If you see, in the spectrum of a planet host star, if you see strange chemical elements, it can be a signal from a civilization which is there and they want to signal about it.
如果你在一个主恒星系统中的行星的光谱中, 如果看到陌生的化学元素, 这可能是一个地外文明的发出的信号 并且他们想要这个信号在那里存在.