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An artist's rendering of the Oort cloud, the Hills cloud, and the Kuiper belt (inset)
An artist's rendering of the Oort cloud, the Hills cloud, and the Kuiper belt (inset)
TNOs and similar bodies

The Oort cloud (pronounced /ort/ ort, alternatively the Öpik-Oort Cloud (IPA: ['øpik])) is a spherical cloud of comets believed to lie roughly 50,000 AU, or nearly a light-year, from the Sun;[1] this distance places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun. As of May 2008, there are six known Neptune trojans (named by analogy to the Trojan asteroids which have the same orbital period as Neptune. A trans-Neptunian object (TNO is any object in the Solar system that Orbits the sun at a greater distance on average than Neptune. The Kuiper belt (ˈkaɪpɚ to rhyme with "viper" sometimes called the Edgeworth-Kuiper belt, is a region of the Solar System beyond the planets extending In astronomy a classical Kuiper Belt object, also called a cubewano (ˌkjuːbiːˈwɑːnoʊ is a Kuiper belt object that Orbits beyond Neptune In Astronomy, a resonant trans-Neptunian object is a Trans-Neptunian object (TNO in mean motion Orbital resonance with Neptune In Astronomy, a plutino is a Trans-Neptunian object in 23 mean motion resonance with Neptune. The scattered disc (or scattered disk) is a distant region of the Solar System that is sparsely populated by icy Minor planets known as scattered A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by The Sun (Sol is the Star at the center of the Solar System. Proxima Centauri ( Latin la ''proximus proxima proximum'' meaning 'next to' or 'nearest to' is a Red dwarf Star approximately 4 A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth The Kuiper belt and scattered disc, the other two known reservoirs of trans-Neptunian objects, are less than one thousandth the Oort cloud's distance. The Kuiper belt (ˈkaɪpɚ to rhyme with "viper" sometimes called the Edgeworth-Kuiper belt, is a region of the Solar System beyond the planets extending The scattered disc (or scattered disk) is a distant region of the Solar System that is sparsely populated by icy Minor planets known as scattered A trans-Neptunian object (TNO is any object in the Solar system that Orbits the sun at a greater distance on average than Neptune. The outer extent of the Oort cloud defines the boundary of our Solar System. The Solar System consists of the Sun and those celestial objects bound to it by Gravity.

The Oort cloud is thought to comprise two separate regions: a spherical outer Oort cloud and a disc-shaped inner Oort cloud, or Hills cloud. Objects in the Oort cloud are largely composed of ices such as water, ammonia and methane. In Planetary science, volatiles, are that group of elements and compounds with low boiling points (see volatile) that are associated with a planet's or moon's Water is a common Chemical substance that is essential for the survival of all known forms of Life. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. Astronomers believe that the matter comprising the Oort cloud formed closer to the Sun, and was scattered far out into space by the gravitational effects of the giant planets early in the Solar System's evolution. Gravitation is a natural Phenomenon by which objects with Mass attract one another A gas giant (sometimes also known as a Jovian planet after the planet Jupiter, or giant planet) is a large Planet that is not primarily [1]

Although no confirmed direct observations of the Oort cloud have been made, astronomers believe that it is the source of all long-period and Halley-type comets entering the inner Solar System, and many of the Centaurs and Jupiter-family comets as well. Halley's Comet, officially designated 1P/Halley and also referred to as Comet Halley after Edmond Halley, is a Comet that can be seen every A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — The Solar System consists of the Sun and those celestial objects bound to it by Gravity. [2] The outer Oort cloud is only loosely bound to the Solar System, and thus is easily affected by the gravitational pull both of passing stars, and of the Milky Way galaxy itself. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply These forces occasionally dislodge comets from their orbits within the cloud and send them towards the inner Solar System. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. [1] Based on their orbits, most of the short-period comets may come from the scattered disc, but some may still have originated from the Oort Cloud. [1][2] Although the Kuiper belt and the farther scattered disc have been observed and mapped, only two currently known trans-Neptunian objects, 90377 Sedna and 2000 CR105, are considered possible members of the inner Oort cloud. TemplateInfobox Planet.--> 90377 Sedna (ˈsɛdnə) is a Trans-Neptunian [3]

Contents

Hypothesis

In 1932 Estonian astronomer Ernst Öpik postulated that long-period comets originated in an orbiting cloud at the outermost edge of the Solar System. Estonia, officially the Republic of Estonia ( Eesti or Eesti Vabariik) is a Country in Northern Europe in the Baltic region Ernst Julius Öpik ( October 23, 1893 – September 10, 1985) was a notable Estonian astronomer and astrophysicist who spent the last In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star [4] In 1950, the idea was independently revived by Dutch astronomer Jan Hendrik Oort as a means to resolve a paradox:[5] over the course of the Solar System's existence, the orbits of comets are unstable; eventually, dynamics dictate that a comet must either collide with the Sun or a planet, or else be ejected from the Solar System by planetary perturbations. The Netherlands ( Dutch:, ˈnedərlɑnt is the European part of the Kingdom of the Netherlands, which consists of the Netherlands the Netherlands Jan Hendrik Oort ( April 28, 1900 &ndash November 5, 1992) was a Dutch Astronomer. In physics the term dynamics customarily refers to the time evolution of physical processes A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is Moreover, their volatile composition means that as they repeatedly approach the Sun, radiation gradually boils off the volatiles until the comet splits or develops an insulating crust that prevents further outgassing. In Planetary science, volatiles, are that group of elements and compounds with low boiling points (see volatile) that are associated with a planet's or moon's Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. Outgassing (sometimes called offgassing, particularly when in reference to indoor Air quality is the slow release of a Gas that was trapped Thus, reasoned Oort, a comet could not have formed on its current orbit, and must have been held in an outer reservoir for almost all of its existence. [5][6][7]

There are two main classes of comet: short-period comets (also called ecliptic comets) and long-period comets (also called nearly isotropic comets). The ecliptic is the apparent path that the Sun traces out in the sky during the year Isotropy is uniformity in all directions Precise definitions depend on the subject area Ecliptic comets have relatively short orbits, below 10 AU, and follow the ecliptic plane, the same plane in which the planets lie. The ecliptic is the apparent path that the Sun traces out in the sky during the year Nearly isotropic comets have very long orbits, on the order of thousands of AU, and appear from every corner of the sky. [7] Oort noted that there was a peak in numbers of nearly isotropic comets with aphelia—their farthest distance from the Sun—of roughly 20,000 AU, which suggested a reservoir at that distance with a spherical, isotropic distribution. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from [7] Those relatively rare comets with orbits of about 10,000 AU have probably gone through one or more orbits through the Solar System and have had their orbits drawn inward by the gravity of the planets. Gravitation is a natural Phenomenon by which objects with Mass attract one another [7]

Structure and composition

The presumed distance of the Oort cloud compared to the rest of the Solar System
The presumed distance of the Oort cloud compared to the rest of the Solar System

The Oort cloud is thought to occupy a vast space from somewhere between 2,000 and 5,000 AU[7] to as far as 50,000 AU[1] from the Sun. Some estimates place the outer edge at between 100,000 and 200,000 AU. [7] The region can be subdivided into a spherical outer Oort cloud (20,000–50,000 AU), and a doughnut-shaped inner Oort cloud (2,000–20,000 AU). The outer cloud is only weakly bound to the Sun and supplies the long-period (and possibly Halley-type) comets to inside the orbit of Neptune. Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. [1] The inner Oort cloud is also known as the Hills cloud, named after J. G. Hills, who proposed its existence in 1981. [8] Models predict that the inner cloud should have tens or hundreds times as many cometary nuclei as the outer halo;[9][8][10] it is seen as a possible source of new comets to resupply the relatively tenuous outer cloud as the latter's numbers are gradually depleted. A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — The Hills cloud explains the continued existence of the Oort cloud after billions of years. [11]

The outer Oort cloud is believed to contain several trillion individual comet nuclei larger than approximately 1. 3 km[1] (about 500 billion with absolute magnitudes[12] brighter than 10. The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand In Astronomy, absolute magnitude (also known as absolute visual magnitude) is the Apparent magnitude an object would have if it were at a standard 9), with neighboring comets typically tens of millions of kilometres apart. [2][13] Its total mass is not known with certainty, but, assuming that Halley's comet is a suitable prototype for all comets within the outer Oort cloud, the estimated combined mass is 3x1028 grams, or roughly five times the mass of the Earth. [1][14] Earlier it was thought to be more massive (up to 380 Earth masses),[15] but improved knowledge of the size distribution of long-period comets has led to much lower estimates. The mass of the inner Oort cloud is not currently known.

If analyses of comets are representative of the whole, the vast majority of Oort cloud objects consist of various ices such as water, methane, ethane, carbon monoxide and hydrogen cyanide. Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. ETHANE is a mnemonic indicating a protocol used by Emergency services to report situations which they may be faced with especially as it relates to major incidents where Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas. Hydrogen cyanide is a Chemical compound with Chemical formula HCN [16] However, the discovery of the object 1996 PW, an asteroid in an orbit more typical of a long-period comet, suggests that the cloud may also be home to rocky objects. [17] Analysis of the carbon and nitrogen isotope ratios in both the Oort cloud and Jupiter-family comets shows little difference between the two, despite their vastly separate regions of origin. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides This suggests that both originated from the original protosolar cloud. [18] This conclusion is also supported by studies of granular size in Oort cloud comets,[19] and by the recent impact study of Jupiter-family comet Tempel 1. 9P/Tempel, also known as Tempel 1 or 9P/Tempel 1, is a periodic Comet. [20]

Origin

The Oort cloud is thought to be a remnant of the original protoplanetary disc that formed around the Sun approximately 4. A protoplanetary disk (or proplyd) is a rotating Circumstellar disk of dense gas surrounding a young newly formed star a T Tauri star or Herbig star The formation and evolution of the Solar System is estimated to have begun 6 billion years ago. [1] The most widely accepted hypothesis is that the Oort cloud's objects initially coalesced much closer to the Sun as part of the same process that formed the planets and asteroids, but that gravitational interaction with young gas giant planets such as Jupiter ejected the objects into extremely long elliptic or parabolic orbits. The Sun (Sol is the Star at the center of the Solar System. A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is Asteroids, sometimes called Minor planets or planetoids', are bodies—primarily of the inner Solar System —that are smaller than planets but In Astrodynamics or Celestial mechanics an elliptic orbit is a Kepler orbit with the eccentricity greater than 0 and less than 1 In Astrodynamics or Celestial mechanics a Parabolic trajectory is a Kepler orbit with the eccentricity equal to 1 [1][21] Simulations of the evolution of the Oort cloud from the beginnings of the Solar System to the present suggest that the cloud's mass peaked around 800 million years after formation, as the pace of accretion and collision slowed and depletion began to overtake supply. [1]

Models by Julio Ángel Fernández suggest that the scattered disc, which is the main source for periodic comets in the Solar System, might also be the primary source for the Oort cloud objects. Dr Julio Ángel Fernández Alves (born Montevideo, 5 April 1946) is a Uruguayan astronomer and member of the department of astronomy at the The scattered disc (or scattered disk) is a distant region of the Solar System that is sparsely populated by icy Minor planets known as scattered Periodic comets are defined for these purposes as those Comets having orbital periods of less than 200 years (also known as "short-period comets" or which According to the models, about half of the objects scattered travel outward towards the Oort cloud, while a quarter are shifted inward to Jupiter's orbit, and a quarter are ejected on hyperbolic orbits. In Geometry, a hyperbola ( Greek, "over-thrown" has several equivalent definitions The scattered disc might still be supplying the Oort cloud with material. [22] A third of the scattered disc's population is likely to end up in the Oort cloud after 2. 5 billion years. [23]

Computer models suggest that collisions of cometary debris during the formation period play a far greater role than was previously thought. According to these models, the number of collisions early in the Solar System's history was so great that most comets were destroyed before they reached the Oort cloud. Therefore, the current cumulative mass of the Oort cloud is far less than was once suspected. [24] The estimated mass of the cloud is only a small part of the 50–100 Earth masses of ejected material. [1]

Gravitational interaction with nearby stars and galactic tides modified cometary orbits to make them more circular. A galactic tide is a Tidal force subjected on objects by the Gravitational field of a Galaxy such as the Milky Way. This explains the nearly spherical shape of the outer Oort cloud. [1] On the other hand, the Hills cloud, which is bound more strongly to the Sun, has yet to acquire a spherical shape. Recent studies have shown that the formation of the Oort cloud is broadly compatible with the hypothesis that the Solar System formed as part of an embedded cluster of 200–400 stars. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. Star clusters are groups of Stars which are gravitationally bound These early stars likely played a role in the cloud's formation, since the number of close stellar passages within the cluster was much higher than today, leading to far more frequent perturbations. [25]

Comets

Comet Hale-Bopp, an archetypal Oort cloud comet
Comet Hale-Bopp, an archetypal Oort cloud comet

Comets are believed to have two separate points of origin in the Solar System. A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — Short-period comets (those with orbits of up to 200 years) are generally accepted to have emerged from the Kuiper belt or scattered disc, two linked flat discs of icy debris beginning at Pluto's orbit at 38 AU and jointly extending out beyond 100 AU from the Sun. The Kuiper belt (ˈkaɪpɚ to rhyme with "viper" sometimes called the Edgeworth-Kuiper belt, is a region of the Solar System beyond the planets extending Long-period comets, such as comet Hale-Bopp, whose orbits last for thousands of years, are thought to originate in the Oort cloud. Comet Hale-Bopp ( formally designated C/1995 O1) was probably the most widely observed Comet of the twentieth century and one of the brightest The orbits within the Kuiper belt are relatively stable, and so very few comets are believed to originate there. The scattered disc, however, is dynamically active, and is far more likely to be the place of origin for comets. [7] Comets pass from the scattered disc into the realm of the outer planets, becoming what are known as centaurs. [26] These centaurs are then sent farther inward to become the short-period comets. [27]

There are two main varieties of short-period comet: Jupiter-family comets (those with semi-major axes of less than 5 AU) and Halley-family comets. In Geometry, the semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae Halley-family comets, named for their prototype, Halley's Comet, are unusual in that while they are short-period comets, their ultimate origin lies in the Oort cloud, not in the scattered disc. Halley's Comet, officially designated 1P/Halley and also referred to as Comet Halley after Edmond Halley, is a Comet that can be seen every Based on their orbits, it is believed they were long-period comets that were captured by the gravity of the giant planets and sent into the inner Solar System. [6] This process may have also created the present orbits of a significant fraction of the Jupiter-family comets, although the majority of such comets are thought to have originated in the scattered disc. [2]

Oort noted that the number of returning comets was far less than his model predicted, and this issue, known as "cometary fading", has yet to be resolved. No known dynamical process can explain this undercount of observed comets. Hypotheses for this discrepancy include the destruction of comets due to tidal stresses, impact or heating; the loss of all volatiles, rendering some comets invisible, or the formation of a non-volatile crust on the surface. In Planetary science, volatiles, are that group of elements and compounds with low boiling points (see volatile) that are associated with a planet's or moon's [28] Dynamical studies of Oort cloud comets have shown that their occurrence in the outer planet region is several times higher than in the inner planet region. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. This discrepancy may be due to the gravitational attraction of Jupiter, which acts as a kind of barrier, trapping incoming comets and causing them to collide with it, just as it did the comet Shoemaker-Levy 9 in 1994. Shoemaker-Levy redirects here For other Shoemaker-Levy comets see List of periodic comets. [29]

Tidal effects

Main article: Galactic tide

Most of the comets seen close to the Sun are believed to have reached their current positions through gravitational distortion of the Oort cloud by the tidal force exerted by the Milky Way galaxy. A galactic tide is a Tidal force subjected on objects by the Gravitational field of a Galaxy such as the Milky Way. The tidal force is a secondary effect of the Force of Gravity and is responsible for the Tides It arises because the gravitational acceleration experienced The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply Just as the Moon's tidal force bends and deforms the Earth's oceans, causing the tides to rise and fall, so the galactic tide also bends and distorts bodies in the outer Solar System, pulling them towards the galactic centre. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. In the charted regions of the Solar System, these effects are negligible compared to the gravity of the Sun. At the outer reaches of the system, however, the Sun's gravity is weaker and the gradient of the Milky Way's gravitational field plays a far more noticeable role. Because of this gradient, galactic tides can deform an otherwise spherical Oort cloud, stretching the cloud in the direction of the galactic centre and compressing it along the other two axes. These small galactic perturbations may be enough to dislodge members of the Oort cloud from their orbits, sending them towards the Sun. [30] The point at which the Sun's gravity concedes its influence to the galactic tide is called the tidal truncation radius. It lies at a radius of 100,000 to 200,000 AU, and marks the outer boundary of the Oort cloud. [7]

Some scholars theorise that the galactic tide may have contributed to the formation of the Oort cloud by increasing the perihelia—closest distances to the Sun—of planetesimals with large aphelia. Planetesimals are solid objects thought to exist in Protoplanetary disks and in Debris disks A widely accepted theory of planet formation the so-called planetesimal [31] The effects of the galactic tide are quite complex, and depend heavily on the behaviour of individual objects within a planetary system. Cumulatively, however, the effect can be quite significant: up to 90% of all comets originating from the Oort cloud may be the result of the galactic tide. [32] Statistical models of the observed orbits of long-period comets argue that the galactic tide is the principal means by which their orbits are perturbed toward the inner Solar System. [33]

Star perturbations and stellar companion hypotheses

Besides the galactic tide, the main trigger for sending comets into the inner Solar System is believed to be interaction between the Sun's Oort cloud and the gravitational fields of near-by stars[1] or giant molecular clouds. See also Solar nebula A molecular cloud, sometimes called a stellar nursery if Star formation is occurring within is a type of Interstellar [29] The orbit of the Sun through the plane of the Milky Way sometimes brings it in relatively close proximity to other stellar systems. For example, during the next 10 million years the known star with the greatest possibility of perturbing the Oort cloud is Gliese 710. Gliese 710 is a Red dwarf Star in the Constellation Serpens Cauda, with Visual magnitude 9 [34] This process also serves to scatter the objects out of the ecliptic plane, potentially also explaining the cloud's spherical distribution. [35][34]

Physicist Richard A. Muller and others have also postulated that the Sun has a heretofore undetected companion, either a brown dwarf or gaseous giant planet, in an elliptical orbit within the Oort cloud. Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. Richard A Muller of San Francisco California, US, is a Physicist who works at the University of California Berkeley and Lawrence Berkeley The Sun (Sol is the Star at the center of the Solar System. Brown dwarfs are sub- stellar objects with a mass below that necessary to maintain Hydrogen -burning Nuclear fusion reactions in their cores as do stars This object, known as Nemesis, is theorized to pass through a portion of the Oort cloud approximately every 26 million years, bombarding the inner Solar System with comets. Nemesis is a hypothetical Red dwarf star or Brown dwarf, orbiting the Sun at a distance of about 50000 to 100000 AU, somewhat The Solar System consists of the Sun and those celestial objects bound to it by Gravity. Although the theory has many proponents, no direct proof of the existence of Nemesis has yet been found. [36] Furthermore, many argue that a companion star at such a great distance could not have a stable orbit, as it would probably be ejected by perturbations from other stars.

A similar hypothesis has been advanced by astronomer John J. Matese of the University of Louisiana. History Timeline 1898 - State approved the creation of an "industrial institute and academy He contends that more comets are arriving in the inner Solar System from a particular region of the Oort cloud than can be explained by the galactic tide or stellar perturbations alone, and that the most likely cause is a bound Jupiter-mass object in a distant orbit. [37]

Alternatives to the Nemesis hypothesis speculate that the purported regularity in extinction events is due not to the regular passage of a distant star but to the Sun's passage through the Milky Way. One hypothesis supposes that vertical oscillations made by the Sun as it orbits the galactic centre cause it to regularly pass through the galactic plane. The Galactic Center is the rotational center of the Milky Way Galaxy. When the Sun's orbit takes it outside the galactic disc, the influence of the galactic tide is weaker; as it re-enters the galactic disc, as it does every 20–25 million years, it comes under the influence of the far stronger "disc tides", which, according to mathematical models, increase the flux of Oort cloud comets into the Solar System by a factor of 4. [38]

However, others argue that the Sun is currently close to the galactic plane, and yet the last great extinction event was 15 million years ago. Therefore the Sun's vertical position cannot alone explain such periodic extinctions, and that extinctions instead occur when the Sun passes through the galaxy's spiral arms. A spiral galaxy is a Galaxy belonging to one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work “The Realm of the Spiral arms are home not only to larger numbers of molecular clouds, whose gravity may distort the Oort cloud, but also to higher concentrations of bright blue giant stars, which live for relatively short periods and then explode violently as supernovae. In Astronomy, a blue giant is a Star with a Spectral type of O or B (thus being noticeably blue in appearance and a luminosity class of III ( giant A supernova (plural supernovae or supernovas) is a stellar Explosion. [39]

Oort cloud objects (OCOs)

Sedna, a possible inner Oort cloud object discovered in 2004
Sedna, a possible inner Oort cloud object discovered in 2004

Only two known objects have orbits which suggest that they may belong to the Oort Cloud: 90377 Sedna and 2000 CR105. TemplateInfobox Planet.--> 90377 Sedna (ˈsɛdnə) is a Trans-Neptunian Unlike scattered disc objects, their perihelia are not within gravitational reach of Neptune, and thus their orbits cannot be explained by perturbations by the gas giant planets. A gas giant (sometimes also known as a Jovian planet after the planet Jupiter, or giant planet) is a large Planet that is not primarily [40] If they formed in their current locations, their orbits must originally have been circular; otherwise accretion would not have been possible because the large relative velocities of planetesimals would have been too disruptive. In Astrophysics, the term accretion is used for at least two distinct processes [41] Their orbits can be explained by a number of hypotheses: these objects could have had their orbits and perihelion distances "lifted" by the passage of a nearby star when the Sun was still embedded in its birth star cluster,[3] their orbits could have been disrupted by an as-yet-unknown planet-sized body within the Oort cloud,[42] they could have been scattered by Neptune during a period of particularly high eccentricity or by the gravity of a far larger primordial trans-Neptunian disc, or they could have been captured from around smaller passing stars. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from Of these, the stellar disruption and "lift" hypothesis appear to agree more closely with observations. [3] Some astronomers prefer to refer to Sedna and 2000 CR105 as belonging to the "extended scattered disc" rather than to the inner Oort cloud. The scattered disc (or scattered disk) is a distant region of the Solar System that is sparsely populated by icy Minor planets known as scattered [41]

Oort cloud object candidates
Number Name Equatorial diameter
(km)		 Perihelion (AU) Aphelion (AU) Year discovered Discoverer Diameter method
90377 Sedna 1180–1800 km 76. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from TemplateInfobox Planet.--> 90377 Sedna (ˈsɛdnə) is a Trans-Neptunian 1 892 2003 Brown, Trujillo, Rabinowitz thermal[43]
148209 2000 CR105 ~250 km 44. Year 2003 ( MMIII) was a Common year starting on Wednesday of the Gregorian calendar. Education Brown is a Huntsville Alabama native and graduated from Virgil Grissom High School in 1983 Early career Trujillo attended Oak Park and River Forest High School in Oak Park Illinois. David Lincoln Rabinowitz (born 1960) is a researcher at Yale University. 3 397 2000 Lowell Observatory assumed[44]

See also

References

  1. ^ a b c d e f g h i j k l m n Alessandro Morbidelli (2008-02-03). 2000 ( MM) was a Leap year that started on Saturday of the Common Era, in accordance with the Gregorian calendar. Lowell Observatory is an astronomical Observatory in Flagstaff Arizona. This is a Partial list of numbered Trans-Neptunian objects (TNOs in order of discovery date 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1112 - Ramon Berenguer III of Barcelona and Douce I of Provence marry uniting the fortunes of those two states Origin and dynamical evolution of comets and their reservoirs (PDF). arxiv. Retrieved on 2007-05-26. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 451 - The Battle of Avarayr between Armenian rebels and the Sassanid Empire takes place
  2. ^ a b c d V. V. Emelyanenko, D. J. Asher, M. E. Bailey (2007). "The fundamental role of the Oort cloud in determining the flux of comets through the planetary system". Monthly Notices of the Royal Astronomical Society 381 (2): 779–789. Royal Astronomical Society. doi:10.1111/j.1365-2966.2007.12269.x. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  3. ^ a b c Alessandro Morbidelli; Harold Levison (2004). "Scenarios for the Origin of the Orbits of the Trans-Neptunian Objects 2000 CR105 and 2003 VB12 (Sedna)". The Astronomical Journal 128 (5): 2564–2576. University of Chicago Press. doi:10.1086/424617. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  4. ^ Ernst Julius Öpik (1932). "Note on Stellar Perturbations of Nearby Parabolic Orbits". Proceedings of the American Academy of Arts and Sciences 67: 169–182.  
  5. ^ a b Jan Oort (1950). "The structure of the cloud of comets surrounding the Solar System and a hypothesis concerning its origin" 11: 91–110.  
  6. ^ a b David C. Jewitt (2001). From Kuiper Belt to Cometary Nucleus: The Missing Ultrared Matter. University of Chicago. Retrieved on 2007-06-26. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 363 - Roman Emperor Julian is killed during the retreat from the Sassanid Empire.
  7. ^ a b c d e f g h Harold F. Levison, Luke Donnes (2007). "Comet Populations and Cometary Dynamics", in Lucy Ann Adams McFadden, Lucy-Ann Adams, Paul Robert Weissman, Torrence V. Johnson: Encyclopedia of the Solar System, 2nd, Academic Press, 575–588. ISBN 0120885891.  
  8. ^ a b Jack G. Hills (November 1981). "Comet showers and the steady-state infall of comets from the Oort cloud". The Astronomical Journal 86: 1730–1740. doi:10.1086/113058. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  9. ^ Harold F. Levison, Luke Dones, Martin J. Duncan (April 2001). The Origin of Halley-Type Comets: Probing the Inner Oort Cloud. The Astronomical Journal 2253–2267. The American Astronomical Society. . Retrieved on 2007-06-27. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1358 - Republic of Dubrovnik is founded 1709 - Peter the Great defeats Charles XII of Sweden
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  12. ^ Absolute magnitude is a measure of how bright an object would be if it were exactly 1 AU from the Sun and Earth; as opposed to apparent magnitude, which measures how bright an object appears from Earth. The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value Because all measurements of absolute magnitude assume the same distance, absolute magnitude is in effect a measurement of an object's true brightness. The lower an object's absolute magnitude, the brighter it is.
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External links



Dictionary

Oort cloud

-proper noun

  1. (astronomy) A roughly spherical region of space from 50,000 to 100,000 astronomical units (approximately 1 light year) from the sun; supposedly the source of most comets.
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