LHS 1140 b is a potentially habitable water world

LHS 1140 b is a temperate planet orbiting in the habitable zone of its M4.5V dwarf host. Recently, it has been the object of multiple re-visits which have refined the nature of the planet. In particular, new ground observations have refined the LHS 1140 b mass, placing the planet as a potential habitable water world. With the existence of an atmosphere on TRAPPIST-1 planets called into question, LHS 1140 b may well present the best current opportunity to detect and characterize a habitable world. In this work, we present the data analysis and interpretation of JWST data between 1.7 and 5.2 μm using NIRSpec. By using Bayesian statistics and our self-consistent models, we calculated that the resulting 1D transmission spectrum is not consistent with a H2-dominated atmosphere with other gases as active absorbers. Although the retrieval process suggested the possibility of a H2 atmosphere with H2O and high clouds with ∼ 2σ confidence over a flat spectrum, our self-consistent models excluded this possibility as it is not physically admissible. Instead, the data favors an heavier envelope (possibly N2-dominated atmosphere) with >3σ confidence. Our models suggest the possibility tomeasure CO2 absorption features with an expected signal of 20ppm at 4.2μm. Based on our findings, further observations are strongly encourage as unveiling the nature of LHS 1140 b presents the rare opportunity to greatly expand our knowledge of temperate habitable alien worlds.