A total of nine spacecraft have been launched on missions that involve visits to the

outer planets The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...

; all nine missions involve encounters with

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

, with four spacecraft also visiting

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

. One spacecraft, ''

Voyager 2 ''Voyager 2'' is a space probe launched by NASA on August 20, 1977, to study the outer planets and interstellar space beyond the Sun's heliosphere. As a part of the Voyager program, it was launched 16 days before its twin, ''Voyager 1'', on a ...

'', also visited

Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...

and

Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...

. The nine missions include two; ''

Ulysses Ulysses is one form of the Roman name for Odysseus, a hero in ancient Greek literature. Ulysses may also refer to: People * Ulysses (given name), including a list of people with this name Places in the United States * Ulysses, Kansas * Ulysse ...

'' and ''

New Horizons ''New Horizons'' is an Interplanetary spaceflight, interplanetary space probe that was launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research ...

'', whose primary objectives are not related to the outer planets, but which flew past Jupiter to gain

gravity assist In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement (e.g. orbit around the Sun) and gravity of a planet or other astronomical object to alter the p ...

s en route to a polar orbit around the Sun, and

Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...

—at the time of its launch considered an outer planet—respectively. ''

Cassini–Huygens ''Cassini–Huygens'' ( ), commonly called ''Cassini'', was a space research, space-research mission by NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a space probe to study the planet Saturn and its system, i ...

'' also flew past Jupiter for a gravity assist on its Mission to explore Saturn. Only three of the missions to the outer planets have been orbiters: ''

Galileo Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...

'' orbited Jupiter for eight years, while ''Cassini'' orbited Saturn for thirteen years. ''

Juno Juno commonly refers to: *Juno (mythology), the Roman goddess of marriage and queen of the gods *Juno (film), ''Juno'' (film), 2007 Juno may also refer to: Arts, entertainment and media Fictional characters *Juno, in the film ''Jenny, Juno'' *Ju ...

'' has been orbiting Jupiter since 2016.

Summary

А sampling of some missions to outer planets

Jupiter

Six spacecraft have been launched to explore

, with spacecraft making gravity-assist flybys. ''New Horizons'', although eventually targeting Pluto, used Jupiter for a gravity assist and had an extensive almost half year observation campaign of Jupiter and its moons.NASA Jupiter Press Kit (pdf)
/ref> :''Missions whose primary objectives were not related to the exploration of Jupiter are indicated in grey''

Saturn

Four spacecraft have visited Saturn; ''Pioneer 11'', ''Voyager 1'' and ''Voyager 2'' made flybys, while ''Cassini–Huygens'' entered orbit, and deployed a probe into the atmosphere of Titan.

Uranus

''Voyager 2'' is the only spacecraft to have visited Uranus, making a single flyby as part of its grand tour of the outer planets.

Neptune

''Voyager 2'' is also the only spacecraft to have visited Neptune, making a single flyby as part of its grand tour of the outer planets.

References