220 research outputs found
Concentration of H, Si, Cl, K, Fe, and Th in the low- and mid-latitude regions of Mars
We report maps of the concentrations of H, Si, Cl, K, Fe, and Th as determined by the Gamma Ray Spectrometer (GRS) on board the 2001 Mars Odyssey Mission for ±∼45° latitudes. The procedures by which the spectra are processed to yield quantitative concentrations are described in detail. The concentrations of elements determined over the locations of the various Mars landers generally agree well with the lander values except for Fe, although the mean of the GRS Fe data agrees well with that of Martian meteorites. The water-equivalent concentration of hydrogen by mass varies from about 1.5% to 7.5% (by mass) with the most enriched areas being near Apollinaris Patera and Arabia Terra. Cl shows a distribution similar to H over the surface except that the Cl content over Medusae Fossae is much greater than elsewhere. The map of Fe shows enrichment in the northern lowlands versus the southern highlands. Silicon shows only very modest variation over the surface with mass fractions ranging from 19% to 22% over most of the planet, though a significant depletion in Si is noted in a region west of Tharsis Montes and Olympus Mons where the Si content is as low as 18%. K and Th show a very similar pattern with depletions associated with young volcanic deposits and enrichments associated with the TES Surface Type-2 material. It is noted that there appears to be no evidence of significant globally distributed thick dust deposits of uniform composition. Copyright 2007 by the American Geophysical Union
North to south asymmetries in the water‐equivalent hydrogen distribution at high latitudes on Mars
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95381/1/jgre2434.pd
Accessible Content and Accessibility Experiences: The Interplay of Declarative and Experiential Information in Judgment
Recall tasks render 2 distinct sources of information available: the recalled content and the experienced ease or difficulty with which it can be brought to mind. Because retrieving many pieces of information is more difficult than retrieving only a few, reliance on accessible content and subjective accessibility experiences leads to opposite judgmental outcomes. People are likely to base judgments on accessibility experiences when they adopt a heuristic processing strategy and the informational value of the experience is not called into question. When the experience is considered nondiagnostic, or when a systematic processing strategy is adopted, people rely on accessible content. Implications for the operation of the availability heuristic and the emergence of knowledge accessibility effects are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68686/2/10.1207_s15327957pspr0202_2.pd
On the spatial variability of the Martian elastic lithosphere thickness: Evidence for mantle plumes?
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Overview of the mars pathfinder mission : launch through landing, surface operations, data sheets, and science results
Mars Pathfinder successfully landed at Ares Vallis on July 4, 1997, deployed and navigated
a small rover about l00 m clockwise around the lander, and collected data from three science
instruments and ten technology experiments. The mission operated for three months and returned
2.3 Gbits of data, including over 16,500 lander and 550 rover images, 16 chemical analyses of
rocks and soil, and 8.5 million individual temperature, pressure and wind measurements. Pathfinder
is the best known location on Mars, having been clearly identified with respect to other features
on the surface by correlating five prominent horizon features and two small craters in lander
images with those in high-resolution orbiter images and in inertial space from two-way ranging
and Doppler tracking. Tracking of the lander has fixed the spin pole of Mars, determined the precession
rate since Viking 20 years ago, and indicates a polar moment of inertia, which constrains a
central metallic core to be between 1300 and ~2000 km in radius. Dark rocks appear to be high in
silica and geochemically similar to anorogenic andesites; lighter rocks are richer in sulfur and
lower in silica, consistent with being coated with various amounts of dust. Rover and lander images
show rocks with a variety of morphologies, fabrics and textures, suggesting a variety of rock
types are present. Rounded pebbles and cobbles on the surface as well as rounded bumps and pits
on some rocks indicate these rocks may be conglomerates (although other explanations are also
possible), which almost definitely require liquid water to form and a warmer and wetter past. Airborne
dust is composed of composite silicate particles with a small fraction of a highly magnetic
mineral, interpreted to be most likely maghemite; explanations suggest iron was dissolved from
crustal materials during an active hydrologic cycle with maghemite freeze dried onto silicate dust
grains. Remote sensing data at a scale of a kilometer or greater and an Earth analog correctly predicted
a rocky plain safe for landing and roving with a variety of rocks deposited by catastrophic
floods, which are relatively dust free. The surface appears to have changed little since it formed billions
of years ago, with the exception that eolian activity may have deflated the surface by ~3-7
cm, sculpted wind tails, collected sand into dunes, and eroded ventifacts (fluted and grooved
rocks). Pathfinder found a dusty lower atmosphere, early morning water ice clouds, and morning
near-surface air temperatures that changed abruptly with time and height. Small scale vortices,
interpreted to be dust devils, were observed repeatedly in the afternoon by the meteorology
instruments and have been imaged
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