Abstract:Repetitive impacts on the Moon lead to mixing of genuine local materials and exotic materials delivered by distal cratering events, controlling the dynamic evolution of lunar regolith (Hörz, 1977). Quantifying the contribution of exotic materials conventionally relies on remote sensing observations Qian, Xiao, Wang, et al., 2021), while investigations on returned lunar samples can provide more specific information on these exotic materials. Chang'E-5 ("CE-5" hereafter) mission has successfully returned 1,731 g… Show more
“…9a ). This observation is consistent with sample analyses that discovered possible ejecta excavated by the Aristarchus crater in the Chang’E-5 regolith 45 . Fig.…”
Section: Discussionsupporting
confidence: 90%
“…On the Moon, the Chang’E-5 mission recently returned regolith from one of the youngest mare units 44 . Minor exotic materials that were ejected from the other regions of the Moon are discovered in the regolith, and their provenances are valuable to deduce the lithological diversity of the Moon and the evolution of local regolith 45 – 47 . Faint impact rays are widespread in the sampling region, yielding ambiguous potential source craters (Fig.…”
Impact ejecta are important references to establish regional and global stratigraphy of planetary bodies. Canonical views advocate radial distributions of distal ejecta with respect to the source crater, and their trajectories are significantly deflected on fast-rotating bodies. The Hokusai crater on Mercury formed a peculiar ray that features a hyperbola shape, and the sharp swerve of orientation was interpreted as a sign of a faster planetary rotation in the near past. Here, we show that this ray was not caused by a hypothesized larger Coriolis force, but due to abruptly-steepened ejection angles. Heterogeneous shock impedances of pre-impact impactor and/or target, such as topographic undulations, affect local propagation paths of shock and rarefaction waves, causing sudden changes of ejection angles. Distal ejecta with non-radial distributions are an inherent product of planetary impacts, and their unobvious provenances could mislead stratigraphic interpretations and hamper age estimations based on spatial densities of impact craters.
“…9a ). This observation is consistent with sample analyses that discovered possible ejecta excavated by the Aristarchus crater in the Chang’E-5 regolith 45 . Fig.…”
Section: Discussionsupporting
confidence: 90%
“…On the Moon, the Chang ’E-5 mission recently returned regolith from one of the youngest mare units 44 . Minor exotic materials that were ejected from the other regions of the Moon are discovered in the regolith, and their provenances are valuable to deduce the lithological diversity of the Moon and the evolution of local regolith 45 – 47 . Faint impact rays are widespread in the sampling region, yielding ambiguous potential source craters (Fig.…”
Impact ejecta are important references to establish regional and global stratigraphy of planetary bodies. Canonical views advocate radial distributions of distal ejecta with respect to the source crater, and their trajectories are significantly deflected on fast-rotating bodies. The Hokusai crater on Mercury formed a peculiar ray that features a hyperbola shape, and the sharp swerve of orientation was interpreted as a sign of a faster planetary rotation in the near past. Here, we show that this ray was not caused by a hypothesized larger Coriolis force, but due to abruptly-steepened ejection angles. Heterogeneous shock impedances of pre-impact impactor and/or target, such as topographic undulations, affect local propagation paths of shock and rarefaction waves, causing sudden changes of ejection angles. Distal ejecta with non-radial distributions are an inherent product of planetary impacts, and their unobvious provenances could mislead stratigraphic interpretations and hamper age estimations based on spatial densities of impact craters.
“…Observations of Saturn’s rings show concentrations of silica that are likely induced through hydrothermal mechanisms on its moon Enceladus . Multiple studies of lunar regolith, collected from both the moon − and from meteorites on earth, , show high concentrations of various silica crystal structures. Lunar silica is shown to be connected to the presence of H 2 O on the moon’s surface, evidence of which is given through infrared observations with the now-retired Stratospheric Observatory For Infrared Astronomy (SOFIA).…”
Silica grains are ubiquitous in both circumstellar media
and rocky
bodies and are vital to cosmic chemical processes, such as surface-catalyzed
reactions and lunar water generation. Despite their pervasiveness,
the chemical processes behind their formation and destruction, both
of which are key to understanding their broader chemistry, are not
fully established as of yet. Using chemically accurate CCSD(T)-F12/cc-pVTZ-F12
quantum chemical calculations, a reaction pathway including the possible
bulk silica precursors Si3O6 and Si6O12 is mapped out herein. Through the reaction of SiO
and H2O, the formation of such precursors is possible under
circumstellar conditions. Expansion of this pathway may contribute
to a complete understanding of silica and silicate chemistry throughout
the universe. The constructed reaction pathway also shows that in
the reverse reaction, processing of lunar silicates under the available
photon flux of the sun can
result in H2O production, following previous observations.
The acceleration of H2O generation may be made possible
through exposure of lunar silica to applied H2 in future
aerospace ventures.
“…In addition, many high-pressure minerals (e.g., ringwoodite, majorite, akimotoite, lingunite, tuite, xieite, and hemleyite) were identified in shocked meteorites, which often show nanoscale microstructures (e.g., planar defects) that can be characterized by TEM. − For example, recent nanoscale mineralogical observations of the defects (stacking faults) and crystal structure analyses of olivine, ringwoodite, and wadsleyite have indicated that shear mechanisms promote polymorphic transformations and the occurrence of an intermediate spinelloid structure (named poirierite by the Commission on New Minerals and Mineral Names of the International Mineralogical Association) . Previous studies − of airless extraterrestrial bodies (e.g., the Moon) have shown that the large number of impact craters of different sizes on their surfaces indicate that the conditions for hypervelocity impacts are capable of forming high-pressure mineral phases and impact melts, which require further investigation using TEM. − …”
Section: Mineral Structure At the Nanoscalementioning
Nanoscale minerals (i.e., nanominerals
and mineral nanoparticles)
in terrestrial and extraterrestrial materials are difficult to characterize
because of their small particle sizes, high surface energy, and/or
poor crystallization. Transmission electron microscopy (TEM) is a
powerful analytical platform for the characterization of minerals
at the nano and even atomic scales, and it can determine their morphology
through imaging, derive structural information using multiple electron-diffraction
techniques, and investigate chemical compositions. Since the 1990s,
the application of TEM to the characterization of nanoscale minerals
has developed rapidly into a core technique in nanoscale Earth and
planetary science (NEPS). This review introduces a brief history and
the general principles of TEM, considers detailed methods of preparing
specimens for nanoscale mineralogical characterization by TEM, and
emphasizes the contributions of TEM to multiple NEPS research fields
in recent decades. These contributions are considered from the perspective
of nanoscale mineralogical studies of morphology, structure, and chemistry
in complex geological materials. Finally, the work provides an outlook
on current opportunities to apply TEM methods to nanoscale mineralogical
study. This review aims to provide common and practical TEM methods
to NEPS researchers and to support the use of TEM for a wide range
of applications in nanoscale mineralogy to promote NEPS development.
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