Cross-sections for heavy atmospheres: H2O continuum

Lara O. Anisman*, Katy L. Chubb, Jonathan Elsey, Ahmed Al-Refaie, Quentin Changeat, Sergei N. Yurchenko, Jonathan Tennyson, Giovanna Tinetti

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


Most of the exoplanets detected up to now transit in front of their host stars, allowing for the generation of transmission spectra; the study of exoplanet atmospheres relies heavily upon accurate analysis of these spectra. Recent discoveries mean that the study of atmospheric signals from low-mass, temperate worlds are becoming increasingly common. The observed transit depth in these planets is small and more difficult to analyze. Analysis of simulated transmission spectra for two small, temperate planets (GJ 1214 b and K2-18 b) is presented, giving evidence for significant differences in simulated transit depth when the water vapor continuum is accounted for when compared to models omitting it. These models use cross-sections from the CAVIAR lab experiment for the water self-continuum up to 10,000 cm−1 ; these cross-sections exhibit an inverse relationship with temperature, hence lower-temperature atmospheres are the most significantly impacted. Including the water continuum strongly affects transit depths, increasing values by up to 60 ppm, with the differences for both planets being detectable with the future space missions Ariel and JWST. It is imperative that models of exoplanet spectra move toward adaptive cross-sections, increasingly optimized for H2O-rich atmospheres. This necessitates including absorption contribution from the water vapor continuum into atmospheric simulations.
Original languageEnglish
Article number108013
Number of pages6
JournalJournal of Quantitative Spectroscopy and Radiative Transfer
Early online date25 Nov 2021
Publication statusPublished - 1 Feb 2022


  • Super-Earths
  • Mini-Neptunes
  • Exoplanets
  • Atmospheres
  • Water vapor
  • Opacities
  • Continuum absorption


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