Our capacity to search for life on other worlds is rapidly advancing, both within our solar system and beyond. In the last few decades robotic missions have explored every major target of astrobiological interest in our solar system, collecting data relevant to assessing habitability across diverse environments, from rocky planets to icy satellites. Outside our solar system, we have now identified thousands of worlds orbiting other stars, many of which may be habitable, suggesting there are many places beyond our solar system where life could, at least in principle, emerge and persist. The next challenge in advancing the search for…
Exoplanet atmosphere spectroscopy enables us to improve our understanding of exoplanets just as remote sensing in our own solar system has increased our understanding of the solar system bodies. The challenge is to quantitatively determine the range of temperatures and molecular abundances allowed by the data, which is often difficult given the low information content of most exoplanet spectra that commonly leads to degeneracies in the interpretation. A variety of spectral retrieval approaches have been applied to exoplanet spectra, but no previous investigations have sought to compare these approaches. We compare three different retrieval methods: optimal estimation, differential evolution
We here report WFC3 spectroscopy of the giant planets HD209458b and XO-1b in transit, using spatial scanning mode for maximum photon-collecting efficiency. We introduce an analysis technique that derives the exoplanetary transmission spectrum without the necessity of explicitly decorrelating instrumental effects, and achieves nearly photon-limited precision even at the high flux levels collected in spatial scan mode. Our errors are within 6-percent (XO-1) and 26-percent (HD209458b) of the photon-limit at a spectral resolving power of 70, and are better than 0.01-percent per spectral channel.