Quantifying the impact of spectral coverage on the retrieval of molecular abundances from exoplanet transmission spectra

John W. Chapman, Robert T. Zellem, Michael Line, Gautam Vasisht, Geoff Bryden, Karen Willacy, Aishwarya R. Iyer, Jacob Bean, Nicolas B. Cowan, Jonathan J. Fortney, Caitlin A. Griffith, Tiffany Kataria, Eliza M.R. Kempton, Laura Kreidberg, Julianne I. Moses, Kevin B. Stevenson, Mark R. Swain

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Using forward models for representative exoplanet atmospheres and a radiometric instrument model, we generated synthetic observational data to explore how well the major C- and O-bearing chemical species (CO, CO2, CH4, and H2O), important for determining atmospheric opacity and radiation balance, can be constrained by transit measurements as a function of spectral wavelength coverage. This work features simulations for a notional transit spectroscopy mission and compares two cases for instrument spectral coverage (wavelength coverage from 0.5-2.5 μm and 0.5-5 μm). The simulation is conducted on a grid with a range of stellar magnitudes and incorporates a full retrieval of atmospheric model parameters. We consider a range of planets from sub-Neptunes to hot Jupiters and include both low and high mean molecular weight atmospheres. We find that including the 2.5-5 μm wavelength range provides a significant improvement in the degree of constraint on the retrieved molecular abundances: up to ~3 orders of magnitude for a low mean molecular weight atmosphere (μ = 2.3) and up to a factor of ~6 for a high mean molecular weight atmosphere (μ = 28). These decreased uncertainties imply that broad spectral coverage between the visible and the mid-infrared is an important tool for understanding the chemistry and composition of exoplanet atmospheres. This analysis suggests that the James Webb Space Telescope’s (JWST) Near-Infrared Spectrograph (NIRSpec) 0.6-5 μm prism spectroscopy mode, or similar wavelength coverage with possible future missions, will be an important resource for exoplanet atmospheric characterization.

Original languageEnglish (US)
Article number104402
JournalPublications of the Astronomical Society of the Pacific
Issue number980
StatePublished - Oct 1 2017


  • Instrumentation: spectrographs
  • Planets and satellites: atmospheres
  • Radiative transfer
  • Techniques: spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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