3D climate modeling of Earth-like extrasolar planets orbiting different types of host stars

Abstract

The potential habitability of a terrestrial planet is usually defined by the possible existence of liquid water on its surface, since life as we know it needs liquid water at least during a part of its life cycle. The potential presence of liquid water on a planetary surface depends on many factors such as, most importantly, surface temperatures. The properties of the planetary atmosphere and its interaction with the radiative energy provided by the planet's host star are thereby of decisive importance. In this study we investigate the influence of different main-sequence stars (F, G, and K-type stars) upon the climate of Earth-like extrasolar planets and their potential habitability by applying a state-of-the-art three-dimensional (3D) Earth climate model accounting for local and dynamical processes. The calculations have been performed for planets with Earth-like atmospheres at orbital distances (and corresponding orbital periods) where the total amount of energy received from the various host stars equals the solar constant. In contrast to previous 3D modeling studies, we include the effect of ozone radiative heating upon the vertical temperature structure of the atmospheres. The global orbital mean results obtained have been compared to those of a one-dimensional (1D) radiative convective climate model to investigate the approximation of global mean 3D results by those of 1D models. The different stellar spectral energy distributions lead to different surface temperatures and due to ozone heating to very different vertical temperature structures. As previous 1D studies we find higher surface temperatures for the Earth-like planet around the K-type star, and lower temperatures for the planet around the F-type star compared to an Earth-like planet around the Sun. However, this effect is more pronounced in the 3D model results than in the 1D model because the 3D model accounts for feedback processes such as the ice-albedo and the water vapor feedback. Whether the 1D model may approximate the global mean of the 3D model results strongly depends on the choice of the relative humidity profile in the 1D model, which is used to determine the water vapor profile. Hence, possible changes in the hydrological cycle need to be accounted for when estimating the potential habitability of an extrasolar planet.

Habitability of planets on eccentric orbits: Limits of the mean flux approximation

“…Oceanic circulation has the effect of homogenizing the climate and facilitating the existence of habitable states. Godolt et al (2015) shows that taking oceanic circulation into account produces surface habitable conditions for planets orbiting F-type stars instead of a snowball state. Our results would likely be different if we had considered other types of planets such as an Earth-like planet, a land planet, a planet with a Pangea-like continent, or a planet with archipelagos (e.g., Yang et al 2014).…”

Characterising the three-dimensional ozone distribution of a tidally locked Earth-like planet

“…When dynamics but no photochemistry or atmospheric chemistry is considered, as in the case of the 3D Godolt et al (2015) study, the stratospheric temperature of an Earth-like planet is also determined by the UV radiation of the stellar spectrum used. Higher UV radiation (e.g.…”

“…M stars have a weaker UV and visible emission than the Sun, with the spectrum peaking in the infrared. The impact of different stellar spectral energy distributions on the ozone distribution of habitable non-tidally locked terrestrial extrasolar planets has been studied by Selsis (2000), Segura et al (2003Segura et al ( , 2005, Grenfell et al (2007), Rugheimer et al (2013), Rauer et al (2011) and Godolt et al (2015). Selsis (2000) used a 1D atmospheric model to simulate how the chemical and thermal structure of the Earth would have evolved, had it been orbiting a F9 and a K2 star.…”

“…For cool M5-M7 stars, the stratospheric ozone photochemistry was completely smog-dominated. Godolt et al (2015) used a state-of-the-art 3D Earth climate model, which accounted for local and dynamical processes, to study the influence of F, G and K stars on the stratospheric temperature, climate and potential habitability of Earth-like extrasolar planets. The planets were positioned at certain orbital distances around the stars, such that the total amount of energy received from the parent stars would equal the solar constant.…”

Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model

“…Nonetheless, in each control simulation the overall climate is not radically changed due to altering only the stellar spectra but not the stellar energy input ( Godolt et al (2015), and is calculated using the StefanBoltzmann law from the difference in upwelling longwave radiation between the surface and the top-of-the-atmosphere implied by clouds and absorbing gases respectively.…”