Upper left: transmission spectrum from the WFC3 G141 data of LHS 1140b analyzed here (black) with various forward models overplotted. The best-fit solution from an atmospheric retrieval favors the presence of a clear, H/He atmosphere with water (blue). Lower left: simulated final spectrum (black) when the current data is combined with two further HST WFC3 G141 observations, increasing the ability to confirm the presence of water. Upper right: expected data from JWST NIRISS GR700XD which suggests that these observations could provide a definitive answer to the question: does LHS 1140b have a clear, H/He-dominated atmosphere? Lower right: transit light source models for the JWST data which are heavily intertwined with the atmospheric signal, highlighting the importance of understanding this effect in the JWST era.