这是引力与行星的相互作用，对吧？
还没有人找到方法来计算从地球到行星的精确距离。
No-one had found a way to calculate accurate distances to the planets from the Earth.
如果它们是行星的影子，它们就会是圆形的，对吧？
If they were shadows of the planets, they would be circular, right?
最常见的一种说法是它们可能包含来自其他行星的访客。
The most popular one is that they may contain visitors from other planets.
这两组行星的构成物质根据熔点分为三类：气体、岩石和冰。
The substances that make up both groups of planets are divided into three groups—gases, rocks, and ices—based on their melting points.
最后，科学家测量了由于行星的引力拖拉而产生的恒星摆动，这就是径向速度。
Finally, scientists measure the star's wobble due to the planet's gravitational tug, known as the radial velocity.
根据一种假设，这颗行星的重力场会对由尘埃和气体组成的原行星盘产生牵引力。
According to one hypothesis, the planet's gravitational field tugs on the protoplanetary disk of dust and gas from which it formed.
如果在这些活动中，这个行星的地理特征遭到破坏，环境不再适合大量物种居住，那么就随它去吧。
If in these activities the physical features of the planet are damaged, if the environment is made inhospitable for a multitude of living species, then so be it.
新发现的这个天体的运行轨和任何其他行星的不同。
The newly discovered world followed an orbital path unlike that of any other planet.
他们回避了在行星的排列和地球上发生的事件之间有联系的看法。
They shunned the belief that there is a link between the alignment of the planets and events on the Earth.
鲁宾认为，小行星的热量可能来自小行星之间的碰撞。
Rubin suggests that asteroids' heat could have derived from collisions between asteroids.
经济和金融的运作方式与天气条件或行星的运行相同吗？
Do economics and finance work in the same way as weather conditions or the movement of planets?
近年来，天文学家已经发现了近400颗新的有行星的恒星。
In recent years, astronomers have found nearly 400 new planets with stars.
在这种情况下，旋转小行星的轨道将非常缓慢地向太阳旋转。
In this case, the orbit of the rotating asteroid will very slowly spiral toward the sun.
巨大的外行星的引力护盾虽然效率很高，但偶尔也会无法保护地球。
The gravitational shield of the giant outer planets, while highly efficient, must occasionally fail to protect Earth.
混沌理论是由科学家提出的，试图解释行星的运动和环境条件的变化。
Chaos theory was developed by scientists, trying to explain the movement of the planets and the changes in environmental conditions.
经过长达六年的观测，发现有五颗行星的质量是地球的13-25倍。
Six years of observations revealed the presence of five planets between 13 and 25 times the mass of Earth.
第三，巨大的外行星的引力屏障虽然非常有效，但偶尔也会无法保护地球。
Third, the gravitational shield of the giant outer planets, while highly efficient, must occasionally fail to protect Earth.
当他教他们天文学的时候，他不仅仅教了行星的名字，还用利用这些名字来教神话学。
When he was teaching them astronomy, he didn't just teach them the names of the planets—he used it as a way to teach mythology.
但是，与内行星的核心不同，月球的核心几乎不含铁，而典型的行星形成物质则富含铁。
But, unlike the cores of the inner planets, the Moon's core contains little or no iron, while the typical planet-forming materials were quite rich in iron.
科学家们在前往另一颗行星的任务中发现的第一件事就是，金星根本不是小说中描绘的人间天堂。
The very first thing that scientists discovered with a mission to another planet was that Venus was not at all the earthly paradise that fiction had portrayed.
现在，冥王星可能是个矮行星，但是，亲爱的克莱德，在我书中你仍然是第一个发现行星的美国人。
Pluto may be a dwarf planet now, Clyde baby, but you're still the first American to discover a planet in my book.
类地行星的密度的平均值大约是水的密度的五倍，而类木行星的密度平均值只有水的密度的1.5倍。
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.
这个系外行星的质量是地球的几倍，但是它足够小，能够由岩石构成，而不是像木星是一团巨大的气体。
The exoplanet is a few times the mass of Earth, but it should still be small enough to be rocky rather than a gas giant like Jupiter.
此外，由于气体的分子运动依赖于温度，在木星行星的低温下，即使是最轻的气体也不可能获得逃逸所需的速度。
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.
在我们的太阳系中，行星的轨道几乎是圆形的，这使得科学家们预测，其他恒星周围的行星也会位于圆形轨道上。
The nearly circular orbits of planets in our solar system led scientists to expect that planets around other stars would also reside in circular orbits.
目标是测量AU；随后，当我们知道了所有围绕太阳的其他行星的轨道速度，对太阳系的规模就有充分的认识了。
The goal was to measure the AU; then, knowing the orbital speeds of all the other planets around the Sun, the scale of the Solar System would fall into place.
怀疑派认为，一次撞击只会使小行星的整体温度上升很小，而且小行星在两次撞击之间会迅速冷却，从而无法积聚大量热量。
Skeptics have argued that a single impact would raise an asteroid's overall temperature very little and that asteroids would cool too quickly between impacts to accumulate much heat.
由于我们这样的行星的寿命是几十亿年，我们可以预测，如果我们星系中有其他生物生存，它们的年龄将从零到几十亿岁不等。
Since the lifetime of a planet like ours is several billion years, we can expect that, if other civilisations do survive in our galaxy, their ages will range from zero to several billion years.
由于我们这样的行星的寿命是几十亿年，我们可以预测，如果我们星系中有其他生物生存，它们的年龄将从零到几十亿岁不等。
Since the lifetime of a planet like ours is several billion years, we can expect that, if other civilisations do survive in our galaxy, their ages will range from zero to several billion years.
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