Speaker
Description
The most common type of exoplanet discovered to date has a size that falls between Earth-sized and Neptune-sized, and orbits its star with a period less than 100 days. Atmospheric characterization of these planets often finds featureless transmission spectra, which is taken as evidence for the presence in the of clouds or hazes in the upper atmosphere that obscure the presence of deeper lying atmospheric constituents. We will present the results of a new model that suggests hazy atmospheres are innate byproducts of planet formation, where volatile ingredients are outgassed from the mantle and transformed in the upper atmosphere after exposure to stellar photons. Our model relates the initial mantle composition of the planet to its formation zone around its star, factoring in the relative contributions of refractories (metals and silicates) and volatile components (solid state organics, water vapor/ice, and hydrogen-dominated nebular gas). We predict that a population of super-Earths will form in particular locations in their protoplanetary disks such that they receive significant inventories of organics, but very low amounts of water. These hydrocarbon-rich planets are not carbon worlds, but rather carbon-rich planets whose subsequent evolution would differ from typically assumed for terrestrial planets. We will show models that encompass the geochemical equilibrium of the mantle and atmosphere, compute the resulting atmospheric chemical equilibrium, haze production, and predicted spectra.
