But there was a problem: those outer planets.

是关于这些外行星的。

It's the most dense of the outer planets and the only planet found by mathematical prediction rather than by empirical observation.

它是密度最大的外行星，也是唯一一颗通过数学预测而非经验观察发现的行星。

The outer planets are more leisurely, but wait long enough and they too will be seen to move, sliding through the constellations.

外行星的移动速度就悠闲的多，但只要等得够久，就能看到它们划过星座。

We think of the outer planets.

我们想到外行星。

Adding the three outer planet adds a bit more complexity, but the same strategy remains.

添加三个外行星会增加一点复杂性，但相同的策略仍然存在。

An asteroid belt runs between the inner and outer planets.

小行星带在内行星和外行星之间运行。

Gas and water make up most of the four larger outer planets.

气体和水构成了四颗较大的外行星的大部分。

Finally, we reach the orbit of the outer planets, the gas giants, but just specks at this distance.

最后，我们到达了外行星的轨道，气态巨行星， 但在这个距离上只是斑点。

Mars is too dry and poor in oxygen, Venus far too hot, and so is Mercury, and the outer planets have temperatures near absolute zero and hydrogen-dominated atmospheres.

火星太干燥又缺氧，金星太热，水星也一样。除此之外，太阳系的其他行星的温度都接近绝对零度，并围绕着以氢气为主的大气层。

Then there was another seriously terrifying event: the Late Heavy Bombardment, a period of intense collisions with comets from the outer solar system, probably triggered by the movement of outer planets.

后期重轰炸，这是一段来自外太阳系的彗星频繁撞击的时期，可能是由外行星的运动引发的。

Coalescing out of a flat disk of material around the Sun, the inner planets were warmer, smaller, and rocky, while the outer planets were in a region that was colder, and grew huge.

内行星由围绕太阳的扁平物质盘凝聚而成，它们温度更高、体积更小且多岩石状构成，而外行星则位于温度更低的区域，它们体积更大。

NASA launched a first-of-its kind mission on Saturday to study Jupiter's Trojan asteroids, two large clusters of space rocks that scientists believe are remnants of primordial material that formed the solar system's outer planets.

美国国家航空航天局周六启动了一项史无前例的任务，对木星的特洛伊小行星进行研究。木星特洛伊小行星是由两大群太空岩石组成的，科学家们认为它们是形成太阳系外行星的原始物质的残留物。