“Until 1991, the only planets known to humans were in our Solar System. In that same year, astronomers discovered the first extrasolar planet, now dubbed as exoplanets, by measuring the Doppler shift of stellar spectral lines, effectively witnessing the planet play gravitational tug-of-war with its parent star as it orbits. Over the next decade or so, astronomers refined their planet hunting skills and found more than 30 exoplanets.