彗星研究和彗星空间探测进展

 彗星是一种冰冻的小天体, 是由冰(主要是水冰)和尘埃组成的“脏雪球”, 俗称扫帚星。彗星是太阳系早期形成时期遗留下的残骸, 被认为是太阳系中最原始的天体, 研究彗星的起源、演化和成分有助于研究太阳系的起源和行星系统形成和演化。此外, 彗星富含水冰和有机分子, 这些都是生命形成的必要元素, 因此研究彗星也有助于研究生命起源。发育完整的彗星由彗核、彗发、氢云、离子彗尾(又称等离子体或Ⅰ型彗尾)和尘埃彗尾(又称Ⅱ型彗尾)构成(图1), 彗核集中了彗星的绝大部分质量, 是彗星的本体。     

太阳系中的双行星

 太阳系是由太阳、行星及其卫星、小行星、彗星及行星际物质组成的天体系统,各天体都绕太阳系质心转动.太阳的质量占太阳系总质量的99.8%以上,自然成为太阳系的中心天体,而常把行星等天体看做是在太阳引力作用下绕太阳公转.行星及其卫星是太阳系的子系统,它们除绕本系统质心转动外,其质心同时绕太阳公转;由于行星的质量比其卫星大得多,而常看作卫星绕行星转动.     

恒星照亮行星定律被打破人马座行星正温暖恒星

恒星照亮行星 ,这是天文学的定律。然而 ,科学家却发现人马座一个巨大炙热的气态行星在磁场作用下 ,产生类似太阳耀斑的活动温暖着其恒星 ;同时 ,科学家也第一次观测到太阳系外行星的磁场状况。这颗炙热的行星与木星大小类似 ,是地球质量的 2 70倍。但与地球和木星不同 ,该行星与其恒星的距离很近 ,仅有大约 70 0万千米左右 ,而地球与太阳的距离约为 1 .5亿千米。这样接近恒星的行星 ,在迄今发现的 1 0 0多颗太阳系外行星中约占 2 0 %。这颗人马座行星在其恒星上产生一个大型磁暴 ,从而形成了一个永久性的热点。该热点伴随着行星以 3天的周…     

玫瑰眼（The Rosette Eye）——大质量恒星周围电离氢区前期形成及演化重要过渡阶段的发现

一个由中英德美多国天文学家组成的工作小组近期在距离太阳系5000光年的玫瑰巨分子云核心大质量星形成区域发现了一个处于早期演化阶段的罕见的年轻大质量恒星系统。据估算,中心星体的质量大约为20个太阳质量。观测表明,该大质量星在其形成的吸积塌缩过程中产生的强大紫外辐射正以大张角电离星风的形式从恒星的两极喷射而出,在近红外宽带和分子氢发射线窄带成像中表现为一个沙漏状的双极电离氢区。     

星际型CH_3CN－H_2含超精细能级的碰撞跃迁速率系数的理论计算

利用ＩＯＳ近似模型，计算了星际分子云条件下Ｅ型ＣＨ３ＣＮ－Ｈ２含超精细能级的的碰撞跃迁速率系数。其温度范围是２０Ｋ－１４０Ｋ。为研究分子云与恒星形成区的物理、化学性质提供了大量有用的基础分子数据。     

太阳系外行星的搜寻和发现

太阳系外行星的搜寻和发现我们都知道，人类生存的地球是属于太阳系的九大行星之一．人们也认为，像地球上的生命，特别是像人类这样的有智慧的生命可能只有在恒星的行星系统中才能产生．天文学的研究告诉我们，在银河系中至少有数千亿颗恒星，而整个宇宙又有上千亿个像银...     

封面说明

国家天文台兴隆基地李金增博士与英国阿尔玛天文台的Michael D.Smith教授合作,成功地解析了整个巨分子云范围内(2°×2°,1.5 kpc)恒星及星团的大尺度结构和形成模式.该中英合作小组开创性地在OB星团的序列形成模式中全面引入了中、低质量原星团,使之更全面、更符合巨分子云中星团形成的实际图景,进而成功描绘出玫瑰巨分子云复合体中原星团形成的全景图(左上图).下面两张图分别是玫瑰巨分子云区的光深分布图和玫瑰巨分子云区的尘埃色温分布图.该系列研究的主要创新成果包括:(1)提出了原星团形成所遵循的多种模式即孤立形成、协同形成及结…     

漫话地球

 地球是宇宙中一个尉蓝色的旋转大球,也是我们已知的唯一有生命的星球．她的产生,演变,兴衰和发展从古至今一直是我们不懈探索的重要科学领域之一．一、地球的形成地球是太阳系里的天体,地球的起源是太阳系起源的一个组成部分．太阳是太阳系的中心天体,质量达２０００亿亿亿吨,是地球质量的３３万多倍,占了整个太阳系数以万计的天体质量总和的９９％左右．太阳几乎“主宰”着太阳系的一切：光和热的效应,生命的维持和发展,以及支配着各天体的运动等．据天文学家推算,６６亿年前的宇宙充满了尘埃,星际有机分子和宇宙射线等“原始星云”．由于星云内部物质密度分布不均匀而形成了各个不同的引力中心,其中之一便形成了原始太阳．     

年轻恒星形成过程的分子谱线诊断

恒星是宇宙的基本天体,理解恒星的起源和早期演化是天体物理最有举的课题之一,目前了解的恒星形成的一个基本图象是,恒星是由一个足够大质量的星际分子气体云在其其自引力作用下塌缩而形成。在早期塌缩过程中形成一颗原恒星（胚胎）,并且伴随该原恒星的吸积盘,原恒星吸积星际介质中的分子物质,通过吸积盘转移到原恒星表面,原恒星的质量随着增大。在吸积过程中也同时伴随物质向外的剧烈喷发,由于盘的存在,这种喷发通常沿垂直于盘的方向进行,出现双极的空间分布。在天文观测上,一种典型的表现是分子气体的外向流,观测表现为从原恒星双极的红蓝移气体运动^[1]。由于恒星形成了星际分子中,因此,对星际分子的谱线探测是研究恒星形成的强有力手段,现在已经发现和证认的星际分子总数有一百多种,其中丰富度最高的气体是H2。在所有的星际分子中,丰度仅次于H2的CO分子的转动跃迁谱易激发,相对于星际介质的不透明度小,观测上易于实现,因此,CO分子就成为探索原恒星形成的有力探针,在毫米波段出现的J＝1－0和J＝2－1跃迁变线以及CO同位素的谱线是最常使用的观测探针,八十年代以来又陆续发现了环形分子SiC2,C3H,C3H2及含磷分子PN和CN等,给宇宙中有机世界的探测提供了丰富的线索。我们对恒形成区内存在的低温原恒星天体进行毫米 波射电谱线观测,测量该原恒星周围分子气体的分布,其物理化学参数,以及速度场分布。根据这些测量结果并运用成熟的数量方法,分析正在发生的物理化学过程,特别是原恒星质量外流的过程。根据观测分析结果得出所观测天体的形成和演化状况。     

恒星身世案 循迹赫罗图

<正>在20世纪天文学中,有两幅至为重要的图:赫罗图和哈勃图。前者是揭开恒星身世之谜的钥匙,后者则是宇宙膨胀乃至大爆炸理论的首要观测证据。今年适逢赫罗图百年诞辰,谨撰此文,以资纪念。孕育中的恒星万物皆有诞生、成长、衰老和死亡的过程,恒星也不例外。那么,一颗恒星究竟如何度过其一生呢?一颗像太阳这样的恒星,从孕育到长成大致可分7个阶段,从成年到老死也可分为7个阶段。现在我们就来从头说起。第1阶段——星际云太空中有着许许多多远比今日之太阳系大得多的星际云。它们由非常稀薄的气体和尘埃组成,最主要的成分是最简单的化学元     

Far-out surface science: radiation-induced surface processes in the solar system

Interplanetary space is a cosmic laboratory for surface scientists. Energetic photons, ions and electrons from the solar wind, together with galactic and extragalactic cosmic rays, constantly bombard surfaces of planets, planetary satellites, dust particles, comets and asteroids. Many of these bodies exist in ultrahigh vacuum environments, so that direct particle–surface collisions dominate the interactions. In this article, we discuss the origins of the very tenuous planetary atmospheres observed on a number of bodies, space weathering of the surface of asteroids and comets, and magnetospheric processing of the surfaces of Jupiter's icy satellites. We emphasize non-thermal processes and the important relationships between surface composition and the gas phase species observed. We also discuss what laboratory and computational modeling should be done to support the current and future space missions––e.g. the Genesis mission to recover solar wind particles, the Cassini mission to probe Saturn, the Europa Lander mission to explore the subsurface ocean hypothesis, and the Pluto/Kuiper Express to sample the outer reaches of the solar system.     

The astrophysical environment of the solar birthplace

Our Sun, like all stars, formed within a cold molecular cloud. Astronomical observations and theory provide considerable detail into this process. Yet cosmochemical observations of short-lived radionuclides in primitive meteorites, in particular ⁶⁰Fe, provide unequivocal evidence that the early solar system inherited fresh nucleosynthetic material from the core of a hot, massive star, almost certainly ejected in a supernova explosion. I give a short introduction to the fields of star formation and meteoritics and discuss how the reconciliation of their disparate clues to our origin places strong constraints on the environment of the solar birthplace. Direct injection of supernova ejecta into a protoplanetary disc or a dense molecular core is unlikely since their small sizes require placement unusually close to the massive star. Lower density molecular cloud clumps can capture more ejecta but the radionuclides decay during the slow gravitational collapse. The most likely scenario is on the largest scales via the formation of enriched molecular clouds at the intersection of colliding supernova bubbles in spiral arms.     

Cosmic dust and our origins

The small solid particles in the space between the stars provide the surfaces for the production of many simple and complex molecules. Processes involving the effects of ultraviolet irradiation of the thin (hundredth micron) mantles are shown to produce a wide range of molecules and ions also seen in comets. Some of the more complex ones inferred from laboratory experiments are expected to play an important role in the origin of life. An outline of the chemical evolution of interstellar dust as observed and as studied in the laboratory is presented. Observations of comets are shown to provide substantial evidence for their being fluffy aggregates of interstellar dust as it was in the protosolar nebula, i.e. the interstellar cloud which collapsed to form the solar system. The theory that comets may have brought the progenitors of life to the earth is summarized.     

Small-angle scattering and diffraction

The direct measurement of magnetic fields by magnetometers, originally made of the Earth's magnetic field, has been now extended to solar planets by numerous satellite missions. Magnetic effects have been observed in the solar neighborhood and even near some comets, such as the Giotto mission to comet Halley. However, observations of magnetic fields in cosmic objects require remote sensing methods.     

It''s a dusty Universe: surface science in space

We live in a dusty Universe! Dust is not only found in our solar system among the planets but is found in a wide variety of objects throughout the Universe, mainly in those regions between the stars known as interstellar clouds. Interstellar dust particles, which consist of cores of silicates and carbonaceous material often surrounded by icy mantles, are most probably highly irregular in shape with a size distribution from micro- to nanometers. Interstellar dust is important for many reasons, including the template it provides for surface chemical reactions that form, among other species, the most important interstellar molecule––H₂. In this article, we discuss the evidence for interstellar dust, its physical and chemical properties, its role in interstellar surface chemistry, and what remains to be learned.     

In‐situ analysis of planetary surfaces by Mössbauer spectroscopy

Iron is one of the key elements in the evolution of the solar system and is highly abundant in terrestrial planets. Its oxidation state reflects the history of the oxidation–reduction reactions on planetary surfaces. The identification of iron mineralogies and the relative abundance of iron oxidation states (2+ and 3+) will contribute to a much deeper understanding of the evolution of planetary bodies and their surfaces. Miniaturized Mössbauer spectrometers are under development primarily for missions to the planet Mars and the Moon, but there is also an interest on using such an instrument for space missions to the planet Venus, comets and asteroids. The instrument MIMOS II developed at TU Darmstadt meets the requirements for space application as low mass (about 500 g), small volume, and low power consumption (about 1 W). The instrument has been tested extensively in the laboratory but also recently in the field mounted on the robotic arm of a prototype Martian Rover under development at JPL/NASA, United States.     

Polarimetry of small bodies of the solar system with large telescopes

During the last 10 years, the FORS instrument of the ESO very large telescope was regularly used to obtain broadband linear polarization measurements of small bodies of the solar system. In particular, FORS was the first (and so far unique) instrument that allowed us to explore polarimetrically objects of the solar system other than planets, moons, asteroids, and active comets. From 2002 to 2010, more than 150 h of telescope time were allocated for the observations of Centaurs, trans-Neptunian objects, and cometary nuclei. With a R magnitude between 16 and 21, these targets are probably the faintest objects of the solar system ever observed in polarimetric mode. In addition to these objects, polarimetric measurements were obtained for asteroids, active comets, Mars, the Saturn moon Iapetus, and the Moon earthshine. Here we present a review of these measurements, from the strategies adopted for the observations to the observational results.     

Infrared remote sensing of planetary atmospheres

Infrared remote sensing is a powerful tool for studying the chemical composition and the thermal structure of planetary atmospheres. Infrared spectra, in particular, are used to derive molecular abundances and to infer elemental and isotopic ratios, which allow to constrain theoretical models of the formation and early evolution of the solar system, as well as the history of planetary atmospheres. Infrared imaging and spectroscopy have been performed from the ground but also from space planetary missions (Mariner 9 on Mars, Voyager on the giant planets, Galileo on Jupiter), and from the ISO Earth-orbiting infrared satellite. In the forthcoming decade, the Cassini mission will explore the Saturn system. Planetary exploration from Earth orbit will be performed by the FIRST and NGST space observatories.     

Silicon carbide in laboratory, in interstellar space and in the solar system

Summary Using theoretical models and our laboratory data on different dust mixtures containing silicon carbide grains, we obtained the best fit of several infrared emission spectra of carbon stars and comets. The results suggest that silicon carbide formed in the envelopes around carbon stars and also present in our solar system may provide an important link between interstellar and interplanetary solid material. Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992.     

On the Inclination of Planetary Orbits

Assuming that planets were formed in the equatorial plane of the Sun and that there was a small perturbation at the start, it is shown that relativistic effects could lead to the planetary orbit tilting observed. On the baais of this analysis, a prediction is made for the velocity of the planet Mercury out of its orbital 'plane'. This prediction is a lower limit. Further, this explanation may possibly provide a method for determining the solar angular momentum.