Mapping Vesta: First Results from Dawn’s Survey Orbit

The geologic objectives of the Dawn Mission [1] are to derive Vesta’s shape, map the surface geology, understand the geological context and contribute to the determination of the asteroids’ 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 sizefrequency distributions, provides the stratigraphic context for the structural and compositional mapping results, thus revealing the geologic history of Vesta. We present here the first results of the Dawn mission from data collected during the approach to Vesta, and its first discrete orbit phase – the Survey Orbit, which lasts 21 days after the spacecraft had established a circular polar orbit at a radius of ~3000 km with a beta angle of 10°-15°

Dark Material On Vesta: Synthesis And Interpretations From Dawn Observations

Unusual deposits of “Dark Material” (DM) on Vesta’s surface were recently discovered by the Dawn Mission [1,2]. A focused study of these deposits is underway within the Dawn team and the three preceeding presentations in this session [3,4,5] treat different aspects (geological, morphological and compositional) of the Dawn observations analysis. This report is a synthesis of these findings, presents some further analysis and interprets them in terms of origin( s) and processes

The epidemiology of ovine toxoplasmosis. III. Observations on outbreaks of clinical toxoplasmosis in relation to possible mechanisms of transmission

The proceeding paper in this series (Blewett &amp; Watson, 1983) described three simple models for the transmission of Toxoplasma in breeding flocks and each model attributed distinctive characteristics to outbreaks of ovine toxoplasmosis. These characteristics referred to such readily observed features of clinical outbreaks as the recurrence of clinical toxoplasmosis in successive lambing seasons, the distribution of losses within the flock, the introduction of bought-in replacement ewes and the range of clinical signs at lambing. This paper tests the three models described earlier by comparing their predictions with the observed properties of outbreaks of clinical ovine toxoplasmosis.</p

Geologic map of the northern hemisphere of Vesta based on Dawn Framing Camera (FC) images

Abstract The Dawn Framing Camera (FC) has imaged the northern hemisphere of the Asteroid (4) Vesta at high spatial resolution and coverage. This study represents the first investigation of the overall geology of the northern hemisphere (22–90°N, quadrangles Av-1, 2, 3, 4 and 5) using these unique Dawn mission observations. We have compiled a morphologic map and performed crater size–frequency distribution (CSFD) measurements to date the geologic units. The hemisphere is characterized by a heavily cratered surface with a few highly subdued basins up to ∼200&#xa0;km in diameter. The most widespread unit is a plateau (cratered highland unit), similar to, although of lower elevation than the equatorial Vestalia Terra plateau. Large-scale troughs and ridges have regionally affected the surface. Between ∼180°E and ∼270°E, these tectonic features are well developed and related to the south pole Veneneia impact (Saturnalia Fossae trough unit), elsewhere on the hemisphere they are rare and subdued (Saturnalia Fossae cratered unit). In these pre-Rheasilvia units we observed an unexpectedly high frequency of impact craters up to ∼10&#xa0;km in diameter, whose formation could in part be related to the Rheasilvia basin-forming event. The Rheasilvia impact has potentially affected the northern hemisphere also with S–N small-scale lineations, but without covering it with an ejecta blanket. Post-Rheasilvia impact craters are small (&lt;60&#xa0;km in diameter) and show a wide range of degradation states due to impact gardening and mass wasting processes. Where fresh, they display an ejecta blanket, bright rays and slope movements on walls. In places, crater rims have dark material ejecta and some crater floors are covered by ponded material interpreted as impact melt