THE INNER EDGE of the HABITABLE ZONE for SYNCHRONOUSLY ROTATING PLANETS AROUND LOW-MASS STARS USING GENERAL CIRCULATION MODELS

Ravi Kumar Kopparapu, Eric T. Wolf, Jacob Haqq-Misra, Jun Yang, James F. Kasting, Victoria Meadows, Ryan Terrien, Suvrath Mahadevan

Research output: Contribution to journalArticle

80 Citations (Scopus)

Abstract

Terrestrial planets at the inner edge of the habitable zone (HZ) of late-K and M-dwarf stars are expected to be in synchronous rotation, as a consequence of strong tidal interactions with their host stars. Previous global climate model (GCM) studies have shown that, for slowly rotating planets, strong convection at the substellar point can create optically thick water clouds, increasing the planetary albedo, and thus stabilizing the climate against a thermal runaway. However these studies did not use self-consistent orbital/rotational periods for synchronously rotating planets placed at different distances from the host star. Here we provide new estimates of the inner edge of the HZ for synchronously rotating terrestrial planets around late-K and M-dwarf stars using a 3D Earth-analog GCM with self-consistent relationships between stellar metallicity, stellar effective temperature, and the planetary orbital/rotational period. We find that both atmospheric dynamics and the efficacy of the substellar cloud deck are sensitive to the precise rotation rate of the planet. Around mid-to-late M-dwarf stars with low metallicity, planetary rotation rates at the inner edge of the HZ become faster, and the inner edge of the HZ is farther away from the host stars than in previous GCM studies. For an Earth-sized planet, the dynamical regime of the substellar clouds begins to transition as the rotation rate approaches ∼10 days. These faster rotation rates produce stronger zonal winds that encircle the planet and smear the substellar clouds around it, lowering the planetary albedo, and causing the onset of the water-vapor greenhouse climatic instability to occur at up to ∼25% lower incident stellar fluxes than found in previous GCM studies. For mid-to-late M-dwarf stars with high metallicity and for mid-K to early-M stars, we agree with previous studies.

Original languageEnglish (US)
Article number84
JournalAstrophysical Journal
Volume819
Issue number1
DOIs
StatePublished - Mar 1 2016

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M stars
general circulation model
planets
planet
dwarf stars
climate models
stars
global climate
climate modeling
metallicity
terrestrial planets
albedo
Earth analogs
planetary rotation
early stars
orbitals
smear
atmospheric dynamics
cloud water
greenhouses

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Kopparapu, Ravi Kumar ; Wolf, Eric T. ; Haqq-Misra, Jacob ; Yang, Jun ; Kasting, James F. ; Meadows, Victoria ; Terrien, Ryan ; Mahadevan, Suvrath. / THE INNER EDGE of the HABITABLE ZONE for SYNCHRONOUSLY ROTATING PLANETS AROUND LOW-MASS STARS USING GENERAL CIRCULATION MODELS. In: Astrophysical Journal. 2016 ; Vol. 819, No. 1.
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abstract = "Terrestrial planets at the inner edge of the habitable zone (HZ) of late-K and M-dwarf stars are expected to be in synchronous rotation, as a consequence of strong tidal interactions with their host stars. Previous global climate model (GCM) studies have shown that, for slowly rotating planets, strong convection at the substellar point can create optically thick water clouds, increasing the planetary albedo, and thus stabilizing the climate against a thermal runaway. However these studies did not use self-consistent orbital/rotational periods for synchronously rotating planets placed at different distances from the host star. Here we provide new estimates of the inner edge of the HZ for synchronously rotating terrestrial planets around late-K and M-dwarf stars using a 3D Earth-analog GCM with self-consistent relationships between stellar metallicity, stellar effective temperature, and the planetary orbital/rotational period. We find that both atmospheric dynamics and the efficacy of the substellar cloud deck are sensitive to the precise rotation rate of the planet. Around mid-to-late M-dwarf stars with low metallicity, planetary rotation rates at the inner edge of the HZ become faster, and the inner edge of the HZ is farther away from the host stars than in previous GCM studies. For an Earth-sized planet, the dynamical regime of the substellar clouds begins to transition as the rotation rate approaches ∼10 days. These faster rotation rates produce stronger zonal winds that encircle the planet and smear the substellar clouds around it, lowering the planetary albedo, and causing the onset of the water-vapor greenhouse climatic instability to occur at up to ∼25{\%} lower incident stellar fluxes than found in previous GCM studies. For mid-to-late M-dwarf stars with high metallicity and for mid-K to early-M stars, we agree with previous studies.",
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THE INNER EDGE of the HABITABLE ZONE for SYNCHRONOUSLY ROTATING PLANETS AROUND LOW-MASS STARS USING GENERAL CIRCULATION MODELS. / Kopparapu, Ravi Kumar; Wolf, Eric T.; Haqq-Misra, Jacob; Yang, Jun; Kasting, James F.; Meadows, Victoria; Terrien, Ryan; Mahadevan, Suvrath.

In: Astrophysical Journal, Vol. 819, No. 1, 84, 01.03.2016.

Research output: Contribution to journalArticle

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