The Carbonate-Silicate Cycle and CO<sub>2</sub>/Climate Feedbacks on Tidally Locked Terrestrial Planets

Edson, Adam R.; Kasting, James F.; Pollard, David; Lee, Sukyoung; Bannon, Peter R.

doi:10.1089/ast.2011.0762

Cited by 76 publications

(60 citation statements)

References 19 publications

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“…Given that a solar-type spectrum was used in their work, and our work here with an M-dwarf spectrum results in greater surface temperatures on M-dwarf planets than on G-dwarf planets that receive equal amounts of instellation, temperature contrasts between the sunlit and dark sides of a synchronously rotating aqua planet orbiting an M-dwarf star at a 1 AU equivalent flux distance may be even further reduced. Previous studies that used GCM simulations of synchronously rotating planets at 1 AU equivalent flux distances from a solar-type star suggest that atmospheric CO 2 concentrations could be nearly 200 times higher than the present atmospheric level on Earth if the substellar point is over a predominantly ocean-covered area, due to a lack of continental weathering (Edson et al, 2012). However, atmospheric CO 2 concentration could be limited by seafloor weathering on an aqua planet, resulting in much lower CO 2 partial pressures (Edson et al, 2012).…”

Section: Effect Of Host Star Sed and Ice-albedo Feedback On Climatementioning

confidence: 96%

The Effect of Host Star Spectral Energy Distribution and Ice-Albedo Feedback on the Climate of Extrasolar Planets

et al. 2013

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Planetary climate can be affected by the interaction of the host star spectral energy distribution with the wavelength-dependent reflectivity of ice and snow. In this study, we explored this effect with a one-dimensional (1-D), line-by-line, radiative transfer model to calculate broadband planetary albedos as input to a seasonally varying, 1-D energy balance climate model. A three-dimensional (3-D) general circulation model was also used to explore the atmosphere's response to changes in incoming stellar radiation, or instellation, and surface albedo. Using this hierarchy of models, we simulated planets covered by ocean, land, and water-ice of varying grain size, with incident radiation from stars of different spectral types. Terrestrial planets orbiting stars with higher near-UV radiation exhibited a stronger ice-albedo feedback. We found that ice extent was much greater on a planet orbiting an F-dwarf star than on a planet orbiting a G-dwarf star at an equivalent flux distance, and that ice-covered conditions occurred on an F-dwarf planet with only a 2% reduction in instellation relative to the present instellation on Earth, assuming fixed CO 2 (present atmospheric level on Earth). A similar planet orbiting the Sun at an equivalent flux distance required an 8% reduction in instellation, while a planet orbiting an Mdwarf star required an additional 19% reduction in instellation to become ice-covered, equivalent to 73% of the modern solar constant. The reduction in instellation must be larger for planets orbiting cooler stars due in large part to the stronger absorption of longer-wavelength radiation by icy surfaces on these planets in addition to stronger absorption by water vapor and CO 2 in their atmospheres, which provides increased downwelling longwave radiation. Lowering the IR and visible-band surface ice and snow albedos for an M-dwarf planet increased the planet's climate stability against changes in instellation and slowed the descent into global ice coverage. The surface ice-albedo feedback effect becomes less important at the outer edge of the habitable zone, where atmospheric CO 2 could be expected to be high such that it maintains clement conditions for surface liquid water. We showed that *3-10 bar of CO 2 will entirely mask the climatic effect of ice and snow, leaving the outer limits of the habitable zone unaffected by the spectral dependence of water ice and snow albedo. However, less CO 2 is needed to maintain open water for a planet orbiting an M-dwarf star than would be the case for hotter main-sequence stars.

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Section: Effect Of Host Star Sed and Ice-albedo Feedback On Climatementioning

confidence: 96%

The Effect of Host Star Spectral Energy Distribution and Ice-Albedo Feedback on the Climate of Extrasolar Planets

et al. 2013

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“…The habitable zone could be reduced by limited CO 2 outgassing (Kadoya & Tajika, 2014;Abbot, 2016), but this reduction would likely be less for M-dwarf planets, given their lower planetary Albedos (Abbot, 2016). Additionally, the amount of CO 2 generated on synchronously-rotating planets could be much higher if the substellar point is located in a region with an ocean versus a land-covered area, creating an even stronger radiative response (Edson et al, 2012) on planets orbiting M-dwarf stars.…”

Section: Radiative Effectsmentioning

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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“…The location of land masses is also important. Should land be concentrated near the substellar point, then silicate weathering is more effective, and cools the planet by drawing down CO 2 (Edson et al 2012). Planet f is a prime candidate for habitability and receives 788 W m −2 of radiation.…”

Section: The Weather Forecastmentioning

confidence: 99%

A dynamically-packed planetary system around GJ 667C with three super-Earths in its habitable zone

Anglada-Escudé

Tuomi

Gerlach

et al. 2013

A&A

142

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Context. Since low-mass stars have low luminosities, orbits at which liquid water can exist on Earth-sized planets are relatively closein, which produces Doppler signals that are detectable using state-of-the-art Doppler spectroscopy. Aims. GJ 667C is already known to be orbited by two super-Earth candidates. We have recently applied developed data analysis methods to investigate whether the data supports the presence of additional companions. Methods. We obtain new Doppler measurements from HARPS extracted spectra and combined them with those obtained from the PFS and HIRES spectrographs. We used Bayesian and periodogram-based methods to re-assess the number of candidates and evaluated the confidence of each detection. Among other tests, we validated the planet candidates by analyzing correlations of each Doppler signal with measurements of several activity indices and investigated the possible quasi-periodic nature of signals.Results. Doppler measurements of GJ 667C are described better by six (even seven) Keplerian-like signals: the two known candidates (b and c); three additional few-Earth mass candidates with periods of 92, 62, and 39 days (d, e and f); a cold super-Earth in a 260-day orbit (g) and tantalizing evidence of a ∼1 M ⊕ object in a close-in orbit of 17 days (h). We explore whether long-term stable orbits are compatible with the data by integrating 8 × 10 4 solutions derived from the Bayesian samplings. We assess their stability using secular frequency analysis. Conclusions. The system consisting of six planets is compatible with dynamically stable configurations. As for the solar system, the most stable solutions do not contain mean-motion resonances and are described well by analytic Laplace-Lagrange solutions. Preliminary analysis also indicates that masses of the planets cannot be higher than twice the minimum masses obtained from Doppler measurements. The presence of a seventh planet (h) is supported by the fact that it appears squarely centered on the only island of stability left in the six-planet solution. Habitability assessments accounting for the stellar flux, as well as tidal dissipation effects, indicate that three (maybe four) planets are potentially habitable. Doppler and space-based transit surveys indicate that 1) dynamically packed systems of super-Earths are relatively abundant and 2) M-dwarfs have more small planets than earlier-type stars. These two trends together suggest that GJ 667C is one of the first members of an emerging population of M-stars with multiple low-mass planets in their habitable zones.

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The Carbonate-Silicate Cycle and CO₂/Climate Feedbacks on Tidally Locked Terrestrial Planets

Cited by 76 publications

References 19 publications

The Effect of Host Star Spectral Energy Distribution and Ice-Albedo Feedback on the Climate of Extrasolar Planets

The Effect of Host Star Spectral Energy Distribution and Ice-Albedo Feedback on the Climate of Extrasolar Planets

The habitability of planets orbiting M-dwarf stars

A dynamically-packed planetary system around GJ 667C with three super-Earths in its habitable zone

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The Carbonate-Silicate Cycle and CO2/Climate Feedbacks on Tidally Locked Terrestrial Planets

Cited by 76 publications

References 19 publications

The Effect of Host Star Spectral Energy Distribution and Ice-Albedo Feedback on the Climate of Extrasolar Planets

The Effect of Host Star Spectral Energy Distribution and Ice-Albedo Feedback on the Climate of Extrasolar Planets

The habitability of planets orbiting M-dwarf stars

A dynamically-packed planetary system around GJ 667C with three super-Earths in its habitable zone

Contact Info

Product

Resources

About

The Carbonate-Silicate Cycle and CO₂/Climate Feedbacks on Tidally Locked Terrestrial Planets