ABOUT THE HWC

The Habitable Worlds Catalog (HWC) is an online database for scientists and educators about potentially habitable world discoveries. The catalog uses habitability metrics and classifications to compare exoplanets. The HWC is a project of the Planetary Habitability Laboratory @ the University of Puerto Rico at Arecibo since 2011.

Catalog Features

The HWC includes stellar and planetary properties not available in other exoplanet catalogs. Some of these properties are:

• Habitable Worlds - Potentially habitable worlds are identified using the Orbit-Size Criteria.

• Multiple Stellar Zones - The snow line, tidal lock zone, abiogenesis zone, and habitable zone of each stellar system.

• Surface Temperature of Planets- The surface temperature of planets is estimated assuming a similar terrestrial atmosphere for comparison purposes. Actual temperatures can be lower or higher than this, depending on other surface and atmospheric properties.

• Habitable Zone (HZ) for Planets in Eccentric Orbits - Some planets move in and out of the HZ due to eccentric orbits, and it's not straightforward to determine if they are, on average, within the HZ.

• Exoplanet Classification - Planets are classified by parent star stellar type, orbit, and size.

• Earth Similarity Index (ESI) - Planets can be sorted by the ESI. This makes it easier to identify those planets that are more similar in size and insolation to Earth (i.e., Earth-like with respect to these properties).

• Multiple Data Source - The catalog uses the NASA Exoplanet Archive as its main data source, but it adds corrections from other databases, or directly from papers.

• Other Physical Properties of Planets - Density, gravity, and escape velocity.

• Constellations - The IAU Constellation of each stellar system.

How to Use the Catalog

Here are some examples of how to use the HWC for research purposes:

• Identify exoplanets of interest for modeling or observations. For example, Armstrong et al. (2015) selected systems to study for superflares, rotation, and activity, and Harpt et al. (2016) selected stars for SETI observations.

• Studies of exoplanet demographics. For example, Childs et al. (2022) compared the system architectures of planets between M and Sun-like stars.

• Provide context for exoplanet discoveries. For example, Kossakowski et al. (2023) put their discovery of another potentially habitable world, Wolf 1609 b, in context.

• Comparative planetology. For example, Boney & Kennefick (2022) used the Earth Similarity Index (ESI) to compare exoplanets.

How to Cite the Catalog

• To credit the content or images in websites, use:

The Habitable Worlds Catalog (HWC), PHL @ UPR Arecibo (phl.upr.edu/hwc), or just PHL @ UPR Arecibo.

• To cite in papers, use:

PHL @ UPR Arecibo (YEAR, MONTH DAY). The Habitable Worlds Catalog (HWC). http://phl.upr.edu/hwc, and inline citation (PHL @ UPR Arecibo, YEAR), where YEAR, MONTH DAY is the date the website information was retrieved.

Acknowledgments

The Habitable Worlds Catalog acknowledges the use of the following resources:

• The NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA) under the Exoplanet Exploration Program.

• GSFC Exoplanet Modeling and Analysis Center (EMAC), a catalog, repository and integration platform for modeling and analysis resources focused on the study of exoplanet characteristics and environments.

• Interactive Data Language (IDL), a registered trademark of NV5 Global, Inc.

• IDLAstro, astronomy-related procedures in the commercial IDL language.

• Astropy, a community-developed core Python package and an ecosystem of tools and resources for astronomy.

• Forecaster, forecast mass (radius) given radius (mass) measurements.

• MR-Plotter, a user-friendly Python tool that creates paper-ready mass-radius diagrams with your favorite theoretical models.

• NatSort, a simple yet flexible natural sorting in Python by Seth M. Morton.

• ImageMagick, a free, open-source software suite, used for editing and manipulating digital images.

• POV-Ray, a high-quality, free software tool for creating stunning three-dimensional graphics.

What happened to the original Habitable Exoplanets Catalog (HEC)?

The HEC was replaced with the HWC in January 2024. The change in name to "worlds" is to be more inclusive and encompass not just exoplanets but also moons and other objects in the Solar System that might be capable of supporting life. There are new plans to combine the exoplanet and Solar System data in the catalog for comparison purposes. All the previous citation links of the HEC will continue to work or point to the new version of the catalog.

Contact

Contact Prof. Abel Méndez for any corrections or suggestions. Follow @PlanetaryHabLab for catalog updates.