The shape of a planetary radius gap points to lost atmospheres
In short: Astronomers studying the sizes of planets orbiting nearby stars found a distinct gap in their distribution. By analyzing a sample of 117 planets with high-precision measurements, the team identified a clear bimodal pattern where planets are either small super-Earths or larger sub-Neptunes, with very few planets falling in between at a radius of about two Earth radii.
The specific slope of this radius valley provides a clue about how these planets formed. The data shows a negative slope, which aligns with models of photoevaporation—where stellar radiation strips away a planet's outer atmosphere—rather than models where rocky planets form late in a gas-poor environment.
The study used asteroseismology to obtain highly accurate stellar parameters, allowing for more precise planetary radius measurements. However, the findings are based on a relatively small sample of planets.
Why it matters: The physical characteristics of the gap between small and large planets suggest they may be stripped of their atmospheres by their stars.
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Sources
- Summary by Intellect · source: Research: Eylen et al. (2018). An asteroseismic view of the radius valley: stripped cores, not born rocky. Monthly Notices of the Royal Astronomical Society.
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