Apollo 16 Geochemical X-ray Fluorescence Experiment: Preliminary Report

Abstract

The lunar surface was mapped with respect to magnesium, aluminum, and silicon as aluminum/ silicon and magnesium/ silicon intensity ratios along the projected ground tracks swept out by the orbiting Apollo 16 spacecraft. The results confirm the observations made during the Apollo 15 flight and provide new data for a number of features not covered before. The data are consistent with the idea that the moon has a widespread differentiated crust (the highlands). The aluminum/ silicon and magnesium/ silicon concentration ratios correspond to those for anorthositic gabbros through gabbroic anorthosites or feldspathic basalts. The x-ray results suggest the occurrence of this premare crust or material similar to it at the Descartes landing site.

The distribution and purity of anorthosite across the Orientale basin: New perspectives from Moon Mineralogy Mapper data

“…The dashed lines indicate the three topographic rings shown in Figure 1 and demonstrate that the brightest pixels in the region are concentrated around the Inner Rook Ring. areas covered by the Apollo 15 and 16 spacecraft [e.g., Adler et al, 1972aAdler et al, , 1972bSpudis and Davis, 1986].…”

“…Instead, they identified areas that were consistent with anorthosite based on spectra that exhibited other characteristics of plagioclase‐dominated rocks, namely, (1) a high albedo and (2) a lack of mafic mineral absorptions, indicating low modal proportions of olivine and pyroxene. The interpretation that these bright, mafic‐poor regions were rich in plagioclase was supported by lower resolution orbital geochemical data, which noted high aluminum and low iron abundances in similar highland areas covered by the Apollo 15 and 16 spacecraft [e.g., Adler et al ., , ; Spudis and Davis , ].…”

MESSENGER detection of electron‐induced X‐ray fluorescence from Mercury's surface

“…The counters each have a 10 cm 2 active area and use both anti‐coincidence wires placed around the inner periphery of the tube and pulse‐shape discrimination to minimize background, due primarily to galactic cosmic rays (GCRs). Balanced filters, similar to those used on the Apollo 15, 16, and Near Earth Asteroid Rendezvous (NEAR) missions, are used to resolve the lower‐energy X‐ray lines from Mg, Al, and Si, at 1.254, 1.487, and 1.740 keV, respectively [ Adler et al , 1972a,1972b; Nittler et al , 2001]. A thin foil of Mg (4.5 μ m) on one detector and of Al (6.3 μ m) on another are mounted over the GPC entrance windows [ Schlemm et al , 2007].…”

“…Atoms near the surface of planetary bodies with no atmosphere may be excited by solar X‐rays, solar wind particles (primarily electrons), and ions, producing line emission and bremsstrahlung. The first planetary X‐ray fluorescence (XRF) detections were made by Luna 12 in 1968 [ Adler et al , 1973] and then by the X‐ray spectrometers on Apollo 15 and 16 [ Adler et al , 1972a, 1972b]. X‐rays from Jupiter and the Galilean satellites, produced by particles (mostly heavy ions) trapped in the Jovian magnetosphere, were originally detected by the Einstein X‐Ray Observatory [ Metzger et al , 1983].…”

“…Such is the case with solar‐induced X‐ray fluorescence, by which measurements of X‐ray emissions from planetary surfaces have been used to infer surface elemental abundances. Orbiting spacecraft at the Moon [ Adler et al , 1972a,1972b; Narendranath et al , 2011; Weider et al , 2012], the asteroids 433 Eros and 25143 Itokawa [ Trombka et al , 2000; Okada et al , 2006], and most recently Mercury [ Nittler et al , 2011] have provided details of surface composition for a number of important rock‐forming elements.…”