---
title: "The HN Boo system"
url: "https://spacecatalog.org/system/hd-128311"
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 HN Boo system

HN Boo is a K3V orange dwarf in Boötes, 53.82 ly away, with 2 known planets. Their orbits run from 1.08 to 1.74 AU. All of them were detected by radial velocity.

## The planets, innermost first

| Planet | Orbit (AU) | Period | Radius | Mass | Equilibrium T |
| --- | --- | --- | --- | --- | --- |
| [HD 128311 b](https://spacecatalog.org/object/hd-128311-b) | 1.08 | 453 d | 13.50 R⊕ | 562 M⊕ | 200 K |
| [HD 128311 c](https://spacecatalog.org/object/hd-128311-c) | 1.74 | 921.5 d | 13.00 R⊕ | 1200 M⊕ | 158 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 | K3V orange dwarf |
| SPECTRAL TYPE | K3V |
| MASS | 0.779 M☉ |
| RADIUS | 0.813 R☉ |
| SURFACE TEMPERATURE | 4760 K |
| LUMINOSITY | 0.242 L☉ |
| DISTANCE FROM EARTH | 53.82 ly |
| APPARENT MAGNITUDE | 7.48 |
| CONSTELLATION | Boötes |

The star itself: https://spacecatalog.org/object/hd-128311

The page itself, with the orbits drawn: https://spacecatalog.org/system/hd-128311