Morphology of fluvial networks on Titan: Evidence for structural control

Although Titan’s surface shows clear evidence of erosional modification, such as fluvial incision, evidence for tectonism has been less apparent. On Earth, fluvial networks with strongly preferred orientations are often associated with structural features, such as faults or joints, that influence flow or erodibility. We delineated and classified the morphologies of fluvial drainages on Titan and discovered evidence of structural control. Fluvial networks were delineated both on synthetic aperture radar (SAR) images covering ∼40% of Titan from the Cassini Titan Radar Mapper up through T71 and on visible light images of the Huygens landing site collected by the Descent Imager/Spectral Radiometer (DISR). The delineated networks were assigned to one of three morphologic classes—dendritic, parallel or rectangular—using a quantitative terrestrial drainage pattern classification algorithm modified for use with Titan data. We validated our modified algorithm by applying it to synthetic fluvial networks produced by a landscape evolution model with no structural control of drainage orientations, and confirmed that only a small fraction of the networks are falsely identified as structurally controlled. As a second validation, we confirmed that our modified algorithm correctly classifies terrestrial networks that are classified in multiple previous works as rectangular. Application of this modified algorithm to our Titan networks results in a classification of rectangular for one-half of the SAR and DISR networks. A review of the geological context of the four terrestrial rectangular networks indicates that tensional stresses formed the structures controlling those terrestrial drainages. Based on the similar brittle response of rock and cryogenic ice to stress, we infer that structures formed under tension are the most likely cause of the rectangular Titan networks delineated here. The distribution of these rectangular networks suggests that tensional stresses on Titan may have been widespread.United States. National Aeronautics and Space Administration (NASA Cassini Data Analysis Program Grant NNX08BA81G

Mars as a "natural laboratory" for studying surface activity on a range of planetary bodies

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AVIATR - Aerial Vehicle for In-situ and Airborne Titan Reconnaissance A Titan Airplane Mission Concept

We describe a mission concept for a stand-alone Titan airplane mission: Aerial Vehicle for In-situ and Airborne Titan Reconnaissance (AVIATR). With independent delivery and direct-to-Earth communications, AVIATR could contribute to Titan science either alone or as part of a sustained Titan Exploration Program. As a focused mission, AVIATR as we have envisioned it would concentrate on the science that an airplane can do best: exploration of Titan's global diversity. We focus on surface geology/hydrology and lower-atmospheric structure and dynamics. With a carefully chosen set of seven instruments-2 near-IR cameras, 1 near-IR spectrometer, a RADAR altimeter, an atmospheric structure suite, a haze sensor, and a raindrop detector-AVIATR could accomplish a significant subset of the scientific objectives of the aerial element of flagship studies. The AVIATR spacecraft stack is composed of a Space Vehicle (SV) for cruise, an Entry Vehicle (EV) for entry and descent, and the Air Vehicle (AV) to fly in Titan's atmosphere. Using an Earth-Jupiter gravity assist trajectory delivers the spacecraft to Titan in 7.5 years, after which the AVIATR AV would operate for a 1-Earth-year nominal mission. We propose a novel 'gravity battery' climb-then-glide strategy to store energy for optimal use during telecommunications sessions. We would optimize our science by using the flexibility of the airplane platform, generating context data and stereo pairs by flying and banking the AV instead of using gimbaled cameras. AVIATR would climb up to 14 km altitude and descend down to 3.5 km altitude once per Earth day, allowing for repeated atmospheric structure and wind measurements all over the globe. An initial Team-X run at JPL priced the AVIATR mission at FY10 $715M based on the rules stipulated in the recent Discovery announcement of opportunity. Hence we find that a standalone Titan airplane mission can achieve important science building on Cassini's discoveries and can likely do so within a New Frontiers budget

Investigations into the Cerberus outflow channels, Mars

Mars Orbiter Camera (MOC) images and Mars Orbiter Laser Altimeter (MOLA) data on the Mars Global Surveyor (MGS) spacecraft show evidence for three catastrophic outflow channels around the Cerberus Plains region, Mars. The morphologies seen in MOC images located within channels seen in gridded MOLA topography are similar to those found in catastrophic flood terrains on Earth, such as the Channeled Scabland. Thus, they indicate the channels' formation by catastrophic flood flow. The morphologies and topography also counterindicate the channels' formation by lava, glaciers or CO₂-charged density flows. Crater counting on lineated terrain, interpreted as diluvially eroded, gives model ages for the channels of extreme Upper Amazonian, ranging from 2-8 Ma for the youngest to 35-140 Ma for the oldest. The distinct age ranges, as well as the geographic/geologic relationships, indicate that the last flood flows down each of the channels were not contemporaneous. Two, and possibly all three, of the channels originate at the Cerberus Fossae volcano-tectonic fissures, although lack of erosion around the channels' origin at the fissures suggests the fissures have been recently reactivated. Neither magmatic melting of ground ice nor gravity-driven groundwater flow can produce a volumetric discharge at a rate commensurate with that estimated from the surface topography. Geomorphic evidence suggests floodwater ponded temporarily in Athabasca Vallis. Two paleoflood height indicators, which are separated by thirty-five kilometers along channel, have very similar heights. This may be explained by temporary ponding of floodwater behind a large crater in the channel, and consequent deposition of sediment in this slower flow. An additional factor contributing to the similar heights of the paleoflood indicators may be post-eruption subsidence near the origin of the channel, although this possibility, without the hypothesized ponding, cannot explain the preferential location of the streamlined forms up slope of the crater

Dynamics of fluid flow in Martian outflow channels

The conditions under which large volumes of water may have flowed at high speeds across the surface of Mars are considered. To assess the likely ranges of initial water temperature and release rate, the possible conditions in subsurface aquifers confined beneath the cryosphere are explored. Then the transfer of water to the surface in fractures induced by volcanic activity or tectonic events is modelled and the physical processes involved in its release into the Martian environment are discussed. The motion of the water across the surface is analysed with standard treatments for fluvial systems on Earth, modified for Mars by taking account of the differing environmental conditions and removing what may be considered to be the unsafe assumption that most channels involved bankfull flows. The most commonly discussed environmental difference is the smaller acceleration due to gravity on Mars. However, an important additional factor may have been the initially vigorous evaporation of water into the low-pressure Martian atmosphere. This process, together with the thermal losses incurred by assimilation of very cold rock and ice eroded from the cryosphere over which the water travels, causes minor changes in the depth and speed of a water flood but, eventually, produces major changes in the flood rheology as the total ice and sediment loads increase. The roles of these processes in determining the maximum distance to which the water may travel, and the relative importance of erosion and deposition in its bed, are discussed

Floods from fossae:A review of Amazonian-aged extensional-tectonic megaflood channels on mars

Summary. The four youngest megaflood channels on Mars – Mangala Valles, Marte Vallis, Grjotá Valles and Athabasca Valles – date to the Amazonian Period and originate at fissures. The channels show common in-channel morphological indications of flood activity (streamlined forms, longitudinal lineations, scour), as well as evidence for volcanic, tectonic, sedimentary and/or glacial/ground ice processes. The fissure sources and channel termini have varied expressions, suggesting various triggering mechanisms and fates for the floodwaters. Possible triggering mechanisms include magmatic processes (dyke intrusion), tectonic processes (extensional faulting) and a combination of both types of processes. Surface morphology suggests that each of these mechanisms may have operated at different times and locations. Upon reaching the surface, the water likely would have fountained at least a few tens of metres above the surface, producing some water and/or ice droplets at the fountain margins. The likely sources of the floodwater are subsurface aquifers of a few kilometres' thickness and a few tens of degrees Celsius in temperature. Introduction. Megaflooding on Mars has varied in origin and amount throughout the history of the planet. During the Noachian Period, the most ancient period, flooding originated from crater basins (Irwin and Grant, this volume Chapter 11). During the Early Hesperian Epoch, megafloods originated at chaos terrain often set within Valles Marineris chasmata (Coleman and Baker, this volume Chapter 9). During the Amazonian Period, the most recent period, megaflooding originated from fossae produced by extensional tectonism

A review of open-channel megflood depositional landforms on Earth and Mars

Large freshwater floods on Earth in recent times and in the Quaternary have often been associated with catastrophic out-bursts of water from lakes impounded by glacial-ice or debris (such as moraine). In either case, large-scale depositional sedimentary landforms are found along the courses of the floodwaters. On Mars, similar floods are believed to have resulted from catastrophic efflux of water from within the Martian surface. Within the Martian flood tracts, landforms have been imaged that appear similar to those identified on Earth. These are primarily suites of giant bars – “streamlined forms” – of varying morphology that occur primarily as longitudinal features within the floodways and along the margins as well as in areas of the floodways that were sheltered from the main flow. In addition, flow-transverse bedforms within the floodways have been identified as giant sedimentary dunes or antidunes. Information concerning the flood hydraulics that created these forms may be deduced from their location and plan view morphology. Some other fluvial landforms which have been associated with megafloods on Earth have yet to be identified on Mars. The examples from Earth are described, so as to spur the search for further water-lain landforms on Mar