NASA has some pretty amazing technology for discovering exoplanets and even the moons of exoplanets (see Gas Giant Exoplanet Can Has Moons?); now they even have a pretty amazing video:
To capture finer details – detecting atmospheres on small, rocky planets like Earth, for instance, to seek potential signs of habitability – astronomers knew they needed what we might call “superhero” telescopes, capable of blasting off the surface into orbit.
“While ground-based telescopes showed us that it is indeed possible to discover new planets, it’s often space-based facilities that allow us to advance from initial detections to well-understood worlds,” said Jennifer Burt, an exoplanet scientist at NASA’s Jet Propulsion Laboratory in Southern California.
Over the past few decades, a team of now-legendary space telescopes answered the call: Hubble, Chandra, Spitzer, Kepler, TESS, and now, the Webb telescope.
Golden Age science fiction master Edmond Hamilton described the idea of an automated habitable planet-finding telescope in his 1936 short story Cosmic Quest:
I was near enough it now to set my automatic astronomical instruments to searching it for a habitable planet.
These instruments were the wonderful ones our astronomers had perfected. With super-telescopic eyes each one scanned a part of the star field before them. And each mechanical eye, when it found planetary systems in its field, automatically shifted upon them a higher powered telespectroscope which recorded on permanent film the size, mean temperature and atmospheric conditions of these worlds.
(Read more about Hamilton's search for habitable planets)