Program: GN-2015B-DD-3

Recent surveys have revealed an extraordinary and unexplained diversity of low−mass exoplanets. Of particular interest are small planets transiting small stars because of the higher signal-to-noise ratio of the transits. Previous spectroscopic observations of the atmospheres of small exoplanets around M dwarfs have resulted in featureless spectra, suggesting the presence of clouds. The infrared transmission spectrum of GJ 3470b, a warm Neptune-size planet transiting an M dwarf, appears flat as well, but broadband observations indicate a larger-than-expected scattering feature in its visible spectrum. This result constitutes a detection of clouds in the atmosphere of GJ 3470b, but existing observations are not sufficiently precise to constrain the composition of the scattering particles. We propose to obtain GMOS-N visible transmission spectroscopy during four GJ 3470b transits in order to better measure the slope of the scattering signature and constrain for the first time the size of the particles that make up the clouds in this sub-jovian planet's atmosphere. These observations will bring us closer to understanding the nature of increasingly smaller planets by making use of an approach which will prove especially useful for exoplanets that exhibit featureless transmission spectra at longer wavelengths.