One day, it might be possible to detect the spread of life among the stars through panspermia--a hypothetical process of life distributed throughout the Milky Way by asteroids, comets, and even spacecraft. Henry Lin and Abraham Loeb of the Harvard-Smithsonian Center for Astrophysics propose, “If future surveys detect biosignatures in the atmospheres of exoplanets,” it ought to be possible to detect the spread of life between stars even without knowing how life spread from host star to host star. That is, we probably wouldn’t be able to detect the mechanisms of panspermia such as asteroid, spacecraft, or what have you. Nonetheless, life might spread “from host to host in a way that resembles the outbreak of an epidemic,” according to Lin and Loeb.
“Just as viruses evolved to brave the ‘harsh’ environment of ‘inter-host’ space to harness the energy of multiple biological hosts, perhaps evolution has or will drive a class of organisms to brave the harsh environment of interstellar space to harness the energy of multiple stellar hosts,” Lin and Loeb speculate.
They postulate, “Even if the earth is the only inhabited planet and primitive life cannot survive an interstellar journey, interstellar travel led by humans may one day lead to colonization of the galaxy.”
Source: STATISTICAL SIGNATURES OF PANSPERMIA IN EXOPLANET SURVEYS