HEC: Description of Methods used in the Catalog

Last Update: October 5, 2020

General Habitability Criteria


In general, a potentially habitable exoplanet is a planet around another star with the right size and orbit to be rocky and support surface liquid water, assuming water and an atmosphere are present. Exoplanets included in the Habitable Exoplanets Catalog are selected based on the following wide criteria:
  1. The planet orbits an F, G, K, or M star.
  2. The planet orbits within the optimistic (aka empirical) habitable zone defined by Kopparapu et al. (2014) and corrected for eccentric orbits by Méndez & Rivera-Valentín (2017).
  3. The planet has a radius between 0.5 to 2.5 Earth radii or a minimum mass between 0.1 to 10 Earth masses*.
* The HEC selects planets up to 10 Earth masses and 2.5 Earth radii to include water-worlds, Mega-Earths, and uncertainties in radius and mass measurements. Therefore, the total sample of exoplanets of the catalog is very optimistic, as not to miss any object of interest. Further filtering can be implemented to select more conservative samples.

Filtering and Sorting Criteria


Planets in the catalog are further subdivided or sorted using the following criteria:
  1. Conservative Sample: Planets in the habitable zone with a radius < 1.5 Earth radii or a minimum mass < 5 Earth masses. These are the best candidates for planets that might be rocky and support surface liquid water. They are also known as warm terrans in the catalog.
  2. Optimistic Sample: Planets in the habitable zone with a radius between 1.5 to 2.5 Earth radii or between 5 to 10 Earth masses. These are planets that are less likely to be rocky or support surface liquid water. Some might be mini-Neptunes instead. They are also known as warm superterrans in the catalog.
  3. Earth Similarity Index (ESI): The ESI is used to sort the planets based on a similar radius, mass, and insolation as Earth. Planets in the catalog generally have ESI values above 0.5.
Data Source


The HEC uses the NASA Exoplanet Archive as its main exoplanet data source and incorporates any corrections or updates from the original papers.




The figure above shows all planets near the habitable zone (darker green shade is the conservative habitable zone and the lighter green shade is the optimistic habitable zone). Only those planets less than 10 Earth masses or 2.5 Earth radii are labeled.