Atmosphere of a world in another solar system might reveal hints of alien biological activity
Our galaxy is teeming with planets. Over the last 25 years, astronomers have cataloged about 2,000 worlds in 1,300 systems scattered around our stellar neighborhood. While most of these exoplanets look nothing like Earth (and in some cases, like nothing that orbits our sun), the bonanza of alien worlds implies a tantalizing possibility: There is a lot of real estate out there suitable for life.
We haven’t explored every corner of our solar system. Life might be lurking beneath the surface of some icy satellites or in the soil of Mars. For such locales, we could conceivably visit and look for anything wriggling or replicating. But we can’t travel (yet) to worlds orbiting remote suns dozens of light-years away. An advanced alien civilization might transmit detectable radio signals, but primitive life would not be able to announce its presence to the cosmos.