The timeline of the Galileo spacecraft spans its launch in 1989 to the conclusion of its mission when it dove into and destroyed itself in the atmosphere of Jupiter in 2003.
The trip from Earth to Jupiter, the probe's exploration of the Jovian atmosphere, and an orbiter tour consisting of 11 orbits of Jupiter constituted Galileo 's primary mission.
On Jupiter Arrival Day (7 December 1995), the Galileo spacecraft was given a gravity-assist from Io and then subjected to the Jupiter orbit insertion (JOI) maneuver, which slowed the spacecraft down so that the planet could "catch" it. These two actions placed the orbiter on its proper trajectory to tour the Jovian moons. The Jupiter orbit insertion maneuver involved an orbit around the planet, which is referred to as the spacecraft's "zeroth" orbit. The spacecraft's "first," and by far longest, orbit around Jupiter followed the JOI and lasted nearly seven months. On 27 June 1996, this initial orbit culminated in a close encounter with Ganymede, the largest of the four Galilean satellites.
After the first Jupiter orbit of seven months, subsequent orbits were much shorter, ranging from one to two and a half months.
The orbiter tour included four close encounters with Ganymede, three with Europa, and three with Callisto. No Io encounters were planned for the primary mission (besides the flyby on arrival day) because mission scientists feared that the high radiation levels so close to Jupiter could damage the spacecraft and possibly end the project.
The primary mission ended in December 1997, two years after Jupiter arrival.
The Galileo mission used a two-character code to specify each orbit. The first character was the first letter of the name of the moon that would receive a flyby on the orbit, while the second character indicated the number of the orbit.
Orbit: C: Callisto; E: Europa; G: Ganymede; I: Io; J: Jovian
|Closest approach in kilometers (miles)
|Date in Pacific time
|Jupiter Arrival Day
|7 December 1995
|No imaging of Io and Europa due to tape-recorder problems.
Because of the high radiation levels around Io and their effect on sensitive instruments, the scientists knew that Arrival Day might be the only time they would get a detailed look at Io—the only time they could obtain high-resolution, closeup images. But concerns regarding Galileo's malfunctioning tape recorder made it necessary to cancel all remote sensing operations during the flyby. Only fields-and-particles instruments were allowed to take and record data. Remote sensing instruments such as the SSI camera required the recorder to run discontinuously, with abrupt starts and stops, and at high speeds. That kind of operation might well have permanently crippled the recorder and, with it, the entire mission.
|27 June 1996
|A gravity-assist during G1 reduced Galileo's orbital period from 210 to 72 days, which allowed more orbits and close encounters each year. The perijove of orbit (point of closest approach to Jupiter) was increased to keep the spacecraft out of the most intense radiation regions. A radio-science experiment analyzed Ganymede's gravitational field and internal structure. The instruments detected evidence of a self-generated magnetosphere around the moon.
|6 September 1996
|A Ganymede gravity-assist put Galileo into coplanar orbit with other Galilean satellites, permitting subsequent encounters with them. A radio-science experiment analyzed Ganymede's gravitational field and internal structure. G1 and G2 radio-science and other data revealed that Ganymede had an interior that was probably differentiated into a core and a mantle. The plasma wave experiment and magnetometer data gave evidence of an internally generated magnetic field.
|4 November 1996
|Observations supported the theory that Callisto has a homogeneous internal structure, 60 percent rock and 40 percent ice.
|19 December 1996
|Galileo's primary science objectives during E4 were to conduct remote sensing observations of Europa's surface, collect data on the moon's interactions with Jupiter's magnetosphere, and analyze Jovian atmospheric features. It included occultations of the Sun and Earth by both Jupiter and Europa, which provided an opportunity to search for indications of an ionosphere and atmosphere on the moon. The return of data from E4 was limited by a solar conjunction on 19 January 1997, occurring approximately midway between the E4 and E6 encounters.
|no close flyby
|No close encounter to a Jovian moon was designed because Earth and Jupiter were in solar conjunction about the time that the closest approach would have occurred, and there would have been minimal communication capability between the spacecraft and Earth.
|20 February 1997
|The main scientific objective was to conduct high-resolution coverage of Europa. This was a similar objective to E4, but with some new Europa surface terrain observed. Monitoring of Io was also conducted. Jupiter atmospheric observations during E4 involved a coordinated effort by all of the Orbiter's remote sensing instruments to analyze white oval features in the infrared and ultraviolet regions of the spectrum. Four occultations of Earth occurred during E6—two by Europa, one by Io, and one by Jupiter. The radio science occultation measurements made during these events provided data on atmospheric profiles of the moons and Jupiter, and also on Europa's gravitational field.
|5 April 1997
|The spacecraft flew over the high latitudes of Ganymede and took high-resolution observations of high-energy impact regions, as well as Jupiter magnetosphere and aurora observations.
|7 May 1997
|The spacecraft passed over the midlatitudes of Ganymede, with closest approach longitudes 180° apart from those of the G7 encounter, allowing new terrain to be imaged.
|25 June 1997
|The spacecraft passed through and studied the magnetotail region of the Jovian magnetosphere during the period between the C9 and C10 flybys. Analysis of the C3, C9, and C10 data suggests that Callisto may have a subsurface, salty ocean that is responsible for a variable magnetic field induced by Jupiter's field.
|17 September 1997
|C10 data suggest that the internal structure of the moon is not homogeneous, but partially differentiated, with a higher percentage of rock than ice having settled toward the center of the satellite. Callisto is probably less differentiated than the other Galilean moons.
|6 November 1997
|The encounter included the longest recording to date, lasting almost 3 hours, of Jovian magnetospheric data close to Europa. The data were helpful not only in the study of Europa, but also for analyzing Io's plasma torus, whose charged particles are strongly influenced by the magnetic fields they encounter. Primary science objectives of E11 included more remote sensing of the moon's surface and more Jovian atmospheric observations. Another objective was to obtain the highest resolution images yet taken of four small, inner Jovian satellites: Thebe, Metis, Amalthea, and Adrastea.
The Galileo project would have been considered a success even if the spacecraft had stayed operational only through the end of the primary mission on 7 December 1997, two years after Jupiter arrival. The orbiter was an extremely robust machine, however, with many backup systems. It showed no sign of quitting at the end of the primary mission, so it was given a highly focused set of new exploration objectives, defined in part by the findings of the primary mission. As some of these new objectives centered on investigating Europa in great detail, the new mission was appropriately called the "Galileo Europa Mission" (GEM). Mission objectives were not limited to Europa, however; they included analyses of other satellites, as well as of Jovian fields and particles and atmospheric characteristics. During GEM, some of the most important and spectacular observations of the volcanic moon Io were taken.
GEM ran for slightly over two years, from 8 December 1997 to 31 December 1999. It was a low-cost mission with a budget of only $30 million. At the end of the primary mission, most of the 200 Galileo staff members left for other assignments. The remaining bare-bones crew, about one-fifth the size of the primary mission, was left to run GEM and achieve the objectives of four separate studies:
On each flyby, the spacecraft took only two days of data versus the seven days it had taken during the primary mission. Minimal Jovian magnetic field data were collected. The GEM team did not include the expertise to deal with unexpected problems, as the primary mission had. When issues arose, specialists who had gone on to other missions were temporarily brought back and placed on "tiger teams" to work through the problems quickly.
|Closest approach in kilometers (miles)
|Date in Pacific time
|16 December 1997
|The instruments observed the Conamara ice raft region and took stereo images of the Pwyll crater region. Stereo imaging discerned the topography of a region.
|10 February 1998
|No remote sensing or magnetospheric data were collected because of the solar conjunction, which reduced the capacity to transmit science data to Earth. Radio science data for studying Europan gravitational field and internal structure were taken.
|29 March 1998
|Stereo imaging of Mannann'an crater and Tyre Macula dark spot was accomplished. The spacecraft observed banded terrain, bright plains, and ice rafts.
|31 May 1998
|The spacecraft carried out stereo and color imaging of Cilix massif, previously believed to be the largest mountain on Europa (but E15 data revealed that it was an impact crater). Created near-terminator maps of unexplored mottled terrain. (The terminator is the boundary between the part of the moon that is illuminated and that which is dark.) Because of the low Sun angles near the terminator, shadows cast by uneven terrain are more measurable, and the heights of mounds, ridges and ice rafts can be determined.
|21 July 1998
|A spacecraft safing event prevented Europan science observations. The cause of the event was believed to be electrostatic discharges in the slip rings between the spun and despun sections of the Orbiter. The spacecraft passed over the Europan south pole.
|26 September 1998
|A south polar pass (like that of E16) allowed observations of many of the targets missed during E16. The spacecraft searched for evidence of large-scale shifting of surface features, which would indicate a possible liquid sublayer. The spacecraft's instruments took images of the Agenor Linea-Thrace Macula region, Libya Linea, a strike-slip fault zone, Rhiannon Crater, Thynia Linea, and south polar terrain (for comparison with E4 and E6 equatorial terrain images). Thermal maps of Europa were generated. Radioscience analyses of the Europan gravity field were made over a 20-hour period. The instruments also made ultraviolet observations of Europa outgassing and atmospheric emissions.
|22 November 1998
|A safing event terminated science observations 6 hours before the Europan closest approach. The primary collection was of radio-science Doppler data.
|1 February 1999
|The instruments carried out global- and regional-scale mapping, along with imaging of Tegid Crater, Rhadmanthys Linea volcanic features, mottled terrain, and a dark spot. The ultraviolet instruments also made observations of atmospheric emissions and possible outgassing. A safing event terminated science observations 4 hours after the Europan closest approach. Outbound distant observations of Europa (as well as Jupiter and Io) were lost.
|5 May 1999
|The perijove reduction campaign began; it involved incremental changes in the closest approach to Jupiter carried out over four Callisto encounters (C20–C23). The campaign was designed to set up flybys of Io, the Galilean moon closest to Jupiter.
|30 June 1999
|NIMS studied the trailing edge of Callisto. The SSI camera observed dark surface material. The PPR studied equatorial region.
|14 August 1999
|The spacecraft observed Callisto's ionosphere and measured the distribution of free electrons.
|16 September 1999
|The spacecraft observed Callisto's ionosphere, measured the distribution of free electrons, and completed the perijove reduction campaign.
|11 October 1999
|Spacecraft safed at 19 hours before Io encounter due to radiation memory hit. The Galileo engineering staff succeeded to get the spacecraft fully operational by 8 P.M. Pacific Time, a mere 2 hours before the closest approach. Obtained valuable imaging of Io volcanism. Observed a 10-kilometer-long eruption of Pele volcano.
|25 November 1999
|Spacecraft safed at 4 hours before encounter due to software problem. With very little time, the Galileo team had to formulate command sequences and get them to Jupiter. The spacecraft recovered only three minutes before the closest encounter with Io. Collected dramatic pictures of Io volcanic activity. Observed mile-high lava fountain.
Because the orbiter was continuing to operate well, a further extension to the original project, the Galileo Millennium Mission (GMM), was added to pursue answers to key questions raised during GEM. The original GMM schedule ran from January 2000 through March 2001, but it was then extended to the end of mission operations in January 2003.
The spacecraft met its demise in September 2003, when its trajectory took it on a collision course toward Jupiter and it burned up in the planet's atmosphere.
GMM conducted additional investigations of Europa, including a magnetic field measurement key to detecting the presence of liquid water. GMM also added to our knowledge of Io, studied the dynamics of Ganymede's unique magnetosphere, determined particle sizes in Jupiter's rings, and performed a joint investigation with the Cassini spacecraft, whose closest approach to Jupiter was on 30 December 2000.
Some of Galileo's instruments were not operating at full performance during GMM because exposure to Jupiter's intense radiation belts had damaged them. This was not surprising; the total radiation that the spacecraft had received was three times the amount that its systems had been built to withstand. But even with its impaired systems, Galileo continued to make valuable observations and generate important scientific data.
|Closest approach in kilometers (miles)
|Date in Pacific time
|3 January 2000
|Only limited observations were made during E26 due to factors such as the decreasing periods of Galileo orbits (allowing less time to develop orbital sequences), a smaller workforce and budget than during GEM, and reduced downlink resources. Recorded observations during E26 included high-resolution pictures near the Europan terminator, images of three of the four Jovian inner moons (Thebe, Amalthea, and Metis), and observations of the Loki volcanic region on Io. The E26 flyby was also designed to better characterize Europa's magnetic field signature to determine whether the moon generated its own magnetic field or had an induced field whose characteristics were affected by Europa's location within Jupiter's magnetosphere.
|22 February 2000
|Discovered volcanoes that change from hot to cool in several weeks. After flyby the spacecraft safed due to transient bus reset. Some Io 27 data played back during Ganymede 28.
|20 May 2000
|Galileo's closest approach to Ganymede coincided with Cassini's. Joint Galileo-Cassini observations revealed solar wind effects and magnetospheric dynamics. High-resolution Ganymede images also were taken. Magnetometer data suggest that a salty water layer exists beneath the icy crust.
|15 June 2000 to 15 November 2000
|Magnetosphere–solar wind interaction measurements.
|28 December 2000
|Real-time data were transmitted as Galileo flew from the inner magnetosphere through the magnetopause and bow shock and into the solar wind. Remote sensing instruments targeted Jupiter, its rings, and the Galilean satellites.
|25 May 2001
|The spacecraft observed the Asgard, Valhalla, and Bran craters in the closest flyby to date (in order to set up an Io encounter in August 2001). Camera problems were possibly due to continued radiation exposure that affected distant images taken of Io. Problems were corrected before the closest approach to Callisto.
|5 August 2001
|Magnetic measurements of Io indicated a weak or absent internally generated field. Spacecraft directly sampled fresh sulfur dioxide "snowfakes" from a volcanic vent.
|16 October 2001
|Galileo observed the Loki volcano (largest in the Solar System) and a new eruption in the southern region of the moon.
|17 January 2002
|This was the closest of all the flybys of Io. The moon provided a gravity-assist necessary for Galileo's ultimate collision course with Jupiter. A safing event 28 minutes before closest approach prevented most of the planned data from being collected. Galileo 's cameras were deactivated, after they had sustained irreparable radiation damage.
|4 November 2002
|Scientists used data from Amalthea encounter in order to better determine the mass and density profile of Amalthea. Combined with previously determined shape and volume information, observations generated a bulk density estimate near 1 gram per cubic centimeter, considerably lower than had been envisioned from the moon's dark albedo and its expected rocky composition. About 10 minutes after the closest approach of the Amalthea flyby, Galileo stopped collecting data, shut down all of its instruments, and went into safe mode. Though most of the Amalthea data was already written to tape, it was found that the recorder refused to play back the data collected. After weeks of troubleshooting, the flight team concluded that the problem was not stuck tape, as had happened when Galileo was first approaching Jupiter in 1995, but was instead the result of radiation damage of one or more of the instrument's infrared light-emitting diodes (LEDs). The damage was believed to consist of the displacement of atoms in the LEDs' crystal lattices, which degraded the LED optical output to only 20 percent of its full power. Laboratory experiments suggested that for the tape recorder to run properly, the LED output had to be at least 50 percent.
The Galileo flight team conducted an exhaustive analysis of possible ways to work around the problem and developed a strategy that might partially repair the damaged lattices. JPL would send commands to the spacecraft to initiate electric currents passing through the LEDs. The strategy did not immediately fix the LEDs, but after multiple applications of electric current, LED optical output increased to 60 percent, allowing the tape recorder to begin running again and download its stored data. After about 100 hours of annealing and playback cycles, the recorder was able to operate for up to an hour at a time. After many subsequent playback and cooling cycles, the complete transmission back to Earth of all recorded Amalthea flyby data was successful.
|21 September 2003
|Galileo's final orbit took it on an elongated loop away from Jupiter, from which it returned on 21 September 2003 to plow into the parent planet's 60,000-kilometer-thick atmosphere. This demise was planned in order to avoid any chance that the spacecraft might strike and contaminate the moon Europa, where scientists believe that simple life-forms may exist. If such life-forms are discovered in future missions, scientists must be sure that they are not Earth organisms that were accidentally carried to Europa aboard Galileo.
The Galilean moons, or Galilean satellites, are the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto. They are the most readily visible Solar System objects after Saturn, the dimmest of the classical planets, which are readily visible from Earth by the unaided eye, even under night sky conditions of high light pollution. Visible with common binoculars, the invention of the telescope enabled the discovery of the moons in 1610. Through this they became the first Solar System objects discovered since humans have started tracking the classical planets, and the first objects to be found to orbit a planet other than the Earth.
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 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 gravitational assist flybys of Venus and Earth, and became the first spacecraft to orbit Jupiter. It launched the first probe into Jupiter, directly measuring 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.
Jupiter is the fifth planet from the Sun and the 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, and slightly less than one one-thousandth the mass of the Sun. Jupiter is the third brightest natural object in the Earth's night sky after the Moon and Venus, and it has been observed since prehistoric times. It was named after Jupiter, the chief deity of ancient Roman religion.
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 as large as the smallest planet Mercury, though only about a third as massive. Callisto is, with a diameter of 4821 km, roughly a third larger than the Moon and orbits Jupiter on average at a distance of 1883000 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 as well as in the Solar System, being a planetary-mass moon. It is the largest Solar System object without an atmosphere, despite being the only moon of the Solar System with a magnetic field. Like Titan, it is larger than the planet Mercury, but has somewhat less surface gravity than Mercury, Io or the Moon.
There are 95 moons of Jupiter with confirmed orbits as of 23 March 2023. This number does not include a number of meter-sized moonlets thought to be shed from the inner moons, nor hundreds of possible kilometer-sized outer irregular moons that were only briefly captured by telescopes. All together, Jupiter's moons form a satellite system called the Jovian system. The most massive of the moons are the four Galilean moons: Io, Europa, Ganymede, and Callisto, which were independently discovered in 1610 by Galileo Galilei and Simon Marius and were the first objects found to orbit a body that was neither Earth nor the Sun. Much more recently, beginning in 1892, dozens of far smaller Jovian moons have been detected and have received the names of lovers or daughters of the Roman god Jupiter or his Greek equivalent Zeus. The Galilean moons are by far the largest and most massive objects to orbit Jupiter, with the remaining 91 known moons and the rings together composing just 0.003% of the total orbiting mass.
Io, or Jupiter I, is the innermost and third-largest of the four Galilean moons of the planet Jupiter. Slightly larger than Earth’s moon, Io is the fourth-largest moon in the Solar System, has the highest density of any moon, the strongest surface gravity of any moon, and the lowest amount of water of any known astronomical object in the Solar System. It was discovered in 1610 by Galileo Galilei and was named after the mythological character Io, a priestess of Hera who became one of Zeus's lovers.
Juno is a NASA space probe orbiting the planet Jupiter. It was built by Lockheed Martin and is operated by NASA's Jet Propulsion Laboratory. The spacecraft was launched from Cape Canaveral Air Force Station on August 5, 2011 UTC, as part of the New Frontiers program. Juno entered a polar orbit of Jupiter on July 5, 2016, UTC, to begin a scientific investigation of the planet. After completing its mission, Juno will be intentionally deorbited into Jupiter's atmosphere.
The magnetosphere of Jupiter is the cavity created in the solar wind by Jupiter's magnetic field. Extending up to seven million kilometers in the Sun's direction and almost to the orbit of Saturn in the opposite direction, Jupiter's magnetosphere is the largest and most powerful of any planetary magnetosphere in the Solar System, and by volume the largest known continuous structure in the Solar System after the heliosphere. Wider and flatter than the Earth's magnetosphere, Jupiter's is stronger by an order of magnitude, while its magnetic moment is roughly 18,000 times larger. The existence of Jupiter's magnetic field was first inferred from observations of radio emissions at the end of the 1950s and was directly observed by the Pioneer 10 spacecraft in 1973.
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 2023, has continued with eight further spacecraft missions in the vicinity of Jupiter. All of these missions were undertaken by the National Aeronautics and Space Administration (NASA), and all but two 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.
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 exploration of Io, Jupiter's innermost Galilean and third-largest moon, began with its discovery in 1610 and continues today with Earth-based observations and visits by spacecraft to the Jupiter system. Italian astronomer Galileo Galilei was the first to record an observation of Io on January 8, 1610, though Simon Marius may have also observed Io at around the same time. During the 17th century, observations of Io and the other Galilean satellites helped with the measurement of longitude by map makers and surveyors, with validation of Kepler's Third Law of planetary motion, and with measurement of the speed of light. Based on ephemerides produced by astronomer Giovanni Cassini and others, Pierre-Simon Laplace created a mathematical theory to explain the resonant orbits of three of Jupiter's moons, Io, Europa, and Ganymede. This resonance was later found to have a profound effect on the geologies of these moons. Improved telescope technology in the late 19th and 20th centuries allowed astronomers to resolve large-scale surface features on Io as well as to estimate its diameter and mass.
JunoCam is the visible-light camera/telescope onboard NASA's Juno spacecraft currently orbiting Jupiter. The camera is operated by the JunoCam Digital Electronics Assembly (JDEA). Both the camera and JDEA were built by Malin Space Science Systems. JunoCam takes a swath of imaging as the spacecraft rotates; the camera is fixed to the spacecraft, so as it rotates, it gets one sweep of observation. It has a field of view of 58 degrees with four filters.
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 that was launched on 14 April 2023 from Guiana Space Centre in the French Guiana by the European Space Agency (ESA) with Airbus Defence and Space as the main contractor. The mission is planned to study Ganymede, Callisto, and Europa, three of Jupiter's Galilean moons. They are thought to have significant bodies of liquid water beneath their icy surfaces which would make them potentially habitable environments.
Europa Clipper is an interplanetary mission in development by NASA comprising an orbiter. Planned for launch in October 2024, the spacecraft is being developed to study the Galilean moon Europa through a series of flybys while in orbit around Jupiter.
The following outline is provided as an overview of and topical guide to Jupiter:
Tianwen-4, formerly known as Gan De, is a planned interplanetary mission by China to study the Jovian system and its environs, sharing a launch with a spacecraft which will make a flyby of Uranus.