Equatorial CO2 Distribution Suggests Active CO2 Supply on Europa

The James Webb Space Telescope's (JWST) observation of Europa recently revealed CO2 accumulation around geologically young chaos terrains Tara Regio and Powys Regio. The spatial heterogeneity in CO2 distribution suggests an endogenic source of CO2 in these terrains, although the timescale of CO2 supply remains uncertain. Here, we investigate CO2 distribution on Europa by conducting Monte Carlo simulations considering sublimation, ballistic transport, and loss via photoionization. With a hypothetical CO2 source at the equator, a CO2 molecule is transported to the polar regions over a timescale of similar to 10 days before being lost via photoionization. Accordingly, CO2 accumulates around the poles, with minimal CO2 around the hypothetical source under steady-state conditions. To achieve a CO2 distribution similar to that observed by the JWST, an unknown effective loss process of CO2 on Europa, >100 times faster than photoionization, would be required. Such a process may include CO2 dissociation/ionization by irradiation of high-energy particles. Since CO2 at the equatorial regions would be lost via either transport to the polar regions or dissociation/ionization within tens of days after CO2 supply, CO2 at around the equatorial regions observed by the JWST suggests its ongoing supply to the surface. Further continuous observations of Europa provide insights into the chemistry and dynamics of CO2.