Ernst Hauber

Perennial water ice identified in the south polar cap of Mars.

The inventory of water and carbon dioxide reservoirs on Mars are important clues for understanding the geological, climatic and potentially exobiological evolution of the planet. From the early mapping observation of the permanent ice caps on the martian poles, the northern cap was believed to be mainly composed of water ice, whereas the southern cap was thought to be constituted of carbon dioxide ice. However, recent missions (NASA missions Mars Global Surveyor and Odyssey) have revealed surface structures, altimetry profiles, underlying buried hydrogen, and temperatures of the south polar regions that are thermodynamically consistent with a mixture of surface water ice and carbon dioxide. Here we present the first direct identification and mapping of both carbon dioxide and water ice in the martian high southern latitudes, at a resolution of 2 km, during the local summer, when the extent of the polar ice is at its minimum. We observe that this south polar cap contains perennial water ice in extended areas: as a small admixture to carbon dioxide in the bright regions; associated with dust, without carbon dioxide, at the edges of this bright cap; and, unexpectedly, in large areas tens of kilometres away from the bright cap.

Large-scale spring deposits on Mars?

We present a large-scale spring hypothesis for the formation of various enigmatic light-toned deposits (LTDs) on Mars. Layered to massive LTDs occur extensively in Valles Marineris, chaotic terrains, and several large craters, in particular, those located in Arabia Terra. Most of these deposits are not easily explained with either a single process or multiple ones, either in combination or occurring sequentially. Spring deposits can have a very wide range of internal facies and exhibit complex architectural variations. We propose the concept of large-scale spring deposits for explaining LTDs on Mars. Stable volcano-tectonic settings, such as the ones typical on Mars, are compatible with a large-scale, long-term, multistage formation of spring deposits. The large-scale spring deposit model can explain the formation of LTDs with a common process, although active in different times and locations, compatible with coeval local or regional processes and deposits, such as volcaniclastic ones. LTDs, if formed as spring deposits derived from subsurface fluids, could potentially offer favorable conditions both to life and to the fossilization of past life forms.

Deposition and degradation of a volatile‐rich layer in Utopia Planitia and implications for climate history on Mars

[1] We investigate the surface morphology of a study area in western Utopia Planitia, Mars, which is characterized by a variety of landforms that resemble those of terrestrial periglacial landscapes. Polygonally fractured ground and thermokarst-like depressions are found to be located in a young mantling deposit with a thickness of several tens of meters. We observe a latitudinal dependence of the degradation of this mantling deposit. Larger depressions, whose floors reveal the underlying basement rocks, cover a higher fraction of the total terrain in the southern part of the study area than in the northern part, indicating a more intense degradation of the mantle in the south. All depressions have an asymmetric cross section in north-south direction, interpreted to be the result of the different solar radiation on differently oriented slopes. On the basis of our morphological observations, we develop a conceptual model for landscape evolution in western Utopia Planitia. It involves subaerial deposition of a layered, ice-rich mantle and its subsequent degradation by polygon formation and sublimation. A terrestrial analog to the polygonally fractured mantling deposit and its thermokarst-like depressions is the Siberian Ice Complex or ‘‘Yedoma,’’ which consists of subaerial ice-rich deposits and is connected to nonglaciated landscapes with highly continental cold-climatic environmental conditions. Our comparison suggests that no unusual or exotic processes need to be invoked to explain the current morphology of western Utopia. However, the young age of the deposition and degradation implies climatic excursions in the very recent past on Mars.

Sequence of infilling events in Gale Crater, Mars: Results from morphology, stratigraphy, and mineralogy

Gale Crater is filled by sedimentary deposits including a mound of layered deposits, Aeolis Mons. Using orbital data, we mapped the crater infillings and measured their geometry to determine their origin. The sediment of Aeolis Mons is interpreted to be primarily air fall material such as dust, volcanic ash, fine-grained impact products, and possibly snow deposited by settling from the atmosphere, as well as wind-blown sands cemented in the crater center. Unconformity surfaces between the geological units are evidence for depositional hiatuses. Crater floor material deposited around Aeolis Mons and on the crater wall is interpreted to be alluvial and colluvial deposits. Morphologic evidence suggests that a shallow lake existed after the formation of the lowermost part of Aeolis Mons (the Small yardangs unit and the mass-wasting deposits). A suite of several features including patterned ground and possible rock glaciers are suggestive of periglacial processes with a permafrost environment after the first hundreds of thousands of years following its formation, dated to ~3.61 Ga, in the Late Noachian/Early Hesperian. Episodic melting of snow in the crater could have caused the formation of sulfates and clays in Aeolis Mons, the formation of rock glaciers and the incision of deep canyons and valleys along its flanks as well as on the crater wall and rim, and the formation of a lake in the deepest portions of Gale.

Geological Processes and Evolution

Geological mapping and establishment of stratigraphic relationships provides an overview of geological processes operating on Mars and how they have varied in time and space. Impact craters and basins shaped the crust in earliest history and as their importance declined, evidence of extensive regional volcanism emerged during the Late Noachian. Regional volcanism characterized the Early Hesperian and subsequent to that time, volcanism was largely centered at Tharsis and Elysium, continuing until the recent geological past. The Tharsis region appears to have been largely constructed by the Late Noachian, and represents a series of tectonic and volcanic centers. Globally distributed structural features representing contraction characterize the middle Hesperian. Water-related processes involve the formation of valley networks in the Late Noachian and into the Hesperian, an ice sheet at the south pole in the middle Hesperian, and outflow channels and possible standing bodies of water in the northern lowlands in the Late Hesperian and into the Amazonian. A significant part of the present water budget occurs in the present geologically young polar layered terrains. In order to establish more firmly rates of processes, we stress the need to improve the calibration of the absolute timescale, which today is based on crater count systems with substantial uncertainties, along with a sampling of rocks of unknown provenance. Sample return from carefully chosen stratigraphic units could calibrate the existing timescale and vastly improve our knowledge of Martian evolution.

Very recent and wide-spread basaltic volcanism on Mars

New spacecraft data provide increasing evidence for a dynamic environment on presentA¢Â�Â�day Mars. Exogenic processes such as impact cratering, mass wasting processes, and active dune migration have all been observed to modify the surface. No traces of current endogenic activity have been found yet, but some studies point to very localized volcanism in the last few millions of years. However, no systematic study of young volcanic surfaces had been performed so far. We present absolute model age determinations of plains volcanism on Mars as derived from impact crater sizefrequency distributions. Extended areas in Tharsis, the largest volcanoA¢Â�Â�tectonic region on Mars, have been resurfaced by lava flows in the last few tens of millions of years. We also present results on the rheologic properties of these lava flows, inferred from morphometric measurements. Yield strengths are in the range of 100A¢Â�Â�300 Pa, and viscosities reach values of 10^2 to 10^3 Pa s, indicating basaltic compositions. The results imply that Mars retained until recently, and probably still retains, enough internal heat to produce wideA¢Â�Â�spread plainA¢Â�Â�style volcanism, producing lowA¢Â�Â�viscosity lava flows throughout large parts of Tharsis

Geomorphologic Evidence for Liquid Water

Besides Earth, Mars is the only planet with a record of resurfacing processes and environmental circumstances that indicate the past operation of a hydrologic cycle. However the present-day conditions on Mars are far apart of supporting liquid water on the surface. Although the large-scale morphology of the Martian channels and valleys show remarkable similarities with fluid-eroded features on Earth, there are major differences in their size, small-scale morphology, inner channel structure and source regions indicating that the erosion on Mars has its own characteristic genesis and evolution. The different landforms related to fluvial, glacial and periglacial activities, their relations with volcanism, and the chronology of water-related processes, are presented.

Tempe Fossae, Mars : A planetary analogon to a terrestrial continental rift?

Tempe Terra, the northeastern part of the Tharsis Region on Mars, is characterized by several extensional structures differing in style and age. The Tempe Fossae, a particularly well-developed system of graben striking N45°E, have been studied for the first time in detail on the basis of Viking Orbiter imagery and Mars Observer Laser Altimeter (MOLA) topographic data. The graben system appears to be unique in the whole region because of its extent, the remarkable width and depth of the graben, the varying graben pattern, and the associated volcanism. Single graben can be up to 35 km wide and 120 km long, while their depth can reach nearly 3000 m. They typically show an asymmetric architecture, often in halfgraben or step fault style. The graben system widens and changes its style along strike from NE to SW from a single, very deep, and narrow graben to a complex set of several shallower, sinuous graben and halfgraben. Crustal extension was measured in the northeastern part from the observable throw and amounts to 2.5–3.1 km. Volcanic structures can be found at several locations along the graben. In the SW the graben system seems to be connected with the Tempe Terra volcanic province marked by flood basalts and plains volcanism. Craters were counted on volcanic units unaffected by extensional tectonics. Crater statistics indicate an absolute crater model age for the upper end of the extensional deformation of ∼3.5 Ga. The dimensions and the characteristics of the mapped graben system resemble those of terrestrial continental rifts, and a comparison between them and the Kenya Rift reveals striking similarities. Therefore the Tempe Fossae are interpreted as a Martian analog to a continental rift associated with an underlying mantle plume. This hypothesis seems to be supported by recent geophysical models based on topography and gravity data from Mars Global Surveyor which indicate regional uplift for Tempe Terra.

Modeling volcanic deformation in a regional stress field: Implications for the formation of graben structures on Alba Patera, Mars

Abundant grabens transect the volcano Alba Patera. Their complex geometry and formation mechanisms are still poorly understood. Tectonic processes and magmatic intrusions are responsible for these long surface features. Cross-cutting relationships of the grabens show radial fractures that were formed during early stages and were progressively overprinted by concentric fractures on the mid and upper flanks of the volcano. Two modeling methods are used to understand the formation of the observed structures and to evaluate their implications for hidden subvolcanic processes. Surface deformation and fault arrangements predicted in finite element models are compared to the graben systems observed in Viking images. The orientation and position of the concentric grabens are found to be best reproduced by local crustal subsidence, superimposed on a regional NW-SE oriented extension with decreasing magnitude from south to north. In analogue sandbox models we also simulate surface structures of arrangements that almost perfectly mimic the observed lineaments on Alba Patera. Formation of the grabens spans a period on the order of a billion years, suggesting long-term geodynamic processes to be responsible for the subsidence of the central Alba Patera area. The progressive change toward higher concentricity is likely resultant from an increase in density in the crust by accumulation of intrusive material and cooling, thus causing subsidence of the region above this volcanic root.

Landscape evolution in Martian mid-latitude regions: insights from analogous periglacial landforms in Svalbard

Abstract Periglacial landforms on Spitsbergen (Svalbard, Norway) are morphologically similar to landforms on Mars that are probably related to the past and/or present existence of ice at or near the surface. Many of these landforms, such as gullies, debris-flow fans, polygonal terrain, fractured mounds and rock-glacier-like features, are observed in close spatial proximity in mid-latitude craters on Mars. On Svalbard, analogous landforms occur in strikingly similar proximity, which makes them useful study cases to infer the spatial and chronological evolution of Martian cold-climate surface processes. The analysis of the morphological inventory of analogous landforms on Svalbard and Mars allows the processes operating on Mars to be constrained. Different qualitative scenarios of landscape evolution on Mars help to better understand the action of periglacial processes on Mars in the recent past.