Coronae on Venus observations and models of origin

The Venera 15/16 spacecraft revealed a number of features of unknown origin including coronae, elongate to circular structures with a complex interior surrounded by an annulus of concentric ridges. Eighteen coronae were identified in Venera 15/16 data of Venus; an additional thirteen possible coronae are found in Pioneer Venus and Arecibo data. Coronae, with maximum widths of 160 to over 650 km, are found primarily in two clusters in the Northern Hemisphere located to the east and west of Ishtar Terra. Another possible cluster is located in Themis Regio in the Southern Hemisphere. The majority of coronae are at least partially raised less than 1.5 km above the surrounding region, and over half are partially surrounded by a peripheral trough. A sequence of events for coronae has been determined through mapping. Prior to corona formation, regional compression or extension creates bands of lineaments along which coronae tend to later form. During the early stages of corona formation, relatively raised topography is produced by uplift and volcanic construction. The evolution of coronae and their general characteristics have been compared to two models of corona origin: hotspots and sinking mantle diapirs. In the hotspot or rising mantle diapir model, heating and melting at depth create uplift at the surface. Uplift is accompanied by central extension, facilitating volcanism. Gravitational relaxation of the uplifted region follows producing the compressional features within the annulus and the peripheral trough. Both models can predict the major characteristics and evolutionary sequence of coronae. The sinking diapir model does predict an early-time low and central compression as well as broadening and shallowing of the peripheral trough with time, all of which are not observed at current data resolution. In addition, the sinking mantle diapir mode predicts more simultaneous formation of the high topography, annulus and trough unlike the hotspot or rising mantle diapir mode. High resolution Magellan data will be used to distinguish between the two models of corona origin

EXPERIMENTAL INVESTIGATION OF THE SLOSH-DAMPING EFFECTIVENESS OF POSITIVE-EXPULSION BAGS AND DIAPHRAGMS IN SPHERICAL TANKS

Slosh damping effectiveness of positive expulsion bags and diaphragms in spherical tank

Experimental investigation of liquid sloshing in a scale-model Centaur liquid-hydrogen tank

Liquid sloshing in scale model Centaur liquid hydrogen tan

Phytoplankton Sampling in Quantitative Baseline and Monitoring Programs

An overview of phytoplankton sampling and analysis methods as they apply to quantitative baseline and monitoring surveys is provided. A need for inclusion of a preliminary field survey of the area under investigation and of flexibility in sampling design is stressed. An extensive bibliography pertinent to phytoplankton sampling and analysis is included in the report

Geologic Mapping of V-19

A geologic map of the Sedna Planitia (V-19) quadrangle is being completed at the 1:5,000,000 scale as part of the NASA Planetary Geologic Mapping Program, and will be submitted for review by September 2009

Morphology and models for the evolution of eastern Hecate Chasma, Venus

Hecate Chasma is a deep trough characterized by a chain-like concentration of coronae and corona-like features trending approximately southwest-northeast between approximately 200 and 260 degrees east longitude (terminating at Beta Regio). The section of Hecate in which we have concentrated our study is centered at 15N, 249, where the trough is especially well-defined. Nearby, a smaller chain of eight coronae lies along a minor trough parallel to the general trend of the greater chain. The trough itself is unusual in this area because it has a highly asymmetric profile. Using Magellan radar and topography data, we have examined the morphology of this area in order to assess the tectonic and volcanic history of the area. After examining the most important types of features (linear, arcuate and circular) in eastern Hecate, we present two possible models of origin. A companion abstract presents an overview of the Hecate and Parga linear deformation zones

Geologic Mapping of V-19

A geologic map of the Sedna Planitia (V-19) quadrangle is being completed at 1:5,000,000 scale as part of the NASA Planetary Geologic Mapping Program, and will be submitted for review by September 2010. Overview: The Sedna Planitia quadrangle (V-19) extends from 25 N - 50 N latitude, 330 - 0 longitude. The quadrangle contains the northernmost portion of western Eistla Regio and the Sedna Planitia lowlands. Sedna Planitia consists of low-lying plains units, with numerous small volcanic edifices including shields, domes and cones. The quadrangle also contains several tholi, the large flowfield Neago Fluctus, the Manzan-Gurme Tesserae, and Zorile Dorsa and Karra-mahte Fossae which run NW-SE through the southwestern part of the quadrangle. There are six coronae in the quadrangle (Table 1), the largest of which is Nissaba (300 km x 220 km), and there are fourteen impact craters (Table 2). The V-19 quadrangle contains a variety of mappable volcanic landforms including two shield volcanoes (Evaki Tholus and Toci Tholus) and the southern portion of a large flow field (Neago Fluctus). A total of sixteen units associated with volcanoes have been mapped in this quadrangle, with multiple units mapped at Sif Mons, Sachs Patera and Neago Fluctus. An oddly textured, radarbright flow is also mapped in the Sedna plains, which appears to have originated from a several hundred kilometer long fissure. The six coronae within V-19 have a total of eighteen associated flow units. Several edifice fields are also mapped, in which the small volcanic edifices both predate and postdate the other units. Impact crater materials are also mapped

Geologic Mapping of V-19, V-28, and V-53

The Sedna Planitia Quadrangle (V-19) extend from 25 deg N - 50 deg N latitude, 330 deg - 0 deg longitude. The quadrangle contains the northern-most portion of western Eistla Regio and the Sedna Planitia lowlands. Geologic maps of Sedna Planitia (V-199), Hecate Chasma (V-28) quadrangles have been completed at the 1:5,000,000 scale as part of the NASA Planetary Geologic Mapping Program. All quadrangles (V-53, V-28 and V-19) have been reviewed at lease once and will be resubmitted. In V-28 and V-53, more plains materials units have been mapped than in previously mapped quadrangles V-46 and V-39. V-19 is more comparable to these latter maps in terms of numbers of plains units. In V-28, all of the plains materials units to the south of the rift have an unusually high concentration of volcanic edifices, which both predate and postdate the units. A similar situation is seen in V-53 and V-19, where small edifice formation is not confined to any specific time period. In the two chasma-related quadrangles, coronae are located along the rift, as well as to the north and the south of the rifts. Coronae in both quadrangles exhibit all forms of corona topographic shapes, including depressions, rimmed depressions, plateaus and domes. In V-28 and V-53, some coronae along the rift do not have much associated volcanism; coronae with the most volcanism in these quadrangles are located at least 500 km off the rifts or on the Themis Regio highland. All three quadrangles have very horizontal stratigraphic columns, as limited contact between units prevents clear age determinations. While this results in the appearance that all units formed at the same time, the use of hachured columns for each unit illustrates the limited nature of our stratigraphic knowledge in these quadrangles, allowing for numerous possible geologic histories. The scale of resurfacing in these quadrangles is on the scale of 100s of kilometers, consistent with the fact that they lie in the most volcanic region of Venus

Characterizing Volcanic Eruptions on Venus: Some Realistic (?) Scenarios

When Pioneer Venus arrived at Venus in 1978, it detected anomalously high concentrations of SO2 at the top of the troposphere, which subsequently declined over the next five years. This decline in SO2 was linked to some sort of dynamic process, possibly a volcanic eruption. Observations of SO2 variability have persisted since Pioneer Venus. More recently, scientists from the Venus Express mission announced that the SPICAV (Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus) instrument had measured varying amounts of SO2 in the upper atmosphere; VIRTIS (Visible and Infrared Thermal Imaging Spectrometer) measured no similar variations in the lower atmosphere (ESA, 4 April, 2008). In addition, Fegley and Prinn stated that venusian volcanoes must replenish SO2 to the atmosphere, or it would react with calcite and disappear within 1.9 my. Fegley and Tremain suggested an eruption rate on the order of approx 1 cubic km/year to maintain atmospheric SO2; Bullock and Grinspoon posit that volcanism must have occurred within the last 20-50 my to maintain the sulfuric acid/water clouds on Venus. The abundance of volcanic deposits on Venus and the likely thermal history of the planet suggest that it is still geologically active, although at rates lower than Earth. Current estimates of resurfacing rates range from approx 0.01 cubic km/yr to approx 2 cubic km/yr. Demonstrating definitively that Venus is still volcanically active, and at what rate, would help to constrain models of evolution of the surface and interior, and help to focus future exploration of Venus