Exoplanets & Exomoons

How Do We Optimally Sample Model Grids Of Exoplanet Spectra?

By Keith Cowing
June 26, 2022
Filed under
How Do We Optimally Sample Model Grids Of Exoplanet Spectra?
Comparison of our analytical models with the corresponding models from Goyal et al. (2019), shown for different parameter values. The analytical model is shown in blue and the model from Goyal et al. (2019) is shown in red.

The construction and implementation of atmospheric model grids is a popular tool in exoplanet characterisation. These typically vary a number of parameters linearly, containing one model for every combination of parameter values.

Here we investigate alternative methods of sampling parameters, including random sampling and Latin hypercube (LH) sampling, and how these compare to linearly sampled grids. We use a random forest to analyse the performance of these grids for two different models, as well as investigate the information content of the particular model grid from Goyal et al. 2019. We also use nested-sampling to implement mock atmospheric retrievals on simulated JWST transmission spectra by interpolating on linearly sampled model grids.

Our results show that random or LH sampling out-performs linear sampling in parameter predictability for our higher dimensional models, requiring fewer models in the grid, and thus allowing for more computationally intensive forward models to be used. We also find that using a traditional retrieval with interpolation on a linear grid can produce biased posterior distributions, especially for parameters with non-linear effects on the spectrum. In particular, we advise caution when performing linear interpolation on the C/O ratio, cloud properties, and metallicity.

Finally, we find that the information content analysis of the grid from Goyal et al. 2019 is able to highlight key areas of the spectra where the presence or absence of certain molecules can be detected, providing good indicators for parameters such as temperature and C/O ratio.

Chloe Fisher, Kevin Heng

Comments: 14 pages, 8 figures. Accepted for publication in ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2206.12194 [astro-ph.EP] (or arXiv:2206.12194v1 [astro-ph.EP] for this version)
Submission history
From: Chloe Fisher
[v1] Fri, 24 Jun 2022 10:07:19 UTC (932 KB)
Astrobiology, Astrochemistry,

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻