Little has been measured for any extrasolar planet except (usually minimum) mass, (rarely) radius, and heating. The "hot Jupiter" extrasolar planets found were entirely unpredicted and may be a new class of giant planet distinct from Jupiters and Neptunes. Models indicate that the planet around the star HD 209458 formed hot, but there are no entirely consistent scenarios for how it formed. Measuring chemical abundances, cloud locations, and the temperature of even one planet would guide modeling efforts that are now almost unconstrained. The investigators are developing a new technique for analyzing extrasolar planet transit spectra, and will apply it to their observations of the transiting extrasolar planet HD 209458b. They observed this system successfully on 16 nights at four observatories. The data span a wide range in the infrared. a region rich in molecular absorptions from water, methane, and carbon monoxide. In transit, the planet's atmosphere should modulate the stellar spectrum by a part in a thousand, providing a way to measure this "hot Jupiter" planet directly. Only novel techniques can detect such a weak signal from the ground. The investigators' abundant and high-quality data enable a better approach, based on principal components analysis, that can derive the transit modulation independently of a model since the planetary signature should turn on and off at the start and end of the transit.
Broader Impact: The public is interested in water on other planets (even water vapor on hot Jupiters), because of the connection with life and habitable planets. The project is compelling enough that lay people tend to be interested in learning how the spectroscopy works, so it is a useful educational example. The data are so exhaustive that either success or failure will provide valuable lessons for space-based extrasolar planetary science.
