Publications

Abstract Theoretical consideration of the magma vesiculation process under observed and inferred venusian surface conditions suggests that vesicles should form in basaltic melts, especially if CO 2 is the primary magmatic volatile. However, the high surface atmospheric pressure ((∼90 bars) and density on Venus retard bubble coalescence and disruption sufficiently to make explosive volcanism unlikely. The products of explosive volcanism (fire fountains, convecting eruption clouds, pyroclastic flows, and topography-mantling deposits of ash, spatter, and scoria) should be rare on Venus, and effusive eruptions should dominate. The volume fraction of vesicles in basaltic rocks on Venus are predicted to be less than in chemically similar rocks on Earth. Detection of pyroclastic landforms or eruption products on Venus would indicate either abnormally high volatile contents of Venus magmas (2.5–4 wt%) or different environmental conditions (e.g., lower atmospheric pressure) in previous geologic history.

The origins of the surficial materials in the geologic units surrounding the Martian southern polar region have been poorly constrained on the basis of pre‐Mars Global Surveyor (MGS) data and studies. MGS studies suggest that these units are the remnant of volatile loss from an originally massive volatile‐rich debris blanket or the result of fluidized slurries resulting from magma/volatile interactions or impact shaking. We use Mars Orbiter Laser Altimeter data to examine a region adjacent to the south polar layered terrain at 72°–79°S and 230°–275°E, generally equivalent to the mapped Parva member of the Dorsa Argentea Formation (DAF). The pedestal and “ghost” impact crater morphologies in this area suggest that extensive deposits of loosely consolidated materials have been removed from this region. The Parva member is thus likely to be the remaining debris blanket from the deflated remnant of an unprotected deposit that was originally similar to the buried DAF deposits in the adjacent Cavi member. Crater counts indicate that the Parva member is of Hesperian age and overlies an older Noachian surface, likely the highland cratered terrain (Npl 1 ). If regional deflation began in the Hesperian and continues through today, the region has been exposed to erosion rates of 1.3–1.6 × 10 −7 m/yr. However, if deflation started later than the assumed times or ceased in the Amazonian, when deposition of the polar layered deposits began, erosion rates as high as 2.–5.2 × 10 −7 m/yr might have existed. These erosion rates are within the range of published Martian nonbedrock erosion rates of 10 −8 –10 −5 m/yr.

This study is a continuation of a preliminary assessment of latitude-dependent impact crater morphologies in Mars.

The recently selected missions to Venus have opened a new era for the exploration of this planet. These missions will provide information about the chemistry of the atmosphere, the geomorphology, local-to-regional surface composition, and the rheology of the interior. One key scientific question to be addressed by these future missions is whether Venus remains volcanically active, and if so, how its volcanism is currently evolving. Hence, it is fundamental to analyze appropriate terrestrial analog sites for the study of possibly active volcanism on Venus. To this regard, we propose Mount Etna - one of the most active and monitored volcanoes on Earth - as a suitable terrestrial laboratory for remote and in-situ investigations to be performed by future missions to Venus. Being characterized by both effusive and explosive volcanic products, Mount Etna offers the opportunity to analyze multiple eruptive styles, both monitoring active volcanism and identifying the possible occurrence of pyroclastic activity on Venus. We directly compare Mount Etna with Idunn Mons, one of the most promising potentially active volcanoes of Venus. Despite the two structures show a different topography, they also show some interesting points of comparison, and in particular: a) comparable morpho-structural setting, since both volcanoes interact with a rift zone, and b) morphologically similar volcanic fields around both Mount Etna and Idunn Mons. Given its ease of access, we also propose Mount Etna as an analog site for laboratory spectroscopic studies to identify the signatures of unaltered volcanic deposits on Venus.

Our knowledge of the age of the layered polar deposits and their activity in the volatile cycling and climate history of Mars is based to a large extent on their apparent ages as determined from crater counts. Interpretation of the polar stratigraphy (in terms of climate change) is complicated by reported differences in the ages of the northern and southern layered deposits. The north polar residual ice deposits are thought to be relatively young, based on the reported lack of any fresh impact craters in Viking Orbiter Images. Herkenhoff et al., report no craters at all on the North polar layered deposits or ice cap, and placed an upper bound on the surface age (or, alternatively, the vertical resurfacing rate) of 100 thousand years to 10 million years, suggesting that the north polar region is an active resurfacing site. In contrast, the southern polar region was found to have at least 15 impact craters in the layered deposits and cap. Plaut et al, concluded that the surface was less than or = 120 million years old. This reported age difference factor of 100 to 1000 increases complexity in climate and volatile modeling. Recent MOLA results for the topography of the northern polar cap document a handful or more of possible craters, which could result in revised age or resurfacing estimates for the northern cap. This study is a preliminary look at putative craters in both polar caps. Additional information is contained in the original extended abstract.