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Tharsis Tholus, a more than 3.9 Ga old composite shield volcano to the east of the major Tharsis Montes, has experienced a complex history of growth and destruction. On the basis of new high resolution images we analysed the morphology as well as the tectonic structures of the Tharsis Tholus volcano in detail. From morphological data, cross-cutting relations of the surface structures, and crater modelling ages we propose a chronostratigraphy for the volcano-tectonic history of Tharsis Tholus. The strongly faulted volcano reveals two large-scale landslide events followed by two subsequent shield re-growth phases between 3.8 and 1.7 Ga and two caldera collapses. Tharsis Tholus was also affected by regional extensional tectonics between 1.7 Ga and 0.4 Ga recorded by sub-parallel sets of NE trending graben structures. The steep and up to 5.4 km high landslide scarps on Tharsis Tholus suggest deep faulting of the edifice. In order to confirm this hypothesis we used analogue sand box models in which we demonstrated that gravitational flank movement on top of weak basal substrata may have produced the deformation structures as observed on Tharsis Tholus. (C) 2011 Elsevier B.V. All rights reserved.

Martian gullies show morphologic characteristics that indicate the presence of a flowing liquid during their formation process. However, the current climate in the northern hemisphere of Mars does not allow the existence of substantial amounts of liquid water and, therefore, an assessment of the regional distribution and characteristics of gullies is required in order to understand the most recent climatic development of Mars. We examined High Resolution Stereo Camera (HRSC) and Mars Orbiter Camera—Narrow Angle (MOC-NA) data covering the northern hemisphere in order to determine the distribution, geological setting and orientation of gullied slopes. We used these results to test the consistency of formation models proposed in earlier works and to define the climate dependence. Gully orientations were analyzed only at impact crater walls, because craters have an azimuthally uniform distribution of slopes. This is ideal when investigating the influence of insolation on the distribution and development of landforms. We examined 230 HRSC and ~ 21,000 MOC-NA images and identified more than 2200 gullies on HRSC and more than 3100 gullies in MOC-NA data. Both surveys show the highest densities of gullies between 35°N and 55°N and a shift of gully orientation at 40°N from pole-facing slopes to slopes facing the equator. Orientation trends as well as the latitudinal distribution of identified gullies strongly support the view of gully formation caused by insolation/climatic conditions. This result suggests that formation mechanisms based on the assumption of atmospheric water-ice deposition proposed in earlier work are more likely than processes related to groundwater flow. Further support for a theory related to deposition is gained through observation of the high occurrence of gullies at isolated knobs and hills, which cannot be associated with formation models based upon groundwater flow.

We have investigated 12 prominent regions on Mars in detail with respect to their geologic evolution through time on the basis of detailed geologic mapping exercises and determining age relationships through crater counting techniques using imagery. New data in combination with previously obtained data have been analyzed by way of a refined method of cratering age extraction that also gives fine details of periods of resurfacing. We have found that there has been volcanic and fluvial/glacial geologic activity on the Martian surface at all times from > 4 Ga ago until today. This activity shows episodic pulses in intensity of both volcanic and fluvial/glacial processes at ~ 3.8–3.3 Ga, 2.0–1.8 Ga, 1.6 to 1.2 Ga, ~ 800 to 300 m.y., ~ 200 m.y., and ~ 100 m.y., and a possible weaker phase around ~ 2.5–2.2 Ga ago. In between these episodes, there was relative quiescence of volcanic and/or fluvial/glacial activity. The episodes we find on the Martian surface in the crater frequency analyses of HRSC, MOC and THEMIS data coincide with some age groups of the Martian meteorites (~ 1.3 Ga, ~ 600–300 m.y., ~ 170 m.y.). It appears that the surface activity expressions and their episodicity are related to the interior evolution of the planet when convection in the asymptotic stationary state changes from the so-called stagnant-lid regime to an episodic behavior. Similarities in episodic behavior are found for the other terrestrial planets: Venus, the Earth's moon, and the Earth itself suggesting a common general relationship in the evolutionary tracks.

Four prominent fluvial systems, Dao, Niger, and Harmakhis Valles, and a system of smaller channels between Niger and Harmakhis Valles characterize a wide topographic trough that connects Hesperia Planum and Hellas Planitia (Hesperia–Hellas trough, HHT). The source depressions of the canyons of Dao and Harmakhis Valles are at the lowermost level (about − 5.4 km and lower), the system of Niger Vallis is at medium elevation (about − 3 to − 4 km), and the small channels occur at the highest topographic levels (about − 2.5 to − 3.2 km). All systems are among the youngest features in the region. They formed due to the release of subsurface water and apparently have their sources at different topographic levels below or within the layered suite of volcanic deposits in HHT. Two scenarios can explain the subsurface nature of their sources: (1) flow of liquid ground water from extensive watershed toward the source areas and accumulation of water there and (2) deposition of ice-bearing materials in and around the sources. The first scenario requires the existence of extensive confining layers at different topographic levels corresponding to the levels of the floors of the canyons/channels. Because the presence of such confining layers on Mars is problematic, we consider the first scenario to be less likely. We believe that the deposition of ice-bearing materials at different levels during the growth of the lava plateau in HHT can better explain the key features of the fluvial systems: the subsurface nature of the sources and the relatively young age. In this scenario, the higher topographic position of the ice-bearing deposits corresponds to the younger age of deposition. The possible accumulations of ice were buried by successive volcanic deposits, including lava flows in HHT and later were heated from below by magmatic intrusions that caused melting of the icy deposits, release of water, and formation of the fluvial structures.

We describe the procedure to fit a cumulative production function polynomial to a partial crater size–frequency distribution. The technique is of particular use in deriving ages for surfaces which have undergone partial resurfacing events: namely, erosional or depositional events which have affected a limited diameter range of the crater population. We demonstrate its use in obtaining times for both the surface formation and the resurfacing event. We give a practical outline of the method for making age measurements from crater counts and how to identify resurfacing effects in the results. We discuss the conversion of production function polynomials between common presentations, and the statistical uncertainty of the determined ages with respect to the non-linear chronology function, and a minor refinement of data binning.

An improved technique is presented to determine more accurately deposit thicknesses of any surface units using crater size-frequency distributions (CSFDs). This new approach enables thickness estimates of deposits that completely cover their underlying unit, i.e., where no flooded craters are observed. Here, the crater populations of the unit of interest and its underlying unit (or a representative surface area) are measured and their cratering model ages determined. The CSFD of the younger unit is then treated as if it had the same age as the older unit and the expected cumulative numbers of craters for each bin size are calculated. The crater deficiency for each bin size is then determined by subtracting the expected cumulative crater number from the observed cumulative crater number per bin. The probability is calculated such that the crater deficiency corresponds to the age of the older, underlying unit. The crater bin size where we are 95% confident that these craters are there but just covered by the younger unit is chosen to derive the deposit thickness value using known crater diameter-rim height relationships. We demonstrate the use of the method at two sites of different scales and settings on Mars: Pickering crater and Lunae Planum, and compare our estimates with those obtained by other methods. For the Lunae Planum area a significantly higher minimum thickness of > 840 m is predicted.

Residual meteoritic material has been detected on the surface of crater interiors on lunar samples 60315,29 and 65315,68. Iron-nickel micrometeoroid residues are present in the form of mettallic spherules embedded in or attached to the crater glass-linings; stony-iron meteorite residual material is homogeneously mixed with the glass-linings. Crater simulation experiments show the dependence of crater diameter to depth ratio on projectile density. On the other hand, the projectile velocities exceeding 4 km/s have no measurable influence on the D/T ratios of microcraters. As a result, diameter-to-depth measurements on lunar microcraters yield three groups of micrometeorites in the size range between 1 μm and 1 mm: iron-nickel, stony-iron and low-density particles. The measured D/T values correspond directly to the kind of determined projectile residues: craters showing residues of iron-nickel meteorites have ratios of D/T = 1.3–1.4 and craters with stony-iron residues have ratios ofD/T = 1.9–2.1. Craters with diameters ≲30 μm seem to have been formed predominantly by iron-nickel micrometeorites, whereas craters with diameters ≳80 μm predominantly by stony meteorites.

In this paper a theory is evaluated to describe the development of the lunar crater population with time under the bombardment by meteoroids and solar wind. Starting from a general mass distribution law a differential equation has been established and solved separately for meteoroid impact and solar wind bombardment. The theory permits the calculation of absolute formation ages of the lunar surface as well as the particle flux, supposing the crater distributions on the moon have been measured. As an important result it includes a D−2 equilibrium crater distribution law (D =crater diameter), actually measured in Mare Tranquillitatis and Oceanus Procellarum. Additionally, the exponential decrease of particle flux with time is confirmed.

The NASA lunar surface samples 10019 and 10046 from the Apollo 11 mission were searched for micrometeorite impact craters by means of an optical reflecting microscope and a Stereoscan electron microscope. Craters with diameters between 2 microns and 0.8 mm were observed. Approx. 1 crater larger than 0.15 mm in diameter per 1 mm 2 and 1 crater larger than 2 μm per 500 μm 2 could be found. The time of exposure is calculated from crater number densities and cosmic dust influx values to be 10 000 yr and 100 yr for layers of respectivethicknesses. On lunar glassy spherules impact features were found which yield the same crater number densities. The phenomenology of high velocity impacts was studies by shooting microspheres on targets similar to lunar material using a 2 MV dust accelerator.