Astro biology is the science of looking for microbes and other forms of life that may not be broadcasting any form of life at all. What sciencists tend to look for is a planet that's in the goldy lock zone around its star. Oxygen only exists on earth because of photo synthesis, methane is another bio signature. And astroboologists have calculated that there's probably something like three and a half thousand the signatures of life, thatere small molecules. These things are not dead serts for life, but they would start to build the evidence that you're seeing chemistry that is life like on the planet that you're looking at.