Atomic and Molecular Spectral Models of Biosignatures in Exoplanetary Atmospheres

As thousands of extra-solar planets are being discovered the next big step is the search for life as we might understand. Spectral analysis of atomic-ionic-molecular features is the primary mechanism for detection of biosignature elements H, C, N, O, P and S. We have adapted a general-purpose software package as a new toolkit Geant4-EXOP (G4-EXOP), for modeling host-star radiation transmission through planetary atmospheric layers. G4-EXOP uses eclipse geometry with radiation propagated through various layers of exoplanetary atmosphere to analyze potential biosignature spectral features and abundances. G4-EXOP is based on Geant4, a Monte Carlo program package enabling modeling of radiation and particle transmission through matter. Our toolkit uses atomic and molecular data to generate emission and absorption spectra to ascertain abundances from line strengths. We focus on atomic-ionic biosignatures (H, C, N, etc.) in emission, superimposed on and molecular absorption from common molecules H₂O, CO₂, CH₄, etc. Phosphorus in particular is a focus of these studies, as it is vital for DNA-based life. We calculate atomic transition data using SUPERSTRUCTURE and R-matrix codes and report new results for P, C, O and other elements. We obtain molecular data from the database ExoMol using calculated oscillator strengths for H₂O and CO₂. Numerical experiments are carried out for different temperature-density regimes, and broadening mechanisms to elicit spectral features in wavelength ranges detectable from ground-based telescopes or space-based observatories such as the James Webb Space Telescope.