Remote Sensing of Planetary Properties and Biosignatures on Extrasolar Terrestrial Planets

Marais, David J. Des; Harwit, Martin; Jucks, K. W.; Kasting, James F.; Lin, D. N. C.; Lunine, Jonathan I.; Schneider, Jean; Seager, Sara; Traub, Wesley A.; Woolf, N. J.

doi:10.1089/15311070260192246

Cited by 485 publications

(472 citation statements)

References 28 publications

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“…Terrestrial Planet Finder (TPF) (Marsh et al 2006;Martin et al 2007) and Darwin (Léger et al 1996;Cockell et al 2009a). The detection of life depends upon the concentration and detectability of an atmospheric constituent out of equilibrium with abiotic processes (Lovelock 1975;DesMarais et al 2002;Tinetti et al 2006;Kaltenegger and Selsis 2007;Kaltenegger et al 2009). …”

Section: Introductionmentioning

confidence: 99%

Planetary targets in the search for extrasolar oxygenic photosynthesis

Cockell

Raven

Kaltenegger

et al. 2009

Plant Ecology & Diversity

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Background:In the coming decades space telescopes will be constructed that will attempt to find the gaseous products of oxygenic photosynthesis, the most promising biosignatures of life, in the atmospheres of temperate Earth-like planets orbiting distant stars. Aims: This paper aims to provide a synthesis of the range of feasible targets -either planets or their satellites -that could harbour photosynthesis. Methods: We calculated photosynthetically active radiation (PAR) fluxes on a diversity of planetary bodies including those receiving direct light from a single star, similarly to the Earth, and investigated the potential of these fluxes to support photosynthesis. Results: All main sequence stars emit radiation that is capable of supporting photosynthesis on Earth-like planets. We discuss tidally-locked M star planets as a special case. Less conventional targets for searches include large moons orbiting gas giant planets, which receive reflected light from their host planets and from the host star, planets in stable orbits in binary star systems, and the search for two planets within the same star system with photosynthetic signatures. Conclusions: A diversity of planetary bodies are targets in the search for extrasolar photosynthesis. The demonstration that many or none of these candidate planetary bodies harbour photosynthesis would be an important conclusion in understanding the evolution and prevalence of photosynthesis.

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Section: Introductionmentioning

confidence: 99%

Planetary targets in the search for extrasolar oxygenic photosynthesis

Cockell

Raven

Kaltenegger

et al. 2009

Plant Ecology & Diversity

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“…Schindler & Kasting (2000) modeled the longwave thermal infrared for Earth, a methane rich early Earth, Mars, and early Venus. Des Marais et al (2002) investigated molecular bands of biomarker and greenhouse gases in order to provide wavelength regions and spectral features useful for characterizing potentially habitable exoplanets. The problem of "falsepositive detection" of biosignatures with NASA's Terrestrial Planet Finder or ESA's Darwin has been discussed by Schindler & Kasting (2000) and Selsis et al (2002), respectively.…”

Section: Introductionmentioning

confidence: 99%

Infrared radiative transfer in atmospheres of Earth-like planets around F, G, K, and M stars

Vasquez

Schreier

García

et al. 2013

A&A

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Context. 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 N 2 O band, the 4.3 µm and 15 µm CO 2 bands, the 7.7 µm CH 4 band, the 6.3 µm H 2 O band, and the 9.6 µm O 3 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 (CO 2 , CH 4 , N 2 O) 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 CO 2 bands facilitates their interpretation and can help avoid false positive or negative estimates of O 3 . 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.

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“…Nevertheless, studies of the potential atmospheric signatures of terrestrial habitable planets have been performed, to predict signal strengths and assess observation strategies (e.g., Des Marais et al 2002;Segura et al 2003;Ehrenreich et al 2006;Kaltenegger & Traub 2009;Miller-Ricci et al 2009;Deming et al 2009;Belu et al 2011;Rauer et al 2011).…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic characterization of the atmospheres of potentially habitable planets: GL 581 d as a model case study

Paris¹,

Cabrera²,

Godolt³

et al. 2011

A&A

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Context. Were a potentially habitable planet to be discovered, the next step would be the search for an atmosphere and its characterization. Eventually, surface conditions, hence habitability, and biomarkers as indicators for life would be assessed. Aims. The super-Earth candidate Gliese (GL) 581 d is the first potentially habitable extrasolar planet so far discovered. Therefore, GL 581 d is used to illustrate a hypothetical detailed spectroscopic characterization of such planets. Methods. Atmospheric profiles for a wide range of possible one-dimensional (1D) radiative-convective model scenarios of GL 581 d were used to calculate high-resolution synthetic emission and transmission spectra. Atmospheres were assumed to be composed of N 2 , CO 2 , and H 2 O. From the spectra, signal-to-noise ratios (SNRs) were calculated for a telescope such as the planned James Webb Space Telescope (JWST). Exposure times were set to be equal to the duration of one transit. Results. The presence of the model atmospheres can be clearly inferred from the calculated synthetic spectra thanks to strong water and carbon-dioxide absorption bands. Surface temperatures can be inferred for model scenarios with optically thin spectral windows. Dense, CO 2 -rich (potentially habitable) scenarios do not enable us to determine the surface temperatures nor assess habitability. Degeneracies between CO 2 concentration and surface pressure complicate the interpretation of the calculated spectra, hence the determination of atmospheric conditions. Still, inferring approximative CO 2 concentrations and surface pressures is possible. In practice, detecting atmospheric signals is challenging because the calculated SNR values are well below unity in most of the cases. The SNR for a single transit was only barely larger than unity in some near-IR bands for transmission spectroscopy. Most interestingly, the false-positive detection of biomarker candidates such as methane and ozone might be possible in low resolution spectra because CO 2 absorption bands overlap biomarker spectral bands. This can be avoided, however, by observing all main CO 2 IR bands instead of concentrating on, e.g., the 4.3 or 15 μm bands only. Furthermore, a masking of ozone signatures by CO 2 absorption bands is shown to be possible. Simulations imply that such a false-negative detection of ozone would be possible even for rather high ozone concentrations of up to 10 −5 .

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Remote Sensing of Planetary Properties and Biosignatures on Extrasolar Terrestrial Planets

Cited by 485 publications

References 28 publications

Planetary targets in the search for extrasolar oxygenic photosynthesis

Planetary targets in the search for extrasolar oxygenic photosynthesis

Infrared radiative transfer in atmospheres of Earth-like planets around F, G, K, and M stars

Spectroscopic characterization of the atmospheres of potentially habitable planets: GL 581 d as a model case study

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