My research comprises the characterisation of the low-mass planets: super-Earths and mini-Neptunes. The former are planets that are mostly solid, either rocky or icy in composition, while the latter posses also a volatile envelope. My goal is to determine if planets with masses between 1-15 Earth-masses are scaled up versions of Earth, or scaled-down versions of Neptune in terms of their composition, evolution and physical properties.

To date, out of the ~600 discovered exoplanets, and 1000+ planet candidates reported by space mission Kepler, there are a handful of low-mass planets with measured masses and radii. This number will continue to increase as new data from Kepler arrives, and new discoveries are reported from other missions such as ground-based MEarth, or space mission CoRoT, as well as follow-up work to radial velocity planets.

Composition of Super-Earths & mini-Neptunes

The first step towards characterising a planet is to determine its composition, which can only be done if at least its mass and radius are known. I determine the composition of the low-mass exoplanets from these two measurements plus a detailed internal structure model (see Valencia et al. 2006, 2007, 2010).

A few prominent results are that CoRoT-7b and Kepler-10b are very similar planets with a rocky composition enriched in iron with respect to Earth. Their composition is very close to that of Mercury. On the other hand, 55Cnc-e is a volatile planet with a water-rich envelope of tens of percents by mass.

M-R relationships for low-mass exoplanets

Composition & Formation

I am interested in tying the composition of low-mass planets to formation processes. The composition of a planet reflects the initial chemical inventory of the building blocks during formation, plus any secondary process that may alter the composition (such as giant impacts and atmospheric evaporation).

Current work comprises the study of atmospheric evaporation as a systematic process that may enrich the iron content of hot rocky planets, as well as the coupling of dynamics and chemistry to predict likely composition of refractory planets.

CoRoT-7b artist impression
CNRS/F. Catalano

Interior Dynamics

To understand the thermal evolution of a planet it is imperative to understand its mechanisms for losing heat, in particular its internal dynamics. For rocky and icy planets this translates to understanding the convective evolution of their mantles. We suggested earlier that terrestrial massive planets were likely to maintain plate tectonics through simple parameterized convection analysis. I have now moved to investigate the topic with the numerical model 'stagyy' (developed by Dr. Paul Tackley).

The aim is to understand the interior dynamics of these planets, establish the connections to the composition of their atmospheres, and trace the evolutionary pathways to habitability.

Convection calculation for a 3 earth-mass planet (with STAGYY) -- Temp Structure

And other projects ...


Updated October 2011