Modelling the atmosphere of lava planet K2-141b: implications for low and high resolution spectroscopy

TL;DR

This study models the atmospheres of lava planets like K2-141b, comparing different atmospheric compositions and their observability, revealing that SiO$_2$ atmospheres are more detectable despite lower vapor pressure.

Contribution

The paper provides the first detailed simulations of lava planet atmospheres, analyzing how different compositions affect observability and atmospheric dynamics.

Findings

SiO$_2$ atmospheres are easier to observe via transit spectroscopy.

Na atmospheres are less sustainable due to higher surface flow rates.

High radial velocities facilitate high dispersion spectroscopy observations.

Abstract

Transit searches have uncovered Earth-size planets orbiting so close to their host star that their surface should be molten, so-called lava planets. We present idealized simulations of the atmosphere of lava planet K2-141b and calculate the return flow of material via circulation in the magma ocean. We then compare how pure Na, SiO, or SiO$_2$ atmospheres would impact future observations. The more volatile Na atmosphere is thickest followed by SiO and SiO$_2$, as expected. Despite its low vapour pressure, we find that a SiO$_2$ atmosphere is easier to observe via transit spectroscopy due to its greater scale height near the day-night terminator and the planetary radial velocity and acceleration are very high, facilitating high dispersion spectroscopy. The special geometry that arises from very small orbits allows for a wide range of limb observations for K2-141b. After determining the magma ocean depth, we infer that the ocean circulation required for SiO steady-state flow is only $10^{-4}$ m/s while the equivalent return flow for Na is several orders of magnitude greater. This suggests that a steady-state Na atmosphere cannot be sustained and that the surface will evolve over time.