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Planetessimal
Planetesimals are solid objects thought to exist in protoplanetary disks and debris disks. Per the Chamberlin–Moulton planetesimal hypothesis, they are believed to form out of cosmic dust grains. Believed to have formed in the Solar System about 4.6 billion years ago, they aid study of its formation. Formation A widely accepted theory of planet formation, the so-called planetesimal hypotheses, the Chamberlin–Moulton planetesimal hypothesis and that of Viktor Safronov, states that planets form from cosmic dust grains that collide and stick to form ever-larger bodies. Once a body reaches around a kilometer in size, its constituent grains can attract each other directly through mutual gravity, enormously aiding further growth into moon-sized protoplanets. Smaller bodies must instead rely on Brownian motion or turbulence to cause the collisions leading to sticking. The mechanics of collisions and mechanisms of sticking are intricate. Alternatively, planetesimals may for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
American Astronomical Society
The American Astronomical Society (AAS, sometimes spoken as "double-A-S") is an American society of professional astronomers and other interested individuals, headquartered in Washington, DC. The primary objective of the AAS is to promote the advancement of astronomy and closely related branches of science, while the secondary purpose includes enhancing astronomy education and providing a political voice for its members through lobbying and grassroots activities. Its current mission is to enhance and share humanity's scientific understanding of the universe as a diverse and inclusive astronomical community. History The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
486958 Arrokoth
Arrokoth ( minor-planet designation 486958 Arrokoth; provisional designation ), formerly nicknamed Ultima Thule, is a trans-Neptunian object located in the Kuiper belt. Arrokoth became the farthest and most primitive object in the Solar System visited by a spacecraft when the NASA space probe ''New Horizons'' conducted a flyby on 1 January 2019. Arrokoth is a contact binary long, composed of two planetesimals and across, that are joined along their major axes. With an orbital period of about 298 years and a low orbital inclination and eccentricity, Arrokoth is classified as a cold classical Kuiper belt object. Arrokoth was discovered on 26 June 2014 by astronomer Marc Buie and the New Horizons Search Team using the Hubble Space Telescope as part of a search for a Kuiper belt object for the ''New Horizons'' mission to target in its first extended mission; it was chosen over two other candidates to become the primary target of the mission. Name When Arr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Contact Binary (small Solar System Body)
A contact binary is a small Solar System body such as a minor planet or a comet that is composed of two bodies that have gravitated toward each other until they touch, resulting in a bilobated, peanut-like overall shape. Contact binaries are often rubble piles but distinct from real binary systems such as binary asteroids. The term is also used for stellar contact binaries. An example of what is thought to be a contact binary is the Kuiper belt object 486958 Arrokoth, which was imaged by the ''New Horizons'' spacecraft during its flyby in January 2019. Description Comet Churyumov–Gerasimenko and Comet Tuttle are most likely contact binaries, while asteroids suspected of being contact binaries include the unusually elongated 624 Hektor and the bilobated 216 Kleopatra and 4769 Castalia. 25143 Itokawa, which was photographed by the ''Hayabusa'' probe, also appears to be a contact binary which has resulted in an elongated, bent body. Asteroid 4179& ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar Nebula
The formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a protoplanetary disk out of which the planets, moons, asteroids, and other small Solar System bodies formed. This model, known as the nebular hypothesis, was first developed in the 18th century by Emanuel Swedenborg, Immanuel Kant, and Pierre-Simon Laplace. Its subsequent development has interwoven a variety of scientific disciplines including astronomy, chemistry, geology, physics, and planetary science. Since the dawn of the space age in the 1950s and the discovery of extrasolar planets in the 1990s, the model has been both challenged and refined to account for new observations. The Solar System has evolved considerably since its initial formation. Many moons have formed from circling discs of gas and dust around their paren ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Time Capsule
A time capsule is a historic cache of goods or information, usually intended as a deliberate method of communication with future people, and to help future archaeologists, anthropologists, or historians. The preservation of holy relics dates back for millennia, but the practice of preparing and preserving a collection of everyday artifacts and messages to the future appears to be a more recent practice. Time capsules are sometimes created and buried during celebrations such as a world's fair, a cornerstone laying for a building, or at other ceremonies. History Early examples It is widely debated when time capsules were first used, but the concept is fairly simple, and the idea and first use of time capsules could be much older than is currently documented. The term "time capsule" appears to be a relatively recent coinage dating from 1938. Around 1761, some dated artifacts were placed inside the hollow copper grasshopper weathervane, itself dating from 1742, atop histori ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inclination
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object. For a satellite orbiting the Earth directly above the Equator, the plane of the satellite's orbit is the same as the Earth's equatorial plane, and the satellite's orbital inclination is 0°. The general case for a circular orbit is that it is tilted, spending half an orbit over the northern hemisphere and half over the southern. If the orbit swung between 20° north latitude and 20° south latitude, then its orbital inclination would be 20°. Orbits The inclination is one of the six orbital elements describing the shape and orientation of a celestial orbit. It is the angle between the orbital plane and the plane of reference, normally stated in degree (angle), degrees. For a satellite orbiting a planet, the plane of reference is usually ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin atmosphere (less than 1% that of Earth's), and has a crust primarily composed of elements similar to Earth's crust, as well as a core made of iron and nickel. Mars has surface features such as impact craters, valleys, dunes and polar ice caps. It has two small and irregularly shaped moons, Phobos and Deimos. Some of the most notable surface features on Mars include Olympus Mons, the largest volcano and highest known mountain in the Solar System and Valles Marineris, one of the largest canyons in the Solar System. The Borealis basin in the Northern Hemisphere covers approximately 40% of the planet and may be a large impact feature. Days and seasons on Mars are comparable to those of Earth, as the planets have a similar rotation period a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deimos (moon)
Deimos ( systematic designation: Mars II) is the smaller and outermost of the two natural satellites of Mars, the other being Phobos. Of similar composition to C and D-type asteroids, Deimos has a mean radius of and takes 30.3 hours to orbit Mars. Deimos is from Mars, much farther than Mars's other moon, Phobos. It is named after Deimos, the Ancient Greek god and personification of dread and terror. Discovery and etymology Deimos was discovered by Asaph Hall III at the United States Naval Observatory in Washington, D.C. on 12 August 1877, at about 07:48 UTC. Hall, who also discovered Phobos shortly afterwards, had been specifically searching for Martian moons at the time. The moon is named after Deimos, a figure representing dread in Greek mythology. The name was suggested by academic Henry Madan, who drew from Book XV of the ''Iliad'', where Ares (the Roman god Mars) summons Dread (Deimos) and Fear ( Phobos). Origin The origin of Mars's moons is unknow ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phobos (moon)
Phobos (; systematic designation: ) is the innermost and larger of the two natural satellites of Mars, the other being Deimos. The two moons were discovered in 1877 by American astronomer Asaph Hall. It is named after Phobos, the Greek god of fear and panic, who is the son of Ares (Mars) and twin brother of Deimos. Phobos is a small, irregularly shaped object with a mean radius of . Phobos orbits from the Martian surface, closer to its primary body than any other known planetary moon. It is so close that it orbits Mars much faster than Mars rotates, and completes an orbit in just 7 hours and 39 minutes. As a result, from the surface of Mars it appears to rise in the west, move across the sky in 4 hours and 15 minutes or less, and set in the east, twice each Martian day. Phobos is one of the least reflective bodies in the Solar System, with an albedo of just 0.071. Surface temperatures range from about on the sunlit side to on the shadowed side. The defining surfa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neptune
Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth, and slightly more massive than its near-twin Uranus. Neptune is denser and physically smaller than Uranus because its greater mass causes more gravitational compression of its atmosphere. It is referred to as one of the solar system's two ice giant planets (the other one being Uranus). Being composed primarily of gases and liquids, it has no well-defined "solid surface". The planet orbits the Sun once every 164.8 years at an average distance of . It is named after the Roman god of the sea and has the astronomical symbol , representing Neptune's trident. Neptune is not visible to the unaided eye and is the only planet in the Solar System found by mathematical prediction rather than by empirical observation. U ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jupiter
Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandth the mass of the Sun. Jupiter is the third brightest natural object in the Earth's night sky after the Moon and Venus, and it has been observed since prehistoric times. It was named after the Roman god Jupiter, the king of the gods. Jupiter is primarily composed of hydrogen, but helium constitutes one-quarter of its mass and one-tenth of its volume. It probably has a rocky core of heavier elements, but, like the other giant planets in the Solar System, it lacks a well-defined solid surface. The ongoing contraction of Jupiter's interior generates more heat than it receives from the Sun. Because of its rapid rotation, the planet's shape is an oblate spheroid: it has a slight but noticeable bulge around the equator. The outer atmospher ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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