Friday, March 8, 2013

Violent collision shaped into Vesta

The new model is based on computer simulations of collisions between asteroid Vesta separated and a couple of rocks from 32 km in diameter in the last billion years. The results suggest that cosmic impacts caused Vesta's crust to melt and then re-form, with its thicker crust than can be explained by typical rock layers, the scientists said.

Collisions carved two large impact craters on the surface of Vesta. The oldest, Veneneia, formed about 2,000 million years. With a diameter of 395 km, the crater covers nearly three quarters of the diameter of Vesta Ecuador. Covering 90% of the diameter of Vesta, is one of the largest craters in the Solar System.

The violent origins of Vesta

By modeling the impacts that formed these craters, an international team of scientists said it was able to examine the heart of Vesta.

"It was one of the original aims of our study to find out more about the interior," he told the researcher Martin Jutzi of the University of Bern in Switzerland.

The second most massive asteroid in the solar system, Vesta, began as a protoplanet. However, the nearby presence of Jupiter prevented its growth. Vesta's interior, unlike most asteroids, is separated into layers and reminds of planet with a rocky crust covering a blanket of mineral olivine compound. It has a metallic core in the center.

The collision formed Rheasilvia Veneneia and extracted material to a depth of 100 km in the crust. Since conventional theories give the crust about 40 km thick, these impacts would have dug through the crust and mantle pieces scattered across the surface.

The models developed by Jutzi and his team suggested that under the conventional structure of layers of bark debris would have been thrown across the northern hemisphere, although the southern hemisphere would have been covered by large swathes of mantle olivine and rocks of the deepest recesses of the crust.

Simulations versus reality

In 2011, NASA's Dawn spacecraft entered orbit around the asteroid and discovered another reality. In the past year there before they moved to Ceres, Dawn studied Vesta's surface and found no trace of the mantle that should have covered the ground of Rheasilvia.

"The comments made by Dawn suggest that the south polar basin lack olivine-rich rocks," Jutzi said. "This suggests that Vesta's mantle has not been excavated during the two major impacts in the southern hemisphere."

Scientists suggested three possible reasons for the findings:

The remnants of the mantle on the surface escaped detection Dawn.
Other impacts, even higher earlier in the life of Vesta's surface mixed vigorously. The olivine would have combined with other rocks. "Olivine is very difficult to detect spectroscopically, and this mixture would have become more difficult," said Jutzi.

Current predictions of measurements are not accurate bark Vesta. Previous theories suggested that the crust was thickened by rocks of magma cooled slowly, making it thicker than the 40 km expected.

The thickened crust scenario is favored by the computer model, according to study co-author Jean-Alix Barrat, University of Western Brittany in France. This crust would realize the wealth of the samples from the depth of the crust.

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