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

Mineral Diversity at Vesta's South Pole

This image, made from data obtained by NASA's Dawn spacecraft, shows the mineral distribution in the southern hemisphere of the giant asteroid Vesta. The mineral data came from Dawn's visible and infrared mapping spectrometer, which captures different wavelengths of reflected and emitted radiation. The areas in purple have a higher proportion of diogenite minerals, and yellow areas have a higher proportion of eucrite minerals. Diogenites are silicate rocks with more magnesium than the eucrites, which are richer in iron. The mineral data lies on a mosaic obtained by Dawn's framing camera.

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

Eucrites from Vesta

The HED (howardite, eucrite and diogenite) meteorites are a large group of meteorites believed to originate from Vesta, a hypothesis that is consistent with current Dawn observations. The eucrites are crystallized lavas that have the composition of basalt, the most common lava type on the Earth. The QUE 97053 (left) and EET 90020 (right) eucrites, pictured here, were recovered in Antarctica.

Credit: Hap McSween (University of Tennessee), and Andrew Beck and Tim McCoy (Smithsonian Institution)

Howardites from Vesta

The HED (howardite, eucrite and diogenite) meteorites are a large group of meteorites believed to originate from Vesta, a hypothesis that is consistent with current Dawn observations. Howardites are regolith breccia rocks, meaning that they formed through the grinding and fusion of rock and dust that occurs during meteor impacts on the surface of Vesta. 

Credit: Hap McSween (University of Tennessee), and Andrew Beck and Tim McCoy (Smithsonian Institution)

Diogenites from Vesta

The diogenites originated deep within the crust of Vesta and resemble rocks, both in texture and composition, which we find in the lower crust of the Earth. The QUE 99050 (left) and GRA 98108 (right) diogenites, pictured here, were recovered in Antarctica. These images are of thin slices of the meteorites as viewed through a polarizing microscope. 

Credit: Hap McSween (University of Tennessee), and Andrew Beck and Tim McCoy (Smithsonian Institution)