Galileo was an American robotic space program that studied the planet Jupiter and its moons,as well as several other Solar System bodies. Named after the Italian astronomer Galileo Galilei,the Galileo spacecraft consisted of an orbiter and an atmospheric entry probe. It was delivered into Earth orbit on October 18,1989,by Space ShuttleAtlantis on the STS-34 mission,and arrived at Jupiter on December 7,1995,after gravity assist flybys of Venus and Earth,and became the first spacecraft to orbit Jupiter. The spacecraft then launched the first probe to directly measure its atmosphere. Despite suffering major antenna problems,Galileo achieved the first asteroid flyby,of 951 Gaspra,and discovered the first asteroid moon,Dactyl,around 243 Ida. In 1994,Galileo observed Comet Shoemaker–Levy 9's collision with Jupiter.
Callisto,or Jupiter IV,is the second-largest moon of Jupiter,after Ganymede. In the Solar System it is the third-largest moon after Ganymede and Saturn's largest moon Titan,and nearly as large as the smallest planet Mercury. Callisto is,with a diameter of 4,821 km,roughly a third larger than Earth's Moon and orbits Jupiter on average at a distance of 1,883,000 km,which is about six times further out than the Moon orbiting Earth. It is the outermost of the four large Galilean moons of Jupiter,which were discovered in 1610 with one of the first telescopes,being visible from Earth with common binoculars.
Europa,or Jupiter II,is the smallest of the four Galilean moons orbiting Jupiter,and the sixth-closest to the planet of all the 95 known moons of Jupiter. It is also the sixth-largest moon in the Solar System. Europa was discovered independently by Simon Marius and Galileo Galilei and was named after Europa,the Phoenician mother of King Minos of Crete and lover of Zeus.
Ganymede,or Jupiter III,is the largest and most massive natural satellite of Jupiter,and in the Solar System. Despite being the only moon in the Solar System with a substantial magnetic field,it is the largest Solar System object without a substantial atmosphere. Like Saturn's largest moon Titan,it is larger than the planet Mercury,but has somewhat less surface gravity than Mercury,Io,or the Moon due to its lower density compared to the three. Ganymede orbits Jupiter in roughly seven days and is in a 1:2:4 orbital resonance with the moons Europa and Io,respectively.
Project Prometheus was established in 2003 by NASA to develop nuclear-powered systems for long-duration space missions. This was NASA's first serious foray into nuclear spacecraft propulsion since the cancellation of the SNTP project in 1995. The project was planned to design,develop,and fly multiple deep space missions to the outer planets.
The following outline is provided as an overview of and topical guide to space exploration.
The exploration of Jupiter has been conducted via close observations by automated spacecraft. It began with the arrival of Pioneer 10 into the Jovian system in 1973,and,as of 2024,has continued with eight further spacecraft missions in the vicinity of Jupiter and two more en route. All but one of these missions were undertaken by the National Aeronautics and Space Administration (NASA),and all but four were flybys taking detailed observations without landing or entering orbit. These probes make Jupiter the most visited of the Solar System's outer planets as all missions to the outer Solar System have used Jupiter flybys. On 5 July 2016,spacecraft Juno arrived and entered the planet's orbit—the second craft ever to do so. Sending a craft to Jupiter is difficult,mostly due to large fuel requirements and the effects of the planet's harsh radiation environment.
TAU was a proposed uncrewed interstellar probe that would go to a distance of one thousand astronomical units from the Earth and Sun by the NASA Jet Propulsion Laboratory in 1987 using tested technology. One scientific purpose would be to measure the distance to other stars via stellar parallax. Studies continued into 1990,working with a launch in the 2005–2010 timeframe.
The Europa Orbiter was a planned NASA mission to Jupiter's Moon Europa,that was cancelled in 2002. Its main objectives included determining the presence or absence of a subsurface ocean and identifying candidate sites for future lander missions. Europa Orbiter received pre-project funding in 1998,and resulted from NASA's Fire and Ice project.
The Europa Jupiter System Mission –Laplace (EJSM-Laplace) was a proposed joint NASA/ESA uncrewed space mission slated to launch around 2020 for the in-depth exploration of Jupiter's moons with a focus on Europa,Ganymede and Jupiter's magnetosphere. The mission would have comprised at least two independent elements,NASA's Jupiter Europa Orbiter (JEO) and ESA's Jupiter Ganymede Orbiter (JGO),to perform coordinated studies of the Jovian system.
The Jupiter Magnetospheric Orbiter is a cancelled space probe proposed by the Japanese Aerospace Exploration Agency (JAXA),to undertake detailed in situ studies of the magnetosphere of Jupiter as a template for an astrophysical magnetised disk.
Jupiter Ganymede Orbiter (JGO) was a part of the international Europa Jupiter System Mission (EJSM). It was a proposed orbiter by the ESA slated for lift-off in 2020. Plans for the mission include detailed studies of Jupiter's moons,Ganymede and Callisto,as well as the Jovian magnetosphere.
Laplace-P was a proposed orbiter and lander by the Russian Federal Space Agency designed to study the Jovian moon system and explore Ganymede with a lander.
The Jupiter Icy Moons Explorer is an interplanetary spacecraft on its way to orbit and study three icy moons of Jupiter:Ganymede,Callisto,and Europa. These planetary-mass moons are planned to be studied because they are thought to have significant bodies of liquid water beneath their frozen surfaces,which would make them potentially habitable for extraterrestrial life.
Nuclear power in space is the use of nuclear power in outer space,typically either small fission systems or radioactive decay for electricity or heat. Another use is for scientific observation,as in a Mössbauer spectrometer. The most common type is a radioisotope thermoelectric generator,which has been used on many space probes and on crewed lunar missions. Small fission reactors for Earth observation satellites,such as the TOPAZ nuclear reactor,have also been flown. A radioisotope heater unit is powered by radioactive decay and can keep components from becoming too cold to function,potentially over a span of decades.
Europa Clipper is a space probe developed by NASA to study Europa,a Galilean moon of Jupiter. It was launched on October 14,2024. The spacecraft will use gravity assists from Mars on March 1,2025,and Earth on December 3,2026,before arriving at Europa in April 2030. The spacecraft will then perform a series of flybys of Europa while in orbit around Jupiter.
The Europa Lander is an astrobiology mission concept by NASA to send a lander to Europa,an icy moon of Jupiter. If funded and developed as a large strategic science mission,it would be launched in 2027 to complement the studies by the Europa Clipper orbiter mission and perform analyses on site.
The Ocean Worlds Exploration Program (OWEP) is a NASA program to explore ocean worlds in the outer Solar System that could possess subsurface oceans to assess their habitability and to seek biosignatures of simple extraterrestrial life.
Tianwen-4,formerly known as Gan De,is a planned Chinese interplanetary mission to study the Jovian system,possibly sharing a launch with a spacecraft which will make a flyby of Uranus.
