Exoplanets
An exoplanet is any planet beyond our solar system. Most of them orbit other stars, but some free-floating exoplanets, called rogue planets, are untethered to any star. We’ve confirmed more than 5,800 exoplanets out of the billions that we believe exist.
Overview
Most of the exoplanets discovered so far are in a relatively small region of our galaxy, the Milky Way. (“Small” meaning within thousands of light-years of our solar system; one light-year equals 5.88 trillion miles, or 9.46 trillion kilometers.) Even the closest known exoplanet to Earth, Proxima Centauri b, is still about 4 light-years away. We know there are more planets than stars in the galaxy.
By measuring exoplanets’ sizes (diameters) and masses (weights), we can see compositions ranging from rocky (like Earth and Venus) to gas-rich (like Jupiter and Saturn). Some planets may be dominated by water or ice, while others are dominated by iron or carbon. We’ve identified lava worlds covered in molten seas, puffy planets the density of Styrofoam and dense cores of planets still orbiting their stars.
Featured Exoplanet
K2-18 b
Researchers studying this potential ocean world have found water vapor, carbon-bearing molecules, and — more recently — possible dimethyl sulfide, a molecule that on Earth is produced by marine life.
K2-18 b is a super-Earth exoplanet, nearly nine times the mass of Earth, and is about 124 light-years away. It only takes about 33 days to orbit its star, a red dwarf that’s smaller and cooler than our Sun, but it resides in the “Habitable Zone” — the region around a star neither too hot not too cold, where liquid water could exist on a planet’s surface.
The Hubble Space Telescope detected water vapor in K2-18 b’s atmosphere in 2019 — the first time for a habitable-zone exoplanet. And the James Webb Space Telescope has since found carbon-bearing molecules including methane and carbon dioxide in K2-18 b’s atmosphere. Webb telescope observations also revealed the possible detection of a molecule called dimethyl sulfide. On Earth, most dimethyl sulfide in the atmosphere is emitted by marine phytoplankton.
More About K2-18 b
How NASA’s Webb Telescope Supports Our Search for Life Beyond Earth
With its unprecedented sensitivity and resolution, Webb can study the chemical composition of exoplanet atmospheres, offering clues about habitability and potential biosignatures. But this requires hundreds of hours of observing time for a single planet, follow-up studies, and multiple converging lines of evidence to confirm true biosignatures and rule out false positives.
Hubble Finds Water Vapor on Habitable-Zone Exoplanet for First Time
K2-18 b, In Depth
Find more details about K2-18 b, see an artist's concept of the planet, and explore a 3D interactive view, in its Exoplanet Catalog entry.
Kepler/K2
NASA's planet-hunting space telescope that discovered K2-18 b, and most of the other exoplanets we know about — 3,327 confirmed, so far.
James Webb Space Telescope
One of the main uses of the Webb telescope is to study the atmospheres of exoplanets, to search for the building blocks of life elsewhere in the universe.
Hubble Space Telescope
Learn about Hubble's exoplanet observations
Exoplanet Types
So far scientists have categorized exoplanets into the following types: Gas giant, Neptunian, super-Earth, and terrestrial, with subcategories — such as mini-Neptunes — within those groups. How are they alike or different? What makes them special?
Learn More about Exoplanet Types
Other Stars, Other Habitable Worlds?
The Target Star Catalog is a guide to intriguing nearby stars that astronomers want to study with future missions, such as the Habitable Worlds Observatory, which will be built specifically to find and observe Earth-like exoplanets, to search for signs of life.
Browse the Target Star Catalog
Exoplanet Catalog
Learn more about every confirmed exoplanet — 5,800+ and counting — in this continuously updated resource. View interactive 3D models, read descriptions and vital statistics, and filter by exoplanet type, or by the method used to discover it, or by the spacecraft, observatory, or other facility that found it.
Browse the Exoplanet Catalog
