Exoplanetary Origins: Unraveling Planetary Formation and Accretion Histories with CNO Isotopologues

The abundances of volatile elements like carbon, oxygen, and nitrogen (CNO) bridge the gap between protoplanetary disk chemistry, stellar composition, and planetary formation, accretion, and migration mechanisms. CNO abundances can trace a planet’s formation location relative to H2O, CO2, CO, and N2 “snowlines”, or the distance from the star at which these volatile elements sublimate. By comparing elemental and isotopic CNO ratios measured in giant exoplanet atmospheres to complementary measurements in their host stars, we can determine whether the planet inherited stellar abundances consistent with in situ formation near the host star, or abundances consistent with formation in outer regions of the protoplanetary disk followed by an inward migration and accretion of materials from various portions of the disk. Here, I provide an overview of host star and companion planet CNO isotope ratios (12C/13C, 14N/15N, and 16O/18O) as they relate to the formation and evolution of planetary systems. To date, there are still only a handful of exoplanet systems where we can make a direct comparison of elemental and isotopic CNO abundances between an exoplanet and its host star. I will also discuss recent CNO isotope ratio detections in sub-stellar objects from both ground- and space-based observatories. Finally, I will share my near-infrared spectroscopic analysis to derive 12C/13C, 14N/15N, and 16O/18O in planet-hosting cool dwarf stars using MARCS model atmospheres and the spectral synthesis code TurboSpectrum, as well as a custom set of atomic and molecular line lists.