The Kuiper belt (/ˈkaɪpər/), occasionally called the Edgeworth–Kuiper belt, is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune (at 30 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 to 200 times as massive. Like the asteroid belt, it consists mainly of small bodies or remnants from when 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 three officially recognized dwarf planets: Pluto, Haumea and Makemake. Some of the Solar System’s moons, such as Neptune’s Triton and Saturn‘s Phoebe, may have originated in the region.
柯伊伯带（/ ˈkaɪpər /）有时被称为埃奇沃思-库伊珀带，是外太阳系中的一个恒星盘，从海王星的轨道（30 AU）延伸到太阳约50 AU。 2]它与小行星带相似，但远大于小行星带-宽20倍，大20-200倍。 像小行星带一样，它主要由小物体或太阳系形成时的残余物组成。尽管许多小行星主要由岩石和金属组成，但大多数柯伊伯带天体主要由冷冻挥发物（称为“冰”）组成，例如甲烷，氨和水。柯伊伯带是三个公认的矮行星的所在地：冥王星，豪梅阿和马克马克。太阳系的某些卫星，例如海王星的海卫一和土星的菲比，可能起源于该地区。 
The Kuiper belt was named after Dutch-American astronomer Gerard Kuiper, though he did not predict its existence. In 1992, Albion was discovered, the first Kuiper belt object (KBO) since Pluto and Charon. 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 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.[nb 1]
柯伊伯带以荷兰裔美国天文学家杰拉德·柯伊伯（Gerard Kuiper）的名字命名，尽管他没有预言它的存在。 1992年，阿尔比恩（Albion）被发现，这是冥王星和夏隆（Charon）之后的第一个柯伊伯带天体（KBO）。自发现以来，已知的KBO数量已增加到数千个，并且直径超过100公里（62英里）的100,000个KBO被认为存在。最初认为柯伊伯带是周期性彗星（轨道持续时间不到200年的彗星）的主要存放地。自1990年代中期以来的研究表明，该带是动态稳定的，并且彗星的真正起源是散布的盘，这是一个由45亿年前海王星向外运动形成的动态活动区； 因为埃里斯（Eris）的轨道非常偏心，所以它们离太阳的距离可达100 AU。[nb 1]
The Kuiper belt is distinct from the theoretical Oort cloud, which is a thousand times more distant and is 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 the scattered disc.[nb 1] 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.
柯伊伯带与理论上的奥尔特云不同，后者的距离是奥特云的千倍，并且大部分为球形。柯伊伯带内的物体与散布盘的成员以及任何潜在的希尔斯云或奥尔特云的物体一起统称为海王星横穿天体（TNO）。冥王星是柯伊伯带中最大，质量最大的成员，也是已知的最大，第二大质量的TNO，仅在散布的盘片中被埃里斯超越。[nb 1]最初被认为是行星，冥王星是行星的一部分。柯伊伯带使它在2006年被重新归类为矮行星。它的构成与柯伊伯带的许多其他天体相似，并且其轨道周期是一类KBO（称为“ plutinos”）的特征，它们具有相同的2： 3与海王星共鸣。
The Kuiper Belt and Neptune are noted as one of the ways to define the extent of the Solar System, along with the heliopause and the radius at which the Sun’s gravitational influence is matched by other stars, estimated to be between 50000 AU to about 2 light-years.
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 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.
1930年冥王星被发现后，许多人猜测它可能并不孤单。 几十年来，人们以各种形式假设了现在称为柯伊伯带的区域。 直到1992年，它的存在才找到了第一个直接证据。 先前关于柯伊伯带性质的推测的数量和种类繁多，导致对于谁应该首先提出该提议值得赞扬的不确定性持续存在。
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 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.”
第一个暗示存在海王星跨界人口的天文学家是Frederick C. Leonard。 克莱德·汤博（Clyde Tombaugh）在1930年发现冥王星后不久，伦纳德（Leonard）思索“在冥王星中是否有可能发现了一系列超海王星天体中的第一个，剩下的成员仍在等待发现，但最终将有目的地 被检测到。”  同年，天文学家Armin O. Leuschner建议冥王星“可能是许多尚待发现的长周期行星天体之一。” 
Astronomer Gerard Kuiper, after whom the Kuiper belt is named
In 1943, in the Journal of the British Astronomical Association, Kenneth Edgeworth hypothesized that, in 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 of 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 the inner solar system”, becoming a comet.
1943年，肯尼思·埃奇沃思（Kenneth Edgeworth）在《英国天文学协会杂志》中假设，在海王星以外的区域中，原始太阳星云中的物质分布太宽，无法凝结成行星，因此凝结成无数个较小的天体。 由此他得出结论，“太阳系的外部区域，超出了行星的轨道，被大量的相对较小的天体占据” ，并且不时地，它们的其中之一“徘徊”。 变成了一颗彗星。
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, but he did not think that such a belt still existed today. 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 the Oort cloud or out of the Solar System. Were Kuiper’s hypothesis correct, there would not be a Kuiper belt today.
1951年，Gerard Kuiper在《天体物理学：一个专题研讨会》上的一篇论文中推测了在太阳系演化初期形成的类似盘状结构，但他认为这样的带状结构至今仍不存在。 柯伊珀以当时普遍的假设为依据，即冥王星是地球的大小，因此将这些天体散布到了奥尔特云或太阳系之外。 如果柯伊伯的假设是正确的，那么今天就不会有柯伊伯带了。
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 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.
在接下来的几十年中，该假设采取了许多其他形式。 1962年，物理学家Al G.W. 卡梅伦推测“在太阳系郊区存在大量的小物质”。 1964年，弗雷德·怀普尔（Fred Whipple）推广了著名的彗星结构“脏雪球”假说，他认为“彗星带”可能足够大，足以引起天王星轨道上的所谓差异，从而引发了对X行星的搜寻，或者 至少足以影响已知彗星的轨道。 观察排除了这一假设。
In 1977, Charles Kowal discovered 2060 Chiron, an icy planetoid with an orbit between Saturn and Uranus. He used a blink comparator, 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 the centaurs therefore must be frequently replenished by some outer reservoir.
1977年，查尔斯·科瓦尔（Charles Kowal）发现了2060 Chiron，这是一颗冰土小行星，在土星和天王星之间运行。 他使用了眨眼比较器，该设备使克莱德·汤博（Clyde Tombaugh）在近50年前发现了冥王星。 1992年，在类似的轨道上发现了另一个物体5145 Pholus。 如今，已知在木星和海王星之间的区域中存在着全部称为彗星的类似彗星的物体。 半人马座的轨道是不稳定的，动力学寿命为几百万年。 从基隆（Chiron）于1977年被发现之时起，天文学家就推测，因此必须经常通过一些外部水库来补充半人马座。
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 the age of the Solar System, they must be replenished frequently. One such area of replenishment is the Oort cloud, 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.
柯伊伯带存在的进一步证据后来从对彗星的研究中获得。 已知彗星的寿命有限已经有一段时间了。 当它们接近太阳时，其热量会导致其挥发性表面升华到太空中，并逐渐分散它们。 为了使彗星在太阳系的整个年龄中继续可见，必须经常补充它们。 这样的补给领域是奥尔特云，这是一个球形的彗星群，从1950年荷兰天文学家扬·奥尔特首先提出的假设开始，就从太阳延伸超过50,000 AU。 奥尔特云被认为是长周期彗星的起源，像Hale–Bopp这样的彗星，其轨道持续了数千年。
There 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 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 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 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”.
继费尔南德斯（Fernández）的工作之后，1988年，加拿大马丁·邓肯（Martin Duncan），汤姆·奎因（Tom Quinn）和斯科特·特雷梅（Scott Tremaine）的加拿大团队进行了许多计算机模拟，以确定是否所有观测到的彗星都可能来自奥尔特云。他们发现奥尔特云无法解释所有短时彗星，特别是短时彗星聚集在太阳系平面附近，而奥尔特云彗星则倾向于从天空的任何点到达。正如费尔南德斯描述的那样，在公式中添加了“皮带”，模拟结果与观察结果相符。据报道，由于费尔南德斯论文的开头句中出现了“ Kuiper”和“彗星地带”两个词，特雷梅因将此假想区域称为“ Kuiper地带”。
The array of telescopes atop Mauna Kea, with which the Kuiper belt was discovered
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 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 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.
1987年，当时在麻省理工学院的天文学家David Jewitt对“外部太阳系的明显空虚”感到越来越困惑。 他鼓励当时的研究生简·卢（Jane Luu）帮助他努力寻找冥王星轨道以外的另一个物体，因为正如他告诉她的那样，“如果我们不这样做，没人会这么做。” 在基特峰国家公园使用望远镜 吉威特和卢进行搜索的过程与亚利桑那州的天文台和智利的塞罗·托洛洛美洲国家天文台的搜索方式几乎相同，而克莱德·汤博和查尔斯·科瓦尔则使用眨眼比较器。 最初，每对板的检查大约需要8个小时，，但是随着电子电荷耦合器件或CCD的出现，该过程加快了，尽管它们的视野较窄，但在 收集光线（它们保留了撞击它们的90％的光线，而不是照片所获取的10％的光线），但允许在计算机屏幕上虚拟完成闪烁过程。
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 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 August 30, 1992 the “Discovery of the candidate Kuiper belt object 1992 QB1”. Six months later, they discovered a second object in the region, (181708) 1993 FW.
如今，CCD构成了大多数天文探测器的基础。 1988年，Jewitt移居到夏威夷大学的天文学研究所。 后来，Luu和他一起在夏威夷大学的莫纳克亚山（Mauna Kea）的2.24 m望远镜上工作。 最终，CCD的视场增加到1024 x 1024像素，这使得搜索的速度大大提高了。 最终，经过五年的搜索，Jewitt和Luu于1992年8月30日宣布“发现柯伊伯带对象1992 QB1候选物”。 六个月后，他们在该地区发现了第二个物体，（181708）1993 FW。
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 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 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.
自从首次绘制海王星横穿海域图以来，进行的研究表明，现在称为柯伊伯带的区域不是短周期彗星的起源点，而是它们来自一个称为散盘的联系种群。 当海王星向外迁移到原库珀带时产生了分散的圆盘，当时该库珀带离太阳更近，并留下了一群动态稳定的物体，这些物体永远不会受到其轨道的影响（柯伊伯带） ）和近日点足够近的海王星在围绕太阳（散布的盘）行进时仍会打扰他们的人群。 由于分散的盘是动态活动的，而柯伊伯带相对稳定，因此，现在将分散的盘视为周期性彗星最可能的起源点。
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 the credit for predicting the Kuiper Belt.”
天文学家有时使用替代名称Edgeworth–Kuiper带来称赞Edgeworth，而KBO有时也称为EKO。 布赖恩·马斯登（Brian G. Marsden）声称都不应该得到应有的荣誉：“埃奇沃思和库珀都没有写过像我们现在看到的那样遥远的东西，但弗雷德·惠普尔做了。”  戴维·杰维特（David Jewitt）评论说：“如果有的话……费尔南德斯几乎可以以预测柯伊伯带而闻名。” 
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 the Kuiper belt.
KBO有时也称为“ kuiperoids”，这是Clyde Tombaugh建议的名称。 几个科学团体建议在该带中的物体使用“海王星天体”（TNO）一词，因为该术语的争议性小于其他所有物体；尽管它不是确切的同义词，因为TNO包括绕太阳公转的所有物体。 海王星的轨道，而不仅仅是在柯伊伯带的轨道。
At its fullest extent (but excluding the scattered disc), including its outlying regions, the Kuiper belt stretches from roughly 30 to 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 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.
在最大范围内（但不包括分散的盘），包括其外围区域，柯伊伯带的延伸范围约为30到55 AU。 皮带的主体通常被认为从39.5 AU的2：3平均运动共振（见下文）延伸到大约48 AU的1：2共振。 柯伊伯带很厚，主要集中区向黄道平面外延伸了十度之多，物体的分散分布更远了几倍。 总体而言，它比皮带更像圆环或甜甜圈。 它的平均位置相对于黄道倾斜1.86度。
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 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.
海王星的存在由于轨道共振而对柯伊伯带的结构产生深远的影响。 在与太阳系年龄相当的时间尺度上，海王星的引力破坏了恰好位于某些区域的任何物体的轨道的稳定性，并将其送入内部太阳系或送入了散射盘或星际空间。 这导致柯伊伯带在其当前布局中具有明显的间隙，类似于小行星带中的柯克伍德间隙。 例如，在40至42 AU之间的区域中，没有物体可以在这段时间内保持稳定的轨道，并且在该区域中观察到的任何物体都必须相对较近地迁移到那里。
Main article: Classical Kuiper belt object
Between 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 QB1), 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.
在大约42–48 AU与海王星的2：3和1：2共振之间，与海王星的引力相互作用会在较长的时间范围内发生，并且物体的轨道基本不变。 该地区被称为古典柯伊伯带，其成员约占迄今为止观察到的KBO的三分之二。  因为发现的第一个现代KBO（Albion，但长期以来称为（15760）1992 QB1）被视为该组的原型，所以经典KBO通常被称为cubewanos（“ QB-1-os”）。 [48 ] 国际天文学联合会制定的指导方针要求给经典的KBO赋予与创造相关的神话人物的名字。
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 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 contain 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 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.
经典的柯伊伯带似乎是两个独立种群的复合体。 第一个被称为“动态寒冷”种群，其轨道非常类似于行星。 几乎是圆形的，轨道偏心率小于0.1，倾斜度相对较低，最高约10°（它们靠近太阳系的平面，而不是成一定角度）。 寒冷的种群中还包含一些被称为核的物体，其半长轴为AU 44.4至44.5。 第二个是“动态高温”种群，其轨道更偏向黄道，最高达30°。 以这种方式命名这两个族群并不是因为温度存在任何重大差异，而是以类似于气体中的颗粒的形式出现的，气体在加热时会增加它们的相对速度。
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 a different size distribution, and lacks very large objects. 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 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.
不仅这两个种群处于不同的轨道，寒冷种群的颜色和反照率也不同，更红和更亮，具有更大的二元物体比例，具有不同的尺寸分布，并且缺少非常大的物体 。 颜色的差异可能反映了不同的成分，这表明它们形成在不同的区域。 有人提出，热人口是在海王星原轨道附近形成的，并在巨型行星的迁移过程中散布开来。  另一方面，有人提出，寒冷的种群或多或少在目前的位置上已经形成，因为松散的二进制文件不太可能在与海王星的相遇中生存。 尽管尼斯模型似乎能够至少部分解释成分差异，但也有人提出颜色差异可能反映了表面演化的差异。
Main article: Resonant trans-Neptunian object
Orbit classification (schematic of semi-major axes)
When an object’s orbital period 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 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.
当一个物体的轨道周期与海王星的精确比例（一种称为平均运动共振的情况）时，它可以与海王星锁定在同步运动中，并且如果它们的相对排列合适，可以避免被干扰。 例如，如果某个物体每三个海王星轨道绕太阳公转两次，并且如果它与海王星一起到达近日点，则海王星离它约四分之一的轨道，那么每当它返回近日点时，海王星将始终处于相同的相对位置 一开始，因为它将同时完成1 1⁄2个轨道。 这被称为2：3（或3：2）共振，它对应于大约39.4 AU的特征半长轴。 这种2：3共振由大约200个已知物体组成，包括冥王星及其卫星。
In recognition of this, the members of this family are known as plutinos. Many plutinos, including Pluto, have orbits that cross that of Neptune, though 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 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 ~47.7AU, 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 a 1:1 mean-motion resonance with Neptune and often have very stable orbits.
认识到这一点，该家族的成员被称为plutinos。 许多冥王星（包括冥王星）的轨道都跨越海王星的轨道，尽管它们的共振意味着它们永远不会碰撞。 Plutinos的轨道偏心率很高，这表明它们并不是当前位置所固有的，而是被海王星的迁徙随意地抛入了轨道。 国际天文学联合会的准则规定，所有冥王星都必须像冥王星一样以黑社会神的名字命名。 1：2共振（其物体完成每个海王星轨道的一半轨道）对应于〜47.7AU的半长轴，并且分布稀疏。 它的居民有时被称为twotinos。 其他共振也存在于3：4、3：5、4：7和2：5。 海王星有许多特洛伊木马物体，占据了其拉格朗日点，并在重力稳定区域中在其轨道上前后移动。 海王星木马与海王星以1：1的平均运动共振，并且通常具有非常稳定的轨道。
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.
另外，存在相对较长的物体，其半长轴低于39 AU，这显然不能通过当前的共振来解释。 当前引起这种现象的假设是，当海王星向外迁移时，不稳定的轨道共振逐渐在该区域移动，因此其中的任何物体都被扫起或从地心引力中弹出。
Histogram of the semi-major axes of Kuiper belt objects with inclinations above and below 5 degrees. Spikes from the plutinos and the ‘kernel’ are visible at 39–40 AU and 44 AU.
柯伊伯带对象的半长轴的直方图，其倾斜度大于或小于5度。 来自plutinos和“内核”的尖峰在39–40 AU和44 AU处可见。
The 1:2 resonance at 47.8 AU appears to be an edge beyond which few objects are known. It 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.
在47.8 AU处的1：2共振似乎是一个边缘，在此边缘之外，鲜为人知。 目前尚不清楚这实际上是古典皮带的外缘还是仅仅是巨大差距的开始。 在大约55 AU的2：5共振处检测到物体，远在经典传送带之外。 这些共振之间的经典轨道上大量物体的预测尚未通过观察得到证实。
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 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. In 2003, Bernstein, Trilling, et al. 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 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.
根据形成天王星和海王星所需的原始质量以及像冥王星一样大的天体的估计（请参见质量和大小分布），早期的柯伊伯带模型表明超过50 AU的大天体的数量将继续增长，因此，这种突然的急剧下降（称为居伊珀悬崖）是出乎意料的，迄今为止原因尚不清楚。 在2003年，Bernstein，Trilling等人。 发现的证据表明，半径超过50 AU的100 km或100 km以上物体的数量快速下降是真实的，而不是由于观察偏差。 可能的解释包括，在那个距离处的物质太稀少或太分散而无法积聚成大物体，或者随后的过程除去或破坏了那些确实存在的物质。 神户大学的帕特里克·利卡沃卡（Patryk Lykawka）声称，一个看不见的大型行星物体（可能是地球或火星大小）的引力吸引可能是造成这种现象的原因。 
Simulation showing outer planets and Kuiper belt: a) before Jupiter/Saturn 1:2 resonance, b) scattering of Kuiper belt objects into the Solar System after the orbital shift of Neptune, c) after ejection of Kuiper belt bodies by Jupiter
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 the future LSST, which should reveal many currently unknown KBOs. These surveys will provide data that will help determine answers to these questions.
The Kuiper belt is thought to consist of planetesimals, fragments from the original protoplanetary disc around 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 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.
柯伊伯带被认为是由小行星组成的，它们是来自原始围绕太阳的原行星盘的碎片，这些碎片未能完全融合成行星，而是形成了较小的物体，最大直径小于3000公里（1900英里）。 对冥王星和夏隆的陨石坑数量的研究表明，缺乏小型陨石坑，表明这些陨石直接形成为直径数十公里范围内的大型陨石，而不是从小得多，大约千米规模的天体上形成的。 形成这些较大天体的假想机制包括在湍流原行星盘 或在流不稳定性中涡流之间聚集的卵石云的重力塌陷。 这些塌陷的云可能破碎，形成二元云。
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 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 the orbits of Uranus and Neptune, causing them to be scattered outward onto high-eccentricity orbits that crossed the primordial planetesimal disc.
现代计算机模拟表明，柯伊伯带受到木星和海王星的强烈影响，也暗示天王星和海王星都不可能在它们当前的位置上形成，因为在该范围内存在的原始物质太少，无法产生如此高质量的物体。 取而代之的是，估计这些行星的形成更接近木星。 在太阳系历史的早期，小行星的散射会导致巨型行星的轨道迁移：土星，天王星和海王星向外漂移，而木星向内漂移。 最终，轨道移动到木星和土星达到精确的1：2共振点的位置； 木星每一个土星轨道绕太阳公转两次。 这种共振的引力作用最终使天王星和海王星的轨道不稳定，使它们向外散布到与原始行星盘交叉的高偏心率轨道上。  
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 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.
当海王星的轨道高度偏心时，其平均运动共振重叠，并且小行星的轨道混乱地发展，使小行星向外移动直至海王星的1：2共振，从而形成了一个低倾角物体的动态冷带。 后来，在其离心率降低之后，海王星的轨道向外扩展到当前位置。 在这种迁移过程中，许多行星被捕获并保留在共振中，其他行星演化为高倾角和低偏心率轨道，并从共振中逃逸到稳定轨道。 更多的行星小行星向内散布，一小部分被捕获为木星特洛伊木马，绕行巨型行星的不规则卫星以及外带小行星。 其余的又被木星再次向外散射，在大多数情况下从太阳系中弹出，使原始的柯伊伯带种群减少了99％或更多。
The original version of 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, 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.
目前最受欢迎的起源模型，“Nice model”，再现了柯伊伯带的许多特征，例如“冷”和“热”种群，共振物体和散布的盘，但仍无法解释它们分布的某些特征。 该模型预测经典KBO轨道的平均偏心率要比观察到的高（0.10–0.13对0.07），并且其预测的倾斜度分布包含的倾斜度太高。 此外，冷带中二元物体的频率（其中许多物体相距很远且松散地束缚）也给模型带来了问题。 预计这些物质在与海王星的相遇中是分开的，导致一些人提出，冷盘就是在其目前位置形成的，代表了太阳系中唯一真正的局部小天体。
A recent modification of the Nice model has 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 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.
Nice model的最新修改形式是太阳系以平均运动共振链中的五个巨型行星开始，其中包括一个额外的冰巨星。 太阳系形成后约4亿年，共振链断裂。 冰巨星没有散落到圆盘中，而是先向外迁移了几个天文单位。 这种不同的迁移最终导致 resonance crossing ，从而破坏了行星的轨道。 多余的冰巨星与土星相遇，并向内散布到木星穿越的轨道上，并且在一系列相遇从太阳系中弹出之后。 然后，其余的行星继续迁移，直到行星盘几乎被耗尽，在各个位置残留少量碎片。
As in the original Nice model, objects are captured into resonances with Neptune during its outward migration. Some remain in 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.
与最初的尼斯模型一样，海王星在向外迁移过程中会捕获物体，使其产生共振。 一些保留在共振中，另一些演化成较高倾角，较低偏心率的轨道，并释放到形成动态热经典带的稳定轨道上。 如果海王星在30 Myr的时间尺度上从24 AU迁移到30 AU，则可以再现热带的倾斜分布。 当海王星迁移到28 AU时，它会与额外的冰巨星发生引力相遇。
Objects captured from 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 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.
当海王星的半长轴向外跳动时，从冷带捕获的物体与海王星以1：2的平均运动共振被留在44 AU时作为局部集中而留在后面。 沉积在冷带中的物体包括一些松散结合的“蓝色”二元物体，这些二元物体比冷带当前位置更近。 如果海王星的离心率在这次相遇期间保持较小，则可以避免原始Nice model的轨道的混沌演化，并保留原始的冰冷带。 在海王星迁移的后期，缓慢移动平均运动共振会从冷带中移走偏心率较高的物体，从而截断其偏心率分布。
The infrared spectra of both Eris and Pluto, highlighting their common methane absorption lines
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 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 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 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 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.
分析表明，柯伊伯带物体是由岩石和各种冰（例如水，甲烷和氨）的混合物组成的。 带的温度只有大约50开尔文，因此，在接近太阳时呈气态的许多化合物保持固态。 对于少数已经确定直径和质量的物体，密度和岩石冰分数是已知的。 可以通过使用高分辨率望远镜（如哈勃太空望远镜）进行成像，通过在物体经过恒星前时进行掩星的定时，或者最常见的是使用根据其自身计算出的物体的反照率来确定直径 红外发射。
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/cm3. 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 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.
使用卫星的半长轴和半周期来确定质量，因此，半卫星的半长轴和半周期仅对于几个二进制对象才已知。 密度范围从小于0.4到2.6 g / cm3。 密度最小的物体被认为主要由冰组成并且具有明显的孔隙度。 最稠密的物体很可能是由岩石和薄薄的冰壳组成的。 小物体的密度低，而最大物体的密度高。 这种趋势的一种可能解释是，当分化的物体碰撞形成最大的物体时，冰会从表层流失。
plutino 以及可能的前C型小行星的艺术想象图（120216）2004 EW95 
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 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.
最初，不可能对KBO进行详细分析，因此天文学家只能确定有关其构成的最基本事实，主要是颜色。 这些最初的数据显示了KBO的颜色范围很广，从中性灰色到深红色。 这表明它们的表面由各种各样的化合物组成，从脏冰到碳氢化合物。 这种多样性令人吃惊，因为天文学家原来以为KBOs就是一团黑，并在宇宙射线的作用下大部分挥发的冰从其表面流失 。许多假说被用来解释这种现象，包括由于冲击和outgassing造成的表面重构。
Jewitt and Luu’s spectral analysis of 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.
Jewitt和Luu在2001年对已知的柯伊伯带天体的光谱分析发现，颜色变化过大，以致于无法通过随机撞击轻易解释。 人们认为，来自太阳的辐射在化学上改变了KBOs表面的甲烷，从而产生了诸如tholins的产物。 事实证明，makemake具有许多甲烷辐射加工衍生的碳氢化合物，包括乙烷，乙烯和乙炔。
Although to date most KBOs still appear spectrally featureless due to their faintness, there have been 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 is hypothesized to be due to the retention or the loss of hydrogen sulfide (H2S) on the surface of these objects, with the surfaces of those that formed far enough from the Sun to retain H2S being reddened due to irradiation.
尽管迄今为止，大多数KBO都因其在光谱上模糊仍然没有特征，但是在确定其组成方面已经取得了许多成功。 1996年，Robert H. Brown等人。 在KBO 1993 SC上获得的光谱数据表明，其表面组成与冥王星以及海王星的卫星Triton相似，并带有大量甲烷冰。 对于较小的物体，仅确定了颜色，在某些情况下还确定了反照率。 这些物体大致分为两类：反照率低的灰色或反照率高的红色。 假定颜色和反射率的差异是由于这些物体表面上硫化氢（H2S）的保留或损失，而那些离太阳足够远以保留H2S的表面由于辐射而变红 。
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 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 the Haumea family such as 1996 TO66, 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.
最大的KBO（例如冥王星和Quaoar）的表面富含挥发性化合物，例如甲烷，氮气和一氧化碳。这些分子的存在很可能是由于它们在柯伊伯带的30–50 K温度范围内具有适度的蒸气压。这使它们偶尔会沸腾，然后像雪一样再次掉落，而沸点较高的化合物将保持固态。在最大的KBO中，这三种化合物的相对丰度与它们的表面重力和环境温度直接相关，这决定了它们可以保留哪些。在几个KBO中都检测到了水冰，包括Haumea家族的成员，例如1996 TO66，中型物体，例如38628 Huya和20000 Varuna，，还有一些小物体。大中型物体上存在结晶冰，包括50000 Quaoar，其中还检测到氨水合物，这可能表明过去构造活动是由于存在氨而熔点降低所致。
质量和尺寸分布Mass and size distribution
Illustration of the power law
Despite its vast extent, the collective mass of the Kuiper belt is relatively low. The total mass is estimated to range between 1/25 and 1/10 the mass of the Earth. Conversely, models of the Solar System’s formation predict a collective mass for the Kuiper belt of 30 Earth masses. This missing >99% of the mass can hardly be dismissed, because it is required for the accretion of any KBOs larger than 100 km (62 mi) in diameter. If the 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.
尽管规模很大，但柯伊伯带的集体质量却相对较低。 总质量估计在地球质量的1/25到1/10之间。 相反，太阳系形成模型却预测柯伊伯带总质量是地球质量的30倍。 重量> 99％的缺失几乎无法忽略，因为任何直径大于100 km（62 mi）的KBO都需要增加。 如果柯伊伯带始终具有当前的低密度，那么这些大物体根本不可能由较小的小行星的碰撞和合并形成。
Moreover, the eccentricity and inclination of current orbits makes the encounters quite “violent” resulting in destruction rather than accretion. It appears that either the current residents of the Kuiper belt have been created closer to the Sun, or some mechanism dispersed the original mass. Neptune’s current influence is too weak to explain such a massive “vacuuming”, though the Nice model proposes that it could have been the cause of mass removal in the past. Although the question remains open, the conjectures vary from a passing star scenario to grinding of smaller objects, via collisions, into dust small enough to be affected by solar radiation. 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.
而且，当前轨道的偏心率和倾斜度使相遇非常“剧烈”，从而导致破坏而不是增加。 看来，柯伊伯带的当前居民是在离太阳更近的地方产生的，或者某种机制分散了原始质量。 海王星目前的影响力太弱，无法解释如此大规模的“真空”，尽管Nice model提出，它过去可能是大规模清除的原因。 尽管问题仍然悬而未决，但猜想从恒星的场景到通过碰撞将较小的物体磨成粉尘，小到足以受到太阳辐射影响。 碰撞研磨造成的质量损失程度受到冷盘中存在松散结合的二元的限制，这些二元很可能在碰撞中被破坏。
Bright objects are rare compared with the dominant dim population, as expected from accretion models of origin, given that only some objects of a given size would have grown further. This relationship between N(D) (the number of objects of diameter greater than D) and D, referred to as brightness slope, has been confirmed by observations. The slope is inversely proportional to some power of the diameter D
where the current measures give q = 4 ±0.5.
目前测得的q = 4±0.5。
(The constant may be non-zero only if the power law doesn’t apply at high values of D.)
Less formally, if q is 4, for example, there are 8 (=23) times more objects in the 100–200 km range than in the 200–400 km range, and for every object with a diameter between 1000 and 1010 km there should be around 1000 (=103) objects with diameter of 100 to 101 km.
正式地计算，例如，如果q为4，则100-200 km范围内的对象比200-400 km范围内的对象多8（= 23）倍，并且对于每个直径在1000至1010 km之间的对象， 应当是大约1000（= 103）个直径为100至101 km的对象。
If q was 1 or less, the law would imply an infinite number and mass of large objects in the Kuiper belt. If 1<q≤4 there will be a finite number of objects greater than a given size, but the expected value of their combined mass would be infinite. If q is 4 or more, the law would imply an infinite mass of small objects. More accurate models find that the “slope” parameter q is in effect greater at large diameters and lesser at small diameters. It seems that Pluto is somewhat unexpectedly large, having several percent of the total mass of the Kuiper belt. It is not expected that anything larger than Pluto exists in the Kuiper belt, and in fact most of the brightest (largest) objects at inclinations less than 5° have probably been found.
如果q为1或更小，则定律暗示在柯伊伯带中无穷无尽的大型物体。 如果1 <q≤4，则将有数量大于给定大小的对象，但是它们的合并质量的期望值将是无限的。 如果q为4或更大，则定律意味着无穷小物体。 更精确的模型发现，“斜率”参数q实际上在大直径时更大，在小直径时更小。 冥王星似乎有点出乎意料地大，占了柯伊伯带总质量的百分之几。 柯伊伯带中不大可能存在比冥王星更大的物体，其实大部分倾斜度小于5°的最亮（最大）物体可能已经被找到了。
Recent research has revealed that the size distributions of the hot classical and cold classical objects have differing slopes. The slope for 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 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.
最近的研究表明，经典热天体和经典冷天体的尺寸分布具有不同的斜率。 大直径的热物体的斜率为q = 5.3，小直径的q = 2.0，斜率变化为110 km。 大直径的冷物体的斜率为q = 8.2，小直径的斜率为q = 2.9，且在140 km处斜率发生变化。 散射对象，plutinos和Neptune特洛伊木马的大小分布具有与其他动态热天体相似的斜率，但可能有一个斜率，即特定大小以下的对象数量急剧减少。 据推测，这种斜率是由于天体群的碰撞演变所致，或者是由于天体群形成时没有形成任何小于该大小的物体，而更小的物体是原始物体的碎片。 
As of December 2009, the smallest Kuiper belt object detected is 980 m across. It is too dim (magnitude 35) to be seen by Hubble directly, but it was detected by Hubble’s star tracking system when it occulted a star.
截至2009年12月，发现的最小柯伊伯带物体跨度为980 m。 它太暗了（大小为35），无法直接被哈勃看到，但是当它掩星时被哈勃的恒星追踪系统检测到。
Comparison of the orbits of scattered disc objects (black), classical KBOs (blue), and 2:5 resonant objects (green). Orbits of other KBOs are gray. (Orbital axes have been aligned for comparison.)Main articles: Scattered disc and Centaur (minor planet)
散射盘天体（黑色），典型KBO（蓝色）和2：5共振对象（绿色）的轨道比较。 其他KBO的轨道为灰色。 （已对轨道轴进行对齐以进行比较。）主要文章：分散盘和半人马座（小行星）
The scattered disc 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, 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.
散射盘是一个稀疏的区域，与柯伊伯带重叠，但延伸到100 AU以上。 分散的圆盘对象（SDO）具有非常椭圆的轨道，通常也非常倾向于黄道。 太阳系形成的大多数模型都显示，KBO和SDO都首先在原始带中形成，随后发生重力相互作用，尤其是与海王星相互作用，从而将物体向外发射，有的进入稳定轨道（KBO），有的进入不稳定的轨道，即散射盘。  由于其不稳定的性质，散布的圆盘被怀疑是许多太阳系短周期彗星的起源。 它们的动态轨道有时会迫使它们进入太阳系内部，首先成为半人马座，然后成为短周期的彗星。
According to the Minor Planet Center, which officially catalogues all trans-Neptunian objects, a KBO, strictly speaking, is any object that orbits exclusively within 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 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.
根据对所有跨海王星天体进行正式分类的小行星中心的说法，严格来讲，KBO是任何只在定义的柯伊伯带区域内绕行的物体，无论其起源或成分如何。 在带外发现的物体被归类为分散的物体。 在某些科学界中，“ 柯伊伯带天体”一词已成为外层太阳系中任何被认为属于该初始类的冰冷小行星的代名词，即使其在整个太阳系历史上的轨道超出了其范围。 柯伊伯带（例如在分散盘区域）。 他们经常将分散的盘状物体描述为“分散的柯伊伯带状物体”。 埃里斯（Eris）比冥王星重得多，通常被称为KBO，但从技术上讲是SDO。 天文学家尚未就柯伊伯带的精确定义达成共识，这一问题仍未解决。
The centaurs, which are not normally considered part of 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.
Main article: Triton (moon)
During its period of migration, Neptune is thought to have captured a large KBO, Triton, which is the only large moon in the Solar System with a retrograde orbit (it orbits opposite to Neptune’s rotation). This suggests that, unlike the large moons of Jupiter, Saturn and Uranus, which are thought to have coalesced from rotating discs of material around their young parent planets, Triton was a fully formed body that was captured from surrounding space. Gravitational capture of an object is not easy: it requires some mechanism to slow down the object enough to be caught by the larger object’s gravity.
在其迁移期间，海王星被认为捕获了一个大型的KBO，Triton，这是太阳系中唯一具有逆行轨道（与海王星自转相反的轨道）的大型卫星。 这表明，与木星，土星和天王星的大型卫星不同，Triton是从周围空间捕获的完全成形的物体，而木星，土星和天王星的大型卫星，被认为是由围绕其幼小的母行星旋转的旋转物质盘融合而成的。 重力捕获物体并不容易：它需要某种机制来减慢物体的速度，使其足以被较大物体的重力捕获。
A possible explanation is that Triton was part of a binary when it encountered Neptune. (Many KBOs are members of binaries. See below.) Ejection of the other member of the binary by Neptune could then explain Triton’s capture. Triton is only 14% larger than Pluto, and spectral analysis of both worlds shows that their surfaces are largely composed of similar materials, such as methane and carbon monoxide. All this points to the conclusion that Triton was once a KBO that was captured by Neptune during its outward migration.
一个可能的解释是Triton遇到海王星时是二元天体的一部分。 （许多KBO是二元天体的成员。请参见下文。）然后，海王星抛出二进制文件的另一个成员可以解释Triton的俘获。 海卫一（Triton）仅比冥王星大14％，对这两个世界的光谱分析表明，它们的表面主要由相似的物质组成，例如甲烷和一氧化碳。 所有这些都表明结论，特里顿曾经是海王星在向外迁移过程中被俘虏的KBO。
Since 2000, a number of KBOs with diameters of between 500 and 1,500 km (932 mi), more than half that of Pluto (diameter 2370 km), have been discovered. 50000 Quaoar, a classical KBO discovered in 2002, is over 1,200 km across. Makemake and Haumea, both announced on July 29, 2005, are larger still. Other objects, such as 28978 Ixion (discovered in 2001) and 20000 Varuna (discovered in 2000), measure roughly 500 km (311 mi) across.
Main article: Pluto
The discovery of these large KBOs in orbits similar to Pluto’s led many to conclude that, aside from its relative size, Pluto was not particularly different from other members of the Kuiper belt. Not only are these objects similar to Pluto in size, but many also have satellites, and are of similar composition (methane and carbon monoxide have been found both on Pluto and on the largest KBOs). Thus, just as Ceres was considered a planet before the discovery of its fellow asteroids, some began to suggest that Pluto might also be reclassified.
The issue was brought to a head by the discovery of Eris, an object in the scattered disc far beyond the Kuiper belt, that is now known to be 27% more massive than Pluto. (Eris was originally thought to be larger than Pluto by volume, but the New Horizons mission found this not to be the case.) In response, the International Astronomical Union (IAU) was forced to define what a planet is for the first time, and in so doing included in their definition that a planet must have “cleared the neighbourhood around its orbit”. As Pluto shares its orbit with many other sizable objects, it was deemed not to have cleared its orbit, and was thus reclassified from a planet to a dwarf planet, making it a member of the Kuiper belt.
Although Pluto is currently the largest known KBO, there is at least one known larger object currently outside the Kuiper belt that probably originated in it: Neptune’s moon Triton (which, as explained above, is probably a captured KBO).
As of 2008, only five objects in the Solar System (Ceres, Eris, and the KBOs Pluto, Makemake and Haumea) are listed as dwarf planets by the IAU. 90482 Orcus, 28978 Ixion and many other Kuiper-belt objects are large enough to be in hydrostatic equilibrium; most of them will probably qualify when more is known about them.
The six largest TNOs (Eris, Pluto, 2007 OR10, Makemake, Haumea and Quaoar) are all known to have satellites, and two have more than one. A higher percentage of the larger KBOs have satellites than the smaller objects in the Kuiper belt, suggesting that a different formation mechanism was responsible. There are also a high number of binaries (two objects close enough in mass to be orbiting “each other”) in the Kuiper belt. The most notable example is the Pluto–Charon binary, but it is estimated that around 11% of KBOs exist in binaries.
Main article: New Horizons
The KBO 2014 MU69 (green circles), the selected target for the New Horizons Kuiper belt object mission
KBO 2014 MU69（绿色圆圈），是“新视野”柯伊伯带天体任务的选定目标
Diagram showing the location of 2014 MU69 and trajectory for rendezvous
New Horizons color composite image of 2014 MU69 showing its red color, suggesting organic compounds. So far, it is the only KBO besides Pluto and its satellites to be visited by a spacecraft.
2014 MU69的新视野彩色合成图像显示红色，表明是有机化合物。 到目前为止，它是除冥王星及其卫星外唯一由航天器访问的KBO。【吐槽，之前还没有色彩的时候，就被人说像是花生了，现在再加上色彩，花生实锤了。】
On January 19, 2006, the first spacecraft to explore the Kuiper belt, New Horizons, was launched, which flew by Pluto on July 14, 2015. Beyond the Pluto flyby, the mission’s goal was to locate and investigate other, farther objects in the Kuiper belt.
On October 15, 2014, it was revealed that Hubble had uncovered three potential targets, provisionally designated PT1 (“potential target 1”), PT2 and PT3 by the New Horizons team. The objects’ diameters were estimated to be in the 30–55 km range; too small to be seen by ground telescopes, at distances from the Sun of 43–44 AU, which would put the encounters in the 2018–2019 period. The initial estimated probabilities that these objects were reachable within New Horizons‘ fuel budget were 100%, 7%, and 97%, respectively.
2014年10月15日，据透露，哈勃发现了三个潜在目标，    被新视野临时指定为PT1（“潜在目标1”），PT2和PT3 球队。 物体的直径估计在30-55 km范围内。 太小了，无法用地面望远镜看到，离太阳43-44 AU的距离很远，这将使相遇发生在2018-2019年期间。 在“新视野”的燃料预算内，这些目标可达到的初始估计概率分别为100％，7％和97％。
All were members of the “cold” (low-inclination, low-eccentricity) classical Kuiper belt, and thus very different from Pluto. PT1 (given the temporary designation “1110113Y” on the HST web site), the most favorably situated object, was magnitude 26.8, 30–45 km in diameter, and was encountered in January 2019. Once sufficient orbital information was provided, the Minor Planet Center gave official designations to the three target KBOs: 2014 MU69 (PT1), 2014 OS393 (PT2), and 2014 PN70 (PT3). By the fall of 2014, a possible fourth target, 2014 MT69, had been eliminated by follow-up observations. PT2 was out of the running before the Pluto flyby.
它们都是“冷”（低倾角，低偏心率）经典柯伊伯带的成员，因此与冥王星有很大的不同。 PT1（HST网站上的临时名称“ 1110113Y” ）是位置最有利的对象，其大小为26.8，直径为30-45 km，于2019年1月遇到。 一旦提供了足够的轨道信息，小行星中心就正式指定了三个目标KBO：2014 MU69（PT1），2014 OS393（PT2）和2014 PN70（PT3）。 到2014年秋季，后续观察消除了可能的第四个目标2014 MT69。 PT2在冥王星飞越之前就已退出比赛。 
On August 26, 2015, the first target, 2014 MU69, was chosen. Course adjustment took place in late October and early November 2015, leading to a flyby in January 2019. On July 1, 2016, NASA approved additional funding for New Horizons to visit the object.
2015年8月26日，选择了第一个目标2014 MU69。 在2015年10月下旬和2015年11月上旬进行了路线调整，导致2019年1月飞越。  2016年7月1日，美国国家航空航天局（NASA）批准了“新视野”计划的额外资助。
On December 2, 2015, New Horizons detected what was then called 1994 JR1 (Later named 15810 Arawn) from 270 million kilometres (170×106 mi) away, and the photographs show the shape of the object and one or two details.
2015年12月2日，新视野号在2.7亿公里（170×106英里）处探测到了当时称为1994 JR1（后来称为15810 Arawn）的东西，这些照片显示了物体的形状和一个或两个细节。[122 ]
On January 1, 2019, New Horizons successfully flew by 2014 MU69, returning data showing 2014 MU69 to be a contact binary 32 km long by 16 km wide. The Ralph instrument aboard New Horizons confirmed 2014 MU69‘s red color. Data from the fly by will continue to be downloaded over the next 20 months.
在2019年1月1日，新视野号在2014年MU69上成功飞行，返回的数据显示2014年MU69是长32公里，宽16公里的 contact binary 。 New Horizons上的Ralph仪器确认了2014 MU69的红色。 在接下来的20个月中，fly by的数据将继续下载。
No follow up missions for New Horizons are planned, though at least two concepts for missions that would return to orbit or land on Pluto have been studied. Beyond Pluto, there exist many large KBOs that cannot be visited with New Horizons, such as the dwarf planets Makemake and Haumea. New missions would be tasked to explore and study these objects in detail. Thales Alenia Space has studied the logistics of an orbiter mission to Haumea, a high priority scientific target due to its status as the parent body of a collisional family that includes several other TNOs, as well as Haumea’s ring and two moons.
“新视野”没有后续飞行任务，尽管已经研究了至少两种将返回轨道或在冥王星上降落的飞行任务的概念。 除冥王星外，还有许多新地平线好无法拜访的大型KBO，例如矮行星Makemake和Haumea。新任务将负责详细探索和研究这些物体。泰雷兹·阿莱尼亚太空公司（Thales Alenia Space）研究了前往Haumea的轨道飞行任务的后勤工作，这是一项高度优先的科学目标，因为它是包括多个其他TNO以及Haumea的环和两颗卫星的碰撞家庭的母体。
The lead author, Joel Poncy, has advocated for new technology that would allow spacecraft to reach and orbit KBOs in 10–20 years or less. New Horizons Principal Investigator Alan Stern has informally suggested missions that would flyby the planets Uranus or Neptune before visiting new KBO targets, thus furthering the exploration of the Kuiper belt while also visiting these ice giant planets for the first time since the Voyager 2 flybys in the 1980s.
第一作者乔尔·庞西（Joel Poncy）提倡使用新技术，使航天器能够在10至20年或更短的时间内到达并绕过KBO。新视野首席研究员艾伦·斯特恩（Alan Stern）非正式建议在访问新的KBO目标之前会绕过天王星或海王星的飞行任务，因此，这进一步促进了柯伊伯带的探索，同时也是旅行者2以来首次访问这些冰巨行星1980年代的飞越。
设计研究和概念任务Design studies and concept missions
Design for an advanced probe concept from 1999
Quaoar has been considered as a flyby target for a probe tasked with exploring the interstellar medium, as it currently lies near the heliospheric nose; Pontus Brandt at Johns Hopkins Applied Physics Laboratory and his colleagues have studied a probe that would flyby Quaoar in the 2030s before continuing to the interstellar medium through the heliospheric nose. Among their interests in Quaoar include its likely disappearing methane atmosphere and cryovolcanism. The mission studied by Brandt and his colleagues would launch using SLS and achieve 30 km/s using a Jupiter flyby. Alternatively, for an orbiter mission, a study published in 2012 concluded that Ixion and Huya are among the most feasible targets. For instance, the authors calculated that an orbiter mission could reach Ixion after 17 years cruise time if launched in 2039.
Quaoar被认为是探空星际介质的探测器的飞越目标，因为它目前位于日圆层的鼻子附近。 约翰·霍普金斯大学应用物理实验室的Pontus Brandt和他的同事们研究了一种在2030年代飞越Quaoar的探测器，然后继续通过日圆鼻子进入星际介质。  他们对Quaoar的兴趣之一包括可能消失的甲烷气和低温火山作用。 布兰特和他的同事研究的任务将使用SLS发射，并使用木星飞越以30 km / s的速度飞行。 另外，对于轨道飞行器来说，2012年发表的一项研究得出结论，艾克西翁（Ixion）和虎牙（Huya）是最可行的目标之一。 例如，作者计算出，如果在2039年发射，则在经过17年的巡航时间后，轨道飞行器任务可能会到达艾克西恩。
In the late 2010s, one design study discussed orbital capture and multi-target scenarios for Kuiper belt objects. Some Kuiper belt objects studied in that particular paper included 2002 UX25, 1998 WW31, and 47171 Lempo.
在2010年代后期，一项设计研究讨论了柯伊伯带天体的轨道捕获和多目标场景。  在该特定论文中研究的一些柯伊伯带天体包括2002 UX25、1998 WW31和47171 Lempo。
In 2011, a design study explored a spacecraft survey of Quaoar, Sedna, Makemake, Haumea, and Eris.
Interstellar missions have evaluated including a flyby of Kuiper Belt objects as part of their mission.
外太阳系柯伊伯带Extrasolar Kuiper belts
Main article: Debris disc
恒星HD 139664和HD 53143周围的碎片光盘–从摄像机隐藏的恒星到显示光盘的黑色圆圈。
By 2006, astronomers had resolved dust discs thought to be Kuiper belt-like structures around nine stars other than the Sun. They appear to fall into two categories: wide belts, with radii of over 50 AU, and narrow belts (tentatively like that of the Solar System) with radii of between 20 and 30 AU and relatively sharp boundaries. Beyond this, 15–20% of solar-type stars have an observed infrared excess that is suggestive of massive Kuiper-belt-like structures. Most known debris discs around other stars are fairly young, but the two images on the right, taken by the Hubble Space Telescope in January 2006, are old enough (roughly 300 million years) to have settled into stable configurations. The left image is a “top view” of a wide belt, and the right image is an “edge view” of a narrow belt. Computer simulations of dust in the Kuiper belt suggest that when it was younger, it may have resembled the narrow rings seen around younger stars.
到2006年，天文学家已经解决了尘埃盘的问题，这些尘埃盘是围绕太阳以外九颗恒星的柯伊伯带状结构。 它们似乎分为两类：半径超过50 AU的宽带和半径在20 AU到30 AU之间且边界相对尖锐的窄带（暂时类似于太阳系）。 除此之外，观察到的太阳型恒星中有15–20％的红外过量，这暗示了巨大的柯伊伯带状结构。 最著名的其他恒星周围的碎片圆盘还很年轻，但是右图是哈勃太空望远镜于2006年1月拍摄的，这两个图像已经足够老（大约3亿年），已经稳定下来。 左图是宽皮带的“顶视图”，右图是窄皮带的“边缘”视图。  对柯伊伯带中尘埃的计算机模拟表明，它年轻时可能类似于年轻恒星周围的窄环。