"particular for his research on the Galilean satellites, the four largest moons of Jupiter, namely Io, Europa, Ganymede, and Callisto. The official naming citation was published by the Minor Planet Center before November 1977 (). 2067 Aksnes 2067 Aksnes, provisional designation , is a rare-type Hildian asteroid from the outermost region of the asteroid belt, approximately 44 kilometers in diameter. The asteroid was discovered on 23 February 1936, by Finnish astronomer Yrjö Väisälä at Turku Observatory in Southwest Finland. It was named after astronomer Kaare Aksnes. ""Aksnes"" is a member of the Hilda family, the outermost orbital group of asteroids"
"facilitate remote exploration of Europa, or be an ideal location for a Jovian system waystation servicing spacecraft heading farther into the outer Solar System, using a gravity assist from a close flyby of Jupiter after departing Callisto. In December 2003, NASA reported that a manned mission to Callisto might be possible in the 2040s. Callisto (moon) </math>.</ref> Callisto (Jupiter IV) is the second-largest moon of Jupiter, after Ganymede. It is the third-largest moon in the Solar System after Ganymede and Saturn's largest moon Titan, and the largest object in the Solar System not to be properly differentiated. Callisto was discovered"
"disk, in which formation timescales were comparable to or shorter than orbital migration timescales. Io is anhydrous and likely has an interior of rock and metal. Europa is thought to contain 8% ice and water by mass with the remainder rock. These moons are, in increasing order of distance from Jupiter: Io (Jupiter I) is the innermost of the four Galilean moons of Jupiter and, with a diameter of 3642 kilometers, the fourth-largest moon in the Solar System. It was named after Io, a priestess of Hera who became one of the lovers of Zeus. Nevertheless, it was simply referred"
"green glows in the same image) have also been observed. Io (moon) Io (Jupiter I) is the innermost of the four Galilean moons of the planet Jupiter. It is the fourth-largest moon, has the highest density of all the moons, and has the least amount of water of any known astronomical object in the Solar System. It was discovered in 1610 and was named after the mythological character Io, a priestess of Hera who became one of Zeus' lovers. With over 400 active volcanoes, Io is the most geologically active object in the Solar System. This extreme geologic activity is"
"Io (moon) Io (Jupiter I) is the innermost of the four Galilean moons of the planet Jupiter. It is the fourth-largest moon, has the highest density of all the moons, and has the least amount of water of any known astronomical object in the Solar System. It was discovered in 1610 and was named after the mythological character Io, a priestess of Hera who became one of Zeus' lovers. With over 400 active volcanoes, Io is the most geologically active object in the Solar System. This extreme geologic activity is the result of tidal heating from friction generated within Io's"
"that their mean density decreases with distance from Jupiter. Callisto, the outermost and least dense of the four, has a density intermediate between ice and rock whereas Io, the innermost and densest moon, has a density intermediate between rock and iron. Callisto has an ancient, heavily cratered and unaltered ice surface and the way it rotates indicates that its density is equally distributed, suggesting that it has no rocky or metallic core but consists of a homogeneous mix of rock and ice. This may well have been the original structure of all the moons. The rotation of the three inner"
"Europa (moon) </math></ref> Europa ( ) (Jupiter II) is the smallest of the four Galilean moons orbiting Jupiter, and the sixth-closest to the planet. It is also the sixth-largest moon in the Solar System. Europa was discovered in 1610 by Galileo Galilei and was named after Europa, the mythological mother of King Minos of Crete and lover of Zeus (the Greek equivalent of the Roman god Jupiter). Slightly smaller than Earth's Moon, Europa is primarily made of silicate rock and has a water-ice crust and probably an iron–nickel core. It has a very thin atmosphere composed primarily of oxygen. Its"
"other two have lights on them which are gradually spreading. These three bodies are the moons Io, Callisto, and Ganymede, the latter two of which are presently being colonised by humans. Humans have been attempting to explore Europa ever since Lucifer was created in 2010. However, none of these attempts has been successful. Every probe that has attempted to land on Europa has been destroyed on approach. The debris from every probe falls to the surface of the planet, and the debris from some of the first ships to be destroyed is venerated by the Europans. Finally, there is a"
"degrees to the left or right of these moons in its orbit. Callisto, still further out, would appear only a quarter the size of Io. None of the surface features on Jupiter's moons would appear as prominent as the lunar maria do when the Moon is viewed from Earth. Dark and light patches would be visible on Io's surface due to the coloration of sulfur that covers Io, and the largest volcanoes would be designated by dark points, but the lack of large, contrasting features results in a poor view of it. Europa, however, would appear as a completely featureless"
"thin atmosphere made up mostly of sulfur dioxide (SO). If a surface data or collection vessel were to land on Io in the future, it would have to be extremely tough (similar to the tank-like bodies of the Soviet Venera landers) to survive the radiation and magnetic fields that originate from Jupiter. Europa (Jupiter II), the second of the four Galilean moons, is the second closest to Jupiter and the smallest at 3121.6 kilometers in diameter, which is slightly smaller than the Moon. The name comes from a mythical Phoenician noblewoman, Europa, who was courted by Zeus and became the"
"to eclipse. Different versions of Eclipse have been given different science-related names. The versions named after Callisto, Europa, and Ganymede, which are moons of Jupiter, were followed by a version named after Galileo the discoverer of those moons. These were followed by two sun-themed names, Helios of Greek mythology, and Indigo, one of the seven colors of a rainbow (which is produced by the sun). The version after that, Juno, has a triple meaning: a Roman mythological figure, an asteroid, and a spacecraft to Jupiter. Kepler, Luna, and Mars continued the astronomy theme, and then Neon and Oxygen constitutes a"
"it was found that Europa has primarily amorphous ice, Ganymede has both amorphous and crystalline ice, and Callisto is primarily crystalline. This is thought to be the result of competing forces: the thermal crystallization of amorphous ice versus the conversion of crystalline to amorphous ice by the flux of charged particles from Jupiter. Closer to Jupiter than the other three moons, Europa receives the highest level of radiation and thus through irradiation has the most amorphous ice. Callisto is the furthest from Jupiter, receiving the lowest radiation flux and therefore maintaining its crystalline ice. Ganymede, which lies between the two,"
"white disc. Even when viewed from nearby, most spacecraft images use contrast enhancements to clearly show the cracks in the Europan ice, which are only about 10–15 percent darker than the rest of the surface. Vague dark and light patches would be visible on Ganymede, whereas Callisto is much too distant for any features to be made out. All four Galilean moons stand out because of the swiftness of their motion, compared to the Moon. They are all also large enough to fully eclipse the Sun. Because Jupiter's axial tilt is minimal, and the Galilean moons all orbit in the"
"In February–March 2007, the ""New Horizons"" probe on its way to Pluto obtained new images and spectra of Callisto. The next planned mission to the Jovian system is the European Space Agency's Jupiter Icy Moon Explorer (JUICE), due to launch in 2022. Several close flybys of Callisto are planned during the mission. Formerly proposed for a launch in 2020, the Europa Jupiter System Mission (EJSM) was a joint NASA/ESA proposal for exploration of Jupiter's moons. In February 2009 it was announced that ESA/NASA had given this mission priority ahead of the Titan Saturn System Mission. ESA's contribution still faced funding"
"only being heated by radioactive elements, whereas Europa has tidal energy as well, from its greater proximity to Jupiter. Based on the considerations mentioned above and on other scientific observations, it is thought that of all of Jupiter's moons, Europa has the greatest chance of supporting microbial life. The ""Pioneer 10"" and ""Pioneer 11"" Jupiter encounters in the early 1970s contributed little new information about Callisto in comparison with what was already known from Earth-based observations. The real breakthrough happened later with the ""Voyager 1"" and ""Voyager 2"" flybys in 1979. They imaged more than half of the Callistoan surface"
"calendar. Therefore, the night Galileo first observed Jupiter's moons was January 7, 1610 on the Gregorian calendar -— December 28, 1609 on the Julian calendar (Marius claimed to have first observed Jupiter's moons on December 29, 1609) Although Galileo did indeed discover Jupiter's four moons before Marius, Io, Europa, Ganymede, and Callisto are now the names of Galileo's four moons. Galileo's drawings of an imperfect moon directly contradicted Ptolemy’s and Aristotle’s cosmological descriptions of perfect and unchanging heavenly bodies made of quintessence (the fifth element in ancient and medieval philosophy of which the celestial bodies are composed). Before the publication"
"what he thought were three stars near Jupiter, including what turned out to be Ganymede, Callisto, and one body that turned out to be the combined light from Io and Europa; the next night he noticed that they had moved. On January 13, he saw all four at once for the first time, but had seen each of the moons before this date at least once. By January 15, Galileo came to the conclusion that the stars were actually bodies orbiting Jupiter. He claimed the right to name the moons; he considered ""Cosmian Stars"" and settled on ""Medicean Stars"". The"
"on the icy crust of Europa. The presence of the minerals may have been the result of a collision with an asteroid or comet. Some scientists have speculated that life on Earth could have been blasted into space by asteroid collisions and arrived on the moons of Jupiter in a process called lithopanspermia. Europa (moon) </math></ref> Europa ( ) (Jupiter II) is the smallest of the four Galilean moons orbiting Jupiter, and the sixth-closest to the planet. It is also the sixth-largest moon in the Solar System. Europa was discovered in 1610 by Galileo Galilei and was named after Europa,"
"thermal emission and the distribution of sulfur dioxide frost, the absorption bands of which dominate Io's near-infrared spectrum. In December 1997, NASA approved an extended mission for ""Galileo"" known as the Galileo Europa Mission, which ran for two years following the end of the primary mission. The focus of this extended mission was to follow up on the discoveries made at Europa with seven additional flybys to search for new evidence of a possible sub-surface water ocean. Starting in May 1999, ""Galileo"" used four flybys (20 to 23) with Callisto to lower its periapse, setting up a chance for it"
"considered by the Planetary Decadal Survey to be too expensive. The survey supported a cheaper alternative to JEO. While scientists require further evidence to determine the extent of a rocky core on Jupiter, its Galilean moons provide the potential opportunity for future human exploration. Particular targets are Europa, due to its potential for life, and Callisto, due to its relatively low radiation dose. In 2003, NASA proposed a program called Human Outer Planets Exploration (HOPE) that involved sending astronauts to explore the Galilean moons. NASA has projected a possible attempt some time in the 2040s. In the Vision for Space"
"of the four Galilean moons. Despite this, its volcanoes could be energy resources for the other moons, better to colonize. The Artemis Project proposed a plan to colonize Europa. Scientists would inhabit igloos and drill down into the Europan ice crust, exploring any subsurface ocean. The report also discusses use of air pockets for human habitation. Ganymede is the largest moon in the Solar System. Ganymede is the only moon with a magnetosphere, but it is overshadowed by Jupiter's magnetic field. Ganymede receives about 8 rem of radiation per day. Due to its distance from Jupiter's powerful radiation belt, Callisto"
"launch in 2021. It would involve multiple flybys of Io while in orbit around Jupiter beginning in 2026. Io orbits Jupiter at a distance of from Jupiter's center and from its cloudtops. It is the innermost of the Galilean satellites of Jupiter, its orbit lying between those of Thebe and Europa. Including Jupiter's inner satellites, Io is the fifth moon out from Jupiter. It takes Io about 42.5 hours to complete one orbit around Jupiter (fast enough for its motion to be observed over a single night of observation). Io is in a 2:1 mean-motion orbital resonance with Europa and"
"5 arcminutes, less than a quarter of its size as seen from Earth. Aside from the Sun, the most prominent objects in Jupiter's sky are the four Galilean moons. Io, the nearest to the planet, would be slightly larger than the full moon in Earth's sky, though less bright, and would be the largest moon in the Solar System as seen from its parent planet. The higher albedo of Europa would not overcome its greater distance from Jupiter, so it would not outshine Io. In fact, the low solar constant at Jupiter's distance (3.7% Earth's) ensures that none of the"
"a German astronomer who had studied with Tycho Brahe, was the first to publish a book of his observations. Marius attacked Galileo in ""Mundus Jovialis"" (published in 1614) by insisting that he had found Jupiter's four moons before Galileo and had been observing them since 1609. Marius believed that he therefore had the right to name them, which he did: he named them after Jupiter's love conquests: Io, Europa, Ganymede, and Callisto. But Galileo was not confounded —- he pointed out that being outside the Church, Marius had not yet accepted the Gregorian calendar and was still using the Julian"
"Mensa, Tvashtar Paterae, and Tsũi Goab Fluctus. The first reported observation of Io was made by Galileo Galilei on 7 January 1610 using a 20x-power, refracting telescope at the University of Padua. However, in that observation, Galileo could not separate Io and Europa due to the low power of his telescope, so the two were recorded as a single point of light. Io and Europa were seen for the first time as separate bodies during Galileo's observations of the Jovian system the following day, 8 January 1610 (used as the discovery date for Io by the IAU). The discovery of"
"Exploration of Io The exploration of Io, Jupiter's 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."
"ions farther from the planet, where they are implanted preferentially on the trailing hemispheres of Europa and Ganymede. On Callisto however, for unknown reasons, sulfur is concentrated on the leading hemisphere. Plasma may also be responsible for darkening the moons' trailing hemispheres (again, except Callisto's). Energetic electrons and ions, with the flux of the latter being more isotropic, bombard surface ice, sputtering atoms and molecules off and causing radiolysis of water and other chemical compounds. The energetic particles break water into oxygen and hydrogen, maintaining the thin oxygen atmospheres of the icy moons (since the hydrogen escapes more rapidly). The"
"in fact, ""three stars in the heavens moving about Jupiter, as Venus and Mercury round the Sun."" These were the first moons of a planet other than the Earth to be discovered. The discoveries of Io and the other Galilean satellites of Jupiter were published in Galileo's ""Sidereus Nuncius"" in March 1610. While the Jovian moons he discovered would later be known as the Galilean satellites, after himself, he proposed the name ""Medicea Sidera"" (Medicean Stars) after his new patrons, the de'Medici family of his native Florence. Initially, he proposed the name ""Cosmica Sidera"" (Cosmic Stars), after the head of"
"to 357"" at aphelion. Unlike the near coincidence of the apparent sizes of the Moon and Sun as viewed from Earth, this perspective exaggerates the apparent diameters of all the Galilean moons in comparison to the Sun. Even distant Callisto is over 50% larger, and Io is nearly six times as large. This disparity in angular size makes the moons' shadows on Jupiter more defined than the lunar shadow on Earth during a total solar eclipse, as it narrows the penumbra for a given distance. Solar eclipses on Jupiter Solar eclipses on Jupiter occur when any of the natural satellites"
"results of the ""Galileo"" mission include: On December 11, 2013, NASA reported, based on results from the Galileo mission, the detection of ""clay-like minerals"" (specifically, phyllosilicates), often associated with organic materials, on the icy crust of Europa, moon of Jupiter. The presence of the minerals may have been the result of a collision with an asteroid or comet according to the scientists. NASA launched ""Juno"" on August 5, 2011 to study Jupiter in detail. It entered a polar orbit of Jupiter on July 5, 2016. The spacecraft is studying the planet's composition, gravity field, magnetic field, and polar magnetosphere. ""Juno"""
"The second series of euro banknotes is known as the Europa Series and bears her likeness in the watermark and hologram. The metal ""europium"", a rare-earth element, was named in 1901 after the continent. The invention of the telescope revealed that the planet Jupiter, clearly visible to the naked eye and known to humanity since prehistoric times, has an attendant family of moons. These were named for male and female lovers of the god and other mythological persons associated with him. The smallest of Jupiter's Galilean moons was named after Europa. Europa (consort of Zeus) In Greek mythology, Europa (;"
"charged-particle flux from Jupiter's magnetosphere at its surface is relatively low—about 300 times lower than, for example, that at Europa. Hence, unlike the other Galilean moons, charged-particle irradiation has had a relatively minor effect on Callisto's surface. The radiation level at Callisto's surface is equivalent to a dose of about 0.01 rem (0.1 mSv) per day, which is over ten times higher than Earth's average background radiation. The average density of Callisto, 1.83 g/cm, suggests a composition of approximately equal parts of rocky material and water ice, with some additional volatile ices such as ammonia. The mass fraction of ices"
"mass. It is named after the Greek mythological nymph Callisto, a lover of Zeus who was a daughter of the Arkadian King Lykaon and a hunting companion of the goddess Artemis. The moon does not form part of the orbital resonance that affects three inner Galilean satellites and thus does not experience appreciable tidal heating. Callisto is composed of approximately equal amounts of rock and ices, which makes it the least dense of the Galilean moons. It is one of the most heavily cratered satellites in the Solar System, and one major feature is a basin around 3000 km wide"