Ascertain atmospheric mean molecular weight for rocky exoplanets to enable informative transit designs

Ascertain the mean molecular weight of atmospheres on rocky exoplanets to constrain expected signal amplitudes in transmission spectroscopy and to guide the design of informative transit observations.

Background

Transmission spectroscopy signal amplitudes depend strongly on atmospheric scale height, which in turn depends on mean molecular weight. Without constraints on mean molecular weight, required signal-to-noise ratios are uncertain and transit program designs may be suboptimal.

The authors highlight that this parameter is currently unknown for rocky exoplanets and that degeneracies (e.g., flat spectra caused by clouds/hazes or bare rocks) further motivate approaches that do not rely solely on transmission spectroscopy to infer atmospheric properties.