---
title: "The HD 20781 system"
url: "https://spacecatalog.org/system/hd-20781"
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 20781 system

HD 20781 is a G9.5V yellow main-sequence star in Fornax, 115.4 ly away, with 4 known planets. Their orbits run from 0.0529 to 0.337 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-20781-b) | 0.0529 | 5.314 d | 1.21 R⊕ | 1.93 M⊕ | 1006 K |
| [c](https://spacecatalog.org/object/hd-20781-c) | 0.100 | 13.89 d | 2.17 R⊕ | 5.33 M⊕ | 730 K |
| [d](https://spacecatalog.org/object/hd-20781-d) | 0.165 | 29.16 d | 3.25 R⊕ | 10.6 M⊕ | 570 K |
| [e](https://spacecatalog.org/object/hd-20781-e) | 0.337 | 85.51 d | 3.83 R⊕ | 14 M⊕ | 398 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 | G9.5V yellow main-sequence star |
| SPECTRAL TYPE | G9.5V |
| RADIUS | 0.882 R☉ |
| SURFACE TEMPERATURE | 5184 K |
| LUMINOSITY | 0.442 L☉ |
| DISTANCE FROM EARTH | 115.4 ly |
| APPARENT MAGNITUDE | 8.48 |
| CONSTELLATION | Fornax |

The star itself: https://spacecatalog.org/object/hd-20781

The page itself, with the orbits drawn: https://spacecatalog.org/system/hd-20781