Thirty years ago, astronomers didn’t know if planets around other stars were common. Today, NASA says we’ve confirmed 6,000 exoplanets — a staggering number considering the first definitive discovery only happened in the 1990s. Each of those worlds is a place with its own physics, chemistry, and history. Each is a reminder that our solar system isn’t the only way to build a planetary family.

“This milestone represents decades of cosmic exploration driven by NASA space telescopes, exploration that has completely changed the way humanity views the night sky,” said Shawn Domagal-Goldman, acting director of NASA’s Astrophysics Division, in a statement. “Step by step, from discovery to characterisation, NASA missions have built the foundation to answering a fundamental question: Are we alone?”

From Pulsars to Planet Catalogs

The age of exoplanets began in 1992 with two tiny worlds discovered orbiting a pulsar, the super-dense remnant of a dead star. In 1995, astronomers Michel Mayor and Didier Queloz detected 51 Pegasi b, the first planet found around a Sun-like star. That discovery won them a Nobel Prize.

Fast-forward to today: we’ve gone from one lonely planet to a catalog of thousands. The pace is accelerating. In 2015, NASA’s Kepler telescope had confirmed its 1,000th exoplanet. By 2022, the tally hit 5,000. Just three years later, we’re at 6,000 — and there are more than 8,000 candidates waiting for confirmation.

But the science is messy. As NASA noted, there isn’t a single “6,000th planet.” Confirmations happen on a rolling basis as teams across the globe compare data and rule out false positives. “We really need the whole community working together if we want to maximize our investments in these missions that are churning out exoplanets candidates,” said Aurora Kesseli, deputy science lead for the NASA Exoplanet Archive, in a press statement.

The tools for planet hunting have also evolved. Most discoveries come from the transit method, when a planet crosses in front of its star and dims the light. Others come from the radial velocity method, detecting the tiny wobbles of a star as it’s tugged by an orbiting planet. A few rare worlds have been spotted directly, usually massive gas giants glowing in infrared. NASA’s TESS mission alone has added hundreds, while the retired Kepler delivered thousands.

A Growing Catalog of Alien Worlds

The 6,000 planets confirmed thus far revealed a menagerie of worlds stranger than anything science fiction writers dared to imagine.

There are hot Jupiters, massive gas giants that whip around their stars in days, roasting in blistering heat. Some planets are tidally locked, one side permanently fried while the other remains in endless night. Astronomers have even proposed that certain worlds may rain molten glass or iron.

Others are super-Earths and mini-Neptunes, categories missing from our own solar system but apparently common in the galaxy. Some are “puffy” exoplanets, no denser than styrofoam. Some may be cloaked in oceans or shrouded in toxic atmospheres. And NASA’s catalog already includes 700 rocky worlds and more than 2,000 Neptune-like planets. A few even orbit dead stars or drift freely through space with no star at all; these are known as rogue planets.

“Each of the different types of planets we discover gives us information about the conditions under which planets can form and, ultimately, how common planets like Earth might be, and where we should be looking for them,” said Dawn Gelino, head of NASA’s Exoplanet Exploration Program. “If we want to find out if we’re alone in the universe, all of this knowledge is essential.”

And yet, as NASA admitted in its milestone video, “There’s one we haven’t found — a planet just like ours. At least, not yet.”

The Hunt for Earth 2.0

Now that we’ve proven planets are everywhere — astronomers estimate every star has at least one — the search is narrowing. The next chapter is all about habitable worlds.

NASA’s James Webb Space Telescope is already probing atmospheres for biosignatures, or the chemical fingerprints that might hint at life. Meanwhile, the Nancy Grace Roman Space Telescope (launching in 2027) will use microlensing to discover thousands more planets, including Earth-sized ones. Europe’s PLATO mission, set for 2026, will zero in on rocky planets orbiting Sun-like stars. And the proposed Habitable Worlds Observatory could finally give us the power to image Earth-like exoplanets directly.

Even China is stepping in with its Earth 2.0 Space Telescope, launching in 2028 to survey Earth-sized planets. The race is no longer just about finding as many exoplanets as possible — it’s about finding another pale blue dot.

The fact that we’ve found 6,000 exoplanets in just three decades is wild. But compared to the hundreds of billions of planets thought to exist in the Milky Way, we’ve barely scratched the surface. Each discovery is another reminder that our universe is teeming with strange and beautiful worlds. And somewhere out there, one might look back at us.

Timeline of Exoplanet Discovery Milestones

1992

• First confirmed exoplanets discovered.
• Two small worlds detected orbiting a pulsar (PSR B1257+12).

1995

• First planet around a Sun-like star: 51 Pegasi b.
• Discovery by Michel Mayor and Didier Queloz, later awarded the Nobel Prize.

2009

• NASA launches the Kepler Space Telescope.
• Revolutionizes exoplanet science by using the transit method to detect thousands of candidates.

2015

• Kepler confirms its 1,000th exoplanet.
• Marks the beginning of large-scale statistical studies of planetary systems.

2016

• Record year: nearly 1,500 new exoplanets confirmed.
• Includes the discovery of Proxima Centauri b, Earth’s closest known neighbor.

2017

• Discovery of the TRAPPIST-1 system with seven Earth-sized planets, three in the habitable zone.

2018

• NASA’s TESS (Transiting Exoplanet Survey Satellite) launches.
• Begins an all-sky survey for exoplanets around bright, nearby stars.

2022

• Exoplanet tally reaches 5,000 confirmed worlds.
• Represents three decades of discovery since the 1990s.

2023–2025

• James Webb Space Telescope begins probing exoplanet atmospheres.
• First detections of complex molecules and possible biosignature hints.

2025

• NASA announces 6,000 confirmed exoplanets.
• Over 8,000 candidates still awaiting confirmation.

2026–2028 (Upcoming)

• ESA’s PLATO mission (2026): will search for rocky planets around Sun-like stars.
• Nancy Grace Roman Space Telescope (2027): will use microlensing to discover thousands more worlds.
• China’s Earth 2.0 Telescope (2028): will hunt for Earth-sized planets.