My research in extrasolar planets includes studies of the long-term stability of resonant systems, the observable consequences of planet formation models, and the use of transit timing to infer the presence of secondary planets in transiting planetary systems. I helped develop this new planet detection technique (Transit Timing Variations or TTV) and was the first to apply it to transit data. In particular data for the TrES-1 and the HD 209458 systems. In those studies we showed that this technique can be sensitive to Earth-mass planets in orbit about a Sun-like star using only modest, ground-based telescopes (see below). I am also a participating scientist for NASA's Kepler mission, where I chair the working group that analyzes the transit times of the planetary systems discovered by Kepler to probe for additional, unseen planets. Our group has published several papers on multiple planet systems and, in a four month span, made the cover of both Science and Nature (with Kepler-9 and Kepler-11 respectively).

I also authored a paper with Dan Hooper on the possibility of heating a planet through the annihilations of dark matter particles in its interior.