The numbers tell us that 15-20 percent of Sun-like stars harbor worlds similar in size to the Earth, orbiting stellar parents at distances implying that their surfaces might be temperate. We have not found the nearest such world yet, but statistically it should be within about 15 light years of us – a stone’s throw in cosmic terms.
现在，天文学家已经发现有数不胜数的行星围绕其他恒星转动。数据告诉我们有15-20%的类日恒星孕育的世界与地球大小相似，其运行轨道与恒星的距离可能带来温和的地表温度。人类尚未找到距离我们最近的世界，但从统计学的角度它应该离我们约15光年——这在宇宙学中仅仅是一箭之遥而已。我们很可能会在十年内找到类似的星球，并进而搜索上述世界的大气成分或气候有没有外星生物的痕迹。