CAREER: Super-Earth or Mini-Neptune? Exploring the Mysterious Origins of the Smallest Transiting Planets

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Ongoing surveys of nearby stars have revealed a diverse array of planetary systems, many of which have characteristics that differ substantially from those of our solar system. 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 one of the most common types of extrasolar planet. We currently 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 around a rocky core. THE PI and her students will conduct a carefully-designed observational program to distinguish between these two scenarios and to measure the properties of these exoplanets. These measurements will offer key insights into the formation and migration histories of this surprising new class of planets. This program will support thesis work for two graduate students as well as a series of undergraduate summer research projects. Students will have the opportunity to observe remotely on Keck and to travel to the telescope for observing runs at Palomar.The PI and her students will combine a Keck/HIRES radial velocity campaign with Palomar transit photometry and spectroscopy in order to characterize new low-mass transiting planets and to develop improved cloud models for their atmospheres. They will use radial velocity studies to measure planetary masses, thereby constraining bulk compositions, and they will measure precise orbital ephemerides. For low-density super-Earths, they will use transmission spectroscopy to characterize the mean molecular weight of their atmosphere to distinguish between those that are water-rich and those with rocky cores surrounded by H/He envelopes. Transmission spectroscopy details can be obscured by upper-level clouds, so they will also study "cool Neptunes" in order to develop a better understanding of the cloud formation processes. These observations will utilize new capabilities for precision photometry and spectroscopy at Palomar and significantly enhance the science return from future atmospheric characterization studies with HST and JWST.