The Atmospheric Composition of the Rocky Super-Earth GJ 1132b - No Evidence for a H/He-rich Atmosphere

If the terrestrial worlds of our own Solar System are any indicator, atmospheres of rocky exoplanets are likely to be diverse and complicated. Characterizing them will contribute new insights into their formational and evolutionary histories, yield a better understanding of the stellar environment that shapes their atmospheres, and even possibly assess their potential habitability. Rocky planets around M dwarfs provide the most tantalizing targets in part because their large planet-to-star radius ratios produce the most accessible signals for transmission spectroscopy. Here we use the Hubble Space Telescope’s Wide Field Camera 3 to study the transmission spectrum of the rocky super-Earth GJ 1132b. Orbiting a nearby mid-M dwarf, GJ 1132b receives 19x more bolometric flux than Earth, making it an important test case for whether planets at such high irradiation can maintain atmospheres. We measure a featureless spectrum between 1.1 to 1.7 microns given the 34 ppm precision of the data. We discuss our methods and what our results mean for GJ 1132b’s atmospheric composition. We also detail our probabilistic approach for approximating starspot size, coverage, and contamination in the transmission spectrum. Both our atmospheric and starspot results provide useful context for interpreting future planned JWST observations of GJ 1132b at higher precision and resolution.