Vesta, more than an asteroid. Indeed, almost a planet

Even though it doesn’t quite qualify as a ‘proper’ planet, the second most massive asteroid in the Solar System, Vesta – which has a diameter of approximately 530 kilometres – exhibits numerous planetary characteristics. This is just one of the many significant results of NASA’s Dawn mission, published in the journal Science on 11 May 2012. The Dawn spacecraft has been orbiting Vesta since 16 July 2011.

Three impact craters of different sizes, arranged in the shape of a snowman, make up one of the most striking features on Vesta. In this view the three 'snowballs' are upside down, so that the shadows make the features easily recognisable. North is to the lower right in the image, which has a resolution of 70 metres per pixel. The image is composed of many individual photographs taken during the high-altitude mapping orbit, at about 680 kilometres above Vesta's surface. The largest of the three craters, Marcia, has a diameter of 60 kilometres. The central crater, which is about 50 kilometres in diameter, is named Calpurnia, and the lower crater, named Minucia, has a diameter of about 22 kilometres. Marcia and Calpurnia are possibly the result of an impact by doublet asteroids, whereas Minucia was formed by a later impact. To derive the colour information, images acquired by the German camera system on the Dawn spacecraft in two near-infrared channels (917 nanometres and 749 nanometres) and an ultraviolet channel (438 nanometres) were combined to create what is referred to as a pseudo-true colour image. The true colours of the surface of Vesta appear somewhat different, but the subtle changes in material properties across the craters and impact ejecta can be detected. In both Marcia and Calpurnia, landslides can be seen; also, dark material has been exposed below the rim of Marcia. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

You're beautiful, Vesta

When UCLA's Christopher T. Russell looks at the images of the protoplanet Vesta produced by NASA's Dawn mission, he talks about beauty as much as he talks about science.

South polar impacts on Vesta. The map indicates that the Vesta surface is not uniform, with a sharp contrast between the northern and southern regions. These data suggest that the region around the Rheasilvia basin is richer in diogenites than the equatorial regions. The north-south variation in minerals indicates that the deep crust exposed in the southern Rheasilvia region is dominated by pyroxene-rich, diogenitic material while the equatorial region seems to retain the most ancient eucrite-rich mineralogy. In this image, blue shows a richer concentration of diogenite minerals and yellow shows a richer concentration of eucrite minerals. The visible and infrared mapping spectrometer collected the data used to create this mosaic image in August 2011, from an average altitude of about 1,700 miles or (2,700 kilometers). Credit: NASA/JPL-Caltech/UCLA/INAF/MPS/DLR/IDA

The violent past of Vesta

A team of researchers led by a NASA Lunar Science Institute (NLSI) member based at Southwest Research Institute has discovered evidence that the giant impact crater Rheasilvia on Asteroid Vesta was created in a collision that occurred only about 1 billion years ago, much more recently than previously thought. This result is based on the analysis of high-resolution images obtained with the Dawn spacecraft, which entered orbit around Vesta in July 2011.

This movie uses data from NASA’s Dawn spacecraft to simulate the view from the spacecraft flying over the surface of the giant asteroid Vesta. Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA