陪你去看流星雨

茫茫黑夜中，一闪而过。流星，又常称为火流星，真可谓“来无影，去无踪”。原来，在浩瀚的太阳系中，有无数的尘埃和固体碎块，纷纷沿着椭圆形轨道绕太阳转动，它们被称做流星体。大多数流星体都很小。当它们偶然地闯入地球大气层时，由于速度达到每秒十几千米甚至七八十千米，和大气发生剧烈的摩擦，温度升高到几千甚至上万摄氏度，于是燃烧发光，这时我们就看到，天空中出现了一颗流星。小的流星体在地面上空好几千米的地方就燃烧完了，而一些大的流星体却可以把一大片天空照得通亮，这叫大流星。最后没有烧尽的流星体落到地面上，成为陨…     

为什么不能利用彗星和流星?

在太空中还有一些资源是不能利用的,如彗星和流星体。彗星被称为“脏雪球”,因为它是由灰尘、冻结的气体和冰集结而成。彗星的速度极快,不是经常能遇到,因此不适宜做建设太空城的资源。 流星体不仅不可利用,而且是太空城的一种潜在危害。科学家们曾从地球上、月球上和太空中对流星体进行过大量的观测。他们发现,在太空中每平方千米面积上被一颗质量在1克以上的流星体穿过的可能性是每10年有1次,被100克以上的流星体穿     

火星探测微流星体环境模型及风险预测

微流星体是自然存在的微型天体.在太阳系空间范围内,微流星体的主要起源为彗星及小行星.在地球至火星的空间范围内,微流星体的飞行速度范围为24.13~42.2km·-1.高速飞行的微流星体一旦撞击火星探测器,将有可能对探测器造成毁灭性的损害.本文基于太阳神探测器的观测结果及彗星轨道观测统计结果,针对火星探测,分别建立了地火转移段及环火飞行段的微流星体环境模型,并基于有限元离散方法建立了火星探测任务的微流星体碰撞风险预测方法.设计了一个虚拟火星探测器,分别对其在地火转移段及环火飞行段的微流星体撞击通量进行了分析.结果显示,在探测器有效任务期内,探测器正面受微流星撞击次数约为背面的10倍.根据本文模型计算结果,将探测器顶板铝合金蒙皮的厚度增加至0.7mm后,在整个任务周期内可将探测器正面受微流星体撞击出现击穿损伤的风险降低为每平米7次.      

热处理对纳米氧化锆热障涂层热物性的影响

采用大气等离子喷涂(APS)在GH33基体上制备了氧化锆纳米结构涂层,运用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电镜(TEM)和拉曼光谱(RS)等分析手段对原料粉末和涂层的显微结构、相组成进行了观察和确定,分别利用激光脉冲技术测量了热处理前后涂层的热扩散率.实验结果表明,等离子喷涂氧化锆纳米涂层颗粒分布在65~110nm之间,大于原料粉末的40~70nm,涂层主要由亚稳四方相氧化锆组成.1050℃下热处理34h后,涂层的热扩散率从制备态的2.15×10-3~2.75×10-3cm2/s升高到2.65×10-3~3.25×10-3cm2/s.      

我国小天体探测任务设想

1 小天体简介 根据国际天文学联合会(IAU)修订后的行星定义,太阳系天体被分为行星、矮行星以及太阳系小天体. 小天体主要包括小行星和彗星.其中,小行星是太阳系内类似行星环绕太阳运动,但体积和质量比行星小的岩石或金属天体.彗星是进入太阳系内,亮度和形状随日距变化而变化的绕日运动天体,一般由彗核、彗发和彗尾等组成.主带彗...     

长时间流星不均匀体母体特征个例研究

流星体坠入地球大气烧蚀电离产生流星等离子体尾迹,在等离子体不稳定性过程作用下产生流星不均匀体.利用光学视频和无线电雷达在低纬三亚开展流星体烧蚀和流星不均匀体综合探测结果,发展了一种获取流星不均匀体母体（流星体）特征参数的方法,并对2015年12月双子座流星雨期间观测的一次长持续时间流星不均匀体事例进行了分析,得到了其母体速度、质量和轨道等特征,结果显示产生这次流星不均匀体的流星体速度和轨道等具有双子座流星特点.该方法可应用于流星不均匀体及其母体特征研究.      

质谱计在行星系统与小天体探测中的应用

质谱计多次应用于行星系统和小天体的大气层与土壤吸附气体或挥发组分及其同位素含量探索,是太阳系行星系统和小天体探测计划中的首选载荷之一。大气和土壤元素及其同位素组分探测对资源勘探、行星系统的宜居性、天体演化、起源及其重要事件的精准时间坐标研究等具有重要意义。质谱计已多次成功应用于火星、土星系、木星系、彗星等探测任务中开展大气环境探测。质谱计的探测对象主要包括太阳系行星、行星卫星如月球、木星伽利略卫星、土卫,以及地外小行星和彗星。四极杆质谱计在当前的深空空间环境探测活动中应用最为广泛。利用四极杆质谱计除可用于探测稀薄天体大气与土壤析出气体外,如增加抽真空能力的前端设计,则具备探测稠密大气成分的能力。中科院空间中心研发的星载质谱计已多次成功应用于地球行星大气成分和密度探测。     

0.033—1.0T标准磁场系统

本标准磁场系统由电磁铁、激磁稳流电源、核磁共振测场仪三大部分组成,电磁铁较小,均匀区达φ60mm(1×10~(-1));激磁稳流电源保证了磁通密度高度稳定,达3×10~(-6)/5分钟,核磁共振测场仪准确度达6×10~(-6)。文中重点介绍了它们的理论依据及采取的主要技术措施。     

流星落到地面时仍然很热

你也许认为,一颗流星体在被加热到那么高的温度后一定不会在几分钟的时间里冷却下来。但实际的情况要复杂许多。流星体的快速运动使其前方的空气形成激波,就像超音速飞机一样。激波与流星体的表面有数厘米的距离(具体取决于流星体的大小),其间的空气则运动缓慢。流星体被其前方的     

美苏拟进行航天飞机—礼炮号联合飞行

美国和苏联已经选定了5个研究领域,以期在1982年或晚些时候可能进行的航天飞机/礼炮联合飞行中予以实施。它们是: 1) 高能天文物理(γ-射线、X-射线和宇宙线天文学),2) 大气研究,3) 磁层和电离层的活动实验,4) 医学和生物实验,5) 射电天文学。     

论彗星的起源

彗星富含挥发物,这表明它们形成并长期保存于太阳系外部低温区。本文分析了星云盘外缘区的结构,论证了那里不可能存在彗星形成带。作者认为,彗星是木星到海王星这个区域中的残存星子演变而成的。      

Meteorites,asteroids and comets — A study of their interrelationship

The origins of the three kinds of extra-terrestrial bodies, meteorites, asteroids and comets can be traced to the origin of solar system. From a study of their properties, a generic relatinship of the form interstellar gas and dust condensing in the primitive solar nebula leading to the formation of comets, the comets getting degassed and ablated to become asteroids and the asteroids on fragmentation due to collisions becoming meteorites, is advocated here. The isotopic abundances of carbon are suggested as the key to unlock the mystery of this relationship.     

High-velocity impact experiments needed to improve our understanding of the asteroids

The lifetime of almost all the asteroids against catastrophic impact events is less than the age of the solar system, implying that the asteroids can be considered as outcomes of catastrophic collisions. Therefore to understand their physical properties (structure, shape, rotation, regolith development) and their family memberships (since families are generated by the escape of breakup fragments), a systematic knowledge of the outcomes of catastrophic impacts under a variety of conditions seems needed. In particular, interesting fields to be explored by laboratory experiments are: the dependence of the critical energy densities associated with various degrees of fragmentation on the target's size and composition; the velocity distribution of the fragments and the inelasticity of the process in different cases; the shape of the fragments and its possible correlation with other quantities; the way a dust- or regolith-covered target affects the collisional outcomes; the angular momentum partitioning and the rotation of the fragments. On this latter problem very few experimental results are presently available; on the other hand, the rotation of small asteroids presents several intriguing “anomalies”.

A significant progress of our understanding of asteroid collisional evolution and related phenomena can be provided by new laboratory experiments of collisional breakup. The targets should have spherical and/or irregular shape (up to axial ratios of the order of 2), and should be made of (possibly different) geological materials. The interesting projectile velocities are of the order of the relative velocities commonly found among asteroids, i.e., in the range 1 to 10 Kms⁻¹. In order to get catastrophic collisions, the ratio of the projectile kinetic energy to the target mass (≡E/M) has to be chosen within a “critical” range (for basalt targets, from 10⁶ to 10⁸ erg/g). In some particular cases, this kind of experiments has been already performed in past (Gault and Wedekind [10]; Fujiwara et al. [7]; Fujiwara and Tsukamoto [9]); however the generalization of the results to a wide range of experimental conditions is lacking, and many problems of outstanding importance to model asteroid evolution are still completely open.     

A sample collector for robotic sample return missions I: Temperature effect on collected mass

Sample return is playing an increasingly important role in solar system exploration. Among the possible mission on the horizon, are sample return from asteroids, comets, the Moon and Mars. A collector initially intended for near-Earth asteroids is the touch-and-go-impregnable-pad (TGIP). Here we explore the effect of temperature on its collection capabilities. Temperatures expected on near-Earth asteroid mission targets range from −43 to 36 °C. Experiments were conducted at −75, −50, −25, 23, 65, and 105 °C. It was found that the mass of sample collected by the TGIP increased almost linearly to 23 °C and then leveled off at higher temperatures. We also found that the collector did not lose its ability to collect samples after being subjected to −75 °C temperatures (essentially frozen) and then thawed. These experiments have shown that the TGIP can operate effectively at temperatures expected on near-Earth asteroids, especially if collection is performed on the sunward side of the asteroid.     

On tethered sample and mooring systems near irregular asteroids

A tethered asteroid sample and mooring system is investigated in this paper. In this system the spacecraft is moored to the surface of an irregular asteroid such as 216 Kleopatra by using a rocket-propelled anchor with a cable. The rocket-propelled anchor is a kind of space penetrator, which can inject into asteroids at high speeds generated by its own rocket engine. It can be used to explore the interior structure of asteroids, and it can also be used as a sample collector. When the sampling mission is done, the sample can be pulled back to the spacecraft with the anchor. Using this method, the spacecraft can be kept in a safe region in which it cannot be trapped by the gravitational field of the asteroid. This work is concerned with the dynamics of the tethered system near irregular asteroids. First, a shape model and gravitational field model of irregular asteroids are built. Then, the configuration and the stability of the tethered system are investigated, and the quasi-periodic motion near the equilibrium point of the tethered system is analyzed. Finally, the non-uniform density distribution of the asteroids is considered. The deployment process and the oscillation of the tethered system in the uncertain asteroid gravity field are simulated using the Monte Carlo method. The feasibility of the tethered asteroid sample and mooring system is proved.     

Dark matter in the solar system

Many small bodies in the solar system, including planetary satellites, comets, and asteroids, have a surface component consisting at least in part of a very low albedo (0.06 or less) solid substance of neutral or red color in the wavelength region 0.3–2.5 μm. Laboratory spectra of organic residues from meteorites and mixtures with hydrous silicates suggest that complex mixtures of complex organic molecules (kerogens) together with aqueous alteration products of igneous minerals may be the source of the dark matter that is distributed so widely throughout the solor system.     

基于最小轨道交叉距离的小行星顺访探测目标预筛选方法

小行星探测有助于研究太阳系演化等重要科学问题,在深空探测任务转移途中实施小行星顺访探测可增加科学研究回报。直接通过轨道递推筛选小行星探测目标计算量大、效率低,针对该问题提出了基于最小轨道交叉距离的目标预筛选方法。在推导出适用于计算双曲线轨道的最小轨道交叉距离公式后,将此理论应用到小行星顺访探测目标筛选中。首先基于探测器与小行星轨道的形状、空间位置计算二者轨道在空间中的几何最近距离,预筛选出可能满足接近距离标准的小行星目标;然后基于轨道递推模型,筛选出真实最近距离小于可接近标准的目标小行星。仿真结果显示,基于最小轨道交叉距离的预筛选方法可有效减少计算量,降低计算时间,提高小行星顺访目标筛选的效率。      

The flux of Earth-crossing and moon-cratering interplanetary bodies

Methods of determining the present flux and total number of kilometer-sized Earth-crossing objects are discussed, including (1) probability considerations based on the frequency of chance rediscoveries of the lost objects, (2) evaluation of large-scale photographic surveys for the detection of fast moving objects, and (3) evaluation of close encounters of interplanetary bodies with the Earth. The results are interfaced with the lunar and terrestrial cratering history. It is shown that the discrepancies between these two independent lines of evidence are still within the margin of uncertainty set by observational biases, cratering efficiencies, and surface reflectivities of the objects, in particular as regards extinct cometary nuclei. Impacts of active comets can only be held responsible for a very small fraction of the craters, and impacts of high-albedo Apollo asteroids are consistent with a steady state. There is no definite enhancement of the present-day flux as compared with the average level of cratering during the last 3 Gyr which would require significant variations in the stellar environment of the solar system, affecting the rate of delivery of new comets from the Oort cloud. There is also no evidence of a recent major collisional event in the asteroid belt. Deviations from an equilibrium between source and sink only become effective in the size range of meteor particles, where no long-term cratering record is available. They are apparently due to a very limited number of parent objects, and appear on a time scale which is very short compared with the age of the solar system.     

The dynamical environments analysis of surface particles for different shaped asteroids

Asteroids are coming to be a popular topic in the areas of astrophysical studies and deep space exploration recently. However, surface dynamics of asteroids is still a difficult problem. This paper aims at the motion analysis of surface particles for different asteroids. The dynamical analysis method of particles’ movement is given for three parts: global motion trend, local motion trend and static analysis. A dimensionless parameter ζ is defined to distinguish the predominant term to determine the distribution of effective potential. Three kinds of common asteroids: spheroidal asteroid, spindle-shaped asteroid and dumbbell-shaped asteroid are all discussed for those three parts with different parameter ζ. The motion trend of particles on the surface of each kind of asteroid is given. The static analysis of surface particles for different asteroids is also illustrated. Based on them, some common rules for different shaped asteroids are revealed. This paper could not only provide a reference for asteroid exploration missions but also be meaningful for the research of morphologic evolution of asteroids.