2000—2049年行星天象（一）

本文给出 2 0 0 0 - 2 0 4 9年行星天象的一部分 ,包括水星、金星的东、西大距 ,留及上、下合日 ;金星最亮和最接近地球 ;外行星冲日、最接近地球、合日、留 ;地球和外行星过远近日点计1 5个表     

2月天象指南

术语和图标若无特别说明,天象介绍中使用的时间均为北京时间;赤经和赤纬赤道坐标系统所使用的经度和纬度,用来描述天体在天球上的位置,与地球表面的经度和纬度类似;合行星、月球、恒星、深空天体相合,指它们的赤经相同的时刻。     

第十三届国际天文奥林匹克竞赛实测试题

高年组： 一、系外行星凌星。探测系外行星的最可靠方法之一,就是观测行星凌恒星现象。当凌星发生时,由于行星遮挡在恒星之前,恒星的辐射流量F会从正常的F0暂时性地下降。     

宇宙信息

HARPS新发现32颗太阳系外行星 高精度视向速度行星搜寻（HARPS）计划宣布新发现了32颗太阳系外行星,这使得系外行星的发现总数超过了400颗。这批新发现的系外行星涵盖了过去发现的所有类型,从热类木星、超级海王星和超级地球再到低质量、贫金属恒星周围以及多行星系统中的行星。     

太阳系外行星系统轨道参数的统计研究

自1995年第一颗类太阳恒星周围的系外行星发现以来,随着已发现的系外行星数目的增多,对系外行星性质的统计分析变得重要和有意义。截至2011年6月9日,共发现系外行星555颗。以这些系外行星的轨道参数为依据,对系外行星的性质进行统计分析,得出了一些有意义的结论。同时简要介绍现有的行星形成与演化模型并依据得出的行星统计性质对其进行检验,这对于系外行星的进一步探测具有一定的指导作用。     

天津纬度站天顶仪1970—1980年纬度观测的均一化处理结果

对1970—1980年间的纬度观测资料,统一使用IAU1964系统天文常数,按直角坐标法计算全部星对的视赤纬,用统一的公式进行了全部观测结果的归算处理。本文给出全部星对的赤纬及自行改正以及纬度观测结果的每组月平均值。     

观测角

12月3日水星西大距今年水星共有3次酉大距（4月16日、8月14日和12月3日）,以12月3日这次大距对观测最为有利。这是因为水星的赤纬高于太阳的赤纬,水星在日出时地平高度较高,利于观测。对于北京（地理纬度40°N）纬度的地区来说,日出时（北京时间7时04分）,水星的地平高度近于20°,方位角为东偏南约40°。而水星升出地平的时刻为北京时间5时37分。晨光始的时刻为6时34分。日出前可见水星的时间较久。地理纬度越高,可见条件越好,地理纬度越低,日出前可见水星时间越短。12月14日双子座流星雨极盛12月7日～18日双子座流星雨出现,14日…     

基于Kepler Q1–Q17数据对类太阳型恒星的行星生成率估算

近30年来的系外行星探测揭示了行星在宇宙中普遍存在的事实.为了深入研究适宜生命居住行星的普遍性,一方面需要了解宜居行星的特性;另一方面可以通过分析已发现系外行星的分布特征,推算该类行星在恒星周围的存在几率.在目前已发现的系外行星中,凌星法发现的占据了绝大多数,如Kepler空间望远镜所观测的系外行星共有2344颗. 2018年Kepler正式退役,其科学团队发布了最终版的Kepler Data Release (DR25),包含观测季度Q1–Q17的恒星共198709颗.通过对Kepler数据的分析,使用逆检测效率法和最大似然分析法两种不同的方法对系外行星半径周期参数空间内的行星生成率进行了估算,同时将计算样本根据恒星的光谱类型进行分类,分别估算得到了F、G、K型的Kepler恒星周围的行星生成率及其整体的生成率.对于半径范围1–20 R_⊕(R_⊕为一个地球半径),轨道周期范围0.4–400 d的Kepler凌星系外行星,宿主恒星为F型时逆检测效率法和最大似然法估算得到的行星生成率分别为0.36±0.02和0.47±0.02,宿主恒星为G型时的...     

深入“特丝”巡星之旅

凌星太阳系外行星巡天卫星正在革新人类对太阳邻域中行星的认识,但发现新的行星只是开始。1995年,在类太阳恒星旁发现了首颗太阳系外行星。到2005年,太阳系外行星搜寻仍处于襁褓中。天文学家当时依然不清楚,环绕其他恒星的行星是普遍存在的,还是罕见的个案。     

系外行星的形状与其内部结构

随着观测技术不断进步,已经有了很多对系外行星扁率和拱点进动的观测进展.行星的扁率是由行星的内部密度剖面与其自转决定的,勒夫数k_2与其核的大小存在明显的负相关.故扁率与k_2可以很好地限定系外行星的内部结构.从Lane-Emden方程出发,构建了不同多方指数下的行星模型.继而通过解算Wavre的积分微分方程得到其扁率,结果表明:多方指数越小,自转越快,扁率越大.从NASA(美国国家航空航天局)系外行星表中,挑选了469个同时具有质量、半径和轨道周期观测或估算值的系外行星,在两种不同自转周期假设下,计算了它们的扁率.结果表明:如果采用潮汐锁定假设,绝大多数系外行星的扁率非常小,约97%的行星小于0.01,难以被观测到;而在固定的10.55 h自转周期假设下,有28%的行星扁率大于0.1.通过解算Zharkov简化的2阶微分方程,得到了不同多方模型下的勒夫数,并讨论了k_2与核大小的关系.     

Solar activity and planetary luminosity

The Chree superposition analysis of the luminosities of the planets Jupiter, Saturn, Uranus and Neptune indicates a correlation between solar activity and planetary luminosity. The variations of the solar constant in the visible range are considered to be too small to explain the observed changes in brightness. The interaction of solar extreme ultraviolet or solar wind particles with the atmospheres of these planets is probably responsible for the increased albedo during periods of high solar activity.     

系外类地行星的内部结构及大气成分研究进展

系外类地行星是目前搜寻地外生命的主要目标.随着观测仪器的发展,现在已经能探测到低于10个地球质量的系外行星.该文简要回顾了系外类地行星的形成与演化,介绍了当前研究它们内部结构的模型和方法,以及由此得出的类地行星质量-半径关系.同时,对应不同的行星初始物质成分,讨论了各种可能的大气结构.最后介绍了未来的空间任务在相关方面的工作.     

Gravitational microlensing of planets: the influence of planetary phase and caustic orientation

Recent studies have demonstrated that detailed monitoring of gravitational microlensing events can reveal the presence of planets orbiting the microlensed source stars. With the potential of probing planets in the Galactic bulge and Magellanic Clouds, such detections greatly increase the volume over which planets can be found. This paper expands on the original studies by considering the effect of planetary phase on the form of the resultant microlensing light curve. It is found that crescent-like sources can undergo substantially more magnification than a uniformly illuminated disc, the model typically employed in studying such planets. In fact, such a circularly symmetric model is found to suffer a minimal degree of magnification when compared with the crescent models. The degree of magnification is also a strong function of the planet's orientation with respect to the microlensing caustic. The form of the magnification variability is strongly dependent on the planetary phase and from which direction the planet is swept by the caustic, providing further clues to the geometry of the planetary system. As the amount of light reflected from a planet also depends on its phase, the detection of extreme crescent-like planets requires the advent of 30-m class telescopes, while light curves of planets at more moderate phases can be determined with today's 10-m telescopes.     

Comments on The Jupiter Effect

Several statements, on which the recent book The Jupiter Effect is based, are invalid: The planets will not be “aligned” in 1982, and such an alignment has no effect on solar activity; planetary tides on the Sun are negligible; tides raised on the Sun by Venus, Earth, and Jupiter have a period of 4 mo, not 11 yr, and Wood's curve has no physical justification; there are not more sunspots visible at the eastern limb of the Sun than at the western one; the mean number of sunspots is the same at Venus' inferior and superior conjunctions; the influence of solar flares on sudden changes in the Earth's rotation and on earthquakes is not proved. This leads to the conclusion that there is no evidence for a correlation between planetary positions and earthquakes. The “Jupiter effect” does not exist.     

Computer simulations of planetary accretion dynamics: Sensitivity to initial conditions

We have tested the implications and limitations of Program ACRETE, a scheme based merely on Newtonian physics and accretion with unit sticking efficiency, devised by Dole in 1970 to simulate the origin of the planets. The dependence of the results on a variety of radial and vertical density distribution laws, on the ratio of gas to dust in the solar nebula, on the total nebula mass, and on the orbital eccentricity, ?, of the accreting grains are explored. Only for a small subset of conceivable cases are planetary systems closely like our own generated. Many models have tendencies toward one of two preferred configurations: multiple-star systems, or planetary systems in which Jovian planets either have substantially smaller masses than in our system or are absent altogether. But for a wide range of cases recognizable planetary systems are generated, ranging from multiple-star systems with accompanying planets, to systems with Jovian planets at several hundred astronomical units, to single stars surrounded only by asteroids. Many systems exhibit planets like Pluto and objects of asteroidal mass, in addition to usual terrestrial and Jovian planets. No terrestrial planets were generated more massive than five Earth masses. The number of planets per system is for most cases of order 10, and, roughly, inversely proportional to ?. All systems generated obey a relation of the Titius-Bode variety for relative planetary spacing. The case with which planetary systems are generated using such elementary and incomplete physical assumptions supports the idea of abundant and morphologically diverse planetary systems throughout the Galaxy.     

The role of cluster evolution in disrupting planetary systems and discs: the Kozai mechanism

We examine the effects of dynamical evolution in clusters on planetary systems or protoplanetary discs orbiting the components of binary stars. In particular, we look for evidence that the companions of host stars of planetary systems or discs could have their inclination angles raised from zero to between the threshold angles (39.23° and 140.77°) that can induce the Kozai mechanism. We find that up to 20 per cent of binary systems have their inclination angles increased to within the threshold range. Given that half of all extrasolar planets could be in binary systems, we suggest that up to 10 per cent of extrasolar planets could be affected by this mechanism.     

Fresip: A mission to determine the character and frequency of extra-solar planets around solar-like stars

FRESIP (FRequency of Earth-Sized Inner Planets) is a mission designed to detect and characterize Earth-sizes planets around solar-like stars. The sizes of the planets are determined from the decrease in light from a star that occurs during planetary transits, while the orbital period is determined from the repeatability of the transits. Measurements of these parameters can be compared to theories that predict the spacing of planets, their distribution of size with orbital distance, and the variation of these quantities with stellar type and multiplicity. Because thousands of stars must be continually monitored to detect the transits, much information on the stars can be obtained on their rotation rates and activity cycles. Observations of p-mode oscillations also provide information on their age and composition. These goals are accomplished by continuously and simultaneously monitoring 500 solar-like stars for evidence of brightness changes caused by Earth-sized or larger planetary transits. To obtain the high precision needed to find planets as small as the Earth and Venus around solar-like stars, a wide field of view Schmidt telescope with an array of CCD detectors at its focal plane must be located outside of the Earth's at mosphere. SMM (Solar Maximum Mission) observations of the low-level variability of the Sun (1:100,000) on the time scales of a transit (4 to 16 hours), and our laboratory measurements of the photometric precision of charge-coupled devices (1:100,000) show that the detection of planets as small as the Earth is practical. The probability for detecting transits is quite favorable for planets in inner orbits. If other planetary systems are similar to our own, then approximately 1% of those systems will show transits resulting in the discovery of 50 planetary systems in or near the habitable zone of solar-like stars.     

Obliquity variations of terrestrial planets in habitable zones

We have investigated obliquity variations of possible terrestrial planets in habitable zones (HZs) perturbed by a giant planet(s) in extrasolar planetary systems. All the extrasolar planets so far discovered are inferred to be jovian-type gas giants. However, terrestrial planets could also exist in extrasolar planetary systems. In order for life, in particular for land-based life, to evolve and survive on a possible terrestrial planet in an HZ, small obliquity variations of the planet may be required in addition to its orbital stability, because large obliquity variations would cause significant climate change. It is known that large obliquity variations are caused by spin-orbit resonances where the precession frequency of the planet's spin nearly coincides with one of the precession frequencies of the ascending node of the planet's orbit. Using analytical expressions, we evaluated the obliquity variations of terrestrial planets with prograde spins in HZs. We found that the obliquity of terrestrial planets suffers large variations when the giant planet's orbit is separated by several Hill radii from an edge of the HZ, in which the orbits of the terrestrial planets in the HZ are marginally stable. Applying these results to the known extrasolar planetary systems, we found that about half of these systems can have terrestrial planets with small obliquity variations (smaller than 10°) over their entire HZs. However, the systems with both small obliquity variations and stable orbits in their HZs are only 1/5 of known systems. Most such systems are comprised of short-period giant planets. If additional planets are found in the known planetary systems, they generally tend to enhance the obliquity variations. On the other hand, if a large/close satellite exists, it significantly enhances the precession rate of the spin axis of a terrestrial planet and is likely to reduce the obliquity variations of the planet. Moreover, if a terrestrial planet is in a retrograde spin state, the spin-orbit resonance does not occur. Retrograde spin, or a large/close satellite might be essential for land-based life to survive on a terrestrial planet in an HZ.     

The contribution of the ARIEL space mission to the study of planetary formation

The study of extrasolar planets and of the Solar System provides complementary pieces of the mosaic represented by the process of planetary formation. Exoplanets are essential to fully grasp the huge diversity of outcomes that planetary formation and the subsequent evolution of the planetary systems can produce. The orbital and basic physical data we currently possess for the bulk of the exoplanetary population, however, do not provide enough information to break the intrinsic degeneracy of their histories, as different evolutionary tracks can result in the same final configurations. The lessons learned from the Solar System indicate us that the solution to this problem lies in the information contained in the composition of planets. The goal of the Atmospheric Remote-Sensing Infrared Exoplanet Large-survey (ARIEL), one of the three candidates as ESA M4 space mission, is to observe a large and diversified population of transiting planets around a range of host star types to collect information on their atmospheric composition. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres, which should show minimal condensation and sequestration of high-Z materials and thus reveal their bulk composition across all main cosmochemical elements. In this work we will review the most outstanding open questions concerning the way planets form and the mechanisms that contribute to create habitable environments that the compositional information gathered by ARIEL will allow to tackle.