A More Comprehensive Habitable Zone for Finding Life on Other Planets

Ramirez, Ramses M.

doi:10.3390/geosciences8080280

Cited by 68 publications

(77 citation statements)

References 284 publications

(693 reference statements)

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“…Such conditions, similar to "Snowball Earth" episodes experienced on Earth, would be detrimental to the development of complex land life. CO 2 sequestration beneath water ice, owing to the high density of CO 2 ice (1.5 gcm −3 ) compared to H 2 O ice (1 g cm −3 ), could potentially reduce or eliminate the deglaciation episodes (Turbet et al 2017;Ramirez 2018). Limit cycles may also occur at higher stellar fluxes, near the inner edge of the HZ, at low outgassing rates (Paradise & Menou 2017).…”

Section: Discussionmentioning

confidence: 99%

Habitable Zone Boundaries for Circumbinary Planets

Cukier¹,

Kopparapu²,

Kane³

et al. 2019

PASP

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We use a one-dimensional (1-D) cloud-free climate model to estimate habitable zone (HZ) boundaries for terrestrial planets of masses 0.1 M E and 5 M E around circumbinary stars of various spectral type combinations. Specifically, we consider binary systems with host spectral types -M and M-M. Scaling the background N 2 atmospheric pressure with the radius of the planet, we find that the inner edge of the HZ moves inwards towards the star for 5 M E compared to 0.1 M E planets for all spectral types. This is because the water-vapor column depth is smaller for larger planets and higher temperatures are needed before water vapor completely dominates the outgoing longwave radiation. The outer edge of the HZ changes little due to competing effects of the albedo and greenhouse effect. While these results are broadly consistent with the trend of single star HZ results for different mass planets, there are significant differences between single star and binary star systems for the inner edge of the HZ. Interesting combinations of stellar pairs from our 1-D model results can be used to explore for in-depth climate studies with 3-D climate models. We identify a common HZ stellar flux domain for all circumbinary spectral types.

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Section: Discussionmentioning

confidence: 99%

Habitable Zone Boundaries for Circumbinary Planets

Cukier¹,

Kopparapu²,

Kane³

et al. 2019

PASP

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“…One of the main drivers of exoplanet research is to find an Earth-like planet that orbits within the habitable zone of the planet's host star. The exact definition and boundaries of habitable zones vary, but it is generally accepted that the habitable zone is the location where water can exist in liquid form (Kasting et al 1993;Ramirez 2018), as on Earth.…”

Section: Introductionmentioning

confidence: 99%

Enlarging habitable zones around binary stars in hostile environments

Wootton

Parker

2019

Monthly Notices of the Royal Astronomical Society: Letters

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Habitable zones are regions around stars where large bodies of liquid water can be sustained on a planet or satellite. As many stars form in binary systems with nonzero eccentricity, the habitable zones around the component stars of the binary can overlap and be enlarged when the two stars are at periastron (and less often when the stars are at apastron). We perform N-body simulations of the evolution of dense star-forming regions and show that binary systems where the component stars originally have distinct habitable zones can undergo interactions that push the stars closer together, causing the habitable zones to merge and become enlarged. Occasionally, overlapping habitable zones can occur if the component stars move further apart, but the binary becomes more eccentric. Enlargement of habitable zones happens to 1-2 binaries from an average initial total of 352 in each simulated star-forming region, and demonstrates that dense star-forming regions are not always hostile environments for planet formation and evolution.

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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%

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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A More Comprehensive Habitable Zone for Finding Life on Other Planets

Cited by 68 publications

References 284 publications

Habitable Zone Boundaries for Circumbinary Planets

Habitable Zone Boundaries for Circumbinary Planets

Enlarging habitable zones around binary stars in hostile environments

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

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