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Exoplanets with sizes of up to a few earth radii display a gap in their radius distribution, interpreted as a footprint of atmospheric evaporation - planets which formed with only a moderate gaseous envelope can be stripped to rocky cores. This atmospheric escape is thought to be mainly driven by X-ray and UV irradiation by the host star, which is in turn driven by the stellar magnetic activity. Stellar high-energy emission is strong at young stellar ages and decreases by roughly three orders of magnitude on the main sequence. This means that old star-exoplanet systems display a fossilized view of the radius gap, which depends on the past magnetic activity evolution of the star. A complementary view is given by exoplanets in young stellar clusters, of which a sizeable number has been discovered over the past few years. Those may be systems that are still in the process of crossing the radius gap. We present estimates for different stellar activity evolution tracks and how they relate to the distance planets can travel in the radius vs. stellar rotation period diagram. We will present the special cases of young multi-planet systems and their X-ray irradiation, which can give unique clues about the history and fate of Neptunes and Earths over time.

Katja Poppenhaeger: Connecting the exoplanet radius gap with stellar activity evolution