After 30 Years of Discovery, These Are Astronomers’ Top Five Exoplanets

Thirty years ago this week, two Swiss astronomers announced that they had spotted the first known planet orbiting a Sun-like star. The Nobel Prize-winning discovery, later published in the pages of Naturewas the culmination of centuries of dreaming and decades of searching for worlds beyond the solar system.

It was also the beginning of a whirlwind of discoveries. Since then, astronomers have discovered more than 6,000 exoplanets, as well as thousands more. Many were detected by NASA’s Kepler and Transiting Exoplanet Survey Satellite (TESS) missions, to which other telescopes also contributed (see graphic below).

The exoplanetary zoo is home to a diversity of beasts. There are “hot Jupiters” that orbit their stars closely, including the planet discovered 30 years ago that orbits the star 51 Pegasi. There are “super-Earths” and “mini-Neptunes” – classified based on how their masses compare to those of the solar system’s planets – which are among the most common exoplanets found so far. There are systems filled with multiple planets that move with each other in almost musical rhythms; rogue planets floating freely in the Galaxy; and alien worlds that circle two stars at once, much like the fictional Star Wars planet Tatooine.

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“Each is a whole new world, brimming with possibilities and potential, typically unlike anything we’ve seen before and challenging our notions of what ‘normal’ planets and planetary systems look like,” says Jessie Christiansen, an astronomer at the California Institute of Technology in Pasadena.

Nature asked some astronomers about their favorite exoplanets and got a wide range of suggestions.

Proxima Centauri: Nearby and visitable

At the top of many recommendation lists are the two, or even three, small planets orbiting Proxima Centauri, which is the closest star to the Sun, just 1.3 parsecs away in the constellation Centaurus.

The first planet Proxima was discovered in 2016 thanks to the European Southern Observatory in Chile. It is probably Earth-sized and orbits in its star’s habitable zone, the distance at which liquid water could exist on its surface. A second confirmed planet lies just outside the habitable zone and is likely somewhat smaller than Earth.

The proximity of Proxima Centauri means these planets are the best choice for an interstellar spacecraft, says Jean Schneider, an astronomer at the Paris Observatory in France. The first effort to develop such a craft – a $100 million project known as Breakthrough Starshot – reportedly failed.

However, “we will go there before the end of the century,” says Schneider.

TRAPPIST-1: terrestrial worlds in a row

Another favorite is the planetary system around the star TRAPPIST-1, located about 12 parsecs from Earth in the constellation Aquarius. Seven Earth-sized worlds orbit the star, discovered in 2016 and 2017.

Some TRAPPIST-1 planets are in the habitable zone, making the system an ideal laboratory for exploring the evolution of Earth-sized planets at different distances from their stars. The James Webb Space Telescope (JWST), in particular, has been scouring the TRAPPIST-1 planets for any signs of atmosphere. So far, the news has been mostly negative – perhaps not surprising, as the star is extremely active.

But astronomers say there is much to learn about the conditions that could lead to habitable conditions on some TRAPPIST-1 planets. Last month, for example, astronomers using JWST reported that planet “e” still had a chance of having an atmosphere.

“Plus, if you were on its surface, the other planets would look like moons in its sky,” says Néstor Espinoza, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland. “Isn’t that just beyond science fiction?”

K2-138: Musical resonances

The K2-138 planetary system has six planets aligned around its star, approximately 200 parsecs away in the constellation Aquarius.

First discovered by citizen scientists combing through data from NASA’s Kepler mission, the K2-138 planets move in a 3:2 resonance series. This means that some planets orbit the star three times while it takes others to orbit twice. Researchers have transformed this resonance, similar to the perfect fifth in music, into a sonification of the planets.

The existence of the resonances suggests that the planets eventually reached their final configuration in a slow, gradual process, Christiansen says. Many other planetary systems, including the solar system, have experienced violent and chaotic reshuffling that destroyed these resonances. K2-138 thus preserves rare clues about the formation of planetary systems, she says.

TOI-178: The power of several telescopes

About 63 parsecs away in the constellation Sculptor lies a group of six planets tightly packed around their star, TOI-178. All six, if they were in the solar system, would be in the orbit of Mercury, the planet closest to the Sun.

The theory predicts that such compact systems could form when the planets move around a lot in their early years. The discovery of the TOI-178 system was therefore “a great success of predictive theory,” says Christopher Broeg, an astronomer at the University of Bern in Switzerland.

This discovery also highlights a common theme in exoplanet discovery: how multiple telescopes can work together to find, confirm and study planets. NASA’s TESS satellite was the first to spot signs of planets around TOI-178, but it took the European Space Agency’s Cheops satellite, which Broeg works on, to confirm their details.

Kepler-47: Twin Suns

It turns out that planets don’t have to orbit a single star. Astronomers know of at least two dozen “circumbinary” systems, in which at least one planet orbits two stars.

Of these, the Kepler-47 planets are the favorite of Nader Haghighipour, an astronomer at the University of Hawaii at Mānoa. The Kepler mission detected these three planets orbiting a pair of stars located just over 1,000 parsecs away in the constellation Cygnus. At least one of the planets is in the habitable zone of both stars – although the chances of finding extraterrestrial life there are minimal.

Yet the very existence of this system “supports the idea that planet formation in circumbinary disks can take place in the same way as around single stars,” says Haghighipour. “This is a very important discovery.”

This article is reproduced with permission and has been published for the first time October 2, 2025.