Fork me on GitHub
an open source database of all discovered extrasolar planets


The planetary system Kapteyn hosts at least 2 planets.

  System parameters
Primary system name Kapteyn
Alternative system names Kapteyn's Star
Right ascension 05 11 40.58112
Declination -45 01 06.2899
Distance [parsec] 3.911±0.014
Distance [lightyears] 12.76±0.05
Number of stars in system 1
Number of planets in system 2

ArchitectureArchitecture of the system

This list shows all planetary and stellar components in the system. It gives a quick overview of the hierarchical architecture.

  •  Kapteyn, stellar object
    •  Kapteyn b, planet, semi-major axis: 0.168+0.006−0.008 AU
      •  Kapteyn c, planet, semi-major axis: 0.311+0.038−0.014 AU

      PlanetsPlanets in the system

      This table lists all planets in the system Kapteyn.

        Kapteyn b Kapteyn c
      Alternative planet names Kapteyn's Star b, Kapteyn's b, HD 33793 b, Gliese 191 b Kapteyn's Star c, Kapteyn's c, HD 33793 c, Gliese 191 c
      Description Kapteyn's star is named in honor of its discoverer, the Dutch astronomer Jacobus Kapteyn. It is visible through binoculars or a small telescope. The planet Kapteyn b is one of the oldest known potentially habitable planets. It's roughly 11 billion years old. The system contains at least one other planet, Kapteyn c, which is close to a 5:2 period commensurability. Kapteyn's star is named in honor of its discoverer, the Dutch astronomer Jacobus Kapteyn. The planetary system is roughly 11 billion years old and contains at least one other planet, Kapteyn b, which is close to a 5:2 period commensurability.
      Lists Confirmed planets
      Mass [Mjup] 0.015±0.003 0.022+0.004−0.003
      Mass [Mearth] 4.8+0.9−1.0 7.0+1.2−1.0
      Radius [Rjup] N/A N/A
      Radius [Rearth] N/A N/A
      Orbital period [days] 48.62+0.04−0.03 121.5±0.2
      Semi-major axis [AU] 0.168+0.006−0.008 0.311+0.038−0.014
      Eccentricity 0.21+0.11−0.10 0.23+0.10−0.12
      Equilibrium temperature [K] N/A N/A
      Discovery method RV
      Discovery year 2014
      Last updated [yy/mm/dd] 17/12/09

      starStars in the system

      This table lists all stars in the system Kapteyn.

      Alternative star names Kapteyn's Star, HD 33793, Gliese 191, Gl 191, GJ 191, HIP 24186, TYC 8078-1749-1, CD-45 1841, CPD-44 612, 2MASS J05114046-4501051, LHS 29
      Mass [MSun] 0.281±0.014
      Radius [RSun] 0.29±0.03
      Age [Gyr] 11+4−11
      Metallicity [Fe/H] -0.860
      Temperature [K] 3550±50
      Spectral type M1VIp
      Visual magnitude 8.85

      Planet sizes

      The following plot shows the approximate sizes of the planets in this system The Solar System planets are shown as a comparison. Note that unless the radius has been determined through a transit observation, this is only an approximation (see Lissauer et al. 2011b).

      PlutoMercuryMarsVenusEarthNeptuneUranusSaturnJupiterKapteyn bKapteyn c

      Habitable zone

      The following plot shows the approximate location of the planets in this system with respect to the habitable zone (green) and the size of the star (red). This is only an estimate, using the star's spectral type and mass. Note that if no green band is shown in the plot, then the planet's orbit is far outside the habitable zone. The equations of Selsis, Kasting et al are used to draw the inner and outer boundaries.

      Habitable zoneKapteyn bKapteyn c

      referencesScientific references and contributors

      Links to scientific papers and other data sources


      This table lists all links which are relevant to this particular system. Note that this is just a summary. More references to the scientific publications and comments can be found in the commit messages. To see these, head over the github or click here to directly go to the git blame output of this system. In the left column of the output you can see the commit message corresponding to each parameter. It also lists the date of the last commit and the person making the changes. Within the commit message, you will find a link to the scientific publication where the data is taken from. Note that this is a new feature and not all system parameters might have a reference associated with it yet. Please help making this catalogue better and contribute data or references!

      Open Exoplanet Catalogue contributors

      Contributor E-mail Number of commits
      Andrew Tribick ajtribick(at) 2
      Christian Sturm Sol-d(at) 1
      Hanno Rein hanno(at) 3

      This table lists all people who have contributed to the Open Exoplanet Catalogue. Please consider contributing! Click here to find out how. You can also view all commits contributing to this file on github.

      xmlData download

      You can download the xml file corresponding to this planetary system, which is part of the Open Exoplanet Catalogue. All information on this page has been directly generated from this XML file. You can also download the entire catalogue over at github. If you prefer to download the dataset as an ASCII tables, you might find the oec_tables repository useful.


      If you spot an error or if you can contribute additional data to this entry, please send an e-mail to Please include the corrected xml file and a reference to where the new data is coming from, ideally a scientific paper. If you are fluent with git and github, you can also create a pull request or open an issue on the Open Exoplanet Catalogue repository. Please include the reference to the relevant scientific paper in your commit message.