The Experts below are selected from a list of 56106 Experts worldwide ranked by ideXlab platform
Brian M Hynek - One of the best experts on this subject based on the ideXlab platform.
-
a new global database of mars impact Craters 1 km 2 global Crater properties and regional variations of the simple to complex transition diameter
Journal of Geophysical Research, 2012Co-Authors: S J Robbins, Brian M HynekAbstract:[1] We have generated a new, 384,343-entry global Crater database of Mars, statistically complete for Craters with diameters D ≥ 1 km. In this release, the database contains detailed morphologic and morphometric data for Craters D ≥ 3 km (future releases will extend these to smaller diameters). With detailed topographic data for the largest Crater database to-date, we analyzed Crater depth-to-diameter ratios for simple and complex morphologies across various terrains and for the planet as a whole and investigated the simple-to-complex morphology transition. Our results are similar to those in the published literature, but we found a substantial terrain dependence of the simple-to-complex transition that occurs at ∼11-km-diameter Craters at high latitudes. This suggests a model that requires melting of volatiles during high-latitude Crater formation that fill the Crater during the modification phase but will still support the simple morphology to larger diameters. We also use this database to reexamine previously observed distributions and patterns to show its fidelity and to further explore other global relationships of fresh Craters, those with central peaks, pits, and summit pits. We present the global distribution of Craters with different types of ejecta and morphometric properties. Overall, this database is shown to be comparable to previous databases where there is overlap and to be useful in extending prior work into new regimes.
-
the size frequency distribution of elliptical impact Craters
Earth and Planetary Science Letters, 2011Co-Authors: G S Collins, D Elbeshausen, T M Davison, Stuart J Robbins, Brian M HynekAbstract:Abstract Impact Craters are elliptical in planform if the impactor's trajectory is below a threshold angle of incidence. Laboratory experiments and 3D numerical simulations demonstrate that this threshold angle decreases as the ratio of Crater size to impactor size increases. According to impact Cratering scaling laws, this implies that elliptical Craters occur at steeper impact angles as Crater size or target strength increases. Using a standard size-frequency distribution for asteroids impacting the terrestrial planets we estimate the fraction of elliptical Craters as a function of Crater size on the Moon, Mars, Earth, Venus and Mercury. In general, the expected fraction of elliptical Craters is ~ 2–4% for Craters between 5 and 100-km in diameter, consistent with the observed population of elliptical Craters on Mars. At larger Crater sizes both our model and observations suggest a dramatic increase in the fraction of elliptical Craters with increasing Crater diameter. The observed fraction of elliptical Craters larger than 100-km diameter is significantly greater than our model predictions, which may suggest that there is an additional source of large elliptical Craters other than oblique impact.
-
distant secondary Craters from lyot Crater mars and implications for surface ages of planetary bodies
Geophysical Research Letters, 2011Co-Authors: S J Robbins, Brian M HynekAbstract:[1] The population of secondary Craters - Craters formed by the ejecta from an initial impact event - is important to understand when deriving the age of a solid body's surface. Only one Crater on Mars, Zunil, has been studied in-depth to examine the distribution, sizes, and number of these features. Here, we present results from a much larger and older Martian Crater, Lyot, and we find secondary Crater clusters at least 5200 km from the primary impact. Individual Craters with diameters >800 m number on the order of 104. Unlike the previous results from Zunil, these Craters are not contained in obvious rays, but they are linked back to Lyot due to the clusters' alignment along great circles that converge to a common origin. These widespread and abundant Craters from a single impact limit the accuracy of Crater age-dating on the Martian surface and beyond.
Jianzhong Liu - One of the best experts on this subject based on the ideXlab platform.
-
a reanalysis of the relationship between the size of boulders and Craters in lunar surface
Icarus, 2019Co-Authors: Mengna Jia, Bin Liu, Zongyu Yue, Jianzhong LiuAbstract:Abstract To distinguish secondary Craters from primary Craters is very important in lunar studies that involve such tasks as dating the lunar surface and investigating the meteoritic flux. However, this is usually difficult since distant secondary Craters generally have an appearance similar to primary ones. Bart and Melosh, 2007a , Bart and Melosh, 2007b proposed a method to distinguish the two types of Craters based on the relationship between the Crater diameter (D) and the size of the largest boulder (B) around the Crater: B=KD2/3, where K is the fitting coefficient. They concluded that secondary Craters have a 60% larger fitting coefficient (K) than primary Craters. However, because of the poor quality of the available data and an insufficient number of Crater samples, their results need further substantiation, as they have suggested. This research aims to examine their results with recently obtained very high resolution data and many more sampled Craters. Our results indicate that the criterion proposed by Bart and Melosh, 2007a , Bart and Melosh, 2007b is actually not applicable, i.e., the fitted coefficient (K), in cases of primary and secondary Craters, cannot be confidently distinguished.
-
lunar orientale impact basin secondary Craters spatial distribution size frequency distribution and estimation of fragment size
Journal of Geophysical Research, 2018Co-Authors: Jianzhong Liu, Dijun Guo, J W Head, M A KreslavskyAbstract:Secondary impact Craters, features created by projectiles ejected from a primary impact, contain important information about the primary Cratering event and the nature and distribution of its ejecta. The Orientale impact basin (D similar to 930km) is the youngest and the least degraded large impact basin on the Moon and has the most recognizable secondary impact Craters. We identified and mapped 2,728 secondary Craters in the investigated area of similar to 1.66x10(7)km(2), covering an area from the rim of Orientale to six radii. Secondary Crater diameters range from similar to 2 to 27km, and the median diameter decreases as distance increases. Secondary Craters are concentrated predominantly in the northwest and southwest. The ejecta deposit pattern inferred from secondary Crater distribution suggests that the Orientale basin was formed by an oblique impact in which the downrange direction was 240 degrees-265 degrees in azimuth, and the incidence angle was steeper than 20 degrees. The cumulative size-frequency distribution of mapped secondary Craters steepens as diameter increases and is very well approximated with a Weibull distribution with an exponent 1.32. A widely used Crater scaling relationship predicts that the fragments that produced the secondary Craters were predominantly in similar to 0.5-2-km diameter range over the investigated area; the diameter of the largest fragment, however, decreases with increasing distance from Orientale. On the basis of the diameter of the largest secondary Crater of Orientale, and other Craters and basins, the largest secondary Crater of the South Pole-Aitken basin is estimated to be similar to 40km in diameter. We explore the implications of these findings for the evolution of the megaregolith and future sample return missions.
Zhiyong Xiao - One of the best experts on this subject based on the ideXlab platform.
-
effect of topography degradation on Crater size frequency distributions implications for populations of small Craters and age dating
Geophysical Research Letters, 2017Co-Authors: Minggang Xie, Menghua Zhu, Zhiyong XiaoAbstract:Whether or not background secondary Craters dominate populations of small impact Craters on terrestrial bodies is a half-century controversy. It has been suggested that small Craters on some planetary bodies are dominated by background secondary Craters based partly on the steepened slope of Crater size-frequency distribution (CSFD) towards small diameters, such as the less than ~1 km diameter Crater population on the lunar mare. Here we show that topography degradation enlarges Craters and increases CSFD slopes with time. When topography degradation is taken into account, for various-aged Crater populations, the observed steep CSFD at small diameters is uniformly consistent with an originally shallower CSFD, whose slope is undifferentiated from the CSFD slope estimated from near-Earth objects and terrestrial bolides. The results show that the effect of topography degradation on CSFD is important in dating planetary surfaces, and the steepening of CSFD slopes is not necessarily caused by secondary Cratering, but rather a natural consequence of topography degradation.
Anna C Ratcliffe - One of the best experts on this subject based on the ideXlab platform.
-
snow avalanche impact Craters in southern norway their morphology and dynamics compared with small terrestrial meteorite Craters
Geomorphology, 2017Co-Authors: John A Matthews, Geraint Owen, Lindsey Mcewen, Richard A Shakesby, Jennifer Hill, Amber E Vater, Anna C RatcliffeAbstract:Abstract This regional inventory and study of a globally uncommon landform type reveals similarities in form and process between Craters produced by snow-avalanche and meteorite impacts. Fifty-two snow-avalanche impact Craters (mean diameter 85 m, range 10–185 m) were investigated through field research, aerial photographic interpretation and analysis of topographic maps. The Craters are sited on valley bottoms or lake margins at the foot of steep avalanche paths ( α = 28–59°), generally with an easterly aspect, where the slope of the final 200 m of the avalanche path ( β ) typically exceeds ~ 15°. Crater diameter correlates with the area of the avalanche start zone, which points to snow-avalanche volume as the main control on Crater size. Proximal erosional scars (‘blast zones’) up to 40 m high indicate up-range ejection of material from the Crater, assisted by air-launch of the avalanches and impulse waves generated by their impact into water-filled Craters. Formation of distal mounds up to 12 m high of variable shape is favoured by more dispersed down-range deposition of ejecta. Key to the development of snow-avalanche impact Craters is the repeated occurrence of topographically-focused snow avalanches that impact with a steep angle on unconsolidated sediment. Secondary Craters or pits, a few metres in diameter, are attributed to the impact of individual boulders or smaller bodies of snow ejected from the main avalanche. The process of Crater formation by low-density, low-velocity, large-volume snow flows occurring as multiple events is broadly comparable with Cratering by single-event, high-density, high-velocity, small-volume projectiles such as small meteorites. Simple comparative modelling of snow-avalanche events associated with a Crater of average size (diameter 85 m) indicates that the kinetic energy of a single snow-avalanche impact event is two orders of magnitude less than that of a single meteorite-impact event capable of producing a Crater of similar size, which is consistent with the incremental development of snow-avalanche impact Craters through the Holocene.
Yi Zhou - One of the best experts on this subject based on the ideXlab platform.
-
Lunar Crater Detection Based on Terrain Analysis and Mathematical Morphology Methods Using Digital Elevation Models
IEEE Transactions on Geoscience and Remote Sensing, 2018Co-Authors: Min Chen, Kejian Qian, Jun Li, Yi ZhouAbstract:Lunar impact Craters are the most typical geomorphic feature on the moon and are of great importance in studies of lunar terrain features. This paper presents a Crater detection algorithm (CDA) that is based on terrain analysis and mathematical morphology methods. The proposed CDA is applied to digital elevation models (DEMs) to identify the boundaries of impact Craters. The topographic and morphological characteristics of impact Craters are discussed, and detailed steps are presented to detect different types of Craters, such as dispersal Craters, connective Craters, and con-Craters. The DEM from the Lunar Reconnaissance Orbiter, which has a resolution of 100 m, is used to verify the proposed CDA. The results show that the boundaries of impact Craters can be detected. The results enable increased understanding of surface processes through the characterization of Crater morphometry and the use of Crater size-frequency distributions to estimate the ages of planetary surfaces.
-
Morphological Features-Based Descriptive Index System for Lunar Impact Craters
ISPRS International Journal of Geo-Information, 2017Co-Authors: Min Chen, Yi Zhou, Mengling Lei, Danyang Liu, Hao Zhao, Kejian QianAbstract:Lunar impact Craters are important for studying lunar surface morphology because they are the most typical morphological units of the Moon. Impact Crater descriptive indices can be used to describe morphological features and thus provide direct evidence for both the current state and evolution history of the Moon. Current description methods for lunar impact Craters are predominantly qualitative, and mostly focus on their morphological profiles. Less attention is paid to the detailed morphological features inside and outside of the Craters. A well-established and descriptive index system is required to describe the real morphological features of lunar impact Craters, which are complex in a systematic way, and further improve study, such as heterogeneity analyses of lunar impact Craters. This study employs a detailed lunar surface morphological analysis to propose a descriptive index system for lunar impact Craters, including indices for the description of individual Craters based on their morphological characteristics, spatial structures and basic composition (i.e., Crater rim, Crater wall, Crater floor, central uplift, and ejecta), and indices for Crater groups, including spatial distribution and statistical characteristics. Based on the proposed descriptive index system, a description standard for lunar impact Craters is designed for categorising and describing these indices in a structured manner. To test their usability and effectiveness, lunar impact Craters from different locations are manually detected, and corresponding values for different indices are extracted and organised for a heterogeneity analysis. The results demonstrate that the proposed index system can effectively depict the basic morphological features and spatial characteristics of lunar impact Craters.
-
Boundary Detection of Dispersal Impact Craters Based on Morphological Characteristics Using Lunar Digital Elevation Model
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2017Co-Authors: Min Chen, Kejian Qian, Yi ZhouAbstract:Lunar impact Craters are the most typical geomorphic unit found on the moon and are of great significance for the study of terrain features. Currently, most mainstream detection algorithms for lunar impact Craters represent Craters as circles, but these methods counter difficulty in expressing the real shapes in an accurate manner. It is difficult to conduct an advanced analysis, such as characteristic and spatial heterogeneity analyses of the lunar surface. The lunar terrain characteristics were analyzed using dispersal impact Craters as the object, and a dispersal Crater detection algorithm (CDA) based on a digital elevation model (DEM-based CDA) was proposed. By analyzing the surface catchment, the impact Crater can be treated as a closed basin structure. The raw impact Crater region is detected using watershed algorithm. This algorithm can detect the real boundaries of an impact Crater based on the actual terrain. Several morphological factors, such as posture ratio and rectangle factor, are used to filter the raw impact Crater regions. A suborbicular raw impact Crater region is treated as the desired result after the elimination of false impact Craters. For the remaining raw impact Crater regions, terrain profile analysis is applied to accurately identify the boundaries of impact Craters. The DEM data produced from the Chang'E-2 imagery and LRO laser altimeter data (20 and 60 m) are used in verification. The results show that the impact Crater boundaries with real terrain characteristics can be effectively expressed and used in further exploration.
