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123-470: The Kuiper belt ( / ˈ k aɪ p ər / KY -pər ) is a circumstellar disc in the outer Solar System , extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun . It is similar to the asteroid belt , but is far larger—20 times as wide and 20–200 times as massive . Like the asteroid belt, it consists mainly of small bodies or remnants from when

246-400: A "comet belt" might be massive enough to cause the purported discrepancies in the orbit of Uranus that had sparked the search for Planet X , or, at the very least, massive enough to affect the orbits of known comets. Observation ruled out this hypothesis. In 1977, Charles Kowal discovered 2060 Chiron , an icy planetoid with an orbit between Saturn and Uranus. He used a blink comparator ,

369-570: A 1:1 mean-motion resonance with Neptune and often have very stable orbits. Additionally, there is a relative absence of objects with semi-major axes below 39 AU that cannot apparently be explained by the present resonances. The currently accepted hypothesis for the cause of this is that as Neptune migrated outward, unstable orbital resonances moved gradually through this region, and thus any objects within it were swept up, or gravitationally ejected from it. The 1:2 resonance at 47.8 AU appears to be an edge beyond which few objects are known. It

492-507: A broad range of colors among KBOs, ranging from neutral grey to deep red. This suggested that their surfaces were composed of a wide range of compounds, from dirty ices to hydrocarbons . This diversity was startling, as astronomers had expected KBOs to be uniformly dark, having lost most of the volatile ices from their surfaces to the effects of cosmic rays . Various solutions were suggested for this discrepancy, including resurfacing by impacts or outgassing . Jewitt and Luu's spectral analysis of

615-616: A circumstellar disc can be used to determine the timescales involved in its evolution. For example, observations of the dissipation process in transition discs (discs with large inner holes) estimate the average age of a circumstellar disc to be approximately 10 Myr. Dissipation process and its duration in each stage is not well understood. Several mechanisms, with different predictions for discs' observed properties, have been proposed to explain dispersion in circumstellar discs. Mechanisms like decreasing dust opacity due to grain growth, photoevaporation of material by X-ray or UV photons from

738-413: A coronagraph, adaptive optics or differential images to take an image of the disk with a telescope. These optical and infrared observations, for example with SPHERE , usually take an image of the star light being scattered on the surface of the disk and trace small micron-sized dust particles. Radio arrays like ALMA on the other hand can map larger millimeter-sized dust grains found in the mid-plane of

861-409: A different size distribution, and lacks very large objects. The mass of the dynamically cold population is roughly 30 times less than the mass of the hot. The difference in colors may be a reflection of different compositions, which suggests they formed in different regions. The hot population is proposed to have formed near Neptune's original orbit and to have been scattered out during the migration of

984-511: A divot, a sharp decrease in the number of objects below a specific size. This divot is hypothesized to be due to either the collisional evolution of the population, or to be due to the population having formed with no objects below this size, with the smaller objects being fragments of the original objects. The smallest known Kuiper belt objects with radii below 1 km have only been detected by stellar occultations , as they are far too dim ( magnitude 35) to be seen directly by telescopes such as

1107-438: A few weeks per year. Analysis of observed phenomena, along with making predictions as to the causes of what they observe, takes the majority of observational astronomers' time. Astronomers who serve as faculty spend much of their time teaching undergraduate and graduate classes. Most universities also have outreach programs, including public telescope time and sometimes planetariums , as a public service to encourage interest in

1230-405: A large fraction of the mass of the dynamically cold population is thought to be unlikely. Neptune's current influence is too weak to explain such a massive "vacuuming", and the extent of mass loss by collisional grinding is limited by the presence of loosely bound binaries in the cold disk, which are likely to be disrupted in collisions. Instead of forming from the collisions of smaller planetesimals,

1353-585: A lecture Kuiper gave in 1950, also called On the Origin of the Solar System , Kuiper wrote about the "outermost region of the solar nebula, from 38 to 50 astr. units (i.e., just outside proto-Neptune)" where "condensation products (ices of H20, NH3, CH4, etc.) must have formed, and the flakes must have slowly collected and formed larger aggregates, estimated to range up to 1 km. or more in size." He continued to write that "these condensations appear to account for

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1476-517: A marker of the extent of the Solar System, alternatives being the heliopause and the distance at which the Sun's gravitational influence is matched by that of other stars (estimated to be between 50 000  AU and 125 000  AU ). After the discovery of Pluto in 1930, many speculated that it might not be alone. The region now called the Kuiper belt was hypothesized in various forms for decades. It

1599-428: A mixture of rock and a variety of ices such as water, methane , and ammonia . The temperature of the belt is only about 50 K , so many compounds that would be gaseous closer to the Sun remain solid. The densities and rock–ice fractions are known for only a small number of objects for which the diameters and the masses have been determined. The diameter can be determined by imaging with a high-resolution telescope such as

1722-566: A number of successes in determining their composition. In 1996, Robert H. Brown et al. acquired spectroscopic data on the KBO 1993 SC, which revealed that its surface composition is markedly similar to that of Pluto , as well as Neptune's moon Triton , with large amounts of methane ice. For the smaller objects, only colors and in some cases the albedos have been determined. These objects largely fall into two classes: gray with low albedos, or very red with higher albedos. The difference in colors and albedos

1845-417: A second object in the region, (181708) 1993 FW . By 2018, over 2000 Kuiper belts objects had been discovered. Over one thousand bodies were found in a belt in the twenty years (1992–2012), after finding 1992 QB 1 (named in 2018, 15760 Albion), showing a vast belt of bodies in addition to Pluto and Albion. Even in the 2010s the full extent and nature of Kuiper belt bodies was largely unknown. Finally,

1968-434: A significant region of the inner circumbinary disk up to ∼ 10 a b {\displaystyle \sim 10a_{b}} . This eccentricity may in turn affect the inner cavity accretion as well as dynamics further out in the disk, such as circumbinary planet formation and migration. It was originally believed that all binaries located within circumbinary disk would evolve towards orbital decay due to

2091-445: A significant warp or tilt to an initially flat disk. Strong evidence of tilted disks is seen in the systems Her X-1, SMC X-1, and SS 433 (among others), where a periodic line-of-sight blockage of X-ray emissions is seen on the order of 50–200 days; much slower than the systems' binary orbit of ~1 day. The periodic blockage is believed to result from precession of a circumprimary or circumbinary disk, which normally occurs retrograde to

2214-436: A sizable mass is required for accretion of KBOs larger than 100 km (62 mi) in diameter. If the cold classical Kuiper belt had always had its current low density, these large objects simply could not have formed by the collision and mergers of smaller planetesimals. Moreover, the eccentricity and inclination of current orbits make the encounters quite "violent" resulting in destruction rather than accretion. The removal of

2337-499: A source for short-period comets. In 1992, minor planet (15760) Albion was discovered, the first Kuiper belt object (KBO) since Pluto (in 1930) and Charon (in 1978). Since its discovery, the number of known KBOs has increased to thousands, and more than 100,000 KBOs over 100 km (62 mi) in diameter are thought to exist. The Kuiper belt was initially thought to be the main repository for periodic comets , those with orbits lasting less than 200 years. Studies since

2460-464: A star for 0.3 seconds. In a subsequent study published in December 2012, Schlichting et al. performed a more thorough analysis of archival Hubble photometry and reported another occultation event by a sub-kilometre-sized Kuiper belt object, estimated to be 530 ± 70 m in radius or 1060 ± 140 m in diameter. From the occultation events detected in 2009 and 2012, Schlichting et al. determined

2583-738: A system of stars or a galaxy to complete a life cycle, astronomers must observe snapshots of different systems at unique points in their evolution to determine how they form, evolve, and die. They use this data to create models or simulations to theorize how different celestial objects work. Further subcategories under these two main branches of astronomy include planetary astronomy , astrobiology , stellar astronomy , astrometry , galactic astronomy , extragalactic astronomy , or physical cosmology . Astronomers can also specialize in certain specialties of observational astronomy, such as infrared astronomy , neutrino astronomy , x-ray astronomy , and gravitational-wave astronomy . Historically , astronomy

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2706-457: A thin crust of ice. There is a trend of low densities for small objects and high densities for the largest objects. One possible explanation for this trend is that ice was lost from the surface layers when differentiated objects collided to form the largest objects. Initially, detailed analysis of KBOs was impossible, and so astronomers were only able to determine the most basic facts about their makeup, primarily their color. These first data showed

2829-407: A tilted circumbinary disc will undergo rigid precession with a period on the order of years. For discs around a binary with a mass ratio of one, differential torques will be strong enough to tear the interior of the disc apart into two or more separate, precessing discs. A study from 2020 using ALMA data showed that circumbinary disks around short period binaries are often aligned with the orbit of

2952-917: A very long timescale. As mentioned, circumstellar discs are not equilibrium objects, but instead are constantly evolving. The evolution of the surface density Σ {\displaystyle \Sigma } of the disc, which is the amount of mass per unit area so after the volume density at a particular location in the disc has been integrated over the vertical structure, is given by: ∂ Σ ∂ t = 3 r ∂ ∂ r [ r 1 / 2 ∂ ∂ r ν Σ r 1 / 2 ] {\displaystyle {\frac {\partial \Sigma }{\partial t}}={\frac {3}{r}}{\frac {\partial }{\partial r}}\left[r^{1/2}{\frac {\partial }{\partial r}}\nu \Sigma r^{1/2}\right]} where r {\displaystyle r}

3075-507: Is a sparsely populated region, overlapping with the Kuiper belt but extending to beyond 100 AU. Scattered disc objects (SDOs) have very elliptical orbits, often also very inclined to the ecliptic. Most models of Solar System formation show both KBOs and SDOs first forming in a primordial belt, with later gravitational interactions, particularly with Neptune, sending the objects outward, some into stable orbits (the KBOs) and some into unstable orbits,

3198-436: Is an empirical connection between accretion from a disc onto the star and ejections in an outflow. Mid-disc dissipation , occurs at the mid-disc region (1-5 AU ) and is characterized for the presence of much more cooler material than in the inner part of the disc. Consequently, radiation emitted from this region has greater wavelength , indeed in the mid-infrared region, which makes it very difficult to detect and to predict

3321-450: Is an exact ratio of Neptune's (a situation called a mean-motion resonance ), then it can become locked in a synchronised motion with Neptune and avoid being perturbed away if their relative alignments are appropriate. If, for instance, an object orbits the Sun twice for every three Neptune orbits, and if it reaches perihelion with Neptune a quarter of an orbit away from it, then whenever it returns to perihelion, Neptune will always be in about

3444-497: Is another comet population, known as short-period or periodic comets , consisting of those comets that, like Halley's Comet , have orbital periods of less than 200 years. By the 1970s, the rate at which short-period comets were being discovered was becoming increasingly inconsistent with their having emerged solely from the Oort cloud. For an Oort cloud object to become a short-period comet, it would first have to be captured by

3567-419: Is believed to be a thousand times more distant and mostly spherical. The objects within the Kuiper belt, together with the members of the scattered disc and any potential Hills cloud or Oort cloud objects, are collectively referred to as trans-Neptunian objects (TNOs). Pluto is the largest and most massive member of the Kuiper belt and the largest and the second-most-massive known TNO, surpassed only by Eris in

3690-448: Is considered the prototype of this group, classical KBOs are often referred to as cubewanos ("Q-B-1-os"). The guidelines established by the IAU demand that classical KBOs be given names of mythological beings associated with creation. The classical Kuiper belt appears to be a composite of two separate populations. The first, known as the "dynamically cold" population, has orbits much like

3813-407: Is hypothesized to be due to the retention or the loss of hydrogen sulfide (H 2 S) on the surface of these objects, with the surfaces of those that formed far enough from the Sun to retain H 2 S being reddened due to irradiation. The largest KBOs, such as Pluto and Quaoar , have surfaces rich in volatile compounds such as methane, nitrogen and carbon monoxide ; the presence of these molecules

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3936-502: Is likely due to their moderate vapor pressure in the 30–50 K temperature range of the Kuiper belt. This allows them to occasionally boil off their surfaces and then fall again as snow, whereas compounds with higher boiling points would remain solid. The relative abundances of these three compounds in the largest KBOs is directly related to their surface gravity and ambient temperature, which determines which they can retain. Water ice has been detected in several KBOs, including members of

4059-532: Is not clear whether it is actually the outer edge of the classical belt or just the beginning of a broad gap. Objects have been detected at the 2:5 resonance at roughly 55 AU, well outside the classical belt; predictions of a large number of bodies in classical orbits between these resonances have not been verified through observation. Based on estimations of the primordial mass required to form Uranus and Neptune, as well as bodies as large as Pluto (see § Mass and size distribution ) , earlier models of

4182-408: Is observed with increasing levels of angular momentum: The indicative timescale that governs the short-term evolution of accretion onto binaries within circumbinary disks is the binary's orbital period P b {\displaystyle P_{b}} . Accretion into the inner cavity is not constant, and varies depending on e b {\displaystyle e_{b}} and

4305-446: Is the inner radius. Protoplanetary disks and debris disks can be imaged with different methods. If the disk is seen edge-on, the disk can sometimes block the light of the star and the disk can be directly observed without a coronagraph or other advanced techniques (e.g. Gomez's Hamburger or Flying Saucer Nebula ). Other edge-on disks (e.g. Beta Pictoris or AU Microscopii ) and face-on disks (e.g. IM Lupi or AB Aurigae ) require

4428-406: Is the radial location in the disc and ν {\displaystyle \nu } is the viscosity at location r {\displaystyle r} . This equation assumes axisymmetric symmetry in the disc, but is compatible with any vertical disc structure. Viscosity in the disc, whether molecular, turbulent or other, transports angular momentum outwards in the disc and most of

4551-472: Is the same as the binary orbital period due to each binary component scooping in matter from the circumbinary disk each time it reaches the apocenter of its orbit. Eccentric binaries also see accretion variability over secular timescales hundreds of times the binary period. This corresponds to the apsidal precession rate of the inner edge of the cavity, which develops its own eccentricity e d {\displaystyle e_{d}} , along with

4674-610: The Hubble Space Telescope , by the timing of an occultation when an object passes in front of a star or, most commonly, by using the albedo of an object calculated from its infrared emissions. The masses are determined using the semi-major axes and periods of satellites, which are therefore known only for a few binary objects. The densities range from less than 0.4 to 2.6 g/cm. The least dense objects are thought to be largely composed of ice and have significant porosity. The densest objects are likely composed of rock with

4797-421: The Hubble Space Telescope . The first reports of these occultations were from Schlichting et al. in December 2009, who announced the discovery of a small, sub-kilometre-radius Kuiper belt object in archival Hubble photometry from March 2007. With an estimated radius of 520 ± 60 m or a diameter of 1040 ± 120 m , the object was detected by Hubble 's star tracking system when it briefly occulted

4920-718: The Kitt Peak National Observatory in Arizona and the Cerro Tololo Inter-American Observatory in Chile, Jewitt and Luu conducted their search in much the same way as Clyde Tombaugh and Charles Kowal had, with a blink comparator . Initially, examination of each pair of plates took about eight hours, but the process was sped up with the arrival of electronic charge-coupled devices or CCDs, which, though their field of view

5043-480: The Oort cloud or out of the Solar System; there would not be a Kuiper belt today if this were correct. The hypothesis took many other forms in the following decades. In 1962, physicist Al G.W. Cameron postulated the existence of "a tremendous mass of small material on the outskirts of the solar system". In 1964, Fred Whipple , who popularised the famous " dirty snowball " hypothesis for cometary structure, thought that

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5166-550: The Solar System formed . While many asteroids are composed primarily of rock and metal , most Kuiper belt objects are composed largely of frozen volatiles (termed "ices"), such as methane , ammonia , and water . The Kuiper belt is home to most of the objects that astronomers generally accept as dwarf planets : Orcus , Pluto , Haumea , Quaoar , and Makemake . Some of the Solar System's moons , such as Neptune's Triton and Saturn 's Phoebe , may have originated in

5289-421: The ecliptic plane and a more diffuse distribution of objects extending several times farther. Overall it more resembles a torus or doughnut than a belt. Its mean position is inclined to the ecliptic by 1.86 degrees. The presence of Neptune has a profound effect on the Kuiper belt's structure due to orbital resonances . Over a timescale comparable to the age of the Solar System, Neptune's gravity destabilises

5412-568: The origin or evolution of stars , or the formation of galaxies . A related but distinct subject is physical cosmology , which studies the Universe as a whole. Astronomers usually fall under either of two main types: observational and theoretical . Observational astronomers make direct observations of celestial objects and analyze the data. In contrast, theoretical astronomers create and investigate models of things that cannot be observed. Because it takes millions to billions of years for

5535-399: The scattered disc . The scattered disc was created when Neptune migrated outward into the proto-Kuiper belt, which at the time was much closer to the Sun, and left in its wake a population of dynamically stable objects that could never be affected by its orbit (the Kuiper belt proper), and a population whose perihelia are close enough that Neptune can still disturb them as it travels around

5658-426: The 2:3 and 1:2 resonances with Neptune, at approximately 42–48 AU, the gravitational interactions with Neptune occur over an extended timescale, and objects can exist with their orbits essentially unaltered. This region is known as the classical Kuiper belt , and its members comprise roughly two thirds of KBOs observed to date. Because the first modern KBO discovered ( Albion , but long called (15760) 1992 QB 1 ),

5781-511: The Canadian team of Martin Duncan, Tom Quinn and Scott Tremaine ran a number of computer simulations to determine if all observed comets could have arrived from the Oort cloud. They found that the Oort cloud could not account for all short-period comets, particularly as short-period comets are clustered near the plane of the Solar System, whereas Oort-cloud comets tend to arrive from any point in

5904-454: The Haumea family such as 1996 TO 66 , mid-sized objects such as 38628 Huya and 20000 Varuna , and also on some small objects. The presence of crystalline ice on large and mid-sized objects, including 50000 Quaoar where ammonia hydrate has also been detected, may indicate past tectonic activity aided by melting point lowering due to the presence of ammonia. Despite its vast extent,

6027-520: The Kuiper belt had suggested that the number of large objects would increase by a factor of two beyond 50 AU, so this sudden drastic falloff, known as the Kuiper cliff , was unexpected, and to date its cause is unknown. Bernstein, Trilling, et al. (2003) found evidence that the rapid decline in objects of 100 km or more in radius beyond 50 AU is real, and not due to observational bias . Possible explanations include that material at that distance

6150-574: The Kuiper belt object size distribution slope to be q = 3.6 ± 0.2 or q = 3.8 ± 0.2, with the assumptions of a single power law and a uniform ecliptic latitude distribution. Their result implies a strong deficit of sub-kilometer-sized Kuiper belt objects compared to extrapolations from the population of larger Kuiper belt objects with diameters above 90 km. Observations made by NASA's New Horizons Venetia Burney Student Dust Counter showed "higher than model-predicted dust fluxes" as far as 55 au, not explained by any existing model. The scattered disc

6273-459: The Kuiper belt, are also thought to be scattered objects, the only difference being that they were scattered inward, rather than outward. The Minor Planet Center groups the centaurs and the SDOs together as scattered objects. Circumstellar disc According to the widely accepted model of star formation, sometimes referred to as the nebular hypothesis , a young star ( protostar ) is formed by

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6396-430: The Kuiper belt. At its fullest extent (but excluding the scattered disc), including its outlying regions, the Kuiper belt stretches from roughly 30–55 AU. The main body of the belt is generally accepted to extend from the 2:3 mean-motion resonance ( see below ) at 39.5 AU to the 1:2 resonance at roughly 48 AU. The Kuiper belt is quite thick, with the main concentration extending as much as ten degrees outside

6519-545: The PhD level and beyond (as of 2024). Contrary to the classical image of an old astronomer peering through a telescope through the dark hours of the night, it is far more common to use a charge-coupled device (CCD) camera to record a long, deep exposure, allowing a more sensitive image to be created because the light is added over time. Before CCDs, photographic plates were a common method of observation. Modern astronomers spend relatively little time at telescopes, usually just

6642-408: The Solar System begin with five giant planets, including an additional ice giant , in a chain of mean-motion resonances. About 400 million years after the formation of the Solar System the resonance chain is broken. Instead of being scattered into the disc, the ice giants first migrate outward several AU. This divergent migration eventually leads to a resonance crossing, destabilizing the orbits of

6765-408: The Solar System's history would have led to migration of the orbits of the giant planets: Saturn , Uranus, and Neptune drifted outwards, whereas Jupiter drifted inwards. Eventually, the orbits shifted to the point where Jupiter and Saturn reached an exact 1:2 resonance; Jupiter orbited the Sun twice for every one Saturn orbit. The gravitational repercussions of such a resonance ultimately destabilized

6888-603: The Sun (the scattered disc). Because the scattered disc is dynamically active and the Kuiper belt relatively dynamically stable, the scattered disc is now seen as the most likely point of origin for periodic comets. Astronomers sometimes use the alternative name Edgeworth–Kuiper belt to credit Edgeworth, and KBOs are occasionally referred to as EKOs. Brian G. Marsden claims that neither deserves true credit: "Neither Edgeworth nor Kuiper wrote about anything remotely like what we are now seeing, but Fred Whipple did". David Jewitt comments: "If anything ... Fernández most nearly deserves

7011-464: The Sun that failed to fully coalesce into planets and instead formed into smaller bodies, the largest less than 3,000 kilometres (1,900 mi) in diameter. Studies of the crater counts on Pluto and Charon revealed a scarcity of small craters suggesting that such objects formed directly as sizeable objects in the range of tens of kilometers in diameter rather than being accreted from much smaller, roughly kilometer scale bodies. Hypothetical mechanisms for

7134-489: The University of Hawaii's 2.24 m telescope at Mauna Kea . Eventually, the field of view for CCDs had increased to 1024 by 1024 pixels, which allowed searches to be conducted far more rapidly. Finally, after five years of searching, Jewitt and Luu announced on 30 August 1992 the "Discovery of the candidate Kuiper belt object 1992 QB 1 ". This object would later be named 15760 Albion. Six months later, they discovered

7257-431: The age of the Solar System, they must be replenished frequently. A proposal for such an area of replenishment is the Oort cloud , possibly a spherical swarm of comets extending beyond 50,000 AU from the Sun first hypothesised by Dutch astronomer Jan Oort in 1950. The Oort cloud is thought to be the point of origin of long-period comets , which are those, like Hale–Bopp , with orbits lasting thousands of years. There

7380-452: The agglomeration of larger objects into planetesimals , and the growth and orbital evolution of planetesimals into the planetary systems, like our Solar System or many other stars. Major stages of evolution of circumstellar discs: Material dissipation is one of the processes responsible for circumstellar discs evolution. Together with information about the mass of the central star, observation of material dissipation at different stages of

7503-484: The behavior of the gas along the innermost region of the cavity. For non-eccentric binaries, accretion variability coincides with the Keplerian orbital period of the inner gas, which develops lumps corresponding to m = 1 {\displaystyle m=1} outer Lindblad resonances. This period is approximately five times the binary orbital period. For eccentric binaries, the period of accretion variability

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7626-413: The binary orbit as a result of the same differential torque which creates spiral density waves in an axissymmetric disk. Evidence of tilted circumbinary disks can be seen through warped geometry within circumstellar disks, precession of protostellar jets, and inclined orbits of circumplanetary objects (as seen in the eclipsing binary TY CrA). For disks orbiting a low secondary-to-primary mass ratio binary,

7749-411: The binary. Binaries with a period longer than one month showed typically a misalignment of the disk with the binary orbit. Stages in circumstellar discs refer to the structure and the main composition of the disc at different times during its evolution. Stages include the phases when the disc is composed mainly of submicron-sized particles, the evolution of these particles into grains and larger objects,

7872-410: The centaurs therefore must be frequently replenished by some outer reservoir. Further evidence for the existence of the Kuiper belt later emerged from the study of comets. That comets have finite lifespans has been known for some time. As they approach the Sun, its heat causes their volatile surfaces to sublimate into space, gradually dispersing them. In order for comets to continue to be visible over

7995-519: The central star ( stellar wind ), or the dynamical influence of a giant planet forming within the disc are some of the processes that have been proposed to explain dissipation. Dissipation is a process that occurs continuously in circumstellar discs throughout the lifetime of the central star, and at the same time, for the same stage, is a process that is present in different parts of the disc. Dissipation can be divided in inner disc dissipation, mid-disc dissipation, and outer disc dissipation, depending on

8118-527: The central star, mainly in the form of gas which is itself mainly hydrogen . The main accretion phase lasts a few million years, with accretion rates typically between 10 and 10 solar masses per year (rates for typical systems presented in Hartmann et al. ). The disc gradually cools in what is known as the T Tauri star stage. Within this disc, the formation of small dust grains made of rocks and ices can occur, and these can coagulate into planetesimals . If

8241-429: The cold belt into the 1:2 mean-motion resonance with Neptune are left behind as a local concentration at 44 AU when this encounter causes Neptune's semi-major axis to jump outward. The objects deposited in the cold belt include some loosely bound 'blue' binaries originating from closer than the cold belt's current location. If Neptune's eccentricity remains small during this encounter, the chaotic evolution of orbits of

8364-467: The collective mass of the Kuiper belt is relatively low. The total mass of the dynamically hot population is estimated to be 1% the mass of the Earth . The dynamically cold population is estimated to be much smaller with only 0.03% the mass of the Earth. While the dynamically hot population is thought to be the remnant of a much larger population that formed closer to the Sun and was scattered outward during

8487-408: The comets, in size, number and composition." According to Kuiper "the planet Pluto, which sweeps through the whole zone from 30 to 50 astr. units, is held responsible for having started the scattering of the comets throughout the solar system." It is said that Kuiper was operating on the assumption, common in his time, that Pluto was the size of Earth and had therefore scattered these bodies out toward

8610-421: The core sciences, a competency examination, experience with teaching undergraduates and participating in outreach programs, work on research projects under the student's supervising professor, completion of a PhD thesis , and passing a final oral exam . Throughout the PhD training, a successful student is financially supported with a stipend . While there is a relatively low number of professional astronomers,

8733-477: The credit for predicting the Kuiper Belt." KBOs are sometimes called "kuiperoids", a name suggested by Clyde Tombaugh . The term " trans-Neptunian object " (TNO) is recommended for objects in the belt by several scientific groups because the term is less controversial than all others—it is not an exact synonym though, as TNOs include all objects orbiting the Sun past the orbit of Neptune , not just those in

8856-485: The currently most popular model, the " Nice model ", reproduces many characteristics of the Kuiper belt such as the "cold" and "hot" populations, resonant objects, and a scattered disc, but it still fails to account for some of the characteristics of their distributions. The model predicts a higher average eccentricity in classical KBO orbits than is observed (0.10–0.13 versus 0.07) and its predicted inclination distribution contains too few high inclination objects. In addition,

8979-418: The defined Kuiper belt region regardless of origin or composition. Objects found outside the belt are classed as scattered objects. In some scientific circles the term "Kuiper belt object" has become synonymous with any icy minor planet native to the outer Solar System assumed to have been part of that initial class, even if its orbit during the bulk of Solar System history has been beyond the Kuiper belt (e.g. in

9102-538: The disc is sufficiently massive, the runaway accretions begin, resulting in the appearance of planetary embryos. The formation of planetary systems is thought to be a natural result of star formation. A sun-like star usually takes around 100 million years to form. The infall of gas onto a binary system allows the formation of circumstellar and circumbinary discs. The formation of such a disc will occur for any binary system in which infalling gas contains some degree of angular momentum. A general progression of disc formation

9225-450: The disk. Astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth . Astronomers observe astronomical objects , such as stars , planets , moons , comets and galaxies – in either observational (by analyzing the data) or theoretical astronomy . Examples of topics or fields astronomers study include planetary science , solar astronomy ,

9348-404: The disk. Radio arrays like ALMA can also detect narrow emission from the gas of the disk. This can reveal the velocity of the gas within and around the disk. In some cases an edge-on protoplanetary disk (e.g. CK 3 or ASR 41 ) can cast a shadow onto the surrounding dusty material. This cast shadow works like a shadow play , and the projection of the disk is much larger than the true size of

9471-411: The ecliptic, by up to 30°. The two populations have been named this way not because of any major difference in temperature, but from analogy to particles in a gas, which increase their relative velocity as they become heated up. Not only are the two populations in different orbits, the cold population also differs in color and albedo , being redder and brighter, has a larger fraction of binary objects, has

9594-474: The field is popular among amateurs . Most cities have amateur astronomy clubs that meet on a regular basis and often host star parties . The Astronomical Society of the Pacific is the largest general astronomical society in the world, comprising both professional and amateur astronomers as well as educators from 70 different nations. As with any hobby , most people who practice amateur astronomy may devote

9717-489: The field. Those who become astronomers usually have a broad background in physics, mathematics , sciences, and computing in high school. Taking courses that teach how to research, write, and present papers are part of the higher education of an astronomer, while most astronomers attain both a Master's degree and eventually a PhD degree in astronomy, physics or astrophysics . PhD training typically involves 5-6 years of study, including completion of upper-level courses in

9840-660: The formation of these larger bodies include the gravitational collapse of clouds of pebbles concentrated between eddies in a turbulent protoplanetary disk or in streaming instabilities . These collapsing clouds may fragment, forming binaries. Modern computer simulations show the Kuiper belt to have been strongly influenced by Jupiter and Neptune , and also suggest that neither Uranus nor Neptune could have formed in their present positions, because too little primordial matter existed at that range to produce objects of such high mass. Instead, these planets are estimated to have formed closer to Jupiter. Scattering of planetesimals early in

9963-463: The frequency of binary objects in the cold belt, many of which are far apart and loosely bound, also poses a problem for the model. These are predicted to have been separated during encounters with Neptune, leading some to propose that the cold disc formed at its current location, representing the only truly local population of small bodies in the solar system. A recent modification of the Nice model has

10086-490: The future LSST , which should reveal many currently unknown KBOs. These surveys will provide data that will help determine answers to these questions. Pan-STARRS 1 finished its primary science mission in 2014, and the full data from the Pan-STARRS 1 surveys were published in 2019, helping reveal many more KBOs. The Kuiper belt is thought to consist of planetesimals , fragments from the original protoplanetary disc around

10209-613: The giant planets. In a paper published in Monthly Notices of the Royal Astronomical Society in 1980, Uruguayan astronomer Julio Fernández stated that for every short-period comet to be sent into the inner Solar System from the Oort cloud, 600 would have to be ejected into interstellar space . He speculated that a comet belt from between 35 and 50 AU would be required to account for the observed number of comets. Following up on Fernández's work, in 1988

10332-438: The giant planets. The cold population, on the other hand, has been proposed to have formed more or less in its current position because the loose binaries would be unlikely to survive encounters with Neptune. Although the Nice model appears to be able to at least partially explain a compositional difference, it has also been suggested the color difference may reflect differences in surface evolution. When an object's orbital period

10455-400: The gravitational collapse of a pocket of matter within a giant molecular cloud . The infalling material possesses some amount of angular momentum , which results in the formation of a gaseous protoplanetary disc around the young, rotating star. The former is a rotating circumstellar disc of dense gas and dust that continues to feed the central star. It may contain a few percent of the mass of

10578-518: The gravitational torque of the circumbinary disk, primarily from material at the innermost edge of the excised cavity. This decay is no longer guaranteed when accretion from the circumbinary disk onto the binary occurs, and can even lead to increased binary separations. The dynamics of orbital evolution depend on the binary's parameters, such as the mass ratio q b {\displaystyle q_{b}} and eccentricity e b {\displaystyle e_{b}} , as well as

10701-476: The hot objects is q = 5.3 at large diameters and q = 2.0 at small diameters with the change in slope at 110 km. The slope for the cold objects is q = 8.2 at large diameters and q = 2.9 at small diameters with a change in slope at 140 km. The size distributions of the scattering objects , the plutinos, and the Neptune trojans have slopes similar to the other dynamically hot populations, but may instead have

10824-498: The inner solar system", becoming a comet . In 1951, in a paper in Astrophysics: A Topical Symposium , Gerard Kuiper speculated on a similar disc having formed early in the Solar System's evolution and concluded that the disc consisted of "remnants of original clusterings which have lost many members that became stray asteroids, much as has occurred with open galactic clusters dissolving into stars." In another paper, based upon

10947-529: The known Kuiper belt objects in 2001 found that the variation in color was too extreme to be easily explained by random impacts. The radiation from the Sun is thought to have chemically altered methane on the surface of KBOs, producing products such as tholins . Makemake has been shown to possess a number of hydrocarbons derived from the radiation-processing of methane, including ethane , ethylene and acetylene . Although to date most KBOs still appear spectrally featureless due to their faintness, there have been

11070-448: The larger object may have formed directly from the collapse of clouds of pebbles. The size distributions of the Kuiper belt objects follow a number of power laws . A power law describes the relationship between N ( D ) (the number of objects of diameter greater than D ) and D , and is referred to as brightness slope. The number of objects is inversely proportional to some power of the diameter D : (The constant may be non-zero only if

11193-694: The majority of their time working on research, although they quite often have other duties such as teaching, building instruments, or aiding in the operation of an observatory. The American Astronomical Society , which is the major organization of professional astronomers in North America , has approximately 8,200 members (as of 2024). This number includes scientists from other fields such as physics, geology , and engineering , whose research interests are closely related to astronomy. The International Astronomical Union comprises about 12,700 members from 92 countries who are involved in astronomical research at

11316-468: The makeup of the earliest Solar System. Due to their small size and extreme distance from Earth, the chemical makeup of KBOs is very difficult to determine. The principal method by which astronomers determine the composition of a celestial object is spectroscopy . When an object's light is broken into its component colors, an image akin to a rainbow is formed. This image is called a spectrum . Different substances absorb light at different wavelengths, and when

11439-646: The mass inwards, eventually accreting onto the central object. The mass accretion onto the star M ˙ {\displaystyle {\dot {M}}} in terms of the disc viscosity ν {\displaystyle \nu } is expressed: M ˙ = 3 π ν Σ [ 1 − r in r ] − 1 {\displaystyle {\dot {M}}=3\pi \nu \Sigma \left[1-{\sqrt {\frac {r_{\text{in}}}{r}}}\right]^{-1}} where r in {\displaystyle r_{\text{in}}}

11562-415: The mid-1990s have shown that the belt is dynamically stable and that comets' true place of origin is the scattered disc , a dynamically active zone created by the outward motion of Neptune 4.5 billion years ago; scattered disc objects such as Eris have extremely eccentric orbits that take them as far as 100 AU from the Sun. The Kuiper belt is distinct from the hypothesized Oort cloud , which

11685-551: The migrating Neptune. IAU guidelines dictate that all plutinos must, like Pluto, be named for underworld deities. The 1:2 resonance (whose objects complete half an orbit for each of Neptune's) corresponds to semi-major axes of ~47.7 AU, and is sparsely populated. Its residents are sometimes referred to as twotinos . Other resonances also exist at 3:4, 3:5, 4:7, and 2:5. Neptune has a number of trojan objects , which occupy its Lagrangian points , gravitationally stable regions leading and trailing it in its orbit. Neptune trojans are in

11808-437: The migration of the giant planets, in contrast, the dynamically cold population is thought to have formed at its current location. The most recent estimate (2018) puts the total mass of the Kuiper belt at (1.97 ± 0.30) × 10 Earth masses based on the influence that it exerts on the motion of planets. The small total mass of the dynamically cold population presents some problems for models of the Solar System's formation because

11931-698: The orbits of Uranus and Neptune, causing them to be scattered outward onto high-eccentricity orbits that crossed the primordial planetesimal disc. While Neptune's orbit was highly eccentric, its mean-motion resonances overlapped and the orbits of the planetesimals evolved chaotically, allowing planetesimals to wander outward as far as Neptune's 1:2 resonance to form a dynamically cold belt of low-inclination objects. Later, after its eccentricity decreased, Neptune's orbit expanded outward toward its current position. Many planetesimals were captured into and remain in resonances during this migration, others evolved onto higher-inclination and lower-eccentricity orbits and escaped from

12054-547: The orbits of any objects that happen to lie in certain regions, and either sends them into the inner Solar System or out into the scattered disc or interstellar space. This causes the Kuiper belt to have pronounced gaps in its current layout, similar to the Kirkwood gaps in the asteroid belt . In the region between 40 and 42 AU, for instance, no objects can retain a stable orbit over such times, and any observed in that region must have migrated there relatively recently. Between

12177-522: The original Nice model is avoided and a primordial cold belt is preserved. In the later phases of Neptune's migration, a slow sweeping of mean-motion resonances removes the higher-eccentricity objects from the cold belt, truncating its eccentricity distribution. Being distant from the Sun and major planets, Kuiper belt objects are thought to be relatively unaffected by the processes that have shaped and altered other Solar System objects; thus, determining their composition would provide substantial information on

12300-472: The outer rim of the classical Kuiper belt resembles that of the outer main asteroid belt with a gap at about 72 AU, far from any mean-motion resonances with Neptune; the outer main asteroid belt exhibits a gap induced by the 5:6 mean-motion resonance with Jupiter at 5.875 AU. The precise origins of the Kuiper belt and its complex structure are still unclear, and astronomers are awaiting the completion of several wide-field survey telescopes such as Pan-STARRS and

12423-410: The part of the disc considered. Inner disc dissipation occurs at the inner part of the disc (< 0.05 – 0.1 AU ). Since it is closest to the star, this region is also the hottest, thus material present there typically emits radiation in the near-infrared region of the electromagnetic spectrum . Study of the radiation emitted by the very hot dust present in that part of the disc indicates that there

12546-451: The planets. The extra ice giant encounters Saturn and is scattered inward onto a Jupiter-crossing orbit and after a series of encounters is ejected from the Solar System. The remaining planets then continue their migration until the planetesimal disc is nearly depleted with small fractions remaining in various locations. As in the original Nice model, objects are captured into resonances with Neptune during its outward migration. Some remain in

12669-410: The planets; nearly circular, with an orbital eccentricity of less than 0.1, and with relatively low inclinations up to about 10° (they lie close to the plane of the Solar System rather than at an angle). The cold population also contains a concentration of objects, referred to as the kernel, with semi-major axes at 44–44.5 AU. The second, the "dynamically hot" population, has orbits much more inclined to

12792-434: The power law doesn't apply at high values of D .) Early estimates that were based on measurements of the apparent magnitude distribution found a value of q = 4 ± 0.5, which implied that there are 8 (=2) times more objects in the 100–200 km range than in the 200–400 km range. Recent research has revealed that the size distributions of the hot classical and cold classical objects have differing slopes. The slope for

12915-467: The region beyond Neptune , the material within the primordial solar nebula was too widely spaced to condense into planets, and so rather condensed into a myriad smaller bodies. From this he concluded that "the outer region of the solar system, beyond the orbits of the planets, is occupied by a very large number of comparatively small bodies" and that, from time to time, one of their number "wanders from its own sphere and appears as an occasional visitor to

13038-457: The region. The Kuiper belt is named in honor of the Dutch astronomer Gerard Kuiper , who conjectured the existence of the belt in 1951. There were researchers before and after him who also speculated on its existence, such as Kenneth Edgeworth in the 1930s. The astronomer Julio Angel Fernandez published a paper in 1980 suggesting the existence of a comet belt beyond Neptune which could serve as

13161-409: The resonances onto stable orbits. Many more planetesimals were scattered inward, with small fractions being captured as Jupiter trojans, as irregular satellites orbiting the giant planets, and as outer belt asteroids. The remainder were scattered outward again by Jupiter and in most cases ejected from the Solar System reducing the primordial Kuiper belt population by 99% or more. The original version of

13284-415: The resonances, others evolve onto higher-inclination, lower-eccentricity orbits, and are released onto stable orbits forming the dynamically hot classical belt. The hot belt's inclination distribution can be reproduced if Neptune migrated from 24 AU to 30 AU on a 30 Myr timescale. When Neptune migrates to 28 AU, it has a gravitational encounter with the extra ice giant. Objects captured from

13407-463: The same device that had allowed Clyde Tombaugh to discover Pluto nearly 50 years before. In 1992, another object, 5145 Pholus , was discovered in a similar orbit. Today, an entire population of comet-like bodies, called the centaurs , is known to exist in the region between Jupiter and Neptune. The centaurs' orbits are unstable and have dynamical lifetimes of a few million years. From the time of Chiron's discovery in 1977, astronomers have speculated that

13530-717: The same relative position as it began, because it will have completed 1 + 1 ⁄ 2 orbits in the same time. This is known as the 2:3 (or 3:2) resonance, and it corresponds to a characteristic semi-major axis of about 39.4 AU. This 2:3 resonance is populated by about 200 known objects, including Pluto together with its moons . In recognition of this, the members of this family are known as plutinos . Many plutinos, including Pluto, have orbits that cross that of Neptune, although their resonance means they can never collide. Plutinos have high orbital eccentricities, suggesting that they are not native to their current positions but were instead thrown haphazardly into their orbits by

13653-507: The scattered disc. Due to its unstable nature, the scattered disc is suspected to be the point of origin of many of the Solar System's short-period comets. Their dynamic orbits occasionally force them into the inner Solar System, first becoming centaurs , and then short-period comets. According to the Minor Planet Center , which officially catalogues all trans-Neptunian objects, a KBO is any object that orbits exclusively within

13776-403: The scattered disc. Originally considered a planet, Pluto's status as part of the Kuiper belt caused it to be reclassified as a dwarf planet in 2006. It is compositionally similar to many other objects of the Kuiper belt, and its orbital period is characteristic of a class of KBOs, known as " plutinos ," that share the same 2:3 resonance with Neptune. The Kuiper belt and Neptune may be treated as

13899-412: The scattered-disc region). They often describe scattered disc objects as "scattered Kuiper belt objects". Eris , which is known to be more massive than Pluto, is often referred to as a KBO, but is technically an SDO. A consensus among astronomers as to the precise definition of the Kuiper belt has yet to be reached, and this issue remains unresolved. The centaurs, which are not normally considered part of

14022-617: The sky. With a "belt", as Fernández described it, added to the formulations, the simulations matched observations. Reportedly because the words "Kuiper" and "comet belt" appeared in the opening sentence of Fernández's paper, Tremaine named this hypothetical region the "Kuiper belt". In 1987, astronomer David Jewitt , then at MIT , became increasingly puzzled by "the apparent emptiness of the outer Solar System". He encouraged then-graduate student Jane Luu to aid him in his endeavour to locate another object beyond Pluto 's orbit, because, as he told her, "If we don't, nobody will." Using telescopes at

14145-412: The spectrum for a specific object is unravelled, dark lines (called absorption lines ) appear where the substances within it have absorbed that particular wavelength of light. Every element or compound has its own unique spectroscopic signature, and by reading an object's full spectral "fingerprint", astronomers can determine its composition. Analysis indicates that Kuiper belt objects are composed of

14268-485: The thermodynamics of the accreting gas. Once a circumstellar disk has formed, spiral density waves are created within the circumstellar material via a differential torque due to the binary's gravity. The majority of these discs form axissymmetric to the binary plane, but it is possible for processes such as the Bardeen-Petterson effect, a misaligned dipole magnetic field and radiation pressure to produce

14391-624: The timescale of this region's dissipation. Studies made to determine the dissipation timescale in this region provide a wide range of values, predicting timescales from less than 10 up to 100 Myr. Outer disc dissipation occurs in regions between 50 – 100 AU , where temperatures are much lower and emitted radiation wavelength increases to the millimeter region of the electromagnetic spectrum . Mean dust masses for this region has been reported to be ~ 10 solar masses. Studies of older debris discs (10 - 10 yr) suggest dust masses as low as 10 solar masses, implying that diffusion in outer discs occurs on

14514-458: The unmanned spacecraft New Horizons conducted the first KBO flybys, providing much closer observations of the Plutonian system (2015) and then Arrokoth (2019). Studies conducted since the trans-Neptunian region was first charted have shown that the region now called the Kuiper belt is not the point of origin of short-period comets, but that they instead derive from a linked population called

14637-658: Was "not likely that in Pluto there has come to light the first of a series of ultra-Neptunian bodies, the remaining members of which still await discovery but which are destined eventually to be detected". That same year, astronomer Armin O. Leuschner suggested that Pluto "may be one of many long-period planetary objects yet to be discovered." In 1943, in the Journal of the British Astronomical Association , Kenneth Edgeworth hypothesized that, in

14760-498: Was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using physical laws . Today, that distinction has mostly disappeared and the terms "astronomer" and "astrophysicist" are interchangeable. Professional astronomers are highly educated individuals who typically have a PhD in physics or astronomy and are employed by research institutions or universities. They spend

14883-521: Was narrower, were not only more efficient at collecting light (they retained 90% of the light that hit them, rather than the 10% achieved by photographs) but allowed the blinking process to be done virtually, on a computer screen. Today, CCDs form the basis for most astronomical detectors. In 1988, Jewitt moved to the Institute of Astronomy at the University of Hawaii . Luu later joined him to work at

15006-434: Was only in 1992 that the first direct evidence for its existence was found. The number and variety of prior speculations on the nature of the Kuiper belt have led to continued uncertainty as to who deserves credit for first proposing it. The first astronomer to suggest the existence of a trans-Neptunian population was Frederick C. Leonard . Soon after Pluto's discovery by Clyde Tombaugh in 1930, Leonard pondered whether it

15129-457: Was too scarce or too scattered to accrete into large objects, or that subsequent processes removed or destroyed those that did. Patryk Lykawka of Kobe University claimed that the gravitational attraction of an unseen large planetary object , perhaps the size of Earth or Mars , might be responsible. An analysis of the TNO data available prior to September 2023 shows that the distribution of objects at

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