EXPLOSIVE VOLCANISM ON THE MOON, MERCURY AND MARS: NEW INSIGHTS FROM NEW DATA

Explosive volcanism is a critical process on the terrestrial planets because of implications for the presence of volatiles within, and outgassing of planetary interiors in space and time. Landforms and deposits provide important evidence for the recognition of the location, timing and durations of such events. New spacecraft data from missions such as Lunar Reconnaissance Orbiter, Chandrayaan-1, MESSENGER, Mars Express and Mars Reconnaissance Orbiter, have increased the spatial and spectral resolution available for the analysis of such deposits, and provided key new insights into the role of explosive volcanism in the history of the Moon, Mars and Mercury. New lunar data suggest the presence of more volatiles than previously suspected, and increased spectral resolution is providing insights into the mineralogy and mode of emplacement of pyroclastic deposits. A 154-km diameter Ionian-like pyroclastic ring around a central elongate vent structure in southern Orientale basin has been characterized and placed in the spectrum of explosive lunar volcanism, ranging from pyroclastic spatter cones to regional dark mantle deposits. Mercury, thought to be deficient in volatiles like the Moon, has recently been shown to contain an abundance of pyroclastic deposits more widespread globally than those on the Moon. Thirty-five deposits have been identified and are located principally on the floors of craters and along the edge of an impact basin. Deposit diameters, mapped to lunar gravity conditions, are larger than their lunar counterparts, implying more abundant volatiles present during typical eruptions than on the Moon. For Hawaiian-style eruptions, the volatile contents required would be much greater than previously predicted for Mercury. The role and scale of pyroclastic volcanism on Mars and its influence on climate history has been debated for years. New models for the ascent and eruption of magma leading to plininan eruptions, and the mapping of these eruptions into atmospheric general circulation models (GCMs) has led to predictions about locations, grain size distribution, accumulation rates, and volumes of pyroclastic deposits. These models suggest that the Medusae Fossae Formation may be a pyroclastic deposit derived from eruptions of Apollinaris Patera.