Sara Seager comes to Carnegie from the Institute for Advanced Study in Princeton, where she was a longterm member and a Keck Fellow.

This artist’s conception of an extrasolar planet shows a view from a close-in extrasolar giant planet looking toward the Sun-like parent star. The colors or banded structures of extrasolar giant planets are not yet known, but Seager’s models, used to predict and interpret observations, are working toward this goal.

(Illustration courtesy Lynnette Cook.)

A decade ago, few scientists imagined that it would become almost commonplace to find planets orbiting nearby stars. To learn more about the physical characteristics of these objects, Sara Seager searches for transiting extrasolar planets and models extrasolar planet atmospheres. One extrasolar giant planet transits its parent star every 3.5 days. As it passes in front of the star, the star’s light dims by the ratio of the planet-to-star areas, allowing a measurement of the planet’s radius. The radius gives modelers, such as Seager, information on the planet’s evolution, composition, atmosphere, and interior properties. With postdoctoral fellow Kaspar von Braun and colleague Gabriela Mallén-Ornelas, Seager is leading a search for more of these objects by monitoring tens to hundreds of thousands of stars simultaneously. Using several telescopes, including Carnegie’s Swope telescope, she investigates field stars and open star clusters to find short-period planets by identifying their characteristic dips in brightness.

Extrasolar giant planets orbiting very close to their parent stars are called close-in extrasolar giant planets (CEGPs). They cannot be spatially separated from their stars, but because of their proximity to them, they are very hot and possibly very bright in reflected light. The combined planet and starlight is being used to characterize the planets’ atmospheres. Seager models these atmospheres, and her models are used by observational astronomers to design experiments to make specific measurements. Her work can predict atmospheric signatures and was used for the first successful detection of an extrasolar planet atmosphere in November 2001. Seager is working on models to help interpret observational results.

Seager’s interest extends to finding and characterizing Earth-like extrasolar planets. Of particular interest is detecting atmospheres with severe chemical disequilibrium and specific chemical species that are indicative of habitable conditions. Because the parent star is millions to billions times brighter than the planet, these objects are very difficult to detect and study. Around the year 2015, NASA is planning to launch the Terrestrial Planet Finder mission for this effort. Seager is working on atmospheric models to help determine the mission goals, the instrument design, and the best wavelengths for study.

Seager also studies cosmology. She investigates the early universe when electrons and protons combined to form hydrogen and helium during the “recombination epoch,” some 300,000 years after the Big Bang. This era—when photons last interacted with matter—is seen today as the cosmic background radiation. In 2000 Seager and colleagues published a paper on this subject that has become the new standard for this research.