K2-18 b
K2-18 b orbits the star K2-18, 124 light-years from Earth. It completes an orbit in 32.94 Earth days.
Get to know this world ↓
Size-based classification; composition may be uncertain.
Around 137% wider than Earth.
Time to complete one orbit.
Its light travels for roughly 124 years to reach us.
Transit
1 Earth radius
2.37 Earth radii
32.94 Earth days
This is how long the planet takes to complete one orbit around its star.
Overview
K2-18 b is one of the confirmed worlds in the NASA Exoplanet Archive. Recorded as discovered in 2015. The credited discovery facility is K2. Its Transit evidence gives us a way to study a planet that is usually too faint to see directly.
Its recorded radius is 2.37 times Earth's radius. Size is useful for comparison, but it cannot establish surface conditions by itself.
The planet
The archive lists a mass or minimum-mass value of 8.92 Earth masses (Mass). Radius: 2.37 Earth radii.
Mass and radius constrain possible interiors; multiple compositions can fit a given set of measurements.
Orbit & year
A year here lasts 32.94 Earth days. Its recorded semi-major axis is 0.143 AU. One AU is roughly the Earth–Sun distance.
Eccentricity: 0.2. Zero describes a circular orbit; increasing values describe more elongated ellipses.
Host star
Planetary system
Discovery
Reported discovery year: 2015. Method: Transit. Facility: K2.
First stored in this atlas: 04/10/2026. This is an ingestion date, not a confirmation date.
How these methods work ↗Potential habitability
The data here does not establish habitability, liquid water, or life. An appropriate atmosphere and many other conditions would be needed.
The listed equilibrium temperature is 284 K. This is an estimated energy-balance temperature, not a measured surface temperature.
Understand the habitable zone ↗What do we actually know?
The underlying light, motion or timing signal. Usually not a photograph of the planet.
Parameters derived from observations, with instrument and model uncertainty.
Our light-year conversion and browsing class are calculated from archive values.
Equilibrium temperature is an energy-balance estimate, not surface weather.
Possible composition depends on models and may not be unique.
Surface conditions and the presence of life are not established here.
Measured signals are interpreted through models. The archive’s composite table combines published values and may include calculated estimates. Values do not necessarily form one self-consistent solution.
Radius and mass can be estimated or inferred, orbital period comes from recurring observations, and size classification is calculated by this site. Atmospheric and surface conditions remain unknown unless established by specific observations.
Consult the archive for individual parameter references and uncertainty intervals before scientific use.
Scientific data
| Radius | 2.37 Earth radii |
|---|---|
| Mass / minimum mass | 8.92 Earth masses (Mass) |
| Orbital period | 32.93962 Earth days |
| Semi-major axis | 0.1429 AU |
| Eccentricity | 0.2 |
| Equilibrium temperature | 284 K · estimated, not surface temperature |
| Host star temperature | 3,457 K |
| Host star mass | 0.359 Solar masses |
| Host star radius | 0.411 Solar radii |
| Distance | 38.0266 parsecs |
| Discovery year | 2,015 |
| Discovery method | Transit |
| Discovery facility | K2 |
| Discovery publication | 2015-08 |
| Stellar spectral type | M2.5 V |
Uncertainties and parameter provenance
Archive uncertainty ranges and published references, where available. A missing uncertainty does not imply an exact value.
| Parameter | Uncertainty / source |
|---|---|
| Radius | +0.22 / -0.22Sarkis et al. 2018 |
| Mass / minimum mass | +1.7 / -1.6Sarkis et al. 2018 |
| Orbital period | +0.0001 / -0.0001Sarkis et al. 2018 |
| Equilibrium temperature | +15 / -15Sarkis et al. 2018 |
Sources
Hypothetical cloudy atmosphere. No surface or ocean is established by this illustration.
Commissioned for Worlds Beyond using image generation. Appearance is interpretive. Image policy and credits.
NASA Exoplanet Archive · Planetary Systems Composite Parameters (PSCompPars).
Open the scientific archive record ↗Last changed in this atlas: 04/10/2026, 11:39:41. Read our methodology.