Circumstellar Habitable Zone Archives

The simulated occurrence rates of planets in both simulated (blue) and known (orange) planetary systems around nearby stars. Top left: All planet periods. Top right: All planet radii. Bottom left: Small planet (R < 6 R⊕) periods. Bottom right: Giant planet (R > 6 R⊕) periods. Additional predicted planets in the systems with known planets are not shown. astro-ph.EP

Astronomy & Telescopes, Exoplanets, -moons, -comets, Gaia - Planetary Perspectives, Habitable Zones, Imaging & Spectroscopy, Status Report, Stellar Cartography

Predictive Rankings of the Probability for Temperate Terrestrial Worlds for the HWO ExEP Mission Star List

by Keith CowingJune 4, 2026June 4, 2026

The Habitable Worlds Observatory (HWO) is NASA’s flagship mission design from the Decadal Survey on Astronomy and Astrophysics 2020, meant to observe temperate terrestrial planets via direct imaging and use […]

Biophysics, Exoplanets, -moons, -comets, Gaia - Planetary Perspectives, Habitable Zones, Radiation, Space Weather & Heliophysics, Status Report

Flare-driven Habitability: Expanding Life’s Potential Around Low-mass Stars

by Keith CowingMay 2, 2026May 2, 2026

The traditional definition of the circumstellar habitable zone (HZ) focuses on liquid water, but neglects the crucial role of ultraviolet (UV) radiation in prebiotic chemistry.

Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Exoplanets, -moons, -comets, Habitable Zones, Radiation, Status Report

Flare-driven Habitability: Expanding Life’s Potential Around Low-mass Stars

by Keith CowingMarch 31, 2026March 31, 2026

The traditional definition of the circumstellar habitable zone (HZ) focuses on liquid water, but neglects the crucial role of ultraviolet (UV) radiation in prebiotic chemistry.

Panel (a): H–R diagram of the open cluster members stars with GALEX observations. The blue solid line is the fitting results of main sequences. green dashed lines represent the upper and lower bounds of the main sequence fitted with a ±0.5 offset, and the red dashed lines is the same sequence shifted upwards by 2. Panel (b): H–R diagram of the field stars with GALEX observations. Panel (c): The galactic distribution of the selected sources from open clusters. The color bar represent the age of the stars. Panel (d): The galactic distribution of the selected sources from field stars. -- astro-ph.SR

Exoplanets, -moons, -comets, Habitable Zones, Space Weather & Heliophysics, Status Report, Stellar Cartography

Evolution of Stellar Activity and Habitable zone: I. Ultraviolet Emission of Dwarfs in Open Clusters and Field Stars

by Keith CowingSeptember 24, 2025

Near-ultraviolet (NUV) radiation from dwarf stars plays a critical role in shaping the habitability of planetary systems, yet its long-term evolution across different spectral types remains poorly investigated.

Astronomy & Telescopes, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Gas Giants, Habitable Zones, Ice Giant, Imaging & Spectroscopy, Science Fiction, Status Report, Water/Hycean Worlds & Oceanography

Formation Of Habitable Moons Around Giant Planets

by Keith CowingMay 27, 2025May 27, 2025

Of the few thousand discovered exoplanets, a significant number orbit in the habitable zone of their star.

Cartoon depiction of the sulfur-cycle in different planetary regimes. In the Earthlike case (A), atmospheric SO2 is scrubbed from the atmosphere by wet deposition (19). In the Venus-like case with high-UV irradiation (B), for example irradiation by the Sun, SO2 can be abundant in the deep atmosphere, however in the upper atmosphere SO2 is efficiently catalysed into H2SO4 by UV photons and subsequent reaction with H2O (80). In the Venus-like case with low-UV irradiation (C), such as irradiation by a low-UV M-dwarf, SO2 can survive in the upper atmosphere (20), potentially enabling SO2 to be identified in spectroscopic observation and thereby revealing the lack of a surface water ocean. -- astro-ph.EP

Astronomy & Telescopes, Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Habitable Zones, Status Report, Stellar Cartography

Tracing the Inner Edge of the Habitable Zone with Sulfur Chemistry

by Keith CowingJanuary 31, 2025January 31, 2025

The circumstellar liquid-water habitable zone guides our search for potentially inhabited exoplanets, but remains observationally untested. We show that the inner edge of the habitable zone can now be mapped […]

Time averages of the surface temperature for the 1st quintile of the training and test models in rotation period, ordered fastest to slowest. While the rotation periods are organized in increasing order from top left to bottom right, the remaining spin and orbital parameters (obliquity, eccentricity, and longitude of periapse) vary according to the configuration from the Latin Hypercube Sampling algorithm, and are themselves not in any particular order. -- astro-ph.EP

Analog Studies, Astrogeology, Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Habitable Zones, Icy Worlds, Status Report, Water/Hycean Worlds & Oceanography

Habitability in 4-D: Predicting the Climates of Earth Analogs across Rotation and Orbital Configurations

by Keith CowingJanuary 7, 2025January 7, 2025

Earth-like planets in the circumstellar habitable zone (HZ) may have dramatically different climate outcomes depending on their spin-orbit parameters, altering their habitability for life as we know it.

Left panel: The relation between the effective temperatures of the host stars and the effective fluxes incident on their planets. The blue, green, orange, and red dots represent gas giants, Neptunian-like planets, super-Earths, and terrestrial planets, respectively. The gray shaded area is the CHZ for each star, and the black, red, and purple lines represent the inner and outer boundaries of the CHZ for Earth mass, 5 Earth masses, and 0.1 Earth masses, respectively. Note that the three outer boundary lines overlap. The black dots represent the planets in our Solar System. Right panel: the relation between the NUV luminosities of the host stars and the distances between the stars and their planets. The pink, green, and blue shaded areas represent the UHZ for different NUV transmission rates of planetary atmospheres. The blue, green, orange, and red asterisks represent gas giants, Neptunian-like planets, super-Earths, and terrestrial planets that are located within both the CHZ and UHZ. -- astro-ph.SR

Astronomy & Telescopes, Biosignatures & Paleobiology, Habitable Zones, Imaging & Spectroscopy, Status Report, Stellar Cartography

Ultraviolet Photometry and Habitable Zones of Over 2700 Planet-Hosting Stars

by Keith CowingNovember 1, 2024November 1, 2024

The ongoing discovery of exoplanets has sparked significant interest in finding suitable worlds that could potentially support life. Stellar ultraviolet (UV; 100-3000 Å) radiation may play a crucial role in […]

Top panels: evolution of CHZ and UVH for Trappist-1, Proxima Centauri, GJ 273, GJ 163, K2-18, GJ 832, GJ 357, GJ 229A, HD 40307 and Kepler-62. In each plot the vertical gray line represents the host star age found in the literature and the relative errors (the gray shaded region around the gray line). Yellow, orange and dark orange lines represent the ages at which fraction of systems with at least one rocky planet without a primordial envelope in the CHZ is equal to 20%, 30%, 40% for each system (according to NGPPS model). The dashed line represents the time where each star settled onto the main sequence. Bottom panels: evolution of the fraction of the radial extension of the CHZ that is overlapping the radial extension of the UVZ for three different values of the NUV atmospheric transmission. -- astro-ph.EP

Biophysics, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Proxima Centauri, Radiation, Space Weather & Heliophysics, Status Report, TRAPPIST-1, Water/Hycean Worlds & Oceanography

The Time Evolution Of The Ultraviolet Habitable Zone

by Keith CowingSeptember 5, 2024September 5, 2024

For stars hosting Circumstellar Habitable Zone (CHZ) exoplanets, we investigate the time-evolution of their ultraviolet habitable zone (UHZ), the annular region around a star where an exoplanet could experience a […]

Count-up and portion of confirmed single-hosted exoplanets’ habitable zone status per the chosen parameters of this analysis. -- astro-ph.EP

Astronomy & Telescopes, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Status Report, Stellar Cartography

Analysis Of Habitability And Stellar Habitable Zones From Observed Exoplanets

by Keith CowingAugust 20, 2024August 20, 2024

The investigation of exoplanetary habitability is integral to advancing our knowledge of extraterrestrial life potential and detailing the environmental conditions of distant worlds.