A population-based Habitable Zone perspective

Abstract

What can we tell about exoplanet habitability if currently only the stellar properties, planet radius, and the incoming stellar flux are known? A planet is in the Habitable Zone (HZ) if it harbors liquid water on its surface. The HZ is traditionally conceived as a sharp region around stars because it is calculated for one planet with specific properties. Such an approach is limiting because the planets' atmospheric and geophysical properties, which influence the presence of liquid water on the surface, are currently unknown but expected to be diverse. A statistical HZ description is outlined which does not favor one planet type. Instead the stellar and planet properties are treated as random variables and a continuous range of planet scenarios are considered. Various probability density functions are assigned to each random variable, and a combination of Monte Carlo sampling and climate modeling is used to generate synthetic exoplanet populations with known surface climates. Then, the properties of the liquid water bearing subpopulation is analyzed. Given our current observational knowledge, the HZ takes the form of a weakly-constrained but smooth probability function. The HZ has an inner edge but a clear outer edge is not seen. Currently only optimistic upper limits can be derived for the potentially observable HZ occurrence rate. Finally, we illustrate through an example how future data on exoplanet atmospheres will help to narrow down the probability that an exoplanet harbors liquid water and we identify the greatest observational challenge in the way of finding a habitable exoplanet.

published, ApJ, 813, 9

References in corpus (12)

• Prevalence of Earth-size planets orbiting Sun-like stars
• Mass-Radius Relationships for Solid Exoplanets
• Most 1.6 Earth-Radius Planets are not Rocky
• Habitable Zones Around Main-Sequence Stars: Dependence on Planetary Mass
• The Mass-Radius Relation for 65 Exoplanets Smaller than 4 Earth Radii
• Habitable planets around the star Gl 581?
• Atmospheric Retrieval for Super-Earths: Uniquely Constraining the Atmospheric Composition with Transmission Spectroscopy
• Exoplanet population inference and the abundance of Earth analogs from noisy, incomplete catalogs
• Constraining Exoplanet Mass from Transmission Spectroscopy
• Using Dimers to Measure Biosignatures and Atmospheric Pressure for Terrestrial Exoplanets
• Dynamical evolution and spin-orbit resonances of potentially habitable exoplanets. The case of GJ 581d
• Some inconvenient truths about biosignatures involving two chemical species on Earth-like exoplanets

Cited by in corpus (13)

• How to Characterize Habitable Worlds and Signs of Life
• Atmospheric reconnaissance of the habitable-zone Earth-sized planets orbiting TRAPPIST-1
• Exoplanet Biosignatures: A Framework for Their Assessment
• Atmospheric escape from the TRAPPIST-1 planets and implications for habitability
• The MeerKAT Telescope as a Pulsar Facility: System verification and early science results from MeerTime
• Exoplanet Biosignatures: Observational Prospects
• The Indian Pulsar Timing Array: First data release
• Physical constraints for the evolution of life on exoplanets
• Habitability Models for Astrobiology
• Large Interferometer For Exoplanets (LIFE): VI. Detecting rocky exoplanets in the habitable zones of Sun-like stars
• The Indian Pulsar Timing Array Data Release 2: I. Dataset and Timing Analysis
• Relative Habitability of Exoplanet Systems with Two Giant Planets
• Low-frequency pulse-jitter measurement with the uGMRT I : PSR J0437$-$4715