The geologic history of the Moon

Wilhelms, D. E.; Trask, N.J.

doi:10.3133/pp1348

Cited by 873 publications

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“…The sharpness of the boundaries of these albedo patches distinguishes them from the diffuse downslope edges ofbright albedo patches found on Deimos (Thomas, 1979). Finally, on Eros high-albedo and relatively blue ejecta patterns are not found around small craters, while such features are found on the Main Belt S asteroids (Gaspra and Ida), Phobos and Deimos, and the lunar maria (Wilhelms, 1987;Carr et al, 1994;Sullivanetat., 1996;Pieters et al, 2001). Additionally, it was noted by Murchie et al (2002b) that on Eros there is a measurable dependence of the 950 to 750 nm ratio with incidence angle-materials appear "redder" at higher incidence angles, a common characteristic of silicate powders measured in the laboratory (Gradie et al, 1980;Gradie and Veverka, 1986).…”

Section: Introductionmentioning

confidence: 99%

“…High-resolutionLunar Orbiter images (-1 rn!pixel) revealed abundant evidence of a global lunar regolith in the form of boulders, partially buried or infilled craters, and slumps and slides on crater walls and on massifslopes. Apollo astronauts sampled the regolith to several meters depth, probed it with active and passive seismic experiments, and photographed it at extremely high resolution (see summaries and references in Heiken et al, 1991 andWilhelms, 1987). Conceptualizing the depth of the regolith on the lunar mare is perhaps a simpler exercise than in the lunar highlands or on Eros.…”

Section: Regolithmentioning

confidence: 99%

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The geology of 433 Eros

Robinson

Thomas

Veverka

et al. 2002

Meteorit & Planetary Scien

155

140

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Abstract-The global high-resolution imaging of asteroid 433 Eros by the Near-Earth Asteroid Rendezvous (NEAR) Shoemaker spacecraft has made it possible to develop the first comprehensive picture of the geology of a small S-type asteroid. Eros displays a variety of surface features, and evidence of a substantial regolith. Large scale facets, grooves, and ridges indicate the presence of at least one global planar structure. Directional and superposition relations of smaller structural features suggest that fracturing has occurred throughout the object. As with other small objects, impact craters dominate the overall shape as well as the small-scale topography of Eros. Depth/diameter ratios of craters on Eros average -0.13, but the freshest craters approach lunar values of -0.2. Ejecta block production from craters is highly variable; the majority oflarge blocks appear to have originated from one 7.6 km crater (Shoemaker). The interior morphology of craters does not reveal the influence of discrete mechanical boundaries at depth in the manner of craters formed on lunar mare regolith and on some parts of Phobos. This lack of mechanical boundaries, and the abundant evidence of regolith in nearly every high-resolution image, suggests a gradation in the porosity and fracturing with depth. The density of small craters is deficient at sizes below -200 m relative to predicted slopes of empirical saturation. This characteristic, which is also found on parts ofPhobos and lunar highland areas, probably results from the efficient obliteration of small craters on a body with significant topographic slopes and a thick regolith. Eros displays a variety ofregolith features, such as debris aprons, fine-grained "ponded" deposits, talus cones, and bright and dark streamers on steep slopes indicative ofefficient downslope movement ofregolith. These processes serve to mix materials in the upper loose fragmental portion ofthe asteroid (regolith). In the instance of "ponded" materials and crater wall deposits, there is evidence of processes that segregate finer materials into discrete deposits. The NEAR observations have shown us that surface processes on small asteroids can be very complex and result in a wide variety of morphologic features and landforms that today seem exotic. Future missions to comets and asteroids will surely reveal still as yet unseen processes as well as give context to those discovered by the NEAR Shoemaker spacecraft.

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Section: Introductionmentioning

confidence: 99%

Section: Regolithmentioning

confidence: 99%

The geology of 433 Eros

Robinson

Thomas

Veverka

et al. 2002

Meteorit & Planetary Scien

155

140

View full text Add to dashboard Cite

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“…2). Based on its degraded appearance, the Serenitatis basin is thought by some to be one of the oldest on the Moon (Wilhelms, 1987). However, radiometric ages of Apollo 17 samples suggest that it is a young basin (Staudacher et al, 1978).…”

Section: Introductionmentioning

confidence: 99%

“…They are generally thought to be compressional features (Bryan, 1973;Muehlberger, 1974;Maxwell et al, 1975;Lucchitta, 1976Lucchitta, , 1977Maxwell and Phillips, 1978;Sharpton andHead, 1982, 1988) resulting from a combination of folding and thrust faulting (Plescia and Golombek, 1986;Watters, 1988;Golombek et al, 199 1 ;Watters, 1991 ;Watters and Robinson, 1997;Schultz, 2000). Arcuate rilles are linear to arcuate troughs with flat floors and steep walls (see Wilhelms, 1987). These troughs are interpreted to be graben formed by extensional stresses (Baldwin, 1963;McGill, 197 1 ;Golombek, 1979).…”

Section: Introductionmentioning

confidence: 99%

The topography and gravity of Mare Serenitatis: implications for subsidence of the mare surface

Watters

Konopliv

2001

Planetary and Space Science

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“…To understand such events and to predict the risk of future impacts it is necessary to study the past and current impact rate in the solar system. One approach to this is to date impact craters (Ivanov 2002;Bottke et al 2005), although many terrestrial craters have large age uncertainties and very few ages exist for extraterrestrial craters (Wilhelms, McCauley & Trask 1987;Culler et al 2000;Jourdan, Reimold & Deutsch 2012). Another approach is to dynamically simulate the motions of asteroids and comets and to calculate their impact rates.…”

Section: Introductionmentioning

confidence: 99%

Finding the imprints of stellar encounters in long-period comets

Feng

Bailer‐Jones

2015

Mon. Not. R. Astron. Soc.

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The solar system's Oort cloud can be perturbed by the Galactic tide and by individual passing stars. These perturbations can inject Oort cloud objects into the inner parts of the solar system, where they may be observed as the long-period comets (periods longer than 200 years). Using dynamical simulations of the Oort cloud under the perturbing effects of the tide and 61 known stellar encounters, we investigate the link between long-period comets and encounters. We find that past encounters were responsible for injecting at least 5% of the currently known long-period comets. This is a lower limit due to the incompleteness of known encounters. Although the Galactic tide seems to play the dominant role in producing the observed long-period comets, the non-uniform longitude distribution of the cometary perihelia suggests the existence of strong -but as yet unidentified -stellar encounters or other impulses. The strongest individual future and past encounters are probably HIP 89825 (Gliese 710) and HIP 14473, which contribute at most 8% and 6% to the total flux of long-period comets, respectively. Our results show that the strength of an encounter can be approximated well by a simple proxy, which will be convenient for quickly identifying significant encounters in large data sets. Our analysis also indicates a smaller population of the Oort cloud than is usually assumed, which would bring the mass of the solar nebula into line with planet formation theories.

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The geologic history of the Moon

Cited by 873 publications

References 0 publications

The geology of 433 Eros

The geology of 433 Eros

The topography and gravity of Mare Serenitatis: implications for subsidence of the mare surface

Finding the imprints of stellar encounters in long-period comets

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