Goro Komatsu

Channels and valleys on Venus: Preliminary analysis of Magellan data

A preliminary survey of Magellan imagery reveals more than 200 newly discovered relic channel and valley landform complexes. For purposes of discussion the channels can be classed as simple, complex, and compound. Integrated valleys also occur. Simple channels include (1) sinuous rules that closely resemble their lunar counterparts and (2) a newly recognized long sinuous form of high width-to-depth ratio and remarkably constant width. Herein designated canali, the most spectacular of these channels is 6800 km long. One of the compound channels, an outflow complex in Lada Terra, extends over 1200 km and is up to 30 km wide. Streamlined hills and spill relationships at a cross-axial ridge are similar to features in flood channels. Venusian channels have a global distribution with most of the large canali-type channels developed on volcanic plains. Alternative hypotheses for the channel-forming processes include genesis by the following erosive fluids: ultramafic silicate melts, sulfur, and carbonate lavas. Each of these causative agents has profound implications for Venusian planetology. The remote possibility of an aqueous origin, indicated by apparent regime behavior of the active channeling process, cannot be excluded with absolute certainty.

A possible terrestrial analogue for haematite concretions on Mars

Recent exploration has revealed extensive geological evidence for a water-rich past in the shallow subsurface of Mars. Images of in situ and loose accumulations of abundant, haematite-rich spherical balls from the Mars Exploration Rover ‘Opportunity’ landing site at Meridiani Planum bear a striking resemblance to diagenetic (post-depositional), haematite-cemented concretions found in the Jurassic Navajo Sandstone of southern Utah. Here we compare the spherical concretions imaged on Mars to these terrestrial concretions, and investigate the implications for analogous groundwater-related formation mechanisms. The morphology, character and distribution of Navajo haematite concretions allow us to infer host-rock properties and fluid processes necessary for similar features to develop on Mars. We conclude that the formation of such spherical haematite concretions requires the presence of a permeable host rock, groundwater flow and a chemical reaction front.

Paleohydrology and flood geomorphology of Ares Vallis

Ares Vallis is a Martian outflow channel which is about 1500 km long and locally exceeds 100 km in width and 1000 m in depth. We estimate the channels paleoflow capacity using paleohydraulic techniques. At a constricted and unusually deep reach, not affected by tributaries or secondary inflows, the estimated possible maximum peak discharges are of the order of 108–109 m3/s. These values are 1 to 2 orders of magnitude larger than any known terrestrial floods. These high-discharge flows were theoretically capable of transporting boulders larger than 10 m in diameter. The downstream depositional plain, where Ares debauches into the Chryse Planitia, displays geomorphological features indicative of high erosional capacity by the flooding. In this area, site of the proposed Pathfinder landing, we expect to find a complex sequence of sediments created by varying paleoflood flow hydraulics, sediment transport characteristics, and probable secondary modification of the primary flood landforms.

Stratigraphy and erosional landforms of layered deposits in Valles Marineris, Mars

The complex stratigraphy of layered deposits suggests a diversity of origins, ages, and post-depositional modification histories. The complexities within some layered deposits indicate changes in the dominant source materials in space and time. The stratigraphy of layered deposits in the isolated Martian chasmata Hebes, Juventae and Gangis is not well correlated. This indicates that at least these chasmata had isolated depositional environments resulting in different stratigraphic sequences. Separated layered deposits in Ophir-Candor and Melas Chasmata might have been a single continuous deposit in each chasma. Chaotic terrains are found in conjunction with layered deposits in Juventae, Gangis and Capri-Eos Chasmata. In these chasmata, layered deposits unconformably overlie chaotic terrains. Chaotic terrain formation may have provided water to form paleolakes, and lacustrine deposition of thick layered deposits may have occurred if the canyons were closed. A very thick sequence of the layered deposits has been exposed by erosion. A combination of gradual processes such as evaporation of ice and eolian and fluvial transport in addition to structural processes may be responsible for this erosion. Another alternative is that catastrophic water release under the layered deposits disrupted and initiated erosion of the layered deposits. Newly identified units of anomalous color are confined to the depressions or reentrants in western Candor Chasma. The difference in color between these units and the surrounding terrain is most consistent with a somewhat greater content of bulk crystalline hematite in these anomalous units. The presence of the Candor units is a result of original and/or secondary deposition which is different from the primary and dominant formation of the layered deposits.

Red rock and red planet diagenesis: Comparisons of Earth and Mars concretions

Compelling similarities between concretions on Earth and “blueberries” on Mars are used to suggest the blueberries are concretions that formed from a history of watery diagenesis. In the terrestrial examples, groundwater flow produces variations in sandstone color and iron oxide concretions in the Jurassic Navajo Sandstone of Utah. Variations in concretion mineralogy, form, and structure reflect different conditions at chemical reaction fronts, the influence of preferential fluid flow paths, the relative roles of advection and diffusion during precipitation, the presence of multiple events, fluid geochemistry, and time. The terrestrial concretions are analogs that can be used to understand the water-saturated conditions that formed spherical hematite concretions on Mars.

Paleoshoreline geomorphology of Böön Tsagaan Nuur, Tsagaan Nuur and Orog Nuur: the Valley of Lakes, Mongolia

Abstract We conducted a preliminary study of paleoshoreline features associated with Boon Tsagaan Nuur, Tsagaan Nuur, and Orog Nuur, lakes located in the Gobi–Altai transition zone of the Valley of Lakes (Dolina Ozor) which stretches from central to western Mongolia. The paleoshoreline features were first identified on RADARSAT satellite SAR imagery. We investigated the features during the 1998 field season of the Joint Mongolian–Russian–American Archaeological Expedition to the Gobi–Altai region. We identified paleoshorelines of multiple elevations in the field, which are considered to be relict beach ridges and wave-cut terraces. Other paleolake landforms include spits and Gilbert-type deltas. These landforms are complex, large and well established, implying that the paleolakes were stable for extended periods. The reconstructed paleolakes cover extensive areas of the valley floor, implying that hydrological and climatic conditions were very different in the past. Paleolake expansions may have occurred under a variety of circumstances. One hypothesis is that the high lake stands occurred during the wetter period corresponding to the Oxygen Isotope Stage 3 prior to the Last Glacial Maximum (LGM), during the warmest early Holocene and the late Holocene, or during all these periods. If low evaporation rates due to lower temperatures, glacier meltwater and possibly increased precipitation are important factors, then the expansions may have occurred during the terminal Late Glacial period after the Last Glacial Maximum. The greatly expanded lakes in the Gobi–Altai could have significantly affected the Quaternary human demography and migration in the region.

Meander properties of Venusian channels

Venusian channels, which probably are lava channels, have meander properties that relate to their mode of formation. Their channel meanders probably formed in response to flow dynamics, as in the case of terrestrial rivers, but low sinuosity indicates less developed morphology. The meanders generally follow terrestrial river trends for wavelength ( L ) to width ( W ) ratios, suggesting an equilibrium adjustment of channel form. Slightly higher L/W , in comparison to terrestrial rivers, occurs for Venusian channel types other than sinuous rilles. The unusually low L/W values for some Venusian and lunar sinuous rifles probably indicate modification of original meander patterns by erosional channel widening by lavas. The slightly larger radius of curvature to wavelength ratios of Venusian channels may be attributed to the short time during which the lava channels formed, and/or they may represent a quasi-equilibrium state for the system. Multiple wavelength meanders of specific Venusian channels may have resulted from changes in discharge or from structural control.

Canali‐type channels on Venus: Some genetic constraints

Canali-type channels on Venus are unique because of their great lengths (up to 6800 km) and nearly constant channel cross sectional shapes along their paths. A simple model incorporating channel flow and radiative cooling suggests that common terrestrial-type tholeiite lava cannot sustain a superheated and turbulent state for the long distances required for thermal erosion of canali within allowable discharge rates. If canali formed mainly by constructional processes, laminar tholeiitic flows of relatively high, sustained discharge rates might travel the observed distances, but the absence of levees would need to be explained. An exotic low temperature, low viscosity lava like carbonatite or sulfur seems to be required for the erosional genesis of canali.

Tier-Scalable Reconnaissance Missions For The Autonomous Exploration Of Planetary Bodies

A fundamentally new (scientific) reconnaissance mission concept, termed tier-scalable reconnaissance, for remote planetary (including Earth) atmospheric, surface and subsurface exploration recently has been devised that soon will replace the engineering and safety constrained mission designs of the past, allowing for optimal acquisition of geologic, paleohydrologic, paleoclimatic, and possible astrobiologic information of Venus, Mars, Europa, Ganymede, Titan, Enceladus, Triton, and other extraterrestrial targets. This paradigm is equally applicable to potentially hazardous or inaccessible operational areas on Earth such as those related to military or terrorist activities, or areas that have been exposed to biochemical agents, radiation, or natural disasters. Traditional missions have performed local, ground-level reconnaissance through rovers and immobile landers, or global mapping performed by an orbiter. The former is safety and engineering constrained, affording limited detailed reconnaissance of a single site at the expense of a regional understanding, while the latter returns immense datasets, often overlooking detailed information of local and regional significance.

Hydrogeologic processes of large-scale tectonomagmatic complexes in Mongolia–southern Siberia and on Mars

Large-scale tectonomagmatic complexes are common on Earth and Mars. Many of these complexes are created or at least influenced by mantle processes, including a wide array of plume types ranging from superplumes to mantle plumes. Among the most prominent complexes, the Mongolian plateau on Earth and the Tharsis bulge on Mars share remarkable similarities in terms of large domal uplifted areas, great rift canyon systems, and widespread volcanism on their surfaces. Water has also played an important role in the development of the two complexes. In general, atmospheric and surface water play a bigger role in the development of the present-day Mongolian plateau than for the Tharsis bulge, as evidenced by highly developed drainages and thick accumulation of sediments in the basins of the Baikal rift system. On the Tharsis bulge, however, water appears to have remained as ground ice except during periods of elevated magmatic activity. Glacial and periglacial processes are well documented for the Mongolian plateau and are also reported for parts of the Tharsis bulge. Ice-magma interactions, which are represented by the formation of subice volcanoes in parts of the Mongolian plateau region, have been reported for the Valles Marineris region of Mars. The complexes are also characterized by cataclysmic floods, but their triggering mechanism may differ: mainly ice-dam failures for the Mongolian plateau and outburst of groundwater for the Tharsis bulge, probably by magma-ice interactions, although ice-dam failures within the Valles Marineris region cannot be ruled out as a possible contributor. Comparative studies of the Mongolian plateau and Tharsis bulge provide excellent opportunities for understanding surface manifestations of plume-driven processes on terrestrial planets and how they interact with hydro-cryospheres.