Terminator Habitability: The Case for Limited Water Availability on M-dwarf Planets

Lobo, Ana H.; Shields, Aomawa L.; Palubski, Igor; Wolf, Eric T.

doi:10.3847/1538-4357/aca970

Cited by 10 publications

(4 citation statements)

References 87 publications

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“…However, it is almost certainly tidally locked, and it is not clear how or if photosynthetic life can proceed on tidally locked planets. Furthermore, the global circulation models of tidally locked planets by Lobo et al (2023) find that the HZ is limited to a narrow strip along the terminator for water-limited rocky planets. This reduces both the fraction of planet surface area for liquid water and cyanobacteria mats, and potentially the amount of water for photosynthesis.…”

Section: Discussionmentioning

confidence: 99%

A New Definition of Exoplanet Habitability: Introducing the Photosynthetic Habitable Zone

Hall

Stancil

Terry

et al. 2023

ApJL

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It may be possible to detect biosignatures of photosynthesis in an exoplanet’s atmosphere. However, such a detection would likely require a dedicated study, occupying a large amount of telescope time. It is therefore prudent, while searching for signs of life that we may recognize, to pick the best target possible. In this work, we present a new region, the photosynthetic habitable zone (PHZ)—the distance from a star where both liquid water and oxygenic photosynthesis can occur. It is therefore the region where detectable biosignatures of oxygenic photosynthesis are most likely to occur. Our analysis indicates that in the most ideal conditions for life and no atmospheric effects, the PHZ is almost as broad as the habitable zone. On the other hand, if conditions for life are anything less than excellent and atmospheric effects are even moderate, the PHZ is concentrated at larger separations around more massive stars. Such cases are also not tidally locked to their host star, which could result in planetary rotation periods similar to the Earth’s. We identify five planets, Kepler-452 b, Kepler-1638 b, Kepler-1544 b, Kepler-62 e, and Kepler-62 f, that are consistently in the PHZ for a variety of conditions, and we predict their day lengths to be between 9 and 11 hr. We conclude that the parameter space in which we should search for signs of life is much narrower than the standard habitable zone.

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Section: Discussionmentioning

confidence: 99%

A New Definition of Exoplanet Habitability: Introducing the Photosynthetic Habitable Zone

Hall

Stancil

Terry

et al. 2023

ApJL

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“…ExoCAM is a modified version of the Community Earth System Model (CESM) version 1.2.1 (Neale et al 2012) that adds ExoRT, 2 a nongray correlated-k radiative transfer scheme. ExoCAM is a widely established and accessible model used to study the climate and atmospheric properties of exoplanets (Kopparapu et al 2017;Haqq-Misra et al 2018;Komacek & Abbot 2019;May et al 2021;Lobo et al 2023), including the TRAPPIST-1 system (Wolf 2018;Hu et al 2020;Rushby et al 2020;Sergeev et al 2021;Hochman et al 2022;Rotman et al 2023).…”

Section: Exocam Setupmentioning

confidence: 99%

The Coupled Impacts of Atmospheric Composition and Obliquity on the Climate Dynamics of TRAPPIST-1e

Hammond,

Komacek

2024

ApJ

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Planets in multiplanet systems are expected to migrate inward as near-resonant chains, thus allowing them to undergo gravitational planet–planet interactions and possibly maintain a nonzero obliquity. The TRAPPIST-1 system is in such a near-resonant configuration, making it plausible that TRAPPIST-1e has a nonzero obliquity. In this work, we use the ExoCAM general circulation model to study the possible climates of TRAPPIST-1e at varying obliquities and atmospheric compositions. We vary obliquity from 0° to 90° and the partial pressure of carbon dioxide from 0.0004 bar (modern Earth-like) to 1 bar. We find that models with a higher obliquity are hotter overall and have a smaller day–night temperature contrast than the lower-obliquity models, which is consistent with previous studies. Most significantly, the superrotating high-altitude jet becomes subrotating at high obliquity, thus impacting cloud and surface temperature patterns. As the amount of carbon dioxide increases, the climate of TRAPPIST-1e becomes hotter, cloudier, and less variable. From modeled thermal phase curves, we find that the impact of obliquity could potentially have observable consequences due to the effect of cloud coverage on the outgoing longwave radiation.

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“…This is the circular band dividing a hemisphere in permanent daylight from another in permanent night in the case where the planet is in synchronous rotation around its star, expected of M-dwarfsa possible habitable region where available solar energy would change drastically across a sharp gradient (e.g. Wandel, 2018;Lobo et al, 2023).…”

Section: Ecosystemsmentioning

confidence: 99%

Astroecology: bridging the gap between ecology and astrobiology

Meurer,

Haqq-Misra,

Mendonça

2023

International Journal of Astrobiology

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Although astrobiology studies how life functions and evolves, ecology is still largely overlooked in astrobiology research. Here we present an argument for astroecology, a merger of ecology and astrobiology, a self-aware scientific endeavour. Ecology is rarely mentioned in influential documents like the NASA Astrobiology Strategy (2015), and terms such as ‘niche’ can end up being used in a less precise fashion. As ecology deals with sequential levels of organization, we suggest astrobiologically-relevant problems for each of these levels. Organismal ecology provides ecological niche modelling, which can aid in evaluating the probability that Earth-like life would survive in extraterrestrial environments. Population ecology provides a gamut of models on the consequences of dispersal, and if lithopanspermia can be validated as a form of space dispersal for life, then metabiospheres and similar astrobiological models could be developed to understand such complex structure and dynamics. From community ecology, the discussion of habitability should include the concept of true vacant habitats (a misnomer, perhaps better called ‘will-dwells’) and contributions from the blossoming field of microbial ecology. Understanding ecosystems by focusing on abiotic properties is also key to extrapolating from analogue environments on Earth to extraterrestrial ones. Energy sources and their distribution are relevant for ecological gradients, such as the biodiversity latitudinal gradient – would tropics be species-rich in other inhabited planets? Finally, biosphere ecology deals with integration and feedback between living and non-living systems, which can generate stabilized near-optimal planetary conditions (Gaia); but would this work for other inhabited planets? Are there ‘strong’ (like Earth) and ‘weak’ (perhaps like Mars) biospheres? We hope to show ecology can contribute relevant ideas to the interdisciplinary field of astrobiology, helping conceptualize further levels of integration. We encourage new partnerships and for astrobiologists to take ecology into account when studying the origin, evolution and distribution of life in the universe.

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Terminator Habitability: The Case for Limited Water Availability on M-dwarf Planets

Cited by 10 publications

References 87 publications

A New Definition of Exoplanet Habitability: Introducing the Photosynthetic Habitable Zone

A New Definition of Exoplanet Habitability: Introducing the Photosynthetic Habitable Zone

The Coupled Impacts of Atmospheric Composition and Obliquity on the Climate Dynamics of TRAPPIST-1e

Astroecology: bridging the gap between ecology and astrobiology

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