Research Areas
From the statistics of the numerous planet finding surveys we have learned that nearly every star in the galaxy hosts a planet. That amounts to hundreds of billions of planets within our own galaxy! It is unlikely in the near future that we will send probes and landers to these planets that are many light years away, hence we are limited to studying these planets from afar from our own pale blue dot. We also know that many of these planets will host some type of atmosphere; hence an atmosphere (provided it exists) is the most readily observable portion of any planetary object. This means that, most of the information we can learn about the processes occurring on or within these far-way planets will come from observing their atmospheres. Our team uses a combination of spectral observations, statistics, and theoretical methods to reveal the mysteries of these worlds. img cr. NASA/JPL-Caltech
Atmospheres from Stars to Planets: Our group studies a wide range of planetary-like atmospheres from thick brown dwarf envelopes too cool transiting exoplanet atmospheres, using a combination of theoretical and observational methods. Determining fundamental atmospheric properties over a wide range of conditions is a necessary first step towards developing a comprehensive theory of atmospheres, their evolution, and their interactions with their surface, interior, local space environment, and any potential interaction biologic processes may have with them.
Spectra as a Diagnostic of Planetary Processes: Transmission and emission spectra of an exoplanet contain information about the composition and temperature structure of its atmosphere. Determining these properties is the key to understanding the climate and chemical processes occurring in their atmospheres as well as links to their formation histories. Most of what we have learned about exoplanet atmospheres comes from large Jupiter and Neptune-like planets orbiting really close to their stars (<~0.5 AU) because they are the most readily observable given current telescope capabilities. Interpreting exoplanet atmosphere observations is tremendously difficult as we have to tease out the planetary signal from the blindingly bright backdrop of their host stars. Our team focuses on the development of the atmospheric models that can be used to describe these spectra.
Atmospheric Retrievals: One of the core tools used by our team to extract information from these small spectral signals is "atmospheric retrieval". Atmospheric retrieval is effectively "bayesian inference" (using an MCMC type sampler) which uses a model atmosphere that maps atmospheric properties like temperature, composition, clouds, and anything else that might matter into a spectrum, like those obtained with JWST. Our group has developed a many of the key atmospheric parameterizations and strategies commonly implemented within atmospheric retrievals. img cr. Luis Welbanks
Brown Dwarf Inference: Brown dwarfs are often considered “failed stars” (or overachieving planets if you will) as they are not massive enough to fuse hydrogen like stars. They are in effect, the important “sub-stellar” link in the continuum between stars and planets. We know of ~1500 brown dwarfs from various all sky surveys. They are typically about the size of Jupiter but much more massive. Because of their “cool” temperatures, relative to stars, the physics and chemistry in their atmospheres are very similar to the exoplanet population, which makes them excellent analogues but with far more telling data as their emitted light signatures are not washed out by any host star. Our team developed the first retrieval tools that enabled the extraction of temperature profiles and molecular abundances from brown dwarf spectra. This approach and subsequent results have departed from the standard decades-old inference paradigm, enabling key new insights into substellar atmospheric processes and strengthens the connection between stars, brown dwarfs, and planets.
M-Dwarf Atmospheric Properties: M-dwarfs are the most common star in our galaxy, comprising 75% of the total stars by number. M-dwarfs are also ideal targets for finding and characterizing transiting exoplanets due to the more favorable planet-to-star radius ratio. However, in order to place the properties of a planet in the appropriate context, knowledge of the basic stellar properties like radius, effective temperature, gravity, and composition are needed. Our team is developing novel methods for inferring these fundamental properties by combining state-of-the art, in house, cool stellar atmosphere models with sophisticated bayesian inference tools.
High Resolution Cross-Correlation Spectroscopy: This is an alternative approach to characterizing the atmospheres of transiting (and non transiting) planets by leveraging the large apertures and high spectral resolutions of ground based telescopes. While ground based observations typically have to contend with contamination from Earths' own atmosphere, by leveraging the orbital motion/velocity of the planet, these contaminating effects can be removed. The high spectral resolutions enable unique identification of molecular species as well as well as planetary scale winds. Our team developed breakthrough methods to extract abundances and temperature profile from these kinds of observations, opening up a frontier in characterizing the atmospheres of exoplanets from the ground.
