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.

另一方面，像地球的卫星这种相对温暖、表面引力较小的天体，它们连最重的气体也无法容纳，因此也没有大气层。

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And then the planet has to have the right surface gravity.

如此以来，这个星球表面就有一定的重力存在。

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This difference in surface gravity is due to a number of factors - mass, density, and radius being the foremost.

地表重力的差异源于很多因素的影响——质量，密度，半径(这是最重要的因素)。

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For example, we know that if a body is near the surface of the Earth, the force of gravity of that object seems to be m times g, where g is 9.8.

例如,我们知道,如果在地球表面有一个物体,该物体受到的重力大小为 m 与 g 的乘积,g 等于 9.8

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