One of the big questions for us, humanity, is if alien life exists elsewhere in the universe. So, if we want to discover alien life, the best place to look for it is on earth like planets located in what we call the habitable zone around cool stars.
In 1995, the first exoplanet discovered around a sun like star was 51 Pegasi b. Now, almost thirty years later, more than 5.500 exoplanets have been discovered. And a lot of them are planets of a size comparable to our own planet.