Today Angie Wolfgang (UCSC) gave a short morning seminar about hierarchical inference of exoplanet compositions (like are they ice or gas or rock?). She showed that the super-Earth (1 to 4 Earth-radius) planet radius distribution fairly simply translates into a composition distribution, if you are willing to make the (pretty justified, actually) assumption that the planets are rocky cores with a hydrogen/helium envelope. She inferred the distribution of gas fractions for these presumed rocky planets and got some reasonable numbers. Nice! There is much more to do, of course, since she cut to a very clean sample, and hasn't yet looked at the interdependence of composition, period, and host-star properties. There is a lot to do in exoplanet populations still!