacecraft of all time.

'The little spacecraft that could'

Launched individually in the summer of 1977, Voyager was a twin-spacecraft primary mission developed by NASA to explore Jupiter and Saturn and their larger moons.

Following successful completion of the Voyager mission's primary objectives, a rare planetary alignment offered up remarkable opportunities for the two craft to continue space exploration.

"Voyager took advantage of alignment of the outer planets, which are Jupiter, Saturn, Uranus and Neptune, to be able to go by all four of those planets in a 12-year period. That alignment of planets only happens every 176 years," says Dodd -- who has described Voyager 1 as "the little spacecraft that could."

So in 1980 the Voyager mission was officially extended and renamed the Interstellar mission. The probes were now participating in an exploratory odyssey to the farthest reaches of the heliosphere . and beyond.

Through remote-control reprogramming -- a technological advancement unavailable at launch -- using Saturn's gravitational field, the Voyager 1 probe was fired like a slingshot on a trajectory that would take it onwards into interstellar space.

Meanwhile Voyager 2 was redirected onto a new flight path, taking in the sights of Neptune and Uranus, before it will eventually follow its counterpart out of the heliosphere. To this day, it remains the only man-made object to have visited Neptune and Uranus.

Not bad for vintage technology that has just 70 kilobytes of memory on board a 16 gigabyte iPhone 5 has more than 240,000 times that amount.

Voyager 1 is now so far from Earth that commands take more than 17 hours to reach it. But it will be a little while before the spacecraft will encounter any more planets.

"It is going to take us 40,000 years to come within three light years of the next nearest sun or the next nearest star," says Dodd. "And that is a long, long time."


History of Saturn

Saturn is easily visible with the unaided eye, so it’s hard to say when the planet was first discovered. The Romans named the planet after Saturnus, the god of the harvest – it’s the same as the Greek god Kronos.

You can also check out these cool telescopes that will help you see the beauty of planet Saturn.

Nobody realized the planet had rings until Galileo first turned his rudimentary telescope on the planet in 1610. Of course, Galileo didn’t realize what he was looking at, and thought the rings were large moons on either side of the planet.

It wasn’t until Christian Huygens used a better telescope to see that they were actually rings. Huygens was also the first to discover Saturn’s largest moon Titan.

Jean-Domanique Cassini uncovered the gap in Saturn’s rings, later named the Cassini Division, and he was the first to see 4 more of Saturn’s moons: Iapetus, Rhea, Tethys, and Dione.

There weren’t many more major discoveries about Saturn until the spacecraft flybys in the 70s and 80s. NASA’s Pioneer 11 was the first spacecraft to visit Saturn, getting within 20,000 km of the planet’s cloud layers. It was followed by Voyager 1 in 1980, and Voyager 2 in August 1981.

It wasn’t until July 2004 that NASA’s Cassini spacecraft arrived at Saturn, and began the most detailed exploration of the system. Cassini has performed multiple flybys of many of Saturn’s moons, and sent back thousands of images of the planet and its moons. It has discovered 4 new moons, a new ring, and saw liquid hydrocarbon seas on Titan.

This article was published when Cassini had finished half its primary mission, and discusses many of the discoveries made so far, and another article when its primary mission was complete.

This article has a timeline of Saturn history, and more history from NASA.

We have recorded two episodes of Astronomy Cast just about Saturn. The first is Episode 59: Saturn, and the second is Episode 61: Saturn’s Moons.


1980: Encounter with Saturn

Next stop on Voyager 1’s cosmic odyssey was Saturn and its system of moons and rings. It made its closest approach to the gas giant on 12 November 1980, coming within 64,200 kilometres (40,000 miles) of the planet’s cloud tops. It sent back the first high-resolution shots of Saturn’s rings and discovered that the planet’s gassy atmosphere was made almost entirely of hydrogen and helium, making it the only planet less dense than water. It also took close-up shots of some of Saturn’s many moons.


How Voyager missions became a grand tour of the Solar System

Launched nearly 40 years ago, the Voyager missions began life as a cheap alternative to the Grand Tour they are on now.

Over the past year, Voyager 1 has made headlines every time it looks like the 36-year-old spacecraft had crossed into interstellar space. But every announcement has been marred with doubt, and Voyager 1’s interstellar status has been quickly revoked.

Ed Stone, the principal scientist behind the Voyager mission, announced that the spacecraft is indeed flying through the unknown environment of interstellar space, making it the first in history to do so (though it hasn’t yet left the Solar System behind).

This historic announcement marks more than just a technological achievement. That the Voyager spacecraft has lasted this long and continues to return valuable scientific data is an incredible triumph for the men and women behind the mission. The story of Voyager is a brilliant illustration of how a team of scientists can transform a single mission into a big science project imbued with technology to make it last well beyond its intended lifetime. And in light of this success, it’s incredible we haven’t seen more missions built along the Voyager model.

Voyager in a nutshell

The Voyager mission is among NASA’s most well-known planetary missions. Two twin spacecrafts, Voyager 1 and Voyager 2, were launched in the fall of 1977. Each visited Jupiter then Saturn to complete their primary missions before flying off in different directions Voyager 1 flew north from the plane on which all the planets orbit, while Voyager 2 was directed to visit both Uranus and Neptune.

After their final planetary encounters in the 1980s, both spacecraft have been rushing out towards the edge of our Solar System. And ever since, scientists have been eagerly awaiting the moment the spacecrafts would cross into interstellar space. This means leaving the heliosphere, the bubble of plasma originating from our Sun that envelopes the whole Solar System. This is what Voyager 1 has just done.

Voyager 1 didn’t set out to be history’s first interstellar spacecraft, and Voyager 2 didn’t set out to visit all four giant planets … but before they were dual-planet missions, NASA expected its exploration of the outer planets to be a grand affair.

Getting to this point is like the cherry on an already heavily frosted cake. Voyager 1 didn’t set out to be history’s first interstellar spacecraft, and Voyager 2 didn’t set out to visit all four giant planets. Both launched as relatively simple dual planet flybys of Jupiter and Saturn. But before they were dual-planet missions, NASA expected its exploration of the outer planets to be a grand affair.

Origins of the Grand Tour

NASA started thinking about its future after Apollo in 1965, three years before the first manned mission of the lunar programmeme flew. There were a number of possible manned missions on the horizon ranging from exploration of our neighbouring planets to the construction of an orbital space station. But there was also a move to bring unmanned planetary exploration to the fore, and just what those missions might look like fell to the National Academy of Sciences’ Space Science Board. In a meeting that summer, the board prepared a study urging NASA to shift its focus from the Moon to the planets, paying special attention to Mars and Venus, without ignoring the outer giant planets.

The study suggested NASA explore the outer planets either with a series of small reconnaissance spacecraft or with one large multi-planet survey mission. The latter mission was an attractive option. Not only was launching one spacecraft cheaper than launching a series of smaller ones, the multi-planet profile took advantage of a once-in-175-years planetary alignment that happened to be on the horizon a favourable launch window for a multi-planet survey of Jupiter, Saturn, Uranus, Neptune, and Pluto existed between 1976 and 1980. But support for the multi-planet mission wasn’t unanimous. Many scientists preferred multiple small missions that brought redundancy into planetary exploration as well as the chance to hone each mission towards answering a specific question.

Choosing between these profiled missions fell to the Outer Planets Working Group NASA established in 1969. The Working Group endorsed the multi-planet flyby mission but expanded it from one to two missions, each of which would visit three planets – a Jupiter-Saturn-Pluto mission launched in 1977, and a Jupiter-Uranus-Neptune mission launched in 1979. Two missions rather than one could visit all five planets in a shorter timeframe, simplifying the technology. Once scientists from the Space Science Board backed this decision, NASA management included this Grand Tour (GT) in its 1971 request for funding.

Perhaps the greatest champion for the multi-planet flyby mission was NASA’s Jet Propulsion Laboratory. In 1967, long before NASA headquarters formally signed off on the project, JPL started promoting the the idea of the GT as a JPL mission. And the mission JPL imagined, lived up to its name. It consisted of four launches: two Jupiter-Saturn-Pluto missions in 1976 and 1977, and two Jupiter-Uranus-Neptune missions in 1979.

At the heart of all four missions was a new spacecraft to be developed by JPL called TOPS. Designed to last up to 10 years, the time each spacecraft would need to visit three planets, the heart of this new spacecraft was a self-testing and repairing computer called STAR. JPL argued that while the more durable spacecraft and sophisticated computer would increase both the cost and weight of the mission, developing these new technologies would create plenty of jobs.

Drawing from experience

As the GT idea took shape, one thing became clear: sending a single spacecraft to visit the outer planets was a hugely costly mission. Sending four was impossible. And the era of bloated budgets was fast coming to an end. When Richard Nixon assumed the presidency in January 1969, he brought even stricter budget cuts to NASA’s already dwindling funding. For Nixon, space was no longer a Cold War battleground and Apollo, which he viewed as a Kennedy programme, was not worth continuing.

Nixon, instead, chose the space shuttle programme. Between the new shuttle and the existing Viking mission to land two crafts on Mars, it was clear Nixon wasn’t going to approve a GT mission as well.

Unwilling to shelve the idea, NASA went back to the drawing board to consider cheaper alternatives. Luckily, the agency and JPL specifically had prior experience with planetary missions to draw from with the Mariner programme.

The Mariner series of missions was designed to launch the the first US spacecraft to other planets, specifically Mars and Venus. The programme achieved this goal: Mariner 2 became the first spacecraft to fly by Venus in 1962 and Mariner 4 managed to get a good look at Mars in 1965. The Mariner programme even saw the successful use of a planetary flyby to slingshot from one planet to the next. A Mariner-type mission to Jupiter and Saturn would be another dual flyby mission with familiar technology. It looked like exploring the outer planets would happen in a piecemeal fashion, but at least it was within NASA’s budget.

NASA’s 1973 budget request included funding for a pair of Mariner class spacecraft, the Mariner Jupiter-Saturn spacecraft to be launched in 1977. These missions would be two-planet alternatives to the GT. The missions were signed into existence on May 18, 1972.

Voyager 2, the only one of the pair on the right trajectory, would be able to visit Uranus and eventually Neptune. It hadn’t been swift or certain, but the pieces of the former Grand Tour were finally coming back together.

From Mariner to Voyager

To reduce the overall cost, NASA decided to leave the design and construction of the Mariner Jupiter-Saturn spacecraft to JPL rather than deal an external contractor. This had the bonus effect of giving JPL scientists and engineers the opportunity to preserve their larger vision for the GT mission. Though the official word was that the Mariner Jupiter-Saturn would visit Uranus and Neptune only if the Saturn encounters were successful, the JPL team had every intention of building a pair of spacecraft that would last long enough to visit all the giant planets.

Right from the start, the team understood the mission’s enormous potential, that it could be one of the truly outstanding if not the most outstanding mission in the whole planetary exploration programme. They set out to fullfill that potential.

The Mariner Jupiter-Saturn mission developed under Stone, a magnetospheric physicist from JPL who had started working on the GT idea in 1970 and was named the mission’s lead scientist in 1972. As it took shape, the Mariner design was supplemented with subsystems designed to increase the mission’s longevity, technology that was being used on the Viking Mars orbiters.

At NASA’s order, the Atomic Energy Commission upgraded the plutonium batteries to be launched with the Mariner Jupiter-Saturn spacecraft so they might last more than ten years, solving the problem of powering the spacecraft through its eventual encounter with Neptune. An additional $7m to the programme enabled a series of scientific and technological enhancements, among which was a re-programmable computer similar to the STAR concept that had been cancelled along with the TOPS spacecraft.

The science payload, too, was developed with longevity in mind. NASA organised the mission scientists into 11 science teams corresponding to the 11 areas of investigation: imaging, radio science, infrared and ultraviolet spectroscopy, magnetometry, charged particles, cosmic rays, photopolarimetry, planetary radio astronomy, plasma, and particulate matter. As for specific objectives, the physical properties of the giant plants – surface features, periods of rotation, energy balances, and thermal regimes of the planets and moons, and investigation of electromagnetic and gravitational fields throughout the Solar System – were the main concerns.

Rolling with the punches

On March 4, 1977, about six months before launch, the twin Mariner Jupiter-Saturn spacecrafts were renamed Voyagers 1 and 2. Voyager 2 launched first on August 22 and Voyager 1 followed on September 5.

It wasn’t long before systems and instruments started to fail. Before it reached Jupiter, Voyager 1’s scan platform, which turns on three axis and aims the cameras, spectrometres, and photopolarimetre in the most scientifically interesting directions, became stuck. Voyager 2’s scan platform similarly jammed after its encounter with Saturn.

Voyager 2 also had significant problems with its radio systems failing early in the mission, but a series of commands uploaded into the re-programmable computer ensured scientists would at least have minimal communications with their proxy when it encountered planets. And both spacecraft were affected by the high radiation levels around Jupiter commands became difficult to send and some instruments were damaged. But the consistent threat of full failure was never realised.

When Voyager 1 left Saturn in 1980, the science return from the mission was very impressive, and Voyager 2 was deemed to be in good enough health that the mission was granted an extension. Voyager 2, the only one of the pair on the right trajectory, would be able to visit Uranus and eventually Neptune. It hadn’t been swift or certain, but the pieces of the former Grand Tour were finally coming back together.

Voyager 1 is about to leave the solar system after being launched 35 years ago making it the farthest manmade object from Earth and very close to entering interstellar space [AP]

Continued success through the primary and extended missions has been due in no small part to the science team’s’ continued improvement to spacecraft as they fly further from Earth every minute. In upgrading the Mariner 10 camera to image Mercury, JPL engineers developed a new electronic technique that read out the image signal three times more slowly. They applied the same technique to the Voyager cameras and found that it not only facilitated data transfer from Saturn, it was a necessary procedure for imaging at Uranus.

Engineers also developed a new type of coding that promised error-free data transmission, and this was transmitted to Voyager 2 in preparation for its Uranus encounter. Once NASA’s Deep Space Network of tracking stations became unable to ensure consistent communication with the increasingly distant Voyager spacecraft, JPL engineers borrowed a technique from radio astronomy and arrayed two antennas together to improve signal strength. Among the tracking sites it upgraded, NASA upgraded the facilities at the Very Large Array radio telescope in New Mexico making it at once the communications point for Voyager 2’s encounter with Neptune, and a state-of-the-art facility for planetary radar astronomy.

An incredible success

This continual revision and upgrading continues to be a major part of Voyager’s success, as does the team’s familiarity with the mission. And more recently, the clever use of instruments to answer questions they weren’t designed to answer, has allowed the science team to continue making new discoveries. Case in point, the announcement of Voyager 1’s interstellar status . Plasma is the key indicator that the spacecraft is in a new region of space, but Voyager 1‘s plasma-measuring instrument failed long ago. So the team used the two antennae that measure magnetic fields instead. A change in the direction of the magnetic field, they determined, was indicative of a change in the plasma environment. This is just what Voyager 1 registered as it passed into interstellar space.

It’s incredible to think that the Voyager missions that took us on a grand tour of the Solar System began life as the cheaper version of the ideal Grand Tour mission. And the mission isn’t over. Both Voyager spacecraft are still talking to Earth with what instruments they have that are still working, returning information on the furthest reaches of the solar system and interstellar space.

But they can’t go on forever. Starting in 2020, the science team will have to turn off one instrument per year to preserve power. In 2025, with their fuel depleted, both spacecraft will be permanently shut down. Hopefully by then, we’ll have a new, long term, deep space mission in the pipeline to look forward to. Even if it’s a small one that has the potential to grow into something much bigger.

Amy Shira Teitel has an academic background in the history of science and now works as a freelance science writer specialising in spaceflight history. She maintains her own blog, Vintage Space, and contributes regularly to Discovery News, Scientific American, Motherboard, DVICE.


Saturn’s Secrets Revealed: The 40th Anniversary Of The Voyager 1 Flyby

In 1980, Voyager 1 became only the second space probe to ever fly past the planet Saturn. Voyagers 1 and 2 were twin space probes that were launched in 1977. They were designed for what was to be called the grand tour of the outer planets. A rare alignment of planets that only occurs every 175 years would allow a space probe to visit all four outer gas giants. Both Voyager 1 and Voyager 2 would fly past Jupiter and Saturn. Voyager 2 would continue on to Uranus in 1986, and finally Neptune in 1989.

On September 1, 1979, Pioneer 11 became the first space probe to fly past Saturn. The cameras and instruments on this probe were not as sophisticated as those on Voyager however. It would be up to the Voyager probes to truly reveal in detail the majesty of Saturn and its moons. On November 12, 1980, Voyager 1 made a close approach of Saturn, coming within 124,000 kilometers of Saturn’s cloud-tops. The probe confirmed that the majority of Saturn’s atmosphere is made up of Hydrogen gas. Voyager 1 measured the rotation of Saturn at 10 hours, 39 minutes. Hundreds of photos of Saturn and its ring system were taken. The rings were determined to be made almost entirely of water ice, with a small amount of rocky material.

False Color Voyager Image of Saturn

In addition to studying Saturn up close, Voyager 1 also photographed and gathered data on the many moons of Saturn. Of particular interest was Saturn’s largest moon, Titan. Titan is unique in the solar system as being the only moon with a thick, substantial atmosphere.The atmosphere of Titan is largely made up of nitrogen with methane and ethane clouds and nitrogen-rich organic smog. In order to make a close fly-by of Titan, Voyager 1 would be unable to continue to Uranus and Neptune. The Titan encounter was considered very important by the mission scientists. If Voyager 1 had failed to acquire the Titan data, Voyager 2 would have been rerouted to Titan and would not have continued on to Uranus and Neptune.

Titan’s surface taken by Huygen’s Titan Lander Probe

After the successful encounter with Saturn and its moon Titan, Voyager 1 would continue on a journey to the heliopause. The heliopause is the theoretical boundary where the Sun’s solar wind is stopped by the interstellar medium. Here, the solar wind’s strength is no longer great enough to push back the stellar winds of the surrounding stars. On August 25, 2012, Voyager 1 became the first spacecraft to cross the heliopause and enter the interstellar medium.

Other spacecraft would also visit Saturn. Voyager 2 would fly past in August 1981. The Cassini spacecraft went into orbit around Saturn on July 1, 2004. Cassini would continue to send back pictures and data until the mission ended on September 15, 2017, when the probe’s trajectory took it into Saturn’s upper atmosphere where it burned up. The Cassini spacecraft also delivered the Huygens Titan lander probe. Huygens became the first spacecraft to land on Titan on January 14, 2005, giving us our first detailed views of the surface of this mysterious moon.

It was the Voyager 1 spacecraft in November 1980 though that really paved the way for these future missions by giving us our first close-up look at Saturn, its rings and its moons. A true milestone mission in space exploration.

Voyager image taken November 3, 1980 of Saturn and two of its moons: Tethys and Dione

Voyager 1: 'The little spacecraft that could'

Scientists may dispute the exact location of Voyager 1, but the spacecraft remains one of NASA's greatest success stories. Take a look at some of the amazing images the probe has provided its Earthbound audience.

Jupiter, its Great Red Spot and three of its four largest satellites are visible in this photo taken February 5, 1979, by Voyager 1.

A dramatic view of Jupiter's Great Red Spot and its surroundings was obtained by Voyager 1 on February 25, 1979.

This image of Jupiter was assembled from three black and white negatives from different color filters and recombined to produce the color image.

Voyager 1 captured the first evidence of a ring around the planet Jupiter. The multiple exposure of the extremely thin faint ring appears as a broad light band crossing the center of the picture. The background stars look like broken hairpins because of spacecraft motion during the 11-minute exposure. The black dots are geometric calibration points in the camera.

This mosaic image of Jupiter's moon "Io" shows a variety of features that appear linked to the intense volcanic activity. The circular, doughnut-shaped feature in the center has been identified as a known erupting volcano.

Another image of "Io" shows an active plume of a volcano dubbed "Loki."

This August 1998 NASA file image shows a true color photo of Saturn assembled from the Voyager 2 spacecraft.

A mosaic image of Saturn's rings, taken by NASA's Voyager 1 on November 6, 1980, shows approximately 95 individual concentric features in the rings. The ring structure was once thought to be produced by the gravitational interaction between Saturn's satellites and the orbit of ring particles, but has now been found to be too complex for this explanation alone.

This image of Rhea, the largest airless satellite of Saturn, was acquired by the Voyager 1 spacecraft on November 11, 1980.

The cratered surface of Saturn's moon "Mimas" is seen in this image taken by Voyager 1 on November 12, 1980. Impact craters made by the infall of cosmic debris are shown the largest is more than 100 kilometers (62 miles) in diameter and displays a prominent central peak.

Uranus' outermost and largest moon, Oberon, is seen in this Voyager 2 image, obtained January 22, 1986.

This image of Earth, dubbed "Pale Blue Dot," is a part of the first "portrait" of the solar system taken by Voyager 1. The spacecraft acquired a total of 60 frames for a mosaic of the solar system from a distance of more than 4 billion miles from Earth. Earth lies right in the center of one of the scattered light rays, which are the result of taking the image so close to the sun.

This image of Jupiter's moon "Callisto" was captured from a distance of 350,000 kilometers. The large "bull's-eye" at the top of the image is believed to be an impact basin formed early in Callisto's history. The bright center of the basin is about 600 kilometers across and the outer ring is about 2,600 kilometers across.

A gold record in its cover was attached to the Voyager 1 space probe prior to launch. The record, entitled "The Sounds Of Earth" contains a selection of recordings of life and culture on Earth. The cover also contains instructions for any extraterrestrial being wishing to play the record.

  • Launched in 1977, Voyager 1 was part of a twin-spacecraft mission on a multi-planet tour
  • A rare planetary alignment let the mission travel past Jupiter, Saturn, Uranus, Neptune
  • The two Voyagers have provided unparalleled insight into our solar system
  • NASA announced Voyager 1 had left heliosphere last year, but some dispute that

The Art of Movement is a monthly show that highlights the most significant innovations in science and technology that are helping shape our modern world.

(CNN) -- Hurtling across the Milky Way like an eternal explorer -- the Voyager 1 spacecraft continues to nonchalantly reveal the mysteries of the solar system to a captivated Earthbound audience.

Active volcanoes, methane rain, icy geysers and intricate details about Saturn's rings -- the list of revelations attributed to the mission reads like fantastical sci-fi novel but it has revolutionized planetary astronomy.

Thirty-seven years after it launched, Voyager 1 is still out in the vast expanse of space, periodically relaying new data back home. But in 2013, NASA made the groundbreaking announcement that Voyager 1 had left the heliosphere -- a magnetic boundary "bubble," if you will, which scientists use to explain the separation of our solar system from the rest of the galaxy.

"That means Voyager has traveled outside the bubble of our sun," explains Voyager project manager Suzy Dodd. "The data Voyager 1 sends us now is data from other stars and from super nova eruptions and the remnant of stars that have exploded over the course of history."

It's an incredible achievement for a probe built for an initial five-year mission. But now, not for the first time since the extraordinary statement, doubts have been cast on whether the craft has actually made the historic crossing.

While measurements allowed NASA to feel confident enough to confirm Voyager 1 had entered interstellar space, two University of Michigan scientists who have worked on the Voyager missions remain skeptical.

Reliving the moon landing Solar flares caught on camera Zero gravity training with NASA Maneuvering NASA's Curiosity rover

"This controversy will continue until it is resolved by measurements," said George Gloeckler, a University of Michigan professor of atmospheric, oceanic and space sciences, and lead author of a new study, in an American Geophysical Union press release.

To that end, Gloeckler and fellow University of Michigan professor and study co-author Len Fisk, predict that when Voyager does cross the threshold into interstellar space, the probe will identify a reversal in the magnetic field, which will be relayed back to scientists on Earth, conclusively determining the spacecraft's location. They expect this magnetic field shift to occur in the next two years, and if it doesn't, this would confirm that Voyager 1 has already left the heliosphere.

But while we may not know the exact location of Voyager 1, we do know that it's one of the most successful spacecraft of all time.

'The little spacecraft that could'

Launched individually in the summer of 1977, Voyager was a twin-spacecraft primary mission developed by NASA to explore Jupiter and Saturn and their larger moons.

Following successful completion of the Voyager mission's primary objectives, a rare planetary alignment offered up remarkable opportunities for the two craft to continue space exploration.

"Voyager took advantage of alignment of the outer planets, which are Jupiter, Saturn, Uranus and Neptune, to be able to go by all four of those planets in a 12-year period. That alignment of planets only happens every 176 years," says Dodd -- who has described Voyager 1 as "the little spacecraft that could."

So in 1980 the Voyager mission was officially extended and renamed the Interstellar mission. The probes were now participating in an exploratory odyssey to the farthest reaches of the heliosphere . and beyond.

Through remote-control reprogramming -- a technological advancement unavailable at launch -- using Saturn's gravitational field, the Voyager 1 probe was fired like a slingshot on a trajectory that would take it onwards into interstellar space.

Meanwhile Voyager 2 was redirected onto a new flight path, taking in the sights of Neptune and Uranus, before it will eventually follow its counterpart out of the heliosphere. To this day, it remains the only man-made object to have visited Neptune and Uranus.

Not bad for vintage technology that has just 70 kilobytes of memory on board a 16 gigabyte iPhone 5 has more than 240,000 times that amount.

Voyager 1 is now so far from Earth that commands take more than 17 hours to reach it. But it will be a little while before the spacecraft will encounter any more planets.

"It is going to take us 40,000 years to come within three light years of the next nearest sun or the next nearest star," says Dodd. "And that is a long, long time."


Voyager 1 Explores Saturn - HISTORY

The Voyager 1 and 2 Saturn encounters occurred nine months apart, in November 1980 and August 1981. Voyager 1 is leaving the solar system. Voyager 2 completed its encounter with Uranus in January 1986 and with Neptune in August 1989, and is now also en route out of the solar system.

The two Saturn encounters increased our knowledge and altered our understanding of Saturn. The extended, close-range observations provided high-resolution data far different from the picture assembled during centuries of Earth-based studies.

Here is a summary of scientific findings by the two Voyagers at Saturn.

Saturn's atmosphere is almost entirely hydrogen and helium. Voyager 1 found that about 7 percent of the volume of Saturn's upper atmosphere is helium (compared with 11 percent of Jupiter's atmosphere), while almost all the rest is hydrogen. Since Saturn's internal helium abundance was expected to be the same as Jupiter's and the Sun's, the lower abundance of helium in the upper atmosphere may imply that the heavier helium may be slowly sinking through Saturn's hydrogen that might explain the excess heat that Saturn radiates over energy it receives from the Sun. (Saturn is the only planet less dense than water. In the unlikely event that a lake could be found large enough, Saturn would float in it.)

Subdued contrasts and color differences on Saturn could be a result of more horizontal mixing or less production of localized colors than in Jupiter's atmosphere. While Voyager 1 saw few markings, Voyager 2's more sensitive cameras saw many: long-lived ovals, tilted features in east-west shear zones, and others similar to, but generally smaller than, on Jupiter.

Winds blow at high speeds in Saturn. Near the equator, the Voyagers measured winds about 500 meters a second (1,100 miles an hour). The wind blows mostly in an easterly direction. Strongest winds are found near the equator, and velocity falls off uniformly at higher latitudes. At latitudes greater than 35°, winds alternate east and west as latitude increases. Marked dominance of eastward jet streams indicates that winds are not confined to the cloud layer, but must extend inward at least 2,000 kilometers (1,200 miles). Furthermore, measurements by Voyager 2 showing a striking north-south symmetry that leads some scientists to suggest the winds may extend from north to south through the interior of the planet.

While Voyager 2 was behind Saturn, its radio beam penetrated the upper atmosphere, and measured temperature and density. Minimum temperatures of 82 Kelvin (-312°F) were found at the 70-millibar level (surface pressure on Earth is 1,000 millibars). The temperature increased to 143 Kelvins (-202 °F) at the deepest levels probed - - about 1,200 millibars. Near the north pole temperatures were about 10°C (18°F) colder at 100 millibars than at mid-latitudes. The difference may be seasonal.

The Voyagers found aurora-like ultraviolet emissions of hydrogen at mid-latitudes in the atmosphere, and auroras at polar latitudes (above 65°). The high-level auroral activity may lead to formation of complex hydrocarbon molecules that are carried toward the equator. The mid-latitude auroras, which occur only in sunlit regions, remain a puzzle, since bombardment by electrons and ions, known to cause auroras on Earth, occurs primarily at high latitudes.

Both Voyagers measured the rotation of Saturn (the length of a day) at 10 hours, 39 minutes, 24 seconds.

Perhaps the greatest surprises and the most perplexing puzzles the two Voyagers found are in the rings.

Voyager 1 found much structure in the classical A-, B- and C-rings. Some scientists suggest that the structure might be unresolved ringlets and gaps. Photos by Voyager 1 were of lower resolution than those of Voyager 2, and scientists at first believed the gaps might be created by tiny satellites orbiting within the rings and sweeping out bands of particles. One such gap was detected at the inner edge of the Cassini Division.

Voyager 2 measurements provided the data scientists need to understand the structure. High-resolution photos of the inner edge of the Cassini Division showed no sign of satellites larger than five to nine kilometers (three to six miles). No systematic searches were conducted in other ring gaps.

Voyager 2's photopolarimeter provided more surprises. The instrument measured changes in starlight from Delta Scorpii as Voyager 2 flew above the rings and the light passed through them. The photopolarimeter could resolve structures smaller than 300 meters (1,000 feet).

The star-occultation experiment showed that few clear gaps exist in the rings. The structure in the B-ring, instead, appears to be variations in density waves or other, stationary, forms of waves. Density waves are formed by the gravitational effects of Saturn's satellites. (The resonant points are places where a particle would orbit Saturn in one-half or one-third the time needed by a satellite, such as Mimas.) For example, at the 2:1 resonant point with Janus (1980S1), a series of outward-propagating density waves has about 60 grams of material per square centimeter of ring area, and the velocity of particles relative to one another is about one millimeter per second. Small-scale structure of the rings may therefore be transitory, although larger-scale features, such as the Cassini and Encke Divisions, appear more permanent.

The edges of the rings where the few gaps exist are so sharp that the ring must be less than about 200 meters (650 feet) thick there, and may be only 10 meters (33 feet) thick.

In almost every case where clear gaps do appear in the rings, eccentric ringlets are found. All show variations in brightness. Some differences are due to the existence of clumps or kinks, and others to nearly complete absence of material. Some scientists believe the only plausible explanation for the clear regions and kinky ringlets is the presence of nearby undetected satellites.

Two separate, discontinuous ringlets were found in the A-ring gap, known as Encke's Gap, about 73,000 kilometers (45,000 miles) from Saturn's cloud tops. At high resolution, at least one of the ringlets has multiple strands.

Saturn's F-ring was discovered by Pioneer 11 in 1979. Photos of the F-ring taken by Voyager 1 showed three separate strands that appear twisted or braided. At higher resolution, Voyager 2 found five separate strands in a region that had no apparent braiding, and surprisingly revealed only one small region where the F-ring appeared twisted. The photopolarimeter found the brightest of the F-ring strands was subdivided into at least 10 strands. The twists are believed to originate in gravitational perturbations caused by one of two shepherding satellites, Prometheus (1980S27). Clumps in the F-ring appear uniformly distributed around the ring every 9,000 kilometers (5,600 miles), a spacing that very nearly coincides with the relative motion of F-ring particles and the interior shepherding satellite in one orbital period. By analogy, similar mechanisms might be operating for the kinky ringlets that exist in the Encke Gap.

The spokes found in the B-ring appear only at radial distances between 43,000 kilometers (27,000 miles) and 57,000 kilometers (35,000 miles) above Saturn's clouds. Some spokes, those thought to be most recently formed, are narrow and have a radial alignment, and appear to corotate with Saturn's magnetic field in 10 hours, 39.4 minutes. The broader, less radial spokes appear to have formed earlier than the narrow examples and seem to follow Keplerian orbits. Individual areas corotate at speeds governed by distances from the center of the planet. In some cases, scientists believe they see evidence that new spokes are reprinted over older ones. Their formation is not restricted to regions near the planet's shadow, but seems to favor a particular Saturnian longitude. As both spacecraft approached Saturn, the spokes appeared dark against a bright ring background. As the Voyagers departed, the spokes appeared brighter than the surrounding ring areas, indicating that the material scatters reflected sunlight more efficiently in a forward direction, a quality that is characteristic of fine, dust-sized particles. Spokes are also visible at high phase angles in light reflected from Saturn on the un-illuminated underside of the rings.

Another challenge scientists face in understanding the rings is that even general dimensions do not seem to remain true at all positions around Saturn: The distance of the B-ring's outer edge, near a 2:1 resonance with Mimas, varies by at least 140 kilometers (90 miles) and probably by as much as 200 kilometers (120 miles). Furthermore, the elliptical shape of the outer edge does not follow a Keplerian orbit, since Saturn is at the center of the ellipse, rather than at one focus. The gravitational effects of Mimas are most likely responsible for the elliptical shape, as well as for the variable width of the Huygens Gap between the B-ring and the Cassini Division.

Titan is the largest of Saturn's satellites. It is the second largest satellite in the solar system, and the only one know to have a dense atmosphere.

It may be the most interesting body, from a terrestrial perspective, in the solar system. For almost two decades, space scientists have searched for clues to the primeval Earth. The chemistry in Titan's atmosphere may be similar to what occurred in Earth's atmosphere several billion years ago.

Because of its thick, opaque atmosphere, astronomers believed Titan was the largest satellite in the solar system. Their measurements were necessarily limited to the cloud tops. Voyager 1's close approach and diametric radio occultation show Titan's surface diameter is only 5,150 kilometers (3,200 miles) - - slightly smaller than Ganymede, Jupiter's largest satellite. Both are larger than Mercury. Titan's density appears to be about twice that of water ice it may be composed of nearly equal amounts of rock and ice.

Titan's surface cannot be seen in any Voyager photos it is hidden by a dense, photochemical haze whose main layer is about 300 kilometers (200 miles) above Titan's surface. Several distinct, detached haze layers can be seen above the opaque haze layer. The haze layers merge with the main layer over the north pole of Titan, forming what scientists first thought was a dark hood. The hood was found, under the better viewing conditions of Voyager 2, to be a dark ring around the pole. The southern hemisphere is slightly brighter than the northern, possibly the result of seasonal effects. When the Voyagers flew past, the season on Titan was the equivalent of mid-April and early May on Earth, or early spring in the northern hemisphere and early fall in the south.

Atmospheric pressure near Titan's surface is about 1.6 bars, 60 percent greater than Earth's. The atmosphere is mostly nitrogen, also the major constituent of Earth's atmosphere.

The surface temperature appears to be about 95 Kelvins (-289°F), only 4 Kelvins above the triple-point temperature of methane. Methane, however, appears to be below its saturation pressure near Titan's surface rivers and lakes of methane probably don't exist, in spite of the tantalizing analogy to water on Earth. On the other hand, scientists believe lakes of ethane exist, and methane is probably dissolved in the ethane. Titan's methane, through continuing photochemistry, is converted to ethane, acetylene, ethylene, and (when combined with nitrogen) hydrogen cyanide. The last is an especially important molecule it is a building block of amino acids. Titan's low temperature undoubtedly inhibits more complex organic chemistry.

Titan has no intrinsic magnetic field therefore it has no electrically conducting and convecting liquid core. Its interaction with Saturn's magnetosphere creates a magnetic wake behind Titan. The big satellite also serves as a source for both neutral and charged hydrogen atoms in Saturn's magnetosphere.

Before the first Voyager encounter, astronomers believed Saturn had 11 satellites. Now they know it has at least 17 and possibly more. Three of the 17 were discovered by Voyager 1. Three additional possible satellites have been identified in imaging data since the Voyager 2 encounter. (Three others were discovered in ground-based observations.)

The innermost satellite, Atlas, orbits near the outer edge of the A-ring and is about 40 by 20 kilometers (25 by 15 miles) in size. It was discovered in Voyager 1 images.

The next satellite outward, Prometheus, shepherds the inner edge of the F-ring and is about 140 by 100 by 80 kilometers (90 by 60 by 50 miles) in size. Next is Pandora, the outer shepherd of the F-ring and is 110 by 90 by 80 kilometers (70 by 55 by 50 miles) in size. Both shepherds were found by Voyager 1.

Next are Epimetheus and Janus, which share about the same orbit -- 91,000 kilometers (56,600 miles) above the clouds. As they near each other, the satellites trade orbits (the outer is about 50 kilometers, or 30 miles, farther from Saturn than the inner). Janus is 220 by 200 by 160 kilometers (140 by 125 by 100 miles), and Epimetheus is 140 by 120 by 100 kilometers (90 by 70 by 50 miles) in size. Both were discovered by ground-based observers.

One new satellite, Helene, shares the orbit of Dione, about 60° ahead of its larger companion, and is called the Dione Trojan. It is about 36 by 32 by 30 kilometers (22 by 20 by 19 miles). Helene was discovered in ground-based photographs.

Two more satellites are called the Tethys Trojans because they circle Saturn in the same orbit as Tethys, about 60° ahead of and behind that body. They are Telesto (the leading Trojan) and Calypso (the trailing Trojan). Both were found in 1981 among ground-based observations made in 1980. Telesto is 34 by 28 by 26 kilometers (21 by 17 by 16 miles) and Calypso is 34 by 22 by 22 kilometers (21 by 14 by 14 miles).

There are three unconfirmed satellites. One circles Saturn in the orbit of Dione, a second is located between the orbits of Tethys and Dione, and the third, between Dione and Rhea. All three were found in Voyager photographs, but were not confirmed by more than one sighting.

Mimas, Enceladus, Tethys, Dione, and Rhea are approximately spherical in shape and appear to be composed mostly of water ice. Enceladus reflects almost 100 percent of the sunlight that strikes it. All five satellites represent a size range that had not been explored before.

Mimas, Tethys, Dione, and Rhea are all cratered Enceladus appears to have by far the most active surface of any satellite in the system (with the possible exception of Titan, whose surface was not photographed). At least five types of terrain have been identified on Enceladus. Although craters can be seen across portions of its surface, the lack of craters in other areas implies an age less than a few hundred million years for the youngest regions. It seems likely that parts of the surface are still undergoing change, since some areas are covered by ridged plains with no evidence of cratering down to the limit of resolution of Voyager 2's cameras (2 kilometers or 1.2 miles). A pattern of linear faults crisscrosses other areas. It is not likely that a satellite as small as Enceladus could have enough radioactive material to produce the modification. A more likely source of heating appears to be tidal interaction with Saturn, caused by perturbations in Enceladus' orbit by Dione (like Jupiter's satellite Io). Theories of tidal heating do not predict generation of enough energy to explain all the heating that must have occurred. Because it reflects so much sunlight, Enceladus' current surface temperature is only 72 Kelvins (-330°F).

Photos of Mimas show a huge impact crater. The crater, named Herschel, is 130 kilometers (80 miles) wide, one-third the diameter of Mimas. Herschel is 10 kilometers (6 miles) deep, with a central mountain almost as high as Mount Everest on Earth.

Photos of Tethys taken by Voyager 2 show an even larger impact crater, named Odysseus, nearly one-third the diameter of Tethys and larger than Mimas. In contrast to Mimas' Herschel, the floor of Odysseus returned to about the original shape of the surface, most likely a result of Tethys' larger gravity and the relative fluidity of water ice. A gigantic fracture covers three-fourths of Tethys' circumference. The fissure is about the size scientists would predict if Tethys were once fluid and its crust hardened before the interior, although the expansion of the interior due to freezing would not be expected to cause only one large crack. The canyon has been named Ithaca Chasma. Tethys' surface temperature is 86 Kelvins (-305°F).

Hyperion shows no evidence of internal activity. Its irregular shape causes an unusual phenomenon: each time Hyperion passes Titan, the larger satellite's gravity gives Hyperion a tug and it tumbles erratically, changing orientation. The irregular shape of Hyperion and evidence of bombardment by meteors make it appear to be the oldest surface in the Saturn system.

Iapetus has long been known to have large differences in surface brightness. Brightness of the surface material on the trailing side has been measured at 50 percent, while material on the leading side reflects only 5 percent of the sunlight. Most dark material is distributed in a pattern directly centered on the leading surface, causing conjecture that dark material in orbit around Saturn was swept up by Iapetus. The trailing face of Iapetus, however, has craters with dark floors. That implies that the dark material originated in the satellite's interior. It is possible that the dark material on the leading hemisphere was exposed by ablation (erosion) of a thin, overlying, bright surface covering.

Voyager 2 photographed Phoebe after passing Saturn. Phoebe orbits Saturn in a retrograde direction (opposite to the direction of the other satellites' orbits) in a plane much closer to the ecliptic than to Saturn's equatorial plane. Voyager 2 found that Phoebe has a roughly circular shape, and reflects about 6 percent of the sunlight. It also is quite red. Phoebe rotates on its axis about once in nine hours. Thus, unlike the other Saturnian satellites (except Hyperion), it does not always show the same face to the planet. If, as scientists believe, Phoebe is a captured asteroid with its composition unmodified since its formation in the outer solar system, it is the first such object that has been photographed at close enough range to show shape and surface brightness.

Both Dione and Rhea have bright, wispy streaks that stand out against an already-bright surface. The streaks are probably the results of ice that evolved from the interior along fractures in the crust.

The size of Saturn's magnetosphere is determined by external pressure of the solar wind. When Voyager 2 entered the magnetosphere, the solar-wind pressure was high and the magneto- sphere extended only 19 Saturn radii (1.1 million kilometers or 712,000 miles) in the Sun's direction. Several hours later, however, the solar-wind pressure dropped and Saturn's magneto- sphere ballooned outward over a six-hour period. It apparently remained inflated for at least three days, since it was 70 percent larger when Voyager 2 crossed the magnetic boundary on the outbound leg.

Unlike all the other planets whose magnetic fields have been measured, Saturn's field is tipped less than one degree relative to the rotation poles. That rare alignment was first measured by Pioneer 11 in 1979 and was later confirmed by Voyagers 1 and 2.

Several distinct regions have been identified within Saturn's magnetosphere. Inside about 400,000 kilometers (250,000 miles) there is a torus of H+ and O+ ions, probably originating from water ice sputtered from the surfaces of Dione and Tethys. (The ions are positively charged atoms of hydrogen and oxygen that have lost one electron.) Strong plasma-wave emissions appear to be associated with the inner torus.

At the outer regions of the inner torus some ions have been accelerated to high velocities. In terms of temperatures, such velocities correspond to 400 million to 500 million Kelvins (700 to 900 million degrees F).

Outside the inner torus is a thick sheet of plasma that extends out to about 1 million kilometers (620,000 miles). The source for material in the outer plasma sheet is probably Saturn's ionosphere, Titan's atmosphere, and the neutral hydrogen torus that surrounds Titan between 500,000 kilometers (300,000 miles) and 1.5 million kilometers (1 million miles).

Radio emissions from Saturn had changed between the encounters of Voyager 1 and 2. Voyager 2 detected Jupiter's magnetotail as the spacecraft approached Saturn in the winter and early spring of 1981. Soon afterward, when Saturn was believed to be bathed in the Jovian magnetotail, the ringed planet's kilometric radio emissions were undetectable.

During portions of Voyager 2's Saturn encounter, kilometric radio emissions again were not detected. The observations are consistent with Saturn's being immersed in Jupiter's magnetotail, as was also the apparent reduction in solar-wind pressure mentioned earlier, although Voyager scientists say they have no direct evidence that those effects were caused by Jupiter's magnetotail.

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40 Years Ago: Voyager 1 Explores Jupiter

[NASA] Today, Voyager 1 is the most distant spacecraft from Earth, more than 13 billion miles away. Forty years ago, the spacecraft fairly close to the beginning of its incredible journey through and out of our solar system. On March 5th, 1979,Voyager 1 was making its closest approach to Jupiter.

[Trajectory of Voyager 1 through the Jovian system.]

Although it was not the first to explore the giant planet, Pioneer 10 and 11 completed earlier flybys in 1973 and 1974, respectively, Voyager carried sophisticated instruments to conduct more in-depth investigations. Managed by the Jet Propulsion Laboratory in Pasadena, California, the Voyagers were a pair of spacecraft launched in 1977 to explore the outer planets. Initially targeted only to visit Jupiter and Saturn, Voyager 2 went on to investigate Uranus and Neptune as well, taking advantage of a rare planetary alignment that occurs once every 175 years to use the gravity of one planet to redirect it to the next.

[Schematic of the Voyager spacecraft, illustrating the science experiments.]

The suite of 11 instruments included: an imaging science system consisting of narrow-angle and wide-angle cameras to photograph the planet and its satellites a radio science system to determine the planet’s physical properties an infrared interferometer spectrometer to investigate local and global energy balance and atmospheric composition an ultraviolet spectrometer to measure atmospheric properties a magnetometer to analyze the planet’s magnetic field and interaction with the solar wind a plasma spectrometer to investigate microscopic properties of plasma ions a low energy charged particle device to measure fluxes and distributions of ions a cosmic ray detection system to determine the origin and behavior of cosmic radiation a planetary radio astronomy investigation to study radio emissions from Jupiter a photopolarimeter to measure the planet’s surface composition and a plasma wave system to study the planet’s magnetosphere.

[Launch of Voyager 1, September 5th, 1977.]

Two weeks after its launch from Florida on Sep. 5, 1977, Voyager 1 turned its cameras back toward its home planet and took the first single-frame image of the Earth-Moon system, providing a taste of future discoveries at the outer planets. It successfully crossed the asteroid belt between Dec. 10, 1977, and Sep. 8, 1978.

[The first single-frame image of the Earth-Moon system, taken by Voyager 1.]

The spacecraft began its encounter phase with the Jovian system on Jan. 6, 1979, sending back its first images and taking the first science measurements. On Mar. 5, still inbound toward the planet, it flew at 262,000 miles of Jupiter’s small inner moon Amalthea, taking the first close-up photograph of that satellite revealing it to be oblong in shape and reddish in color. About five hours later, Voyager 1 made its closest approach to Jupiter, flying within 174,000 miles of the planet’s cloud tops. On the outbound leg of its encounter, it flew by and imaged the large satellites Io (closest approach of 12,800 miles), Europa (456,000 miles), Ganymede (71,300 miles), and Callisto (78,600 miles), all discovered by Italian astronomer Galileo in 1610 using his newly invented telescope. The Voyager images revealed each satellite to have a unique appearance, the most remarkable discovery being an active volcano on Io.

[Composite image of Jupiter’s four large Galilean satellites, shown to scale (clockwise from top left) Io, Europa, Callisto, and Ganymede.]

Voyager 1 also discovered two previously unknown moons orbiting Jupiter, later named Thebe and Metis. Looking back at Jupiter as it was backlit by the Sun, Voyager 1 discovered that the planet is surrounded by a thin ring. Observations of Jupiter concluded on Apr. 13.

[Voyager 1 took the image of Jupiter backlit by the Sun, and discovered that the planet has a thin ring system.]

After its successful exploration of the Jovian system, Voyager 1 sailed on toward Saturn. During its encounter in November 1980, the spacecraft returned a wealth of information about the planet, its spectacular rings and its satellites especially Titan, known to have a dense atmosphere. Saturn’s gravity imparted enough acceleration on Voyager 1 that it achieved escape velocity from the solar system. More than 41 years after its launch, several of the spacecraft’s instruments are still returning useful data about conditions on the very edges of the solar system and even beyond.

[Model of the Voyager spacecraft]

In August 2012, Voyager 1 crossed the heliopause, the boundary between the heliosphere, the bubble-like region of space created by the Sun, and the interstellar medium. It is expected that Voyager 1 will continue to return data from interstellar space until about 2025. And just in case it may one day be found by an alien intelligence, Voyager 1 and its twin carry gold plated records that contain information about its home planet, including recordings of terrestrial sounds, music and greetings in 55 languages. Instructions on how to play the record are also included.