How many planets are out there?

The NASA Exoplanet Archive passed 6000 confirmed planets in 2025, and the number keeps growing. Most came from two space telescopes. Kepler (2009–2018) stared at about 150,000 stars in one patch of sky. TESS (launched in 2018) scans nearly the whole sky, a section at a time, looking for planets around nearby, bright stars.

Can we just count? Not directly. A census of planets found is a census of what our methods can find. Short-period, large planets give the deepest and most frequent dips, so they are found first. Small planets, and planets on long orbits, are much harder. If you fish with a net with big holes, you catch only big fish and then conclude that the sea has only big fish.

Astronomers correct for this. Studies using microlensing, which does not care how close the planet is to its star, suggest that on average there is at least one planet per star in our Galaxy. Most stars have planets.

What do those planets look like? The most common sizes found are between the size of Earth and Neptune: super-Earths and mini-Neptunes, planets that are several times heavier than Earth. The Solar System has no planet of this kind. In the period-radius chart our planets sit in a sparse region. This does not mean the Solar System is a freak, but it does mean it may not be typical.

How common are Earth-size planets in the habitable zone of Sun-like stars? Published estimates range widely, from a few percent of stars to roughly one per star. The answer is still being measured.