Voyager 2
A NASA artist's rendition of a Voyager spacecraft
Organization:	NASA
Mission type:	Fly-by
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Voyager 2 is an unmanned interplanetary spacecraft, launched on August 20, 1977.

It is identical to its sister Voyager program craft, Voyager 1, but unlike Voyager 1, Voyager 2 followed a slower trajectory that allowed it to be kept in the ecliptic (the plane of the Solar System) so that it could be sent to Uranus and Neptune by means of gravity assist during the 1981 encounter at Saturn. Because of this, Voyager 2 could not see the moon Titan up close like its twin, but it allowed the probe to become the first spacecraft to travel to Uranus and Neptune, thus completing the Planetary Grand Tour, a rare geometric arrangement of the outer planets that only occurs once every 176 years.^[1]

Voyager 2 is perhaps the most productive space probe yet deployed, visiting four planets and their moons, including two primary visits to previously unexplored planets, with powerful cameras and a multitude of scientific instruments, at a fraction of the money later spent on specialized probes such as the Galileo spacecraft and the Cassini-Huygens probe.

For details on the Voyager instrument package, see the separate article on the Voyager program.

Mission profile

Voyager 2 was originally planned to be Mariner 12, part of the Mariner program.

Voyager 2 was launched on August 20, 1977, from Cape Canaveral, Florida, aboard a Titan III-E Centaur rocket.

Ground crews became engrossed in a launch problem with Voyager 1 and forgot to send an important activation code to Voyager 2. This caused the probe to shut down its main high-gain antenna. Fortunately, ground crews were able to establish contact through the craft's low-gain antenna and reactivate it.

Jupiter

The closest approach to Jupiter occurred on July 9, 1979. It came within 570,000 km (350,000 miles) of the planet's cloud tops. It discovered a few rings around Jupiter, as well as volcanic activity on the moon Io. That was the first time an active volcano has been observed on another celestial body.

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 63 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 ft) on Io's surface, compared with typical tidal bulges on Earth of one meter (three ft).

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

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

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

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

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

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

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

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

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

Voyager 2 left Jupiter a couple of days after arriving. The space probe was able to take many photographs of the planet.

Saturn

The closest approach to Saturn occurred on August 25, 1981.

While behind Saturn (as viewed from Earth), Voyager 2 probed Saturn's upper atmosphere with its radar, to measure temperature and density profiles. Voyager 2 found that at the highest levels (7 kilopascals pressure) Saturn's temperature was 70 kelvins (−203 °C), while at the deepest levels measured (120 kilopascals) the temperature increased to 143 kelvins (−130 °C). The north pole was found to be 10 kelvins cooler, although this may be seasonal (see also Saturn Oppositions).

After the Saturn fly-by, the camera platform on Voyager 2 locked up briefly, putting plans to officially extend the mission to Uranus and Neptune in jeopardy. Fortunately, the mission team was able to fix the problem — caused by overuse that temporarily depleted its lubricant — and the probe was given the go-ahead to examine Uranus.

Saturn taken by Voyager 2.	Iapetus by Voyager 2 spacecraft, August 22, 1981.	Color image of Enceladus, almost full disk.	Titan.

Uranus

Main article: Exploration of Uranus

The closest approach to Uranus occurred on January 24, 1986. Voyager 2 discovered 10 previously unknown moons; studied the planet's unique atmosphere, caused by its axial tilt of 97.77°; and examined its ring system. In its first solo planetary flyby, Voyager 2 made its closest approach to Uranus on January 24, 1986, coming within 81,500 kilometers (50,600 miles) of the planet's cloud tops.

Uranus is the third largest planet in the solar system. It orbits the Sun at a distance of about 2.8 billion kilometers (1.7 billion miles) and completes one orbit every 84 years. The length of a day on Uranus as measured by Voyager 2 is 17 hours, 14 minutes. Uranus is distinguished by the fact that it is tipped on its side. Its unusual position is thought to be the result of a collision with a planet-sized body early in the solar system's history. Given its odd orientation, with its polar regions exposed to sunlight or darkness for long periods, scientists were not sure what to expect at Uranus.

Voyager 2 found that one of the most striking influences of Uranus' 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.

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.

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 reaggregation of material from an earlier time when the moon was fractured by a violent impact.

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.

Uranus viewed from 18 million kilometers.	A photo of Uranus taken by Voyager 2.	Uranus Final Image.	Voyager 2 shot of the Uranian rings.

Neptune

The closest approach to Neptune occurred on August 25, 1989. Since this was the last major planet Voyager 2 could visit, it was decided to make a close flyby of the moon Triton, regardless of the consequences to the trajectory, as with Voyager 1's encounter with Saturn and its moon Titan.

The probe also discovered the Great Dark Spot, which has since disappeared, according to Hubble Space Telescope observations. Originally thought to be a large cloud itself, it was later postulated to be a hole in the visible cloud deck.

With the 2006 decision of the International Astronomical Union to demote Pluto to a "dwarf planet," the 1989 fly-by of Neptune by Voyager 2 became the point when every planet in the solar system had been visited at least once by spacecraft.

Voyager 2 image of Neptune

Voyager 2 image of Triton

Escaping the solar system

Since its planetary mission is over, Voyager 2 is now described as working on an interstellar mission, which NASA is using to find out what the solar system is like beyond the heliosphere. Unlike Voyager 1, which is believed to have crossed the termination shock into the heliosheath in December 2004, Voyager 2 is currently not believed to have left the heliosphere yet. Each Voyager carries a gold-plated audio-visual disc in the event that either spacecraft is ever found by intelligent aliens. The disc carries images of Earth and its lifeforms, a range of scientific information, and a medley, "Sounds of Earth", that includes the sounds of whales, a baby crying, waves breaking on a shore and a variety of music.

As of August 10, 2007, Voyager 2 is at a distance of around 83.5 AU (approximately 12.5 terameters) from the Sun, deep in the scattered disc, and traveling outward at roughly 3.3 AUs a year. ^[2] It is more than twice as far from the Sun as Pluto, and far beyond the perihelion of 90377 Sedna, but not yet beyond the outer limits of the orbit of Eris.

Voyager 2 is expected to keep transmitting into the 2020s.

Year	End of specific capabilities as a result of the available electrical power limitations
1998	Terminate scan platform and UV observations
~2012	Termination of gyro operations
~2012	Termination of DTR operations (limited by ability to capture 1.4 kbit/s data using a 70 m/34 m antenna array)
~2016	Initiate instrument power sharing
> 2020	Can no longer power any single instrument[3]

Current status

Voyager 2, as of 19 September 2007, is at −53.72° declination and 19.674 h Right Ascension, placing it in the constellation Telescopium as observed from Earth.

On November 30, 2006, a command was incorrectly decoded by the spacecraft as an instruction to turn on heaters associated with the probe's magnetometer. The heaters remained on until December 4, 2006, resulting in extremely high temperatures (above 130 °C), and in sensor rotation away from the correct orientation. It has not been possible to fully diagnose and correct for the damage to the Voyager 2 magnetometer, although efforts to do so are ongoing.^[4]

Information about ongoing telemetry exchanges with Voyager 2 is available from Voyager Weekly Reports. Information on the current location of Voyager 2 can be found at this website.

Voyager 2 in fiction and popular culture

This section contains specific references to Voyager 2. For other references to the Voyagers, see Voyager in fiction and popular culture in the Voyager program article.

• "Voyager 2" is the title of a song by the band Virginia Coalition. It appeared on the "Ok To Go" Album.
• The motion picture Starman portrayed Voyager 2 as having been located by an alien intelligence who subsequently sent one of their own race to investigate intelligent life on Earth.
• In the episode "Parasites Lost" of the animated show Futurama, Leela scrubs the remains of Voyager 2 off the windscreen of her spaceship while refueling at an interplanetary service station.
• The introduction movie for the computer game depicts Voyager 2 as a discreetly armed reconnaissance probe, and is subsequently destroyed by an anti-satellite missile after discovering a secret military base on the undiscovered Dark Planet.
• In the television series "Beast Wars" Megatron mentions that the Golden Disk (which was a major plot element of the second season) shown in the series was from the Voyager 2 (and even shows an animated Voyager 2 launching from earth).

See also

• Voyager program for more information about this spacecraft.
• Voyager Golden Record
• Voyager 1
• Pioneer 10
• Pioneer 11

References

Footnotes

• Saturn Science Results. Voyager Science Results at Saturn. Retrieved on February 8, 2005.
• Uranus Science Results. Voyager Science Results at Uranus. Retrieved on February 8, 2005.

External links

• NASA Voyager website
• Voyager Spacecraft Lifetime
• Voyager 2 Mission Profile by NASA's Solar System Exploration
• Spacecraft Escaping the Solar System - current positions and diagrams
• Mission state
• VOYAGER RECENT 6-HOUR HISTORY
• Voyager 2 Detects Odd Shape of Solar System's Edge 23 May 2006

•  • [ e] Spacecraft Missions to Jupiter
Flybys	Pioneer 10 • Pioneer 11 • Voyager 1 • Voyager 2 • Ulysses • Cassini • New Horizons
Orbiters	Galileo
Descent probes	Galileo probe
Future missions	2011: Juno
Canceled missions	JIMO • Europa Orbiter
(Bold: Active missions)

•  • [ e] Spacecraft Missions to Saturn
Flybys	Pioneer 11 • Voyager 1 • Voyager 2
Orbiters	Cassini
(Bold: Active missions)