Mars: simply red?

Mars has been known as the Red Planet since ancient times, and the small flotilla of spacecraft that has visited our solar system neighbour over the past few years could only confirm this basic observation from those ancient civilizations. However, the enormous amount of data returned from the varied instruments has significantly increased our knowledge of almost every aspect of the planet's evolution. Three orbiters and two rovers are currently operating there, and NASA's Mars Reconnaissance Orbiter is on its way. One of the three orbiters is Mars Express, ESA's first spacecraft to another planet. It is considered a major success of ESA's science programme, and one of the highlights of the agency's increasing efforts in planetary exploration. A wealth of scientific results has been published in journals and presented at conferences. The instrument on Mars Express that probably has the largest appeal to the public is the High Resolution Stereo Camera (HRSC). Two years ago we gave a description of its scientific goals and presented the first images obtained from orbit (Hauber and Neukum 2004). Here we give an overview of the technical and scientific achievements of HRSC made over the two years of the nominal mission, and show some of the most appealing images. But don't be fooled: despite the spectacular false-colour images shown here to enhance the subtle colour variations of the martian surface, HRSC's multispectral images have shown that Mars is red in varying tones everywhere, except at small parts of its ice-covered poles. Many other aspects of the data are harder to understand. Mars may still be red, but it is by no means simple