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Understanding the radius valley as a by-product of planet formation

Presentation #103.02 in the session Formation 1.

Published onJun 20, 2022
Understanding the radius valley as a by-product of planet formation

Observations have revealed a lack of planets of sizes ~1.5–2.0 Earth radii, i.e. a radius ‘valley’ in the size distribution of small, short-period exoplanets. This observation has been typically attributed to atmospheric mass-loss due to photoevaporation. However, it has recently been demonstrated that atmospheric mass-loss, powered by the cooling luminosity of a planet and its host star’s bolometric luminosity, can also explain the origin of this radius valley, even in the absence of photoevaporation or any other process. In my talk, I will describe the key physical processes that drive this core-powered mass-loss mechanism followed by a comparison of our results with observations and the testable predictions we can make as a function of planet and host-star properties. This will include sharing our latest work where we present lists of planets that could be undergoing considerable atmospheric mass-loss or that might harbor secondary atmospheres, low-density interiors or both. I will then conclude with a discussion of our upcoming work where we investigate the evolution of planets around the low-mass stars and find that if the planet evolution is indeed dictated by the core-powered mass-loss mechanism, the magnitude of the radius valley slope should decrease in the planet size-stellar mass space as the stellar mass approaches ~0.1 Solar mass.

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