Space weathering on airless planetary bodies: Clues from the lunar mineral hapkeite

Abstract

Physical and chemical reactions occurring as a result of the highvelocity impacts of meteorites and micrometeorites and of cosmic rays and solar-wind particles are major causes of space weathering on airless planetary bodies, such as the Moon, Mercury, and asteroids. These weathering processes are responsible for the formation of their regolith and soil. We report here the natural occurrence of the mineral hapkeite, a Fe 2Si phase, and other associated Fe-Si phases (iron-silicides) in a regolith breccia clast of a lunar highland meteorite. These Fe-Si phases are considered to be a direct product of impact-induced, vapor-phase deposition in the lunar soil, all part of space weathering. We have used an in situ synchrotron energy-dispersive, single-crystal x-ray diffraction technique to confirm the crystal structure of hapkeite as similar to the structure of synthetic Fe 2Si. This mineral, hapkeite, is named after Bruce Hapke of the University of Pittsburgh, who predicted the presence and importance of vapor-deposited coatings on lunar soil grains some 30 years ago. We propose that this mineral and other Fe-Si phases are probably more common in the lunar regolith than previously thought and are directly related to the formation of vapor-deposited, nanophase elemental iron in the lunar soils.

Hybridization of partial least squares and neural network models for quantifying lunar surface minerals

“…Such compositional information can be used to examine the 'magma ocean' model of lunar crust formation and structural evolution, basaltic volcanism, impact crater/basin formation and ejecta emplacement, and lunar soil evolution and mixing mechanisms (Cahill et al, 2009;Elkins-Tanton et al, 2002;Longhi, 1978;Pieters, 1986;Pieters et al, 1993Pieters et al, , 1997Solomon and Longhi, 1977;Taylor, 1979;Tompkins and Pieters, 1999;Warren, 1990;Wood, 1975). In addition, variations in the chemical and mineralogical composition of lunar soils can inform us on the effects of space weathering (Anand et al, 2004;McKay et al, 1974;Noble et al, 2001;Starukhina and Shkuratov, 2001;Taylor et al, 2003Taylor et al, , 2010, and accurate global maps of lunar mineral composition and abundance are necessary for the exploration of mineral resources on the Moon.…”

The structure and electronic properties of hexagonal Fe2Si

“…However, hapkeite could be synthesized under the space weathering in airless environment and on the effect of meteorite impact. Since the hapkeite was found in lunar meteorites(Dhofar 280), it also contains Fe and Si elements as FeSi and FeSi 2 compounds, 6 the difference between hexagonal Fe 2 Si structure and the hapkeite as well as the possibility of mutual transformation are worth further study.…”

“…5 Thereafter, it was indeed found in a lunar meteorite of a highland-regolith breccia named as Dhofar 280. 6 This kind of tetragonal Fe 2 Si is called hapkeite. A similar isomer, hexagonal Fe 2 Si of P3-m1 symmetry group and Ni 2 In structure was also found in 1977.…”

Identification of tectonic deformations on the south polar surface of the moon

“…It has also been proposed that such kind of thermal stress may also have been responsible for the formation of lineaments/faults observed on the lunar crust (Solomon and Head, 1979). Such lineaments are tectonic landforms which indicate the occurrence of subsurface geological perturbations as a result of dislocation along fault planes resulting in surface disruptions, evidence of which gets buried over time under the lunar regolith or degraded due to space weathering (Anand et al, 2004). m-χ decomposition of Mini-SAR data has therefore been used to demarcate such hidden lineaments and associated dislocation features in the study region.…”