---
title: "The HD 187123 system"
url: "https://spacecatalog.org/system/hd-187123"
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 HD 187123 system

HD 187123 is a G2V yellow main-sequence star in Cygnus, 157.4 ly away, with 2 known planets. Their orbits run from 0.0426 to 4.89 AU. All of them were detected by radial velocity.

## The planets, innermost first

| Planet | Orbit (AU) | Period | Radius | Mass | Equilibrium T |
| --- | --- | --- | --- | --- | --- |
| [b](https://spacecatalog.org/object/hd-187123-b) | 0.0426 | 3.097 d | 14.20 R⊕ | 166 M⊕ | 1451 K |
| [c](https://spacecatalog.org/object/hd-187123-c) | 4.89 | 10.43 yr | 13.20 R⊕ | 912 M⊕ | 135 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 | G2V yellow main-sequence star |
| SPECTRAL TYPE | G2V |
| MASS | 0.954 M☉ |
| RADIUS | 1.176 R☉ |
| SURFACE TEMPERATURE | 5704 K |
| LUMINOSITY | 1.5 L☉ |
| DISTANCE FROM EARTH | 157.4 ly |
| APPARENT MAGNITUDE | 7.83 |
| CONSTELLATION | Cygnus |

The star itself: https://spacecatalog.org/object/hd-187123

The page itself, with the orbits drawn: https://spacecatalog.org/system/hd-187123