Effects of Obliquity on the Habitability of Exoplanets Around M Dwarfs

Wang, Yuwei; Liu, Yonggang; Tian, Feng; Yang, Jun; Ding, Feng; Zhou, Linjiong; Hu, Yongyun

doi:10.3847/2041-8205/823/1/l20

Cited by 61 publications

(35 citation statements)

References 43 publications

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“…There is a general agreement between the models that seasonal variability increases by increasing the obliquity. Most of these studies though focus mainly on the effect of obliquity on the planetary habitability (Williams & Kasting 1997;Spiegel et al 2009;Armstrong et al 2014;Ferreira et al 2014;Linsenmeier et al 2015;Wang et al 2016;Nowajewski et al 2018). Mitchell et al (2014) studied the seasonality effect on climate, using an idealized parameterization for the seasonality and radiative timescale.…”

Section: Introductionmentioning

confidence: 99%

Atmospheric Dynamics on Terrestrial Planets: The Seasonal Response to Changes in Orbital, Rotational, and Radiative Timescales

Guendelman

Kaspi

2019

ApJ

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Thousands of exoplanets have been detected to date, and with future planned missions this tally will increase. Understanding the climate dependence on the planetary parameters is vital for the study of terrestrial exoplanet habitability. Using an idealized general circulation model with a seasonal cycle, we study the seasonal response of the surface temperature and Hadley circulation to changes in the orbital, rotational and radiative timescales. Analyzing the climate's seasonal response to variations in these timescales, we find a regime transition between planets controlled by the annual mean insolation to planets controlled by the seasonal variability depending on the relation between the length of the orbital period, obliquity and radiative timescale. Consequently, planets with obliquity greater than 54 • and short orbital period will have a minimum surface temperature at the equator. We also show that in specific configurations, mainly high atmospheric mass and short orbital periods, high obliquity planets can still have an equable climate. Based on the model results, we suggest an empirical power law for the ascending and descending branches of the Hadley circulation and its strength. These power laws show that the Hadley circulation becomes wider and stronger by increasing the obliquity and orbital period or by decreasing the atmospheric mass and rotation rate. Consistent with previous studies, we show that the rotation rate plays an essential role in dictating the width of the Hadley circulation.

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Section: Introductionmentioning

confidence: 99%

Atmospheric Dynamics on Terrestrial Planets: The Seasonal Response to Changes in Orbital, Rotational, and Radiative Timescales

Guendelman

Kaspi

2019

ApJ

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“…Most of these studies used some form of atmospheric GCM coupled to a shallow mixed-layer ocean and a thermodynamic sea ice model, and thus included representations of the seasonal cycle, dynamical heat transport by the atmosphere, and feedbacks from water vapor and surface albedo. More recent studies of high-obliquity climate have been motivated instead by exoplanet considerations (Williams & Kasting 1997;Williams & Pollard 2003;Spiegel et al 2009;Abe et al 2011;Armstrong et al 2014;Ferreira et al 2014;Wang et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Ice Caps and Ice Belts: The Effects of Obliquity on Ice−Albedo Feedback

Rose

Cronin

Bitz

2017

ApJ

122

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Planetary obliquity determines the meridional distribution of the annual mean insolation. For obliquity exceeding 55°, the weakest insolation occurs at the equator. Stable partial snow and ice cover on such a planet would be in the form of a belt about the equator rather than polar caps. An analytical model of planetary climate is used to investigate the stability of ice caps and ice belts over the widest possible range of parameters. The model is a nondimensional diffusive Energy Balance Model, representing insolation, heat transport, and ice−albedo feedback on a spherical planet. A complete analytical solution for any obliquity is given and validated against numerical solutions of a seasonal model in the "deep-water" regime of weak seasonal ice line migration. Multiple equilibria and unstable transitions between climate states (ice-free, Snowball, or ice cap/belt) are found over wide swaths of parameter space, including a "Large Ice-Belt Instability" and "Small Ice-Belt Instability" at high obliquity. The Snowball catastrophe is avoided at weak radiative forcing in two different scenarios: weak albedo feedback and inefficient heat transport (favoring stable partial ice cover), or efficient transport at high obliquity (favoring ice-free conditions). From speculative assumptions about distributions of planetary parameters, three-fourths to four-fifths of all planets with stable partial ice cover should be in the form of Earth-like polar caps.

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“…And planets that experience high-frequency oscillations in obliquity may avoid global glaciation, as neither pole of the planet faces away from the star for a long enough time for thick ice sheets to develop (Armstrong et al, 2014). A reduced negative cloud feedback on tidally-locked M-dwarf planets with non-zero obliquities could increase surface temperatures (Wang et al, 2016). The presence of moons may help stabilize a planet's obliquity (Sasaki & Barnes, 2014), as is the case on the Earth (Laskar et al, 1993).…”

Section: Planetary Environmentmentioning

confidence: 99%

The habitability of planets orbiting M-dwarf stars

2016

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The prospects for the habitability of M-dwarf planets have long been debated, due to key differences between the unique stellar and planetary environments around these low-mass stars, as compared to hotter, more luminous Sunlike stars. Over the past decade, significant progress has been made by both space-and ground-based observatories to measure the likelihood of small planets to orbit in the habitable zones of M-dwarf stars. We now know that most M dwarfs are hosts to closely-packed planetary systems characterized by a paucity of Jupiter-mass planets and the presence of multiple rocky planets, with roughly a third of these rocky M-dwarf planets orbiting within the habitable zone, where they have the potential to support liquid water on their surfaces. Theoretical studies have also quantified the effect on climate and habitability of the interaction between the spectral energy distribution of M-dwarf stars and the atmospheres and surfaces of their planets. These and other recent results fill in knowledge gaps that existed at the time of the previous overview papers published nearly a decade ago by Tarter et al. (2007) and Scalo et al. (2007). In this review we provide a comprehensive picture of the current knowledge of M-dwarf planet occurrence and habitability based on work done in this area over the past decade, and summarize future directions planned in this quickly evolving field.

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Effects of Obliquity on the Habitability of Exoplanets Around M Dwarfs

Cited by 61 publications

References 43 publications

Atmospheric Dynamics on Terrestrial Planets: The Seasonal Response to Changes in Orbital, Rotational, and Radiative Timescales

Atmospheric Dynamics on Terrestrial Planets: The Seasonal Response to Changes in Orbital, Rotational, and Radiative Timescales

Ice Caps and Ice Belts: The Effects of Obliquity on Ice−Albedo Feedback

The habitability of planets orbiting M-dwarf stars

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