The official number of exoplanets—planets outside our solar system—tracked by NASA has reached 6,000. Confirmed planets are added to the count on a rolling basis by scientists from around the world, so no single planet is considered the 6,000th entry. The number is monitored by NASA's Exoplanet Science Institute (NExScI), based at Caltech's IPAC in Pasadena, California. There are more than 8,000 additional candidate planets awaiting confirmation, with NASA leading the world in searching for life in the universe.

"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, Astrophysics Division, NASA Headquarters in Washington.

"Step by step, from discovery to characterization, NASA missions have built the foundation to answering a fundamental question: Are we alone? Now, with our upcoming Nancy Grace Roman Space Telescope and Habitable Worlds Observatory, America will lead the next giant leap—studying worlds like our own around stars like our sun. This is American ingenuity, and a promise of discovery that unites us all."

The milestone comes 30 years after the first exoplanet was discovered around a star similar to our sun, in 1995. (Prior to that, a few planets had been identified around stars that had burned all their fuel and collapsed.)

Although researchers think there are billions of planets in the Milky Way galaxy, finding them remains a challenge. In addition to discovering many individual planets with fascinating characteristics as the total number of known exoplanets climbs, scientists are able to see how the general planet population compares to the planets of our own solar system.