Analysis of the planetary mass uncertainties on the atmospherical retrieval accuracy

C. Di Maio, Q. Changeat, S. Benatti, G. Micela

Submitted on 5 November 2022, last revised on 16 November 2022


The properties of the atmospheres of the exoplanets depend on several interconnected parameters, making it difficult to determine them. The mass of the planets plays a role in determining the scale height of atmospheres, similarly to that covered by the average molecular weight of the gas. We investigated the relevance of planetary mass knowledge in spectral retrievals, identifying in which cases a mass measurements is needed for clear or cloudy, primary or secondary atmospheres, and at which precision, in the context of the ESA M4 Ariel Mission. We used TauREx to simulate the Ariel transmission spectra of representative targets of the Ariel mission reference sample assuming different scenarios: a primordial cloudy atmosphere of a hot-Jupiter and hot-Neptune and a secondary atmosphere of a super-Earth, also in presence of clouds. We extract information about various properties of the atmospheres for the cases of unknown mass, or mass with different uncertainty. We also test how the signal-to-noise impacts the atmospheric retrieval for different wavelength ranges. We accurately retrieved the primordial atmospheric composition independently from mass uncertainties for clear atmospheres, while the uncertainties increased for high altitude clouds. We highlighted the importance of signal-to-noise ratio in the Rayleigh scattering region of the spectrum. For the secondary atmosphere cases a mass uncertainty no larger than 50% is sufficient to retrieve the atmospheric parameters, even in presence of clouds. Our analysis suggests that even in worst case scenarios a 50% mass precision level is enough for producing reliable retrievals, while an atmospheric retrieval without any knowledge of a planetary mass could lead to biases in cloudy primary atmosphere and in secondary atmosphere.


Comment: 29 pages, 21 figures. Accepted for publication in Section 10. Planets and planetary systems of Astronomy and Astrophysics. The official date of acceptance is 15/11/2022. Abstract shortened for the arXiv listing

Subject: Astrophysics - Earth and Planetary Astrophysics