Robustness Measures for Molecular Detections using High-Resolution Transmission Spectroscopy of Exoplanets

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   Towards robust corrections for stellar contamination in JWST exoplanet transmission spectra

   Benjamin V. Rackham, Julien de Wit · 2023 · Earth and Planetary Astrophysics · AI summary available

   Abstract

   Transmission spectroscopy is still the preferred characterization technique for exoplanet atmospheres, although it presents unique challenges which translate into characterization bottlenecks when robust mitigation strategies are missing. Stellar contamination is one of such challenges that can overpower the planetary signal by up to an order of magnitude, and thus not accounting for stellar contamination can lead to significant biases in the derived atmospheric properties. Yet, accounting for stellar contamination may not be straightforward, as important discrepancies exist between state-of-the-art stellar models and measured spectra and between models themselves. Here we explore the extent…

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   The Impending Opacity Challenge in Exoplanet Atmospheric Characterization

   Prajwal Niraula, Julien de Wit, Iouli E. Gordon et al. · 2022 · Nature Astronomy, Sept 15, 2022 · AI summary available

   Abstract

   With a new generation of observatories coming online this decade, the process of characterizing exoplanet atmospheres will need to be reinvented. Currently mostly on the instrumental side, characterization bottlenecks will soon stand by the models used to translate spectra into atmospheric properties. Limitations stemming from our stellar and atmospheric models have already been highlighted. Here, we show that the current limitations of the opacity models used to decode exoplanet spectra propagate into an accuracy wall at ~0.5-1.0 dex (i.e., 3 to 10x) on the atmospheric properties, which is an order of magnitude above the precision targeted by JWST Cycle 1 programs and needed for, e.g., mean…

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   A quantitative assessment of the VO line list: Inaccuracies hamper high-resolution VO detections in exoplanet atmospheres

   S. de Regt, A. Y. Kesseli, I. A. G. Snellen et al. · 2022 · A&A 661, A109 (2022) · AI summary available

   Abstract

   Metal hydrides and oxides are important species in hot-Jupiters since they can affect their energy budgets and the thermal structure of their atmospheres. One such species is VO, which is prominent in stellar M-dwarf spectra. Evidence for VO has been found in the low-resolution transmission spectrum of WASP-121b, but this has not been confirmed at high resolution. It has been suggested that this is due to inaccuracies in its line list. In this paper, we quantitatively evaluate the VO line list and assess whether inaccuracies are responsible for the non-detections at high resolution in WASP-121b. Furthermore, we investigate whether the detectability can be improved by selecting only those lin…

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   Comparing Apples with Apples: Robust Detection Limits for Exoplanet High-Contrast Imaging in the Presence of non-Gaussian Noise

   Markus J. Bonse, Emily O. Garvin, Timothy D. Gebhard et al. · 2023 · Earth and Planetary Astrophysics · AI summary available

   Abstract

   Over the past decade, hundreds of nights have been spent on the worlds largest telescopes to search for and directly detect new exoplanets using high-contrast imaging (HCI). Thereby, two scientific goals are of central interest: First, to study the characteristics of the underlying planet population and distinguish between different planet formation and evolution theories. Second, to find and characterize planets in our immediate Solar neighborhood. Both goals heavily rely on the metric used to quantify planet detections and non-detections. Current standards often rely on several explicit or implicit assumptions about the noise. For example, it is often assumed that the residual noise after …

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   Directly imaged exoplanets in reflected starlight. The importance of knowing the planet radius

   Óscar Carrión-González, Antonio García Muñoz, Juan Cabrera et al. · 2020 · A&A 640, A136 (2020) · AI summary available

   Abstract

   We have investigated the information content in reflected-starlight spectra of exoplanets. We specify our analysis to Barnard's Star b candidate super-Earth, for which we assume a radius 0.6 times that of Neptune, an atmosphere dominated by H$_2$-He, and a CH$_4$ volume mixing ratio of 5$\cdot$10$^{-3}$. The main conclusions of our study are however planet-independent. We set up a model of the exoplanet described by seven parameters including its radius, atmospheric methane abundance and basic properties of a cloud layer. We generate synthetic spectra at zero phase (full disk illumination) from 500 to 900 nm and spectral resolution R$\sim$125-225. We simulate a measured spectrum with a simpl…

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   Ultimate limits of exoplanet spectroscopy: a quantum approach

   Zixin Huang, Christian Schwab, Cosmo Lupo · 2022 · Earth and Planetary Astrophysics · AI summary available

   Abstract

   One of the big challenges in exoplanet science is to determine the atmospheric makeup of extrasolar planets, and to find biosignatures that hint at the existence of biochemical processes on another world. The biomarkers we are trying to detect are gases in the exoplanet atmosphere like oxygen or methane, which have deep absorption features in the visible and near-infrared spectrum. Here we establish the ultimate quantum limit for determining the presence or absence of a spectral absorption line, for a dim source in the presence of a much brighter stellar source. We characterise the associated error exponent in both the frameworks of symmetric and asymmetric hypothesis testing. We found that …

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   There's more to life than O$_2$: Simulating the detectability of a range of molecules for ground-based high-resolution spectroscopy of transiting terrestrial exoplanets

   Miles H. Currie, Victoria S. Meadows, Kaitlin C. Rasmussen · 2023 · Earth and Planetary Astrophysics · AI summary available

   Abstract

   Within the next decade, atmospheric O$_2$ on Earth-like M dwarf planets may be accessible with visible--near-infrared, high spectral resolution extremely large ground-based telescope (ELT) instruments. However, the prospects for using ELTs to detect environmental properties that provide context for O$_2$ have not been thoroughly explored. Additional molecules may help indicate planetary habitability, rule out abiotically generated O$_2$, or reveal alternative biosignatures. To understand the accessibility of environmental context using ELT spectra, we simulate high-resolution transit transmission spectra of previously-generated evolved terrestrial atmospheres. We consider inhabited pre-indus…

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   Machine Learning for Exoplanet Detection in High-Contrast Spectroscopy: Revealing Exoplanets by Leveraging Hidden Molecular Signatures in Cross-Correlated Spectra with Convolutional Neural Networks

   Emily O. Garvin, Markus J. Bonse, Jean Hayoz et al. · 2024 · Earth and Planetary Astrophysics · AI summary available

   Abstract

   The new generation of observatories and instruments (VLT/ERIS, JWST, ELT) motivate the development of robust methods to detect and characterise faint and close-in exoplanets. Molecular mapping and cross-correlation for spectroscopy use molecular templates to isolate a planet's spectrum from its host star. However, reliance on signal-to-noise ratio (S/N) metrics can lead to missed discoveries, due to strong assumptions of Gaussian independent and identically distributed noise. We introduce machine learning for cross-correlation spectroscopy (MLCCS); the method aims to leverage weak assumptions on exoplanet characterisation, such as the presence of specific molecules in atmospheres, to improve…