Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model
Year: 2017
Type: article
Abstract: Conventional definitions of habitability require abundant liquid surface water to exist continuously over geologic timescales. Water in each of its thermodynamic phases interacts with solar and thermal radiation and is the cause for strong climatic feedbacks. Thus, assessments of the habitable zone require models to include a complete treatment of the hydrological cycle over geologic time. Here, we use the Community Atmosphere Model from the National Center for Atmospheric Research to study the evolution of climate for an Earth-like planet at constant CO 2 , under a wide range of stellar fluxes from F-, G-, and K-dwarf main sequence stars. Around each star we find four stable climate states defined by mutually exclusive global mean surface temperatures ( T s ); snowball ( T s ≤ 235 K), waterbelt (235 K ≤ T s ≤ 250 K), temperate (275 K ≤ T s ≤ 315 K), and moist greenhouse ( T s ≥ 330 K). Each is separated by abrupt climatic transitions. Waterbelt, temperate, and cooler moist greenhouse climates can maintain open-ocean against both sea ice albedo and hydrogen escape processes respectively, and thus constitute habitable worlds. We consider the warmest possible habitable planet as having T s ∼ 355 K, at which point diffusion limited water-loss could remove an Earth ocean in ∼1 Gyr. Without long timescale regulation of non-condensable greenhouse species at Earth-like temperatures and pressures, such as CO 2 , habitability can be maintained for an upper limit of ∼2.2, ∼2.4, and ∼4.7 Gyr around F-, G-, and K-dwarf stars respectively, due to main sequence brightening.
Source: The Astrophysical Journal
Institutions: University of Colorado Boulder, Laboratory for Atmospheric and Space Physics, University of California, Los Angeles, NASA Astrobiology Institute, University of California, Irvine, Center for Astrophysics Harvard & Smithsonian, Goddard Space Flight Center, Blue Marble Space Institute of Science, University of Maryland, College Park
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
SDG: Climate action
Open Access status: bronze
Awards: G1488140574, IN THIS PROPOSAL, WE WILL DETERMINE THE INNER EDGE OF THE HZ AROUND DIFFERENT TYPES OF M-DWARFS (WITH EFFECTIVE TEMPERATURE RANGING FROM 2500 K TO 37, G3274742622, FPDS BASE DESCRIPTION, MULTIPLE YEAR AWARD&INCREMENTAL FUNDING FOR YEARS 1 OF 5. THIS PROPOSAL IS ENTITLED, "THE VIRTUAL PLANETARY LABORATORY." THI, G465804250, OVER THE PAST TWO DECADES, THE STUDY OF PLANETS ORBITING AROUND OTHER STARS HAS EMERGED FROM RELATIVE OBSCURITY TO THE FOREFRONT OF MODERN SCIENCE., MRI-Consortium: Acquisition of a Supercomputer by the Front Range Computing Consortium, Extremely Close and Not Alone: Exploring the Habitability of M-dwarf Multi-planet Systems
OpenAlex ID: W2590644194