A tentative detection of a potentially rocky exoplanet’s atmosphere from spectral features

We are moving from an era of exoplanet discovery into an era of exoplanet characterization, but small (less than 1.5 Rearth), potentially-rocky planets orbiting bright, nearby stars that are suitable for atmospheric characterization studies are relatively scarce. Amongst these candidates for atmospheric characterization is L 98-59 c. This 1.35 Rearth planet is one of three known to orbit the bright (H = 7.4), nearby (10.6 pc), M3V star L 98-59. HST/WFC3 observed a transit of L 98-59 c and revealed the first tentative signs of an atmosphere on a predominantly-rocky exoplanet. However, this detection was of fairly low signal-to-noise, and we are pursuing the collection of additional observations. If confirmed, this first detection of an atmosphere on a potentially rocky exoplanet from spectral features would enable us to measure the chemical composition of the atmosphere. This planet could become a touchstone exoplanet for atmospheric studies and a key planet for demonstrating the precision of JWST.