Orbit 25.000 of Mars Express could not have been pictured in a more spectacular scene than in this fantastic high-altitude observation of the HRSC camera. The image provides a rare look not only at several large Martian volcanoes in the Tharsis volcanic province but also shows the Martian moon Phobos passing by!

The Tharsis region covers one quarter of the Martian surface. Even the smaller volcanos like Jovis Tholus, Biblis and Ulysses patera can be found in the image. The fractured Noctis Labyrinthus canyons can be easily spotted, as are many other surface features observed in previous orbits, like for example the large Lycus Sulci landslide north of Olympus Mons or the Tantalus Fossae in the upper portion of the image. Check the annotated image for prominent features and use the zoom function to further explore this high-resolution image. In the lower portion of the image, a small cloud band and lee wave clouds can be found. The latter develop when air passes over an obstacle like a topographic ridge and receives a pulse which is then transformed into kinetic energy. The stack of air, consisting of different layers, then forms a wave-like structure at the lee side of the obstacle.

Mars Express has a polar orbit and the spacecraft travels on elongated ellipses. During each seven-hour orbit, the spacecraft approaches the surface to about 300 km and then moves away to a distance of about 10.000 km. Images from this high altitude are typically obtained to observe weather patterns, for creating global views of the surface and for calibration purpose. The sensors of the HRSC are directed over a wide extended area in a sweeping movement. That is why this type of observation is also called 'broom calibration'. The field of view of the line sensors that are arranged perpendicular to the flight path are pushed across the surface like a broad 'brush stroke'. In this way, all the sensors scan the surface at the same angle of observation one after the other, resulting in a time interval. This becomes visible in the color overview image (Mars with grid), where Phobos can be spotted at different locations because it moved on during the scan process. In the post-processing for such images as presented here, the individual color images are then overlain to create the full color view. Phobos was individually reconstructed to give a consistent impression of the scene.