Abstract

We are discovering more and more super-Earths, and we would like constraints on their compositions to investigate whether they are more similar to rocky Earth or gaseous Neptune. We therefore need numerical models of their interiors. These models often exclude any thermal effects, but this is not a good choice for planets with thick oceans or watery atmospheres. Water has a rich and interesting thermal behaviour: at high pressure and temperature it can be in any of several exotic plasma and ice phases. Planets with thick water layers, known as waterworlds, cannot therefore be accurately represented by models that treat them as cold spheres. But understanding how waterworlds vary in size and structure is important as we seek to interpret new observations of super-Earths. During my PhD, I developed temperature-dependent structure models of waterworlds, treating both the interior structure and the atmosphere and including both internal and external heating. I showed the following: heat can significantly affect a watery planet’s size and structure; these planets can have large and diffuse yet opaque atmospheres; and a planet can have a hot extended steam atmosphere even if only moderately heated from the inside. I also considered what happens when a waterworld migrates and what this could mean for the astrobiological properties of such a planet. I will present some of these results from my recently submitted PhD.