Exoplanetary Atmospheres


Spectra & Aggregate Hazes


Since the discovery of exoplanets, the next question has been: how do we characterize them? Learning the atmospheric compositions helps us learn what these worlds are like, but obtaining this info is tricky!

Exoplanet aerosols can absorb light and obscure molecular features across a wide range of wavelengths. Some spectra are nearly flat (e.g., GJ 1214b)! Previous studies considered the microphysics of hazes composed of spherical particles, but these produce sloped spectra due to Rayleigh scattering. Instead, I worked with Peter Gao and Imke de Pater (UC Berkeley), and we provide the first study to consider the microphysics of aggregate hazes in warm exoplanet atmospheres.

Example of a fractal aggregate.

Example of a fractal aggregate.

Our aggregate hazes reach larger sizes than spherical hazes do, and they are much more optically thick (more efficient at absorbing light) across a broad wavelength range. We generate synthetic spectra with these hazes at GJ 1214b. Our model fits the data very well (with a reduced chi-squared of 1.36), and we conclude that aggregate hazes may be important at exoplanets

 Photos From: <http://hubblesite.org/image/2271/news_release/2008-11> and <http://www.unige.ch/cabe/research2.html>

Kepler: Optical Phase Curves

Planets of comparable effective temperatures span a range of observed optical albedos, as demonstrated by the figure below.


One possible explanation for the anomalously reflective planets is that clouds high in their atmospheres scatter incident starlight, making them bright in the optical.

We are currently using GCM output as input to an equilibrium cloud code in order to learn the cloud structure that may be in the atmospheres of the six planets boxed above. We then use a 3D albedo program to learn how the scattering properties of these clouds would affect the observed albedo.