---
title: "The Kepler-391 system"
url: "https://spacecatalog.org/system/kepler-391"
release: "DR1"
licence: "No licence stated; acknowledgement requested"
citation: "This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Cite Christiansen et al. (2025), Planetary Science Journal (doi:10.3847/PSJ/ade3c2), and the literature reference given with each value."
---

# The Kepler-391 system

Kepler-391 is a K2 III-IV orange star in Cygnus, 2835 ly away, with 2 known planets. Their orbits run from 0.0830 to 0.164 AU. All of them were detected by transit.

## The planets, innermost first

| Planet | Orbit (AU) | Period | Radius | Mass | Equilibrium T |
| --- | --- | --- | --- | --- | --- |
| [b](https://spacecatalog.org/object/kepler-391-b) | 0.0830 | 7.418 d | 2.50 R⊕ | 1100 M⊕ | 930 K |
| [c](https://spacecatalog.org/object/kepler-391-c) | 0.164 | 20.5 d | 2.88 R⊕ | 450 M⊕ | 662 K |

Every figure is the planet's composite parameter from the [NASA Exoplanet Archive (Planetary Systems Composite Parameters)](https://exoplanetarchive.ipac.caltech.edu/cgi-bin/TblView/nph-tblView?app=ExoTbls&config=PSCompPars), one consistent set per world. Semi-major axes are orbits about the star, not distances from Earth.

This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Cite Christiansen et al. (2025), Planetary Science Journal (doi:10.3847/PSJ/ade3c2), and the literature reference given with each value.

## The host star

| Quantity | Value |
| --- | --- |
| CLASS | K2 III-IV orange star |
| SPECTRAL TYPE | K2 III-IV |
| MASS | 1.27 M☉ |
| RADIUS | 2.879 R☉ |
| SURFACE TEMPERATURE | 5038 K |
| LUMINOSITY | 4.81 L☉ |
| DISTANCE FROM EARTH | 2835 ly |
| APPARENT MAGNITUDE | 13.18 |
| CONSTELLATION | Cygnus |
| STARS IN SYSTEM | 1 |

The star itself: https://spacecatalog.org/object/kepler-391

The page itself, with the orbits drawn: https://spacecatalog.org/system/kepler-391