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; though their closeness to bright Jupiter makes naked-eye observation very difficult, they are readily seen with common binoculars, even under night sky conditions of high light pollution. 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 any planet beyond Earth.
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 five 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, and is today visible from Earth with common binoculars.
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.
Kittu crater is a crater on Jupiter's moon Ganymede. It is approximately 15 km (9.3 mi) in diameter.
Neith crater is a crater on Jupiter's moon Ganymede, the largest moon in the solar system.
Nergal crater is a crater on Jupiter's moon Ganymede. It has a distinctive ejecta blanket surrounding it that's darker nearer the craters and brighter further away. The inner region of the ejecta is characterized by a lobate appearance indicative of the flow of a liquid substance over the surface. The flow was probably icy surface material melted by the energy released during the impact that formed the crater.
Located on Jupiter's moon Callisto, Valhalla is the largest multi-ring impact crater in the Solar System. It is named after Valhalla, the hall where warriors are taken after death in Norse mythology.
A crater chain is a line of craters along the surface of an astronomical body. The descriptor term for crater chains is catena, plural catenae, as specified by the International Astronomical Union's rules on planetary nomenclature.
Enki Catena is a crater chain on Ganymede measuring 161.3 kilometres (100.2 mi) long.
Achelous is a relatively fresh crater on Ganymede adjacent to the similarly sized Gula. It was found on April 5, 1997 by the Galileo Spacecraft. It has an outer lobate ejecta deposit which extends with a radius of about a crater from the rim
Galileo Regio is a large, dark surface feature on Jupiter's moon Ganymede.
El is a crater on Ganymede. It has a small "pit" in its center. Craters with such a "central pit" are common across Ganymede and are especially intriguing since they may reveal secrets about the structure of the satellite's shallow subsurface.
Memphis Facula is a palimpsest, or "ghost crater", on Ganymede, the largest of the Jovian satellites.
Lofn is a large and relatively young impact crater on Jupiter's Galilean satellite Callisto. It was identified in 1997 and named after the goddess of marriage in Norse mythology. Located near the south pole of this moon, Lofn is classified as a flat floored or anomalous dome impact crater. It is superimposed on Adlinda multilayer structure obscuring about 30 percent of it. Another multi-ring structure—Heimdall is found to the south-west of Lofn.
Sinlap is a shallow impact crater on Titan, a natural satellite of Saturn. Located in the Fensal region, Sinlap is one of the most pristine craters on Titan, surrounded by a bright ejecta blanket.
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.
The following outline is provided as an overview of and topical guide to Jupiter:
Epigeus is the largest known impact crater on Jupiter's Galilean satellite Ganymede, with a diameter of 343 km. It is 6.5% the mean equatorial diameter of Ganymede, 5,270 km (3,270 mi). It is located in Marius Regio at 22.96°N 179.35°E.
Tectonic activity has been studied on several icy moons.
In modern times, numerous impact events on Jupiter have been observed, the most significant of which was the collision of Comet Shoemaker–Levy 9 in 1994. Jupiter is the most massive planet in the Solar System and thus has a vast sphere of gravitational influence, the region of space where an asteroid capture can take place under favorable conditions.
