Scattered disc

【机器翻译自Wiki】

The scattered disc (or scattered disk) is a distant circumstellar disc in the Solar System that is sparsely populated by icy small solar system bodies, which are a subset of the broader family of trans-Neptunian objects. The scattered-disc objects (SDOs) have orbital eccentricities ranging as high as 0.8, inclinations as high as 40°, and perihelia greater than 30 astronomical units (4.5×109 km; 2.8×109 mi). These extreme orbits are thought to be the result of gravitational “scattering” by the gas giants, and the objects continue to be subject to perturbation by the planet Neptune.

scattered disc 是太阳系中的一个遥远的星际圆盘,由冰冷的小型太阳系天体稀疏组成,这些天体是海王星跨海天体家族的一个子集。 散盘物体(SDO)的轨道偏心率高达0.8,倾角高达40°,近日点大于30个天文单位(4.5×109 km; 2.8×109 mi)。 这些极端的轨道被认为是天然气巨头的引力“散射”的结果,这些天体继续受到海王星行星的干扰。

Although the closest scattered-disc objects approach the Sun at about 30–35 AU, their orbits can extend well beyond 100 AU. This makes scattered objects among the coldest and most distant objects in the Solar System.[1] The innermost portion of the scattered disc overlaps with a torus-shaped region of orbiting objects traditionally called the Kuiper belt,[2] but its outer limits reach much farther away from the Sun and farther above and below the ecliptic than the Kuiper belt proper.[a]

尽管最接近的分散盘物体在30-35 AU处接近太阳,但它们的轨道可以远远超过100 AU。 这使分散的物体成为太阳系中最冷和最远的物体。[1] 散射盘的最内部分与传统称为柯伊伯带的环形物体的环形区域重叠,[2],但其外边界比柯伊伯带本身更远离太阳,并且距黄道的上方和下方更远。 [一种]

Because of its unstable nature, astronomers now consider the scattered disc to be the place of origin for most periodic comets in the Solar System, with the centaurs, a population of icy bodies between Jupiter and Neptune, being the intermediate stage in an object’s migration from the disc to the inner Solar System.[4] Eventually, perturbations from the giant planets send such objects towards the Sun, transforming them into periodic comets. Many objects of the proposed Oort cloud are also thought to have originated in the scattered disc. Detached objects are not sharply distinct from scattered disc objects, and some such as Sedna have sometimes been considered to be included in this group.

由于其不稳定的性质,天文学家现在认为散盘是太阳系中大多数周期性彗星的起源地,以及半人马,木星和海王星之间的大量冰物体,是物质从散射圆盘到内部太阳系的过渡阶段[4] 最终,巨大行星的扰动将这些物体送向太阳,将它们转变成周期性的彗星。 提议的奥尔特云的许多天体也被认为起源于散射圆盘。 分离的物体与分散的盘状物体并没有明显的区别,某些物体(例如Sedna)有时被认为包括在该组中。

发现Discovery

See also: History of the Kuiper belt

Traditionally, devices like a blink comparator were used in astronomy to detect objects in the Solar System, because these objects would move between two exposures—this involved time-consuming steps like exposing and developing photographic plates or films, and people then using a blink comparator to manually detect prospective objects. During the 1980s, the use of CCD-based cameras in telescopes made it possible to directly produce electronic images that could then be readily digitized and transferred to digital images. Because the CCD captured more light than film (about 90% versus 10% of incoming light) and the blinking could now be done at an adjustable computer screen, the surveys allowed for higher throughput. A flood of new discoveries was the result: over a thousand trans-Neptunian objects were detected between 1992 and 2006.[5]

传统上,天文学中使用眨眼比较器之类的设备来检测太阳系中的物体,因为这些物体会在两次曝光之间移动-这涉及耗时的步骤,例如曝光和显影照相底片或胶片,然后人们使用眨眼比较器 手动检测预期对象。 在1980年代,望远镜中使用基于CCD的相机使得直接产生电子图像成为可能,然后可以将其轻松数字化并转换为数字图像。 由于CCD捕获的光线比胶片要多(大约90%的入射光是10%的入射光),并且现在可以在可调节的计算机屏幕上进行闪烁,因此测量可以提高吞吐量。 结果是大量新发现:在1992年至2006年之间发现了1000多个跨海王星天体。[5]

The first scattered-disc object (SDO) to be recognised as such was 1996 TL66,[6][7] originally identified in 1996 by astronomers based at Mauna Kea in Hawaii. Three more were identified by the same survey in 1999: 1999 CV118, 1999 CY118, and 1999 CF119.[8] The first object presently classified as an SDO to be discovered was 1995 TL8, found in 1995 by Spacewatch.[9]

第一个被这样识别的散射盘物体(SDO)是1996年的TL66 [6] [7],最初是1996年由位于夏威夷的莫纳克亚山的天文学家确定的。 1999年的同一次调查确定了另外三个:1999 CV118、1999 CY118和1999 CF119。[8] 目前被分类为SDO的第一个物体是1995年TL8,这是由Spacewatch在1995年发现的。[9]

As of 2011, over 200 SDOs have been identified,[10] including Gǃkúnǁʼhòmdímà (discovered by Schwamb, Brown, and Rabinowitz),[11] 2002 TC302 (NEAT), Eris (Brown, Trujillo, and Rabinowitz),[12] Sedna (Brown, Trujillo, and Rabinowitz)[13] and 2004 VN112 (Deep Ecliptic Survey).[14] Although the numbers of objects in the Kuiper belt and the scattered disc are hypothesized to be roughly equal, observational bias due to their greater distance means that far fewer SDOs have been observed to date.[15]

截至2011年,已经确定了200多个SDO,[10]包括Gǃkúnǁʼhòmdímà(由Schwamb,Brown和Rabinowitz发现),[11] 2002 TC302(NEAT),Eris(Brown,Trujillo和Rabinowitz),[12] Sedna (布朗,特鲁希略和拉比诺维茨)[13]和2004年VN112(深黄道勘测)。[14] 尽管假设柯伊伯带和散布盘中的物体数量大致相等,但是由于它们之间的距离较大,因此存在观测偏差,这意味着迄今为止观测到的SDO少得多。[15]

跨海王星空间的划分Subdivisions of trans-Neptunian space

Main article: Trans-Neptunian object

The eccentricity and inclination of the scattered-disc population compared to the classical and 5:2 resonant Kuiper-belt objects

与经典的和5:2共振的柯伊伯带物体相比,散盘种群的偏心率和倾角

Known trans-Neptunian objects are often divided into two subpopulations: the Kuiper belt and the scattered disc.[16] A third reservoir of trans-Neptunian objects, the Oort cloud, has been hypothesized, although no confirmed direct observations of the Oort cloud have been made.[2] Some researchers further suggest a transitional space between the scattered disc and the inner Oort cloud, populated with “detached objects“.[17]

已知的跨海王星天体通常分为两个亚群:柯伊伯带和散盘。[16] 尽管没有确认直接观察到的奥尔特云,但已经假设了第三个跨海王星天体的储油库奥尔特云。[2] 一些研究人员进一步提出,在分散的盘片和内部的奥尔特云之间有一个过渡空间,里面充满了“分离的物体”。[17]

Scattered disc versus Kuiper belt

See also: Kuiper belt

The Kuiper belt is a relatively thick torus (or “doughnut”) of space, extending from about 30 to 50 AU[18] comprising two main populations of Kuiper belt objects (KBOs): the classical Kuiper-belt objects (or “cubewanos”), which lie in orbits untouched by Neptune, and the resonant Kuiper-belt objects; those which Neptune has locked into a precise orbital ratio such as 2:3 (the object goes around twice for every three Neptune orbits) and 1:2 (the object goes around once for every two Neptune orbits). These ratios, called orbital resonances, allow KBOs to persist in regions which Neptune’s gravitational influence would otherwise have cleared out over the age of the Solar System, since the objects are never close enough to Neptune to be scattered by its gravity. Those in 2:3 resonances are known as “plutinos“, because Pluto is the largest member of their group, whereas those in 1:2 resonances are known as “twotinos“.

柯伊伯带是一个相对较厚的环形空间,从大约30到50 AU [18]延伸,包括两个主要的柯伊伯带对象(KBO):经典的柯伊伯带对象(或“立方体”) )位于海王星未触及的轨道上,以及共振的柯伊伯带天体; 海王星已将其锁定为精确的轨道比率的卫星,例如2:3(每三个海王星轨道,该物体绕行两次)和1:2(每两个海王星轨道,该物体绕行一次)。 这些比率称为轨道共,,这些KBOs可以 在海王星的引力完全抹除了太阳引力的地带存在。在因为天体永远离海王星太近,无法被其引力散射。 2:3共振的那些被称为“ plutinos”,因为冥王星是他们组中最大的成员,而1:2共振的那些被称为“ twotinos”。

In contrast to the Kuiper belt, the scattered-disc population can be disturbed by Neptune.[19] Scattered-disc objects come within gravitational range of Neptune at their closest approaches (~30 AU) but their farthest distances reach many times that.[17] Ongoing research[20] suggests that the centaurs, a class of icy planetoids that orbit between Jupiter and Neptune, may simply be SDOs thrown into the inner reaches of the Solar System by Neptune, making them “cis-Neptunian” rather than trans-Neptunian scattered objects.[21] Some objects, like (29981) 1999 TD10, blur the distinction[22] and the Minor Planet Center (MPC), which officially catalogues all trans-Neptunian objects, now lists centaurs and SDOs together.[10]

与柯伊伯带不同的是,海王星会打扰分散的碟片种群。[19] [17]散射盘物体在最接近的位置(〜30 AU)处在海王星的重力范围内,但它们的最远距离是其倍数。[17] 正在进行的研究[20]表明,半人马座是一类在木星和海王星之间运行的冰冷小行星,可能只是海王星将SDO抛入太阳系的内部,使它们成为“顺-海王星”而不是跨海王星。 分散的物体。[21] 一些对象,例如(29981)1999 TD10,模糊了这种区分[22],而正式列出所有跨海王星天体的小行星中心(MPC),现在将半人马座和SDO一起列出。[10]

The MPC, however, makes a clear distinction between the Kuiper belt and the scattered disc, separating those objects in stable orbits (the Kuiper belt) from those in scattered orbits (the scattered disc and the centaurs).[10] However, the difference between the Kuiper belt and the scattered disc is not clear-cut, and many astronomers see the scattered disc not as a separate population but as an outward region of the Kuiper belt. Another term used is “scattered Kuiper-belt object” (or SKBO) for bodies of the scattered disc.[23]

但是,MPC明确区分了柯伊伯带和分散盘,将稳定轨道的物体(柯伊伯带)与分散轨道的物体(分散盘和人马圈)分开。[10] 但是,柯伊伯带和散布的盘之间的区别不是很清楚,许多天文学家认为散盘不是单独的种群,而是柯伊布带的向外区域。 所用的另一个术语是散盘体的“散布的柯伊伯带物体”(或SKBO)。[23]

Morbidelli and Brown propose that the difference between objects in the Kuiper belt and scattered-disc objects is that the latter bodies “are transported in semi-major axis by close and distant encounters with Neptune,”[16] but the former experienced no such close encounters. This delineation is inadequate (as they note) over the age of the Solar System, since bodies “trapped in resonances” could “pass from a scattering phase to a non-scattering phase (and vice versa) numerous times.”[16]

莫比德利和布朗提出,柯伊伯带中的天体与散布的天体之间的区别在于,后者的天体“会在半长轴上与近距离和远距离与海王星相遇,” [16] ,但前者就不会靠的那么近。 在太阳系的整个寿命中,这种划分是不充分的(正如他们所指出的那样),因为“陷于共振中的物体”可能“多次从散射阶段进入非散射阶段(反之亦然)” [16]。

 That is, trans-Neptunian objects could travel back and forth between the Kuiper belt and the scattered disc over time. Therefore, they chose instead to define the regions, rather than the objects, defining the scattered disc as “the region of orbital space that can be visited by bodies that have encountered Neptune” within the radius of a Hill sphere, and the Kuiper belt as its “complement … in the a > 30 AU region”; the region of the Solar System populated by objects with semi-major axes greater than 30 AU.[16]

也就是说,海王星跨天物体可能会随时间在柯伊伯带和散布的盘之间来回运动。 因此,他们选择了定义区域而不是对象,而是将散布的圆盘定义为“ Hill球体半径范围内的“遇到海王星的天体可以访问的轨道空间区域”,而柯伊伯带为 其“在> 30 AU区域内的补…”; 半长轴大于30 AU的物体组成的太阳系区域。[16]

分离的物体Detached objects

Main article: Detached objectSee also: Sednoid

The Minor Planet Center classifies the trans-Neptunian object 90377 Sedna as a scattered-disc object. Its discoverer Michael E. Brown has suggested instead that it should be considered an inner Oort-cloud object rather than a member of the scattered disc, because, with a perihelion distance of 76 AU, it is too remote to be affected by the gravitational attraction of the outer planets. [24] Under this definition, an object with a perihelion greater than 40 AU could be classified as outside the scattered disc. [25]

小行星中心将跨海王星天体90377塞德纳(Sedna)归类为散盘对象。 它的发现者迈克尔·E·布朗(Michael E.Brown)则建议将其视为内部奥尔特云物体,而不是散射盘的成员,因为在近日点距为76 AU的情况下,它太遥远而不受重力吸引的影响 外行星。 [24]在此定义下,近日点大于40 AU的物体可以归类为散射盘之外。 [25]

Sedna is not the only such object: (148209) 2000 CR105 (discovered before Sedna) and 2004 VN112 have a perihelion too far away from Neptune to be influenced by it. This led to a discussion among astronomers about a new minor planet set, called the extended scattered disc (E-SDO). [26] 2000 CR105 may also be an inner Oort-cloud object or (more likely) a transitional object between the scattered disc and the inner Oort cloud. More recently, these objects have been referred to as “detached”,[27] or distant detached objects (DDO).[28]

塞德纳不是唯一这样的天体:(148209)2000 CR105(在塞德纳之前发现)和2004 VN112的近日点离海王星太远,以至于无法受到它的影响。 这引起了天文学家之间关于新的小型行星集的讨论,这种行星集称为扩展散射盘(E-SDO)。 [26] 2000 CR105也可以是内部奥尔特云对象,或者(更可能是)分散盘和内部奥尔特云之间的过渡对象。 最近,这些对象已被称为“分离的对象” [27]或远距离分离的对象(DDO)。[28]

There are no clear boundaries between the scattered and detached regions.[25] Gomes et al. define SDOs as having “highly eccentric orbits, perihelia beyond Neptune, and semi-major axes beyond the 1:2 resonance.” By this definition, all distant detached objects are SDOs.[17] Since detached objects’ orbits cannot be produced by Neptune scattering, alternative scattering mechanisms have been put forward, including a passing star[29] or a distant, planet-sized object.[28]

在分散和分离的区域之间没有明确的界限。[25] Gomes等。 将SDO定义为“高度偏心轨道,海王星以外的近日点和1:2共振以外的半长轴”。 根据此定义,所有遥远的分离对象都是SDO。[17] 由于海王星散射无法产生分离的物体的轨道,因此提出了替代的散射机制,包括一颗恒星[29]或一个遥远的行星大小的物体[28]。

A scheme introduced by a 2005 report from the Deep Ecliptic Survey by J. L. Elliott et al. distinguishes between two categories: scattered-near (i.e. typical SDOs) and scattered-extended (i.e. detached objects).[30] Scattered-near objects are those whose orbits are non-resonant, non-planetary-orbit-crossing and have a Tisserand parameter (relative to Neptune) less than 3.[30] Scattered-extended objects have a Tisserand parameter (relative to Neptune) greater than 3 and have a time-averaged eccentricity greater than 0.2.[30]

J. L. Elliott等人在2005年《深黄蚀调查》的报告中提出了一种方案。 区分两类:近距离分散(即典型的SDO)和零散扩展(即分离的对象)。[30] 散点附近的物体是轨道非共振,非行星轨道交叉且Tisserand参数(相对于海王星)小于3的物体。[30] 分散扩展的对象的Tisserand参数(相对于海王星)大于3,并且时间平均偏心率大于0.2。[30]

An alternative classification, introduced by B. J. GladmanB. G. Marsden and C. Van Laerhoven in 2007, uses 10-million-year orbit integration instead of the Tisserand parameter.[31] An object qualifies as an SDO if its orbit is not resonant, has a semi-major axis no greater than 2000 AU, and, during the integration, its semi-major axis shows an excursion of 1.5 AU or more.[31] Gladman et al. suggest the term scattering disk object to emphasize this present mobility.[31] If the object is not an SDO as per the above definition, but the eccentricity of its orbit is greater than 0.240, it is classified as a detached TNO.[31] (Objects with smaller eccentricity are considered classical.) In this scheme, the disc extends from the orbit of Neptune to 2000 AU, the region referred to as the inner Oort cloud.

B. J. Gladman,B。G. Marsden和C. Van Laerhoven在2007年提出的另一种分类方法是使用1000万年的轨道积分而不是Tisserand参数。[31] 如果一个物体的轨道没有共振,其半长轴不大于2000 AU,并且在积分过程中其半长轴显示1.5 AU或更大的偏移,则可以将其视为SDO。[31] Gladman等。 建议用术语“散射盘物体”来强调当前的流动性。[31] 如果根据上述定义,该物体不是SDO,但其轨道的离心率大于0.240,则将其分类为分离的TNO。[31] (偏心率较小的对象被认为是经典的。)在这种方案中,圆盘从海王星的轨道延伸到2000 AU,即内部的奥尔特云。

Orbits

Distribution of trans-Neptunian objects, with semi-major axis on the horizontal, and inclination on the vertical axis. Scattered disc objects are shown in grey, objects that are in resonance with Neptune in red. Classical Kuiper belt objects (cubewanos) and sednoids are blue and yellow, respectively.

跨海王星物体的分布,水平轴为半长轴,垂直轴为倾角。 散布的光盘对象显示为灰色,与海王星共鸣的对象显示为红色。 古典的柯伊伯带天体(立方体)和sednoids分别是蓝色和黄色。

The scattered disc is a very dynamic environment.[15] Because they are still capable of being perturbed by Neptune, SDOs’ orbits are always in danger of disruption; either of being sent outward to the Oort cloud or inward into the centaur population and ultimately the Jupiter family of comets.[15] For this reason Gladman et al. prefer to refer to the region as the scattering disc, rather than scattered.[31] Unlike Kuiper-belt objects (KBOs), the orbits of scattered-disc objects can be inclined as much as 40° from the ecliptic.[32]

分散的光盘是一个非常动态的环境。[15] 由于它们仍然能够被海王星所干扰,因此SDO的轨道始终处于被破坏的危险之中。 [15]要么被送入奥尔特云,要么被送入半人马种群,最终进入木星家族。[15] 由于这个原因,Gladman等人。 更喜欢将区域称为散射盘,而不是分散的。[31] 与柯伊伯带状天体(KBO)不同,散盘状天体的轨道可以相对于黄道倾斜40°。[32]

SDOs are typically characterized by orbits with medium and high eccentricities with a semi-major axis greater than 50 AU, but their perihelia bring them within influence of Neptune.[33] Having a perihelion of roughly 30 AU is one of the defining characteristics of scattered objects, as it allows Neptune to exert its gravitational influence.[8]

SDO的典型特征是半长轴大于50 AU的中高离心率轨道,但它们的近日点使它们受海王星影响。[33] 拥有大约30 AU的近日点是散射物体的定义特征之一,因为它使海王星能够发挥其引力影响。[8]

The classical objects (cubewanos) are very different from the scattered objects: more than 30% of all cubewanos are on low-inclination, near-circular orbits whose eccentricities peak at 0.25.[34] Classical objects possess eccentricities ranging from 0.2 to 0.8. Though the inclinations of scattered objects are similar to the more extreme KBOs, very few scattered objects have orbits as close to the ecliptic as much of the KBO population.[15]

经典天体(立方体形物体)与分散物体有很大不同:所有立方体形物体中有30%以上是在低倾角,近圆形轨道上,其离心率在0.25处达到峰值。[34] 经典对象的偏心率范围为0.2到0.8。 尽管分散物体的倾角与更极端的KBO相似,但很少有分散物体的轨道与黄道附近的黄土一样多。[15]

Although motions in the scattered disc are random, they do tend to follow similar directions, which means that SDOs can become trapped in temporary resonances with Neptune. Examples of possible resonant orbits within the scattered disc include 1:3, 2:7, 3:11, 5:22 and 4:79.[17]

尽管散盘中的运动是随机的,但它们确实倾向于遵循相似的方向,这意味着SDO可能会陷入与海王星的暂时共振中。 散射盘内可能的共振轨道的示例包括1:3、2:7、3:11、5:22和4:79。[17]

Formation

See also: Formation and evolution of the Solar System

Simulation showing Outer Planets and Kuiper Belt: a) Before Jupiter/Saturn 2:1 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

模拟显示外行星和柯伊伯带:a)在木星/土星2:1共振之前b)海王星轨道移动后柯伊伯带天体散射到太阳系中c)木星射出柯伊伯带天体后

The scattered disc is still poorly understood: no model of the formation of the Kuiper belt and the scattered disc has yet been proposed that explains all their observed properties.[16]

分散的盘片仍知之甚少:尚未提出柯伊伯带形成模型和分散的盘片来解释其所有观测特性。[16]

According to contemporary models, the scattered disc formed when Kuiper belt objects (KBOs) were “scattered” into eccentric and inclined orbits by gravitational interaction with Neptune and the other outer planets.[35] The amount of time for this process to occur remains uncertain. One hypothesis estimates a period equal to the entire age of the Solar System;[36] a second posits that the scattering took place relatively quickly, during Neptune’s early migration epoch.[37]

根据当代模型,当柯伊伯带天体(KBOs)通过与海王星和其他外行星的引力相互作用而“分散”为偏心和倾斜轨道时,形成了分散盘。[35] 此过程发生的时间量仍然不确定。 一个假设估计一个周期等于太阳系的整个寿命; [36]第二个假设是,在海王星的早期迁移时期,散射发生得相对较快。[37]

Models for a continuous formation throughout the age of the Solar System illustrate that at weak resonances within the Kuiper belt (such as 5:7 or 8:1), or at the boundaries of stronger resonances, objects can develop weak orbital instabilities over millions of years. The 4:7 resonance in particular has large instability. KBOs can also be shifted into unstable orbits by close passage of massive objects, or through collisions. Over time, the scattered disc would gradually form from these isolated events.[17]

在整个太阳系寿命中连续形成的模型表明,在柯伊伯带内的弱共振(例如5:7或8:1)或强共振的边界处,物体可以在数百万个星体上形成弱的轨道不稳定性。 年份。 特别是4:7共振具有较大的不稳定性。 KBO也可以通过大量物体的近距离通过或碰撞而进入不稳定的轨道。 随着时间的流逝,这些孤立的事件将逐渐形成分散的光盘。[17]

Computer simulations have also suggested a more rapid and earlier formation for the scattered disc. Modern theories indicate that neither Uranus nor Neptune could have formed in situ beyond Saturn, as too little primordial matter existed at that range to produce objects of such high mass. Instead, these planets, and Saturn, may have formed closer to Jupiter, but were flung outwards during the early evolution of the Solar System, perhaps through exchanges of angular momentum with scattered objects.[38] 

计算机模拟也表明散盘的形成更快,更早。 现代理论表明,天王星和海王星都不可能在土星之外原地形成,因为在那个范围内存在的原始物质太少,无法产生如此高质量的物体。 相反,这些行星和土星,形成时可能与木星很接近,但在太阳系早期演化过程中可能是通过与散乱物体交换角动量而向外抛弃的。[38]

Once the orbits of Jupiter and Saturn shifted to a 2:1 resonance (two Jupiter orbits for each orbit of Saturn), their combined gravitational pull disrupted the orbits of Uranus and Neptune, sending Neptune into the temporary “chaos” of the proto-Kuiper belt.[37] As Neptune traveled outward, it scattered many trans-Neptunian objects into higher and more eccentric orbits.[35][39] This model states that 90% or more of the objects in the scattered disc may have been “promoted into these eccentric orbits by Neptune’s resonances during the migration epoch…[therefore] the scattered disc might not be so scattered.”[38]

一旦木星和土星的轨道转变为2:1共振(土星的每个轨道有两个木星轨道),它们的引力结合就破坏了天王星和海王星的轨道,使海王星进入原始库珀的暂时“混乱” 皮带。[37] 当海王星向外传播时,它使许多海王星横越天体散布到更高和更偏心的轨道上。[35] [39] 该模型指出,散射盘中90%或更多的物体可能已经“在迁移时期被海王星的共振推动进入了这些偏心轨道…因此,散射盘可能不会如此分散。” [38]

Composition

The infrared spectra of both Eris and Pluto, highlighting their common methane absorption lines

厄里斯和冥王星的红外光谱,突出了它们共同的甲烷吸收谱线

Scattered objects, like other trans-Neptunian objects, have low densities and are composed largely of frozen volatiles such as water and methane.[40] Spectral analysis of selected Kuiper belt and scattered objects has revealed signatures of similar compounds. Both Pluto and Eris, for instance, show signatures for methane.[41]

像其他跨海王星物体一样,散射的物体密度低,并且主要由水和甲烷等冷冻挥发物组成。[40] 选定的柯伊伯带和散布物体的光谱分析显示出类似化合物的特征。 例如,冥王星和厄里斯都显示出甲烷的特征。[41]

Astronomers originally supposed that the entire trans-Neptunian population would show a similar red surface colour, as they were thought to have originated in the same region and subjected to the same physical processes.[40] Specifically, SDOs were expected to have large amounts of surface methane, chemically altered into complex organic molecules by energy from the Sun. This would absorb blue light, creating a reddish hue.[40] Most classical objects display this colour, but scattered objects do not; instead, they present a white or greyish appearance.[40]

天文学家最初认为整个跨海王星种群将显示出相似的红色表面颜色,因为它们被认为起源于同一地区并经历了相同的物理过程。[40] 具体而言,人们期望SDO具有大量的表面甲烷,它们会被来自太阳的能量化学转化为复杂的有机分子。 这会吸收蓝光,产生淡红色调。[40] 大多数古典物体都显示这种颜色,但分散的物体则不显示这种颜色。 相反,它们呈现白色或灰色外观。[40]

One explanation is the exposure of whiter subsurface layers by impacts; another is that the scattered objects’ greater distance from the Sun creates a composition gradient, analogous to the composition gradient of the terrestrial and gas giant planets.[40] Michael E. Brown, discoverer of the scattered object Eris, suggests that its paler colour could be because, at its current distance from the Sun, its atmosphere of methane is frozen over its entire surface, creating an inches-thick layer of bright white ice. Pluto, conversely, being closer to the Sun, would be warm enough that methane would freeze only onto cooler, high-albedo regions, leaving low-albedo tholin-covered regions bare of ice.[41]

一种解释是通过冲击使更白的地下层暴露。 另一个是,分散物体与太阳的距离更大,形成了一个成分梯度,类似于陆地和天然气巨型行星的成分梯度。[40] 散落天体Eris的发现者Michael E. Brown认为,其较浅的颜色可能是因为在距太阳当前距离处,其甲烷气体被冻结在整个表面上,形成了几英寸厚的明亮的白冰层。 。 相反,冥王星离太阳更近,其温度足以使甲烷仅冻结在较凉爽的高反照率地区,而低反照率的被索林覆盖的地区则没有冰。[41]

Comets

Main article: Comet § Short period

Tempel 1, a Jupiter-family comet

The Kuiper belt was initially thought to be the source of the Solar System’s ecliptic comets. However, studies of the region since 1992 have shown that the orbits within the Kuiper belt are relatively stable, and that ecliptic comets originate from the scattered disc, where orbits are generally less stable.[42]

最初认为柯伊伯带是太阳系黄道彗星的来源。 但是,自1992年以来对该地区的研究表明,柯伊伯带内的轨道相对稳定,黄道彗星起源于散布的盘,而这些盘的轨道通常较不稳定。[42]

Comets can loosely be divided into two categories: short-period and long-period—the latter being thought to originate in the Oort cloud. The two major categories of short-period comets are Jupiter-family comets (JFCs) and Halley-type comets.[15] Halley-type comets, which are named after their prototype, Halley’s Comet, are thought to have originated in the Oort cloud but to have been drawn into the inner Solar System by the gravity of the giant planets,[43] whereas the JFCs are thought to have originated in the scattered disc.[19] The centaurs are thought to be a dynamically intermediate stage between the scattered disc and the Jupiter family.[20]

彗星大致可以分为两类:短期和长期-后者被认为起源于奥尔特云。 短周期彗星的两个主要类别是木星家庭彗星(JFCs)和哈雷型彗星。[15] 以其原型哈雷彗星命名的哈雷型彗星被认为起源于奥尔特云,但被巨型行星的引力吸引到太阳系内部[43],而JFC被认为是 起源于分散的盘片。[19] 半人马被认为是分散盘和木星家族之间的动态中间阶段。[20]

There are many differences between SDOs and JFCs, even though many of the Jupiter-family comets may have originated in the scattered disc. Although the centaurs share a reddish or neutral coloration with many SDOs, their nuclei are bluer, indicating a fundamental chemical or physical difference.[43] One hypothesis is that comet nuclei are resurfaced as they approach the Sun by subsurface materials which subsequently bury the older material.[43]

尽管许多木星族彗星可能起源于散布的盘,但SDO和JFC之间存在许多差异。 尽管半人马与许多SDO共享红色或中性色,但它们的核更蓝,表明存在基本的化学或物理差异。[43] 一种假设是,彗星核在接近太阳时会被地下物质重新覆盖,然后掩埋较旧的物质。[43]

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