Special Physics Seminar

Exploring the Diversity and Formation of Super-Earth Exoplanets

Bjorn Benneke

California Institute of Technology

The discovery of planets intermediate in mass and radius between Earth and Neptune was one of the biggest surprises in the brief history of exoplanet science. These “super-Earths” are an order of magnitude more abundant than close-in giant planets. Despite this ubiquity, we know little about their typical compositions and formation histories. The existence of low-density, low-mass super-Earths is a particular challenge for planet formation theories, as it is difficult to explain how planets with masses similar to Earth could acquire thick gas envelopes similar to the giant planets in the Solar System. Our traditional picture that small planets are composed of rock and volatiles while larger planets have massive hydrogen-dominated envelopes is challenged at the most basic level.

Spectroscopic transit observations can shed new light on these mysterious worlds by probing their atmospheric compositions. In this talk, I will present the main conclusions from three groundbreaking studies of low-mass exoplanets recently published in Nature. In these three studies, we revealed the first unambiguous detection of clouds on a super-Earth as well as the first detection of water vapor on a Neptune-mass planet. Finally, I will give an overview of my ongoing 124-orbit (200-hour) Hubble Space Telescope program to take the next big leap towards understanding the chemical diversity and formation history of super-Earths. This unprecedented survey will provide the first comprehensive look at this intriguing new class of planets ranging from 1 Neptune mass and temperatures close to 2000K to a 1 Earth mass planet near the habitable zone of its host star.