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Comets
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] |
Coma (cometary)
The coma is the nebulous envelope around the nucleus of a comet, formed when the comet passes close to the Sun on its highly elliptical orbit; as the comet warms, parts of it sublimate. This gives a comet a "fuzzy" appearance when viewed in telescopes and distinguishes it from stars. The word ''coma'' comes from the Greek "kome" (κόμη), which means "hair" and is the origin of the word ''comet'' itself. The coma is generally made of ice and comet dust. Water composes up to 90% of the volatiles that outflow from the nucleus when the comet is within 3-4 AU of the Sun. The H2O parent molecule is destroyed primarily through photodissociation and to a much smaller extent photoionization. The solar wind plays a minor role in the destruction of water compared to photochemistry. Larger dust particles are left along the comet's orbital path while smaller particles are pushed away from the Sun into the comet's tail by light pressure. On 11 August 2014, astronomers released stu ... [...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] |
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] |
C/2011 W3 (Lovejoy)
Comet Lovejoy, formally designated C/2011 W3 (Lovejoy), is a long-period comet and Kreutz sungrazer. It was discovered in November 2011 by Australian amateur astronomer Terry Lovejoy. The comet's perihelion took it through the Sun's corona on 16 December 2011, after which it emerged intact, though greatly impacted by the event. As Comet Lovejoy was announced on the 16th anniversary of the SOHO satellite's launch it became known as "The Great Birthday Comet of 2011", and because it was visible from Earth during the Christmas holiday it was also nicknamed "The Great Christmas Comet of 2011". Discovery Comet Lovejoy was discovered on 27 November 2011 by Terry Lovejoy of Thornlands, Queensland, during a comet survey using a Schmidt–Cassegrain telescope and a QHY9 CCD camera. It is the third comet discovered by Terry Lovejoy. He reported that it was "a rapidly moving fuzzy object" of 13th magnitude, and additional observations were made by him over the next couple of nights. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hyperbolic Comet
This is a list of parabolic and hyperbolic comets in the Solar System. Many of these comets may come from the Oort cloud, or perhaps even have interstellar origin. The Oort Cloud is not gravitationally attracted enough to the Sun to form into a fairly thin disk, like the inner Solar System. Thus, comets originating from the Oort Cloud can come from roughly any orientation (inclination to the ecliptic), and many even have a retrograde orbit. By definition, a hyperbolic orbit means that the comet will only travel through the Solar System once, with the Sun acting as a gravitational slingshot, sending the comet hurtling out of the Solar System entirely unless its eccentricity is otherwise changed. Comets orbiting in this way still originate from the Solar System, however. Typically comets in the Oort Cloud are thought to have roughly circular orbits around the Sun, but their orbital velocity is so slow that they may easily be perturbed by passing stars and the galactic tide. Astr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scattered Disc
The scattered disc (or scattered disk) is a distant circumstellar disc in the Solar System that is sparsely populated by icy small solar system bodies, which are a subset of the broader family of trans-Neptunian objects. The scattered-disc objects (SDOs) have orbital eccentricities ranging as high as 0.8, inclinations as high as 40°, and perihelia greater than . These extreme orbits are thought to be the result of gravitational "scattering" by the gas giants, and the objects continue to be subject to perturbation by the planet Neptune. Although the closest scattered-disc objects approach the Sun at about 30–35 AU, their orbits can extend well beyond 100 AU. This makes scattered objects among the coldest and most distant objects in the Solar System. The innermost portion of the scattered disc overlaps with a torus-shaped region of orbiting objects traditionally called the Kuiper belt, but its outer limits reach much farther away from the Sun and farther above and be ... [...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] |
9P/Tempel
Tempel 1 (official designation: 9P/Tempel) is a periodic Jupiter-family comet discovered by Wilhelm Tempel in 1867. It completes an orbit of the Sun every 5.5 years. Tempel 1 was the target of the ''Deep Impact'' space mission, which photographed a deliberate high-speed impact upon the comet in 2005. It was re-visited by the ''Stardust'' spacecraft on February 14, 2011 and came back to perihelion in August 2016. Discovery and orbital history Tempel 1 was discovered on April 3, 1867, by Wilhelm Tempel, who was working at Marseille. At the time of discovery, it approached perihelion once every 5.68 years (designations 9P/1867 G1 and 1867 II). It was subsequently observed in 1873 (9P/1873 G1, 1873 I, 1873a) and in 1879 (1879 III, 1879b). Photographic attempts during 1898 and 1905 failed to recover the comet, and astronomers surmised that it had disintegrated, when in reality, its orbit had changed. Tempel 1's orbit occasionally brings it sufficiently close to Jupiter to be alte ... [...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] |
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