Spectroscopic mapping of Io's surface with HST/STIS: SO$_2$ frost, sulfur allotropes, and large-scale compositional patterns

TL;DR

This study uses HST UV-visible spectroscopy to map Io's surface, revealing extensive SO$_2$ frost, sulfur plains, and sulfur allotropes, advancing understanding of its volcanic surface chemistry and spatial patterns.

Contribution

It provides the first global, spatially resolved spectral maps of Io's surface, linking spectral features to surface composition and processes.

Findings

Extensive stable SO$_2$ frost deposits at the equator.

Widespread sulfur-rich plains around SO$_2$ deposits.

Presence of metastable sulfur allotropes in high-latitude regions.

Abstract

Io's intense volcanic activity results in one of the most colorful surfaces in the solar system. Ultraviolet and visible-wavelength observations of Io are critical to uncovering the chemistry behind its volcanic hues. Here, we present global, spatially resolved UV-visible spectra of Io from the Space Telescope Imaging Spectrograph on the Hubble Space Telescope (HST), which bridge the gap between previous highly resolved imagery and disk-integrated spectroscopy, to provide an unprecedented combination of spatial and spectral detail. We use this comprehensive dataset to investigate spectral endmembers, map observed spectral features associated with SO$_2$ frost and other sulfur species, and explore possible compositions in the context of Io surface processes. In agreement with past observations, our results are consistent with extensive equatorial SO$_2$ frost deposits that are stable over multi-decade timescales, widespread sulfur-rich plains surrounding the SO$_2$ deposits, and the enrichment of Pele's pyroclastic ring and the high-latitude regions in metastable short-chain sulfur allotropes.