Thirty years ago this week, two Swiss astronomers announced that they had spotted the first known planet orbiting a Sun-like star. The Nobel-winning discovery, later published in the pages of Nature1, was the culmination of centuries of dreaming, and decades of searching, for worlds beyond the Solar System.
It was also the start of a whirlwind of discovery. Astronomers have since found more than 6,000 exoplanets, plus hints of thousands more. Many were detected by NASA’s Kepler and Transiting Exoplanet Survey Satellite (TESS) missions, with other telescopes also contributing (see ‘Alien worlds’).
The exoplanetary zoo hosts a diversity of beasts. There are ‘hot Jupiters’ that whirl closely around their stars, including the planet discovered 30 years ago, which is orbiting the star 51 Pegasi. There are ‘super-Earths’ and ‘mini-Neptunes’ — categorized because of how their masses compare with those of planets in the Solar System — which are some of the most common exoplanets found so far. There are systems crammed with multiple planets that move in almost musical rhythms with one another; rogue planets floating freely in the Galaxy; and alien worlds that circle two stars at once, just like the fictional Star Wars planet Tatooine.
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