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, being visible from Earth with common binoculars.
Titan is the largest moon of Saturn and the second-largest in the Solar System. It is the only moon known to have an atmosphere denser than the Earth's and is the only known object in space—other than Earth—on which there is clear evidence that stable bodies of liquid exist. Titan is one of seven gravitationally rounded moons of Saturn and the second-most distant among them. Frequently described as a planet-like moon, Titan is 50% larger in diameter than Earth's Moon and 80% more massive. It is the second-largest moon in the Solar System after Jupiter's Ganymede and is larger than Mercury; yet Titan is only 40% as massive as Mercury, because Mercury is mainly iron and rock while much of Titan is ice, which is less dense.
Rhea is the second-largest moon of Saturn and the ninth-largest moon in the Solar System, with a surface area that is comparable to the area of Australia. It is the smallest body in the Solar System for which precise measurements have confirmed a shape consistent with hydrostatic equilibrium. Rhea has a nearly circular orbit around Saturn, but it is also tidally locked, like Saturn's other major moons; that is, it rotates with the same period it revolves (orbits), so one hemisphere always faces towards the planet.
Tethys, or Saturn III, is the fifth-largest moon of Saturn, measuring about 1,060 km (660 mi) across. It was discovered by Giovanni Domenico Cassini in 1684, and is named after the titan Tethys of Greek mythology.
Enceladus is the sixth-largest moon of Saturn and the 18th-largest in the Solar System. It is about 500 kilometers in diameter, about a tenth of that of Saturn's largest moon, Titan. It is mostly covered by fresh, clean ice, making it one of the most reflective bodies of the Solar System. Consequently, its surface temperature at noon reaches only −198 °C, far colder than a light-absorbing body would be. Despite its small size, Enceladus has a wide variety of surface features, ranging from old, heavily cratered regions to young, tectonically deformed terrain.
The moons of Saturn are numerous and diverse, ranging from tiny moonlets only tens of meters across to the enormous Titan, which is larger than the planet Mercury. There are 146 moons with confirmed orbits, the most of any planet in the solar system. This number does not include the many thousands of moonlets embedded within Saturn's dense rings, nor hundreds of possible kilometer-sized distant moons that have been observed on single occasions. Seven Saturnian moons are large enough to have collapsed into a relaxed, ellipsoidal shape, though only one or two of those, Titan and possibly Rhea, are currently in hydrostatic equilibrium. Three moons are particularly notable. Titan is the second-largest moon in the Solar System, with a nitrogen-rich Earth-like atmosphere and a landscape featuring river networks and hydrocarbon lakes. Enceladus emits jets of ice from its south-polar region and is covered in a deep layer of snow. Iapetus has contrasting black and white hemispheres as well as an extensive ridge of equatorial mountains among the tallest in the solar system.
Stickney is the largest crater on Phobos, which is a satellite of Mars. It is 9 km (5.6 mi) in diameter, taking up a substantial proportion of the moon's surface.
Herschel is an impact crater in Mars's southern hemisphere. At roughly 304 kilometers in diameter, it is a moderately large impact crater. Located at 14.5°S, 130°E, Herschel is in the Mare Tyrrhenum region of Mars. The crater is jointly named after the seventeenth/eighteenth century father and son astronomers William Herschel and John Herschel.
Lunar craters are impact craters on Earth's Moon. The Moon's surface has many craters, all of which were formed by impacts. The International Astronomical Union currently recognizes 9,137 craters, of which 1,675 have been dated.
Tirawa is the largest impact basin on Saturn's moon Rhea. It was glimpsed by Voyager 1 during its flyby of the moon and later photographed in greater detail by the Cassini orbiter. Tirawa is elongated in shape and overlaps Mamaldi, a larger and more degraded basin to its southwest.
Gertrude is the largest known crater on Uranus's moon Titania. A peak-ring impact basin, it is roughly 326–400 kilometers across, 1/5 to 1/4 of Titania's diameter. Gertrude was first observed by the Voyager 2 spacecraft on its January 1986 flyby of the Uranian system. It is named after Gertrude, the mother of Prince Hamlet in William Shakespeare's play Hamlet. The name Gertrude was officially adopted by the International Astronomical Union (IAU) in 1988. Features on Titania are named after female Shakespearean characters.
Penelope is the fourth-largest impact crater on Saturn's moon Tethys. An unusually elliptical crater, it measures roughly 180 by 220 kilometers and is located near the equator near the center of Tethys's trailing hemisphere at 10.8°S, 249.2°W. It is approximately opposite to the largest crater on Tethys—Odysseus. Penelope is named after Queen Penelope of Greek mythology, wife of the legendary King Odysseus from Homer's Odyssey. The name was officially approved by the International Astronomical Union (IAU) in 1983.
Inter-crater plains on Mercury are a land-form consisting of plains between craters on Mercury.
Feralia Planitia is the third-largest known impact structure on the asteroid Vesta, after Rheasilvia and Veneneia. It is one of several old, degraded impact basins that predate the Rheasilvia basin that now dominates Vesta. It is situated near the equator, and is 270 kilometres (170 mi) across east to west, though compressed latitudinally by the Rheasilvia impact.
Main is an impact crater on Mars, located in the Mare Australe quadrangle at 76.6°S latitude and 310.9°W longitude. It measures 109.0 kilometers in diameter and was named after Rev. Robert Main. The name was approved in 1973, by the International Astronomical Union (IAU) Working Group for Planetary System Nomenclature (WGPSN). The floor of Main shows dark portions which are caused by pressurized carbon dioxide blowing dust in the atmosphere in the spring when the temperature goes up. Some of the dust is shaped into streaks if there is a wind.
Kerwan is the largest confirmed impact basin and one of the largest geological features on the dwarf planet Ceres. It was discovered on February 19, 2015 from Dawn images as it approached Ceres. The crater is distinctly shallow for its size, and lacks a central peak. A central peak might have been destroyed by a 15-kilometer-wide crater at the center of Kerwan. The crater is likely to be young relative to the rest of Ceres's surface, as Kerwan has largely obliterated the cratering in the southern part of Vendimia Planitia.
Elivagar Flumina is a network of river channels ranging from 23 km to 210 km in length in the region around the Menrva Crater of Titan. The channel system is at least 120 km wide and shows signs of erosion. At its mouth, an alluvial fan is present. The Elivagar Flumina is interpreted as alluvial due to its closeness to fluvial valleys and as understood from the radar backscatter. Geomorphologic mapping of the Menrva region of Titan has yielded evidence for exogenic processes such as hydrocarbon fluid channelization that are thought to have formed the Flumina network.
PateraPAT-ər-ə is an irregular crater, or a complex crater with scalloped edges on a celestial body. Paterae can have any origin, although the majority of them were created by volcanism. The term comes from Latin, where it refers to a shallow bowl used in antique cultures.
The geology of Titan encompasses the geological characteristics of Titan, the largest moon of Saturn. Titan's density of 1.881 g/cm3 indicates that it is roughly 40–60% rock by mass, with the rest being water ice and other materials. It is differentiated into a rocky core, liquid water ocean, and an icy shell; the core and ocean may be partitioned by a layer of exotic high-pressure ices, and the icy shell may have a chemically distinct surface crust.
