A Volcanic Hydrogen Habitable Zone

摘要

The classical habitable zone (HZ) is the circular region around a star in which liquid water could exist on the surface of a rocky planet. The outer edge of the traditional N-2-CO2-H2O HZ extends out to nearly similar to 1.7 au in our solar system, beyond which condensation and scattering by CO2 outstrips its greenhouse capacity. Here, we show that volcanic outgassing of atmospheric H-2 can extend the outer edge of the HZ to similar to 2.4 au in our solar system. This wider volcanic-hydrogen HZ (N-2-CO2-H2O-H-2) can be sustained as long as volcanic H-2 output offsets its escape from the top of the atmosphere. We use a single-column radiative-convective climate model to compute the HZ limits of this volcanic hydrogen HZ for hydrogen concentrations between 1% and 50%, assuming diffusionlimited atmospheric escape. At a hydrogen concentration of 50%, the effective stellar flux required to support the outer edge decreases by similar to 35%-60% for M-A stars. The corresponding orbital distances increase by similar to 30%-60%. The inner edge of this HZ only moves out similar to 0.1%-4% relative to the classical HZ because H-2 warming is reduced in dense H2O atmospheres. The atmospheric scale heights of such volcanic H-2 atmospheres near the outer edge of the HZ also increase, facilitating remote detection of atmospheric signatures.