chemical composition
| The surface of Vesta is studied using spectroscopy(studies the sunlight reflected off a body and analyzes its spectrum). By recording the spectrum of light reflected off Vesta, scientists discovered which minerals were present on the surface. It is determined that Vesta has a basaltic crust. Basalt is generally composed of plagioclase, pyroxene, and olivine. It is generally accepted that the surface of Vesta has mostly iron- and calcium- rich pyroxenes. Basalt is formed when molten rock cools quickly on the surface and pyroxenes are usually caused by magmatic differentiation, so this confirms that Vesta had volcanic activity and tells us what sort of material the erupted or melted mantle was. The crust is not homogeneous. Looking at Vesta albedo (measure of lightness and darkness of a body), we can conclude that Vesta has dark background with diverse lighter regions. The dark background is identified as eucrite (plagioclase-pyroxene basalt). The lighter regions are thought to be around a crater that has exposed mantle material.They contain olivine and diogenite material that can be found in the mantle. On the South pole of Vesta, there is a large crater around which, according to spectroscopy data, there is either a higher calcium content or part of the olivine mantle was exposed to the surface. As a conclusion, the crust is primarily basalt with regions of olivine from the mantle.
The asteroid Vesta is only the third solar system object beyond Earth where scientists have a laboratory sample (the other extraterrestrial samples are from Mars and the Moon.) The meteorite has fallen on Earth in the 1960s.The meteorite's chemical identity shows it is part of Vesta because it has the same mineral pyroxene. The meteorite also has the same pyroxene content as other small asteroids, discovered near Vesta. This debris extends all the way to an "escape hatch" region in the asteroid belt called the Kirkwood gap. This region is swept free of asteroids because Jupiter's gravitational pull removes material from the main belt and hurls it onto a new orbit that crosses Earth's path around the Sun. The meteorite probably followed this route to Earth. It was torn off Vesta's surface as part of a larger fragment. Subsequent collisions broke apart the parent fragment and threw pieces toward the Kirkwood gap and onto a collision course toward Earth. The fragment's journey ended in 1960 when it fell in Western Australia. The composition of the meteorite indicates that Vesta experienced melting. The abundances of Ni, Co, Mo, W, and P in Vesta's mantle are consistent with equilibrium between metal and molten silicates. Differentiation from melting caused the heavy elements in Vesta's composition, especially iron, to separate and sink to the center to form a core. Evidence of this was shown with experiments. These experiments use the fact that all metals have to separate out from the mantle material before the mantle can melt and produce eucrites. As in Vesta there are eurocites present and the mantle has expeirenced melting, the metals must have suparated, and being too heavy, must have sunk to the center of gravity, forming the core. In order to produce the eucrites, a substanial metling followed by slow cooling areneeded. So the evidence shows Vesta experienced partial melting.
|
|
