Heather Knutson, Assistant Professor of Planetary Science, Caltech
Ongoing surveys of nearby stars have revealed an amazing diversity of planetary systems, many of which have characteristics that differ substantially from those of the solar system planets. Perhaps one of the biggest surprises to come out of these surveys was the discovery that "super-Earths" (planets between 1-10 times the mass of the Earth) are in fact the most common type of extrasolar planet. Despite the name we actually know very little about the compositions of these mysterious planets, and it has been suggested that this mass range may include both "water worlds" and "mini-Neptunes" with thick hydrogen envelopes in addition to more Earth-like terrestrial planets. In my talk I will explore current constraints on the compositions of planets with masses ranging from that of Neptune down into the super-Earth regime, and discuss the corresponding implications for our understanding of planet formation and evolution.