Research Interests

Extrasolar Planets

• Habitable Zones Around Main-Sequence Stars:    (See news articles about this work)
  Most current estimates of habitable zone boundaries are derived from Kasting, Whitmire and Reynolds (1993) study, which assumed that the inner edge is limited by water loss and the outer edge is determined by the maximum greenhouse limit for a dense CO₂ atmosphere. A conservative estimate for the width of the HZ from Kasting et al.(1993) model in our own Solar system is 0.95-1.67 AU. Furthermore, this model is applicable to stars with temperatures between 3700 K and 7200 K--limits that do not include main-sequence M-dwarfs.

  In collaboration with Ramses Ramirez, we calculated new and updated HZ boundaries around stars with temperatures in the range 2600 K - 7200 K, which include FGKM spectral types. Using a 1-D radiative-convective, cloud-free climate model, our new estimates for the width of the HZ in our Solar System is 0.99-1.70 AU. Corresponding HZ boundaries for other stars can also be calculated with our model. Current ground-based surveys (e.g., the MEARTH project) and future space-based characterization missions (e.g., JWST/TPF) can use these HZ boundaries to help guide their efforts to find habitable planets around main-sequence stars.

• Exoplanet characterization from spectroscopy/photochemical modeling: I have developed a 1-D photochemical model applicable to hot jupiter atmospheres. We initially applied our photochemical model to one of the hottest known exoplanet, WASP-12b. This planet is found to have carbon to oxygen ratio (C/O) greater 1 (Madhusudhan et al. (2011)). Results from our model confirmed this observation, but also indicated that acetylene is the major absorber in the atmosphere of WASP-12b and the absorption features detected near 1.6 and 8 micron may be arising from acetylene rather than methane, as proposed by the original discovery paper.
• Planetary architecture and Dynamical stability of extrasolar planets in and around the habitable zone of their host stars. Many extra-solar planetary systems discovered to-date are in wide variety of configurations. How do these planetary system architectures affect the dynamical stability of terrestrial mass planets in the habitable zone ? Which systems are best suited for further scrutiny in the search for habitable planets ? What external factors (eccentricity and obliquity variation, companion perturbation etc.) affect the habitability of a terrestrial planet ? I work on these questions in collaboration with Rory Barnes and Sean Raymond.