Posted on Categories:Solar System, 太阳系, 物理代写

物理代写|太阳系代写Solar System代考|PHYS7810 The Asteroid Belt

如果你也在 怎样代写太阳系Solar System PHYS7810这个学科遇到相关的难题,请随时右上角联系我们的24/7代写客服。太阳系Solar System是由太阳和围绕太阳运行的物体组成的引力约束系统。它在46亿年前由一个巨大的星际分子云的引力坍缩形成。该系统的绝大部分(99.86%)质量都在太阳中,其余大部分质量包含在木星中。内系统的四颗行星–水星、金星、地球和火星–是陆生行星,主要由岩石和金属组成。

太阳系Solar System系统的四颗巨行星比陆生行星大得多,质量也大得多。两个最大的行星,木星和土星,是气态巨行星,主要由氢和氦组成;接下来的两个行星,天王星和海王星,是冰态巨行星,主要由与氢和氦相比熔点较高的挥发性物质组成,如水、氨和甲烷。所有八颗行星都有近乎圆形的轨道,位于地球轨道的平面附近,称为黄道。

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物理代写|太阳系代写Solar System代考|PHYS7810 The Asteroid Belt

物理代写|太阳系代写Solar System代考|The Asteroid Belt

The Asteroid Belt currently contains only enough material to make a planet 2000 times less massive than Earth, even though the spatial extent of the belt is huge. It seems likely that this region once contained much more mass than it does today. A smooth interpolation of the amount of solid material needed to form the inner planets and the gas giants would place about 2 Earth-masses in the Asteroid Belt. Even if most of this mass was lost at an early stage, the surface density of solid material must have been at least 100 times higher than it is today in order to grow bodies the size of Ceres and Vesta (roughly 900 and $500 \mathrm{~km}$ in diameter, respectively) in only a few million years.

Several regions of the Asteroid Belt contain clusters of asteroids with similar orbits and similar spectral features, suggesting they are made of the same material. These clusters are fragments from the collisional breakup of larger asteroids. There are relatively few of these asteroid families, which implies that catastrophic collisions are quite rare. This suggests the Asteroid Belt has contained relatively little mass for most of its history. The spectrum of asteroid Vesta, located 2.4 AU from the Sun, shows that it has a basaltic crust. The HED meteorites, which probably come from Vesta, show this crust formed only a few million years after the solar system, according to several isotopic systems. The survival of Vesta’s crust suggests that the crust formed the impact rate in the belt has never been much higher than it is today. For these reasons, it is thought that most of the Asteroid Belt’s original mass was removed at a very early stage by a dynamical process rather than by collisional erosion.
The Asteroid Belt currently contains a number of orbital resonances associated with the giant planets. Resonances occur when either the orbital period or precession period of an asteroid has a simple ratio with the corresponding period for one of the planets. Many resonances induce large changes in orbital eccentricity, causing asteroids to fall into the Sun, or to come close to Jupiter, leading to close encounters and ejection from the solar system. For this reason, there are very few asteroids that orbit the Sun twice every time Jupiter orbits the Sun once, for example. When the nebular gas was still present, small asteroids moving on eccentric orbits would have drifted inward rapidly due to gas drag. After the giant planets had formed, a combination of resonances and gas drag may have transferred most objects smaller than a few hundred kilometers from the Asteroid Belt into the terrestrial-planet region. Larger planetary embryos would not have drifted very far. However, once oligarchic growth ceased, embryos began to gravitationally scatter one another across the belt. Numerical simulations show that most or all of these bodies would eventually enter a resonance and be removed, leaving an Asteroid Belt greatly depleted in mass and containing no objects bigger than Ceres. The timescale for the depletion of the belt depends sensitively on the orbital eccentricities of the giant planets at the time, which are poorly known. The belt may have been cleared in only a few million years, but it may have required as much as several hundred million years if the giant planets had nearly circular orbits.

物理代写|太阳系代写Solar System代考|Growth of Gas and Ice Giant Planets

Jupiter and Saturn are mostly composed of hydrogen and helium. These elements do not condense at temperatures and pressures found in protoplanetary disks, so they must have been gravitationally captured from the gaseous component of the solar nebula. Observations of young stars indicate that protoplanetary disks survive for only a few million years, and this sets an upper limit for the amount of time required to form giant planets. Uranus and Neptune also contain significant amounts of hydrogen and helium (somewhere in the range 3-25\%), and so they probably also formed quickly, before the solar nebula dispersed.
Jupiter and Saturn also contain elements heavier than helium and they are enriched in these elements compared to the Sun. The gravitational field of Saturn strongly suggests it has a core of dense material at its center, containing roughly one fifth of the planet’s total mass. Jupiter may also have a dense core containing a few Earth masses of material. The interior structure of Jupiter remains quite uncertain because we lack adequate equations of state for the behavior of hydrogen at the very high pressures found in the planet’s interior. The upper atmospheres of both planets are enriched in elements such as carbon, nitrogen, sulfur, and argon, compared to the Sun. It is thought likely that these enrichments extend deep into the planets’ interiors, but this remains uncertain.

Giant planets may form directly by the contraction and collapse of gravitationally unstable regions of a protoplanetary disk. This disk instability is analogous to the gravitational instabilities that may have formed planetesimals, but instead the instability takes place in nebula gas rather than the solid component of the disk. Instabilities will occur if the Toomre stability criterion $Q$ becomes close to or lower than 1 , where
$$
Q=\frac{M_{\mathrm{sun}} c_{\mathrm{s}}}{\sum \pi a^2 v_{\mathrm{kep}}}
$$
where $v_{\mathrm{kep}}$ is the Keplerian velocity, $c_{\mathrm{s}}$ is the sound speed, and $\Sigma$ is the local surface density of gas in the disk. Gas in an unstable region quickly becomes much denser than the surrounding material. Disk instability requires high surface densities and low sound speeds (cold gas), so it is most likely to occur in the outer regions of a massive protoplanetary disk. Numerical calculations suggest instabilities will occur beyond about $5 \mathrm{AU}$ in a nebula a few times more massive than the minimum-mass solar nebula. What happens to an unstable region depends on how quickly the gas cools as it contracts, and this is the subject of much debate. If the gas remains hot, the dense regions will quickly become sheared out and destroyed by the differential rotation of the disk. If cooling is efficient, simulations show that gravitationally bound clumps will form in a few hundred years, and these may ultimately contract to form giant planets. Initially, such planets would be homogeneous and have the same composition as the nebula. Their structure and composition may change subsequently due to gravitational settling of heavier elements to the center and capture of rocky or icy bodies such as comets.

物理代写|太阳系代写Solar System代考|PHYS7810 The Asteroid Belt

太阳系代写

物理代写|太阳系代写太阳系代考|小行星带


尽管小行星带的空间范围很大,但目前小行星带所含的物质只够制造一颗质量比地球小2000倍的行星。这片区域曾经的质量可能比现在大得多。如果将形成内行星和气体巨星所需的固体物质的数量进行平滑插值,将在小行星带中放置大约2个地球质量的物质。即使大部分质量在早期就消失了,固体物质的表面密度也必须至少比今天高100倍,才能在短短几百万年里生长出谷神星和灶神星这样大小的天体(直径分别约为900和$500 \mathrm{~km}$)


小行星带的几个区域包含了轨道相似、光谱特征相似的小行星群,这表明它们是由相同的物质构成的。这些星团是较大的小行星碰撞破裂后的碎片。这些小行星家族相对较少,这意味着灾难性碰撞是相当罕见的。这表明小行星带在其大部分历史中所包含的质量相对较少。距离太阳2.4天文单位的小行星灶神星的光谱显示它有玄武质地壳。HED陨石很可能来自灶神星,根据几个同位素系统的研究,它表明这块地壳形成于太阳系之后的几百万年。灶神星地壳的存活表明地壳形成的冲击率从来没有比今天高很多。由于这些原因,人们认为小行星带的大部分原始质量在非常早期的阶段就被动力过程而不是碰撞侵蚀所去除。小行星带目前包含许多与巨行星有关的轨道共振。当一颗小行星的轨道周期或进动周期与其中一颗行星的相应周期有简单的比例时,就会发生共振。许多共振引起轨道偏心率的巨大变化,导致小行星落入太阳,或接近木星,导致近距离相遇并被逐出太阳系。由于这个原因,很少有小行星能像木星绕太阳运行一圈一样绕太阳运行两圈。当星云气体仍然存在时,在偏心轨道上运动的小行星会由于气体阻力迅速向内漂移。巨行星形成后,共振和气体阻力的共同作用可能将小行星带小于几百公里的大多数物体转移到地行星区域。较大的行星胚胎不会漂流太远。然而,一旦寡头生长停止,胚胎开始在整个带中相互分散。数值模拟表明,大多数或所有这些天体最终将进入共振并被移除,使小行星带的质量大大减少,不再包含比谷神星更大的天体。腰带耗损的时间尺度敏感地取决于巨行星当时的轨道偏心,而这一点知之甚少。这条带可能只花了几百万年就被清理干净了,但如果这些巨行星的轨道接近圆形,则可能需要数亿年的时间

物理代写|太阳系代写太阳系代考|气体和冰巨行星的生长


木星和土星主要由氢和氦组成。这些元素不会在原行星盘的温度和压力下凝结,所以它们一定是从太阳星云的气体成分中引力捕获的。对年轻恒星的观察表明,原行星盘只能存活几百万年,这就为形成巨行星所需要的时间设定了上限。天王星和海王星也含有大量的氢和氦(在3-25%的范围内),所以它们可能在太阳星云分散之前也很快形成。木星和土星也含有比氦重的元素,而且与太阳相比,它们的元素含量更丰富。土星的引力场强烈地表明,它的中心有一个高密度物质组成的核心,大约包含了土星总质量的五分之一。木星也可能有一个密度很大的内核,里面含有一些地球质量的物质。木星的内部结构仍然很不确定,因为我们缺乏足够的状态方程来描述氢在木星内部高压下的行为。与太阳相比,这两颗行星的上层大气富含碳、氮、硫和氩等元素。人们认为,这些富集物质很可能延伸到行星内部深处,但这仍不确定


巨行星可能由原行星盘的引力不稳定区域的收缩和坍缩直接形成。这种圆盘不稳定性类似于可能形成星子的引力不稳定性,但相反,不稳定性发生在星云气体中,而不是在圆盘的固体成分中。如果Toomre稳定判据$Q$变得接近或低于1,其中
$$
Q=\frac{M_{\mathrm{sun}} c_{\mathrm{s}}}{\sum \pi a^2 v_{\mathrm{kep}}}
$$
,其中$v_{\mathrm{kep}}$是开普勒速度,$c_{\mathrm{s}}$是声速,$\Sigma$是圆盘内气体的局部表面密度,则会发生不稳定。不稳定区域的气体密度很快就会比周围的物质大得多。盘的不稳定性需要较高的表面密度和较低的声速(冷气体),所以它最有可能发生在一个大质量原行星盘的外部区域。数值计算表明,在质量比最小质量太阳星云大几倍的星云中,不稳定现象将在大约$5 \mathrm{AU}$以外的地方发生。不稳定区域会发生什么取决于气体收缩时的冷却速度,这是一个备受争议的话题。如果气体保持高温,密集区域将很快被剪切出来,并被圆盘的差动旋转破坏。如果冷却是有效的,模拟表明受引力束缚的团块将在几百年内形成,这些团块可能最终收缩形成巨大的行星。最初,这样的行星应该是均匀的,具有与星云相同的成分。它们的结构和组成可能随后发生变化,这是由于较重元素的引力沉降到中心,以及彗星等岩石或冰体的捕获

物理代写|太阳系代写Solar System代考

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微观经济学代写

微观经济学是主流经济学的一个分支,研究个人和企业在做出有关稀缺资源分配的决策时的行为以及这些个人和企业之间的相互作用。my-assignmentexpert™ 为您的留学生涯保驾护航 在数学Mathematics作业代写方面已经树立了自己的口碑, 保证靠谱, 高质且原创的数学Mathematics代写服务。我们的专家在图论代写Graph Theory代写方面经验极为丰富,各种图论代写Graph Theory相关的作业也就用不着 说。

线性代数代写

线性代数是数学的一个分支,涉及线性方程,如:线性图,如:以及它们在向量空间和通过矩阵的表示。线性代数是几乎所有数学领域的核心。

博弈论代写

现代博弈论始于约翰-冯-诺伊曼(John von Neumann)提出的两人零和博弈中的混合策略均衡的观点及其证明。冯-诺依曼的原始证明使用了关于连续映射到紧凑凸集的布劳威尔定点定理,这成为博弈论和数学经济学的标准方法。在他的论文之后,1944年,他与奥斯卡-莫根斯特恩(Oskar Morgenstern)共同撰写了《游戏和经济行为理论》一书,该书考虑了几个参与者的合作游戏。这本书的第二版提供了预期效用的公理理论,使数理统计学家和经济学家能够处理不确定性下的决策。

微积分代写

微积分,最初被称为无穷小微积分或 “无穷小的微积分”,是对连续变化的数学研究,就像几何学是对形状的研究,而代数是对算术运算的概括研究一样。

它有两个主要分支,微分和积分;微分涉及瞬时变化率和曲线的斜率,而积分涉及数量的累积,以及曲线下或曲线之间的面积。这两个分支通过微积分的基本定理相互联系,它们利用了无限序列和无限级数收敛到一个明确定义的极限的基本概念 。

计量经济学代写

什么是计量经济学?
计量经济学是统计学和数学模型的定量应用,使用数据来发展理论或测试经济学中的现有假设,并根据历史数据预测未来趋势。它对现实世界的数据进行统计试验,然后将结果与被测试的理论进行比较和对比。

根据你是对测试现有理论感兴趣,还是对利用现有数据在这些观察的基础上提出新的假设感兴趣,计量经济学可以细分为两大类:理论和应用。那些经常从事这种实践的人通常被称为计量经济学家。

MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中,其中问题和解决方案以熟悉的数学符号表示。典型用途包括:数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发,包括图形用户界面构建MATLAB 是一个交互式系统,其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题,尤其是那些具有矩阵和向量公式的问题,而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问,这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展,得到了许多用户的投入。在大学环境中,它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域,MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要,工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数(M 文件)的综合集合,可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。