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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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Variations in TSI and gST due to the oscillation of the eccentricity of the planetary orbit.(a) Shows the monthly mean of global-mean TSI as a function of time in the simulations with a semimajor axis of the binary orbit of 0.25 a.u. for a period of 43,200 Earth-days in steady state. A month counts 30 Earth-days. The downward spikes in the TSI are caused by stellar eclipses. (b) Shows a time-slice of 700 Earth-days of global-mean TSI and of gST when the eccentricity of the planetary orbit and hence the variations are large and (c) a time-slice of 700 Earth-days when the eccentricity is small. Note that for (b) the planet is not yet in steady state.
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f7: Variations in TSI and gST due to the oscillation of the eccentricity of the planetary orbit.(a) Shows the monthly mean of global-mean TSI as a function of time in the simulations with a semimajor axis of the binary orbit of 0.25 a.u. for a period of 43,200 Earth-days in steady state. A month counts 30 Earth-days. The downward spikes in the TSI are caused by stellar eclipses. (b) Shows a time-slice of 700 Earth-days of global-mean TSI and of gST when the eccentricity of the planetary orbit and hence the variations are large and (c) a time-slice of 700 Earth-days when the eccentricity is small. Note that for (b) the planet is not yet in steady state.

Mentions: In order to illustrate how changes in magnitude and period of the forcing influence the response of the aforementioned quantities, we performed an additional simulation in which the semimajor axis of the binary orbit is increased from 0.176 to 0.250 a.u. As a consequence, both the period and the amplitude of the forcing from OB increase. Since the planet then would have a higher mean TSI, we moved the planet to a semimajor axis of 1.175 a.u., such that the mean TSI is approximately 1.0 S0 (Table 1). The increase of the semimajor axis of the binary leads to an increased oscillation of the eccentricity of the planetary orbit with a period of around 100 (Earth-) years (Fig. 7). This causes substantial changes in the forcing coming from OP, with an amplitude of around 4 W m−2 in the 10,800-day average when the eccentricity is small (approximately 0.01), to around 15 W m−2 when the eccentricity is large (approximately 0.023) (Fig. 5). When the eccentricity is small, the amplitude of gST, precipitation and OLR from OP is similar or smaller than in the simulations with a semimajor axis of the binary of 0.176 a.u. In particular, OB increases relative to OP. When the eccentricity is large, the amplitude of gST, precipitation and OLR from OP are all considerably larger (Fig. 5). In the temporal average over a 100-year period (not shown), the amplitude of gST from OP is still larger than that from OB, but the difference is considerably smaller than for a semimajor axis of the binary of 0.176 a.u. Hence, the influence of OB on the climate relative to OP is increasing with increasing semimajor axis of the binary. Since both the period and the amplitude of TSI from OB increase, this is in agreement with equation (2).


Climate variations on Earth-like circumbinary planets
Variations in TSI and gST due to the oscillation of the eccentricity of the planetary orbit.(a) Shows the monthly mean of global-mean TSI as a function of time in the simulations with a semimajor axis of the binary orbit of 0.25 a.u. for a period of 43,200 Earth-days in steady state. A month counts 30 Earth-days. The downward spikes in the TSI are caused by stellar eclipses. (b) Shows a time-slice of 700 Earth-days of global-mean TSI and of gST when the eccentricity of the planetary orbit and hence the variations are large and (c) a time-slice of 700 Earth-days when the eccentricity is small. Note that for (b) the planet is not yet in steady state.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f7: Variations in TSI and gST due to the oscillation of the eccentricity of the planetary orbit.(a) Shows the monthly mean of global-mean TSI as a function of time in the simulations with a semimajor axis of the binary orbit of 0.25 a.u. for a period of 43,200 Earth-days in steady state. A month counts 30 Earth-days. The downward spikes in the TSI are caused by stellar eclipses. (b) Shows a time-slice of 700 Earth-days of global-mean TSI and of gST when the eccentricity of the planetary orbit and hence the variations are large and (c) a time-slice of 700 Earth-days when the eccentricity is small. Note that for (b) the planet is not yet in steady state.
Mentions: In order to illustrate how changes in magnitude and period of the forcing influence the response of the aforementioned quantities, we performed an additional simulation in which the semimajor axis of the binary orbit is increased from 0.176 to 0.250 a.u. As a consequence, both the period and the amplitude of the forcing from OB increase. Since the planet then would have a higher mean TSI, we moved the planet to a semimajor axis of 1.175 a.u., such that the mean TSI is approximately 1.0 S0 (Table 1). The increase of the semimajor axis of the binary leads to an increased oscillation of the eccentricity of the planetary orbit with a period of around 100 (Earth-) years (Fig. 7). This causes substantial changes in the forcing coming from OP, with an amplitude of around 4 W m−2 in the 10,800-day average when the eccentricity is small (approximately 0.01), to around 15 W m−2 when the eccentricity is large (approximately 0.023) (Fig. 5). When the eccentricity is small, the amplitude of gST, precipitation and OLR from OP is similar or smaller than in the simulations with a semimajor axis of the binary of 0.176 a.u. In particular, OB increases relative to OP. When the eccentricity is large, the amplitude of gST, precipitation and OLR from OP are all considerably larger (Fig. 5). In the temporal average over a 100-year period (not shown), the amplitude of gST from OP is still larger than that from OB, but the difference is considerably smaller than for a semimajor axis of the binary of 0.176 a.u. Hence, the influence of OB on the climate relative to OP is increasing with increasing semimajor axis of the binary. Since both the period and the amplitude of TSI from OB increase, this is in agreement with equation (2).

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