Dynamics and Evolution of SO2 Gas Condensation around Prometheus-like Volcanic Plumes on Io as Seen by the Near Infrared Mapping Spectrometer

✍ Scribed by Sylvain Douté; Rosaly Lopes; Lucas W. Kamp; Robert Carlson; Bernard Schmitt

• Publisher: Elsevier Science
• Year: 2002
• Tongue: English
• Weight: 861 KB
• Volume: 158
• Category: Article
• ISSN: 0019-1035
• DOI: 10.1006/icar.2002.6889

✦ Synopsis

We analyze a series of spectral image cubes acquired by the Galileo Near Infrared Mapping Spectrometer (NIMS) over the Prometheus region of Io. We use SO 2 frost, a volatile compound ubiquitous on the surface, as a tracer to understand various thermodynamic and volcanic processes acting in this equatorial region. Here we develop a new method to derive, from the 12-wavelength NIMS products, the distribution and physical properties of solid SO 2 . This method is based on the inversion of a bidirectional reflectance model on two observed spectral ratios sensitive to (1) the areal abundance of SO 2 and (2) its mean grain size. As a result, reliable and consistent maps of SO 2 abundance and granularity are obtained which can be correlated to distinguish four different physical units. The distribution of these SO 2 units indicates zones of condensation, metamorphism, and sublimation linked with the thermodynamic and volcanic processes of interest. Our maps depict equatorial plains undisturbed by any kind of vigorous volcanic activity over 35-40% of their surface. Elsewhere, 10-20% of the equatorial plains display abnormally low frost coverage which may imply the recent presence of positive thermal anomalies with temperatures in the range 110-200 K. Hot-spots such as Prometheus, Culann, Surya, and Tupan (to mention the most persistent) emit a great variety of gases, some of which will condense at Io's surface near their source regions. Associated fields of freshly condensed SO 2 are easily observed, and deposits of more refractory compounds with higher (e.g., S 8 ) or lower (e.g., NaCl) molecular weight must also be