81 Cet b
81 Cet b orbits the star 81 Cet, 330.3 light-years from Earth. It completes an orbit in 1,005.57 Earth days.
Get to know this world ↓Size-based classification; composition may be uncertain.
Around 1,210% wider than Earth.
Time to complete one orbit.
Its light travels for roughly 330 years to reach us.
Radial Velocity
Overview
81 Cet b is one of the confirmed worlds in the NASA Exoplanet Archive. Recorded as discovered in 2008. The credited discovery facility is Okayama Astrophysical Observatory. Its Radial Velocity evidence gives us a way to study a planet that is usually too faint to see directly.
Its recorded radius is 13.1 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 1,051.06 Earth masses (Msini). Radius: 13.1 Earth radii.
Mass and radius constrain possible interiors; multiple compositions can fit a given set of measurements.
Orbit & year
A year here lasts 1,005.57 Earth days. Its recorded semi-major axis is 2.104 AU. One AU is roughly the Earth–Sun distance.
Eccentricity: 0.037. Zero describes a circular orbit; increasing values describe more elongated ellipses.
Host star
Planetary system
1 confirmed planets are stored for this star.
81 Cet b · 1,005.57-day orbit
Discovery
Reported discovery year: 2008. Method: Radial Velocity. Facility: Okayama Astrophysical Observatory.
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 527 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 | 13.1 Earth radii |
|---|---|
| Mass / minimum mass | 1,051.05854 Earth masses (Msini) |
| Orbital period | 1,005.57 Earth days |
| Semi-major axis | 2.104 AU |
| Eccentricity | 0.037 |
| Equilibrium temperature | 526.92 K · estimated, not surface temperature |
| Host star temperature | 4,734 K |
| Host star mass | 1.23 Solar masses |
| Host star radius | 11.21 Solar radii |
| Distance | 101.26 parsecs |
| Discovery year | 2,008 |
| Discovery method | Radial Velocity |
| Discovery facility | Okayama Astrophysical Observatory |
| Discovery publication | 2008-12 |
| Stellar spectral type | G5 III |
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 | Upper uncertainty unavailable / Lower uncertainty unavailableCalculated Value |
| Mass / minimum mass | +24.79062 / -21.2945Teng et al. 2023 |
| Orbital period | +1.84 / -1.94Teng et al. 2023 |
| Equilibrium temperature | Upper uncertainty unavailable / Lower uncertainty unavailableCalculated Value |
Sources
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.