  The recently discovered transiting super-Earth LP 890-9 c is potentially one
of the best rocky exoplanets for atmospheric characterization. Orbiting an
ultracool M-dwarf at the inner edge of the habitable zone, LP 890-9 c offers a
new opportunity to study the climate of rocky planets at the inner edge of the
habitable zone. We investigate the molecular detectability with simulated JWST
transmission spectra for five potential atmospheres of LP 890-9 c. We find that
a small three-transit JWST program can infer evidence of H2O (at 3$\sigma$
confidence) for a full runaway greenhouse scenario. Alternatively,
CO2-dominated atmospheres resembling Venus without high-altitude terminator
clouds can be identified with eight transits. However, these predictions could
be complicated by the impact of clouds and/or unocculted starspots.
Nevertheless, JWST observations of LP 890-9 c could provide critical insights
and potentially distinguish between models of rocky planets at the inner edge
of the habitable zone.
