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 of Earth or the Moon, and this observation, together with a low surface Fe abundance, supports the view that Mercury formed from highly reduced precursor materials, perhaps akin to enstatite chondrite meteorites or anhydrous cometary dust particles Low Fe and Ti abundances do not support the proposal that opaque oxides of these elements contribute substantially to Mercury's low and variable surface reflectance

http://science.sciencemag.org/content/sci/333/6051/1847.full.pdf

The Major-Element Composition of Mercury’s Surface from MESSENGER X-ray Spectrometry

The role of lunar volcanism in the history of the moon is documented using lunar-orbit and earth-based data along with characterizations derived from Apollo and Luna sample-return missions. Characteristics of mare and highland volcanic features are described, Apollo and Luna results are discussed, and the characteristics of other mare deposits and of other highland features of possible volcanic origin are summarized. Major conclusions are that: (1) there is little unequivocal morphologic evidence for highland volcanism, (2) lunar mare lavas appear to have originated from depths of 100 to 500 km, (3) impact melting does not appear to have been a factor in the generation of mare lavas, (4) mare volcanism was characterized by massive outpourings of very fluid volatile-poor lava analogous to terrestrial flood basalts, (5) mare volcanism took place from 3.83 to about 2.5 billion years ago, (6) the preferential occurrence of mare deposits in large impact basins appears to be generically unrelated to basin formation, and (7) a thicker farside crust may be responsible for the distinctive nearside-farside asymmetry of mare deposits.

Lunar volcanism in space and time.

Seismic data fron the four stations of the Apollo passive seismic network have been analyzed to obtain the velocity structure of the moon. Analysis of body wave phases from artificial impacts of known impact time and position yields a crustal section. In the Mare Cognitum region the crust is about 60 km thick and is layered. In the 20-km-thick upper layer, velocity gradients are high and microcracks may play an important role. The 40-km-thick lower layer has a nearly constant 6.8-km/sec velocity. There may be a thin high-velocity layer present beneath the crust. The determination of seismic velocities in the lunar mantle is attempted by using natural impacts and deep moonquakes. The simplest model that can be proposed for the mantle consists of a 'lithosphere' overlying an 'asthenosphere'.

Structure of the Moon

http://oro.open.ac.uk/16347/1/Fraser_et_al.pdf

The mercury imaging X-ray spectrometer (MIXS) on BepiColombo

Evidence for geochemical terranes on Mercury: Global mapping of major elements with MESSENGER's X-Ray Spectrometer

Although only part of the information from the x-ray fluorescence geochemical experiment has been analyzed, it is clear that the experiment was highly successful. Significant compositional differences among and possibly within the maria and highlands have been detected. When viewed in the light of analyzed lunar rocks and soil samples, and the data from other lunar orbital experiments (in particular, the Apollo 15 gamma-ray spectroscopy experiment), the results indicate the existence of a differential lunar highland crust, probably feldspathic. This crust appears to be related to the plagioclase-rich materials previously found in the samples from Apollo 11, Apollo 12, Apollo 14, Apollo 15, and Luna 16.

/pdf/apollo-15-geochemical-x-ray-fluorescence-experiment-39y1u92sb2.pdf

Apollo 15 Geochemical X-ray Fluorescence Experiment: Preliminary Report.

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.

/pdf/apollo-16-geochemical-x-ray-fluorescence-experiment-1lr0we3f6y.pdf

Apollo 16 geochemical x-ray fluorescence experiment: preliminary report.

The X-ray fluorescence spectrometer, carried in the SIM bay of the command service module was employed principally for compositional mapping of the lunar surface while in lunar orbit, and secondarily, for X-ray astronomical observations during the trans-earth coast. The lunar surface measurements involved observations of the intensity and characteristics energy distribution of the secondary or fluorescent X-rays produced by the interaction of solar X-rays with the lunar surface. The astronomical observations consisted of relatively long periods of measurements of X-rays from pre-selected galactic sources such as Cyg-X-1 and Sco X-1 as well as from the galactic poles.

/pdf/apollo-15-x-ray-fluorescence-experiment-er8v349tpg.pdf

Apollo 15 X-ray fluorescence experiment

The prime purpose of the X-ray fluorescence spectrometer carried in the Scientific Instrument Module of the Command-Service Module was to map the lunar surface with respect to its chemical composition. Results are presented for Al, Mg, and Si as Al/Si and Mg/Si ratios for the various features overflow by the spacecraft. The lunar surface measurements involved observations of the intensity and characteristic energy distribution of the secondary or fluorescent X rays produced by the interaction of solar X rays with the lunar surface. The results showed that the highlands and maria are chemically different, with the highlands having considerably more Al and less Mg than the maria. The mare-highland contact is quite sharp and puts a limit on the amount of horizontal transport of material. The X-ray data suggest that the dominant rock type of the lunar highlands is a plagioclase-rich pyroxene bearing rock probably anorthositic gabbro or feldspathic basalt.

The Apollo 15 X-ray fluorescence experiment.

The preliminary results from the Sco X-1 and Cyg X-1 obtained from the Apollo 15 X-ray detector data are presented along with preliminary results of the X-ray fluorescence spectrometric data of the lunar surface composition. The production of the characteristic X-rays following the interaction of solar X-rays with the lunar surface is described along with the X-ray spectrometer. Preliminary analyses of the astronomical X-ray observation and the X-ray fluorescence data are presented.

J. Gerard

Papers

Apollo 15 Geochemical X-ray Fluorescence Experiment: Preliminary Report.

Apollo 16 geochemical x-ray fluorescence experiment: preliminary report.

Apollo 15 X-ray fluorescence experiment

The Apollo 15 X-ray fluorescence experiment.

X-ray fluorescence experiment