A search for water vapor plumes on Europa by spatially resolved spectroscopic observation using Subaru/IRCS.

This article focuses on a spatially resolved search for water plumes on Europa using near-infrared high-dispersion spectroscopy with the Infrared Camera and Spectrograph (IRCS) on the Subaru Telescope. The observations, conducted in July 2021, found no direct evidence of water emission, setting upper limits on water vapor column densities between 9.46 × 10¹⁹ and 5.92 × 10²⁰ molecules m⁻² in divided slit areas and 4.61 × 10¹⁹ molecules m⁻² over the entire observed region, assuming a rotational temperature of 50 K. These limits are more sensitive than previous ultraviolet observations by the Hubble Space Telescope but less sensitive than those from the Keck telescope and the James Webb Space Telescope. The study highlights the sporadic and localized nature of Europa’s plume activity and underscores the importance of continued spatially and temporally diverse observations to better characterize plume sources and their variability.