Voyager 2 is a space probe launched by NASA on August 20, 1977, to study the outer planets. Part of the Voyager program, it was launched 16 days before its twin, Voyager 1, on a trajectory that took longer to reach Jupiter and Saturn but enabled further encounters with Uranus and Neptune. It is the only spacecraft to have visited either of these two ice giant planets.
Its primary mission ended with the exploration of the Neptunian system on October 2, 1989, after having visited the Uranian system in 1986, the Saturnian system in 1981, and the Jovian system in 1979. Voyager 2 is now in its extended mission to study the outer reaches of the Solar System and has been operating for 41 years, 8 months and 3 days as of 23 April 2019. It remains in contact through the NASA Deep Space Network.
At a distance of 120 AU (1.80×1010 km) (about 16.5 light-hours) from the Sun as of February 25, 2019, moving at a velocity of 15.341 km/s (55,230 km/h) relative to the Sun, Voyager 2 is the fourth of five spacecraft to achieve the escape velocity that will allow them to leave the Solar System. The probe left the heliosphere for interstellar space on November 5, 2018, becoming the second artificial object to do so, and has begun to provide the first direct measurements of the density and temperature of the interstellar plasma.
Model of the Voyager spacecraft design
|Mission type||Planetary exploration|
|Operator||NASA / JPL|
|Mission duration||41 years, 8 months and 3 days elapsed|
Planetary mission: 12 years, 1 month, 12 days
Interstellar mission: 29 years, 6 months and 21 days elapsed (continuing)
|Manufacturer||Jet Propulsion Laboratory|
|Launch mass||825.5 kilograms (1,820 lb)|
|Power||470 watts (at launch)|
|Start of mission|
|Launch date||August 20, 1977, 14:29:00 UTC|
|Launch site||Cape Canaveral LC-41|
|Flyby of Jupiter|
|Closest approach||July 9, 1979, 22:29:00 UTC|
|Distance||570,000 kilometers (350,000 mi)|
|Flyby of Saturn|
|Closest approach||August 25, 1981, 03:24:05 UTC|
|Distance||101,000 km (63,000 mi)|
|Flyby of Uranus|
|Closest approach||January 24, 1986, 17:59:47 UTC|
|Distance||81,500 km (50,600 mi)|
|Flyby of Neptune|
|Closest approach||August 25, 1989, 03:56:36 UTC|
|Distance||4,951 km (3,076 mi)|
In the early space age, it was realized that a periodic alignment of the outer planets would occur in the late 1970s and enable a single probe to visit Jupiter, Saturn, Uranus, and Neptune by taking advantage of the then-new technique of gravity assists. NASA began work on a Grand Tour, which evolved into a massive project involving two groups of two probes each, with one group visiting Jupiter, Saturn, and Pluto and the other Jupiter, Uranus, and Neptune. The spacecraft would be designed with redundant systems to ensure survival through the entire tour. By 1972 the mission was scaled back and replaced with two Mariner-derived spacecraft, the Mariner Jupiter-Saturn probes. To keep apparent lifetime program costs low, the mission would include only flybys of Jupiter and Saturn, but keep the Grand Tour option open.:263 As the program progressed, the name was changed to Voyager.
The primary mission of Voyager 1 was to explore Jupiter, Saturn, and Saturn's moon, Titan. Voyager 2 was also to explore Jupiter and Saturn, but on a trajectory that would have the option of continuing on to Uranus and Neptune, or being redirected to Titan as a backup for Voyager 1. Upon successful completion of Voyager 1's objectives, Voyager 2 would get a mission extension to send the probe on towards Uranus and Neptune.
Constructed by the Jet Propulsion Laboratory (JPL), Voyager 2 included 16 hydrazine thrusters, three-axis stabilization, gyroscopes and celestial referencing instruments (Sun sensor/Canopus Star Tracker) to maintain pointing of the high-gain antenna toward Earth. Collectively these instruments are part of the Attitude and Articulation Control Subsystem (AACS) along with redundant units of most instruments and 8 backup thrusters. The spacecraft also included 11 scientific instruments to study celestial objects as it traveled through space.
Built with the intent for eventual interstellar travel, Voyager 2 included a large, 3.7 m (12 ft) parabolic, high-gain antenna (see diagram) to transceive data via the Deep Space Network on the Earth. Communications are conducted over the S-band (about 13 cm wavelength) and X-band (about 3.6 cm wavelength) providing data rates as high as 115.2 kilobits per second at the distance of Jupiter, and then ever-decreasing as the distance increased, because of the inverse-square law. When the spacecraft is unable to communicate with Earth, the Digital Tape Recorder (DTR) can record about 64 kilobytes of data for transmission at another time.
Voyager 2 is equipped with 3 Multihundred-Watt radioisotope thermoelectric generators (MHW RTG). Each RTG includes 24 pressed plutonium oxide spheres, and provided enough heat to generate approximately 157 W of electrical power at launch. Collectively, the RTGs supplied the spacecraft with 470 watts at launch (halving every 87.7 years), and will allow operations to continue until at least 2020.
Because of the energy required to achieve a Jupiter trajectory boost with an 1,819-pound (825 kg) payload, the spacecraft included a propulsion module made of a 2,476-pound (1,125 kg) solid-rocket motor and eight hydrazine monopropellant rocket engines, four providing pitch and yaw attitude control, and four for roll control. The propulsion module was jettisoned shortly after the successful Jupiter burn.
Sixteen hydrazine MR-103 thrusters on the mission module provide attitude control. Four are used to execute trajectory correction maneuvers; the others in two redundant six-thruster branches, to stabilize the spacecraft on its three axes. Only one branch of attitude control thrusters is needed at any time.
Thrusters are supplied by a single 28-inch (70 cm) diameter spherical titanium tank. It contained 230 pounds (100 kg) of hydrazine at launch, providing enough fuel until 2034.
|Imaging Science System
|(ISS)||Utilizes a two-camera system (narrow-angle/wide-angle) to provide imagery of Jupiter, Saturn and other objects along the trajectory. More|
|Radio Science System
|(RSS)||Utilized the telecommunications system of the Voyager spacecraft to determine the physical properties of planets and satellites (ionospheres, atmospheres, masses, gravity fields, densities) and the amount and size distribution of material in Saturn's rings and the ring dimensions. More|
|Infrared Interferometer Spectrometer
|(IRIS)||Investigates both global and local energy balance and atmospheric composition. Vertical temperature profiles are also obtained from the planets and satellites as well as the composition, thermal properties, and size of particles in Saturn's rings. More|
|(UVS)||Designed to measure atmospheric properties, and to measure radiation. More|
|Triaxial Fluxgate Magnetometer
|(MAG)||Designed to investigate the magnetic fields of Jupiter and Saturn, the solar-wind interaction with the magnetospheres of these planets, and the interplanetary magnetic field out to the solar wind boundary with the interstellar magnetic field and beyond, if crossed. More|
|(PLS)||Investigates the macroscopic properties of the plasma ions and measures electrons in the energy range from 5 eV to 1 keV. More|
|Low Energy Charged Particle Instrument
|(LECP)||Measures the differential in energy fluxes and angular distributions of ions, electrons and the differential in energy ion composition. More|
|Cosmic Ray System
|(CRS)||Determines the origin and acceleration process, life history, and dynamic contribution of interstellar cosmic rays, the nucleosynthesis of elements in cosmic-ray sources, the behavior of cosmic rays in the interplanetary medium, and the trapped planetary energetic-particle environment. More|
|Planetary Radio Astronomy Investigation
|(PRA)||Utilizes a sweep-frequency radio receiver to study the radio-emission signals from Jupiter and Saturn. More
|(PPS)||Utilized a telescope with a polarizer to gather information on surface texture and composition of Jupiter and Saturn and information on atmospheric scattering properties and density for both planets. More|
|Plasma Wave System
|(PWS)||Provides continuous, sheath-independent measurements of the electron-density profiles at Jupiter and Saturn as well as basic information on local wave-particle interaction, useful in studying the magnetospheres. More|
For more details on the Voyager space probes' identical instrument packages, see the separate article on the overall Voyager Program.
The Voyager 2 probe was launched on August 20, 1977, by NASA from Space Launch Complex 41 at Cape Canaveral, Florida, aboard a Titan IIIE/Centaur launch vehicle. Two weeks later, the twin Voyager 1 probe was launched on September 5, 1977. However, Voyager 1 reached both Jupiter and Saturn sooner, as Voyager 2 had been launched into a longer, more circular trajectory.
In April 1978, a complication arose when no commands were transmitted to Voyager 2 for a period of time, causing the spacecraft to switch from its primary radio receiver to its backup receiver. Sometime afterwards, the primary receiver failed altogether. The backup receiver was functional, but a failed capacitor in the receiver meant that it could only receive transmissions that were sent at a precise frequency, and this frequency would be affected by the Earth's rotation (due to the Doppler effect) and the onboard receiver's temperature, among other things. For each subsequent transmission to Voyager 2, it was necessary for engineers to calculate the specific frequency for the signal so that it could be received by the spacecraft.
Voyager 2's closest approach to Jupiter occurred at 22:29 UT on July 9, 1979. It came within 570,000 km (350,000 mi) of the planet's cloud tops. Jupiter's Great Red Spot was revealed as a complex storm moving in a counterclockwise direction. Other smaller storms and eddies were found throughout the banded clouds.
Voyager 2 returned images of Jupiter, as well as its moons Amalthea, Io, Callisto, Ganymede, and Europa. During a 10-hour "volcano watch", it confirmed Voyager 1's observations of active volcanism on the moon Io, and revealed how the moon's surface had changed in the four months since the previous visit. Together, the Voyagers observed the eruption of nine volcanoes on Io, and there is evidence that other eruptions occurred between the two Voyager fly-bys.
Jupiter's moon 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. Closer high-resolution photos from Voyager 2, however, were puzzling: the features lacked topographic and one scientist said they "might have been painted on with a felt marker". Europa is internally active due to tidal heating at a level about one-tenth that of Io. Europa is thought to have a thin crust (less than 30 km (19 mi) thick) of water ice, possibly floating on a 50-kilometer-deep (30 mile) ocean.
The closest approach to Saturn occurred on August 26, 1981.
While passing behind Saturn (as viewed from Earth), Voyager 2 probed Saturn's upper atmosphere with its radio link to gather information on atmospheric temperature and density profiles. Voyager 2 found that at the uppermost pressure levels (seven kilopascals of pressure), Saturn's temperature was 70 kelvins (−203 °C), while at the deepest levels measured (120 kilopascals) the temperature increased to 143 K (−130 °C). The north pole was found to be 10 kelvins cooler, although this may be seasonal (see also Saturn Oppositions).
After the fly-by of Saturn, the camera platform of Voyager 2 locked up briefly, putting plans to officially extend the mission to Uranus and Neptune in jeopardy. The mission's engineers were able to fix the problem (caused by an overuse that temporarily depleted its lubricant), and the Voyager 2 probe was given the go-ahead to explore the Uranian system.
The closest approach to Uranus occurred on January 24, 1986, when Voyager 2 came within 81,500 kilometers (50,600 mi) of the planet's cloudtops. Voyager 2 also discovered 11 previously unknown moons: Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, Puck and Perdita.[A] The mission also studied the planet's unique atmosphere, caused by its axial tilt of 97.8°; and examined the Uranian ring system. The length of a day on Uranus as measured by Voyager 2 is 17 hours, 14 minutes. Uranus was shown to have a magnetic field that was misaligned with its rotational axis, unlike other planets that had been visited to that point, and a helix-shaped magnetic tail stretching 10 million kilometers (6 million miles) away from the Sun.
When Voyager 2 visited Uranus, much of its cloud features were hidden by a layer of haze; however, false-color and contrast-enhanced images show bands of concentric clouds around its south pole. This area was also found to radiate large amounts of ultraviolet light, a phenomenon that is called "dayglow". The average atmospheric temperature is about 60 K (−350°F/−213°C). Surprisingly, the illuminated and dark poles, and most of the planet, exhibit nearly the same temperatures at the cloud tops.
Detailed images from Voyager 2's flyby of the Uranian moon Miranda showed huge canyons made from geological faults. One hypothesis suggests that Miranda might consist of a reaggregation of material following an earlier event when Miranda was shattered into pieces by a violent impact.
Voyager 2 discovered two previously-unknown Uranian rings. Measurements showed that the Uranian rings are distinctly different from those at Jupiter and Saturn. The Uranian ring system might be relatively young, and it did not form at the same time that Uranus did. The particles that make up the rings might be the remnants of a moon that was broken up by either a high-velocity impact or torn up by tidal effects.
Following a mid-course correction in 1987, Voyager 2's closest approach to Neptune occurred on August 25, 1989. Through repeated computerized test simulations of trajectories through the Neptunian system conducted in advance, flight controllers determined the best way to route Voyager 2 through the Neptune-Triton system. Since the plane of the orbit of Triton is tilted significantly with respect to the plane of the ecliptic, through mid-course corrections, Voyager 2 was directed into a path about 4950 kilometers (3000 mi) above the north pole of Neptune. Five hours after Voyager 2 made its closest approach to Neptune, it performed a close fly-by of Triton, the larger of Neptune's two originally known moons, passing within about 40,000 kilometers (25,000 mi).
Voyager 2 discovered previously unknown Neptunian rings, and confirmed six new moons: Despina, Galatea, Larissa, Proteus, Naiad and Thalassa.[B] While in the neighborhood of Neptune, Voyager 2 discovered the "Great Dark Spot", which has since disappeared, according to observations by the Hubble Space Telescope. The Great Dark Spot was later hypothesized to be a region of clear gas, forming a window in the planet's high-altitude methane cloud deck.
With the decision of the International Astronomical Union to reclassify Pluto as a dwarf planet in 2006, the flyby of Neptune by Voyager 2 in 1989 became the point when every known planet in the Solar System had been visited at least once by a space probe.
Once its planetary mission was over, Voyager 2 was described as working on an interstellar mission, which NASA is using to find out what the Solar System is like beyond the heliosphere. Voyager 2 is currently transmitting scientific data at about 160 bits per second. Information about continuing telemetry exchanges with Voyager 2 is available from Voyager Weekly Reports.
In July 1994, an attempt was made to observe the impacts from fragments of the comet Comet Shoemaker–Levy 9 with Jupiter. The craft's position meant it had a direct line of sight to the impacts and observations were made in the ultraviolet and radio spectrum. Voyager 2 failed to detect anything with calculations showing that the fireballs were just below the craft's limit of detection.
On November 29, 2006, a telemetered command to Voyager 2 was incorrectly decoded by its on-board computer—in a random error—as a command to turn on the electrical heaters of the spacecraft's magnetometer. These heaters remained turned on until December 4, 2006, and during that time, there was a resulting high temperature above 130 °C (266 °F), significantly higher than the magnetometers were designed to endure, and a sensor rotated away from the correct orientation. As of this date it had not been possible to fully diagnose and correct for the damage caused to Voyager 2's magnetometer, although efforts to do so were proceeding.
On August 30, 2007, Voyager 2 passed the termination shock and then entered into the heliosheath, approximately 1 billion miles (1.6 billion km) closer to the Sun than Voyager 1 did. This is due to the interstellar magnetic field of deep space. The southern hemisphere of the Solar System's heliosphere is being pushed in.
On April 22, 2010, Voyager 2 encountered scientific data format problems. On May 17, 2010, JPL engineers revealed that a flipped bit in an on-board computer had caused the issue, and scheduled a bit reset for May 19. On May 23, 2010, Voyager 2 resumed sending science data from deep space after engineers fixed the flipped bit. Currently research is being made into marking the area of memory with the flipped bit off limits or disallowing its use. The Low-Energy Charged Particle Instrument is currently operational, and data from this instrument concerning charged particles is being transmitted to Earth. This data permits measurements of the heliosheath and termination shock. There has also been a modification to the on-board flight software to delay turning off the AP Branch 2 backup heater for one year. It was scheduled to go off February 2, 2011 (DOY 033, 2011–033).
On July 25, 2012, Voyager 2 was traveling at 15.447 km/s relative to the Sun at about 99.13 astronomical units (1.4830×1010 km) from the Sun, at −55.29° declination and 19.888 h right ascension, and also at an ecliptic latitude of −34.0 degrees, placing it in the constellation Telescopium as observed from Earth. This location places it deep in the scattered disc, and traveling outward at roughly 3.264 AU per year. 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 the dwarf planet Eris.
On September 9, 2012, Voyager 2 was 99.077 AU (1.48217×1010 km; 9.2098×109 mi) from the Earth and 99.504 AU (1.48856×1010 km; 9.2495×109 mi) from the Sun; and traveling at 15.436 km/s (34,530 mph) (relative to the Sun) and traveling outward at about 3.256 AU per year. Sunlight takes 13.73 hours to get to Voyager 2. The brightness of the Sun from the spacecraft is magnitude -16.7. Voyager 2 is heading in the direction of the constellation Telescopium. (To compare, Proxima Centauri, the closest star to the Sun, is about 4.2 light-years (or 2.65×105 AU) distant. Voyager 2's current relative velocity to the Sun is 15.436 km/s (55,570 km/h; 34,530 mph). This calculates as 3.254 AU per year, about 10% slower than Voyager 1. At this velocity, 81,438 years would pass before Voyager 2 reaches the nearest star, Proxima Centauri, were the spacecraft traveling in the direction of that star. (Voyager 2 will need about 19,390 years at its current velocity to travel a complete light year)
On November 7, 2012, Voyager 2 reached 100 AU from the sun, making it the third human-made object to reach 100 AU. Voyager 1 was 122 AU from the Sun, and Pioneer 10 is presumed to be at 107 AU. While Pioneer has ceased communications, both the Voyager spacecraft are performing well and are still communicating.
In 2013, Voyager 1 was escaping the Solar System at a speed of about 3.6 AU per year, while Voyager 2 was only escaping at 3.3 AU per year. (Each year Voyager 1 increases its lead over Voyager 2)
By February 25, 2019, Voyager 2 was at a distance of 120 AU (1.80×1010 km) from the Sun. There is a variation in distance from Earth caused by the Earth's revolution around the Sun relative to Voyager 2.
It was originally thought that Voyager 2 would enter interstellar space in early 2016, with its plasma spectrometer providing the first direct measurements of the density and temperature of the interstellar plasma. In December 2018, the Voyager project scientist, Edward C. Stone, announced that Voyager 2 reached interstellar space on November 5, 2018.
Voyager 2 is not headed toward any particular star, although in roughly 42,000 years it will pass 1.7 light-years from the star Ross 248.  And if undisturbed for 296,000 years, Voyager 2 should pass by the star Sirius at a distance of 4.3 light-years. Voyager 2 is expected to keep transmitting weak radio messages until at least the mid 2020s, more than 48 years after it was launched.
|Year||End of specific capabilities as a result of the available electrical power limitations|
|1998||Termination of scan platform and UVS observations|
|2007||Termination of Digital Tape Recorder (DTR) operations (It was no longer needed due to a failure on the High Waveform Receiver on the Plasma Wave Subsystem (PWS) on June 30, 2002.)|
|2008||Power off Planetary Radio Astronomy Experiment (PRA)|
|2016 approx||Termination of gyroscopic operations|
|2020 approx||Initiate instrument power sharing|
|2025 or slightly afterwards||Can no longer power any single instrument|
Each Voyager space probe carries a gold-plated audio-visual disc in the event that either spacecraft is ever found by intelligent life-forms from other planetary systems. The discs carry photos of the Earth and its lifeforms, a range of scientific information, spoken greetings from the people (e.g. the Secretary-General of the United Nations and the President of the United States, and the children of the Planet Earth) and a medley, "Sounds of Earth", that includes the sounds of whales, a baby crying, waves breaking on a shore, and a collection of music, including works by Wolfgang Amadeus Mozart, Blind Willie Johnson, Chuck Berry's "Johnny B. Goode", Valya Balkanska and other Eastern and Western classics and ethnic performers. (see also Music in space)
Despite the name change, Voyager remained in many ways the Grand Tour concept, though certainly not the Grand Tour (TOPS) spacecraft. Voyager 2 was launched on August 20, 1977, followed by Voyager 1 on September 5, 1977. The decision to reverse the order of launch had to do with keeping open the possibility of carrying out the Grand Tour mission to Uranus, Neptune, and beyond. Voyager 2, if boosted by the maximum performance from the Titan-Centaur, could just barely catch the old Grand Tour trajectory and encounter Uranus. Two weeks later, Voyager 1 would leave on an easier and much faster trajectory, visiting Jupiter and Saturn only. Voyager 1 would arrive at Jupiter four months ahead of Voyager 2, then arrive at Saturn nine months earlier. Hence, the second spacecraft launched was Voyager 1, not Voyager 2. The two Voyagers would arrive at Saturn nine months apart, so that if Voyager 1 failed to achieve its Saturn objectives, for whatever reason, Voyager 2 still could be retargeted to achieve them, though at the expense of any subsequent Uranus or Neptune encounter.
Belinda ( bə-LIN-də) is an inner satellite of the planet Uranus. Belinda was discovered from the images taken by Voyager 2 on 13 January 1986 and was given the temporary designation S/1986 U 5. It is named after the heroine of Alexander Pope's The Rape of the Lock. It is also designated Uranus XIV.Belinda belongs to the Portia group of satellites, which also includes Bianca, Cressida, Desdemona, Portia, Juliet, Cupid, Rosalind and Perdita. These satellites have similar orbits and photometric properties. Other than its orbit, radius of 45 km and geometric albedo of 0.08 virtually nothing is known about it.
The Voyager 2 images show Belinda as an elongated object with its major axis pointing towards Uranus. The moon is very elongated, with its short axis 0.5 ± 0.1 times the long axis. Its surface is grey in color.Bianca (moon)
There is also an asteroid called 218 Bianca.Bianca ( bee-AHNG-kə) is an inner satellite of Uranus. It was discovered from the images taken by Voyager 2 on January 23, 1986, and was given the temporary designation S/1986 U 9. It was named after the sister of Katherine in Shakespeare's play The Taming of the Shrew. It is also designated Uranus VIII.Bianca belongs to Portia Group of satellites, which also includes Cressida, Desdemona, Juliet, Portia, Rosalind, Cupid, Belinda and Perdita. These satellites have similar orbits and photometric properties. Other than its orbit, radius of 27 km, and geometric albedo of 0.08 virtually nothing is known about it.
At the Voyager 2 images Bianca appears as an elongated object, the major axis pointing towards Uranus. The ratio of axes of the Bianca's prolate spheroid is 0.7 ± 0.2. Its surface is grey in color.Exploration of Neptune
The exploration of Neptune has only begun with one spacecraft, Voyager 2 in 1989. Currently there are no approved future missions to visit the Neptunian system. NASA, ESA and also independent academic groups have proposed future scientific missions to visit Neptune. Some mission plans are still active, while others have been abandoned or put on hold.
Neptune has also been scientifically studied from afar with telescopes, primarily since the mid 1990s. This includes the Hubble Space Telescope but most importantly ground-based telescopes using adaptive optics.Exploration of Uranus
The exploration of Uranus has, to date, been solely through telescopes and NASA's Voyager 2 spacecraft, which made its closest approach to Uranus on January 24, 1986. Voyager 2 discovered 10 moons, studied the planet's cold atmosphere, and examined its ring system, discovering two new rings. It also imaged Uranus' five large moons, revealing that their surfaces are covered with impact craters and canyons.
A number of dedicated exploratory missions to Uranus have been proposed, but as of 2018 none have been approved.Great Dark Spot
The Great Dark Spot (also known as GDS-89, for Great Dark Spot - 1989) was one of a series of dark spots on Neptune similar in appearance to Jupiter's Great Red Spot. GDS-89 was the first Great Dark Spot on Neptune to be observed in 1989 by NASA's Voyager 2 spaceprobe. Like Jupiter's spot, Great Dark Spots are anticyclonic storms. However, their interiors are relatively cloud-free, and unlike Jupiter's spot, which has lasted for hundreds of years, their lifetimes appear to be shorter, forming and dissipating once every few years or so. Based on observations taken with Voyager 2 and since then with the Hubble Space Telescope, Neptune appears to spend somewhat more than half its time with a Great Dark Spot.Heliosphere
The heliosphere is the vast, bubble-like region of space which surrounds and is created by the Sun. In plasma physics terms, this is the cavity formed by the Sun in the surrounding interstellar medium. The "bubble" of the heliosphere is continuously "inflated" by plasma originating from the Sun, known as the solar wind. Outside the heliosphere, this solar plasma gives way to the interstellar plasma permeating our galaxy. Radiation levels inside and outside the heliosphere differ; in particular, the galactic cosmic rays are less abundant inside the heliosphere, so that the planets inside (including Earth) are partly shielded from their impact. The word "heliosphere" is said to have been coined by Alexander J. Dessler, who is credited with first use of the word in scientific literature in 1967. The scientific study of the heliosphere is heliophysics, which includes space weather and space climate.
Flowing unimpeded through the Solar System for billions of kilometres, the solar wind extends far beyond even the region of Pluto, until it encounters the termination shock, where its motion slows abruptly due to the outside pressure of the interstellar medium. Beyond the shock lies the heliosheath, a broad transitional region between the inner heliosphere and the external environment. The outermost edge of the heliosphere is called the heliopause. The overall shape of the heliosphere resembles that of a comet – being approximately spherical on one side, with a long trailing tail opposite, known as the heliotail.
The two Voyager spacecraft have explored the outer reaches of the heliosphere, passing through the termination shock and the heliosheath. NASA announced in 2013 that Voyager 1 had encountered the heliopause on 25 August 2012, when the spacecraft measured a sudden increase in plasma density of about forty times. In 2018, NASA announced that Voyager 2 had traversed the heliopause on 5 November of that year. Because the heliopause marks the boundary between matter originating from the Sun and matter originating from the rest of the galaxy, spacecraft such as the two Voyagers, which have departed the heliosphere, can be said to have reached interstellar space.List of artificial objects leaving the Solar System
Below is a list of artificial objects leaving the Solar System. All of these objects are space probes and their upper stages launched by NASA.
Of the major spacecraft, Voyager 1, Voyager 2, and New Horizons are still functioning and are regularly contacted by radio communication, while Pioneer 10 and Pioneer 11 are now derelict. In addition to these spacecraft, some third stages and de-spin weights are leaving the Solar System, assuming they continue on their trajectories.
These objects are leaving the Solar System because their velocity and direction are taking them away from the Sun, and at their distance from the Sun, its gravitational pull is not sufficient to pull these objects back or into orbit. They are not impervious to the gravitational pull of the Sun and are being slowed down, but they are predicted to have enough velocity to coast into interstellar space, i.e. retaining sufficient escape velocity to leave the Solar System.Miranda (moon)
Miranda, also designated Uranus V, is the smallest and innermost of Uranus's five round satellites. It was discovered by Gerard Kuiper on 16 February 1948 at McDonald Observatory, and named after Miranda from William Shakespeare's play The Tempest. Like the other large moons of Uranus, Miranda orbits close to its planet's equatorial plane. Because Uranus orbits the Sun on its side, Miranda's orbit is perpendicular to the ecliptic and shares Uranus's extreme seasonal cycle.
At just 470 km in diameter, Miranda is one of the smallest closely observed objects in the Solar System that might be in hydrostatic equilibrium (spherical under its own gravity). The only close-up images of Miranda are from the Voyager 2 probe, which made observations of Miranda during its Uranus flyby in January 1986. During the flyby, Miranda's southern hemisphere pointed towards the Sun, so only that part was studied.
Miranda probably formed from an accretion disc that surrounded the planet shortly after its formation, and, like other large moons, it is likely differentiated, with an inner core of rock surrounded by a mantle of ice. Miranda has one of the most extreme and varied topographies of any object in the Solar System, including Verona Rupes, a 20-kilometer-high scarp that is the highest cliff in the Solar System, and chevron-shaped tectonic features called coronae. The origin and evolution of this varied geology, the most of any Uranian satellite, are still not fully understood, and multiple hypotheses exist regarding Miranda's evolution.Moons of Uranus
Uranus, the seventh planet of the Solar System, has 27 known moons, all of which are named after characters from the works of William Shakespeare and Alexander Pope. Uranus's moons are divided into three groups: thirteen inner moons, five major moons, and nine irregular moons. The inner moons are small dark bodies that share common properties and origins with Uranus's rings. The five major moons are massive enough to have reached hydrostatic equilibrium, and four of them show signs of internally driven processes such as canyon formation and volcanism on their surfaces. The largest of these five, Titania, is 1,578 km in diameter and the eighth-largest moon in the Solar System, and about one-twentieth the mass the Earth's Moon. The orbits of the regular moons are nearly coplanar with Uranus's equator, which is tilted 97.77° to its orbit. Uranus's irregular moons have elliptical and strongly inclined (mostly retrograde) orbits at large distances from the planet.William Herschel discovered the first two moons, Titania and Oberon, in 1787, and the other three ellipsoidal moons were discovered in 1851 by William Lassell (Ariel and Umbriel) and in 1948 by Gerard Kuiper (Miranda). These five have planetary mass, and so would be considered (dwarf) planets if they were in direct orbit about the Sun. The remaining moons were discovered after 1985, either during the Voyager 2 flyby mission or with the aid of advanced Earth-based telescopes.Neptune
Neptune is the eighth and farthest known planet from the Sun in the Solar System. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. Neptune is 17 times the mass of Earth, slightly more massive than its near-twin Uranus. Neptune is denser and physically smaller than Uranus because its greater mass causes more gravitational compression of its atmosphere. Neptune orbits the Sun once every 164.8 years at an average distance of 30.1 AU (4.5 billion km). It is named after the Roman god of the sea and has the astronomical symbol ♆, a stylised version of the god Neptune's trident.
Neptune is not visible to the unaided eye and is the only planet in the Solar System found by mathematical prediction rather than by empirical observation. Unexpected changes in the orbit of Uranus led Alexis Bouvard to deduce that its orbit was subject to gravitational perturbation by an unknown planet. Neptune was subsequently observed with a telescope on 23 September 1846 by Johann Galle within a degree of the position predicted by Urbain Le Verrier. Its largest moon, Triton, was discovered shortly thereafter, though none of the planet's remaining known 13 moons were located telescopically until the 20th century. The planet's distance from Earth gives it a very small apparent size, making it challenging to study with Earth-based telescopes. Neptune was visited by Voyager 2, when it flew by the planet on 25 August 1989. The advent of the Hubble Space Telescope and large ground-based telescopes with adaptive optics has recently allowed for additional detailed observations from afar.
Like Jupiter and Saturn, Neptune's atmosphere is composed primarily of hydrogen and helium, along with traces of hydrocarbons and possibly nitrogen, though it contains a higher proportion of "ices" such as water, ammonia, and methane. However, similar to Uranus, its interior is primarily composed of ices and rock; Uranus and Neptune are normally considered "ice giants" to emphasise this distinction. Traces of methane in the outermost regions in part account for the planet's blue appearance.In contrast to the hazy, relatively featureless atmosphere of Uranus, Neptune's atmosphere has active and visible weather patterns. For example, at the time of the Voyager 2 flyby in 1989, the planet's southern hemisphere had a Great Dark Spot comparable to the Great Red Spot on Jupiter. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, with recorded wind speeds as high as 2,100 km/h (580 m/s; 1,300 mph). Because of its great distance from the Sun, Neptune's outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching 55 K (−218 °C; −361 °F). Temperatures at the planet's centre are approximately 5,400 K (5,100 °C; 9,300 °F). Neptune has a faint and fragmented ring system (labelled "arcs"), which was discovered in 1984, then later confirmed by Voyager 2.Nereid (moon)
Nereid is the third-largest moon of Neptune. It has a highly eccentric orbit. It was the second moon of Neptune to be discovered, by Gerard Kuiper in 1949.Puck (moon)
Puck ( PUK) is an inner moon of Uranus. It was discovered in December 1985 by the Voyager 2 spacecraft. The name Puck follows the convention of naming Uranus's moons after characters from Shakespeare. The orbit of Puck lies between the rings of Uranus and the first of Uranus's large moons, Miranda. Puck is approximately spherical in shape and has diameter of about 162 km. It has a dark, heavily cratered surface, which shows spectral signs of water ice.Rings of Neptune
The rings of Neptune consist primarily of five principal rings and were first discovered (as "arcs") on 22 July 1984 in Chile by Patrice Bouchet, Reinhold Häfner and Jean Manfroid at La Silla Observatory (ESO) during an observing program proposed by André Brahic and Bruno Sicardy from Paris Observatory, and at Cerro Tololo Interamerican Observatory by F. Vilas and L.-R. Elicer for a program led by William Hubbard. They were eventually imaged in 1989 by the Voyager 2 spacecraft. At their densest, they are comparable to the less dense portions of Saturn's main rings such as the C ring and the Cassini Division, but much of Neptune's ring system is quite tenuous, faint and dusty, more closely resembling the rings of Jupiter. Neptune's rings are named after astronomers who contributed important work on the planet: Galle, Le Verrier, Lassell, Arago, and Adams. Neptune also has a faint unnamed ring coincident with the orbit of the moon Galatea. Three other moons orbit between the rings: Naiad, Thalassa and Despina.The rings of Neptune are made of extremely dark material, likely organic compounds processed by radiation, similar to that found in the rings of Uranus. The proportion of dust in the rings (between 20% and 70%) is high, while their optical depth is low to moderate, at less than 0.1. Uniquely, the Adams ring includes five distinct arcs, named Fraternité, Égalité 1 and 2, Liberté, and Courage. The arcs occupy a narrow range of orbital longitudes and are remarkably stable, having changed only slightly since their initial detection in 1980. How the arcs are stabilized is still under debate. However, their stability is probably related to the resonant interaction between the Adams ring and its inner shepherd moon, Galatea.Rings of Uranus
The rings of Uranus are a system of rings around the planet Uranus, intermediate in complexity between the more extensive set around Saturn and the simpler systems around Jupiter and Neptune. The rings of Uranus were discovered on March 10, 1977, by James L. Elliot, Edward W. Dunham, and Jessica Mink. William Herschel had also reported observing rings in 1789; modern astronomers are divided on whether he could have seen them, as they are very dark and faint.By 1978, nine distinct rings were identified. Two additional rings were discovered in 1986 in images taken by the Voyager 2 spacecraft, and two outer rings were found in 2003–2005 in Hubble Space Telescope photos. In the order of increasing distance from the planet the 13 known rings are designated 1986U2R/ζ, 6, 5, 4, α, β, η, γ, δ, λ, ε, ν and μ. Their radii range from about 38,000 km for the 1986U2R/ζ ring to about 98,000 km for the μ ring. Additional faint dust bands and incomplete arcs may exist between the main rings. The rings are extremely dark—the Bond albedo of the rings' particles does not exceed 2%. They are probably composed of water ice with the addition of some dark radiation-processed organics.
The majority of Uranus's rings are opaque and only a few kilometers wide. The ring system contains little dust overall; it consists mostly of large bodies 0.2–20 m in diameter. Some rings are optically thin: the broad and faint 1986U2R/ζ, μ and ν rings are made of small dust particles, while the narrow and faint λ ring also contains larger bodies. The relative lack of dust in the ring system may be due to aerodynamic drag from the extended Uranian exosphere.
The rings of Uranus are thought to be relatively young, and not more than 600 million years old. The Uranian ring system probably originated from the collisional fragmentation of several moons that once existed around the planet. After colliding, the moons probably broke up into many particles, which survived as narrow and optically dense rings only in strictly confined zones of maximum stability.
The mechanism that confines the narrow rings is not well understood. Initially it was assumed that every narrow ring had a pair of nearby shepherd moons corralling them into shape. In 1986 Voyager 2 discovered only one such shepherd pair (Cordelia and Ophelia) around the brightest ring (ε).Space probe
A space probe is a robotic spacecraft that does not orbit Earth, but instead, explores further into outer space. A space probe may approach the Moon; travel through interplanetary space; flyby, orbit, or land on other planetary bodies; or enter interstellar space.
The space agencies of the USSR (now Russia and Ukraine), the United States, the European Union, Japan, China,India, and Israel have collectively launched probes to several planets and moons of the Solar System, as well as to a number of asteroids and comets. Approximately 15 missions are currently operational.Triton (moon)
Triton is the largest natural satellite of the planet Neptune, and the first Neptunian moon to be discovered. The discovery was made on October 10, 1846, by English astronomer William Lassell. It is the only large moon in the Solar System with a retrograde orbit, an orbit in the direction opposite to its planet's rotation. At 2,710 kilometres (1,680 mi) in diameter, it is the seventh-largest moon in the Solar System, the only satellite of Neptune massive enough to be in hydrostatic equilibrium and the second-largest planetary moon in relation to its primary, after Earth's Moon. Because of its retrograde orbit and composition similar to Pluto's, Triton is thought to have been a dwarf planet captured from the Kuiper belt.It has a surface of mostly frozen nitrogen, a mostly water-ice crust, an icy mantle and a substantial core of rock and metal. The core makes up two-thirds of its total mass. The mean density is 2.061 g/cm3, reflecting a composition of approximately 15–35% water ice.Triton is one of the few moons in the Solar System known to be geologically active (the others being Jupiter's Io and Europa, and Saturn's Enceladus and Titan). As a consequence, its surface is relatively young, with few obvious impact craters. Intricate cryovolcanic and tectonic terrains suggest a complex geological history. Part of its surface has geysers erupting sublimated nitrogen gas, contributing to a tenuous nitrogen atmosphere less than 1/70,000 the pressure of Earth's atmosphere at sea level.Uranus
Uranus (from the Latin name Ūranus for the Greek god Οὐρανός) is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. Uranus is similar in composition to Neptune, and both have bulk chemical compositions which differ from that of the larger gas giants Jupiter and Saturn. For this reason, scientists often classify Uranus and Neptune as "ice giants" to distinguish them from the gas giants. Uranus' atmosphere is similar to Jupiter's and Saturn's in its primary composition of hydrogen and helium, but it contains more "ices" such as water, ammonia, and methane, along with traces of other hydrocarbons. It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K (−224 °C; −371 °F), and has a complex, layered cloud structure with water thought to make up the lowest clouds and methane the uppermost layer of clouds. The interior of Uranus is mainly composed of ices and rock.Like the other giant planets, Uranus has a ring system, a magnetosphere, and numerous moons. The Uranian system has a unique configuration because its axis of rotation is tilted sideways, nearly into the plane of its solar orbit. Its north and south poles, therefore, lie where most other planets have their equators. In 1986, images from Voyager 2 showed Uranus as an almost featureless planet in visible light, without the cloud bands or storms associated with the other giant planets. Observations from Earth have shown seasonal change and increased weather activity as Uranus approached its equinox in 2007. Wind speeds can reach 250 metres per second (900 km/h; 560 mph).Uranus is the only planet whose name is derived directly from a figure from Greek mythology, from the Latinised version of the Greek god of the sky Ouranos.Voyager 1
Voyager 1 is a space probe launched by NASA on September 5, 1977. Part of the Voyager program to study the outer Solar System, Voyager 1 was launched 16 days after its twin, Voyager 2. Having operated for 41 years, 7 months and 19 days as of April 24, 2019, the spacecraft still communicates with the Deep Space Network to receive routine commands and to transmit data to Earth. At a distance of 145 AU (21.7 billion km; 13.5 billion mi) from Earth as of February 22, 2019, it is the most distant from Earth of all known human-made objects.The probe's objectives included flybys of Jupiter, Saturn, and Saturn's largest moon, Titan. While the spacecraft's course could have been altered to include a Pluto encounter by forgoing the Titan flyby, exploration of the moon, which was known to have a substantial atmosphere, took priority. Voyager 1 studied the weather, magnetic fields, and rings of the two planets and was the first probe to provide detailed images of their moons.
After completing its primary mission with the flyby of Saturn on November 12, 1980, Voyager 1 became the third of five artificial objects to achieve the escape velocity required to leave the Solar System. On August 25, 2012, Voyager 1 became the first spacecraft to cross the heliopause and enter the interstellar medium.In a further testament to the robustness of Voyager 1, the Voyager team completed a successful test of the spacecraft's trajectory correction maneuver (TCM) thrusters in late 2017 (the first time these thrusters were fired since 1980), a project enabling the mission to be extended by two to three years.Voyager 1's extended mission is expected to continue until about 2025 when its radioisotope thermoelectric generators will no longer supply enough electric power to operate its scientific instruments.Voyager program
The Voyager program is an American scientific program that employs two robotic probes, Voyager 1 and Voyager 2, to study the outer Solar System. The probes were launched in 1977 to take advantage of a favorable alignment of Jupiter, Saturn, Uranus and Neptune. Although their original mission was to study only the planetary systems of Jupiter and Saturn, Voyager 2 continued on to Uranus and Neptune. The Voyagers now explore the outer boundary of the heliosphere in interstellar space; their mission has been extended three times and they continue to transmit useful scientific data. Neither Uranus nor Neptune has been visited by a probe other than Voyager 2.
On 25 August 2012, data from Voyager 1 indicated that it had become the first human-made object to enter interstellar space, traveling "further than anyone, or anything, in history". As of 2013, Voyager 1 was moving with a velocity of 17 kilometers per second (11 mi/s) relative to the Sun.On 5 November 2018, data from Voyager 2 indicated that it also had entered interstellar space.Data and photographs collected by the Voyagers' cameras, magnetometers and other instruments, revealed unknown details about each of the four giant planets and their moons. Close-up images from the spacecraft charted Jupiter's complex cloud forms, winds and storm systems and discovered volcanic activity on its moon Io. Saturn's rings were found to have enigmatic braids, kinks and spokes and to be accompanied by myriad "ringlets". At Uranus, Voyager 2 discovered a substantial magnetic field around the planet and ten more moons. Its flyby of Neptune uncovered three rings and six hitherto unknown moons, a planetary magnetic field and complex, widely distributed auroras. Voyager 2 is the only spacecraft to have visited the two ice giants. In August 2018, NASA confirmed, based on results by the New Horizons spacecraft, of a "hydrogen wall" at the outer edges of the Solar System that was first detected in 1992 by the two Voyager spacecraft.The Voyager spacecraft were built at the Jet Propulsion Laboratory in Southern California and they were funded by the National Aeronautics and Space Administration (NASA), which also financed their launches from Cape Canaveral, Florida, their tracking and everything else concerning the probes.
The cost of the original program was $865 million, with the later-added Voyager Interstellar Mission costing an extra $30 million.
|Images of trajectory|
Voyager 2's trajectory from the earth, following the ecliptic through 1989 at Neptune and now heading south into the constellation Pavo
Path viewed from above the solar system
Path viewed from side, showing distance below ecliptic in gray
|Timeline of travel|
|1977-08-20||Spacecraft launched at 14:29:00 UTC.|
|1977-12-10||Entered asteroid belt.|
|1977-12-19||Voyager 1 overtakes Voyager 2. (see diagram)|
|1978-06||Primary radio receiver fails. Remainder of mission flown using backup.|
|1978-10-21||Exited asteroid belt|
|1979-04-25||Start Jupiter observation phase
|1981-06-05||Start Saturn observation phase.
|1985-11-04||Start Uranus observation phase.
|1987-08-20||10 years of continuous flight and operation at 14:29:00 UTC.|
|1989-06-05||Start Neptune observation phase.
|1989-10-02||Begin Voyager Interstellar Mission.|
|1997-08-20||20 years of continuous flight and operation at 14:29:00 UTC.|
|1998-11-13||Terminate scan platform and UV observations.|
|2007-08-20||30 years of continuous flight and operation at 14:29:00 UTC.|
|2007-09-06||Terminate data tape recorder operations.|
|2008-02-22||Terminate planetary radio astronomy experiment operations.|
|2011-11-07||Switch to backup thrusters to conserve power|
|2017-08-20||40 years of continuous flight and operation at 14:29:00 UTC.|
|2018-11-05||Crossed the heliopause and entered interstellar space.|
Extremes of motion
|Cancelled / Concepts|
Science instruments on satellites and spacecraft
|Policy and history|
(human and robotic)
21st-century space probes
|Active space probes|
(deep space missions)
|Completed after 2000|
(by termination date)
Kosmos 888 | Meteor-2 No.2 | Kosmos 889 | Kosmos 890 | NATO 3B | Kosmos 891 | OPS 3151 | Soyuz 24 | Kosmos 892 | Molniya-2-17 | Kosmos 893 | Tansei 3 | Kosmos 894 | Unnamed | Kiku 2 | Kosmos 895 | Kosmos 896 | Kosmos 897 | Palapa A2 | OPS 4915 | Kosmos 898 | Molniya-1-36 | Kosmos 899 | Kosmos 900 | Meteor-M No.39 | Kosmos 901 | Kosmos 902 | Kosmos 903 | Kosmos 904 | GEOS-1 | Kosmos 905 | Kosmos 906 | Molniya-3 No.19 | Kosmos 907 | OPS 9437 · OPS 9438 | Kosmos 908 | Kosmos 909 | Kosmos 910 | OPS 9751 | Kosmos 911 | Kosmos 912 | Intelsat IVA F-4 | Kosmos 913 | Kosmos 914 | OPS 5644 | Kosmos 915 | Kosmos 916 | Kosmos 917 | GOES 2 | Signe 3 | Kosmos 918 | Kosmos 919 | Kosmos 920 | NTS-2 | Molniya-1 No.45 | Kosmos 921 | OPS 4800 | Meteor-Priroda No.2-2 | Kosmos 922 | Kosmos 923 | Kosmos 924 | Kosmos 925 | Kosmos 926 | Kosmos 927 | Kosmos 928 | Himawari 1 | Kosmos 929 | Kosmos 930 | Kosmos 931 | Kosmos 932 | Kosmos 933 | Gran' No.13L | Kosmos 934 | Kosmos 935 | Kosmos 936 | TKS-VA No.009P · TKS-VA No.009A | Unnamed | HEAO-1 | Voyager 2 | Kosmos 937 | Kosmos 938 | Kosmos 939 · Kosmos 940 · Kosmos 941 · Kosmos 942 · Kosmos 943 · Kosmos 944 · Kosmos 945 · Kosmos 946 | Sirio 1 | Kosmos 947 | Molniya-1-38 | Kosmos 948 | Voyager 1 | Kosmos 949 | Kosmos 950 | Kosmos 951 | OTS-1 | Kosmos 952 | Kosmos 953 | Kosmos 954 | Kosmos 955 | Ekran No.12L | Prognoz 6 | OPS 7471 | Kosmos 956 | Interkosmos 17 | Salyut 6 | Intelsat IVA F-5 | Kosmos 957 | Soyuz 25 | Kosmos 958 | Kosmos 959 | ISEE-1 · ISEE-2 | Kosmos 960 | Kosmos 961 | Molniya-3 No.18 | Transat | Kosmos 962 | Meteosat 1 | Kosmos 963 | Unnamed | Kosmos 964 | Kosmos 965 | OPS 8781 · OPS 8781 SSU-1 · OPS 8781 SSU-2 · OPS 8781 SSU-3 | Soyuz 26 | OPS 4258 | Kosmos 966 | Kosmos 967 | Meteor-2 No.3 | Sakura 1 | Kosmos 968 | Kosmos 969 | Kosmos 970 | Kosmos 971 | Kosmos 972 | Kosmos 973
Payloads are separated by bullets ( · ), launches by pipes ( | ). Manned flights are indicated in bold text. Uncatalogued launch failures are listed in italics. Payloads deployed from other spacecraft are denoted in (brackets).