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Dawn reveals complexities of ancient asteroidal world by 123wert sdfsf
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Dawn reveals complexities of ancient asteroidal world |
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New findings from NASA's Dawn spacecraft lay the groundwork for thefirst geological overview of asteroid (4)Vesta and confirm theexistence of not one but two giant impact basins in its southernhemisphere. The findings, published this week in a set of Sciencepapers, will help scientists better understand the early solarsystem and processes that occurred as it formed and evolved. The Dawn spacecraft, orbiting asteroid Vesta since July 2011, hasalready acquired several thousand images of the asteroid's surface,revealing a complex landscape. The images provide many details thathelp scientists to understand how the surface has evolved since itsformation.
The first paper provides an overview of the true complexity of thisancient world. Vesta is not just a ball of rock; its surface isdominated by abundant impact craters of all shapes and sizes, fromsmall fresh craters to giant basins as seen in the southernhemisphere. The surface of Vesta is complex and varied, with preserved ejectablankets clinging to some craters, large troughs extending aroundthe equatorial region, enormous mountains, and unevenly distributedenigmatic dark material, but as yet an absence of volcanicfeatures. "As a volcanologist, and as one who expected to find evidence ofvolcanism on Vesta based on what we knew from theHowardite-Eucrite-Diogenite (HED) meteorites and prior models ofVesta's formation, the biggest surprise for me was the absence ofany evidence of volcanic features. Vesta's surface has been soheavily modified by impact cratering that any evidence of its earlyvolcanic activity has been destroyed," says Dawn missionparticipating scientist David Williams, co-author on the papers andfaculty research associate in Arizona State University's School ofEarth and Space Exploration.
The present lack of volcanic features detected on Vesta suggeststhat volcanism was only active during the short period of rapidcooling of Vesta's interior within the first 100 million yearsafter formation, and that the surface has been eroded by impactsover time. Like Earth and other terrestrial planets, Vesta has ancientbasaltic materials in its crust and a large iron core. It is anirregular asteroid that also has tectonic features, troughs,ridges, cliffs, hills and a giant mountain. But comparisons of theslopes and topography of Vesta show that they are intermediatebetween planets and small asteroids, underscoring Vesta's uniquerole as a transitional solar system body. Prior to the arrival of the Dawn spacecraft, some Vestan surfacefeatures had already been resolved using the Hubble Space Telescopeand ground-based telescopes.
The most prominent of these surfacefeatures is an enormous crater Dawn found to be about 500kilometers (310 miles) in diameter, centered near the south pole,named Rheasilvia after the mother of Romulus and Remus. Its width is 90 percent the diameter of Vesta and it is estimatedthat the impact responsible excavated about 1 percent of the volumeof Vesta. The second paper is a geological description of this large impactbasin. "Dawn observations enabled us to recognize that there are actuallyTWO large basins at the south pole, an older one named "Veneneia"and a younger one named "Rheasilvia"," explains Williams.
The Rheasilvia basin dominates the geology of Vesta, as the basinitself and its impact ejecta cover most of the southern hemisphere.The center of Rheasilvia has a central peak taller than Mt. Everestor Mauna Loa on Earth, similar in height to Olympus Mons on Mars. This basin appears to have excavated into the mantle of Vesta,exposing material spectrally similar to diogenite meteorites;Vesta's crust is spectrally similar to eucrite and howarditemeteorites, thus confirming that Vesta and its family of asteroidsare the source of the howardite-eucrite-diogenite (HED) family ofbasaltic achondrite meteorites. "For most planets and moons we see the pictures first, then havesamples collected later to confirm our geologic interpretations.
Inthe case of Vesta, thanks to the HED meteorites, we have thesamples first, and must try to relate them to our emerging geologicpicture of Vesta from the Dawn mission," said Williams. I am a professional writer from Gas Lighters, which contains a great deal of information about canvas stretching pliers , wooden frame chalkboard, welcome to visit!
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