A Catalog of Habitable Zone Exoplanets

TL;DR

This paper catalogs all known habitable zone exoplanets, analyzes their properties, compares them with the broader exoplanet population, and identifies prime targets for future spectroscopic and observational studies.

Contribution

It provides a comprehensive catalog of HZ exoplanets with detailed orbit and habitability assessments, highlighting extreme cases and potential observational targets.

Findings

Kepler-296 f is the most eccentric HZ planet under 2 R⊕.

HD 106270 b and HD 38529 c are the most massive HZ planets, ideal for exomoon studies.

GJ 414 A b is the most promising transiting HZ target.

Abstract

The search for habitable planets has revealed many planets that can vary greatly from an Earth analog environment. These include highly eccentric orbits, giant planets, different bulk densities, relatively active stars, and evolved stars. This work catalogs all planets found to reside in the HZ and provides HZ boundaries, orbit characterization, and the potential for spectroscopic follow-up observations. Demographics of the HZ planets are compared with a full catalog of exoplanets. Extreme planets within the HZ are highlighted, and how their unique properties may affect their potential habitability. Kepler-296 f is the most eccentric <2 $R_\oplus$ planet that spends 100% of its orbit in the HZ. HD 106270 b and HD 38529 c are the most massive planets (<13 $M_J$) that orbit within the HZ, and are ideal targets for determining the properties of potential hosts of HZ exomoons. These planets, along with the others highlighted, will serve as special edge-cases to the Earth-based scenario and observations of these targets will help test the resilience of habitability outside the standard model. The most promising observational HZ target that is known to transit is GJ 414 A b. Of the transiting, <2 $R_\oplus$ HZ planets, LHS 1140 b, TRAPPIST-1 d and K2-3 d are the most favorable. Of the non-transiting HZ planets, HD 102365 b and 55 Cnc f are the most promising, and the best non-transiting candidates that are <2 $R_\oplus$ are GJ 667 C c, Wolf 1061 c, Ross 508 b, Teegarden's Star b, and Proxima Cen b.