optical signals
radio signals
microbial life
organic molecules
extraterrestrial communication
biosignatures
technosignatures
extraterrestrial civilizations
alien megastructures
atmospheric anomalies
habitable exoplanets
intelligent life
life in exoplanet atmospheres
life in interstellar space
life on Enceladus
life on Europa
life on Mars
life on Titan
methane on Mars
phosphine on Venus
water on other planets