Geology topics

R.C. Elphic

Publications and source records attributed to R.C. Elphic.

4 recordsLinked to original sources

USGS2007

Vertical distribution of hydrogen at high northern latitudes on Mars: The Mars Odyssey Neutron Spectrometer

Neutron leakage currents measured using the Mars Odyssey Neutron Spectrometer are used to develop a two‐layer model of the distribution of hydrogen (here parameterized as water‐equivalent hydrogen, WEH) at high northern latitudes. The WEH abundance in the upper layer, Wup, was found to range between 1% and about 5%. The maximum value of the apparent thickness, D, of this upper layer peaks at about 60° latitude, giving the appearance of zonal bands of enhanced D in both hemispheres. This maximum is consistent with an expected transition from WEH contained solely in hydrous minerals at lower latitudes, to WEH contained both in the forms of water ice and water of hydration at high latitudes. A strong anti‐correlation between the WEH concentration in the lower layer and apparent depth, D, at high latitudes is observed and may provide clues to the origin of these deposits.

Geophysical Research Letters↗

USGS2007

Global spatial deconvolution of Lunar Prospector Th abundances

We have completed the first global spatial deconvolution analysis of planetary gamma‐ray data for lunar Th abundances as measured by the Lunar Prospector Gamma‐ray Spectrometer. We tested two different spatial deconvolution techniques – Jansson's method and the Pixon method – and determined that the Pixon method provides superior performance. The final deconvolved map results in a spatial resolution improvement of a factor of 1.5–2. The newly deconvolved data allow us to clearly delineate nearside Th enhancements and depressions, validate enhanced Th abundances associated with specific lunar red spots, and reveal new details of the Th distribution at the Aristarchus plateau.

Geophysical Research Letters↗

USGS2006

Refined thorium abundances for lunar red spots: Implications for evolved, nonmare volcanism on the Moon

We have used improved knowledge of the spatial distribution of thorium (Th) on the lunar surface, in conjunction with a forward modeling analysis of Lunar Prospector gamma ray data, to estimate the thorium abundances of lunar red spots. The results from this study can be combined with preexisting compositional and morphologic evidence to suggest that Hansteen Alpha, the Gruithuisen domes, and the Lassell massif are silicic, nonmare, volcanic constructs, similar in nature to terrestrial rhyolite domes. We propose that either silicate liquid immiscibility or, more likely, basaltic underplating could have produced lunar rhyolite domes. Thus the Lunar Prospector data presented in this study provide new information about the full range of volcanic and crustal processes that could have occurred on the Moon.

Journal of Geophysical Research E: Planets↗

USGS2004

Hydrated states of MgSO4 at equatorial latiudes on Mars

The stability of water ice, epsomite, and hexahydrite to loss of H 2O molecules to the atmosphere at equatorial latitudes of Mars was studied to determine their potential contributions to the measured abundance of water-equivalent hydrogen (WEH). Calculation of the relative humidity based on estimates of yearly averages of water-vapor pressures and temperatures at the Martian surface was used for this purpose. Water ice was found to be sufficiently unstable everywhere within 45?? of the equator that if the observed WEH is due to water ice, it requires a low-permeability cover layer near the surface to isolate the water ice below from the atmosphere above. In contrast, epsomite or hexahydrite may be stable in many near-equatorial locations where significant amounts of WEH are observed. Copyright 2004 by the American Geophysical Union.

Geophysical Research Letters↗