James W. Head

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Surface conditions on Mars are currently cold and dry, with water ice unstable on the surface except near the poles. However, geologically recent glacierlike landforms have been identified in the tropics and the midlatitudes of Mars. The ice has been proposed to originate from either a subsurface reservoir or the atmosphere. We present high-resolution(More)
Surface environmental conditions on Mars are currently extremely cold and hyperarid, most equivalent to polar deserts on Earth. Coupling newly acquired Mars data with fieldbased observations regarding the flow, surface morphology, and depositional history of polar glaciers in Antarctica, we show that the multiple facies of an extensive fan-shaped deposit on(More)
[1] Recent Mars Orbiter Laser Altimeter (MOLA) data have provided a new picture of the Martian northern lowland basin topography and surface roughness. In order to assess detailed topographic structure important in understanding the formation and evolution of the northern lowlands, we have removed regional slopes from the topography to produce a series of(More)
[1] Restoration of the dichotomy boundary to its original position to assess its origin requires a thorough knowledge of processes responsible for its degradation and retreat. The unique fretted terrain, located along the DeuteronilusProtonilus Mensae northern mid-latitude portion of the boundary, has been long held to provide clues to dichotomy degradation(More)
Understanding spin orbital parameter-driven climate change on Mars prior to ~ 20 Ma ago requires geological evidence because numerical solutions for that period are chaotic and non-unique. We show geological evidence that lineated valley fill at low midlatitudes in the northern hemisphere of Mars (~ 37.58 N) originated through regional snow and ice(More)
Elevations measured by the Mars Orbiter Laser Altimeter have yielded a high-accuracy global map of the topography of Mars. Dominant features include the low northern hemisphere, the Tharsis province, and the Hellas impact basin. The northern hemisphere depression is primarily a long-wavelength effect that has been shaped by an internal mechanism. The(More)
Introduction [1]: Since their discovery, a variety of formation hypotheses have been proposed to explain the diversity of gully observations. These hypotheses can be divided into three broad categories: entirely dry mechanisms [2,3], wet mechanisms invoking groundwater release [4,5], and wet mechanisms invoking surficial meltwater [6,7,8]. It has been(More)
The origin of plains on Mercury, whether by volcanic flooding or impact ejecta ponding, has been controversial since the Mariner 10 flybys (1974-75). High-resolution images (down to 150 meters per pixel) obtained during the first MESSENGER flyby show evidence for volcanic vents around the Caloris basin inner margin and demonstrate that plains were emplaced(More)
The Caloris basin, the youngest known large impact basin on Mercury, is revealed in MESSENGER images to be modified by volcanism and deformation in a manner distinct from that of lunar impact basins. The morphology and spatial distribution of basin materials themselves closely match lunar counterparts. Evidence for a volcanic origin of the basin's interior(More)