The Habitable Worlds Observatory and JWST propose to identify habitable exoplanets via spectroscopic observations of the atmospheres of potentially Earth-like planets. However, the effect of the likely compositional variability of exoplanets on their habitability and the reaction rates that will be used to differentiate biological from geological sources is largely unexplored. Similarly, the geochemical relationships that are the basis of models that link surfaces and atmospheres are calibrated on Earth-like systems, and many of these relationships are still not well understood. In order to prioritize the most viable observation targets and best interpret their data, our understanding of geochemistry must be extended beyond our solar system. To do this, we must first conduct fundamental experimental studies and improve thermodynamic models by expanding their geochemical scope to encompass wider likely exoplanet chemistries. 

In this presentation, we will discuss our recent efforts to help ensure that future observation targets are likely to have geochemical trends and characteristics similar enough to Earth that they could be habitable to life as we know it. We will touch on results from the first mantle melting experiments on likely rocky exoplanet compositions and hydrogen solubility experiments performed to help improve our understanding of the water budgets of terrestrial planets. These experiments are supported by thermodynamic calculations using the ENKI suite of thermodynamic tools to compare melting temperatures and compositions, as well as to explore potential outgassing from associated volcanism on these planets. We will also present ongoing experimental and modeling work to explore the effect of stellar compositional variability—particularly the role of phosphorous, a “rate-limiting” bio-essential element—on the habitability of rocky planets.