Nikki Miller, PhD

X-ray irradiation and evaporation of exoplanets

How do stars affect the evolution of close-orbiting planets?

A large proportion of the known population of exoplanets are in short-period orbits. Being in such close proximity to a star, especially when the star has a lot of magnetic activity, can lead to planets receiving harsh levels of irradiation in the X-ray and extreme-UV (XUV) part of the spectrum.

Observed gaps in the distribution of rocky planets or a lack of short-period Neptune-like planets supports the idea that some planets lose significant mass due to high-energy irradiation from their host stars. During my masters project, I worked with Prof. Peter Wheatley and others to measure the amount of XUV irradiation that four super-Earth and Neptune sized planets in the Praesepe cluster were experiencing using XMM-Newton and K2. Our results can be found in King et al. (2022).

Two of the the four planets studied lie in the Neptunian desert, a region where there are fewer intermediate-sized planets at short orbital periods than expected, likely due to photo-evaporation.