Up until recently, that was the Solar System -- four Earth-like planets with small radius, smaller than about two times the size of the Earth -- and that was of course Mercury, Venus, Mars, and of course the Earth, and then the two big, giant planets.
人们就已经知道行星有大有小 到现在为止，我们的太阳系 有四个半径较小的类地行星 它们都小于两倍地球的大小 这就包括水星 金星，火星 这个显然是地球 然后是两个巨行星