时差N小时 月球表面的记号为何不消失?(上)（在线收听）

In 1969 when Neil Armstrong said “That’s one small step…”, he made a lasting impression.

1969年，当时阿姆斯特朗的名言“人类一小步”给人留下了难以磨灭的印象。

On the moon, that is. Marks on the surface of the moon don’t disappear the way marks on the Earth do; a great example is the impact craters we can see dotting the moon’s surface.

月球表面也是这样。其表面的记号不会像地球那样轻易消失。最典型的例子就是人类肉眼可见的月球表面密密麻麻的陨石坑。

Many of them are billions of years old!

其中很多陨石坑的历史长达数十亿年。

But Why?

为什么呢？

If you write your name in the sand at the beach, one day later there’s no sign you were there. What’s the difference?

如果你在沙滩上写下自己的名字，那么一天后，名字就会消失。两者的差别在哪呢？

Here’s an experiment you can do to find out. Take two pans and fill them with soil and sand mixed together.

你可以利用实验寻找差别。首先准备两口平底锅，再将土和沙子掺在一起装进锅里。

Now have some young person press her or his hand down into the mixture to make an imprint.

然后让几个年轻人把手放在沙土中留下印记。

One of these surfaces will represent the Earth, and one the moon.

其中一口平底锅代表地球，另一口代表月球。