对Kuiper带中3:2共振天体的轨道根数的分析研究

在太阳系最外层的Kuiper带中，有许多天体处于海王星3：2平运动共振中．对这些天体的主要轨道根数的观测数据分析发现，与其它Kuiper带天体比较，它们普遍具有高偏心率、高倾角和相对稳定的轨道．     

对Kuiper带天体动力学演化的数值模拟

鉴于无法找到描述Kuiper带天体动力学演化的分析解,本文采用数值模拟的方法,即通过数值积分,得到由太阳、海王星和Kuiper带天体组成的限制性三体问题中Kuiper带天体随时间演化的数值解.结果表明,经长期演化后,共振带中的一些天体的偏心率明显被激励;Kuiper带天体的轨道偏心率和倾角的激励程度和天体的初始轨道半长径、偏心率、倾角有关.     

追溯太阳系边界的原始状态

Kuiper带是近10多年来天文学的一大重大发现，它是目前已观测到的太阳系的边界。根据国际天文联合会公布的kuiper带天体的最新的数据，用SWIFT积分器对这些天体的轨道进行了时间反演模拟，得出距今数亿年前的太阳系边界的天体距离分布状态。     

Kuiper带天体轨道的观测特性

对当前已观测到的具有可靠轨道根数、位于30～50AU的Kuiper主带和50AU以外Kuiper散射带的轨道半长径、轨道偏心率和倾角的分布特性分别进行了统计作图分析．结果显示：轨道半长径在40～50AU之间的KBOs的数量呈近似正态分布,KBOs在共振区出现聚集,并且共振区天体普遍具有较大的轨道偏心率;经典KBOs的轨道倾角的分布范围比共振KBOs的还大;散射KBOs的近日点距离大多在30～45AU之间．     

新天体惊现太阳系

美国天文学家去年在太阳系边缘地带观测到一个除冥王星之外个头最大的天体,再次动摇了冥王星作为太阳系九大行星之一的地位。新发现的这一天体绕太阳公转的周期为288年,直径约为1290公里,相当于冥王星的一半,位于太阳系边缘的“柯伊伯带”。     

第十大“行星”引发的争论

7月29日,美国加州理工学院的迈克·布朗等人宣布,他们在冥王星轨道之外发现了一颗巨大的天体,按照他们的估计,这颗天体的体积可能达到冥王星的1.56倍。美国宇航局作为该研究项目的资助机构,在发布新闻时将这颗编号为2003UB313的天体称为“第十大行星”。     

太阳系边缘的天体

最近,美国天文学家新近在太阳系边缘地带观测到一个除冥王星之外个头最大的天体。发现者是加利福尼亚理工学院的迈克·布朗及其同事。新发现的这一天体的临时国际代号为“2002LM60”,它绕太阳公转的周期为288年,直径约1 290 km,相当于冥王星的一半,位于太阳系边缘的“柯伊伯带”。这一发现引起世人的普遍关注。太阳系有九大行星,距太阳最远的是冥王星。这是常识大家都知道。冥王星绕太阳运行轨道与太阳的平均距离大约是地球与太阳距离的40倍,但那还不是太阳系的边缘。天文学家早已发现,作为太阳系家族成员的彗星,他们在远离太阳的时候,通常…     

带环的矮行星

<正>此前,太阳系内只有4颗气态行星(外行星)有环状结构,分别是木星、土星、天王星和海王星。如今,天文学家们又发现,在海王星轨道之外的一颗矮行星——妊神星,也有环状带。该结果已于2017年10月11日发表在Nature上。在太阳系外沿有很多小型天体。渐渐地,人们意识到这些天体并非都是又小又黯淡,某些天体的体积甚至可与冥王星相当。于是,在2006年,天文学家定义了一类新的行星——矮行星。妊神星是继冥王星、谷神星、阋神星、鸟神星之后发现的第5颗矮行星。其形状宛如橄榄,自转速度极快,有两颗卫星,一直以来格外吸引天文学家的目光。"环状带的形成原因实在太多了,有可能是在与其他天体碰撞时产生的,也可能是妊神星本身的自转速度太快造成     

太阳系“新家谱”

一、行星成员包括水星、金星、地球、火星、木星、土星、天王星和海王星。定义:围绕太阳运转,自身引力足以克服其刚体力而使天体呈圆球状,并且能够清11除其轨道附近其他物体的天体。二、矮行星成员包括冥王星和谷神星等。定义:与行星同样具有足够的质量,呈圆球状,但不能清除其轨道附近其他物体的天体。三、太阳系小天体定义:围绕太阳运转但不符合行星和矮行星条件的物体。太阳系“新家谱”     

新知新品-海外

美国启动“新地平线”计划,12年后抵冥王星随着1.1亿美元的首笔款项到位,美国尘封了近13年的“新地平线”计划开始启动。据中国航天报消息,冥王星探测器将于2004年出发。2015年飞抵冥王星,探测冥王星及其卫星卡戎和位于太阳系边缘的柯伊珀带天体。冥王星是太阳系九大行星中唯一没被探测器光顾的一颗。     

用密度波理论描述旋涡星系的演化方向和太阳系的八大行星模式

基于密度波理论的非线性方程,用定性分析理论可导出旋涡星系的演化方向和由观测可得到的演化条件,根据最新的观测结果,作者定量论证了太阳系的八大行星模式：它是对称的四个类地行星和小行星带;四个类木行星和柯伊伯带(包括冥王星)。     

The binary Kuiper-belt object 1998 WW31

The recent discovery of a binary asteroid during a spacecraft fly-by generated keen interest, because the orbital parameters of binaries can provide measures of the masses, and mutual eclipses could allow us to determine individual sizes and bulk densities. Several binary near-Earth, main-belt and Trojan asteroids have subsequently been discovered. The Kuiper belt-the region of space extending from Neptune (at 30 astronomical units) to well over 100 AU and believed to be the source of new short-period comets-has become a fascinating new window onto the formation of our Solar System since the first member object, not counting Pluto, was discovered in 1992 (ref. 13). Here we report that the Kuiper-belt object 1998 WW31 is binary with a highly eccentric orbit (eccentricity e approximately 0.8) and a long period (about 570 days), very different from the Pluto/Charon system, which was hitherto the only previously known binary in the Kuiper belt. Assuming a density in the range of 1 to 2 g cm-3, the albedo of the binary components is between 0.05 and 0.08, close to the value of 0.04 generally assumed for Kuiper-belt objects.     

A giant impact origin for Pluto's small moons and satellite multiplicity in the Kuiper belt

The two newly discovered satellites of Pluto (P1 and P2) have masses that are small compared to both Pluto and Charon-that is, between 5 x 10(-4) and 1 x 10(-5) of Pluto's mass, and between 5 x 10(-3) and 1 x 10(-4) of Charon's mass. This discovery, combined with the constraints on the absence of more distant satellites of Pluto, reveal that Pluto and its moons comprise an unusual, highly compact, quadruple system. These facts naturally raise the question of how this puzzling satellite system came to be. Here we show that P1 and P2's proximity to Pluto and Charon, the fact that P1 and P2 are on near-circular orbits in the same plane as Pluto's large satellite Charon, along with their apparent locations in or near high-order mean-motion resonances, all probably result from their being constructed from collisional ejecta that originated from the Pluto-Charon formation event. We also argue that dust-ice rings of variable optical depths form sporadically in the Pluto system, and that rich satellite systems may be found--perhaps frequently--around other large Kuiper belt objects.     

Discovery of two new satellites of Pluto

Pluto's first known satellite, Charon, was discovered in 1978. It has a diameter (approximately 1,200 km) about half that of Pluto, which makes it larger, relative to its primary, than any other moon in the Solar System. Previous searches for other satellites around Pluto have been unsuccessful, but they were not sensitive to objects less, similar150 km in diameter and there are no fundamental reasons why Pluto should not have more satellites. Here we report the discovery of two additional moons around Pluto, provisionally designated S/2005 P 1 (hereafter P1) and S/2005 P 2 (hereafter P2), which makes Pluto the first Kuiper belt object known to have multiple satellites. These new satellites are much smaller than Charon, with estimates of P1's diameter ranging from 60 km to 165 km, depending on the surface reflectivity; P2 is about 20 per cent smaller than P1. Although definitive orbits cannot be derived, both new satellites appear to be moving in circular orbits in the same orbital plane as Charon, with orbital periods of approximately 38 days (P1) and approximately 25 days (P2).     

The trans-neptunian object UB313 is larger than Pluto

The most distant known object in the Solar System, 2003 UB313 (97 au from the Sun), was recently discovered near its aphelion. Its high eccentricity and inclination to the ecliptic plane, along with its perihelion near the orbit of Neptune, identify it as a member of the 'scattered disk'. This disk of bodies probably originates in the Kuiper belt objects, which orbit near the ecliptic plane in circular orbits between 30 and 50 au, and may include Pluto as a member. The optical brightness of 2003 UB313, if adjusted to Pluto's distance, is greater than that of Pluto, which suggested that it might be larger than Pluto. The actual size, however, could not be determined from the optical measurements because the surface reflectivity (albedo) was unknown. Here we report observations of the thermal emission of 2003 UB313 at a wavelength of 1.2 mm, which in combination with the measured optical brightness leads to a diameter of 3,000 +/- 300 +/- 100 km. Here the first error reflects measurement uncertainties, while the second derives from the unknown object orientation. This makes 2003 UB313 the largest known trans-neptunian object, even larger than Pluto (2,300 km). The albedo is 0.60 +/- 0.10 +/- 0.05, which is strikingly similar to that of Pluto, suggesting that the methane seen in the optical spectrum causes a highly reflective icy surface.     

The formation of the Kuiper belt by the outward transport of bodies during Neptune's migration

The 'dynamically cold Kuiper belt' consists of objects on low-inclination orbits between approximately 40 and approximately 50 au from the Sun. It currently contains material totalling less than a tenth the mass of the Earth, which is surprisingly low because, according to accretion models, the objects would not have grown to their present size unless the cold Kuiper belt originally contained tens of Earth masses of solids. Although several mechanisms have been proposed to produce the observed mass depletion, they all have significant limitations. Here we show that the objects currently observed in the dynamically cold Kuiper belt were most probably formed within approximately 35 au and were subsequently pushed outward by Neptune's 1:2 mean motion resonance during its final phase of migration. Combining our mechanism with previous work, we conclude that the entire Kuiper belt formed closer to the Sun and was transported outward during the final stages of planet formation.     

Saturn's moon Phoebe as a captured body from the outer Solar System

The orbital properties of Phoebe, one of Saturn's irregular moons, suggest that it was captured by the ringed planet's gravitational field rather than formed in situ. Phoebe's generally dark surface shows evidence of water ice, but otherwise the surface most closely resembles that of C-type asteroids and small outer Solar System bodies such as Chiron and Pholus that are thought to have originated in the Kuiper belt. A close fly-by of Phoebe by the Cassini-Huygens spacecraft on 11 June 2004 (19 days before the spacecraft entered orbit around Saturn) provided an opportunity to test the hypothesis that this moon did not form in situ during Saturn's formation, but is instead a product of the larger protoplanetary disk or 'solar nebula'. Here we derive the rock-to-ice ratio of Phoebe using its density combined with newly measured oxygen and carbon abundances in the solar photosphere. Phoebe's composition is close to that derived for other solar nebula bodies such as Triton and Pluto, but is very different from that of the regular satellites of Saturn, supporting Phoebe's origin as a captured body from the outer Solar System.     

Formation of Kuiper-belt binaries by dynamical friction and three-body encounters

The Kuiper belt is a disk of icy bodies that orbit the Sun beyond Neptune; the largest known members are Pluto and its companion Charon. A few per cent of Kuiper-belt bodies have recently been found to be binaries with wide separations and mass ratios of the order of unity. Collisions were too infrequent to account for the observed number of binaries, implying that these binaries formed through collisionless interactions mediated by gravity. These interactions are likely to have been most effective during the period of runaway accretion, early in the Solar System's history. Here we show that a transient binary forms when two large bodies penetrate one another's Hill sphere (the region where their mutual forces are larger than the tidal force of the Sun). The loss of energy needed to stabilize the binary orbit can then occur either through dynamical friction from surrounding small bodies, or through the gravitational scattering of a third large body. Our estimates slightly favour the former mechanism. We predict that five per cent of Kuiper-belt objects are binaries with apparent separations greater than 0.2 arcsec, and that most are in tighter binaries or systems of higher multiplicity.     

Stellar encounters as the origin of distant Solar System objects in highly eccentric orbits

The Kuiper belt extends from the orbit of Neptune at 30 au to an abrupt outer edge about 50 au from the Sun. Beyond the edge is a sparse population of objects with large orbital eccentricities. Neptune shapes the dynamics of most Kuiper belt objects, but the recently discovered planet 2003 VB12 (Sedna) has an eccentric orbit with a perihelion distance of 70 au, far beyond Neptune's gravitational influence. Although influences from passing stars could have created the Kuiper belt's outer edge and could have scattered objects into large, eccentric orbits, no model currently explains the properties of Sedna. Here we show that a passing star probably scattered Sedna from the Kuiper belt into its observed orbit. The likelihood that a planet at 60-80 au can be scattered into Sedna's orbit is about 50 per cent; this estimate depends critically on the geometry of the fly-by. Even more interesting is the approximately 10 per cent chance that Sedna was captured from the outer disk of the passing star. Most captures have very high inclination orbits; detection of such objects would confirm the presence of extrasolar planets in our own Solar System.     

Crystalline water ice on the Kuiper belt object (50000) Quaoar

The Kuiper belt is a disk-like structure consisting of solid bodies orbiting the Sun beyond Neptune. It is the source of the short-period comets and the likely repository of the Solar System's most primitive materials. Surface temperatures in the belt are low ( approximately 50 K), suggesting that ices trapped at formation should have been preserved over the age of the Solar System. Unfortunately, most Kuiper belt objects are too faint for meaningful compositional study, even with the largest available telescopes. Water ice has been reported in a handful of objects, but most appear spectrally featureless. Here we report near-infrared observations of the large Kuiper belt object (50000) Quaoar, which reveal the presence of crystalline water ice and ammonia hydrate. Crystallinity indicates that the ice has been heated to at least 110 K. Both ammonia hydrate and crystalline water ice should be destroyed by energetic particle irradiation on a timescale of about 10(7) yr. We conclude that Quaoar has been recently resurfaced, either by impact exposure of previously buried (shielded) ices or by cryovolcanic outgassing, or by a combination of these processes.