Detectability of oxygen fugacity regimes in the magma ocean world 55 Cancri e at high spectral resolution

ABSTRACT Ultra-short-period exoplanets such as 55 Cancri e (55 Cnc e), hosting dayside magma oceans, present unique opportunities to study surface-atmosphere interactions. The composition of a vaporized mineral atmosphere enveloping the dayside is dictated by that of the surface magma ocean, which in turn is sensitive to its oxygen fugacity (fO$_2$). Observability estimations and characterization of the atmospheric emission of 55 Cnc e have mostly remained limited to low spectral resolution space-based studies. Here, we aim to examine ground-based high-resolution observabilities of a diverse set of mineral atmospheres produced across a grid of mantle fO$_2$s varying over 12 orders of magnitude. We assume a bulk silicate Earth mantle composition and a substellar dayside temperature of T = 2500 K in the near-infrared wavelength region. This spectral range is often featureless for this class of atmospheres at low resolution. Coupling our newly developed simulator for synthesizing realistic observations from high-resolution ground-based spectrographs (Ratri) to a pre-developed high-resolution cross-correlation spectroscopy (HRCCS) analysis pipeline (Upamana), we find that this array of mineral atmospheres would all be detectable with 11 h of observing time of the dayside of 55 Cnc e with CARMENES and each individual scenario can be correctly differentiated within 1$\sigma$. Our analysis is readily able to distinguish between a planet with an Earth-like redox state (with fO$_2$ $\sim$ 3.5 log$_{10}$ units above the iron-wüstite, IW buffer) and a Mercury-like planet (fO$_2$ $\sim$ 5 log$_{10}$ units below IW). We thus conclude that the HRCCS technique holds promise for cataloguing the diversity of redox states among the rocky exoplanetary population.