Hubble WFC3 Spectroscopy of the Habitable-zone Super-Earth LHS 1140 b

TL;DR

This study presents the transmission spectrum of the temperate Super-Earth LHS 1140b using HST, showing tentative water detection but with low significance and potential stellar contamination, highlighting the need for future JWST observations.

Contribution

First transmission spectrum of LHS 1140b with HST, demonstrating challenges in atmospheric detection due to noise and stellar contamination.

Findings

Tentative water detection in LHS 1140b's atmosphere.

Stellar contamination models can mimic or obscure atmospheric signals.

Future JWST observations are needed for confirmation.

Abstract

Atmospheric characterisation of temperate, rocky planets is the holy grail of exoplanet studies. These worlds are at the limits of our capabilities with current instrumentation in transmission spectroscopy and challenge our state-of-the-art statistical techniques. Here we present the transmission spectrum of the temperate Super-Earth LHS 1140b using the Hubble Space Telescope (HST). The Wide Field Camera 3 (WFC3) G141 grism data of this habitable zone (T$_{\rm{eq}}$ = 235 K) Super-Earth (R = 1.7 $R_\oplus$), shows tentative evidence of water. However, the signal-to-noise ratio, and thus the significance of the detection, is low and stellar contamination models can cause modulation over the spectral band probed. We attempt to correct for contamination using these models and find that, while many still lead to evidence for water, some could provide reasonable fits to the data without the need for molecular absorption although most of these cause also features in the visible ground-based data which are nonphysical. Future observations with the James Webb Space Telescope (JWST) would be capable of confirming, or refuting, this atmospheric detection.