Exoplanets & Exomoons

Parameterizing Pressure-temperature Profiles Of Exoplanet Atmospheres With Neural Networks

By Keith Cowing
Status Report
astro-ph.IM
September 7, 2023
Filed under , , ,
Parameterizing Pressure-temperature Profiles Of Exoplanet Atmospheres With Neural Networks
Results for our simulated atmospheric retrieval of an Earth-like planet using petitRADTRANS, LIFEsim, and PyMultiNest. Left: The retrieved PT profiles for the polynomial baseline and our model, together with the emission contribution function. Right: The relative fitting error of the spectrum, computed as (true spectrum − simulated spectrum) / true spectrum. — astro-ph.IM

Atmospheric retrievals (AR) of exoplanets typically rely on a combination of a Bayesian inference technique and a forward simulator to estimate atmospheric properties from an observed spectrum. A key component in simulating spectra is the pressure-temperature (PT) profile, which describes the thermal structure of the atmosphere.

Current AR pipelines commonly use ad hoc fitting functions here that limit the retrieved PT profiles to simple approximations, but still use a relatively large number of parameters. In this work, we introduce a conceptually new, data-driven parameterization scheme for physically consistent PT profiles that does not require explicit assumptions about the functional form of the PT profiles and uses fewer parameters than existing methods.

Our approach consists of a latent variable model (based on a neural network) that learns a distribution over functions (PT profiles). Each profile is represented by a low-dimensional vector that can be used to condition a decoder network that maps P to T. When training and evaluating our method on two publicly available datasets of self-consistent PT profiles, we find that our method achieves, on average, better fit quality than existing baseline methods, despite using fewer parameters.

In an AR based on existing literature, our model (using two parameters) produces a tighter, more accurate posterior for the PT profile than the five-parameter polynomial baseline, while also speeding up the retrieval by more than a factor of three. By providing parametric access to physically consistent PT profiles, and by reducing the number of parameters required to describe a PT profile (thereby reducing computational cost or freeing resources for additional parameters of interest), our method can help improve AR and thus our understanding of exoplanet atmospheres and their habitability.

Timothy D. Gebhard, Daniel Angerhausen, Björn S. Konrad, Eleonora Alei, Sascha P. Quanz, Bernhard Schölkopf

Comments: Accepted for publication in Astronomy & Astrophysics
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP); Machine Learning (cs.LG)
Cite as: arXiv:2309.03075 [astro-ph.IM] (or arXiv:2309.03075v1 [astro-ph.IM] for this version)
Submission history
From: Timothy D. Gebhard
[v1] Wed, 6 Sep 2023 15:22:33 UTC (3,300 KB)
https://arxiv.org/abs/2309.03075
Astrobiology

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