The size distribution in the cold classical Kuiper belt can be approximated by two idealized power laws: one with steep slope for radii R>R* and one with shallow slope for R<R*, where R*~25-50 km. Previous works suggested that the SFD roll-over at R* can be the result of extensive collisional grinding in the Kuiper belt that led to the catastrophic disruption of most bodies with R<R*. Here we use a new code to test the effect of collisions in the Kuiper belt. We find that the observed roll-over could indeed be explained by collisional grinding provided that the initial mass in large bodies was much larger than the one in the present Kuiper belt, and was dynamically depleted. In addition to the size distribution changes, our code also tracks the effects of collisions on binary systems. We find that it is generally easier to dissolve wide binary systems, such as the ones existing in the cold Kuiper belt today, than to catastrophically disrupt objects with R~R*. Thus, the binary survival sets important limits on the extent of collisional grinding in the Kuiper belt. We find that the extensive collisional grinding required to produce the SFD roll-over at R* would imply a strong gradient of the binary fraction with R and separation, because it is generally easier to dissolve binaries with small components and/or those with wide orbits. The expected binary fraction for R<R* is <0.1. The present observational data do not show such a gradient. Instead, they suggest a large binary fraction of ~0.4 for R=30-40 km. This may indicate that the roll-over was not produced by disruptive collisions, but is instead a fossil remnant of the KBO formation process.
Our understanding of the history of the solar system has undergone a revolution in recent years, owing to new theoretical insights into the origin of Pluto and the discovery of the Kuiper belt and its rich dynamical structure. The emerging picture of dramatic orbital migration of the planets driven by interaction with the primordial Kuiper belt is thought to have produced the final solar system architecture that we live in today. This paper gives a brief summary of this new view of our solar system's history, and reviews the astronomical evidence in the resonant populations of the Kuiper belt.
The surface composition of large Kuiper belt object 2007 OR10
我们提出的光度学和光谱的大型柯伊伯带对象2007 OR 10。这些数据显示了由于水冰而产生的显著的近红外吸收特征。虽然柯伊伯带中大多数吸收水冰的天体都具有水冰的光学中性颜色，但2007 OR 10是已知的最红的柯伊伯带天体之一。另一个大型柯伊伯带天体-夸欧尔-有类似的红色和水冰吸收，它的红色被假设是由于照射的少量甲烷能够保留在夸欧尔。2007 OR 10虽然比夸欧尔更温暖，但也有类似的挥发性保留，因为它足够大，其更强的重力仍然可以保留甲烷。因此，我们认为2007 OR 10上的红色也是由少量甲烷的保留引起的。阳性检测将需要2007年甲烷的光谱，或10将需要具有更高信噪比的光谱。柯伊伯带天体上的挥发物保留模型似乎继续在再现所有可用的观测结果方面做得很好。
The central objective of the New Horizons prime mission was to make the first exploration of Pluto and its system of moons. Following that, New Horizons has been approved for its first extended mission, which has the objectives of extensively studying the Kuiper Belt environment, observing numerous Kuiper Belt Objects (KBOs) and Centaurs in unique ways, and making the first close flyby of the KBO 486958 2014 MU69. This review summarizes the objectives and plans for this approved mission extension, and briefly looks forward to potential objectives for subsequent extended missions by New Horizon…
Extrasolar debris disks are the dust disks found around nearby main sequence stars arising from the break-up of asteroids and comets orbiting the stars. Far-IR surveys (e.g., with Herschel) showed that ~20% of stars host detectable dust levels. While dust temperatures suggest a location at 10s of au comparable with our Kuiper belt, orders of magnitude more dust is required implying a planetesimal population more comparable with the primordial Kuiper belt. High resolution imaging (e.g., with ALMA) has mapped the nearest and brightest disks, providing evidence for structures shaped by an underly…
The Classical Kuiper Belt is populated by a group of objects with low inclination orbits, reddish colors and usually belonging to a binary system. This so called Cold Classical Kuiper Belt is considered to have been formed in situ from primordial ice pebbles that coagulated into planetesimals hundreds of kilometers in diameter. According to this scenario, the accretion of pebbles into large planetesimals would have occurred through the streaming instability mechanism that would be effective in the primordial Solar System disk of gas and solids. Nevertheless other objects with the same color ch…
Dynamical mass estimates for the main asteroid belt and the trans-Neptunian Kuiper belt have been found from their gravitational influence on the motion of planets. Discrete rotating models consisting of moving material points have been used to model the total attraction from small or as yet undetected bodies of the belts. The masses of the model belts have been included in the set of parameters being refined and determined and have been obtained by processing more than 800 thousand modern positional observations of planets and spacecraft. We have processed the observations and determined the …
While satellites of mid- to small-Kuiper belt objects tend to be similar in size and brightness to their primaries, the largest Kuiper belt objects preferentially have satellites with small fractional brightness. In the two cases where the sizes and albedos of the small faint satellites have been measured, these satellites are seen to be small icy fragments consistent with collisional formation. Here we examine Dysnomia and Vanth, the satellites of Eris and Orcus, respectively. Using the Atacama Large Millimeter Array, we obtain the first spatially resolved observations of these systems at the…
The density of mid-sized Kuiper belt object 2002 UX25 and the formation of the dwarf planets
柯伊伯带中最大的天体（测得的密度为~1.5 g cm-3或更高）是由测得的密度低于1 g cm-3的小天体凝聚而成的，如果不援引最小天体中的显著孔隙度，就很难解释。如果确实出现这种孔隙，则测量的密度应在不再支持显著孔隙的尺寸处开始增加。在小行星中，这种转变发生在直径大于~350公里的情况下。在柯伊伯带中，在~350 km和~850 km之间没有进行过密度测量，这是孔隙度可能首先开始下降的直径范围。在这个范围内的物体可以提供小型柯伊伯带物体的岩石部分的关键测试。在这里，我们报告的轨道特性，质量和密度测定的2002年UX 25系统在柯伊伯带。对于这个直径约为650公里的天体，我们发现其密度为0.82+/-0.11 g cm-3，使其成为太阳系中已知密度低于纯水冰的最大固体天体。我们认为，该对象的孔隙度不太可能高于~ 20%，这表明岩石分数低。如果目前测量的柯伊伯带天体的密度是样本整体的合理代表，那么很难通过岩石成分与2002年UX 25推断的岩石成分一样低的小天体的凝聚来创建岩石质量成分为70%或更高的~1000 km和更大的柯伊伯带天体。
The non-resonant Kuiper belt objects (KBOs) between the 3:2 and 2:1 Neptunian mean motion resonances can be largely divided between a cold classical belt (CCB) and a hot classical belt (HCB). A notable difference between these two subpopulations is the prevalence of widely spaced, equal-mass binaries in the CCB and a much smaller but non-zero number in the HCB. The primary reason for this difference in binary rate remains unclear. Here using N-body simulations we examine whether close encounters with the giant planets during an early outer solar system instability may have disrupted primordial…
The Kuiper belt includes tens of thousands of large bodies and millions of smaller objects. The main part of the belt objects is located in the annular zone between 39.4 au and 47.8 au from the Sun, the boundaries correspond to the average distances for orbital resonances 3:2 and 2:1 with the motion of Neptune. One-dimensional, two-dimensional, and discrete rings to model the total gravitational attraction of numerous belt objects are considered. The discrete rotating model most correctly reflects the real interaction of bodies in the Solar system. The masses of the model rings were determined…
The outer solar system exhibits an anomalous pattern of orbital clustering, characterized by an approximate alignment of the apsidal lines and angular momentum vectors of distant, long-term stable Kuiper belt objects. One explanation for this dynamical confinement is the existence of a yet-undetected planetary-mass object, "Planet Nine (P9)". Previous work has shown that trans-Neptunian objects, which originate within the scattered disk population of the Kuiper belt, can be corralled into orbital alignment by Planet Nine's gravity over ~Gyr timescales, and characteristic P9 parameters have bee…
A distant, massive planet in the outer solar system has recently been proposed to explain some observed features of extreme trans-Neptunian objects (TNOs). Here we use N-body simulations of the formation of the Kuiper belt and Oort cloud as well as a survey simulator to compare models of the solar system with and without a 9th planet to one another as well as to observations. The main mechanism for TNOs to be deposited into the distant ($a$ > au), detached ($q$ > au) region of the Kuiper Belt in the 8-planet model is Kozai-Lidov oscillation of objects in mean motion resonances (MMR) with Neptu…
Models of the Solar System's dynamical evolution predict the dispersal of primitive planetesimals from their formative regions amongst the gas-giant planets due to the early phases of planetary migration. Consequently, carbonaceous objects were scattered both into the outer asteroid belt and out to the Kuiper Belt. These models predict that the Kuiper Belt should contain a small fraction of objects with carbonaceous surfaces, though to date, all reported visible reflectance spectra of small Kuiper Belt Objects (KBOs) are linear and featureless. We report the unusual reflectance spectrum of a s…
This chapter reviews accretion models for Kuiper belt objects (KBOs), discussing in particular the compatibility of the observed properties of the KBO population with the streaming instability paradigm. Then it discusses how the dynamical structure of the KBO population, including the formation of its 5 sub-components (cold, hot, resonant, scattered and fossilized), can be quantitatively understood in the framewok of the giant planet instability. We also establish the connections between the KBO population and the Trojans of Jupiter and Neptune, the irregular satellites of all giant planets, t…
Origin of the peculiar eccentricity distribution of the inner cold Kuiper belt
Dawson and Murray-Clay（2012）指出，柯伊伯带内冷星群的内部（半长轴a<43.5天文单位），其轨道偏心率远小于稳定性限制的极限。在这里，我们确认他们的结果，在适当的元素空间中的轨道分布和稳定性。我们发现，所观察到的分布可能已经产生的缓慢扫描的4/7平均运动共振与海王星，伴随着海王星的迁移过程结束。热柯伊伯带的轨道分布在这一过程中没有受到明显的影响，原因在正文中讨论。因此，内部冷星群的特殊偏心率分布不能被明确地解释为冷星群在原地形成的证据，并且只有适度的偏心率激发;它可以简单地是海王星径向运动的标志，从适度偏心的轨道开始。我们讨论了这是如何同意的情况下，巨大的行星演化的动力学不稳定性，并可能与冷人口的径向运输。
Dynamically excited objects within the Kuiper belt show a bimodal distribution in their surface colors, and these differing surface colors may be a tracer of where these objects formed. In this work we explore radial color distributions in the primordial planetesimal disk and implications for the positions of ice line/color transitions within the Kuiper belt's progenitor populations. We combine a full dynamical model of the Kuiper belt's evolution due to Neptune's migration with precise surface colors measured by the Colours of the Outer Solar System Origins Survey in order to examine the true…
The flyby of Pluto and Charon by the New Horizons spacecraft provided high-resolution images of cratered surfaces embedded in the Kuiper belt, an extensive region of bodies orbiting beyond Neptune. Impact craters on Pluto and Charon were formed by collisions with other Kuiper belt objects (KBOs) with diameters from ~40 kilometers to ~300 meters, smaller than most KBOs observed directly by telescopes. We find a relative paucity of small craters less than approximately 13 kilometers in diameter, which cannot be explained solely by geological resurfacing. This implies a deficit of small KBOs (les…
Within the dynamically cold low inclination portion of the Classical Kuiper Belt, there exists a population of weakly bound binary systems with a number of unusual properties; most notable of which is their extremely wide orbital separations; beyond 7% of their Hill radii. The stability and evolution of these Ultra-Wide Trans-Neptunian Binaries (TNBs) have, in the past, been studied extensively under the assumption that the primary evolving mechanisms are interactions between the binary components and impacting Trans-Neptunian Objects (TNOs). Here, we instead study their evolution as driven by…
The Hubble Space Telescope (HST) measured the colors of eight Kuiper Belt Objects (KBOs) that will be observed by the New Horizons spacecraft including its 2019 close fly-by target the Cold Classical KBO (486958) 2014 MU69. We find that the photometric colors of all eight objects are red, typical of the Cold Classical dynamical population within which most reside. Because 2014 MU69 has a similar color to that of other KBOs in the Cold Classical region of the Kuiper Belt, it may be possible to use the upcoming high-resolution New Horizons observations of 2014 MU69 to draw conclusions about the …
Preliminary spacecraft trajectories for 45 Kuiper Belt Objects (KBOs) and Pluto suitable for launch between 2025 and 2040 are presented. These 46 objects comprise all objects with H magnitude < 4.0 or which have received a name from the International Astronomical Union as of May 2018. Using a custom Lambert solver, trajectories are modeled after the New Horizons mission to Pluto-Charon, which consisted of a fast launch with a Jupiter gravity assist. In addition to searching for Earth-Jupiter-KBO trajectories, Earth-Saturn-KBO trajectories are examined, with the option to add on a flyby to eith…
The centerpiece objective of the NASA New Horizons first Kuiper Extended Mission (KEM-1) was the close flyby of the Kuiper Belt Object KBO) 2014 MU69, nicknamed Ultima Thule. On 1 Jan 2019 this flyby culminated, making the first close observations of a small KBO. Initial post flyby trajectory reconstruction indicated the spacecraft approached to within ~3500 km of MU69 at 5:33:19 UT. Here we summarize the earliest results obtained from that successful flyby. At the time of this submission, only 4 days of data down-link from the flyby were available; well over an order of magnitude more data wi…
The densities of mid-sized Kuiper belt objects are a key constraint into understanding the assembly of objects in the outer solar system. These objects are critical for understanding the currently unexplained transition from the smallest Kuiper belt objects with densities lower than that of water to the largest objects with significant rock content. Mapping this transition is made difficult by the uncertainties in the diameters of these objects, which maps into an even larger uncertainty in volume and thus density. The substantial collecting area of the Atacama Large Millimeter Array allows si…
Context. A recent observational census of Kuiper belt objects (KBOs) has unveiled anomalous orbital structures. This has led to the hypothesis that an additional $\sim5-10~m_{\oplus}$ planet exists. This planet, known as Planet 9, occupies an eccentric and inclined orbit at hundreds of astronomical units. However, the KBOs under consideration have the largest known semimajor axes at $a>250$ AU; thus they are very difficult to detect.// Aims. In the context of the proposed Planet 9, we aim to measure the mean plane of the Kuiper belt at $a>50$ AU. In a comparison of the expected and observed me…
