303 research outputs found

    Stress distribution and topography of Tellus Regio, Venus

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    The Tellus Regio area of Venus represents a subset of a narrow latitude band where Pioneer Venus Orbiter (PVO) altimetry data, line-of-sight (LOS) gravity data, and Venera 15/16 radar images have all been obtained with good resolution. Tellus Regio also has a wide variety of surface morphologic features, elevations ranging up to 2.5 km, and a relatively low LOS gravity anomaly. This area was therefore chosen in order to examine the theoretical stress distributions resulting from various models of compensation of the observed topography. These surface stress distributions are then compared with the surface morphology revealed in the Venera 15/16 radar images. Conclusions drawn from these comparisons will enable constraints to be put on various tectonic parameters relevant to Tellus Regio. The stress distribution is calculated as a function of the topography, the equipotential anomaly, and the assumed model parameters. The topography data is obtained from the PVO altimetry. The equipotential anomaly is estimated from the PVO LOS gravity data. The PVO LOS gravity represents the spacecraft accelerations due to mass anomalies within the planet. These accelerations are measured at various altitudes and angles to the local vertical and therefore do not lend themselves to a straightforward conversion. A minimum variance estimator of the LOS gravity data is calculated, taking into account the various spacecraft altitudes and LOS angles and using the measured PVO topography as an a priori constraint. This results in an estimated equivalent surface mass distribution, from which the equipotential anomaly is determined

    Evolution of the east rim of the Hellas basin, Mars

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    The Hellas basin is a dominant feature in the ancient, southern cratered highlands of Mars. The east rim of Hellas is a complex geologic region affected by volcanism, tectonism, and channeling. A detailed study of the area between 27.5-42.4 degrees S and 260-275 degrees W was initiated to analyze the processes forming surface materials and to decipher the evolution of this geologically important highland area. Major units include Hadriaca and Tyrrhena Paterae in the north and Hesperian and Amazonian channeled plains and outflow channels in the south. A brief discussion of the findings is presented

    Physical properties of lava flows on the southwest flank of Tyrrhena Patera, Mars

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    Tyrrhena Patera (TP) (22 degrees S, 253.5 degrees W), a large, low-relief volcano located in the ancient southern highlands of Mars, is one of four highland paterae thought to be structurally associated with the Hellas basin. The highland paterae are Hesperian in age and among the oldest central vent volcanoes on Mars. The morphology and distribution of units in the eroded shield of TP are consistent with the emplacement of pyroclastic flows. A large flank unit extending from TP to the SW contains well-defined lava flow lobes and leveed channels. This flank unit is the first definitive evidence of effusive volcanic activity associated with the highland paterae and may include the best preserved lava flows observed in the Southern Hemisphere of Mars. Flank flow unit averages, channelized flow, flow thickness, and yield strength estimates are discussed. Analysis suggests the temporal evolution of Martian magmas

    Timing and formation of wrinkle ridges in the Tyrrhena Patera Region of Mars

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    Wrinkle ridges are distinctive linear to curvilinear arches topped by crenulated ridges and have been identified on the Moon, Mercury, and Mars. The presence of wrinkle ridges on other planetary surfaces has been used as a criterion for identifying volcanic plains. Recently, due to the presence of lava flow lobes and leveed channels, Greeley and Crown identified an area within Hesperia Planum as a flank flow unit associated with Tyrrhena Patera. Hesperia Planum surrounds Tyrrhena Patera and embays the eroded shield of the volcano to the north and south. The Tyrrhena Patera flank flow unit extends approx. 1000 km from the summit caldera to the southwest. More than 55 wrinkle ridges have been identified on this flank flow unit. The relationships between the lava flows and wrinkle ridges within the flank flow unit allow relative ages to be determined. Wrinkle ridges are classified as post flow if flow lobes appear to arch over the rises undeformed, with no evidence of flow ponding on the upstream side of the ridge, or of flows breaching the rises. Wrinkle ridges within Hesperia Planum and Tyrrhena Patera flank flow unit that trend NW-SE appear younger than the flank flow unit

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    Marine propeller blade tip flows

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1982.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.Bibliography: leaves 144-148.by David Scott Greeley.Ph.D

    Autonomous system identification and control of MACE II using the Frequency Domain Expert algorithm

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    Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77122/1/AIAA-1999-4586-175.pd

    Surface properties of Mars' polar layered deposits and polar landing sites

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    On December 3, 1999, the Mars Polar Lander and Mars Microprobes will land on the planet's south polar layered deposits near (76°S, 195°W) and conduct the first in situ studies of the planet's polar regions. The scientific goals of these missions address several poorly understood and globally significant issues, such as polar meteorology, the composition and volatile content of the layered deposits, the erosional state and mass balance of their surface, their possible relationship to climate cycles, and the nature of bright and dark aeolian material. Derived thermal inertias of the southern layered deposits are very low (50–100 J m^(−2) s^(−1/2) K^(−1)), suggesting that the surface down to a depth of a few centimeters is generally fine grained or porous and free of an appreciable amount of rock or ice. The landing site region is smoother than typical cratered terrain on ∼1 km pixel^(−1) Viking Orbiter images but contains low-relief texture on ∼5 to 100 m pixel^(−1) Mariner 9 and Mars Global Surveyor images. The surface of the southern deposits is older than that of the northern deposits and appears to be modified by aeolian erosion or ablation of ground ice
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