One of the most profound findings from NASA’s Kepler mission is the unexpected dearth of close-in exoplanets of sizes 1.5 to 2.0 Earth radii, i.e., a radius valley. This valley divides the population of the most abundant class of planets yet known, those between the sizes of Earth and Neptune, into small planets with Earth-like compositions and large planets with hydrogen-rich atmospheres or ice-rich interiors. Recently, our work and other contemporary studies have demonstrated how atmospheric mass-loss can explain these observations. In this talk, I will describe the key physical processes behind this, with a focus on the core-powered mass-loss mechanism. I will present how our results compare with the observed planet demographics, the insights they give us, and the testable predictions we make as a function of planet and host-star properties.

One of the most significant findings from such studies is that the typical planet forms with a hydrogen atmosphere, resulting in conditions where hydrogen and the planet's molten or super-critical interior interact for millions to billions of years. In our Solar system, we see this for planets such as Jupiter and Neptune, and in more recent JWST observations, this has been inferred for sub-Neptunes as well. However, we hardly understand these interactions, and studying them in a laboratory is difficult. I will discuss how we are addressing this by conducting quantum mechanics-based computational experiments to investigate how hydrogen and water—two of the most important planetary constituents—interact at conditions relevant to Uranus, Neptune, and water-rich exoplanets. To end with, I will share our results' fascinating implications for the formation, evolution, composition, and structure of such planets and their atmospheres. As I will demonstrate, our work highlights the importance of better understanding the interaction between planet atmospheres and interiors, especially as we enter the era of NASA's James Webb Space Telescope, the proposed Uranian orbiter, and other next-generation observatories.   

Host: Rachel Fernandes

Seminar held in 538 Davey or please email CEHW-SEMINAR-QUESTIONS@lists.psu.edu to attend virtually.