Global Mapping of HCl on Mars by IRTF/iSHELL

Abstract

Abstract Hydrogen chloride (HCl)—a key marker of the chlorine cycle on Mars—has been recently discovered in the Martian atmosphere by the ExoMars/TGO mission. In-orbit data indicate that this molecule appears in the atmosphere only in a limited time period and specifically in the southern summer season. A snapshot global mapping of HCl is indispensable to examine its sources and sinks, but such observations are not currently possible from any orbiters. Here, we present the first spatially resolved map of HCl obtained with the ground-based NASA InfraRed Telescope Facility. We find clear features of HCl, demonstrating that HCl is present close to the surface. HCl is detected in the equatorial region for the first time, revealing that HCl is widely distributed on Mars. However, the spatial distribution of HCl is not uniform, and it is enhanced in the southern polar region. Interestingly, this nonuniform spatial distribution of HCl column abundance is strikingly similar to that of water vapor column abundance. This highlights the important role of water vapor in the evolution of HCl through the atmosphere, as previously noted, and suggests its potential involvement in the atmospheric chlorine source processes.