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Crater Diameter (crater + diameter)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Review of the population of impactors and the impact cratering rate in the inner solar system

METEORITICS & PLANETARY SCIENCE, Issue 11 2007
Patrick Michel
The best witness of these events is the lunar surface, which kept the memory of the impacts that it underwent during the last 3.8 Gyr. In this paper, we review the recent studies at the origin of a reliable model of the impactor population in the inner solar system, namely the near-Earth object (NEO) population. Then we briefly expose the scaling laws used to relate a crater diameter to body size. The model of the NEO population and its impact frequency on terrestrial planets is consistent with the crater distribution on the lunar surface when appropriate scaling laws are used. Concerning the early phases of our solar system's history, a scenario has recently been proposed that explains the origin of the Late Heavy Bombardment (LHB) and some other properties of our solar system. In this scenario, the four giant planets had initially circular orbits, were much closer to each other, and were surrounded by a massive disk of planetesimals. Dynamical interactions with this disk destabilized the planetary system after 500,600 Myr. Consequently, a large portion of the planetesimal disk, as well as 95% of the Main Belt asteroids, were sent into the inner solar system, causing the LHB while the planets reached their current orbits. Our knowledge of solar system evolution has thus improved in the last decade despite our still-poor understanding of the complex cratering process. [source]

Laboratory simulation of impacts on aluminum foils of the Stardust spacecraft: Calibration of dust particle size from comet Wild-2

METEORITICS & PLANETARY SCIENCE, Issue 2 2006
A. T. Kearsley
The ability of soft aluminum alloy to record hypervelocity impacts as bowl-shaped craters offers an opportunistic substrate for recognition of impacts by particles of a potentially wide size range. In contrast to impact surveys conducted on samples from low Earth orbit, the simple encounter geometry for Stardust and Wild-2, with a known and constant spacecraft-particle relative velocity and effective surface-perpendicular impact trajectories, permits closely comparable simulation in laboratory experiments. For a detailed calibration program, we have selected a suite of spherical glass projectiles of uniform density and hardness characteristics, with well-documented particle size range from 10 ,m to nearly 100 ,m. Light gas gun buckshot firings of these particles at approximately 6 km s,1 onto samples of the same foil as employed on Stardust have yielded large numbers of craters. Scanning electron microscopy of both projectiles and impact features has allowed construction of a calibration plot, showing a linear relationship between impacting particle size and impact crater diameter. The close match between our experimental conditions and the Stardust mission encounter parameters should provide another opportunity to measure particle size distributions and fluxes close to the nucleus of Wild-2, independent of the active impact detector instruments aboard the Stardust spacecraft. [source]

Geological overview and cratering model for the Haughton impact structure, Devon Island, Canadian High Arctic

METEORITICS & PLANETARY SCIENCE, Issue 12 2005
Gordon R. Osinski
Regional geological mapping has refined the sedimentary target stratigraphy and constrained the thickness of the sedimentary sequence at the time of impact to ,1880 m. New 40Ar,39Ar dates place the impact event at ,39 Ma, in the late Eocene. Haughton has an apparent crater diameter of ,23 km, with an estimated rim (final crater) diameter of ,16 km. The structure lacks a central topographic peak or peak ring, which is unusual for craters of this size. Geological mapping and sampling reveals that a series of different impactites are present at Haughton. The volumetrically dominant crater-fill impact melt breccias contain a calcite-anhydrite-silicate glass groundmass, all of which have been shown to represent impact-generated melt phases. These impactites are, therefore, stratigraphically and genetically equivalent to coherent impact melt rocks present in craters developed in crystalline targets. The crater-fill impactites provided a heat source that drove a post-impact hydrothermal system. During this time, Haughton would have represented a transient, warm, wet microbial oasis. A subsequent episode of erosion, during which time substantial amounts of impactites were removed, was followed by the deposition of intra-crater lacustrine sediments of the Haughton Formation during the Miocene. Present-day intra-crater lakes and ponds preserve a detailed paleoenvironmental record dating back to the last glaciation in the High Arctic. Modern modification of the landscape is dominated by seasonal regional glacial and niveal melting, and local periglacial processes. The impact processing of target materials improved the opportunities for colonization and has provided several present-day habitats suitable for microbial life that otherwise do not exist in the surrounding terrain. [source]

Impact craters on small icy bodies such as icy satellites and comet nuclei

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005
M. J. Burchell
ABSTRACT Laboratory data and the results of modelling are combined to predict the possible size of craters in icy bodies such as a comet nucleus. This is done in particular for the case of a a 370-kg mass impacting a body the size of the nucleus of comet 9P/Temple-1 at 10 km s,1. This reproduces the Deep Impact comet impact to occur in 2005, when a NASA spacecraft will observe at close range an impact on the comet nucleus of an object deployed from the main spacecraft. The predicted crater size depends not only on uncertainties in extrapolation from laboratory scale and the modelling in general, but also on assumptions made about the nature of the target. In particular, allowance is made for the full range of reasonable target porosities; this can significantly affect the outcome of the Deep Impact event. The range of predicted crater sizes covers some 7,30 m crater depth and some 50,150 m crater diameter. An increasingly porous target (i.e. one with a higher percentage of void space) will increase the depth of the crater but not necessarily the diameter, leading to the possibility of an impact event where much of the crater formation is in the interior of the crater, with work going into compaction of void space and some possible lateral growth of the crater below the surface entrance. Nevertheless, for a wide range of scenarios concerning the nature of the impact, the Deep Impact event should penetrate the surface to depths of a few tens of metres, accessing the immediate subsurface regions. In parallel to this, the same extrapolation methods are used to predict the size of impactors that may have caused the features observed on the surfaces of small bodies, e.g. the Saturnian satellite Phoebe and the nucleus of comet P/Wild-2. [source]