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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 variations in TSI and global-mean surface temperature.(a) Shows the daily mean of global-mean TSI and of the global-mean surface temperature (gST) as a function of time for a planet around Kepler-35 AB with a orbital semimajor axis of 1.225 a.u. for a 700-day period in steady state. (b) Shows the same quantities but for a planet around Kepler-35 AB with an orbital semimajor axis of 1.195 a.u., (d) for a semimajor axis of 1.165 a.u. and (e) for a semimajor axis of 1.140. (c) Sketches the Kepler-35 system with Kepler-35 A being the more luminous and Kepler-35 B the less luminous star. Note that in this sketch we always assume the stars to be at the same position whereas in reality (and in our simulations) they would also orbit each other. The orbit of the planet evolves with time. The points in time t1, t2, t3 and t4 in d correspond to the orbital times indicated in c and link the oscillation of TSI to the associated orbital constellations. The downward spikes in the TSI are due to stellar eclipses.
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f1: Temporal variations in TSI and global-mean surface temperature.(a) Shows the daily mean of global-mean TSI and of the global-mean surface temperature (gST) as a function of time for a planet around Kepler-35 AB with a orbital semimajor axis of 1.225 a.u. for a 700-day period in steady state. (b) Shows the same quantities but for a planet around Kepler-35 AB with an orbital semimajor axis of 1.195 a.u., (d) for a semimajor axis of 1.165 a.u. and (e) for a semimajor axis of 1.140. (c) Sketches the Kepler-35 system with Kepler-35 A being the more luminous and Kepler-35 B the less luminous star. Note that in this sketch we always assume the stars to be at the same position whereas in reality (and in our simulations) they would also orbit each other. The orbit of the planet evolves with time. The points in time t1, t2, t3 and t4 in d correspond to the orbital times indicated in c and link the oscillation of TSI to the associated orbital constellations. The downward spikes in the TSI are due to stellar eclipses.

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 variations in TSI and global-mean surface temperature.(a) Shows the daily mean of global-mean TSI and of the global-mean surface temperature (gST) as a function of time for a planet around Kepler-35 AB with a orbital semimajor axis of 1.225 a.u. for a 700-day period in steady state. (b) Shows the same quantities but for a planet around Kepler-35 AB with an orbital semimajor axis of 1.195 a.u., (d) for a semimajor axis of 1.165 a.u. and (e) for a semimajor axis of 1.140. (c) Sketches the Kepler-35 system with Kepler-35 A being the more luminous and Kepler-35 B the less luminous star. Note that in this sketch we always assume the stars to be at the same position whereas in reality (and in our simulations) they would also orbit each other. The orbit of the planet evolves with time. The points in time t1, t2, t3 and t4 in d correspond to the orbital times indicated in c and link the oscillation of TSI to the associated orbital constellations. The downward spikes in the TSI are due to stellar eclipses.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Temporal variations in TSI and global-mean surface temperature.(a) Shows the daily mean of global-mean TSI and of the global-mean surface temperature (gST) as a function of time for a planet around Kepler-35 AB with a orbital semimajor axis of 1.225 a.u. for a 700-day period in steady state. (b) Shows the same quantities but for a planet around Kepler-35 AB with an orbital semimajor axis of 1.195 a.u., (d) for a semimajor axis of 1.165 a.u. and (e) for a semimajor axis of 1.140. (c) Sketches the Kepler-35 system with Kepler-35 A being the more luminous and Kepler-35 B the less luminous star. Note that in this sketch we always assume the stars to be at the same position whereas in reality (and in our simulations) they would also orbit each other. The orbit of the planet evolves with time. The points in time t1, t2, t3 and t4 in d correspond to the orbital times indicated in c and link the oscillation of TSI to the associated orbital constellations. The downward spikes in the TSI are due to stellar eclipses.
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