The vast majority of planets are too distant to visit, so remote observation and subsequent analysis are essential to the search for extrasolar life. Telescopes such as the James Webb Space Telescope are providing an important new opportunity to directly observe exoplanet atmospheres for signs of life, but we currently lack a quantitative framework for understanding what observations of a planet’s atmosphere provide compelling evidence for life on the underlying planet. Developing a framework that allows one to infer whether or not a planet is inhabited is a two-step process: understand atmospheres in the absence of life (abiotic baselines), and understand how life modifies an atmosphere (atmospheric biosignatures).  This grant renews support for a team of modelers and experimentalists -the AEThER collaboration (Atmospheric Empirical, Theoretical, and Experimental Research)- to tackle the former question.AEThER seeks to develop a framework to quantify the abiotic atmospheric baseline for rocky planets commonly found in our galaxy. Developing such a framework will provide a flexible tool for quantifying how different conditions driving the formation and evolution of a planet lead to different abiotic atmospheric baselines.  Funded activities under this grant include a series of experiments to broaden our understanding of how readily so-called “volatile” elements and compounds—which include nitrogen gas, oxygen gas, hydrogen gas, water, ammonia, and carbon and sulfur dioxide—dissolve into magmas and liquid metals at the high temperatures and pressures common during planetary formation and evolution. The solubility of these molecules plays a key role in determining the viscosity and possible solidification of a planet’s mantle, with significant implications for heat transfer throughout the planet and atmosphere, as well as gas release back to the atmosphere, and thus habitability. In addition and informed by this experimental work, AEThER will continue to develop their theoretical models, including modeling the impacts of atmospheric hazes (suspended small particles) on planetary evolution, which, under different conditions, can either raise or lower planetary temperatures appreciably. When completed, the funded grant work will represent a notable advance in our understanding of planetary processes, and serve as an important complement to research aimed at identifying atmospheric biosignatures.