The giant asteroid Vesta possesses many features usually associated with rocky planets like Earth, according to data from a Nasa probe. Vesta has been viewed as a massive asteroid, but after studying the surface in detail, scientists are describing it as “transitional”. The Dawn spacecraft has been orbiting Vesta - one of the Solar System's most primitive objects - since July 2011. They have documented many unexpected features on its battered surface. Mission scientists presented their latest results at the Lunar and Planetary Science Conference (LPSC) in The Woodlands, Texas. Dawn's principal investigator, Christopher T Russell, told the meeting that the science team found it hard not to refer to the object as a planet. He said the rounded asteroid showed evidence of geological processes that characterise rocky worlds like Earth and the Moon. Getting hammered Vesta is the second most massive of the asteroids, measuring some 530km (330mi) in diameter. It is dominated by a huge crater called Rheasilvia and bears many other scars left by the hammering it has received at the hands of other asteroid belt denizens. One important transitional feature of Vesta can be found in its topography, or elevation. Vertical elevation on the Moon or Mars might reach tens of kilometres, but these objects are also very large. “This means the topography is about 1% of the radius,” Dr Ralf Jaumann, from the German Aerospace Center (DLR), told BBC News. If you go to Vesta, it is 15%, and if you go to the largest outer asteroid - Lutetia - it is 40%.” In short, this mathematical relationship between topography and radius (half an object's diameter), puts Vesta in an intermediate position between small asteroids and rocky planets. Another aspect concerns the way its surface has been modified, or “processed”, by the many collisions. This is evident in dark material that can be seen in images of its terrain. The dark material seems to be related to impacts and their aftermath. Scientists think carbon-rich asteroids could have hit Vesta at speeds low enough to produce some of the smaller deposits without blasting away the surface. Higher-speed asteroids could also have collided with Vesta's surface and melted the volcanic basaltic crust, darkening existing surface material. Scientists are confident there has been volcanism on the asteroid during its history. This is because there are hundreds of pieces of Vesta sitting in museums around the world.
