未登录,请登录后再发表信息
最新评论 (0)
播放视频

月球为什么没有天然卫星?

Can a moon have a moon?

阿斯特鲁姆回答
Can a moon have a moon?
月球可以有卫星吗?
Well yes, in theory, it can.
理论上 当然可以有
And yet, we don’t see any examples
然而 我们并没有在太阳系当中
of this in our solar system!
发现任何类似的例子
So why is that?
那么为什么会这样呢?
The first important thing to know is that all celestial objects have gravitational pull.
首先要知道的是 所有的天体都有引力
That includes tiny little asteroids,
包括微小的小行星
all the way to giant stars or even black holes.
恒星 甚至黑洞
The mass of an object dictates how strong its gravitational pull is.
一个物体的质量决定了它的引力有多强
A region around an object where
天体周围的引力影响
its gravitational influence is greater than any other celestial
比附近其他天体的影响要大
object near them is called its Hill sphere.
这个范围就叫做希尔球
Due to the mass of our Earth,
根据我们地球的质量
it has a Hill sphere which has a radius of 1.5 million km,
它的希尔球半径为150万公里
meaning that if you were within this Hill sphere,
意味着如果你在这个希尔球范围内
you would be pulled more towards Earth
你将被拉向地球
than towards the Sun.
而不是太阳
If the Earth was closer to the Sun,
如果地球靠近太阳
its Hill sphere would be smaller, and if it was further away,
它的希尔球会变小 如果远离的话
it would be larger.
它会变大
The Sun also has a Hill sphere, which contains the entire solar system.
太阳也有希尔球 它容纳了整个太阳系
Its Hill sphere is massive,
它的希尔球很巨大
almost 2 light years in radius, as the nearest big celestial
半径差不多有2光年
object its gravity is competing against are other stars.
因为能与其引力抗衡的最近星体只有其他恒星
Which means in a way,
也就是某种程度上
everything orbiting our Sun is the Sun’s moon, or rather, its satellite.
任何围绕太阳运行的物体都是太阳的月亮 更准确的说是卫星
The term moon is really reserved for satellites of planets.
月球一词实际上是为行星的卫星所准备的
So why don’t moons also have natural satellites? Well,
那么为什么卫星没有天然卫星呢?
lots of moons are extremely close to their parent planets,
大量的卫星相当靠近它们的母行星
meaning their Hill spheres
意味着它们的希尔球
are very small.
非常小
Let’s take our moon as an example.
以我们的月球为例
Against the Earth, the Hill sphere of the moon is only 60,000km radius,
相对地球 月球的希尔球半径只有6万公里
or only one
或者说
sixth of the distance from the Moon to the Earth.
只有地月距离的六分之一
Moons like Io have an even smaller Hill sphere,
木卫一的希尔球甚至更小
as it is competing against the gravity of Jupiter.
因为它对抗的是木星的引力
This makes it quite hard for moons to capture an object,
这就导致卫星很难吸引物体
but not technically impossible.
但在理论上也是有可能的
So surely there must be a moon that
所以肯定在某个地方
has a natural satellite somewhere, right?
卫星还是有天然卫星的 对吗?
Well most moons also have one other major problem.
然而大多数卫星还有另一个主要问题
They tend to be tidally locked to their parent planet.
它们通常被母星给潮汐锁定了
Because of this,
因为这样
any satellite that orbits a tidally locked object will have its orbit
环绕物体潮汐锁定的任何卫星将会由于潮汐力
decay from tidal forces until it eventually crashes into the moon. Now,
发生轨道衰变 最后撞击月球
this still takes a lot of time over astronomical standards,
如今 我们仍然花费很多时间来研究新的天文法则
but it means if any of the moons
但这意味着在我们太阳系中
in our solar system did have a satellite at one point,
如果卫星确实曾经有过天然卫星
chances are that it has since crashed into it.
那很可能已经撞进卫星了
This leaves one question I think,
这就留下了一个问题
why don’t moons of planets also eventually crash?
为什么各行星的卫星没有消失呢?
The difference is that none
不同点在于
of our planets are tidally locked to the Sun as they are
太阳与它的行星之间没有潮汐锁定这种现象
far enough away from the parent star,
因为它们离恒星的距离足够远
which means their moons have a stable orbit.
这意味着它们的卫星有一个稳定轨道
This is one of the reasons we believe
而任何特拉普行星系统都没有卫星
that none of the Trappist system planets have moons,
我们认为其中一个原因就是
as they are so close to their parent star
如果认为它们之间有潮汐锁定现象的话
that we assume the planets are all tidally locked.
母星与卫星之间的距离太近了
I hope this hasn’t disappointed you too much,
我希望这没有让你太失望
so I’m going to leave you with this.
剩下的问题就留给你思考了
There are some other curious objects
在太阳系中还有一些
in the solar system far away from any other object,
远离任何天体的奇怪物体
so they aren’t tidally locked to anything.
它们没有被其他天体牵制
This particular asteroid called Ida looks
这个独特的小行星叫做艾达
like a standard 30 km wide asteroid as seen
通过伽利略号宇宙飞船观测是一个
by the Galileo spacecraft, but you might notice this little blob here.
标准的3万公里宽的行星 你也许也注意到了这个小斑点
This is actually Ida’s moon, Dactyl!
这是艾达的月球 达克推尔!
It is only 1.5 km across and orbits only 60km away from Ida.
它只有1.5公里宽 在距离艾达6万公里的轨道上
We don’t know especially how stable this orbit is,
我们不知道这个轨道有多么稳定
but a very cool thing to observe nonetheless!
尽管如此 这仍是一件很酷的事情!
Thanks for watching!
感谢收看!
And thanks for all your support with the channel, no matter how small.
无论多么微小 都十分感谢您对本频道的支持
I love making these videos and learning more in the process,
我喜欢制作这些视频并且从中学到更多
it really is a joy to be running this channel.
运营这个频道真是有乐趣
If you’re new,
如果你是新观众
why not subscribe so you don’t miss out on any space videos in the future.
为什么不订阅呢?这样你以后就不会错过任何太空视频了
All the best!
一切顺利
And see you next time.
下回再见
未知太空

发表评论

译制信息
视频概述

本期视频将告诉你月球为什么没有天然卫星。

听录译者

收集自网络

翻译译者

——向日葵、微笑

审核员

审核员XY

视频来源

https://www.youtube.com/watch?v=FVLjC0YvIo4

相关推荐