h3ppy: An open-source Python package for modelling and fitting H+3 spectra

h3ppy is an open-source Python package for modelling and fitting the near-infrared spectrum of the tri-hydrogen cation H3+ . This molecular ion is a main component of the charged particle ionospheres of the giant planets (Jupiter, Saturn, Uranus, and Neptune), and observations of these systems span over 30 years (Miller et al., 2020), using facilities such as ground-based telescopes (e.g. Keck, Very Large Telescope, NASA Infrared Telescope Facility), orbital spacecraft (e.g. Cassini and Juno), and space-based observatories (e.g., James Webb Space Telescope). By fitting the H3+ spectra, physical properties can be determined: 1) the temperature of the upper atmosphere and 2) the column integrated density of H3+ ions. The spatial and temporal distribution of these parameters reveal the processes and dynamics that govern the upper atmospheres of the giant planets, and in particular, how this region couples to both the lower atmosphere below and to the magnetic field beyond. h3ppy provides the tools required to both model the H3+ spectrum and perform these spectral retrievals.