Vesta in false-colors

First false-color maps of the asteroid show unique surface variations.

Scientists at the Max Planck Institute for Solar System Research (MPS) in Germany have compiled the first false-color map of asteroid Vesta’s surface using high resolution images returned by the framing camera on board NASA’s Dawn spacecraft. Dawn began its yearlong orbital mapping mission of Vesta in July. The false-color images were obtained by using the different filters of the framing camera. In the coming months, these images will help to understand Vesta's mineralogical composition and surface structure. Observations made so far show a distinct color variation between the northern and southern hemisphere of Vesta and also certain impact craters that show remarkable diversity.

The framing camera on board the Dawn spacecraft is unlike a “normal” camera. Developed and built under the leadership of the MPS, the camera is equipped with seven color filters. “Every body in space reflects light back into its surroundings”, Dr. Andreas Nathues from MPS, framing camera lead investigator, explains. “We can decode the exact components of this light with the help of the camera’s filters and then for example make inferences about the body’s mineralogical composition.”

The first false-color map that is now available shows that Vesta is divided into two very different halves: The light reflected from the northern hemisphere differs greatly from the light reflected from the south. In the overall map (see figure 1) this becomes apparent from the predominant blue coloring in the north as compared to extensive yellowish-greenish regions in the south. What exactly these different colors stand for, is still unclear. “However, the new map seems to back up the hypothesis suggesting a giant impact that unsettled Vesta’s south”, says Nathues. The asteroid’s southern hemisphere is also characterized by much fewer craters. This could point to a younger age of this part of the surface.

The small craters created by the constant cosmic barrage hold the key to a deeper understanding of Vesta’s evolutionary history. Here, the false-color maps reveal differences that cannot be seen in a black and white picture. “While some craters look completely unremarkable in these maps, others are surrounded by distinct halos of differently colored material,” Nathues describes. One possible explanation for these halos is that this material originated from the impactors themselves. According to a different hypothesis, the impacts hurled material from layers deeper within Vesta to the surface. In this case, these regions would allow an indirect view into Vesta’s interior.

Understanding Vesta’s inner structure is one of the main goals of the Dawn mission. The scientists suspect that in contrast to all other asteroids, Vesta may be composed of crust, mantle and core – much like the Earth. “We believe that Vesta remained stuck in an early phase of planet formation about 4.5 billion years ago,” says Nathues. A look at Vesta would therefore correspond to a look back into time and into the beginnings of our solar system.

“In order to understand Vesta’s evolutionary history, it is necessary to study the distinct variations of the surface as seen in the false-color maps. This will allow inferences about the composition. We have now begun with this complex analysis,” says Nathues. In this endeavor, the MPS scientists are working closely together with their colleagues from the Institute for Planetary Research of the German Aerospace Agency (DLR), who are mapping the asteroid and creating three-dimensional images.

“Vesta has been a total surprise: We had not expected such a complex geology,” says Prof. Dr. Ralf Jaumann from DLR. “The topography with its differences in altitude of up to 25 kilometers points to massive dynamics in the formation of the surface – as do the differences among the many craters, the long valleys and canyons spanning the whole of Vesta, and the great differences in brightness of the surface material. It will require effort and time to solve Vesta’s mysteries. But thanks to the excellent data provided by the mission it has already been possible to create the maps that are preconditions for these further studies.”

The Dawn spacecraft was launched in September 2007 and entered orbit around Vesta on July 16th, 2011. After Vesta, it will travel to Ceres and is expected to arrive at the dwarf planet in 2015.

The Dawn mission to Vesta and Ceres is managed by NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, for NASA's Science Mission Directorate, Washington. The University of California, Los Angeles, is responsible for overall Dawn mission science. The Dawn framing cameras have been developed and built under the leadership of the Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany, with significant contributions by DLR German Aerospace Center, Institute of Planetary Research, Berlin, and in coordination with the Institute of Computer and Communication Network Engineering, Braunschweig. The Framing Camera project is funded by the Max Planck Society, DLR, and NASA/JPL.