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Arxiv: ARES VI: Viability of one-dimensional retrieval models for transmission spectroscopy characterization of exo-atmospheres in the era of JWST and Ariel Published: 1/8/2024 12:57:10 PM Updated: 1/8/2024 12:57:10 PM

Paper abstract: Observed exoplanet transit spectra are usually retrieved using 1D models todetermine atmospheric composition while planetary atmospheres are 3D. With theJWST and future space telescopes such as Ariel, we will be able to obtainincreasingly accurate transit spectra. The 3D effects on the spectra will bevisible, and we can expect biases in the 1D extractions. In order to elucidatethese biases, we have built theoretical observations of transit spectra, from3D atmospheric modeling through transit modeling to instrument modeling. 3Deffects are observed to be strongly nonlinear from the coldest to the hottestplanets. These effects also depend on the planet's metallicity and gravity.Considering equilibrium chemistry, 3D effects are observed through very strongvariations in certain features of the molecule or very small variations overthe whole spectrum. We conclude that we cannot rely on the uncertainty ofretrievals at all pressures, and that we must be cautious about the results ofretrievals at the top of the atmosphere. However the results are still fairlyclose to the truth at mid-altitudes (those probed). We also need to be carefulwith the chemical models used for planetary atmosphere. If the chemistry of onemolecule is not correctly described, this will bias all the others, and theretrieved temperature as well. Finally, although fitting a wider wavelengthrange and higher resolution has been shown to increase retrieval accuracy, weshow that this could depend on the wavelength range chosen, due to the accuracyon modeling the different features. In any case, 1D retrievals are stillcorrect for the detection of molecules, even in the event of an erroneousabundance retrieval.