Processing and redistribution of surface and subsurface samples by impact cratering

As a portion of the Martian surface becomes more densely cratered, the more the surface and subsurface materials become laterally redistributed and impact metamorphosed. Specimen redistribution is characterized as a function of both impact density and original specimen depth, and the impact histories of those specimens are also characterized

A statistical study of Mercurian crater classes applied to the emplacement of the intercrater plains

Two principal processes have been invoked for emplacement of the intercrater plains: (1) basin ejecta and autochthonous surface materials reworked by that ejecta or (2) volcanic flows. A new approach was taken: the multivariate statistical analysis of crater class. The results of the analysis constrain the formative process of the intercrater plains units to have affected craters on both terrains in a similar manner. Any emplacement process brief in temporal extent (compared to the period of late heavy bombardment), such as emplacement of ejecta from a single event or a brief period of extensive volcanism, violates this constraint. This analysis is briefly discussed

Advances in Planetary Geology

Advances in Planetary Geology is a new series intended to serve the planetary geology community with a form for quick and thorough communications. There are no set lists of acceptable topics or formats, and submitted manuscripts will not undergo a formal review. All submissions should be in a camera ready form, preferably spaced, and submitted to the editor

Advances in planetary geology

This second issue in a new series intended to serve the planetary geology community with a form for quick and thorough communications includes (1) a catalog of terrestrial craterform structures for northern Europe; (2) abstracts of results of the Planetary Geology Program, and (3) a list of the photographic holdings of regional planetary image facilities

Advances in planetary geology

Research reports concerning the planetary geology of Mars are presented. Topics covered include the geomorphology of Martian valleys and various aspects of Martian volcanology

A size-frequency study of large Martian craters

The log normal frequency distribution law was used to analyze the crater population on the surface of Mars. Resulting data show possible evidence for the size frequency evolution of crater producing bodies. Some regions on Mars display excessive depletion of either large or small craters; the most likely causes of the depletion are considered. Apparently, eolian sedimentation has markedly altered the population of the small craters south of -30 deg latitude. The general effects of crater obliteration in the Southern Hemisphere appear to be confined to diameters of less than 20 km. A strong depletion of large craters in a large region just south of Deuteronilus Mensae, and in a small region centered at 35 deg latitude and 10 deg west longitude, may indicate locations of subsurface ice

Crater populations on Ganymede and Callisto

The discovery of heavily cratered surfaces on Ganymede and Callisto by Voyager 1 shows that like the inner Solar System, a period of heavy bombardment also occurred in the outer Solar System. Comparisons among the crater size/density curves of Ganymede, Callisto and the terrestrial planets show several striking features. The overall crater density of the most heavily cratered terrain on Ganymede is down by a factor of about 3 compared to Callisto, and when allowance is made for the difference in crater production rate due to the influence of Jupiter's gravity field it is down by a factor of nearly 6. This indicates that the oldest regions of Ganymede began recording the observed crater population at a later time than Callisto, and therefore Ganymede either experienced a large-scale (perhaps global) diameter-independent resurfacing event or simply developed a rigid crust capable of retaining craters later than Callisto. In either case, this process took place during the period of late heavy bombardment. Based on earlier studies of the terrestrial-planets' cratering record, neither Ganymede nor Callisto is saturated with craters. Compared to Callisto, a diameter-dependent loss of craters in the size range 10–40 km occurs on the grooved terrain of Ganymede and probably results from obliteration of small craters due to the formation of new ice. A similar but less severe loss also occurs on Ganymede's heavily cratered terrain and may be due to an earlier period of ice formation and/or the formation of arcuate troughs in this terrain. Seven different crater curves, in the diameter range of about 40–130 km, representing vastly different crater densities, different surface ages, different terrain types, and even different satellites all possess nearly the same distribution function. This together with other observational evidence strongly suggests that at least in this diameter range the curve basically represents its production function which is completely different from that on the terrestrial planets. This indicates that the population of bodies responsible for the period of late heavy bombardment in the inner Solar System was very different from that responsible for the late heavy bombardment in the outer Solar System. We can only speculate at this early stage that Ganymede and Callisto may principally record a population of bodies that never penetrated the inner Solar System in numbers great enough to leave a recognizable signature

De la matière conquérante à la matière troublante

L’intérêt des naturalistes et des philosophes du xviiie siècle pour la matière n’échappe pas aux créateurs de paysage. La fascination pour la matière brute a aussi son envers, la forme, dont la beauté séduit les amateurs de jardins. Or, en imposant le déguisement de tout geste d’intervention artistique, le principe de dissimulatio artis présidant à la théorie esthétique de l’époque corse la coexistence de ces deux tendances. Considéré comme acte d’agressivité envers la matière, le modelage est proscrit au créateur de paysage. Quel geste reste-t-il alors au paysagiste pour surmonter le décalage entre la matière brute et la forme artistique ? Pour répondre à cette question par une analyse des sources iconographiques et textuelles de l’époque, nous interprétons les lieux de tension entre l’informe et la forme à travers trois configurations : superposition, mise en abyme et cristallisation. Finalement, la comparaison du discours sur la matière dans le contexte urbain et de campagne nous amène à interpréter les prouesses formelles comme réponse à la deuxième facette de la fascination, l’inquiétude.The fascination for raw matter, essential in XVIIIth century science and philosophy, influences garden enthusiasts. Meantime, the interest in new artistic tendencies focuses their attention on development of original forms. Matter represents for them untouched nature, the objective of any landscape project of this time. By contrast, form connotes an artistic intervention which, according to the dissimulatio artis principle, must be concealed. Thus, theoretically, the coexistence of these two tendencies gives rise to a contradiction. What options will be left to the practicing gardener in his quest to tackle the gap between unprocessed material and artistic form ? An analysis of textual and iconographical period sources will help us understand the sites of resistance between the formal and the informal elements of the garden. We examine their relationship in three configurations : superimposition, mise en abyme and crystallization. To conclude, comparing the discourse on matter in both urban and rural settings allows us to interpret formal achievements as a response to the second facet of fascination – anxiety