Exoplanet atmospheres with EChO: spectral retrievals using EChOSim

TL;DR

This paper evaluates the potential of the EChO mission concept to accurately retrieve atmospheric properties of various exoplanets using spectral simulations and atmospheric models.

Contribution

It demonstrates the effectiveness of EChO's spectral retrieval capabilities for different exoplanet types through synthetic data analysis.

Findings

Single transit suffices for hot Jupiters around Sun-like stars.

Multiple transits needed for warm Jupiters and smaller planets.

Atmospheric properties can be constrained within 2 sigma with specified observations.

Abstract

We demonstrate the effectiveness of the Exoplanet Characterisation Observatory mission concept for constraining the atmospheric properties of hot and warm gas giants and super Earths. Synthetic primary and secondary transit spectra for a range of planets are passed through EChOSim (Waldmann & Pascale 2014) to obtain the expected level of noise for different observational scenarios; these are then used as inputs for the NEMESIS atmospheric retrieval code and the retrieved atmospheric properties (temperature structure, composition and cloud properties) compared with the known input values, following the method of Barstow et al. (2013a). To correctly retrieve the temperature structure and composition of the atmosphere to within 2 {\sigma}, we find that we require: a single transit or eclipse of a hot Jupiter orbiting a sun-like (G2) star at 35 pc to constrain the terminator and dayside atmospheres; 20 transits or eclipses of a warm Jupiter orbiting a similar star; 10 transits/eclipses of a hot Neptune orbiting an M dwarf at 6 pc; and 30 transits or eclipses of a GJ1214b-like planet.