New inner boundaries of the habitable zones around M dwarfs

Bin, Jiayu; Tian, Feng; Liu, Lei

doi:10.1016/j.epsl.2018.04.003

Cited by 35 publications

(36 citation statements)

References 44 publications

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“…The inclusion of ozone radiative heating and cooling only has small effects on the IHZ limit. However, our IHZ estimates are closer in (to the respective host stars) than other previous studies−differences stemming from increased water vapor absorption (Kopparapu et al 2017), as well as improved CAM5 aerosol microphysics and cloud treatment (Bin et al 2018). Similarly, disparities between previous GCM calculations of the IHZ (e.g., Toon 2015 andLeconte et al 2013a) can be largely attributed to treatment of moist physics and clouds (Yang et al 2019b).…”

Section: Discussionsupporting

confidence: 56%

Habitability and Spectroscopic Observability of Warm M-dwarf Exoplanets Evaluated with a 3D Chemistry-Climate Model

Chen

Wolf

Zhan

et al. 2019

ApJ

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Planets residing in circumstellar habitable zones (CHZs) offer our best opportunities to test hypotheses of life's potential pervasiveness and complexity. Constraining the precise boundaries of habitability and its observational discriminants is critical to maximizing our chances at remote life detection with future instruments. Conventionally, calculations of the inner edge of the habitable zone (IHZ) have been performed using both 1D radiative-convective and 3D general circulation models. However, these models lack interactive three-dimensional chemistry and do not resolve the mesosphere and lower thermosphere (MLT) region of the upper atmosphere. Here we employ a 3D high-top chemistry-climate model (CCM) to simulate the atmospheres of synchronously-rotating planets orbiting at the inner edge of habitable zones of K-and M-dwarf stars (between T eff = 2600 K and 4000 K). Specifically, we present the first simultaneous 3D investigation of climate, photochemistry, and circulation on moist and runaway greenhouse atmospheres. Simulations are conducted for planets with N 2 -O 2 -H 2 O v -CO 2dominated atmospheres around a range of stellar spectral types with self-consistent stellar spectral energy distribution (SED)-orbital period relationships. While our IHZ climate predictions are in good agreement with GCM studies, we find noteworthy departures in simulated ozone and HO x photochemistry. For instance, climates around inactive stars do not typically enter the classical moist greenhouse regime even with high ( 10 −3 mol mol −1 ) stratospheric water vapor mixing ratios, which suggests that planets around inactive M-stars may only experience minor water-loss over geologically significant timescales. In addition, we find much thinner ozone layers on potentially habitable moist greenhouse atmospheres, as ozone experiences rapid destruction via reaction with hydrogen oxide radicals. Using our CCM results as inputs, our simulated transmission spectra and secondary eclipse thermal emission spectra show that both water vapor and ozone features of these atmospheres could be detectable by instruments NIRSpec and MIRI LRS aboard the James Webb Space Telescope. Our work indicates that simultaneous constraints on the UV emission of low-mass stars and the orbital properties of their attending planets, in conjunction with coupled physical-chemical numerical modeling, will be critical to understanding the habitability and observational prospects of rocky exoplanets.

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Section: Discussionsupporting

confidence: 56%

Habitability and Spectroscopic Observability of Warm M-dwarf Exoplanets Evaluated with a 3D Chemistry-Climate Model

Chen

Wolf

Zhan

et al. 2019

ApJ

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“…The maximum stellar flux investigated by , 1,400 W m −2 , is only about 40-50 % of the stellar flux at the inner edge, according to results from atmosphere-only models Kopparapu et al 2017;Bin et al 2018). Our new experiments show that the day-to-night oceanic heat transport (OHT) at the higher stellar fluxes of planets near the inner edge is much weaker than that for a stellar flux of 1,400 W m −2 (see section 3.2) and that the location of the inner edge would not be shifted by ocean dynamics, at least for a rotation period of 60 Earth days.…”

Section: Introductionmentioning

confidence: 88%

Ocean Dynamics and the Inner Edge of the Habitable Zone for Tidally Locked Terrestrial Planets

Yang

Abbot

Koll

et al. 2019

ApJ

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“…Three dimensional models obtain outer edge results that are also consistent with those from 1-D models (Wolf 2018). The situation is very different for inner edge calculations, however, as differences in convective, cloud, and radiation schemes produce a wide scatter across different 1-D and 3-D models (Yang et al 2013;Kopparapu et al 2016;Kopparapu et al 2017;Bin et al 2018;Ramirez 2018a). These differences partially arise from the difficulty in simulating the water vapour feedback at higher temperatures, which is not a major concern at the HZ outer edge, where water vapour absorption is weaker (Godolt et al 2016;Ramirez and Levi 2018).…”

Section: Comparison Between 1-d and 3-d Models On The Habitable Zone mentioning

confidence: 99%

“…In contrast, Wolf and Toon (2015) used the Community Atmosphere Model (CAM) GCM to calculate a solar system inner edge at ~0.93 AU upon triggering the moist greenhouse. Other CAM GCM calculations find the moist greenhouse for K -M stars hotter than ~ 3000 K or for all M-stars respectively (Fujii et al 2017;Kopparapu et al 2017;Bin et al 2018). Thus, the disagreement between models is large and it remains unclear as to whether the moist greenhouse is achievable or not (and if it is, under which circumstances?…”

Section: Introductionmentioning

confidence: 99%

“…Over the years, many studies have continually revisited the limits of the habitable zone (HZ)(e.g. Dole 1964;Kasting et al 1993;Kopparapu et al 2013;Leconte et al 2013;Yang et al 2013;Ramirez and Kaltenegger 2014;Wolf and Toon 2014;Wolf and Toon 2015;Haqq-Misra et al 2016;Ramirez and Kaltenegger 2017;Bin et al 2018;Ramirez and Kaltenegger 2018), which is the circular region around a star (or multiple stars) where standing bodies of liquid water could exist on the surface of a rocky planet (Ramirez 2018a). Properly defining the habitable zone is and will likely remain (for the foreseeable future) an important scientific consideration because it is the main navigational tool that mission architectures use to find potentially habitable planets around other stars.…”

Section: Introductionmentioning

confidence: 99%

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The effect of high nitrogen pressures on the habitable zone and an appraisal of greenhouse states

Ramirez

2020

Monthly Notices of the Royal Astronomical Society

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The habitable zone (HZ) is the main tool that mission architectures utilize to select potentially habitable planets for follow-up spectroscopic observation. Given its importance, the precise size and location of the HZ remains a hot topic, as many studies, using a hierarchy of models, have assessed various factors including: atmospheric composition, time, and planetary mass. However, little work has assessed how the habitable zone changes with variations in background nitrogen pressure, which is directly connected to the habitability and life-bearing potential of planets. Here, I use an advanced energy balance model with clouds to show that our solar system's HZ is ~0.9 -1.7 AU, assuming a 5-bar nitrogen background pressure and a maximum 100% cloud cover at the inner edge. This width is ~20% wider than the conservative HZ estimate. Similar extensions are calculated for A -M stars. I also show that cooling clouds/hazes and high background pressures can decrease the runaway greenhouse threshold temperature to ~300 K (or less) for planets orbiting any star type. This is because the associated increase in planetary albedo enables stable climates closer to the star, where rapid destabilization can be triggered from a lower mean surface temperature. Enhanced longwave emission for planets with very high stratospheric temperatures also permits stable climates at smaller orbital distances. The model predicts a runaway greenhouse above ∼330 K for planets orbiting the Sun, which is consistent with previous work. However, moist greenhouses only occur for planets orbiting Astars.

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New inner boundaries of the habitable zones around M dwarfs

Cited by 35 publications

References 44 publications

Habitability and Spectroscopic Observability of Warm M-dwarf Exoplanets Evaluated with a 3D Chemistry-Climate Model

Habitability and Spectroscopic Observability of Warm M-dwarf Exoplanets Evaluated with a 3D Chemistry-Climate Model

Ocean Dynamics and the Inner Edge of the Habitable Zone for Tidally Locked Terrestrial Planets

The effect of high nitrogen pressures on the habitable zone and an appraisal of greenhouse states

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