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Climate variations on Earth-like circumbinary planets

View Article: PubMed Central - PubMed

ABSTRACT

The discovery of planets orbiting double stars at close distances has sparked increasing scientific interest in determining whether Earth-analogues can remain habitable in such environments and how their atmospheric dynamics is influenced by the rapidly changing insolation. In this work we present results of the first three-dimensional numerical experiments of a water-rich planet orbiting a double star. We find that the periodic forcing of the atmosphere has a noticeable impact on the planet's climate. Signatures of the forcing frequencies related to the planet's as well as to the binary's orbital periods are present in a variety of climate indicators such as temperature and precipitation, making the interpretation of potential observables challenging. However, for Earth-like greenhouse gas concentrations, the variable forcing does not change the range of insolation values allowing for habitable climates substantially.

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Temporal spectra of global-mean quantities.(a) Shows the temporal spectrum of the global-mean TSI, (b) the temporal spectrum of gST, (c) the temporal spectrum of the global-mean OLR and (d) the temporal spectrum of the global-mean precipitation of the simulation with a semimajor axis of the planetary orbit around Kepler-35 AB of 1.165 a.u. The horizontal axes denote the period in days and OB indicates the period of the binary orbit as seen from the planet and OP the period of the planetary orbit. The temporal spectrum was taken over 10,800 Earth-days in steady state.
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f2: Temporal spectra of global-mean quantities.(a) Shows the temporal spectrum of the global-mean TSI, (b) the temporal spectrum of gST, (c) the temporal spectrum of the global-mean OLR and (d) the temporal spectrum of the global-mean precipitation of the simulation with a semimajor axis of the planetary orbit around Kepler-35 AB of 1.165 a.u. The horizontal axes denote the period in days and OB indicates the period of the binary orbit as seen from the planet and OP the period of the planetary orbit. The temporal spectrum was taken over 10,800 Earth-days in steady state.

Mentions: Owing to changes in the distance of the planet relative to the two stars of the Kepler-35 system, the total solar irradiance (TSI) varies with time. The changes in the TSI of a planet orbiting the Kepler-35 binary show a double periodic behaviour (Fig. 1a,b,d,e). For a (habitable) planet with a semimajor axis of 1.165 a.u., these periods are of around 22 and 360 Earth-days. The oscillation with a period of approximately 22 Earth-days is caused by the rotation of the stars around the common centre of mass and will henceforth be denoted by OB. The maximum of TSI with respect to OB is attained when the more luminous star is closest to the planet (Fig. 1, t1) and the minimum when the less luminous star is closest (Fig. 1, t3). The oscillation with a period of around 360 Earth-days is caused by the eccentricity of the planetary orbit and will henceforth be denoted by OP. The maximum of that oscillation is reached when the planet is closest to the centre of mass (Fig. 1, t2) and the minimum when the planet is at apastron (Fig. 1, t4). Note that an orbit cannot remain circular around a double star, due to angular momentum exchange between the stellar and planetary orbits. In nearly coplanar systems such as Kepler-35, solar eclipses occur in intervals of around 11 Earth-days and result in a brief but substantial reduction in TSI. An interesting peculiarity of this system is that due to the stellar parallax more than one hemisphere of the planet is illuminated at all times except during eclipses. A spectral analysis reveals that the amplitude of the oscillation of the global-mean TSI (which is equal to TSI/4) with a period of OB is 18.8 W m−2 and the one of OP is 5.5 W m−2 (Fig. 2a). Including the solar eclipses, the daily-mean of the global-mean TSI varies roughly from 300 to 370 W m−2 over one orbital period (Fig. 1d) during the time-span we have considered. Owing to oscillations of planet's orbital eccentricity, the variations in TSI from OP change. The climates presented here were evaluated over a 10,800-Earth-day period where the planet's orbital eccentricity was close to the forced eccentricity.


Climate variations on Earth-like circumbinary planets
Temporal spectra of global-mean quantities.(a) Shows the temporal spectrum of the global-mean TSI, (b) the temporal spectrum of gST, (c) the temporal spectrum of the global-mean OLR and (d) the temporal spectrum of the global-mean precipitation of the simulation with a semimajor axis of the planetary orbit around Kepler-35 AB of 1.165 a.u. The horizontal axes denote the period in days and OB indicates the period of the binary orbit as seen from the planet and OP the period of the planetary orbit. The temporal spectrum was taken over 10,800 Earth-days in steady state.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384241&req=5

f2: Temporal spectra of global-mean quantities.(a) Shows the temporal spectrum of the global-mean TSI, (b) the temporal spectrum of gST, (c) the temporal spectrum of the global-mean OLR and (d) the temporal spectrum of the global-mean precipitation of the simulation with a semimajor axis of the planetary orbit around Kepler-35 AB of 1.165 a.u. The horizontal axes denote the period in days and OB indicates the period of the binary orbit as seen from the planet and OP the period of the planetary orbit. The temporal spectrum was taken over 10,800 Earth-days in steady state.
Mentions: Owing to changes in the distance of the planet relative to the two stars of the Kepler-35 system, the total solar irradiance (TSI) varies with time. The changes in the TSI of a planet orbiting the Kepler-35 binary show a double periodic behaviour (Fig. 1a,b,d,e). For a (habitable) planet with a semimajor axis of 1.165 a.u., these periods are of around 22 and 360 Earth-days. The oscillation with a period of approximately 22 Earth-days is caused by the rotation of the stars around the common centre of mass and will henceforth be denoted by OB. The maximum of TSI with respect to OB is attained when the more luminous star is closest to the planet (Fig. 1, t1) and the minimum when the less luminous star is closest (Fig. 1, t3). The oscillation with a period of around 360 Earth-days is caused by the eccentricity of the planetary orbit and will henceforth be denoted by OP. The maximum of that oscillation is reached when the planet is closest to the centre of mass (Fig. 1, t2) and the minimum when the planet is at apastron (Fig. 1, t4). Note that an orbit cannot remain circular around a double star, due to angular momentum exchange between the stellar and planetary orbits. In nearly coplanar systems such as Kepler-35, solar eclipses occur in intervals of around 11 Earth-days and result in a brief but substantial reduction in TSI. An interesting peculiarity of this system is that due to the stellar parallax more than one hemisphere of the planet is illuminated at all times except during eclipses. A spectral analysis reveals that the amplitude of the oscillation of the global-mean TSI (which is equal to TSI/4) with a period of OB is 18.8 W m−2 and the one of OP is 5.5 W m−2 (Fig. 2a). Including the solar eclipses, the daily-mean of the global-mean TSI varies roughly from 300 to 370 W m−2 over one orbital period (Fig. 1d) during the time-span we have considered. Owing to oscillations of planet's orbital eccentricity, the variations in TSI from OP change. The climates presented here were evaluated over a 10,800-Earth-day period where the planet's orbital eccentricity was close to the forced eccentricity.

View Article: PubMed Central - PubMed

ABSTRACT

The discovery of planets orbiting double stars at close distances has sparked increasing scientific interest in determining whether Earth-analogues can remain habitable in such environments and how their atmospheric dynamics is influenced by the rapidly changing insolation. In this work we present results of the first three-dimensional numerical experiments of a water-rich planet orbiting a double star. We find that the periodic forcing of the atmosphere has a noticeable impact on the planet's climate. Signatures of the forcing frequencies related to the planet's as well as to the binary's orbital periods are present in a variety of climate indicators such as temperature and precipitation, making the interpretation of potential observables challenging. However, for Earth-like greenhouse gas concentrations, the variable forcing does not change the range of insolation values allowing for habitable climates substantially.

No MeSH data available.


Related in: MedlinePlus