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99942
99942 Apophis is a near-Earth asteroid and potentially hazardous asteroid with a diameter of that caused a brief period of concern in December 2004 when initial observations indicated a probability up to 2.7% that it would hit Earth on April 13, 2029. Additional observations provided improved predictions that eliminated the possibility of an impact on Earth in 2029. Until 2006, a small probability nevertheless remained that, during its 2029 close encounter with Earth, Apophis would pass through a gravitational keyhole of no more than about in diameter, which would have set up a future impact exactly seven years later on April 13, 2036. This possibility kept it at Level 1 on the Torino impact hazard scale until August 2006, when the probability that Apophis would pass through the keyhole was determined to be very small and Apophis' rating on the Torino scale was lowered to zero. By 2008, the keyhole had been determined to be less than 1 km wide. During the sh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Yarkovsky Effect
The Yarkovsky effect is a force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum. It is usually considered in relation to meteoroids or small asteroids (about 10 cm to 10 km in diameter), as its influence is most significant for these bodies. History of discovery The effect was discovered by the Polish-Russian civil engineer Ivan Osipovich Yarkovsky (1844–1902), who worked in Russia on scientific problems in his spare time. Writing in a pamphlet around the year 1900, Yarkovsky noted that the daily heating of a rotating object in space would cause it to experience a force that, while tiny, could lead to large long-term effects in the orbits of small bodies, especially meteoroids and small asteroids. Yarkovsky's insight would have been forgotten had it not been for the Estonian astronomer Ernst J. Öpik (1893–1985), who read Yarkovsky's pamphlet sometime around 1909. Decades later, Öpik, recall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gravitational Keyhole
A gravitational keyhole is a tiny region of space where a planet's gravity would alter the orbit of a passing asteroid such that the asteroid would collide with that planet on a given future orbital pass. The word "keyhole" contrasts the large uncertainty of trajectory calculations (between the time of the observations of the asteroid and the first encounter with the planet) with the relatively narrow bundle(s) of critical trajectories. The term was coined by P. W. Chodas in 1999. It gained some public interest when it became clear, in January 2005, that the Asteroid 99942 Apophis would miss the Earth in 2029 but may go through one or another keyhole leading to impacts in 2036 or 2037. Further research has since been done, however, which revealed the probability of Apophis passing through the keyhole was extremely low. Keyholes for the nearer or further future are named by the numbers of orbital periods of the planet and the asteroid, respectively, between the two encounters (for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aten Asteroids
The Aten asteroids are a dynamical group of asteroids whose orbits bring them into proximity with Earth. By definition, Atens are Earth-crossing asteroids . The group is named after 2062 Aten, the first of its kind, discovered on 7 January 1976 by American astronomer Eleanor Helin at Palomar Observatory. As of 2020, 1841 Atens have been discovered, of which 13 are named. Many Atens are classified as potentially hazardous asteroids. Description Aten asteroids are defined by having a semi-major axis (a) of less than 1.0 astronomical unit (AU), the roughly average distance from the Earth to the Sun. They also have an aphelion (Q; furthest distance from the Sun) greater than 0.983 AU. This defines them as Earth-crossing asteroids as the orbit of Earth varies between 0.983 and 1.017 AU. Asteroids' orbits can be highly eccentric. Nearly all known Aten asteroids have an aphelion greater than 1 AU. Observation of objects inferior to the Earth's orbit is di ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fabrizio Bernardi
Fabrizio Bernardi (born 1972) is an Italian astronomer and discoverer of minor planets and comets, best known for the co-discovery of the near-Earth and potentially hazardous asteroid 99942 Apophis. He is a member of the IAU, and credited by the Minor Planet Center with the discovery of 7 numbered minor planets during 2002–2005, including , another near-Earth object a member of the Amor group of asteroids, and , a trans-Neptunian object. In 2002, he discovered the outer main-belt asteroid 65001 Teodorescu at Campo Imperatore station, Gran Sasso, Italy, and named it after his wife, the Romanian astronomer Ana Teodorescu. He was involved together with colleagues Marco Micheli and David Tholen, with observations of the Mars-crosser asteroid 2007 WD5 during his stay at the University of Hawaii observatory. While at the Mauna Kea Observatories in Hawaii, he discovered 268P/Bernardi, a Jupiter family comet. The main-belt asteroid 27983 Bernardi, discovered by astron ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tumbling Asteroid
This is a list of tumblers, minor planets, comets and natural satellites whose angular momentum vector is far from the principal axis of inertia, so that they do not rotate in a fairly constant manner with a constant period. Instead of rotating around a constant axis or around a wobbling axis, they appear to tumble (see Poinsot's ellipsoid for an explanation). For true tumbling, the three moments of inertia must be different. If two are equal, then the axis of rotation will simply precess in a circle. As of 2018, there are 3 natural satellites and 198 confirmed or likely tumblers out of a total of nearly 800,000 discovered small Solar System bodies. The data is sourced from the "Lightcurve Data Base" (LCDB). The tumbling of a body can be caused by the torque from asymmetrically emitted radiation known as the YORP effect. Note that the rotation periods given below are approximate. The rotation period is not constant for a tumbler. Natural satellites This is a list of tumbling ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Palermo Technical Impact Hazard Scale
The Palermo Technical Impact Hazard Scale is a logarithmic scale used by astronomers to rate the potential hazard of impact of a near-Earth object (NEO). It combines two types of data—probability of impact and estimated kinetic yield—into a single "hazard" value. A rating of 0 means the hazard is equivalent to the background hazard (defined as the average risk posed by objects of the same size or larger over the years until the date of the potential impact). A rating of +2 would indicate the hazard is 100 times as great as a random background event. Scale values less than −2 reflect events for which there are no likely consequences, while Palermo Scale values between −2 and 0 indicate situations that merit careful monitoring. A similar but less complex scale is the Torino Scale, which is used for simpler descriptions in the non-scientific media. As of December 2022, one asteroid has a cumulative Palermo Scale value above −2: 101955 Bennu (−1.41). Five have cu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radar Astronomy
Radar astronomy is a technique of observing nearby astronomical objects by reflecting radio waves or microwaves off target objects and analyzing their reflections. Radar astronomy differs from ''radio astronomy'' in that the latter is a passive observation (i.e., receiving only) and the former an active one (transmitting and receiving). Radar systems have been conducted for six decades applied to a wide range of Solar System studies. The radar transmission may either be pulsed or continuous. The strength of the radar return signal is proportional to the inverse fourth-power of the distance. Upgraded facilities, increased transceiver power, and improved apparatus have increased observational opportunities. Radar techniques provide information unavailable by other means, such as testing general relativity by observing Mercury and providing a refined value for the astronomical unit. Radar images provide information about the shapes and surface properties of solid bodies, which ca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Torino Scale
The Torino scale is a method for categorizing the impact hazard associated with near-Earth objects (NEOs) such as asteroids and comets. It is intended as a communication tool for astronomers and the public to assess the seriousness of collision predictions, by combining probability statistics and known kinetic damage potentials into a single threat value. The Palermo Technical Impact Hazard Scale is a similar, but more complex scale. Near-Earth objects with a Torino scale of 1 pop up every couple of months or so and may last a few weeks until they have a longer observation arc. Overview The Torino Scale uses an integer scale from 0 to 10. A 0 indicates an object has a negligibly small chance of collision with the Earth, compared with the usual "background noise" of collision events, or is too small to penetrate Earth's atmosphere intact. A 10 indicates that a collision is certain, and the impacting object is large enough to precipitate a global disaster. An object is assigned a 0 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Near-Earth Object
A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). If a NEO's orbit crosses the Earth's orbit, and the object is larger than across, it is considered a potentially hazardous object (PHO). Most known PHOs and NEOs are asteroids, but a small fraction are comets. There are over 30,503 known near-Earth asteroids (NEAs) and over a hundred known short-period near-Earth comets (NECs). A number of solar-orbiting meteoroids were large enough to be tracked in space before striking the Earth. It is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of the Earth. Asteroids as small as in diameter can cause significant damage to the local environment and human populations. Larger asteroids penetrate the atmosphere to the s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Apep
Apep, also spelled Apepi or Aapep, ( Ancient Egyptian: ; Coptic: Erman, Adolf, and Hermann Grapow, eds. 1926–1953. ''Wörterbuch der aegyptischen Sprache im Auftrage der deutschen Akademien''. 6 vols. Leipzig: J. C. Hinrichs'schen Buchhandlungen. (Reprinted Berlin: Akademie-Verlag GmbH, 1971).) or Apophis (; Ancient Greek: ) was the ancient Egyptian deity who embodied chaos ('' ı͗zft'' in Egyptian) and was thus the opponent of light and Ma'at (order/ truth). He appears in art as a giant serpent. Apep was first mentioned in the Eighth Dynasty, and he was honored in the names of the Fourteenth Dynasty king 'Apepi and of the Greater Hyksos king Apophis. Development Ra was the solar deity, bringer of light, and thus the upholder of Ma'at. Apep was viewed as the greatest enemy of Ra, and thus was given the title ''Enemy of Ra'', and also "the Lord of Chaos". Apep was seen as a giant snake or serpent leading to such titles as ''Serpent from the Nile'' and ''E ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Near-Earth Asteroids
A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). If a NEO's orbit crosses the Earth's orbit, and the object is larger than across, it is considered a potentially hazardous object (PHO). Most known PHOs and NEOs are asteroids, but a small fraction are comets. There are over 30,503 known near-Earth asteroids (NEAs) and over a hundred known short-period near-Earth comets (NECs). A number of solar-orbiting meteoroids were large enough to be tracked in space before striking the Earth. It is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of the Earth. Asteroids as small as in diameter can cause significant damage to the local environment and human populations. Larger asteroids penetrate the atmosphere to the surf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
