Information Content of JWST NIRSpec Transmission Spectra of Warm Neptunes

Guzmán-Mesa, Andrea; Kitzmann, Daniel; Fisher, Chloe Elizabeth; Burgasser, Adam J.; Hoeijmakers, H. Jens; Márquez Neila, Pablo; Grimm, Simon L.; Mandell, Avi M.; Sznitman, Raphael; Heng, Kevin (2020). Information Content of JWST NIRSpec Transmission Spectra of Warm Neptunes. The astronomical journal, 160(1), p. 15. American Astronomical Society 10.3847/1538-3881/ab9176

Guzm_n-Mesa_2020_AJ_160_15.pdf - Published Version
Available under License Creative Commons: Attribution (CC-BY).

Download (9MB) | Preview

Warm Neptunes offer a rich opportunity for understanding exo-atmospheric chemistry. With the upcoming James Webb Space Telescope (JWST), there is a need to elucidate the balance between investments in telescope time versus scientific yield. We use the supervised machine-learning method of the random forest to perform an information content (IC) analysis on a 11-parameter model of transmission spectra from the various NIRSpec modes. The three bluest medium-resolution NIRSpec modes (0.7–1.27 μm, 0.97–1.84 μm, 1.66–3.07 μm) are insensitive to the presence of CO. The reddest medium-resolution mode (2.87–5.10 μm) is sensitive to all of the molecules assumed in our model: CO, CO2, CH4, C2H2, H2O, HCN, and NH3. It competes effectively with the three bluest modes on the information encoded on cloud abundance and particle size. It is also competitive with the low-resolution prism mode (0.6–5.3 μm) on the inference of every parameter except for the temperature and ammonia abundance. We recommend astronomers to use the reddest medium-resolution NIRSpec mode for studying the atmospheric chemistry of 800–1200 K warm Neptunes; its corresponding high-resolution counterpart offers diminishing returns. We compare our findings to previous JWST IC analyses that favor the blue orders and suggest that the reliance on chemical equilibrium could lead to biased outcomes if this assumption does not apply. A simple, pressure-independent diagnostic for identifying chemical disequilibrium is proposed based on measuring the abundances of H2O, CO, and CO2.

Item Type:

Journal Article (Original Article)


08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences
08 Faculty of Science > Physics Institute
10 Strategic Research Centers > Center for Space and Habitability (CSH)
08 Faculty of Science > Physics Institute > NCCR PlanetS

UniBE Contributor:

Guzman Mesa, Andrea, Kitzmann, Daniel, Fisher, Chloe Elizabeth, Hoeijmakers, Herman Jens, Márquez Neila, Pablo, Grimm, Simon Lukas, Heng, Kevin


500 Science > 520 Astronomy
500 Science > 530 Physics
600 Technology > 620 Engineering




American Astronomical Society




Simon Lukas Grimm

Date Deposited:

09 Mar 2021 11:41

Last Modified:

05 Dec 2022 15:48

Publisher DOI:





Actions (login required)

Edit item Edit item
Provide Feedback