It's official: humans have discovered 6,000 planets outside the solar system.

Exoplanet science has reached a new milestone. NASA announced that there are now 6,000 confirmed exoplanets. They vary greatly in type and size, as well as the type of stars they orbit. (Image courtesy of NASA's Goddard Space Flight Center)

The era of exoplanets began in 1992, when astronomers discovered a pair of planets orbiting a pulsar. Then, in 1995, astronomers discovered the first exoplanet orbiting a main-sequence star. As NASA's Kepler and TESS missions launched, the number of confirmed exoplanets continued to grow.

By 2015, NASA announced that the Kepler telescope had discovered its 1,000th exoplanet. 2016 was a landmark year for exoplanet discoveries: nearly 1,500 were discovered that year alone. By March 2022, the total number of exoplanets reached 5,000. NASA has now announced 6,000 confirmed exoplanets.

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The vast majority of exoplanet detections are made indirectly. The transit method detects planets by measuring the amount of light an exoplanet blocks as it passes in front of its star. The radial velocity method detects the small tugging motions exoplanets exert on their stars and estimates how the star's brightness changes due to these oscillations. Astrometry detects minute motions, and gravitational lensing, the presence of a planet, introduces anomalies into the observed light. Both Kepler and TESS used the transit method, and it is this method that has led to the majority of exoplanet detections—almost 4,500. The radial velocity method is next in importance, with approximately 1,140 detections.

While effective, they are indirect. Only direct imaging can determine the chemical composition of exoplanet atmospheres and does not require a specific orbital position or orientation. However, this is a complex process, and direct imaging has been obtained for fewer than 100 exoplanets.

This is the HR 8799 system, which contains four exoplanets. The exoplanets and their orbits have been confirmed by direct imaging, making them among the few exoplanets that have been directly imaged.

6,000 confirmed exoplanets is a definite, concrete scientific milestone. But there are thousands of other candidates, and confirming one requires considerable effort. The signal could be something else, such as stellar flares or artifacts produced by the transit method. Subsequent observations, sometimes with a different telescope, confirm their existence, which requires considerable time and resources. As of July 2025, the TESS list included 7,655 exoplanet candidates, of which just over 600 had been confirmed.

“We really need the entire community to work together if we want to make the most effective investments in these missions that generate exoplanet candidates,” said Aurora Kesseli, deputy principal investigator for NASA's Exoplanet Archive at IPAC. “An important part of our work at NExScI is building tools that help the community turn planet candidates into confirmed planets.”

We may be faced with a number of exoplanet discoveries that would have been unthinkable just a couple of decades ago.

Exoplanet candidates are still being detected in Gaia data, despite the mission's end. NASA's Nancy Grace Roman Space Telescope, scheduled to launch in 2027 unless the current administration's threats to cancel it come to fruition, is expected to discover thousands more exoplanets using microlensing.

An artist's rendering of NASA's Nancy Grace Roman Space Telescope, poised to discover thousands of exoplanets using microlensing.

However, the era of exoplanets is beginning to change. Our searches are becoming more focused. Instead of casting a wide net and seeing what comes up, astronomers are seeking to find more specific types of exoplanets. The European Space Agency's (ESA) PLATO mission is poised to discover even more rocky exoplanets around Sun-like stars when it launches in 2026. The Habitable Worlds Observatory, still in development, will search for habitable exoplanets in habitable zones and contribute to the ever-growing list of exoplanets. Other missions, such as CHEOPS and ARIEL, will study known exoplanets in greater detail.

This infographic features artistic renderings of current and future telescopes used in exoplanet research. Some are designed for broad coverage and the discovery of as many different exoplanets as possible. Others are designed to study specific types of exoplanets. Still others are designed to study known exoplanets and more precisely characterize them.

The holy grail of exoplanetology is habitability. Determining habitability is a complex process, and only a few exoplanets demonstrate any potential for habitability. The key to success is detecting biosignatures—specific chemicals that indicate the presence of life on a planet. The JWST observatory, with its infrared atmospheric spectrometry, is just beginning to explore this topic and has already achieved some promising results, though nothing concrete yet.

Like all scientific endeavors, the search for exoplanets has been boosted by technological advances, and this trend will continue. One of the main obstacles in exoplanet research is the orbits of the stars around which planets orbit. Stars are unusually bright, and the presence of a relatively dim exoplanet can be completely obscured by starlight. This is especially relevant for targeted searches for Earth-like worlds around Sun-like stars, which is what the Habitable Worlds Observatory (HWO) is designed to detect.

To operate the HWO, a powerful coronagraph or star screen will be required. If an astronomer were to look for Earth around the Sun, they would have a hard time spotting it amid all that starlight. This is precisely what astronomers will do with the HWO.