2023MNRAS.523L..86Q

The recently discovered super-Earth LP 890-9 c is an intriguing target for atmospheric studies as it transits a nearby, low-activity late-type M-dwarf star at the inner edge of the Habitable Zone. Its position at the runaway greenhouse limit makes it a natural laboratory to study the climate evolution of hot rocky planets. We present the first 3D-Global Climate Model exo-Venus model for a modern Venus-like atmosphere (92 bar surface pressure, realistic composition, and H₂SO₄ radiatively-active clouds), applied to the tidally-locked LP 890-9 c to inform observations by JWST and future instruments. If LP 890-9 c has developed into a modern exo-Venus, then the modelled temperatures suggest that H₂SO₄ clouds are possible even in the substellar region. Like on modern Venus, clouds on LP 890-9 c would create a flat spectrum. The strongest CO₂ bands in transmission predicted by our model for LP 890-9 c are about 10 ppm, challenging detection, given JWST estimated noise floor. Estimated phase curve amplitudes are 0.9 and 2.4 ppm for continuum and CO₂ bands, respectively. While pointing out the challenge to characterise modern exo-Venus analogues, these results provide new insights for JWST proposals and highlight the influence of clouds in the spectrum of hot rocky exoplanet spectra.