ATMOSPHERIC RETRIEVAL FOR SUPER-EARTHS: UNIQUELY CONSTRAINING THE ATMOSPHERIC COMPOSITION WITH TRANSMISSION SPECTROSCOPY

By Björn Benneke, Sara Seager. 2012

281 citations recorded by the source corpus.

We present a retrieval method based on Bayesian analysis to infer the atmospheric compositions and surface or cloud-top pressures from transmission spectra of exoplanets with general compositions. In this study, we identify what can unambiguously be determined about the atmospheres of exoplanets from their transmission spectra by applying the retrieval method to synthetic observations of the super-Earth GJ 1214b. Our approach to inferring constraints on atmospheric parameters is to compute their joint and marginal posterior probability distributions using the Markov Chain Monte Carlo technique in a parallel tempering scheme. A new atmospheric parameterization is introduced that is applicable to general atmospheres in which the main constituent is not known a priori and clouds may be present. Our main finding is that a unique constraint of the mixing ratios of the absorbers and two spectrally inactive gases (such as N2 and primordial H2+ He) is possible if the observations are sufficient to quantify both (1) the broadband transit depths in at least one absorption feature for each absorber and (2) the slope and strength of the molecular Rayleigh scattering signature. A second finding is that the surface pressure or cloud-top pressure can be quantified if a surface or cloud deck is present at low optical depth. A third finding is that the mean molecular mass can be constrained by measuring either the Rayleigh scattering slope or the shapes of the absorption features, thus enabling one to distinguish between cloudy hydrogen-rich atmospheres and high mean molecular mass atmospheres. We conclude, however, that without the signature of molecular Rayleigh scattering—even with robustly detected infrared absorption features (>10σ)—there is no reliable way to tell from the transmission spectrum whether the absorber is a main constituent of the atmosphere or just a minor species with a mixing ratio of Xabs < 0.1%. The retrieval method leads us to a conceptual picture of which details in transmission spectra are essential for unique characterizations of well-mixed exoplanet atmospheres.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/c9b34b00b54b88a3497155d60ce9a6beda041dc3

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Instrumentation

Citations in the corpus

On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets (2014, methodology): “More sophisticated retrieval methods have also been applied to observations of hot Jupiters, including optimal estimation techniques (Lee et al. 2012; Line et al. 2012) and Markov chain Monte Carlo methods (Madhusudhan et al. 2011; Benneke & Seager 2012; Line et al. 2013).”
Detection of carbon monoxide in the high-resolution day-side spectrum of the exoplanet HD 189733b (2013, background): “Obtaining absolute gas abundances for giant exoplanet atmospheres is possible using transit (transmission) measurements if the H2 Rayleigh scattering slope is measured (e.g. Benneke & Seager 2012), although this signature might be difficult to distinguish from that of small haze particles.”
CHARACTERIZING TRANSITING EXOPLANET ATMOSPHERES WITH JWST (2015, methodology): “…coverage, adequate spectral resolution (R & 100), slitless operation, and bright 9 We have also experimented with the centered-log transform (Benneke & Seager 2012) for both solar and high mean molecular weight atmospheres and found no significant qualitative differences limits sufficient…”
WATER VAPOR IN THE SPECTRUM OF THE EXTRASOLAR PLANET HD 189733b. I. THE TRANSIT (2014, background): “High resolution (R> 50), high sensitivity data can place joint constraints on the composition and temperature simultaneously (e.g. Benneke & Seager 2012).”
HUBBLE SPACE TELESCOPE NEAR-IR TRANSMISSION SPECTROSCOPY OF THE SUPER-EARTH HD 97658B (2014, background): “…of several hot Jupiters (e.g., Deming et al. 2013; Wakeford et al. 2013; Mandell et al. 2013; McCullough et al. 2014), and is expected to be present in super-Earths as well over a broad range of atmosphere compositions (e.g., Benneke & Seager 2012; Kreidberg et al. 2014; Hu & Seager 2014).”
HOW TO DISTINGUISH BETWEEN CLOUDY MINI-NEPTUNES AND WATER/VOLATILE-DOMINATED SUPER-EARTHS (2013, methodology): “For general atmospheres that may contain clouds, Benneke & Seager (2012) showed that the unambiguous effect of the mean molecular mass µave on the transmission spectrum is not the overall depths of the molecular features, but the gradient dRP,λ/d(lnσλ) with which the observed planetary radius RP,λ…”
THE INFLUENCE OF NONUNIFORM CLOUD COVER ON TRANSIT TRANSMISSION SPECTRA (2015, background): “Provided there are no other dependencies, only the ratios of abundances can be measured (Benneke & Seager 2012).”
3D mixing in hot Jupiters atmospheres. I. Application to the day/night cold trap in HD 209458b (2013, methodology): “Therefore, interpretation of the data is usually done using one dimensional atmospheric models, assuming an homogenous atmosphere, both in term of temperature structure and composition (e.g., Madhusudhan & Seager 2009; Lee et al. 2012; Benneke & Seager 2012, among others).”
The Complete Transmission Spectrum of WASP-39b with a Precise Water Constraint (2017, background): “Optical transmission spectra have been theoretically shown to be important when measuring the volume mixing ratios of species (Benneke & Seager 2012; Griffith 2014; Line & Parmentier 2016; Heng & Kitzmann 2017), as an infrared-only transmission spectra provides only the relative abundances between…”
A SYSTEMATIC RETRIEVAL ANALYSIS OF SECONDARY ECLIPSE SPECTRA. I. A COMPARISON OF ATMOSPHERIC RETRIEVAL TECHNIQUES (2013, methodology): “Recently, this approach has been applied to the exoplanet atmosphere retrieval problem (Madhusudhan et al. 2011; Benneke & Seager 2012).”
TAU-REX I: A NEXT GENERATION RETRIEVAL CODE FOR EXOPLANETARY ATMOSPHERES (2014, unknown): “E P] 8 S ep 2 trieval modelling (e.g. Fletcher et al. 2007; Terrile et al. 2008; Irwin et al. 2008; Madhusudhan & Seager 2009; Lee et al. 2011; Line et al. 2012; Benneke & Seager 2012; Griffith 2014) has become the industry standard.”
Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life (2017, background): “N 2 (Wordsworth and Pierrehumbert, 2014), which may be revealed through a lack of (N 2) 2 absorption (Schwieterman et al., 2015b) or constraints on atmospheric mass through Rayleigh scattering (e.g., Benneke and Seager, 2012). Highly evolved atmospheres that have experienced signiﬁcant H-loss could ”
A Population Study of Gaseous Exoplanets (2017, background): “Cloud parameterization A variety of cloud parameterizations of varying complexity exist in the context of atmospheric retrieval studies (e.g. Benneke & Seager 2012; Line & Parmentier 2016; Barstow et al. 2013; Griffith 2014).”
WATER LOSS FROM TERRESTRIAL PLANETS WITH CO2-RICH ATMOSPHERES (2013, unknown): “This can be done by transmission spectroscopy, in principle, as long as the planet’s atmosphere is clear enough in the visible at short wavelengths to allow identiﬁcation of the spectral Rayleigh scattering slope (Benneke & Seager 2012).”
HD 209458b in new light: evidence of nitrogen chemistry, patchy clouds and sub-solar water (2017, methodology): “Retrieval is now a mature field, with a wide range of codes developed and deployed to analyse atmospheres in transmission (Benneke & Seager 2012, 2013; Benneke 2015; Waldmann et al. 2015a; Line & Parmentier 2016), thermal emission (Lee et al. 2012; Barstow et al. 2013; Line et al. 2013, 2016;…”