This composite image is a simulated true color image of part of Vesta's south polar region. It was produced by combining images obtained by the Visible and Infrared Imaging Spectrometer (VIR) instrument aboard NASA's Dawn spacecraft. The VIR instrument can image Vesta in many different wavelength regions, called bands, in the near ultraviolet, visible and infrared parts of the electromagnetic spectrum, which corresponds to a wavelength range of 300nm to 5000nm. This is an RGB composite image where red is set as the 700nm band, green is set as the 550nm band and blue is set as the 440nm band. The wavelength of red light is around 700nm, of green light is around 550nm and of blue light is around 440nm, so this image approximates what the human eye would see looking at Vesta. It is an approximation because the human eye can see many more wavelengths than the three used here. There is a lot of spectral diversity (eg. color diversity) in this region of Vesta's surface. There is a concentration of purple-brown in and around a crater in the top right of the image. Surrounding this crater is a distinctly blue area. The rest of the surface visible in this image ranges from a brown to yellow-white color.
NASA's Dawn spacecraft obtained the images used to make this composite image with its Visible and Infrared Imaging Spectrometer on August 15th 2011. The distance to the surface of Vesta is 2740km and the average image resolution is 800 meters per pixel.
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 D.C. UCLA is responsible for overall Dawn mission science. Dawn's VIR was provided by ASI, the Italian Space Agency and is managed by INAF, Italy's National Institute for Astrophysics, in collaboration with Selex Galileo, where it was built.
More information about Dawn is online at http://www.nasa.gov/dawn and http://dawn.jpl.nasa.gov.