Northern Plains Of Mars Research Articles

Evidence for an ancient martian ocean in the topography of deformed shorelines

A suite of observations suggests that the northern plains of Mars, which cover nearly one third of the planet's surface, may once have contained an ocean. Perhaps the most provocative evidence for an ancient ocean is a set of surface features that ring the plains for thousands of kilometres and that have been interpreted as a series of palaeoshorelines of different age. It has been shown, however, that topographic profiles along the putative shorelines contain long-wavelength trends with amplitudes of up to several kilometres, and these trends have been taken as an argument against the martian shoreline (and ocean) hypothesis. Here we show that the long-wavelength topography of the shorelines is consistent with deformation caused by true polar wander--a change in the orientation of a planet with respect to its rotation pole--and that the inferred pole path has the geometry expected for a true polar wander event that postdates the formation of the massive Tharsis volcanic rise.

Evidence that floodwaters filled and overflowed Capri Chasma, Mars

Erosional features on a plateau in the Valles Marineris provide evidence that a lake filled Capri Chasma until it overflowed its eastern rim, carving two large spillover channels. The floodwaters surged into the adjacent lowlands of ancestral Ganges Chasma and eastern Eos Chasma. The channel floor elevation and depth of incision at Daga Vallis reveal that a 1200‐m‐deep lake water column was drained by the flooding. The width, depth, and steep energy slope (∼0.02) of Daga Vallis and the existence of several cataracts, including a 500‐m‐high dry falls, demonstrate the power of the floodwaters. We estimate a possible peak discharge rate of 1–6 × 108 m3·s−1. The catastrophic flows may have been triggered by the collapse of topographic barriers in eastern Coprates Chasma, providing a gateway for lake waters in the central Valles Marineris to pour eastward toward Capri Chasma and the lowlands beyond. These may have been among the earliest flows in Simud‐Tiu Valles, contributing discharge to a possible sea in the northern plains of Mars.

Modification of impact craters in the northern plains of Mars: Implications for Amazonian climate history

Abstract— We measured the depth, wall steepness, and ejecta roughness and surveyed the wall and floor morphology of all craters 10–25 km in diameter within the typical Vastitas Borealis Formation in the northern lowlands of Mars north of 52°N. Two of the 130 craters have unusually rough ejecta; they are deep, have steep walls, and are apparently the youngest in the population. Icy mantles filling the local subkilometer‐scale topographic lows is the main contribution to ejecta smoothing, which occurs at a time scale on the order of tens of Myr. Wall degradation and crater shallowing generally occur at longer time scales, comparable to the duration of the Amazonian period. Many craters are shallow due to filling of the crater with specific ice‐rich material of uncertain origin. We use our collected data to infer the nature of the past climate back through the Amazonian, a period prior to ˜10–20 Myr ago, when orbital parameter solutions are chaotic and one must rely on geological data to infer climate conditions. We conclude that moderately high obliquity and wide obliquity variations were probable during the last 40–160 Myr. We tentatively conclude that high obliquity peaks (>40–45°) may have occurred episodically through the last 210–430 Myr. A sharp step in the frequency distribution of wall steepness at 20° may indicate a geologically long period prior to that time where obliquity never exceeded 40–45°.

Recent high‐latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement

Martian high‐latitude zones are covered with a smooth, layered ice‐rich mantle containing characteristic polygonal patterns. The mantle is especially uniform and homogeneous in the northern plains. We performed a survey of decameter‐scale mantle textures and circular features, including impact craters, in the northern lowlands down to 50°N latitude. Strongly altered and mantled craters of impact and non‐impact origin form a population of subtle circular features below the mantle. Pits of non‐impact origin are numerous in some regions at lower latitudes. Impact craters superposed on the mantle are small and very sparse. The inferred mean crater retention age of the mantle is ∼0.1 Ma. The spatial distribution of young craters suggests an age difference between the highest latitudes (younger) and some lower‐latitude regions (older). Latitudinal trends in polygon textures agree with impact crater evidence for a latitudinal age progression of mantle properties.

Nature and characteristics of the flows that carved the Simud and Tiu outflow channels, Mars

Geomorphic and topographic relations of higher and lower levels of dissection within the Simud and Tiu Valles outflow channels on Mars reveal new insights into their formational histories. We find that the water floods that carved the higher channel floors were primarily sourced from Hydaspis Chaos. The floods apparently branched into distributaries downstream that promoted rapid freezing and sublimation of water and limited discharge into the lowlands. In contrast, we suggest that the lower outflow channels were carved by debris flows from Hydraotes Chaos. Surges within individual debris flows possessed variable volatile contents and led to the deposition of smooth deposits marked by low relief longitudinal ridges. Lower outflow channel discharges resulted in widespread deposition within the Simud/Tiu Valles as well as within the northern plains of Mars.

Huge, CO2-charged debris-flow deposit and tectonic sagging in the northern plains of Mars

The northern plains of Mars contain a vast deposit, covering one-sixth of the planet, that apparently resulted in extensive lithospheric deformation. The center of the deposit may be as much as 2–3 km thick. The deposit has lobate margins consistent with the flow of fluidized debris for hundreds to thousands of kilometers derived from highland and high-plains sources. The deposit surface lowers inward by ∼900 m in places and is locally bordered by a bulge ∼300 m high. Similar deformation accompanied development of Pleistocene ice sheets on Earth. The lack of burial of a large inlier of older terrain and the response time of the mantle to the loading require that the deposit was emplaced in 2 as an active agent in the processes of source-rock collapse and debris flow.

Convection in a catastrophic flood deposit as the mechanism for the giant polygons on Mars

A formational mechanism for the large‐scale polygons that are defined by intersecting fractures in the northern plains of Mars is proposed in this work. The presented model is based on Rayleigh convection of interstitial water driven by an unstable density/temperature gradient within a saturated, porous medium. Catastrophic emplacement of water‐rich sediments into the Martian northern plain basins could have provided a thick sedimentary layer in which Rayleigh convection could have occurred. Convection within this active layer is proposed to have differentially thawed an underlying ice‐rich permafrost layer that had been at the planet's surface before being rapidly buried. The resulting morphology of the permafrost subsurface is thought to have resembled the scalloped solid‐liquid interface morphology produced in terrestrial convective flow visualization studies. The exact size and shape of the scallops on the frozen subsurface would have been controlled by the dimensions of the convection cells, which are estimated to have had width‐to‐depth ratios of between 3.4 and 4.5. Subsequent stresses (e.g., gravity and bending stresses) would have produced maximum tensile stresses in the overlying sediments preferentially above the subsurface topographic highs as described previously by McGill and Hills [1992]. Additional desiccation of the sediments would have required contraction of the sediment cover and would have produced large‐scale polygonal fractures along the preexisting weaknesses located above the raised subsurface topography. Thus the underlying subsurface geometric morphology would have been translated to the surface and would be represented by the large‐scale polygonal fractures visible in the Viking Orbiter and Mars Global Surveyor images of the Martian northern plains.

Evidence of ancient continental glaciation in the Martian northern plains

Whorled ridges, spaced about 2–6 km and forming lobate patterns with lobe widths of about 150 km, occur at many locations in the northern plains of Mars, commonly in close association with sinuous troughs that contain medial ridges. These landforms resemble moraines, tunnel channels, and eskers found in terrestrial glacial terrains, such as the midcontinent of North America. Some Martian landscapes may have formed by disintegration of continental glaciers that covered much of the northern plains into the early Amazonian (i.e., late in Martian geologic history). Meltwater processes apparently were important in the collapse of these hypothesized ice sheets; hence, the glaciers apparently were wet based in part. Whereas striking similarities exist among areas of the northern plains and some glaciated Pleistocene terrains on Earth, there are also important differences; notably, drumlin fields, such as those in many glacial landscapes on Earth, are rare, absent, or not yet resolved in images of the Martian northern plains. Another major difference is that postglacial fluvial and other water‐related modifications (especially erosion) of Pleistocene terrains are substantial, but similar modifications are not observed in the northern plains; a virtually complete and sudden decline in the activity of liquid surface water following glaciation in the northern plains seems to be implied. The climatic implications of the hypothesized Martian glaciers and their decline are unclear. We investigate two possibilities, alternatively involving a relatively warm paleoclimate and the modern Martian climate. The hypothesized ice sheets in the basins within the northern plains (generally at elevations lower than −1 km) suggest a relationship of these frozen bodies of water with former regional lakes or seas, which may have formed in response to huge discharges of water from Martian outflow channels. This possible relationship has been modeled. Glaciers may have evolved from seas by their progressive freezing and then grounding and sublimational redistribution of sea ice. The transition to glaciation may have taken several million years if the climate was very cold, comparable to today's, or tens of thousands of years if the climate was as warm as modern Antarctica. A glacierized sea may have involved an extended period of glaciolacustrine and ice shelf processes.

Chemical weathering and its effects on the morphology of the northern plains of mars

Chemical weathering and its effects on the morphology of the northern plains of mars

Subkilometer Martian volcanoes: Properties and possible terrestrial analogs

Kilometer to subkilometer cones with large central craters are the most numerous volcanic structures in the northern plains of Mars. Based on examination of more than 12,000 high resolution Viking orbiter images, most of these very small cones are located in parts of Eastern Acidalia and Utopia‐Isidis‐Elysium Planitia. Measurements of base and pit diameter for some 2000 well‐resolved features show small variations in the histogram of base diameters between and within regions but remarkable similarity in the distribution of crater/cone diameter ratios. This suggests that the small cones had a similar origin with only minor variations in local conditions. The Acidalia cones are generally larger, more widely distributed, and occur on a greater variety of terrains than those in Utopia‐Isidis‐Elysium. Based on morphology, distribution, and the crater/cone ratio histograms, the smallest Martian cones may be similar to Icelandic pseudocraters. Somewhat larger, steeper cones with smaller crater/cone ratios which also occur in Eastern Acidalia may be analogs of terrestrial cinder cones.