While astronauts have so far only ventured as far as the Moon, robotic explorers have been revolutionising our knowledge of the Solar System since the early 1960s. Among the most significant of these space probes are the Voyager missions, launched in August 1977 to explore the outer planets and still operating today! 

The twin Voyager 1 and 2 spacecraft were initially targeted at exploring the planets Jupiter and Saturn. They revealed how dynamic these planets are, with roiling cloud systems and massive cyclonic storms, lightning, auroras and fierce radiation environments. Voyager 1 discovered that Jupiter has a faint ring system, and the two spacecraft unveiled the incredible complexity of Saturn’s glorious ring system, with twists, kinks and shepherd moons that sculpt the shape of the rings.  

planetary images

These photos of the four Galilean satellites of Jupiter were taken by Voyager 1 during its approach to the planet in early March 1979. Io (top left), Europa (top right), Ganymede (bottom left) and Callisto (bottom right) are shown in their correct relative sizes: Ganymede and Callisto are both larger than the planet Mercury; Io and Europa are about the same size as the Moon. 

Image processing also preserves the relative contrasts of the satellites. Thus it is apparent that Europa has the least contrast; Io the greatest. Io is covered with active volcanoes and a surface composed largely of sulfur. Europa is apparently very different; Voyager 1 did not approach Europa closely enough to show its surface in great detail; that remains for Voyager 2. Ganymede and Callisto are both composed mostly of water and water ice; they have large quantities of ice exposed on their surfaces. 

The Io photo was taken from 1.7 million miles (2.9 million kilometers); Europa, 1.7 million miles (2.9 million kilometers); Ganymede, 2 million miles (3.4 million kilometers); and Callisto, 4.1 million miles (6.9 million kilometers). Resolution of all photos except Callisto is about 30 miles (50 kilometers), and for Callisto it is 60 miles (100 kilometers). 

planetary images

NASA's Voyager 1 image of Io showing active plume of Loki on limb. Heart-shaped feature southeast of Loki consists of fallout deposits from active plume Pele. The images that make up this mosaic were taken from an average distance of approximately 490,000 kilometers (340,000 miles).

planetary images

This montage of images of the Saturnian system was prepared from an assemblage of images taken by the Voyager 1 spacecraft during its Saturn encounter in November 1980. This artist's view shows Dione in the forefront, Saturn rising behind, Tethys and Mimas fading in the distance to the right, Enceladus and Rhea off Saturn's rings to the left, and Titan in its distant orbit at the top.

planetary images

This picture of Neptune was produced from the last whole planet images taken through the green and orange filters on the Voyager 2 narrow angle camera. The images were taken at a range of 4.4 million miles from the planet, 4 days and 20 hours before closest approach. 

The picture shows the Great Dark Spot and its companion bright smudge; on the west limb the fast moving bright feature called Scooter and the little dark spot are visible. These clouds were seen to persist for as long as Voyager's cameras could resolve them. North of these, a bright cloud band similar to the south polar streak may be seen.

planetary images

Voyager 2 has discovered two "shepherd" satellites associated with the rings of Uranus. The two moons -- designated 1986U7 and 1986U8 -- are seen here on either side of the bright epsilon ring; all nine of the known Uranian rings are visible. The image was taken Jan. 21, 1986, at a distance of 4.1 million kilometers (2.5 million miles) and resolution of about 36 km (22 mi). The image was processed to enhance narrow features. The epsilon ring appears surrounded by a dark halo as a result of this processing; occasional blips seen on the ring are also artifacts. 

Lying inward from the epsilon ring are the delta, gamma and eta rings; then the beta and alpha rings; and finally the barely visible 4, 5 and 6 rings. The rings have been studied since their discovery in 1977, through observations of how they diminish the light of stars they pass in front of. This image is the first direct observation of all nine rings in reflected sunlight. They range in width from about 100 km (60 mi) at the widest part of the epsilon ring to only a few kilometers for most of the others. 

The discovery of the two ring moons 1986U7 and 1986U8 is a major advance in our understanding of the structure of the Uranian rings and is in good agreement with theoretical predictions of how these narrow rings are kept from spreading out. Based on likely surface brightness properties, the moons are of roughly 20- and 30-km diameter, respectively. 

spacecraft

This artist's concept depicts NASA's Voyager 1 spacecraft entering interstellar space, or the space between stars. Interstellar space is dominated by the plasma, or ionized gas, that was ejected by the death of nearby giant stars millions of years ago. The environment inside our solar bubble is dominated by the plasma exhausted by our sun, known as the solar wind.

The interstellar plasma is shown with an orange glow similar to the color seen in visible-light images from NASA's Hubble Space Telescope that show stars in the Orion nebula traveling through interstellar space.

The Voyager spacecraft were built and continue to be operated by NASA's Jet Propulsion Laboratory, in Pasadena, Calif. Caltech manages JPL for NASA. The Voyager missions are a part of NASA's Heliophysics System Observatory, sponsored by the Heliophysics Division of the Science Mission Directorate at NASA Headquarters in Washington.

For more information about Voyager, visit http://www.nasa.gov/voyager and http://voyager.jpl.nasa.gov.

A ground station satellite

DSS43 is a 70-meter-wide (230-feet-wide) radio antenna at the Deep Space Network's Canberra facility in Australia. It is the only antenna that can send commands to the Voyager 2 spacecraft.

To infinity and beyond

The largest moons of Jupiter and Saturn, just points of light in telescopes on Earth, were revealed to be fascinating worlds in their own right, with a surprising range of surface features. Jupiter’s moon Io was discovered to have several active volcanoes, the first ever found beyond the Earth, while Saturn’s largest moon Titan proved to have a thick atmosphere of nitrogen, methane, and other complex hydrocarbons. Both spacecraft also discovered several new moons around Jupiter and Saturn. 

The trajectory requirements of its Titan encounter meant that Voyager 1 could not flyby any other planets, but Voyager 2 continued on to visit both Uranus and Neptune, shedding new light on these distant “gas giants”, which had never before been seen close-up. Discoveries of new rings and moons at both planets, in addition to spectacular photos of already known moons were highlights of these encounters. Neptune’s largest moon, Triton, was found to have nitrogen ice “geysers” on its surface. 

Renamed the Voyager Interstellar Mission in 1990, the two spacecraft are now travelling beyond the heliosphere – the giant protective bubble formed around the Sun and its planets by the solar wind. At the beginning of this new phase, Voyager 1, having passed the orbits of Neptune and Pluto, pointed its cameras back toward the Sun and took a series of pictures of the Sun and the planets, which combined to make the first ever 'portrait' of our Solar System as seen from the outside. 

Today, both Voyager spacecraft are still in operation, sending back data about conditions in interstellar space from a small number of instruments. But the Voyagers are showing their age and their have been recent problems. However, the two spacecraft could remain within range of the Deep Space Network until around 2036, depending on how much power they still have to transmit a signal back to Earth.

NASA’s Canberra Deep Space Communication Complex has supported the Voyager spacecraft since they were launched and is today the only station that can communicate with Voyager 2. CSIRO’s Parkes radio telescope, Murriyang, has also supported the Voyager encounters with Uranus and Neptune, as well as the Interstellar Mission. 

People posing with a spacecraft

State of the art: local satellites are taking off

In a landmark moment for Australian space, six satellites funded by state and territory governments launched into orbit within a fortnight.

Explore

Main image caption: 

This is a montage of planetary images taken by spacecraft managed by the Jet Propulsion Laboratory in Pasadena, CA. Included are (from top to bottom) images of Mercury, Venus, Earth (and Moon), Mars, Jupiter, Saturn, Uranus and Neptune. The spacecraft responsible for these images are as follows:

  • the Mercury image was taken by Mariner 10,
  • the Venus image by Magellan,
  • the Earth image by Galileo,
  • the Mars image by Viking, and
  • the Jupiter, Saturn, Uranus and Neptune images by Voyager.  

Credit for all images in this news article: NASA/JPL

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