New View of Mars After Two Years of Mars Express High Resolution Stereo Camera Data Acquisition and Analysis

By December 2005 after two years in orbit the HRSC will have covered ~ 30% of Mars at 10-20 m/pxl resolution in stereo and color. The data are being analyzed by a large international co-investigator team during the proprietary phase (1/2 year after reception on the ground). All data of the first year have been archived in the ESA science data archive and in parallel in the NASA PDS and can be freely accessed and utilized by the science community at large. From the investigations of the HRSC data, we can confirm that Mars experienced long-lasting volcanic activity, starting more than 4 Ga ago and continuing over billions of years. The volcanic activity peaked around 3.5 Ga ago, but went on until very recently in some areas, especially in Tharsis and Elysium. On Olympus Mons we found lava flows as young as 2 Ma. Mars appears to have started out as a wet planet with Earth-like erosional rates, but very early, around 3.5 Ga ago, fell dry rapidly on a global scale. After that point in time, there were no longer-living large open bodies of water on Mars anymore. Erosional levels dropped by eight or nine orders of magnitude on average around or soon after 3.5 Ga ago. Most small channels appear to have fallen dry completely 3.5 Ga ago or soon after, outflow channel activity levels dropped down tremendously at that time, residual activity later was confined to the major parts of the outflow channels, flows turned from fluvial to mainly glacial; no major contributions in terms of drainage to the northern lowlands happened anymore. The northern lowlands also had essentially fallen dry and were covered by lava between 3.5 and 3 Ga ago. Residual fluvial/glacial activity in the investigated outflow channels ended between 1.3 Ga and 1.5 Ga ago (with the exception of some minor local recent activity in Kasei). This is coincident in time with some major volcanic activity coming to an end of most highland volcanoes and with the emplacement of the Medusae Fossae Formation. Over the past ~ 500 Ma until very recently (at least until 4 Ma ago), episodical fluvial/glacial activity was occurring regionally or locally, largely confined to a few areas such as Tharsis, Elysium, the eastern rim of Hellas, and the highland/lowland dichotomy. We have found indication for a close temporal and genetic relationship between volcanic/magmatic and fluvial/glacial activity; i.e. water mostly seems to have been mobilized from underground hydrothermally or in interaction of lava with ice-rich surface layers. In contrast to the prevailing present views of such processes being coupled with climatic variations (e.g. the Tharsis Montes fan-shaped deposits) induced by changes in the obliquity of Mars's rotational axis, we judge from our data that also for such young glaciations as found on the western sides of Olympus Mons and the Tharsis Montes, a major 'triggering' process is volcanic/magmatic activity. We cannot rule out, though, that there may be a superimposed cyclic change of climate coupled to changes in Mars's rotational state or to solar activity.