Major‐element abundances on the surface of Mercury: Results from the MESSENGER Gamma‐Ray Spectrometer

Evans, L. G.; Peplowski, P. N.; Rhodes, E. A.; Lawrence, D. J.; McCoy, Timothy J.; Nittler, L. R.; Solomon, Sean C.; Sprague, A. L.; Stockstill-Cahill, K. R.; Starr, R.; Weider, S. Z.; Boynton, W. V.; Hamara, D.; Goldsten, J.

doi:10.1029/2012je004178

Cited by 160 publications

(146 citation statements)

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“…, because gamma-ray attenuation is not significant for these angles for the 1779-keV Si peak [Peplowski et al, 2012], which is known to be dominated by planet-originating gamma rays [Evans et al, 2012]. The removal of off-nadir pointing data reinforces the bias of these measurements to northern regions, as it disproportionately removes data south of the periapsis latitude (see Figure 2).…”

Section: Messenger Gamma-ray Spectrometer Al Measurementsmentioning

confidence: 57%

“…[2] Gamma-ray spectroscopy is a well-established technique for the remote characterization of the elemental composition of planetary surfaces, as has been demonstrated by its successful utilization from orbit around the Moon [e.g., Bielefeld et al, 1976;Lawrence et al, 1998;Yamashita et al, 2010] and Mars and by the MErcury Surface, Space ENviroment, GEochemisty, and Ranging (MESSENGER) spacecraft at Mercury [Peplowski et al, 2011b;Evans et al, 2012]. The Dawn spacecraft is also carrying a gamma-ray spectrometer to characterize the surface compositions of asteroids 4 Vesta and 1 Ceres [Prettyman et al, 2011].…”

Section: Introductionmentioning

confidence: 99%

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Aluminum abundance on the surface of Mercury: Application of a new background‐reduction technique for the analysis of gamma‐ray spectroscopy data

et al. 2012

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[1] A new technique has been developed for characterizing gamma-ray emission from a planetary surface in the presence of large background signals generated in a spacecraft. This technique is applied to the analysis of Al gamma rays measured by the MESSENGER Gamma-Ray Spectrometer to determine the abundance of Al on the surface of Mercury. The result (Al/Si = 0.29 À0.13 +0.05 ) is consistent with Al/Si ratios derived from the MESSENGER X-Ray Spectrometer and confirms the finding of low Al abundances. The measured abundance rules out a global, lunar-like feldspar-rich crust and is consistent with previously suggested analogs for surface material on Mercury, including terrestrial komatiites, low-iron basalts, partial melts of CB chondrites, and partial melts of enstatite chondrites. Additional applications of this technique include the measurement of other elements on Mercury's surface as well as the analysis of data from other planetary gamma-ray spectrometer experiments.

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Section: Messenger Gamma-ray Spectrometer Al Measurementsmentioning

confidence: 57%

Section: Introductionmentioning

confidence: 99%

Aluminum abundance on the surface of Mercury: Application of a new background‐reduction technique for the analysis of gamma‐ray spectroscopy data

et al. 2012

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“…Our calculations to correct the effect of sulfides on Ca and Mg concentrations in the silicate melt are thus probably the most conservative. Evans et al (2012) have reported a first average abundance estimate of ca. 2.9 wt% Na (3.9 wt% Na 2 O) on Mercury's surface.…”

Section: The Roles Of Sulfur and Iron Metalmentioning

confidence: 99%

“…First, this element reduces the liquidus temperature. The high average amount of Na (3.9 wt% Na 2 O) reported by Evans et al (2012) would also produce significantly different calculated mineral component. As illustrated in Fig.…”

Section: Low-pressure Differentiation Of Mercury Lavasmentioning

confidence: 99%

Phase equilibria of ultramafic compositions on Mercury and the origin of the compositional dichotomy

Charlier

Grove

Zuber

2013

Earth and Planetary Science Letters

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a b s t r a c tMeasurements of major element ratios obtained by the MESSENGER spacecraft using x-ray fluorescence spectra are used to calculate absolute element abundances of lavas at the surface of Mercury. We discuss calculation methods and assumptions that take into account the distribution of major elements between silicate, metal, and sulfide components and the potential occurrence of sulfide minerals under reduced conditions. These first compositional data, which represent large areas of mixed highreflectance volcanic plains and low-reflectance materials and do not include the northern volcanic plains, share common silica-and magnesium-rich characteristics. They are most similar to terrestrial volcanic rocks known as basaltic komatiites. Two compositional groups are distinguished by the presence or absence of a clinopyroxene component. Melting experiments at one atmosphere on the average compositions of each of the two groups constrain the potential mineralogy at Mercury's surface, which should be dominated by orthopyroxene (protoenstatite and orthoenstatite), plagioclase, minor olivine if any, clinopyroxene (augite), and tridymite. The two compositional groups cannot be related to each other by any fractional crystallization process, suggesting differentiated source compositions for the two components and implying multi-stage differentiation and remelting processes for Mercury. Comparison with high-pressure phase equilibria supports partial melting at pressure o10 kbar, in agreement with last equilibration of the melts close to the crust-mantle boundary with two different mantle lithologies (harzburgite and lherzolite). Magma ocean crystallization followed by adiabatic decompression of mantle layers during cumulate overturn and/or convection would have produced adequate conditions to explain surface compositions. The surface of Mercury is not an unmodified quenched crust of primordial bulk planetary composition. Ultramafic lavas from Mercury have high liquidus temperatures (1450-1350 1C) and very low viscosities, in accordance with the eruption style characterized by flooding of pre-existing impact craters by lava and absence of central volcanoes.

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“…On this basis, it has been suggested that hollow-formation involves the loss of the 'darkening' agent within LRM [Blewett et al, 2013], which may be spectrally neutral (making LRM relatively 'blue' by counteracting the 'redness' of other components) [Blewett et al, 2009]. Calcium or magnesium sulfides are most commonly-cited as candidates for the relatively volatile substance [Blewett et al, 2011[Blewett et al, , 2013Helbert et al, 2012], on the basis of the high concentration of sulfur detected at Mercury's surface [Nittler et al, 2011;Evans et al, 2012], expectations for mineralogy under Mercury's highly reducing conditions [Burbine et al, 2002], and correlations between sulfur, calcium and magnesium abundance in heavily-cratered terrains [Weider et al, 2015]. This hypothesis has recently gained further support from observations of anomalously high exospheric calcium above the extensively-hollowed Tyagaraja crater [Bennett et al, 2016].…”

Section: Introductionmentioning

confidence: 99%

Mercury's low-reflectance material: Constraints from hollows

Thomas

Hynek

Rothery

et al. 2016

Icarus

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Highlights We investigate the composition of Mercury's deep volatile-rich low-reflectance layer. Reflectance spectra of lag on sublimation hollow floors within it provide constraints. Analysis supports volatile (Mg,Ca) sulfides and non-volatile graphite within LRM. Unusually low reflectance material, within which depressions known as hollows appear to be actively forming by sublimation, is a major component of Mercury's surface geology. The observation that this material is exhumed from depth by large impacts has the intriguing implication that the planet's lower crust or upper mantle contains a significant volatile-rich, lowreflectance layer, the composition of which will be key for developing our understanding of Mercury's geochemical evolution and bulk composition. Hollows provide a means by which the composition of both the volatile and non-volatile components of the low-reflectance material (LRM) can be constrained, as they result from the loss of the volatile component, and any remaining lag can be expected to be formed of the non-volatile component. However, previous work has approached this by investigating the spectral character of hollows as a whole, including that of bright deposits surrounding the hollows, a unit of uncertain character. Here we use high-resolution multispectral images, obtained as the MESSENGER spacecraft approached Mercury at lower altitudes in the latter part of its mission, to investigate reflectance spectra of inactive hollow floors where sublimation appears to have ceased, and compare this to those of the bright surrounding products and the parent material. This analysis reveals that the final lag after hollow-formation has a flatter spectral slope than that of any other unit on the planet and reflectance approaching that of more space-weathered parent material. This indicates firstly that the volatile material lost has a steeper spectral slope and higher reflectance than the parent material, consistent with (Ca,Mg) sulfides, and secondly, that the low-reflectance component of LRM is non-volatile and may be graphite.

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Major‐element abundances on the surface of Mercury: Results from the MESSENGER Gamma‐Ray Spectrometer

Cited by 160 publications

References 45 publications

Aluminum abundance on the surface of Mercury: Application of a new background‐reduction technique for the analysis of gamma‐ray spectroscopy data

Aluminum abundance on the surface of Mercury: Application of a new background‐reduction technique for the analysis of gamma‐ray spectroscopy data

Phase equilibria of ultramafic compositions on Mercury and the origin of the compositional dichotomy

Mercury's low-reflectance material: Constraints from hollows

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