文档章节

Planets in Our Solar System

o
 osc_f66lkchr
发布于 2019/05/16 06:47
字数 726
阅读 37
收藏 0

「深度学习福利」大神带你进阶工程师,立即查看>>>

Planets in Our Solar System

The Sun is the hub of a huge rotating system consisting of nine planets, their satellites, and numerous small bodies, including asteroids, comets, and meteoroids. An estimated 99.85 percent of the mass of our solar system is contained within the Sun, while the planets collectively make up most of the remaining 0.15 percent. The planets, in order of their distance from the Sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Under the control of the Sun's gravitational force, each planet maintains an elliptical orbit and all of them travel in the same direction.

 

The planets in our solar system fall into two groups: the terrestrial (Earth-like) planets (Mercury, Venus, Earth, and Mars) and the Jovian (Jupiter-like) planets (Jupiter, Saturn, Uranus, and Neptune). Pluto is not included in either category, because its great distance from Earth and its small size make this planet's true nature a mystery.

 

The most obvious difference between the terrestrial and the Jovian planets is their size. The largest terrestrial planet, Earth has a diameter only one quarter as great as the diameter of the smallest Jovian planet, Neptune, and its mass is only one seventeenth as great. Hence, the Jovian planets are often called giants. Also, because of their relative locations, the four Jovian planets are known as the outer planets, while the terrestrial planets are known as the inner planets. There appears to be a correlation between the positions of these planets and their sizes.

 

Other dimensions along which the two groups differ markedly are density and composition. The densities of the terrestrial planets average about 5 times the density of water, whereas the Jovian planets have densities that average only 1.5 times the density of water. One of the outer planets, Saturn, has a density of only 0.7 that of water, which means that Saturn would float in water. Variations in the composition of the planets are largely responsible for the density differences. The substances that make up both groups of planets are divided into three groups—gases, rocks, and ices—based on their melting points. The terrestrial planets are mostly rocks: dense rocky and metallic material, with minor amounts of gases. The Jovian planets, on the other hand, contain a large percentage of the gases hydrogen and helium, with varying amounts of ices: mostly water, ammonia, and methane ices.

 

The Jovian planets have very thick atmospheres consisting of varying amounts of hydrogen, helium, methane, and ammonia. By comparison, the terrestrial planets have meager atmospheres at best. A planet's ability to retain an atmosphere depends on its temperature and mass. Simply stated, a gas molecule can "evaporate" from a planet if it reaches a speed known as the escape velocity. For Earth, this velocity is 11 kilometers per second. Any material, including a rocket, must reach this speed before it can leave Earth and go into space. The Jovian planets, because of their greater masses and thus higher surface gravities, have higher escape velocities (21-60 kilometers per second) than the terrestrial planets. Consequently, it is more difficult for gases to "evaporate" from them. Also, because the molecular motion of a gas depends on temperature, at the low temperatures of the Jovian planets even the lightest gases are unlikely to acquire the speed needed to escape. On the other hand, a comparatively warm body with a small surface gravity, like Earth's moon, is unable to hold even the heaviest gas and thus lacks an atmosphere. The slightly larger terrestrial planets Earth, Venus, and Mars retain some heavy gases like carbon dioxide, but even their atmospheres make up only an infinitesimally small portion of their total mass.

 

The orderly nature of our solar system leads most astronomers to conclude that the planets formed at essentially the same time and from the same material as the Sun. It is hypothesized that the primordial cloud of dust and gas from which all the planets are thought to have condensed had a composition somewhat similar to that of Jupiter. However, unlike Jupiter, the terrestrial planets today are nearly void of light gases and ices. The explanation may be that the   terrestrial planets were once much larger and richer in these materials but eventually lost them because of these bodies' relative closeness to the Sun, which meant that their temperatures were relatively high.

o
粉丝 1
博文 500
码字总数 0
作品 0
私信 提问
加载中
请先登录后再评论。
密码管理程序--pwgrep

为了管理我的密码,我写了一个小的 bash/awk 脚本用来管理一个密码数据库并使用 GnuPG 进行加密。使用 pwgrep 的好处是: 密码加密 密码版本化,不用担心丢失老密码 Since a versioning sys...

匿名
2013/03/11
1.3K
0
商铺记账系统软件--bluebee蓝蜜蜂记账系统

此项目已废弃:) Donate捐助 bluebee accounting system is a popular and free accounting system for individual businesses.This system focus on the individual businesses operation......

刘学炜
2013/04/18
1.4W
10
CSS 框架--1200-grid-system

仿960GRIDCSS制作1200CSS一份,包括1200与全屏CSS,24列设计,欢迎随意使用!

angelrand
2013/06/15
1.8K
0
Android图片剪裁-调用系统实现,完美适配魅族等机型

封装的系统图片剪裁使用库-GITHUB求STAR System-Photo-Cropper Android System Photo Cropper使用系统原生的图片剪裁库,完美适配魅族等机型 Step 1 First you need a sysPhotoCropper to h...

Gemini-Lin
2016/05/04
1.4K
1
Java I/O 模型的演进

原文同步至 什么是同步?什么是异步?阻塞和非阻塞又有什么区别?本文先从 Unix 的 I/O 模型讲起,介绍了5种常见的 I/O 模型。而后再引出 Java 的 I/O 模型的演进过程,并用实例说明如何选择...

waylau
2016/03/01
4.7K
20

没有更多内容

加载失败,请刷新页面

加载更多

汇总你在 Linux 上的命令使用情况

使用合适的命令,你可以快速了解 Linux 系统上使用的命令以及执行的频率。 汇总 Linux 系统上使用的命令只需一串相对简单的命令以及几条管道将它们绑定在一起。当你的历史记录缓冲区保留了最...

osc_bvincwvq
14分钟前
7
0
Hacker News 简讯 2020-08-15

最后更新时间: 2020-08-15 07:01 Welders set off Beirut blast while securing explosives - (maritime-executive.com) 焊工在固定炸药的同时引爆了贝鲁特爆炸 得分:383 | 评论:322 Factor......

FalconChen
今天
24
0
OSChina 周六乱弹 —— 老椅小猫秋乡梦 梦里石台堆小鱼

Osc乱弹歌单(2020)请戳(这里) 【今日歌曲】 @小小编辑 :《MOM》- 蜡笔小心 《MOM》- 蜡笔小心 手机党少年们想听歌,请使劲儿戳(这里) @狄工 :腾讯又在裁员了,35岁以上清退,抖音看到...

小小编辑
今天
111
3
构建高性能队列,你不得不知道的底层知识!

前言 本文收录于专辑:http://dwz.win/HjK,点击解锁更多数据结构与算法的知识。 你好,我是彤哥。 上一节,我们一起学习了如何将递归改写为非递归,其中,用到的数据结构主要是栈。 栈和队列...

彤哥读源码
今天
17
0
Anaconda下安装keras和tensorflow

Anaconda下安装keras和tensorflow 一、下载并安装Anaconda: Anaconda下载 安装步骤: 如果是多用户操作系统选择All Users,单用户选择Just Me 选择合适的安装路径 然后勾选这个,自动配置环境...

Atlantis-Brook
今天
15
0

没有更多内容

加载失败,请刷新页面

加载更多

返回顶部
顶部