(Sen) - Scientists studying the giant asteroid Vesta believe that the large scale structural cracks around its middle are graben - where the ground sinks when two faults move apart. Graben are usually only found on larger planets and moons which have a layered structure of core, mantle and crust. The research supports the view that Vesta was formed in the same way as the inner rocky planets.
Although NASA's Dawn spacecraft has now left the asteroid, the huge amount of data gathered during its visit is still being analysed. Vesta, the second most massive asteroid in the Solar System, measures 578 by 560 by 458 kilometres (359 by 348 by 285 miles) and is heavily scarred by a belt of deep troughs. The largest, Divalia Fossas, is 465km (289 miles) in length, 22km (13.6 miles) wide and 5km (3 miles) deep - longer and deeper than the Grand Canyon. Scientists studying the troughs, led by Debra Buczkowski of the Johns Hopkins University Applied Physics Laboratory, believe the troughs were formed when another asteroid crashed into Vesta. Of interest though is that the troughs are not the usual cracks that appear on asteroids after a collision. According to their research, Vesta's deep troughs are graben - dips in the surface that form when two faults move apart from each other and the ground sinks into the widening gap. The difference between graben and a fracture is significant because graben occur when the body is differentiated, meaning it has an inner core, mantle and crust - a layered structure common to all the inner rocky planets and moons. Debra Buczkowski explained: "By saying it’s differentiated, we’re basically saying Vesta was a little planet trying to happen."
Most asteroids are just giant rocks and their surface cracks are V shaped, but Vesta's troughs are U shaped with distinct walls on either side and a flat or curved floor. Their U shape is a telltale sign of a graben rather than a simple surface crack. The research indicates that Vesta is unusually planet-like for an asteroid in that its mantle can stretch under a lot of pressure - as Buczkowski explains: “It can become almost silly putty-ish, you pull it and it deforms.”
The research paper, entitled Large-scale troughs on Vesta: A signature of planetary tectonics, has been published in Geophysical Research Letters, a journal of the Amercian Geophysical Union.
Launched in 2007, Dawn's mission is to study Vesta and the dwarf planet Ceres with the aim of improving our understanding of the evolution of the early Solar System. Vesta, which orbits the Sun in the asteroid belt between Mars and Jupiter, was chosen as an example of a rocky world in the inner Solar System. Studying the giant asteroid is helping scientists understand how celestial bodies in the Solar System were formed.
Dawn left Vesta in early September and is now on a long journey to study its next target, the dwarf planet Ceres, a very different world to rocky Vesta that formed much further away from the Sun. Ceres, which was classified as dwarf planet in 2006, appears to have similarities to the large icy moons of the outer Solar System. Dawn will arrive at Ceres in 2015.
NASA's Dawn mission is managed by NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology.