ARES.* V. No Evidence For Molecular Absorption in the HST WFC3 Spectrum of GJ 1132 b

Lorenzo V Mugnai,Mario Morvan,Yassin Jaziri,Niall Whiteford,Ingo Waldmann,Gloria Guilluy,Ahmed Al-Refaie,Quentin Changeat,Benjamin Charnay,Michelle Fabienne Bieger,Kai Hou Yip,Nour Skaf,Mathilde Poveda,Doriann Blain,Robin Baeyens,Billy Edwards,Olivia Venot,Jean-Philippe Beaulieu,Sam Wright,William Pluriel,Giuseppe Morello,Darius Modirrousta-Galian,Jérémy Leconte,Amélie Gressier,Tiziano Zingalès ,F Kiefer ,J Bouwman ,P Drossart

doi:10.3847/1538-3881/abf3c3

Abstract

Abstract We present a study on the spatially scanned spectroscopic observations of the transit of GJ 1132 b, a warm (∼500 K) super-Earth (1.13 R ⊕) that was obtained with the G141 grism (1.125–1.650 μm) of the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope. We used the publicly available Iraclis pipeline to extract the planetary transmission spectra from the five visits and produced a precise transmission spectrum. We analyzed the spectrum using the TauREx3 atmospheric retrieval code, with which we show that the measurements do not contain molecular signatures in the investigated wavelength range and are best fit with a flat-line model. Our results suggest that the planet does not have a clear primordial, hydrogen-dominated atmosphere. Instead, GJ 1132 b could have a cloudy hydrogen-dominated atmosphere, have a very enriched secondary atmosphere, be airless, or have a tenuous atmosphere that has not been detected. Due to the narrow wavelength coverage of WFC3, these scenarios cannot be distinguished yet, but the James Webb Space Telescope may be capable of detecting atmospheric features, although several observations may be required to provide useful constraints.

Highlights

One major obstacle that exoplanetary researchers encounter is a general lack of data
Our results suggest that the atmosphere of GJ 1132b is likely to be cloudy but that certain enriched atmospheres, with small scale heights that led to only minor features over the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) range, could explain the data
We present the data analysis of five spectroscopic observations of GJ 1132b obtained with the G141 grism of the WFC3 on board HST

Summary

Introduction

One major obstacle that exoplanetary researchers encounter is a general lack of data This makes it difficult to determine the composition and internal structure of exoplanets, as there is an inevitable strong degeneracy when one tries to fit a model to observations. By making use of geophysical and statistical principles, several studies have determined the degree of degeneracy in exoplanet compositions (e.g., Adams et al 2008; Valencia et al 2013; Dorn et al 2017) They found that knowing the mass and radius of a planet precisely can lead to superior constraints on the ice mass fraction and size of the inner embryo but little improvement on the atmospheric composition. There is a strong motivation to characterize exoplanetary atmospheres, as this would lead to a better understanding on the global properties of their host planets

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Conclusion