100 research outputs found
Geoscientific mapping of Vesta by the Dawn mission
The geologic objectives of the Dawn Mission [1] are to derive Vestaâs shape, map the surface geology, understand the geological context and contribute to the determination of the asteroidsâ origin and evolution. Geomorphology and distribution of surface features will provide evidence for impact cratering, tectonic activity, volcanism, and regolith processes. Spectral measurements of the surface will provide evidence of the compositional characteristics of geological units. Age information, as derived from crater size-frequency distributions, provides the stratigraphic context for the structural and compositional mapping results into the stratigraphic context and thus revealing the geologic history of Vesta
Recommended from our members
Evaluating alternative responses to safeguards alarms
This paper describes a quantitative approach to help evaluate and respond to safeguards alarms. These alarms may be generated internally by a facility's safeguards systems or externally by individuals claiming to have stolen special nuclear material (SNM). This approach can be used to identify the most likely cause of an alarm - theft, hoax, or error - and to evaluate alternative responses to alarms. Possible responses include conducting investigations, initiating measures to recover stolen SNM, and replying to external threats. Based on the results of each alarm investigation step, the evaluation revises the likelihoods of possible causes of an alarm, and uses this information to determine the optimal sequence of further responses. The choice of an optimal sequence of responses takes into consideration the costs and benefits of successful thefts or hoaxes. These results provide an analytical basis for setting priorities and developing contingency plans for responding to safeguards alarms
The geological nature of dark material on Vesta and implications for the subsurface structure
Abstract Deposits of dark material appear on Vestaâs surface as features of relatively low-albedo in the visible wavelength range of Dawnâs camera and spectrometer. Mixed with the regolith and partially excavated by younger impacts, the material is exposed as individual layered outcrops in crater walls or ejecta patches, having been uncovered and broken up by the impact. Dark fans on crater walls and dark deposits on crater floors are the result of gravity-driven mass wasting triggered by steep slopes and impact seismicity. The fact that dark material is mixed with impact ejecta indicates that it has been processed together with the ejected material. Some small craters display continuous dark ejecta similar to lunar dark-halo impact craters, indicating that the impact excavated the material from beneath a higher-albedo surface. The asymmetric distribution of dark material in impact craters and ejecta suggests non-continuous distribution in the local subsurface. Some positive-relief dark edifices appear to be impact-sculpted hills with dark material distributed over the hill slopes. Dark features inside and outside of craters are in some places arranged as linear outcrops along scarps or as dark streaks perpendicular to the local topography. The spectral characteristics of the dark material resemble that of Vestaâs regolith. Dark material is distributed unevenly across Vestaâs surface with clusters of all types of dark material exposures. On a local scale, some craters expose or are associated with dark material, while others in the immediate vicinity do not show evidence for dark material. While the variety of surface exposures of dark material and their different geological correlations with surface features, as well as their uneven distribution, indicate a globally inhomogeneous distribution in the subsurface, the dark material seems to be correlated with the rim and ejecta of the older Veneneia south polar basin structure. The origin of the dark material is still being debated, however, the geological analysis suggests that it is exogenic, from carbon-rich low-velocity impactors, rather than endogenic, from freshly exposed mafic material or melt, exposed or created by impacts
Geologic mapping of the AV-11 Pinaria quadrangle of asteroid 4 Vesta
NASAâs Dawn spacecraft entered orbit of the inner main belt asteroid â4Vestaâ in July 2011, and is spending one year in orbit to characterize its geology, elemental and mineralogical composition, topography, shape, and internal structure before departing to asteroid â1Ceresâ in late 2012. As part of the Dawn data analysis the Science Team is conducting geologic mapping of the surface, in the form of 15 quadrangle maps. This abstract describes the results from mapping quadrangle Av-11 (Pinaria)
- âŠ