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In this work we update the regolith mixing model presented by Gault et al. (1974), including new input values and reworking key parameters. Much as Gault et al. did, we present a way to calculate the rate at which lunar regolith is overturned at depth. The model describes a mixing front that proceeds downward from the surface following a power-law function of time. Our most important update is the...
This work revisits the hypothesis of the so-called ‘lunar terminal cataclysm’ suggested by Tera et al. (1973, 1974) as a strong peak in the meteorite bombardment of the Moon around 3.9 Ga ago. According to the hypothesis, most of the impact craters observed on the lunar highlands formed during this short time period and thus formed the majority of the lunar highland impact breccias and melts. The...
We assessed the morphologies of more than 930 simple impact craters (diameters 40m–10km) on the Moon using digital terrain models (DTMs) of a variety of terrains in order to characterize the variability of fresh crater morphology as a function of crater diameter. From Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) DTMs, we determined depth-to-diameter (d/D) ratios for an extremely...
Bright and dark wind streaks across Mars record wind patterns related to atmospheric circulation. In some cases these streaks represent erosion of a surface veneer; in others, they indicate sand grains mobilized by strong vortices shed off of positive relief, such as crater rims. While many streaks change length or orientation over time, others not only remain unchanged but also may indicate a completely...
The majority of hydrated silicate occurrences on Mars are associated with impact craters (Ehlmann et al., 2011; Carter et al., 2013). Three formation mechanisms have been suggested to account for this correlation: (1) aqueous alteration occurred pre-impact, and was subsequently exposed via the impact (pre-impact; Bibring et al., 2006; Ehlmann et al., 2011), (2) heat generated from the impact facilitated...
Using SELENE/Kaguya Terrain Camera and Lunar Reconnaissance Orbiter Camera (LROC) data, we produced a new, high-resolution (10m/pixel), geomorphological and impact melt distribution map for the lunar crater Tycho. The distal ejecta blanket and crater rays were investigated using LROC wide-angle camera (WAC) data (100m/pixel), while the fine-scale morphologies of individual units were documented using...
To simulate the formation of impact glasses on Mars, an analogue of martian bright soil (altered volcanic soil JSC Mars-1) was melted at relevant oxygen fugacities using a pulsed laser and a resistance furnace. Reduction of Fe3+ to Fe2+ and in some cases formation of nanophase Fe0 in the glasses were documented by Mössbauer spectroscopy and TEM studies. Reflectance spectra for several size fractions...
Viking mission image data revealed the total spatial extent of preserved volcanic surface on Mars. One of the dominating surface expressions is Olympus Mons and the surrounding volcanic province Tharsis. Earlier studies of the global volcanic sequence of events based on stratigraphic relationships and crater count statistics were limited to the image resolution of the Viking orbiter camera. Here,...
The issue of crater retention age estimates on planetary surfaces is discussed with an attempt to quantify the effect of overlapping primary and secondary impact crater populations in restricted crater diameter ranges. The approach to this problem is illustrated with a simple model production function where the secondary crater input is artificially enhanced. Extrapolation of such a secondary crater...
An intense impact flux upon a planet having a CO 2 + N 2 atmosphere, such as Mars, provides energy to synthesize nitric oxide, NO, which is likely converted into nitrate minerals. The same impact flux can decompose nitrate minerals if present in the crust. We build a numerical model to study the effects of early impact processes on the evolution of nitrogen in a dominantly CO 2...
Nitrogen isotopes appear to be escaping from Mars at approximately the primordial ratio 14 N/ 15 N ≈ 275 and to have an atmospheric nitrogen depletion time scale of about 800 Myr. For the standard model of a progressive decline of an initial inventory of atmospheric nitrogen, having no source of N, the agreement of the isotopic ratio of escaping N with primitive nitrogen would be coincidental...
The Lunar Prospector Electron Reflectometer has obtained the first global map of lunar crustal magnetic fields, revealing that the effects of basin-forming impacts dominate the large-scale distribution of remanent magnetic fields on the Moon. The weakest surface magnetic fields (<0.2 nT) are found within two of the largest and most recent impact basins, Orientale and Imbrium. Conversely, the largest...
The quantitative measurement of surface roughness of planetary surfaces at all scales provides insights into geological processes. A characterization of roughness variations at the scale of a few tens of meters is proposed that complements the analysis of local topographic data of the martian surface at kilometer scale, as achieved from the Mars Orbiter Laser Altimeter (MOLA) data, and at the subcentimeter...
Geochronological evidence for and against a late heavy bombardment (LHB) spike in impact rates on the Moon and meteorite parent bodies is re-examined. In particular, we find that the sampling of impact melts on the Moon is strongly biased against older examples, possibly due to preferential surface deposition of such melts and/or blanketing and burial by basin ejecta (arguments that the bias might...
Crater counts at lunar landing sites with measured ages establish a steep decline in cratering rate during the period ∼3.8 to ∼3.1 Gyr ago. Most models of the time dependence suggest a roughly constant impact rate (within factor ∼2) after about 3 Gyr ago, but are based on sparse data. Recent dating of impact melts from lunar meteorites, and Apollo glass spherules, clarifies impact rates from ∼3.2...
The first confirmed lunar impact flash due to a non-Leonid meteoroid is reported. The observed Perseid meteoroid impact occurred at 18 h 28 m 27 s on August 11, 2004 (UT). The selenographic coordinates of the lunar impact flash are 48±1° N and 72±2° E, and the flash had a visual magnitude of ca. 9.5 with duration of about 1/30 s. The mass of the impactor is estimated to have...
The following problems related to the origin of methane on Mars have been considered. (1) Laboratory simulations of the impact phenomena confirm effective heterogeneous chemistry between the products of the fireball. This chemistry lowers the fireball freezing temperature from 2000 to 750 K for methane and to 1100 K for CO/CO 2 . Production of methane on Mars by cometary impacts is 0.8% of...
The extensive impact cratering record on Mars combined with evidence from SNC meteorites suggests that a significant fraction of the surface is composed of materials subjected to variable shock pressures. Pressure-induced structural changes in minerals during high-pressure shock events alter their thermal infrared spectral emission features, particularly for feldspars, in a predictable fashion. To...
Meteoroid impact has been shown to be a source of sodium, and most likely of other elements, on the Moon. The same process could be also relevant for Mercury. In this work we calculate the vapor and neutral Na production rates on Mercury due to the impacts of meteoroids in the radius range of 10 −8 –10 −1 m. We limit our calculations to this size range, because meteoroids with radius...
Lunar rays are filamentous, high-albedo deposits occurring radial or subradial to impact craters. The nature and origin of lunar rays have long been the subjects of major controversies. We have determined the origin of selected lunar ray segments utilizing Earth-based spectral and radar data as well as FeO, TiO 2 , and optical maturity maps produced from Clementine UVVIS images. These include...
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