180 research outputs found
Infrared radiative transfer in atmospheres of Earth-like planets around F, G, K, and M stars - I. Clear-sky thermal emission spectra and weighting functions
No full textContext. The atmosphere of Earth-like extrasolar planets orbiting different types of stars is influenced by the spectral dependence of the incoming stellar radiation. The changes in structure and composition affect atmospheric radiation, hence the spectral appearance of these exoplanets.
Aims. We provide a thorough investigation of infrared radiative transfer in cloud-free exoplanets atmospheres by not only analyzing the planetary spectral appearance but also discussing the radiative processes behind the spectral features in detail and identifying the regions in the atmosphere that contribute most at a given wavelength.
Methods. Using cloud-free scenarios provided by a one-dimensional radiative-convective steady-state atmospheric model, we computed high-resolution infrared transmission and emission spectra, as well as weighting functions for exoplanets located within the habitable zone of F, G, K, and M stars by means of a line-by-line molecular absorption model and a Schwarzschild solver for the radiative transfer. The monochromatic spectra were convolved with appropriate spectral response functions to study the effects of finite instrument resolution.
Results. Spectra of the exoplanets of F, G, K, and M stars were analyzed in the 4.5 μm N2O band, the 4.3 μm and 15 μm CO2 bands, the 7.7 μm CH4 band, the 6.3 μm H2O band, and the 9.6 μm O3 band. Differences in the state of the atmosphere of the exoplanets clearly show up in the thermal infrared spectra; absorption signatures known from Earth can be transformed to emission features (and vice versa). Weighting functions show that radiation in the absorption bands of the uniformly mixed gases (CO2, CH4, N2O) and (to some extent) ozone comes from the stratosphere and upper troposphere, and also indicate that changes in the atmospheres can shift sources of thermal radiation to lower or higher altitudes. Molecular absorption and/or emission features can be identified in the high-resolution spectra of all planets and in most reduced resolution spectra.
Conclusions. Insight into radiative transfer processes is essential for analyzing exoplanet spectral observations; for instance, understanding the impact of the temperature profile (nb. non-existence of an inversion) on the CO2 bands facilitates their interpretation and can help avoid false positive or negative estimates of O3. The detailed analysis of the radiation source and sink regions could even help give an indication about the feasibility of identifying molecular signatures in cloud-covered planets, i.e. radiation mainly coming from the upper atmosphere is less likely to be hidden by clouds. Infrared radiative transfer and biomarker detectability in cloud-covered exoplanets will be presented in a companion paper
Evolution of earth-like extrasolar planetary atmospheres: Assessing the atmospheres and biospheres of early earth analog planets with a coupled atmosphere biogeochemical model
No full textUnderstanding the evolution of Earth and potentially habitable Earth-like worlds is essential to fathom our origin in the Universe. The search for Earth-like planets in the habitable zone and investigation of their atmospheres with climate and photochemical models is a central focus in exoplanetary science. Taking the evolution of Earth as a reference for Earth-like planets, a central scientific goal is to understand what the interactions were between atmosphere, geology, and biology on early Earth. The Great Oxidation Event in Earth's history was certainly caused by their interplay, but the origin and controlling processes of this occurrence are not well understood, the study of which will require interdisciplinary, coupled models. In this work, we present results from our newly developed Coupled Atmosphere Biogeochemistry model in which atmospheric O concentrations are fixed to values inferred by geological evidence. Applying a unique tool (Pathway Analysis Program), ours is the first quantitative analysis of catalytic cycles that governed O in early Earth's atmosphere near the Great Oxidation Event. Complicated oxidation pathways play a key role in destroying O, whereas in the upper atmosphere, most O is formed abiotically via CO photolysis. The O bistability found by Goldblatt et al. (2006) is not observed in our calculations likely due to our detailed CH oxidation scheme. We calculate increased CH with increasing O during the Great Oxidation Event. For a given atmospheric surface flux, different atmospheric states are possible; however, the net primary productivity of the biosphere that produces O is unique. Mixing, CH fluxes, ocean solubility, and mantle/crust properties strongly affect net primary productivity and surface O fluxes. Regarding exoplanets, different "states" of O could exist for similar biomass output. Strong geological activity could lead to false negatives for life (since our analysis suggests that reducing gases remove O that masks its biosphere over a wide range of conditions). © Copyright 2017, Mary Ann Liebert, Inc. 2017.This research was supported by the Helmholtz Gemeinschaft through the research alliance "Planetary Evolution and Life."This study has received financial support from the French State in the frame of the "Investments for the future" Programme IdEx Bordeaux, reference ANR-10-IDEX-03-02.M. Godolt acknowledges funding by the Helmholtz Foundation via the Helmholtz Postdoc Project "Atmospheric dynamics and photochemistry of Super-Earth planets."This work was partially funded by grant AyA 201232237 awarded by the Spanish Ministerio 353 de Economia y Competitividad
3D modelling studies of an Earth-like planet orbiting in the Habitable Zone of main sequence stars
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3D Climate Modeling of Earth-like Extrasolar Planets Orbiting Different Types of Central Stars
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