Asymmetry of ejecta flow during oblique impacts using three‐dimensional particle image velocimetry

Anderson, Jennifer; Schultz, P. H.; Heineck, James T.

doi:10.1029/2003je002075

Cited by 114 publications

(122 citation statements)

References 21 publications

(52 reference statements)

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“…Under-dense, compressible targets result in a two component, late-stage ejecta curtain (Figure 10): first, a vertical plume due to cavitation (temporary containment and redirection of vapor by the transient crater below the surface); second, an outward-moving curtain due to rarefaction-controlled excavation off the free surface. Figure 11a illustrates the vector-velocity field of particles within the curtain during ejection using the 3D-PIV technique for a loose sand target (see Anderson et al, 2003Anderson et al, , 2004. Figure 11b illustrates this velocity field for the ejecta curtain from a sieved perlite target.…”

Section: Crater and Ejecta Evolutionmentioning

confidence: 99%

“…For oblique impacts (30 • and 60 • ), curtain diameter is taken transverse to the trajectory. Laser-illuminated ejecta in the curtain actually left the surface at an earlier stage of crater growth even when scaled time indicates that the crater has finished forming (t/T ∼ 1.0) as described in Anderson et al (2003).…”

Section: Crater and Ejecta Evolutionmentioning

confidence: 99%

“…Theoretical and empirical models of ejecta curtain growth can be readily constructed from existing analytical models based on scaling theory or by extrapolating direct observations of the ejecta-mass velocity field, e.g., using data from 3D-PIV observations (see Anderson et al, 2003Anderson et al, , 2004. This technique provides simultaneous measurements of the evolution of the ejecta curtain dimensions (size and width), opacity, constituent ejection angles, and ejection velocities for a wide range of projectile and target properties.…”

Section: Crater and Ejecta Evolutionmentioning

confidence: 99%

“…If gravity constrains the maximum crater diameter, then empirically derived scaling equations can be used (e.g., Housen et al, 1983;Anderson et al, 2003Anderson et al, , 2004) for extrapolation to the DI impact. More recent analyses reveal that such scaling equations depend on projectile/target density contrast and impact angle (e.g., Anderson et al, 2003Anderson et al, , 2004. At late stages of growth (>50%) the following scaling relation applies for fine-grained sand targets:…”

Section: Crater and Ejecta Evolutionmentioning

confidence: 99%

“…Additionally, new diagnostic tools are being applied to the evolution of the ejecta and their relation to the cratering flow field (e.g., Cintala et al, 1999;Anderson et al, 2003Anderson et al, , 2004.…”

Section: General Considerationsmentioning

confidence: 99%

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Expectations for Crater Size and Photometric Evolution from the Deep Impact Collision

Schultz

Ernst

Anderson

Deep Impact Mission: Looking Beneath the Surface of a Cometary Nucleus

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Abstract. The NASA Discovery Deep Impact mission involves a unique experiment designed to excavate pristine materials from below the surface of comet. In July 2005, the Deep Impact (DI) spacecraft, will release a 360 kg probe that will collide with comet 9P/Tempel 1. This collision will excavate pristine materials from depth and produce a crater whose size and appearance will provide fundamental insights into the nature and physical properties of the upper 20 to 40 m. Laboratory impact experiments performed at the NASA Ames Vertical Gun Range at NASA Ames Research Center were designed to assess the range of possible outcomes for a wide range of target types and impact angles. Although all experiments were performed under terrestrial gravity, key scaling relations and processes allow first-order extrapolations to Tempel 1. If gravity-scaling relations apply (weakly bonded particulate near-surface), the DI impact could create a crater 70 m to 140 m in diameter, depending on the scaling relation applied. Smaller than expected craters can be attributed either to the effect of strength limiting crater growth or to collapse of an unstable (deep) transient crater as a result of very high porosity and compressibility. Larger then expected craters could indicate unusually low density (<0.3 g cm −3 ) or backpressures from expanding vapor. Consequently, final crater size or depth may not uniquely establish the physical nature of the upper 20 m of the comet. But the observed ejecta curtain angles and crater morphology will help resolve this ambiguity. Moreover, the intensity and decay of the impact "flash" as observed from Earth, space probes, or the accompanying DI flyby instruments should provide critical data that will further resolve ambiguities.

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Section: Crater and Ejecta Evolutionmentioning

confidence: 99%

Section: Crater and Ejecta Evolutionmentioning

confidence: 99%

Section: Crater and Ejecta Evolutionmentioning

confidence: 99%

Section: Crater and Ejecta Evolutionmentioning

confidence: 99%

Section: General Considerationsmentioning

confidence: 99%

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Expectations for Crater Size and Photometric Evolution from the Deep Impact Collision

Schultz

Ernst

Anderson

Deep Impact Mission: Looking Beneath the Surface of a Cometary Nucleus

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Revisiting wildfires at the K‐Pg boundary

2013

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[1] The discovery of large amounts of soot in clays deposited at the Cretaceous-Paleogene (K-Pg) boundary and linked to the~65 Ma Chicxulub impact crater led to the hypothesis that major wildfires were a consequence of the asteroid impact. Subsequently, several lines of evidence, including the lack of charcoal in North American sites, were used to argue against global wildfires. Close to the impact site fires are likely to be directly ignited by the impact fireball, whereas globally they could be ignited by radiation from the reentry of hypervelocity ejecta. To-date, models of the latter have yet to take into account that ejection -and thus the emission of thermal radiation-is asymmetric and dependent on impact angle. Here, we model: (1) the impact and ejection of material, (2) the ballistic continuation of ejecta around a spherical Earth, and (3) the thermal pulse delivered to the Earth's surface when ejecta reenters the atmosphere. We find that thermal pulses in the downrange direction are sufficient to ignite flora several thousand kilometers from Chicxulub, whereas pulses at most sites in the uprange direction are too low to ignite even the most susceptible plant matter. Our analyses and models suggest some fires were ignited by the impact fireball and ejecta reentry, but that the nonuniform distribution of thermal radiation across the surface of the Earth is inconsistent with the ignition of fires globally as a direct and immediate result of the Chicxulub impact. Instead, we propose that the desiccation of flora by ejecta reentry, as well as the effects of postimpact global cooling/darkness, left much of the terrestrial flora prone to fires, and that the volume of soot in the global K-Pg layer is explained by a combination of syn-and postimpact wildfires.

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Young Martian crater Gratteri and its secondary craters

et al. 2016

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In response to questions that have been raised about formation and effects of secondary craters on crater chronometry techniques, we studied properties of the secondary crater field around the young Martian primary ray crater Gratteri (diameter 7 km). The crater has an estimated age of 1 to 20 Myr, based on counts of small craters on flat interior surface, consistent with a likely age for a young crater its size (Hartmann et al., 2010). The following are among our findings: (1) We identify an unusual class of craters we call “rampart secondaries” which may suggest low‐angle impacts. (2) We measure size distributions of secondaries as a function of distance from Gratteri and used these data to reconstruct the mass‐velocity distribution of ejecta blasted out of Gratteri. Our data suggest that crater density in rays tends to peak around 120–230 km from Gratteri (roughly 20–30D) and reaches roughly 30–70 times the interray crater density. (3) Comparable total numbers of secondaries form inside rays and outside rays, and about half are concentrated in clusters in 2% of the area around Gratteri, with the others scattered over 98% of the area out to 400 km away from Gratteri. (4) In the old Noachian plains around Gratteri, secondaries have minimal effect on crater chronometry. These results, along with recently reported direct measurements of the rate of formation of 10 m to 20 m primaries on Mars (Daubar et al., 2013), tend to negate suggestions that the numbers and/or clustering of secondaries destroy the effectiveness of crater counting as a chronometric tool.

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Asymmetry of ejecta flow during oblique impacts using three‐dimensional particle image velocimetry

Cited by 114 publications

References 21 publications

Expectations for Crater Size and Photometric Evolution from the Deep Impact Collision

Expectations for Crater Size and Photometric Evolution from the Deep Impact Collision

Revisiting wildfires at the K‐Pg boundary

Young Martian crater Gratteri and its secondary craters

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