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Cometary
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times Earth's diameter, while the tail may stretch beyond one astronomical unit. If sufficiently bright, a comet may be seen from Earth without the aid of a telescope and may subtend an arc of 30° (60 Moons) across the sky. Comets have been observed and recorded since ancient times by many cultures and religions. Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several milli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Comet Nucleus
The nucleus is the solid, central part of a comet, once termed a ''dirty snowball'' or an ''icy dirtball''. A cometary nucleus is composed of Rock (geology), rock, dust, and frozen gases. When heated by the Sun, the gases Sublimation (physics), sublime and produce an atmosphere surrounding the nucleus known as the Coma (cometary), coma. The force exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous tail to form, which points away from the Sun. A typical comet nucleus has an Albedo#Astronomical albedo, albedo of 0.04. This is blacker than coal, and may be caused by a covering of dust. Results from the Rosetta (spacecraft), ''Rosetta'' and Philae (spacecraft), ''Philae'' spacecraft show that the nucleus of 67P/Churyumov–Gerasimenko has no magnetic field, which suggests that magnetism may not have played a role in the early formation of planetesimals. Further, the Rosetta (spacecraft)#Instruments, ALICE spectrograph on ''Rosetta'' determined that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Comet Nuclei
The nucleus is the solid, central part of a comet, once termed a ''dirty snowball'' or an ''icy dirtball''. A cometary nucleus is composed of rock, dust, and frozen gases. When heated by the Sun, the gases sublime and produce an atmosphere surrounding the nucleus known as the coma. The force exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous tail to form, which points away from the Sun. A typical comet nucleus has an albedo of 0.04. This is blacker than coal, and may be caused by a covering of dust. Results from the ''Rosetta'' and ''Philae'' spacecraft show that the nucleus of 67P/Churyumov–Gerasimenko has no magnetic field, which suggests that magnetism may not have played a role in the early formation of planetesimals. Further, the ALICE spectrograph on ''Rosetta'' determined that electrons (within above the comet nucleus) produced from photoionization of water molecules by solar radiation, and not photons from the Sun as thought earl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stardust (spacecraft)
''Stardust'' was a 385-kilogram robotic space probe launched by NASA on 7 February 1999. Its primary mission was to collect dust samples from the coma of comet Wild 2, as well as samples of cosmic dust, and return them to Earth for analysis. It was the first sample return mission of its kind. En route to comet Wild 2, it also flew by and studied the asteroid 5535 Annefrank. The primary mission was successfully completed on 15 January 2006 when the sample return capsule returned to Earth. A mission extension, codenamed ''NExT'', culminated in February 2011 with ''Stardust'' intercepting comet Tempel 1, a small Solar System body previously visited by '' Deep Impact'' in 2005. ''Stardust'' ceased operations in March 2011. On 14 August 2014, scientists announced the identification of possible interstellar dust particles from the ''Stardust'' capsule returned to Earth in 2006. Mission background History Beginning in the 1980s, scientists began seeking a dedicated mis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rosetta (spacecraft)
''Rosetta'' was a space probe built by the European Space Agency launched on 2 March 2004. Along with ''Philae (spacecraft), Philae'', its lander module, ''Rosetta'' performed a detailed study of comet 67P/Churyumov–Gerasimenko (67P). During its journey to the comet, the spacecraft performed planetary flyby, flybys of Earth, Mars, and the asteroids 21 Lutetia and 2867 Šteins. It was launched as the third cornerstone mission of the ESA's Horizon 2000 programme, after ''Solar and Heliospheric Observatory, SOHO'Cluster II (spacecraft), Cluster'' and ''XMM-Newton''. On 6 August 2014, the spacecraft reached the comet and performed a series of manoeuvers to eventually orbit the comet at distances of . On 12 November, its lander module ''Philae'' performed the first successful landing on a comet, though its battery power ran out two days later. Communications with ''Philae'' were briefly restored in June and July 2015, but due to diminishing solar power, ''Rosetta'' communications ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
67P/Churyumov–Gerasimenko
67P/Churyumov–Gerasimenko (abbreviated as 67P or 67P/C–G) is a Jupiter-family comet, originally from the Kuiper belt, with a current orbital period of 6.45 years, a rotation period of approximately 12.4 hours and a maximum velocity of . Churyumov–Gerasimenko is approximately at its longest and widest dimensions. It was first observed on photographic plates in 1969 by Soviet astronomers Klim Ivanovych Churyumov and Svetlana Ivanovna Gerasimenko, after whom it is named. It most recently came to perihelion (closest approach to the Sun) on 2 November 2021, and will next come to perihelion on 9 April 2028. Churyumov–Gerasimenko was the destination of the European Space Agency's ''Rosetta'' mission, launched on 2 March 2004. ''Rosetta'' rendezvoused with Churyumov–Gerasimenko on 6 August 2014 and entered orbit on 10 September 2014. ''Rosetta'' lander, ''Philae'', landed on the comet's surface on 12 November 2014, becoming the first spacecraft to land on a comet nucleu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oort Cloud
The Oort cloud (), sometimes called the Öpik–Oort cloud, first described in 1950 by the Dutch astronomer Jan Oort, is a theoretical concept of a cloud of predominantly icy planetesimals proposed to surround the Sun at distances ranging from 2,000 to 200,000 AU (0.03 to 3.2 light-years).The Oort cloud's outer limit is difficult to define as it varies over the millennia as different stars pass the Sun and thus is subject to variation. Estimates of its distance range from 50,000 to 200,000 au. It is divided into two regions: a disc-shaped inner Oort cloud (or Hills cloud) and a spherical outer Oort cloud. Both regions lie beyond the heliosphere and are in interstellar space. The Kuiper belt, the scattered disc and the detached objects, the other three reservoirs of trans-Neptunian objects, are less than one thousandth as far from the Sun as the Oort cloud. The outer limit of the Oort cloud defines the cosmographic boundary of the Solar System and the extent of the Sun's Hill ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Asteroid
An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. Of the roughly one million known asteroids the greatest number are located between the orbits of Mars and Jupiter, approximately 2 to 4 AU from the Sun, in the main asteroid belt. Asteroids are generally classified to be of three types: C-type, M-type, and S-type. These were named after and are generally identified with carbonaceous, metallic, and silicaceous compositions, respectively. The size of asteroids varies greatly; the largest, Ceres, is almost across and qualifies as a dwarf planet. The total mass of all the asteroids combined is only 3% that of Earth's Moon. The majority of main belt asteroids follow slightly elliptical, stable orbits, revolving in the same direction as the Earth and taking from three to six years to comple ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deep Impact (spacecraft)
''Deep Impact'' was a NASA space probe launched from Cape Canaveral Air Force Station on January 12, 2005. It was designed to study the interior composition of the comet Tempel 1 (9P/Tempel), by releasing an impactor into the comet. At 05:52 UTC on July 4, 2005, the Impactor successfully collided with the comet's nucleus. The impact excavated debris from the interior of the nucleus, forming an impact crater. Photographs taken by the spacecraft showed the comet to be more dusty and less icy than had been expected. The impact generated an unexpectedly large and bright dust cloud, obscuring the view of the impact crater. Previous space missions to comets, such as ''Giotto'', ''Deep Space 1'', and '' Stardust'', were fly-by missions. These missions were able to photograph and examine only the surfaces of cometary nuclei, and even then from considerable distances. The ''Deep Impact'' mission was the first to eject material from a comet's surface, and the mission garnered considerabl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Comet Tail
A comet tail—and coma—are features visible in comets when they are illuminated by the Sun and may become visible from Earth when a comet passes through the inner Solar System. As a comet approaches the inner Solar System, solar radiation causes the volatile materials within the comet to vaporize and stream out of the nucleus, carrying dust away with them. Separate tails are formed of dust and gases, becoming visible through different phenomena; the dust reflects sunlight directly and the gases glow from ionisation. Most comets are too faint to be visible without the aid of a telescope, but a few each decade become bright enough to be visible to the naked eye. Tail formation In the outer Solar System, comets remain frozen and are extremely difficult or impossible to detect from Earth due to their small size. Statistical detections of inactive comet nuclei in the Kuiper belt have been reported from the Hubble Space Telescope observations, but these detections have been que ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
17P/Holmes
Comet Holmes (official designation: 17P/Holmes) is a periodic comet in the Solar System, discovered by the British amateur astronomer Edwin Holmes on November 6, 1892. Although normally a very faint object, Holmes became notable during its October 2007 return when it temporarily brightened by a factor of a million, in what was the largest known outburst by a comet, and became visible to the naked eye. It also briefly became the largest object in the Solar System, as its coma (the thin dissipating dust ball around the comet) expanded to a diameter greater than that of the Sun (although its mass remained minuscule). Discovery Comet Holmes was discovered by Edwin Holmes on November 6, 1892, while he was conducting regular observations of the Andromeda Galaxy (M31). Its discovery in 1892 was possible because of an increase in its magnitude similar to the 2007 outburst; it brightened to an approximate magnitude of 4 or 5 before fading from visibility over a period of several wee ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
81P/Wild
Comet 81P/Wild, also known as Wild 2 (pronounced "vilt two") ( ), is a comet named after Swiss astronomer Paul Wild, who discovered it on January 6, 1978, using a 40-cm Schmidt telescope at Zimmerwald, Switzerland. For most of its 4.5 billion-year lifetime, Wild 2 probably had a more distant and circular orbit. In September 1974, it passed within one million kilometers of the planet Jupiter, the strong gravitational pull of which perturbed the comet's orbit and brought it into the inner Solar System. Its orbital period changed from 43 years to about 6 years, and its perihelion is now about 1.59 astronomical unit (AU). Nucleus parameters * Dimensions: * Density: * Mass: 2.3 x 1013 kg (5.1 x 1013 lb) Exploration NASA's Stardust Mission launched a spacecraft, named '' Stardust'', on February 7, 1999. It flew by Wild 2 on January 2, 2004, and collected particle samples from the comet's coma, which were returned to Earth along with interstellar dust it collected during ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Galactic Tide
A galactic tide is a tidal force experienced by objects subject to the gravitational field of a galaxy such as the Milky Way. Particular areas of interest concerning galactic tides include galactic collisions, the disruption of dwarf or satellite galaxies, and the Milky Way's tidal effect on the Oort cloud of the Solar System. Effects on external galaxies Galaxy collisions Tidal forces are dependent on the gradient of a gravitational field, rather than its strength, and so tidal effects are usually limited to the immediate surroundings of a galaxy. Two large galaxies undergoing collisions or passing nearby each other will be subjected to very large tidal forces, often producing the most visually striking demonstrations of galactic tides in action. Two interacting galaxies will rarely (if ever) collide head-on, and the tidal forces will distort each galaxy along an axis pointing roughly towards and away from its perturber. As the two galaxies briefly orbit each other, thes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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