A Methane Extension to the Classical Habitable Zone

Ramirez, Ramses M.; Kaltenegger, Lisa

doi:10.3847/1538-4357/aab8fa

Cited by 49 publications

(77 citation statements)

References 73 publications

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“…Hence the chemical feedback tends to cool the planets around late-type M dwarfs. This result is consistent with the study of Ramirez & Kaltenegger (2018) who found that for planets around late M dwarfs a CH 4 anti-greenhouse effect can shrink the HZ by about 20%. Our simulations do not include effects on the radiative transfer due to clouds and hazes.…”

Section: Resultssupporting

confidence: 93%

Detectability of atmospheric features of Earth-like planets in the habitable zone around M dwarfs

Wunderlich

Godolt

Grenfell

et al. 2019

A&A

124

140

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Context. The characterisation of the atmosphere of exoplanets is one of the main goals of exoplanet science in the coming decades. Aims. We investigate the detectability of atmospheric spectral features of Earth-like planets in the habitable zone (HZ) around M dwarfs with the future James Webb Space Telescope (JWST). Methods. We used a coupled 1D climate-chemistry-model to simulate the influence of a range of observed and modelled M-dwarf spectra on Earth-like planets. The simulated atmospheres served as input for the calculation of the transmission spectra of the hypothetical planets, using a line-by-line spectral radiative transfer model. To investigate the spectroscopic detectability of absorption bands with JWST we further developed a signal-to-noise ratio (S/N) model and applied it to our transmission spectra. Results. High abundances of methane (CH 4 ) and water (H 2 O) in the atmosphere of Earth-like planets around mid to late M dwarfs increase the detectability of the corresponding spectral features compared to early M-dwarf planets. Increased temperatures in the middle atmosphere of mid-to late-type M-dwarf planets expand the atmosphere and further increase the detectability of absorption bands. To detect CH 4 , H 2 O, and carbon dioxide (CO 2 ) in the atmosphere of an Earth-like planet around a mid to late M dwarf observing only one transit with JWST could be enough up to a distance of 4 pc and less than ten transits up to a distance of 10 pc. As a consequence of saturation limits of JWST and less pronounced absorption bands, the detection of spectral features of hypothetical Earth-like planets around most early M dwarfs would require more than ten transits. We identify 276 existing M dwarfs (including GJ 1132, TRAPPIST-1, GJ 1214, and LHS 1140) around which atmospheric absorption features of hypothetical Earth-like planets could be detected by co-adding just a few transits. Conclusions. The TESS satellite will likely find new transiting terrestrial planets within 15 pc from the Earth. We show that using transmission spectroscopy, JWST could provide enough precision to be able to partly characterise the atmosphere of TESS findings with an Earth-like composition around mid to late M dwarfs.

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Section: Resultssupporting

confidence: 93%

Detectability of atmospheric features of Earth-like planets in the habitable zone around M dwarfs

Wunderlich

Godolt

Grenfell

et al. 2019

A&A

124

140

View full text Add to dashboard Cite

show abstract

“…The single-column radiative-convective climate model has 55 thermal infrared and 38 solar wavelengths (Ramirez and Kaltenegger 2017;Ramirez and Kaltenegger 2018). Atmospheres are subdivided into 100 vertical logarithmically-spaced layers that reach ~1x10 -5 bar at the top of the atmosphere.…”

Section: The Single Column Radiative-convective Climate Modelmentioning

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%

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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“…where T * = T eff − 5780, and S Sun is the stellar incident values at the HZ boundaries in our solar system. Table 2 (Ramirez & Kaltenegger 2018) shows the constants a, b, c, and S Sun needed to derive the stellar flux at the HZ limits valid for T eff between 2,600 to 10,000 K. The inner boundaries of the empirical HZ (recent Venus), as well as an alternative inner edge limit for 3D Global Climate models (3D; Leconte et al (2013)) and the outer limits (early Mars), are all included. The outer HZ limit in 3D and 1D models are consistent and therefore not given in separate columns in Table 2 (see e.g.…”

Section: As Shown Inmentioning

confidence: 99%

Atmospheres and UV Environments of Earth-like Planets throughout Post-main-sequence Evolution

Kozakis

Kaltenegger

2019

ApJ

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During the post-main sequence phase of stellar evolution the orbital distance of the habitable zone, which allows for liquid surface water on terrestrial planets, moves out past the system's original frost line, providing an opportunity for outer planetary system surface habitability. We use a 1D coupled climate/photochemistry code to study the impact of the stellar environment on the planetary atmospheres of Earth-like planets/moons throughout its time in the post-main sequence habitable zone. We also explore the ground UV environments of such planets/moons and compare them to Earth's. We model the evolution of star-planet systems with host stars ranging from 1.0 to 3.5 M throughout the post-main sequence, calculating stellar mass loss and its effects on planetary orbital evolution and atmospheric erosion. The maximum amount of time a rocky planet can spend continuously in the evolving post-MS habitable zone ranges between 56 and 257 Myr for our grid stars. Thus, during the post-MS evolution of their host star, subsurface life on cold planets and moons could become remotely detectable once the initially frozen surface melts. Frozen planets or moons, like Europa in our Solar System, experience a relatively stable environment on the horizontal branch of their host stars' evolution for millions of years.

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A Methane Extension to the Classical Habitable Zone

Cited by 49 publications

References 73 publications

Detectability of atmospheric features of Earth-like planets in the habitable zone around M dwarfs

Detectability of atmospheric features of Earth-like planets in the habitable zone around M dwarfs

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

Atmospheres and UV Environments of Earth-like Planets throughout Post-main-sequence Evolution

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