Circumstellar Habitable Zone Archives

A schematic of the saddle node bifurcation in the carbon cycle suggested by our simulations. The blue curve represents the global weathering rate as a function of pCO2. Weathering increases with increasing pCO2 (and surface temperature) in the green zone, and it decreases with increasing pCO2 (and surface temperature) in the red zone. Weathering rates are equal to outgassing (V ) at pCO2=P1 (orange) and at pCO2=P2 (black). The P1 equilibrium is stable because weathering acts as a negative feedback in that regime, while the P2 equilibrium is unstable due to silicate weathering’s positive feedback behavior. The red arrows indicate the directions CO2 and weathering would evolve for a climate intialized from various points relative to the two equilibria. -- astro-ph.EP

Astrochemistry, Astrogeology, Biogeochemical Cycles & Geobiology, Exoplanets, -moons, -comets, Habitable Zones, Status Report, Water/Hycean Worlds & Oceanography

Carbon Cycle Instability For High-CO2 Exoplanets: Implications For Habitability

by Keith CowingMay 10, 2024May 10, 2024

Implicit in the definition of the classical circumstellar habitable zone (HZ) is the hypothesis that the carbonate-silicate cycle can maintain clement climates on exoplanets with land and surface water across […]

NUV (Near Ultra-Violet) luminosity versus star–planet separation. The UHZ (Ultraviolet Habitable zone, see §2) is defined by the inner (outer) boundary corresponding to the maximum (minimum) UV flux tolerable required) for life resilience (abiogenenesis, considering a specific prebiotic pathways). Three UHZ are shown corresponding to 100, 50 and 10% (as labelled) atmospheric transmission ( 𝑓 ), to the planet’s surface, of the UV flux at the top of the atmosphere. The planets of our sample (§3) selected for being in the CHZ (Circumstellar Habitable Zone) and having UV observations (thus providing 𝐿NUV) are shown by the circle symbols. The color coding corresponds to the 𝑇eff of their host stars (vertical color bar). The horizontal bar of each exoplanet shows the CHZ as derived by Kopparapu et al. (2013). The green shaded regions show the CHZ as derived through the 𝐿NUV ´ 𝑇eff correlation (§5). -- astro-ph.EP

Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Press Release

The Ultraviolet Habitable Zone Of Exoplanets

by Keith CowingMarch 29, 2023March 29, 2023

The dozens of rocky exoplanets discovered in the Circumstellar Habitable Zone (CHZ) currently represent the most suitable places to host life as we know it outside the Solar System.