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X-ray fluorescence spectra obtained by the MESSENGER spacecraft orbiting Mercury indicate that the planet's surface differs in composition from those of other terrestrial planets. Relatively high Mg/Si and low Al/Si and Ca/Si ratios rule out a lunarlike feldspar-rich crust. The sulfur abundance is at least 10 times higher than that of the silicate portion(More)
Using the Gamma-Ray Spectrometer on the Mars Odyssey, we have identified two regions near the poles that are enriched in hydrogen. The data indicate the presence of a subsurface layer enriched in hydrogen overlain by a hydrogen-poor layer. The thickness of the upper layer decreases with decreasing distance to the pole, ranging from a column density of about(More)
The MESSENGER Gamma-Ray Spectrometer measured the average surface abundances of the radioactive elements potassium (K, 1150 ± 220 parts per million), thorium (Th, 220 ± 60 parts per billion), and uranium (U, 90 ± 20 parts per billion) in Mercury's northern hemisphere. The abundance of the moderately volatile element K, relative to Th and U, is inconsistent(More)
Hydrogen has been inferred to occur in enhanced concentrations within permanently shadowed regions and, hence, the coldest areas of the lunar poles. The Lunar Crater Observation and Sensing Satellite (LCROSS) mission was designed to detect hydrogen-bearing volatiles directly. Neutron flux measurements of the Moon's south polar region from the Lunar(More)
Introduction: The Mars Odyssey Gamma Ray Spectrometer (GRS) uniquely determines the chemistry the upper few tens of centimeters of the surface [1,2]. The chemistry of the mobile components (dust, soil, drifts, dunes, mantles, etc.) provides clues to geo-chemical processes during martian history, including possible chemical fractionations between the crust(More)
  • CRATERING MINERALOGY, K. W. Larsen, +16 authors K. Reedy
  • 2004
A laboratory facility has been setup to measure the complex permittivity of soil mixtures as a function of porosity, humidity, and temperature in the range 20 Hz–10 kHz. The influence of porosity and temperature are discussed, and a measurable gravimetric water content threshold is evaluated. We present the first radar mosaic of eastern Sahara that reveals(More)
Introduction: The Lunar Exploration Neutron Detector (LEND) instrument on board the Lunar Reconnaissance Orbiter (LRO) spacecraft will measure both the neutron emission (albedo) from the lunar surface and the local neutron background in orbit [1]. The objectives of the LEND science investigation is to determine with high spatial resolution possible presence(More)
[1] A technique for converting gamma-ray count rates measured by the Gamma-Ray Spectrometer on the MESSENGER spacecraft to spatially resolved maps of the gamma-ray emission from the surface of Mercury is utilized to map the surface distributions of the elements Si, O, and K over the planet's northern hemisphere. Conversion of the K gamma-ray count rates to(More)
The first map of variations in the abundances of thermal-neutron-absorbing elements across Mercury's surface has been derived from measurements made with the anti-coincidence shield on MESSENGER's Gamma-Ray Spectrometer (GRS). The results, which are limited to Mercury's northern hemisphere, permit the identification of four major geochemical terranes at the(More)