RObject { LocName "Sun" Name "Sol" Parent "Solar System" Descr "Sol, or the Sun, is the star at the center of the Solar system. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields. It has a diameter of 1,392,684 km, about 109 times that of Earth, and its mass (about 2·10[sup]30[/sup] kilograms, 330,000 times that of Earth) accounts for about 99.86% of the total mass of the Solar System. Chemically, about three quarters of the Sun's mass consists of hydrogen, while the rest is mostly helium. The remainder (1.69%, which nonetheless equals 5,628 times the mass of Earth) consists of heavier elements, including oxygen, carbon, neon and iron, among others. The Sun formed about 4.6 billion years ago from the gravitational collapse of a region within a large molecular cloud. Most of the matter gathered in the center, while the rest flattened into an orbiting disk that would become the Solar system. The central mass became increasingly hot and dense, eventually initiating thermonuclear fusion in its core. It is thought that almost all other stars form by this process. The Sun's stellar classification, based on spectral class, is G2V, and is informally designated as a yellow dwarf, because its visible radiation is most intense in the yellow-green portion of the spectrum. In the spectral class label, G2 indicates its surface temperature of approximately 5778 K (5505 °C), and V indicates that the Sun, like most stars, is a main-sequence star, and thus generates its energy by nuclear fusion of hydrogen nuclei into helium. In its core, the Sun fuses 620 million metric tons of hydrogen each second. Once regarded by astronomers as a small and relatively insignificant star, the Sun is now thought to be brighter than about 85% of the stars in the Milky Way galaxy, most of which are red dwarfs. The absolute magnitude of the Sun is +4.83; however, as the star closest to Earth, the Sun is the brightest object in the sky with an apparent magnitude of −26.74. The Sun's hot corona continuously expands in space creating the solar wind, a stream of charged particles that extends to the heliopause at roughly 100 astronomical units. The bubble in the interstellar medium formed by the solar wind, the heliosphere, is the largest continuous structure in the Solar system. The Sun is currently traveling through the inner rim of the Orion Arm of the Milky Way galaxy. Of the 50 nearest stellar systems within 17 light-years of Earth (the closest being a red dwarf named Proxima Centauri at approximately 4.2 light-years away), the Sun ranks fourth in mass. The Sun orbits the center of the Milky Way at a distance of approximately 24,000-26,000 light-years from the galactic center, completing one clockwise orbit, as viewed from the galactic north pole, in about 225-250 million years. Since our galaxy is moving with respect to the cosmic microwave background radiation (CMB) in the direction of the constellation Hydra with a speed of 550 km/s, the Sun's resultant velocity with respect to the CMB is about 370 km/s in the direction of Crater or Leo. The mean distance of the Sun from the Earth is approximately 149.6 million kilometers (1 AU), though the distance varies as the Earth moves from perihelion in January to aphelion in July. At this average distance, light travels from the Sun to Earth in about 8 minutes and 19 seconds. The energy of this sunlight supports almost all life on Earth by photosynthesis, and drives Earth's climate and weather." } RObject { LocName "Mercury" Name "Mercury" Parent "Sol" Descr "Mercury is the innermost planet in the Solar system. It is also the smallest, and its orbit is the most eccentric. It orbits the Sun once in about 88 Earth days, completing three rotations about its axis for every two orbits. The planet is named after the Roman god Mercury, the messenger to the gods. Mercury's surface is heavily cratered, indicating that it has been geologically inactive for billions of years. Due to its near lack of an atmosphere to retain heat, Mercury's surface experiences the steepest temperature gradient of all the planets, ranging from a very cold 100 K at night to a very hot 700 K during the day. Mercury's axis has the smallest tilt of any of the Solar system's planets, but Mercury's orbital eccentricity is the largest. The seasons on the planet's surface are caused by the variation of its distance from the sun rather than by the axial tilt, which is the main cause of seasons on Earth and other planets. At perihelion, the intensity of sunlight on Mercury's surface is more than twice the intensity at aphelion. Because the seasons of the planet are produced by the orbital eccentricity instead of the axial tilt, the season does not differ between its two hemispheres. Mercury has a significant stable global magnetic field around 1.1% as strong as Earth's. It has an equatorial field strength of 300 nT (nanoteslas), compared to ~35,000 nT at Earth's equator. This field is strong enough to deflect the Solar wind around the planet, creating a magnetosphere. The solar wind plasma trapped within the magnetosphere contributes to space weathering on Mercury's surface. Like that of Earth, Mercury's magnetic field is dipolar and is likely being generated by a dynamo effect (circulation in the liquid, iron-rich core)." } RObject { LocName "Venus" Name "Venus" Parent "Sol" Descr "Venus is the second planet in the Solar system, and the second-largest of the terrestrial (rocky) planets. It is the most similar planet in the Solar system to Earth in terms of size and bulk composition. It also has the most circular orbit of any planet and orbits the Sun in about 224.7 days. Its carbon dioxide atmosphere is extremely thick and creates a greenhouse effect strong enough to make Venus the hottest world in the Solar system, with a surface temperature exceeding 735 K (462 [deg]C). Venus is entirely covered with a thick layer of bright sulfuric acid clouds. Abundant lightning has been recorded in the atmosphere. The planet has a very slight axial tilt but has a retrograde rotation, and completes just one rotation in over 243 days. Its rotation is the most anomalous of all the major planets. The surface of Venus has been largely shaped by volcanic activity which likely continues today." } RObject { LocName "Earth" Name "Earth" Parent "Earth-Moon" Descr "Earth (or the Earth) is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the World, the Blue Planet, or by its Latin name, Terra. Astronomical symbol is [EARTH]. Earth formed 4.54 billion years ago, and life appeared on its surface within one billion years. The planet is home to millions of species, including humans. Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks harmful solar radiation, permitting life on land. The physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist during this period. Estimates on how much longer the planet will to be able to continue to support life range from a mere 500 million years, to as long as 2.3 billion years. Earth's outer surface is divided into several rigid segments, or tectonic plates, that migrate across the surface over periods of many millions of years. About 71% of the surface is covered by salt water oceans, with the remainder consisting of continents and islands which together have many lakes and other sources of water that contribute to the hydrosphere. Earth's poles are mostly covered with solid ice (Antarctic ice sheet) or sea ice (Arctic ice cap). The planet's interior remains active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid iron inner core. Earth interacts with other objects in space, especially the Sun and the Moon. At present, Earth orbits the Sun once every 366.26 times it rotates about its own axis, which is equal to 365.26 solar days, or one sidereal year. The Earth's axis of rotation is tilted 23.4[deg] away from the perpendicular of its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). Earth's only known natural satellite, the Moon, which began orbiting it about 4.53 billion years ago, provides ocean tides, stabilizes the axial tilt, and gradually slows the planet's rotation. Between approximately 3.8 billion and 4.1 billion years ago, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment." } RObject { LocName "Moon" Name "Moon" Parent "Earth-Moon" Descr "The Moon (Latin: Luna) is Earth's only natural satellite. It is fifth-largest and the second-densest (after Jupiter's satellite Io) natural satellite in the Solar System. The Moon is exceptionally large relative to Earth: a quarter its diameter and 1/81 its mass. It is the largest moon in the Solar System relative to the size of its planet (though Charon is larger relative to the dwarf planet Pluto, at 1/9 Pluto's mass). Earth and the Moon are nevertheless still considered a planet-satellite system, rather than a double planet, because their barycentre, the common centre of mass, is located 1700 km (1100 mi) (about a quarter of Earth's radius) beneath Earth's surface. The Moon is thought to have formed approximately 4.5 billion years ago, not long after Earth. Although there have been several hypotheses for its origin in the past, the current most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body called Theia. The Moon is in synchronous rotation with Earth, always showing the same face with its near side marked by dark volcanic maria that fill between the bright ancient crustal highlands and the prominent impact craters. It is the second-brightest regularly visible celestial object in Earth's sky (after the Sun), as measured by illuminance on Earth's surface. Although it can appear a very bright white, its surface is actually dark, with a reflectance just slightly higher than that of worn asphalt. Its prominence in the sky and its regular cycle of phases have, since ancient times, made the Moon an important cultural influence on language, calendars, art, and mythology. The Moon's gravitational influence produces the ocean tides and the slight lengthening of the day. The Moon's current orbital distance is about thirty times the diameter of Earth, causing it to have an apparent size in the sky almost the same as that of the Sun. This allows the Moon to cover the Sun nearly precisely in total solar eclipse. This matching of apparent visual size is a coincidence. The Moon's linear distance from Earth is currently increasing at a rate of 3.82 ± 0.07 centimetres (1.504 ± 0.028 in) per year, but this rate is not constant. [big]Surface environment[/big] The Moon has a heavily cratered surface, due to the lack of geological activity for billions of years. The most prominent feature of the far side of the Moon is the South Pole-Aitken basin, which is around 2,240 km in diameter and is the largest crater in the Solar System. The most prominent feature of the near side of the Moon are the lunar maria-large, dark, basaltic plains formed by ancient volcanic eruptions. They cover about 16% of the lunar surface. Although liquid water is not possible on the surface of the Moon, pockets of frozen water exist in permanently shadowed craters. [big]Internal structure[/big] A solid iron-rich inner core with a radius of 240 km is surrounded by a liquid outer core of around 300 km. The heterogenous mantle makes up most of the rest of the Moon's total volume, while the crust is only around 50 km in diameter. [big]Atmosphere[/big] The Moon effectively has no atmosphere. It is so small that it has a total mass of less than 10 metric tons. The two main elements in the atmosphere of the Moon are sodium and potassium. [big]Exploration[/big] The Moon was explored intensely during the Cold War. The Luna 1 spacecraft was the first to escape Earth's gravity, Luna 2 was the first to crash into the Moon, Luna 3 made pictures of the Moon's dark side and Luna 9 was the first to make a soft landing on the surface. In 1968, the American Apollo 8 made the first crewed mission to lunar orbit. In 1969, Neil Armstrong and Buzz Aldrin became the first humans to set foot on the Moon, during the Apollo 11 mission. Apollo missions 11-17 returned substantial amounts of lunar rock in more than 2000 separate samples. As of Apollo 17, no manned missions have been made, with only unmanned spacecraft visiting the surface of the Moon." } RObject { LocName "Mars" Name "Mars" Parent "Sol" Descr "Mars is the fourth planet in the Solar system and the outermost of the terrestrial (rocky) planets. It has a thin carbon dioxide atmosphere which has slowly been escaping to space for billions of years and is too thin to significantly moderate the planet's climate. Enormous dust storms can grow to cover the entire world. The planet's moderate axial tilt and fairly eccentric orbit yield mild seasons in the north and extreme seasons in the south. Mars has the most Earth-like surface environment of any planet in the Solar system, with average temperatures in many locations comparable to Antarctica. Mars has extensive sheets of water-ice on and just below much of the surface, and small amounts of liquid water may occasionally flow in some locations. Mars shows evidence of having had a warmer and wetter past in which water flowed across much of the surface for extended periods. Some of these locations were good environments for life, though it is not known whether such life existed. The surface today, though cold and dry, boasts some of the largest geological features in the Solar system, including a 5000 km rift valley and canyon system, and a 22 km tall and 600 km wide volcano." } RObject { LocName "Phobos" Name "Phobos" Parent "Mars" Pioneer "Asaph Hall" Date "1877.08.18" } RObject { LocName "Deimos" Name "Deimos" Parent "Mars" Pioneer "Asaph Hall" Date "1877.08.12" } RObject { LocName "Ceres" Name "Ceres" Parent "Sol" Pioneer "Giuseppe Piazzi" Date "1801.01.01" Descr "[big]Overview[/big] Ceres is the Solar system's smallest dwarf planet and the largest object in the main asteroid belt. It was also the first object in the asteroid belt to be discovered, and was initially categorized as a planet until the discovery of many other similar objects led to their re-categorization as asteroids. Ceres is slightly less than 1,000 km in diameter and is composed of rock and ice. It comprises one-third of the mass of the asteroid belt. It may also have a tenuous atmosphere. No natural satellites have been discovered around Ceres. [big]Surface Environment[/big] Ceres has a surface composition largely similar to carbonaceous (C-type) asteroids, with some notable differences. The characteristic most dissimilar from C-type asteroid composition is the existence of hydrated materials. The surface may also contain carbonates and iron-rich clays, materials that are also uncommon on C-type asteroids. Temperatures on the surface can reach 235 K (-38 [deg]C), relatively warm for a body so distant from the sun, thanks to Ceres' low albedo. Very few features have been identified on the surface of Ceres. Even the most powerful near-Earth telescopes can not resolve details much smaller than 30 km across. Several bright and dark features have been mapped, though nothing is known about any of them. Ceres also does not appear to be geologically active, and its surface is likely altered only by impact events. [big]Internal Structure[/big] Due to its large size, oblate spheroidal shape, and some observed surface characteristics, many astronomers suspect that Ceres has a differentiated interior with a rocky core and a mantle composed largely of water ice. If true, this would make Ceres the largest surviving protoplanet in the inner Solar system. However, this has yet to be confirmed by close observation, and alternative possible explanations for its shape and surface characteristics do exist. If a water ice mantle does exist, then it is possible that a liquid ocean layer exists or did exist as well. [big]Atmosphere[/big] There are indications that Ceres may have a thin atmosphere, and possibly exposed water ice or frost on its surface. Any such ice would sublimate if directly exposed to sunlight, escaping away into space. Hydroxide ions detected near the north pole of Ceres may be caused by this process." } RObject { LocName "Vesta" Name "Vesta" Parent "Sol" Pioneer "Heinrich Wilhelm Olbers" Date "1807.03.29" Descr "[big]Overview[/big] Vesta is the second most massive object in the main asteroid belt and ranks third in volume, after Ceres and Pallas. It was fourth object in the asteroid belt to be discovered, and like Ceres, Pallas, and Juno was initially categorized as a planet until the discovery of many other similar objects led to their re-categorization as asteroids. Vesta roughly 570 kilometers in diameter at its equator, and significantly flattened at the poles. It comprises an estimated 9% of the mass of the asteroid belt. Vesta has no atmosphere and no natural satellites. Its high albedo and large size combine to make it the brightest object in the asteroid belt. Vesta is unique in that it is the last known surviving rocky protoplanet in the Solar system, and as such has a differentiated interior. The planet suffered a massive impact less than one billion years ago which excavated about 1% of its volume and left a crater over 500 kilometers wide near its south pole. The members of the prominent Vesta family of asteroids are likely debris from this event. [big]Surface Environment[/big] Vesta's surface is covered with numerous craters of all sizes. The largest of these, and also by far the dominant surface feature on the planet, is Rheasilvia crater, over 500 kilometers in diameter with a deep floor and an enormous central peak. This crater is of such magnitude that Vesta's shape is significantly distorted by it, giving it a concave ring around the south pole with a giant protrusion in the center. The central peak of Rheasilvia crater is the tallest known mountain in the Solar system, slightly taller than Mars' Olympus Mons, though Olympus is is larger by volume. There are also several large concentric troughs on the Vestan surface, in two separate sets, which are among the longest chasms in the Solar system. One set, running along the equator, likely resulted from the Rheasilvia impact event, while another set probably resulted from an older impact. Vesta shares its surface spectral characteristics with the V-type asteroids, not surprising since most V-type asteroids are thought to have originated from the upper layers of Vesta after one or more large impact events. As Vesta is a differentiated body, its surface and upper layers are composed predominantly of stony minerals, with metals being relatively deficient. Temperatures on the surface range from as high as 270 K (-3 [deg]C) to as low as 85 K (-188 [deg]C). [big]Internal Structure[/big] Vesta has a differentiated interior, with a crust, mantle, and core. The crust is composed of rocks of varying composition, layered by depth, and is roughly 10 kilometers thick. Below the crust is a rocky olivine-rich mantle over 400 kilometers thick. At the center of Vesta, below the mantle, is metallic core of iron and nickel roughly 110 kilometers in radius. These layers formed very early in Vesta's history, not long after it was formed, when radioactive decay melted the majority of the world. This caused the heavist materials to collect in the center, and the lighest to rise to the surface. [big]Protoplanets[/big] Protoplanets are worlds which form in the protoplanetary disks around young stars. These worlds are relatively large and have interiors which are differentiated into layers of differing densities. Protoplanets range in size from a few hundred to a few thousand kilometers in diameter. Hundreds or thousands of protoplanets may form in the protoplanetary disk. Eventually these worlds collide with each other and merge to form larger and larger worlds, ultimately leading to the creation of the system's major planets. Protoplanets can also play a principal role in the formation of large moons. For example, Earth's moon was thought to have formed when a large protoplanet collided with Earth, with material from the upper layers of both bodies being blasted into orbit while the remainder of the two worlds merged together to form one. The debris coalesced to form the Moon. Observations of protoplanetary disks around other stars show such collisions to be relatively common, implying that moons similar to Earth's may be as well." } RObject { LocName "Jupiter" Name "Jupiter" Parent "Sol" Descr "[big]Overview[/big] Jupiter is the fifth planet from the sun and the largest of the Solar System, as well as the planet with the most moons. Viewed from Earth, Jupiter can reach an apparent magnitude of nearly −3[mag], making it the third brightest object in the night sky after the Moon and Venus. It has been considered a powerful deity for thousands of years in many mythologies due to its brightness, and modern-day explorations are proving that these ideas were more accurate than otherwise might have been assumed. [big]Composition and Atmosphere[/big] As a gas giant, Jupiter has nothing that could be considered a 'surface' — its atmosphere simply transitions smoothly from gas to liquid to solid as it gets deeper. It's composed mostly of hydrogen and helium, with only small amounts of other elements. Numerous storms exist on its surface at any one time, notably the Great Red Spot, an anticyclonic storm the size of the Earth which has been active for at least three hundred years. [big]Moons[/big] Jupiter's first four moons were discovered by Galileo Galilei in 1610, and today are known as the 'Galilean' moons in his honor — of its total of 67 moons, the Galilean moons are the largest and most massive, making up 99.9997% of the total mass in orbit around Jupiter, and all except Europa are larger than the Earth's moon. The remaining 63 moons are very small by comparison, barely more than asteroids. The innermost Galilean moon, Io, is currently the only location in the solar system other than the Earth to exhibit active volcanism. Second is Europa, the smallest of the Galilean moons, covered in a shell of thick ice and theorized to possess an ocean of liquid water underneath this ice sheet. Third and Fourth are Ganymede and Callisto, respectively. Both are composed mostly of water ice, and may also hold subsurface oceans like Europa. [big]Rings[/big] Like all gas giants in the solar system, Jupiter has rings. However, they are very tenuous and dark, being mostly composed of material ejected from Io's volcanoes, and the debris from meteoroid impacts on various moons. [big]Orbit[/big] Jupiter occupies a typical circular orbit, with a semi-major axis of 5.2 AU, an inclination of 1.3[deg], and a low eccentricity value of 0.04. [big]Exploration[/big] Jupiter wasn't explored directly until 1973, when Pioneer 10 conducted a flyby, returning the first images from beyond the orbit of Mars. Pioneer 10 was followed a few months later by Pioneer 11 (which later went on to explore Saturn). In 1979, the twin Voyager probes arrived. In 1992, the Ulysses probe used Jupiter's strong gravity to alter its trajectory, allowing it to pass over the poles of the Sun a few years later. In 1995, the Galileo spacecraft became the first to orbit Jupiter, and operated continuously until 2003, when it was intentionally crashed into the atmosphere to avoid any chance of the inactive spacecraft impacting (and contaminating) Europa. The Cassini spacecraft, en-route to Saturn, conducted a flyby in 2000, returning the highest resolution imagery of Jupiter to date. Finally, in 2007, the New Horizons spacecraft en-route to Pluto conducted a flyby of Jupiter, testing its instruments to help prepare for the Pluto encounter in 2015." } RObject { LocName "Amalthea" Name "Amalthea" Parent "Jupiter" Pioneer "Edward Barnard" Date "1892.09.09" } RObject { LocName "Thebe" Name "Thebe" Parent "Jupiter" Pioneer "Stephen Synnott" Date "1979.03.05" } RObject { LocName "Io" Name "Io" Parent "Jupiter" Pioneer "Galileo Galilei" Date "1610.01.08" Descr "[big]Overview[/big] Io (Jupiter I) is the first of the Galilean moons by distance from Jupiter, and the fourth largest moon in the Solar System with a diameter of 3,642 km. It is the most geologically active object in the Solar System, with over 400 active volcanoes. Discovered in 1610 by Galileo Galileo, it was originally thought to be a single object with Europa, however it was determined on the following day that it is, in fact, a completely separate object. [big]Surface Environment[/big] Io's surface is composed of a wide variety sulfurous compounds, which make the surface look colorful. It lacks impact craters, which indicates that it's surface is geologically young, as volcanic materials constantly bury the craters that are made. The surface is mostly composed of plains, with infrequent mountains and volcanic lava flows. The colorful surface is mainly composed of silicates, sulfur and sulfur dioxide, mostly of volcanic origin. [big]Internal structure[/big] Io is the densest moon in the entire Solar System, with a density of 3.52 g/cm3. It contains a silicate-rich crust and mantle and an iron-rich core, which makes up around 20% of Io's total mass. The main source of volcanism on Io is tidal heating- it's gravitational interaction with Jupiter and the other Galilean moons. [big]Atmosphere[/big] Io has an extremely thin atmosphere consisting mainly of sulfur dioxide. This is mostly due to the fact that most of Io's atmosphere is stripped away by Jupiter's magnetosphere. [big]Orbit[/big] Io is in a 2:1 mean-motion orbital resonance with Europa and a 4:1 mean-motion orbital resonance with Ganymede. This causes Io's orbital eccentricity, which in turn is the main heating source for geological activity. [big]Exploration[/big] The Pioneer spacecraft were the first ones to conduct any major examination of Io, determining it's approximate mass and suggesting that it has the highest density of the Galilean satellites. They also produced the only good image of Io's surface. The Voyager spacecraft were the ones to detect it's colorful surface, along with it's volcanic activity. The Galileo spacecraft arrived in 1995, determining that Io has a large iron core, observed a major eruption and confirmed that they are mostly composed of silicate magmas." } RObject { LocName "Europa" Name "Europa" Parent "Jupiter" Pioneer "Galileo Galilei" Date "1610.01.08" Descr "[big]Overview[/big] Europa (Jupiter II) is Jupiter's sixth moon by distance, the second Galilean moon by distance from Jupiter and the smallest of the Galilean moons. Discovered in 1610 by Galileo Galilei, it was originally thought to be a single object with Io, but was confirmed to be a separate object the following day. Its surface is primarily composed of ice, and is thought to have a sub-surface water ocean due to the heat generated from tidal flexing. [big]Surface environment[/big] Europa is one of the smoothest objects in the Solar System. It has few craters, due to the fact that its surface is tectonically active and young. The most noticeable features of the surface are the lineae, a series of dark streaks present on most of the surface area of the moon. They are probably formed by the movement of the ice sheets. [big]Internal structure and subsurface ocean[/big] The existence of a subsurface ocean on Europa is a popular and widely discussed theory. Due to the heat energy from tidal flexing, a region in the interior of the moon could have a temperature adequate for liquid water to exist. Such an ocean could be up to 100 km deep, under a 10-30 km thick crust. If this ocean does exist, it would contain twice the volume of water that the Earth's oceans contain. Europa has a rocky mantle, and a metallic core. [big]Atmosphere[/big] Europa has a very thin atmosphere, with atmospheric pressure being a mere 1 microPa. The tenuous atmosphere is composed mainly of molecular oxygen. [big]Exploration[/big] Despite its possibility of containing liquid water beneath its surface and potential for hosting extraterrestrial life, no serious Europa mission has been conducted to date. The Pioneer spacecraft were the first to provide close-up images, although they were low-quality and provided little clues to Europa's icy surface and potential for a subsurface ocean. The Voyager spacecraft returned higher-quality images which would spark the theory of a subsurface ocean. The New Horizons spacecraft, headed for Pluto is the most recent to pass by Europa." } RObject { LocName "Ganymede" Name "Ganymede" Parent "Jupiter" Pioneer "Galileo Galilei" Date "1610.01.07" Descr "[big]Overview[/big] Ganymede (Jupiter III) is Jupiter's largest moon, and the largest moon in the Solar system overall, bigger than the planet Mercury. It is the seventh moon by distance from Jupiter, and the third Galilean moon.It is also the only moon to have a magnetic field. Discovered by Galileo Galilei in 1610 it was, like the other Galilean moons, originally thought to have been a star. [big]Surface environment[/big] The surface of Ganymede can be divided into the old, dark regions and relatively younger and lighter regions. Although both have craters, the dark regions appear to have a much more extensive amount than the lighter regions. Most of these craters are thought to have formed around 3.5-4 billion years ago during a period of heavy cratering. The surface of Ganymede also contains a large amount of grooves and ridges, whose formation is currently not completely understood, although are generally thought to be of tectonic origin. [big]Internal structure[/big] The Ganymedian crust, along with the outer mantle, is composed mainly of ice, while the inner mantle is composed of silicates. Ganymede has a liquid iron core, confirmed by the presence of a magnetic field around the planet. The core is thought to be around 700-900 km in diameter, while the icy mantle is around 800-1000 km. [big]Atmosphere[/big] Essentially vacuum, Ganymede has an extremely tedious atmosphere with an atmospheric pressure of around 1 µPa. The little atmosphere it has is thought to be composed mainly of molecular oxygen. [big]Exploration[/big] The first probes to attempt to collect data about the satellite were Pioneer 10 and Pioneer 11 in the 1970's. The Voyager spacecraft were the ones to determine that Ganymede was larger than Titan, previously thought to have been bigger and to detect the grooved terrain. The Galileo spacecraft was the one that made the closest contact with the moon, passing just 264 km above it's surface. Recently, New Horizons passed by Ganymede in 2007 on its way to Pluto, making topography and composition maps while passing by." } RObject { LocName "Callisto" Name "Callisto" Parent "Jupiter" Pioneer "Galileo Galilei" Date "1610.01.07" Descr "[big]Overview[/big] Callisto (Jupiter IV) is the second-largest moon of Jupiter, after Ganymede. It is the third-largest moon in the Solar System and the largest object in the Solar System not to be properly differentiated. Callisto was discovered in 1610 by Galileo Galilei. At 4821 km in diameter, Callisto has about 99% the diameter of the planet Mercury but only about a third of its mass. It is the fourth Galilean moon of Jupiter by distance, with an orbital radius of about 1,883,000 km. It is not in an orbital resonance like the three other Galilean satellites — Io, Europa, and Ganymede — and is thus not appreciably tidally heated. Callisto's rotation is tidally locked to its orbit around Jupiter, so that the same hemisphere always faces inward; Jupiter appears to stand nearly still in Callisto's sky. It is less affected by Jupiter's magnetosphere than the other inner satellites because of its more remote orbit, located just outside Jupiter's main radiation belt. Callisto is composed of approximately equal amounts of rock and ices, with a density of about 1.83 g/cm[sup]3[/sup], the lowest density and surface gravity of Jupiter's major moons. Compounds detected spectroscopically on the surface include water ice, carbon dioxide, silicates, and organic compounds. Investigation by the Galileo spacecraft revealed that Callisto may have a small silicate core and possibly a subsurface ocean of liquid water at depths greater than 100 km. The surface of Callisto is the oldest and most heavily cratered in the Solar System. Its surface is completely covered with impact craters. It does not show any signatures of subsurface processes such as plate tectonics or volcanism, with no signs that geological activity in general has ever occurred, and is thought to have evolved predominantly under the influence of impacts. Prominent surface features include multi-ring structures, variously shaped impact craters, and chains of craters (catenae) and associated scarps, ridges and deposits. At a small scale, the surface is varied and made up of small, sparkly frost deposits at the tips of high spots, surrounded by a low-lying, smooth blanket of dark material. This is thought to result from the sublimation-driven degradation of small landforms, which is supported by the general deficit of small impact craters and the presence of numerous small knobs, considered to be their remnants. The absolute ages of the landforms are not known. Callisto is surrounded by an extremely thin atmosphere composed of carbon dioxide and probably molecular oxygen, as well as by a rather intense ionosphere.[19] Callisto is thought to have formed by slow accretion from the disk of the gas and dust that surrounded Jupiter after its formation. Callisto's gradual accretion and the lack of tidal heating meant that not enough heat was available for rapid differentiation. The slow convection in the interior of Callisto, which commenced soon after formation, led to partial differentiation and possibly to the formation of a subsurface ocean at a depth of 100–150 km and a small, rocky core. The likely presence of an ocean within Callisto leaves open the possibility that it could harbor life. However, conditions are thought to be less favorable than on nearby Europa. Various space probes from Pioneers 10 and 11 to Galileo and Cassini have studied Callisto. Because of its low radiation levels, Callisto has long been considered the most suitable place for a human base for future exploration of the Jovian system." } RObject { LocName "Himalia" Name "Himalia" Parent "Jupiter" Pioneer "Charles Perrine" Date "1904.12.03" } RObject { LocName "Elara" Name "Elara" Parent "Jupiter" Pioneer "Charles Perrine" Date "1905.01.05" } RObject { LocName "Pasiphae" Name "Pasiphae" Parent "Jupiter" Pioneer "Philibert Melotte" Date "1908.01.27" } RObject { LocName "Saturn" Name "Saturn" Parent "Sol" Descr "[big]Composition and Climate[/big] Saturn is the outer of Sol's two gas giants — massive worlds composed primarily of hydrogen and helium. It has no solid surface. Instead, it has a steadily thickening hydrogen/helium atmosphere which eventually becomes liquid metallic hydrogen as depth increases. At the center of the planet there is likely a solid rocky core. Circulation in the liquid metallic hydrogen layer is the probable source of Saturn's magnetic field. Saturn's aurorae are the tallest in the Solar system, reaching over 1000 kilometers in height. Saturn's poles are ringed with huge rotating cloud structures. In particular the north pole is surrounded by a giant hexagonal structure and the pole itself is the center of a powerful vortex. The south pole has a warm polar vortex, unique in the Solar system. Temperatures in this vortex are over 60 [deg]C warmer than the rest of the planet, making it the warmest spot on Saturn. Elsewhere in its atmosphere can be found strong storms that can persist for months. One of the most spectacular storm features is the periodic 'Great White Spot', a massive storm that erupts about once every Saturnian year (30 Earth years) in the northern hemisphere during summer. Similar but smaller outbreaks of large white storms can occur with greater frequency. Winds on Saturn can reach speeds of 500 m/s (1800 km/h), second only to Neptune. Saturn's seasons are driven not only by its axial tilt as with most planets, but also by its rings. The rings block sunlight to the autumnal/winter hemisphere, making it even darker than it would otherwise be. This can lead to dramatic seasonal effects, including a subsidence of cloud levels across the winter hemisphere, after which the now-clear air takes on a bright blue color. [big]Rings[/big] Saturn's majestic rings are easily its most prominent feature. The rings are tens of thousands of kilometers wide but average only 20 meters thick. They are composed mainly of water ice and modest amounts of carbon. The particles in the rings range in size from dust grains to chunks of material in tens of meters wide or more. The main ring disk has several gaps carved out by gravitational perturbations and by small moons orbiting among the rings. Moons orbiting in or near the rings cause ripples, waves, and spirals to form in the rings due to their gravitational effects. Tiny moonlets also exist embedded in the rings, and along the forward edge of the B ring material has piled up into vertical structures a few kilometers in height. It is not known exactly how old the rings are, but they may be nearly as old as the planet itself, having formed along with or shortly after the rest of the Saturn system. Beyong the main ring disk are other, fainter rings. Among these is the E ring, the outermost ring in Saturn's equatorial ring system. Unlike the other rings it is very thick and diffuse, and composed of primarily microscopic particles of ice. When backlit by the sun the ring becomes visible and has a noticeable blue color. The source of the E ring is material erupting from the cryovolcanic geysers near the south pole of Enceladus. Material erupting from the moon escapes its weak gravity and goes into orbit around Saturn, thus forming the ring. Material from this ring accumulates on the moons that pass through it, giving Tethys its blue-tinted leading hemisphere and smoothing out the features on moons such as Telesto and Helene. The outermost of these faint rings is the very large and diffuse Phoebe ring, not discovered until 2009. The ring occupies roughly the same region of space as the moon Phoebe, hence its name, and is aligned with Saturn's orbital plane. The ring is over a million kilometers thick and perhaps seven million kilometers wide from inner to outer edge. Impacts with Phoebe are thought to be the source of the ring's material. This material is partly responsible for the strong bicoloration on Iapetus and probably initiated that process. [big]Moons[/big] Saturn has a system of 62 known moons. Several of these are large, round satellites which rank among the largest moons in the Solar system. The largest of these, Titan, comprises 90% of the mass orbiting Saturn, and is the second largest moon in the Solar system. It also is the only moon with a thick atmosphere and the only known world other than Earth to have stable bodies of liquid on its surface. Among Saturn's other large moons are Iapetus, Rhea, Dione, Tethys, Enceladus, and Mimas. All of these orbit near Saturn and in its equatorial plane except for Iapetus, which orbits at a greater distance and with an inclined orbit. It is notable for having a strong two-toned appearance, with half of the moon being very dark and the other half being very light, and for its tall equatorial mountain ridge. Enceladus is also a noteworthy moon: it is the brightest (most reflective) object in the Solar system, reflecting over 99% of the light that strikes it; it also has powerful cryovolcanic geysers located near its south pole, in fissures known as 'Tiger Stripes'. These geysers are the source of Saturn's E ring. Also among the near-Saturn moons are many small satellites. Some of these satellites shepherd ring material. There are five of these 'shepherd moons': Pan, Daphnis, Atlas, Prometheus, and Pandora. They are responsible for sculpting many of the gaps and edges in the rings, specifically the Encke gap, Keeler gap, A ring, and F ring respectively (the latter being shepherded by both Prometheus and Pandora). Two other small moons, Janus and Epimetheus, form a co-orbital pair; that is, they share almost exactly the same orbit. They approach each other every four years and their gravitational interaction causes them to switch orbits instead of colliding. Methone, Anthe, and Pallene are small moons that orbit between Mimas and Enceladus. The Saturn system uniquely features trojan moons, moons that orbit at the L[sub]4[/sub] or L[sub]5[/sub] Lagrange point of a much larger moon. Telesto and Calypso are trojans of Tethys, while Helene and Polydeuces are trojans of Dione. While Saturn has dozens of other, irregular satellites, two are especially noteworthy. First is Hyperion, which orbits just beyond Titan. It is nearly 300 kilometers wide yet extremely irregular in shape. It has a reddish, spongey appearance, and a very low density, indicating that it is largely porous. It also has unpredictable rotational behavior, essentially tumbling chaotically through space. The second noteworthy outer irregular satellite is Phoebe. It is over 200 kilometers wide, has a retrograde orbit, rotates every 9.3 hours, and is the source of Saturn's Phoebe ring. It is nearly spherical in shape and relatively dense. Its dark surface is composed of water ice, carbon dioxide, phyllosilicates, and organics. Phoebe is most likely a captured centaur and probably originated in the Kuiper Belt (visit 'Chiron' to learn more about Centaurs)." } RObject { LocName "Prometheus" Name "Prometheus" Parent "Saturn" Pioneer "Voyager 1" Date "1980.10.01" } RObject { LocName "Pandora" Name "Pandora" Parent "Saturn" Pioneer "Voyager 1" Date "1980.10.01" } RObject { LocName "Janus" Name "Janus" Parent "Saturn" Pioneer "Audouin Dolfus" Date "1966.12.15" } RObject { LocName "Epimetheus" Name "Epimetheus" Parent "Saturn" Pioneer "Richard Walker" Date "1966.12.18" } RObject { LocName "Mimas" Name "Mimas" Parent "Saturn" Pioneer "William Herschel" Date "1789.09.17" } RObject { LocName "Enceladus" Name "Enceladus" Parent "Saturn" Pioneer "William Herschel" Date "1789.08.28" } RObject { LocName "Tethys" Name "Tethys" Parent "Saturn" Pioneer "Giovanni Cassini" Date "1684.03.21" } RObject { LocName "Dione" Name "Dione" Parent "Saturn" Pioneer "Giovanni Cassini" Date "1684.03.21" } RObject { LocName "Rhea" Name "Rhea" Parent "Saturn" Pioneer "Giovanni Cassini" Date "1672.12.23" } RObject { LocName "Titan" Name "Titan" Parent "Saturn" Pioneer "Christiaan Huygens" Date "1655.03.25" Descr "[big]Overview[/big] Titan is the largest moon of Saturn and the second-largest moon in the Solar system. It is also the only moon to possess a substantial atmosphere, as well as the only body other than Earth to hold liquid on its surface. [big]Composition and Atmosphere[/big] Titan is composed of roughly 50% rock and 50% water ice, with a thick atmosphere of 98% nitrogen, 1.4% methane, 0.2% hydrogen, and 0.4% other gases. At ground level the pressure is 1.5 times greater than Earth's sea level pressure. Scattered across the surface are lakes of liquid hydrocarbons, the only known bodies of liquid on the surface of an object other than the Earth. It is suspected that, like Europa, Titan possesses a subsurface ocean of liquid water, which makes it a plausible host for some form of life. [big]Exploration[/big] The Cassini spacecraft has provided the majority of the current information regarding Titan, as previous spacecraft were unable to penetrate its thick atmospheric haze. The child mission to Cassini, Huygens, detached from its parent in late December 2004, and entered the Titanian atmosphere before parachuting to a safe landing on its surface in mid-January 2005. While Huygens returned large amounts of data on the atmosphere during its descent, it rapidly succumbed to the intense cold once on the surface, though not before returning several images at ground level." } RObject { LocName "Hyperion" Name "Hyperion" Parent "Saturn" Pioneer "William Bond, George Bond, William Lassell" Date "1848.09.16" } RObject { LocName "Iapetus" Name "Iapetus" Parent "Saturn" Pioneer "Giovanni Cassini" Date "1671.10.25" } RObject { LocName "Phoebe" Name "Phoebe" Parent "Saturn" Pioneer "William Pickering" Date "1899.03.17" } RObject { LocName "Uranus" Name "Uranus" Parent "Sol" Pioneer "William Herschel" Date "1781.03.13" Descr "Uranus is the inner of Sol's two ice giants — gaseous worlds composed primarily of volatile materials heavier than hydrogen and helium, such as methane, water, and ammonia, which are known in planetary science as 'ices'. It has no solid surface, instead having a steadily thickening atmosphere composed of hydrogen, helium and methane which gives way to a thick, liquid, ice-rich mantle as depth increases, ending eventually in a solid rocky core. The planet's upper atmosphere is the coldest place known on any of the major planets, with temperatures as low as 49 K (-224 [deg]C). Uranus is an unusual world in that its axis of rotation is almost parallel to its orbital plane, meaning that it is 'laying on its side'. Because of this, the planet's poles receive more light from the sun than its equator. The cause of this unusual tilt is thought to be from an impact between Uranus and another protoplanet early in the Solar system's history. The Uranian magnetic field is dramatically offset from the planet's center of mass and not aligned with its rotational axis. Uranus has a system of rings which is second only to Saturn's in prominence, but it has the smallest system of moons of any of the gas planets. The rings are extremely dark, reflecting less than 2% of the radiation that strikes them, and are mostly lacking in dust due to Uranus' extended thermosphere. They are thought to be young, less than 600 million years old, and likely are the remains of small moons that were destroyed by collisions. The rings and moons orbit along Uranus' orbital plane, meaning that they experience the same extreme rotational tilt as their parent planet." } RObject { LocName "Bianca" Name "Bianca" Parent "Uranus" Pioneer "Bradford Smith" Date "1986.01.23" } RObject { LocName "Cressida" Name "Cressida" Parent "Uranus" Pioneer "Stephen Synnott" Date "1986.01.09" } RObject { LocName "Desdemona" Name "Desdemona" Parent "Uranus" Pioneer "Stephen Synnott" Date "1986.01.13" } RObject { LocName "Juliet" Name "Juliet" Parent "Uranus" Pioneer "Stephen Synnott" Date "1986.01.03" } RObject { LocName "Portia" Name "Portia" Parent "Uranus" Pioneer "Stephen Synnott" Date "1986.01.03" } RObject { LocName "Rosalind" Name "Rosalind" Parent "Uranus" Pioneer "Stephen Synnott" Date "1986.01.13" } RObject { LocName "Belinda" Name "Belinda" Parent "Uranus" Pioneer "Stephen Synnott" Date "1986.01.13" } RObject { LocName "Puck" Name "Puck" Parent "Uranus" Pioneer "Stephen Synnott" Date "1985.12.30" } RObject { LocName "Miranda" Name "Miranda" Parent "Uranus" Pioneer "Gerard Kuiper" Date "1948.02.16" } RObject { LocName "Ariel" Name "Ariel" Parent "Uranus" Pioneer "William Lassell" Date "1851.10.24" } RObject { LocName "Umbriel" Name "Umbriel" Parent "Uranus" Pioneer "William Lassell" Date "1851.10.24" } RObject { LocName "Titania" Name "Titania" Parent "Uranus" Pioneer "William Herschel" Date "1787.01.11" } RObject { LocName "Oberon" Name "Oberon" Parent "Uranus" Pioneer "William Herschel" Date "1787.01.11" } RObject { LocName "Caliban" Name "Caliban" Parent "Uranus" Pioneer "Philip Nicholson, Brett Gladman, Joseph Burns, John Kavelaars" Date "1997.09.06" } RObject { LocName "Sycorax" Name "Sycorax" Parent "Uranus" Pioneer "Philip Nicholson, Brett Gladman, Joseph Burns, John Kavelaars" Date "1997.01.03" } RObject { LocName "Neptune" Name "Neptune" Parent "Sol" Pioneer "Urbain Le Verrier" Date "1846.09.23" Descr "Neptune is the outer of Sol's two ice giants — gaseous worlds composed primarily of volatile materials heavier than hydrogen and helium, such as methane, water, and ammonia, which are known in planetary science as 'ices'. It has no solid surface, instead having a steadily thickening atmosphere composed of hydrogen, helium and methane which gives way to a thick, liquid, ice-rich mantle as depth increases, ending eventually in a solid rocky core. The planet has some of the fastest winds in the Solar system, with top speeds of almost 600 m/s (over 2100 km/h) occurring in its dynamic and impressive storm systems. Neptune has a moderate axial tilt of 28.32[deg]. Because of its long orbital period, the planet's seasons last for 40 years. When one pole of the planet is exposed to sunlight it warms up enough to allow methane to sublimate and leak into space. The Neptunian magnetic field is dramatically offset from the planet's center of mass and not aligned with its rotational axis. Neptune has a system of 13 known moons, the largest of which by far is Triton. Triton has a retrograde orbit around Neptune and is thought to be a former Kuiper Belt Object like Pluto that was captured by Neptune when it passed too close to the planet. Neptune also has a system of rings, though they are the smallest of any major planet, and rich in dust like the rings of Jupiter. The rings are extremely dark, reflecting less than 2% of the radiation that strikes them. The large outer ring is not smooth and continuous, but rather has several short clumps of material known as 'arcs' along one section. In about 3.6 billion years, Triton's orbit will have decayed inside the Roche limit and the moon will be torn apart into a colossal ring system perhaps more spectacular than Saturn's." } RObject { LocName "Naiad" Name "Naiad" Parent "Neptune" Pioneer "Voyager 2" Date "1989.09.01" } RObject { LocName "Thalassa" Name "Thalassa" Parent "Neptune" Pioneer "Voyager 2" Date "1989.09.01" } RObject { LocName "Despina" Name "Despina" Parent "Neptune" Pioneer "Voyager 2" Date "1989.07.01" } RObject { LocName "Galatea" Name "Galatea" Parent "Neptune" Pioneer "Voyager 2" Date "1989.07.01" } RObject { LocName "Larissa" Name "Larissa" Parent "Neptune" Pioneer "Harold Reitsema, William Hubbard, Larry Lebofsky, David Tholen" Date "1981.05.24" } RObject { LocName "Proteus" Name "Proteus" Parent "Neptune" Pioneer "Stephen Synnott, Bradford Smith" Date "1989.07.01" } RObject { LocName "Triton" Name "Triton" Parent "Neptune" Pioneer "William Lassell" Date "1846.10.10" Descr "Triton is the largest natural satellite of the planet Neptune. It was discovered on October 10, 1846, by English astronomer William Lassell. It is the only large moon in the Solar System with a retrograde orbit, an orbit in the opposite direction to its planet's rotation. At 2,700 kilometres (1,700 mi) in diameter, it is the seventh-largest moon in the Solar System. Because of its retrograde orbit and composition similar to Pluto's, Triton is thought to have been a dwarf planet captured from the Kuiper belt. Triton has a surface of mostly frozen nitrogen, a mostly water-ice crust, an icy mantle and a substantial core of rock and metal. The core makes up two-thirds of its total mass. Triton has a mean density of 2.061 g/cm[sup]3[/sup] and is composed of approximately 15-35% water ice. Triton is one of the few moons in the Solar System known to be geologically active. As a consequence, its surface is relatively young with sparse impact craters, and a complex geological history revealed in intricate cryovolcanic and tectonic terrains. Part of its surface has geysers erupting sublimated nitrogen gas, contributing to a tenuous nitrogen atmosphere less than 1/70,000 the pressure of Earth's atmosphere at sea level." } RObject { LocName "Nereid" Name "Nereid" Parent "Neptune" Pioneer "Gerard Kuiper" Date "1949.05.01" } RObject { LocName "Neso" Name "Neso" Parent "Neptune" Pioneer "Matthew Holman, Brett Gladman" Date "2002.07.14" } RObject { LocName "Pluto" Name "Pluto" Parent "Pluto-Charon" Pioneer "Clyde W. Tombaugh" Date "1930.02.18" Descr "[big]Overview[/big] Originally considered the ninth planet of the solar system, Pluto is now considered a dwarf planet after a decision by the IAU in 2006, along with Ceres, Haumea, Makemake, and Eris. [big]Composition and Atmosphere[/big] Pluto is thought to consist of roughly 60% rock and 40% water ice. Surface is covered mostly by nitrogen ice as determined by spectroscopic analysis, with traces of methane and carbon dioxide ices. Pluto also periodically holds a thin atmosphere, created by the sublimation of surface ice as it nears perihelion. This sublimation of ice also has the effect of altering its appearance over the course of a single orbit. [big]Moons[/big] Pluto has five known moons. The largest of these, Charon, is so large that it and Pluto form a binary system — both orbiting a common center of mass between the two objects. The other four moons are small asteroidal bodies all orbiting beyond Charon. From innermost to outermost, they are: Styx, Nix, Kerberos, and Hydra. [big]Orbit[/big] Pluto's orbit is normal for a Kuiper Belt Object, with a semi-major axis of 39.26 AU, an inclination of 17[deg], and an eccentricity value of 0.248. [big]Exploration[/big] While no spacecraft have yet visited Pluto, ground-based observations have yielded large amounts of information about the object. However, the New Horizons spacecraft will become the first to visit Pluto upon its arrival in mid-2015. However, due to the large relative velocity between the spacecraft and Pluto during the encounter, it will not be able to enter orbit." } RObject { LocName "Charon" Name "Charon" Parent "Pluto-Charon" Pioneer "James W. Christy" Date "1978.06.22" Descr "Charon (134340 I) — the largest satellite of the dwarf planet Pluto, sometimes considered as a smaller component of a binary Pluto-Charon system. It has large canyon and ridges on its surprisingly young surface, and a large dark area in its North pole, informally dubbed 'Mordor'." } RObject { LocName "Styx" Name "Styx" Parent "Pluto-Charon" Pioneer "Mark R. Showalter, Hubble Space Telescope" Date "2012.06.26" } RObject { LocName "Nix" Name "Nix" Parent "Pluto-Charon" Pioneer "Pluto Companion Search Team, Hubble Space Telescope" Date "2005.06.15" } RObject { LocName "Kerberos" Name "Kerberos" Parent "Pluto-Charon" Pioneer "Pluto Companion Search Team, Hubble Space Telescope" Date "2011.06.28" } RObject { LocName "Hydra" Name "Hydra" Parent "Pluto-Charon" Pioneer "Pluto Companion Search Team, Hubble Space Telescope" Date "2005.06.15" } RObject { LocName "Haumea" Name "Haumea" Parent "Sol" Pioneer "Michael Brown" Date "2004.12.28" } RObject { LocName "Namaka" Name "Namaka" Parent "Haumea" Pioneer "Mike Brown, Chad Trujillo, David Rabinowtiz" Date "2005.06.30" } RObject { LocName "Hiʻiaka" Name "Hiʻiaka" Parent "Haumea" Pioneer "Mike Brown, Chad Trujillo, David Rabinowtiz" Date "2005.01.26" } RObject { LocName "Makemake" Name "Makemake" Parent "Sol" Pioneer "Michael Brown, Chad Trujillo, David Rabinowtiz" Date "2005.03.31" } RObject { LocName "S/2015 (136472) 1" Name "S/2015 (136472) 1" Parent "Makemake" Pioneer "Alex Parker, Marc Buie, William Grundy, Keith Noll" Date "2015.04.01" } RObject { LocName "Eris" Name "Eris" Parent "Sol" Pioneer "Michael Brown, Chad Trujillo, David Rabinowtiz" Date "2005.01.05" } RObject { LocName "Dysonomia" Name "Dysonomia" Parent "Eris" Pioneer "Michael Brown" Date "2005.09.10" } RObject { LocName "Chiron" Name "Chiron" Parent "Sol" Pioneer "Charles T. Kowal" Date "1977.10.18" Descr "[big]Overview[/big] Chiron was the first object to be identified as a centaur, a class of bodies that orbit the Sun between the orbits of Jupiter and Neptune. It has a very eccentric orbit that takes it from inside the orbit of Saturn to past the perihelion distance of Uranus. Its size is uncertain, but the most recent estimates yield a diameter of around 230 km. Its rotation period is 5[hour]55[min]04[sec]13. Chiron has been observed to have comet-like behavior, developing a coma and a tail as it nears perihelion. Like all centaurs, Chrion will eventually move into an orbit that will place it into a different category of objects, likely becoming a short period comet. [big]Centaurs[/big] Centaurs are objects that orbit the Sun between the orbits of Jupiter and Neptune. It is suspected that centaurs are former Kuiper belt objects that were perturbed into Neptune-crossing orbits and gravitationally interacted with that planet to be pulled into orbits that crossed the orbits of the other outer planets. Objects like Chiron that orbit in the midst of the giant planets do not have stable orbits; all centaurs are temporary. Some become asteroids or short period comets, some may collide with or be captured by one of the outer planets, and some are ejected from the Solar system altogether, becoming interstellar objects. Observations have revealed a definitive bicoloration in the centaur population; some centaurs are red, while others are blue-gray. The reason for this is currently unknown, as the Kuiper belt population considered the candidate source of origin for centaurs does not share this feature. One Kuiper belt population — the plutinos — does also have a bicolored nature. Plutinos have been thought to have stable orbits and thus are not likely candidates for the origin of the centaurs, however it is possible that some of their orbits are less stable than previously suspected." } RObject { LocName "46P Wirtanen" Name "46P Wirtanen" Parent "Sol" Pioneer "Carl A. Wirtanen" Date "1948.01.17" Descr "[big]Overview 46P/Wirtanen is a small short-periodic comet discovered accidentally in 1948 by American astronomer Carl A. Wirtanen. [big]Orbit[/big] 46P/Wirtanen has an orbital period of 5.4 years. It belongs to the Jupiter family of comets, with it's perihelion being around 1 AU from the Sun, near Earth, and it's aphelion being 5-6 AU, near Jupiter. [big]Exploration[/big] Originally a target for close investigation by the Rosetta spacecraft, it is now a target of the proposed 2016 Comet Hopper mission." } RObject { LocName "1998 KY26" Name "1998 KY26" Parent "Sol" Pioneer "Spacewatch" Date "1998.05.28" Descr "[big]Overview[/big] 1998 KY26 is a very small near-Earth asteroid, discovered in 1998 by Spacewatch using radar and optical telescopes. [big]Structure[/big] 1998 KY26 is only 30 m in diameter, so small that it is near the boundary of being considered a meteoroid, although by definition an asteroid is larger than 10 m, which makes 1998 KY26 an asteroid. It has a rotational period of only 10.7 minutes, making it the fastest spinning object at the time of it's discovery. It is roughly spherical and confirmed to be water-rich [big]Orbit[/big] 1998 KY26 occupies an orbit which brings it on a path very similar to the Earth-Mars transfer orbit. Its closest ever encounter with Earth was 800,000 km, only a little more than 2 lunar distances." } RObject { LocName "Castalia" Name "Castalia" Parent "Sol" Pioneer "Eleanor F. Helin" Date "1989.08.09" Descr "[big]Overview[/big] Castalia was the first asteroid to be modeled by radar imaging, discovered by Eleanor F. Helin on photographic plates taken at the Palomar Observatory. [big]Structure[/big] Castalia has a peanut shape. This is due to the fact that it is made of two 800-meter pieces, attracted to each other by their respective gravities. This anomaly is called a contact binary. [big]Orbit[/big] Castalia crosses the orbits of Mars, Earth and Venus. Due to the proximity to Earth's orbit, it is also classified as a potentially hazardous object. In 1989, Castalia passed at 11 lunar distances from Earth." }