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1.
We carried out 16 collision experiments in the drop tower in Bremen, Germany. Dust projectiles and solid projectiles of several mm in size impacted a dust target 5 cm in depth and width at velocities between 3.5 and 21.5 m/s. For solid impactors we found significant mass loss on the front (impact) side of the target. Mass loss depended on the impact velocity and projectile type (solid sphere or dust) and was up to 35 times the projectile mass for targets of the lowest tensile strength. Typical fragment velocities on the front side of the target ranged from 3 to 12 cm/s. The ejecta velocity was independent of the impact velocity but it increased with projectile mass. On the back side of the target (opposite to the impact side) mass was ejected from the target above a certain threshold impact velocity. Ejection velocity on the back side increased with impact velocity and is larger for solid projectiles than for dust projectiles. In one case a slightly stronger target gained mass in a slow dust-dust collision. We verified that collisions of dust projectiles with compact, very strong dust targets lead to a more massive target accreting part of the projectile. Applied to planetesimal formation, the experiments suggest that the maximum possible ejecta velocity from a body of several cm in size after a collision is small. Ejecta were slow enough that they were reaccreted by means of gas flow if large pores were part of the body's morphology. While very weak bodies cannot grow in the primary collision at the given velocities, this can lead to growth by secondary collisions. Slight compression, which could result from preceding collisions, might lead to immediate growth of a body in slow collisions by adding projectile mass.  相似文献   

2.
Abstract— Here we present the results of a geochemical study of the projectile component in impactmelt rocks from the Lappajärvi impact structure, Finland. Main‐ and trace‐element analyses, including platinum group elements (PGEs), were carried out on twenty impact‐melt rock samples from different locations and on two shocked granite fragments. The results clearly illustrate that all the impact melt rocks are contaminated with an extraterrestrial component. An identification of the projectile type was performed by determining the projectile elemental ratios and comparing the corresponding element ratios in chondrites. The projectile elemental ratios suggest an H chondrite as the most likely projectile type for the Lappajärvi impact structure. The PGE composition of the highly diluted projectile component (?0.05 and 0.7 wt% in the impact‐melt rocks) is similar to the recent meteorite population of H chondrites reaching Earth. The relative abundance of ordinary chondrites, including H, L, and LL chondrites, as projectiles at terrestrial impact structures is most likely related to the position of their parent bodies relative to the main resonance positions. This relative abundance of ordinary chondrites suggests a strong bias of the impactor population toward inner Main Belt objects.  相似文献   

3.
Abstract– Despite its centennial exploration history, there are still unresolved questions about Meteor Crater, the first recognized impact crater on Earth. This theoretical study addresses some of these questions by comparing model results with field and laboratory studies of Meteor Crater. Our results indicate that Meteor Crater was formed by a high‐velocity impact of a fragmented projectile, ruling out a highly dispersed swarm as well as a very low impact velocity. Projectile fragmentation caused many fragments to fall separately from the main body of the impactor, making up the bulk of the Canyon Diablo meteorites; most of these fragments were engulfed in the expansion plume as they approached the surface without suffering high shock compression, and were redistributed randomly around the crater. Thus, the distribution of Canyon Diablo meteorites is not representative of projectile trajectory, as is usual for impactor fragments in smaller strewn fields. At least 50% of the main impactor was ejected from the crater during crater excavation and was dispersed mostly downrange of the crater as molten particles (spheroids) and highly shocked solid fragments (shrapnel). When compared with the known distribution, model results suggest an impactor from the SW. Overall, every model case produced much higher amounts of pure projectile material than observed. The projectile‐target mixing was not considered in the models; however, this process could be the main sink of projectile melt, as all analyzed melt particles have high concentrations of projectile material. The fate of the solid projectile fragments is still not completely resolved. Model results suggest that the depth of melting in the target can reach the Coconino sandstone formation. However, most of the ejected melt originates from 30–40 m depth and, thus, is limited to Moenkopi and upper Kaibab material. Some melt remains in the target; based on the estimated volume of the breccia lens at Meteor Crater, our models suggest at most a 2% content of melt in the breccia. Finally, a high water table at the time of impact could have aided strong dispersion of target and projectile melt.  相似文献   

4.
The lunisolar perturbation is the principal factor that causes variation in the orbit of a GTO (geosychronous transfer orbit) space debris. In the present article the analytical expression of the long-periodic term of the altitude of the GTO orbital perigee caused by the lunisolar perturbation is derived, and the basic characteristics of the variation of the perigee caused by the lunisolar perturbation are analyzed. A method of selecting a launch window that will help to improve the space debris situation is given, and its correctness is tested and verified through simulation calculation.  相似文献   

5.
Impact angle plays a significant role in determining the fate of the projectile. In this study, we use a suite of hypervelocity impact experiments to reveal how impact angle affects the preservation, distribution, and physical state of projectile residues in impact craters. Diverse types of projectiles, including amorphous silicates, crystalline silicates, and aluminum, in two sizes (6.35 and 12.7 mm), were launched into blocks of copper or 6061 aluminum at speeds between 1.9 and 5.7 km s−1. Crater interiors preserve projectile residues in all cases, including conditions relevant to the asteroid belt. These residues consist of projectile fragments or projectile-rich glasses, depending on impact conditions. During oblique impacts at 30° and 45°, the uprange crater wall preserves crystalline fragments of the projectile. The fragments of water-rich projectiles such as antigorite remain hydrated. Several factors contribute to enhanced preservation on the uprange wall, including a weaker shock uprange, uprange acceleration as the shock reflects off the back of the projectile, and rapid quenching of melts along the projectile–target interface. These findings have two broader implications. First, the results suggest a new collection strategy for flyby sample return missions. Second, these results predict that the M-type asteroid Psyche should bear exogenic, impactor-derived debris.  相似文献   

6.
Abstract— The three major geochemical methods for impactor identification are evaluated with respect to their potential and limitations with regards to the precise detection and identification of meteoritic material in impactites. The identification of a projectile component in impactites can be achieved by determining certain isotopic and elemental ratios in contaminated impactites. The isotopic methods are based on Os and Cr isotopic ratios. Osmium isotopes are highly sensitive for the detection of minute amounts of extraterrestrial components of even <<0.05 wt% in impactites. However, this only holds true for target lithologies with almost no chemical signature of mantle material or young mantle‐derived mafic rocks. Furthermore, this method is not currently suitable for the precise identification of the projectile type. The Cr‐isotopic method requires the relatively highest projectile contamination (several wt%) in order to detect an extraterrestrial component, but may allow the identification of three different groups of extraterrestrial materials, ordinary chondrites, an enstatite chondrites, and differentiated achondrites. A significant advantage of this method is its independence of the target lithology and post‐impact alteration. The use of elemental ratios, including platinum group elements (PGE: Os, Ir, Ru, Pt, Rh, Pd), in combination with Ni and Cr represents a very powerful method for the detection and identification of projectiles in terrestrial and lunar impactites. For most projectile types, this method is almost independent of the target composition, especially if PGE ratios are considered. This holds true even in cases of terrestrial target lithologies with a high component of upper mantle material. The identification of the projectile is achieved by comparison of the “projectile elemental ratio” derived from the slope of the mixing line (target‐projectile) with the elemental ratio in the different types of possible projectiles (e.g., chondrites). However, this requires a set of impactite samples of various degree of projectile contamination.  相似文献   

7.
The interstellar collector on NASA's Stardust mission captured many particles from sources other than the interstellar dust stream. Impact trajectory may provide a means of discriminating between these different sources, and thus identifying/eliminating candidate interstellar particles. The collector's aerogel preserved a clear record of particle impact trajectory from the inclination and direction of the resultant tracks. However, the collector also contained aluminum foils and, although impact crater studies to date suggest only the most inclined impacts (>45° from normal) produce crater morphologies that indicate trajectory (i.e., distinctly elliptical), these studies have been restricted to much larger (mm and above) scales than are relevant for Stardust (μm). It is unknown how oblique impact crater morphology varies as a function of length scale, and therefore how well Stardust craters preserve details of impactor trajectory. Here, we present data from a series of impact experiments, together with complementary hydrocode modeling, that examine how crater morphology changes with impact angles for different‐sized projectiles. We find that, for our smallest spherical projectiles (2 μm diameter), the ellipticity and rim morphology provide evidence of their inclined trajectory from as little as 15° from normal incidence. This is most likely a result of strain rate hardening in the target metal. Further experiments and models find that variation in velocity and impactor shape complicate these trends, but that rim morphology remains useful in determining impact direction (where the angle of impact is >20° from normal) and may help identify candidate interstellar particle craters on the Stardust collector.  相似文献   

8.
Joshua E. Colwell 《Icarus》2003,164(1):188-196
We present the results of the second flight of the Collisions Into Dust Experiment (COLLIDE-2), a space shuttle payload that performs six impact experiments into simulated planetary regolith at speeds between 1 and 100 cm/s. COLLIDE-2 flew on the STS-108 mission in December 2001 following an initial flight in April 1998. The experiment was modified since the first flight to provide higher quality data, and the impact parameters were varied. Spherical quartz projectiles of 1-cm radius were launched into quartz sand and JSC-1 lunar regolith simulant targets 2-cm deep. At impact speeds below ∼20 cm/s the projectile embedded itself in the target material and did not rebound. Some ejecta were produced at ∼10 cm/s. At speeds >25 cm/s the projectile rebounded and significant ejecta was produced. We present coefficients of restitution, ejecta velocities, and limits on ejecta masses. Ejecta velocities are typically less than 10% of the impact velocity, and the fraction of impact kinetic energy partitioned into ejecta kinetic energy is also less than 10%. Taken together with a proposed aerodynamic planetesimal growth mechanism, these results support planetesimal growth at impact speeds above the nominal observed threshold of about 20 cm/s.  相似文献   

9.
Abstract– A Devonian siltstone from Orkney, Scotland, shows survival of biomarkers in high‐velocity impact experiments. The biomarkers were detected in ejecta fragments from experiments involving normal incidence of steel projectiles at 5–6 km s?1, and in projectile fragments from impact experiments into sand and water at 2–5 km s?1. The associated peak shock pressures were calculated to be in the range of 110–147 GPa for impacts of the steel projectiles into the siltstone target, and hydrocode simulations are used to show the variation of peak pressure with depth in the target and throughout the finite volume projectiles. Thermally sensitive biomarker ratios, including ratios of hopanoids and steranes, and the methylphenanthrene ratio, showed an increase in thermal maturity in the ejecta, and especially the projectile, fragments. Measurement of absolute concentrations of selected biomarkers indicates that changes in biomarker ratios reflect synthesis of new material rather than selective destruction. Their presence in ejecta and projectile fragments suggests that fossil biomarkers may survive hypervelocity impacts, and that experiments using biomarker‐rich rock have high potential for testing survival of organic matter in a range of impact scenarios.  相似文献   

10.
Abstract— Repeated impacts into fragmental targets simulating unconsolidated debris on planetary surfaces have provided empirical insight into the evolution of planetary regoliths. Quantitative understanding and interpretation of these results, however, are often made difficult by the complex, multivariate nature of the impact process, even under controlled laboratory conditions. The techniques of dimensional analysis have been employed to quantify and examine the relationships between the more important variables in the evolution of these experimental regoliths. Application of this method to the results of ten experimental series shows that the quantity of comminuted target mass is directly proportional to (a) the number of impacts sustained by the target, (b) the diameter of the projectile, (c) the mean size of the crystals composing the target rock, (d) the mean grain-size of the evolving “regolith,” (e) the total target mass, (f) the impactor density, and (g) the ratio of the impact velocity to the velocity of sound in the target rock. The comminuted mass is inversely proportional to the density of the target rock and the sorting of the “regolith.” Similar results hold for the creation of new surfaces by fracturing, except that the initial surface area possessed by the target takes the place of the total target mass. In addition, the ease with which new surfaces are created is independent of the mean crystal-size. Although it appears that the ratio between impactor and target densities is an important parameter in both cases, more experiments will be necessary to establish the quantitative contribution of that parameter, as well as those of the total target mass and the effective strengths of the individual minerals composing the target rock.  相似文献   

11.
In this paper, we present the final report of the data obtained from the Space Dust (SPADUS) instrument on the Earth-orbiting Advanced Research and Global Observation Satellite (ARGOS). The University of Chicago's SPADUS instrument on the US Air Force's Advanced Research and Global Observation Satellite has been operating in a nearly polar orbit, at an altitude of approximately 850 km, since soon after its launch on day 54, 1999 (23 February) until termination of the SPADUS operations on day 248, 2001 (5 September).The instrument consists of a polyvinylidene fluoride (PVDF) dust trajectory system, which includes two planar arrays of PVDF sensors (a total of 16 sensors per array) separated by 20.25 cm to provide time of flight (TOF) measurements. The trajectory system measures dust particle flux, mass distribution, velocity and trajectory. The instrument also includes the SPADUS Ancillary Diagnostic Sensor (ADS) subsystem, which measured energetic charged particles (electrons, protons, etc).The PVDF dust trajectory system detected a total of 368 dust impacts over the SPADUS live-time interval of 739 days, yielding an average particle flux of 0.50 impacts/day. Of these 368 impacts, 35 were D1-D2 type events—where particles impacted and penetrated a D1 sensor, then impacted a D2 rear array sensor—allowing for time-of-flight measurements. Of the 35 D1-D2 impacts on SPADUS, we identified 19 D1-D2 impacts yielding TOF values. Of these 19 events, 14 were ambiguous (either bound or interplanetary) and 5 were unambiguous interplanetary impacts. Examples of particle orbits for debris particles as well as D1-D2 impacts are detailed. We also describe transient particle streams detected by the SPADUS trajectory system, resulting from the passage of ARGOS through streams of debris particles in Earth orbit. One of the streams was shown to result from detection by SPADUS of the debris generated by the explosion of a Chinese booster rocket.The SPADUS flight data accumulated over the 30-month mission shows that PVDF-based dust instruments utilizing two planar arrays of PVDF dust sensors in a TOF arrangement—can provide useful measurements of particle velocity, mass distribution, flux, trajectory and particle orbital elements.  相似文献   

12.
Hydrocode modeling of oblique impacts: The fate of the projectile   总被引：1，自引：0，他引：1  
Abstract— All impacts are oblique to some degree. Only rarely do projectiles strike a planetary surface (near) vertically. The effects of an oblique impact event on the target are well known, producing craters that appear circular even for low impact angles (>15° with respect to the surface). However, we still have much to learn about the fate of the projectile, especially in oblique impact events. This work investigates the effect of angle of impact on the projectile. Sandia National Laboratories' three‐dimensional hydrocode CTH was used for a series of high‐resolution simulations (50 cells per projectile radius) with varying angle of impact. Simulations were carried out for impacts at 90, 60, 45, 30, and 15° from the horizontal, while keeping projectile size (5 km in radius), type (dunite), and impact velocity (20 km/s) constant. The three‐dimensional hydrocode simulations presented here show that in oblique impacts the distribution of shock pressure inside the projectile (and in the target as well) is highly complex, possessing only bilateral symmetry, even for a spherical projectile. Available experimental data suggest that only the vertical component of the impact velocity plays a role in an impact. If this were correct, simple theoretical considerations indicate that shock pressure, temperature, and energy would depend on sin2θ, where θ is the angle of impact (measured from the horizontal). However, our numerical simulations show that the mean shock pressure in the projectile is better fit by a sin θ dependence, whereas shock temperature and energy depend on sin3/2 θ. This demonstrates that in impact events the shock wave is the result of complex processes that cannot be described by simple empirical rules. The mass of shock melt or vapor in the projectile decreases drastically for low impact angles as a result of the weakening of the shock for decreasing impact angles. In particular, for asteroidal impacts the amount of projectile vaporized is always limited to a small fraction of the projectile mass. In cometary impacts, however, most of the projectile is vaporized even at low impact angles. In the oblique impact simulations a large fraction of the projectile material retains a net downrange motion. In agreement with experimental work, the simulations show that for low impact angles (30 and 15°), a downrange focusing of projectile material occurs, and a significant amount of it travels at velocities larger than the escape velocity of Earth.  相似文献   

13.
We report on the microscopic impactor debris around Kamil crater (45 m in diameter, Egypt) collected during our 2010 geophysical expedition. The hypervelocity impact of Gebel Kamil (Ni‐rich ataxite) on a sandstone target produced a downrange ejecta curtain of microscopic impactor debris due SE–SW of the crater (extending ~300,000 m2, up to ~400 m from the crater), in agreement with previous determination of the impactor trajectory. The microscopic impactor debris include vesicular masses, spherules, and coatings of dark impact melt glass which is a mixture of impactor and target materials (Si‐, Fe‐, and Al‐rich glass), plus Fe‐Ni oxide spherules and mini shrapnel, documenting that these products can be found in craters as small as few tens of meters in diameter. The estimated mass of the microscopic impactor debris (<290 kg) derived from Ni concentrations in the soil is a small fraction of the total impactor mass (~10 t) in the form of macroscopic shrapnel. That Kamil crater was generated by a relatively small impactor is consistent with literature estimates of its pre‐atmospheric mass (>20 t, likely 50–60 t).  相似文献   

14.
It is shown that the size-frequency distribution (SFD) of a time-averaged projectile population derived from the lunar crater SFD of Neukum and Ivanov (in Hazards Due to Comets and Asteroids (T. Gehrels, Ed.), 1994, pp. 359-416, Univ. of Arizona Press, Tucson) provides a convincing fit to the SFD of the current near-Earth asteroid (NEA) population, as deduced from the results of asteroid search programs. Our results suggest that the shape of the SFD of the impactor flux has remained in a steady state since the late heavy bombardment, so that the current NEA population can be viewed as a snapshot of the flux of impactors on the Moon. The number of bodies in the projectile population with diameters of 1 km or more is 700±130, which is in good agreement with recent estimates of the total number of NEAs in this size range. Our results imply that the contribution to the projectile flux from comets is small for diameters below 10 km.  相似文献   

15.
?pik’s formulae for the probability of collision are applied to the analysis of the collision risk against space debris in Low-Earth Orbit (LEO) and Medium Earth Orbit. The simple analytical formulation of ?pik’s theory makes it applicable to complex dynamical systems, such as the interaction of the ISS with the whole debris population in LEO The effect of a fragmentation within a multiplane constellation can also be addressed. The analysis of the evolution of the collision risk in Earth orbit shows the need of effective mitigation measures to limit the growth of the collision risk and of the fragmentation debris in the next century.  相似文献   

16.
Abstract– We carried out hypervelocity cratering experiments with steel projectiles and sandstone targets to investigate the structural and mineralogical changes that occur upon impact in the projectile and target. The masses of coherent projectile relics that were recovered in different experiments ranged between 58% and 92% of their initial projectile masses. A significant trend between impact energy, the presence of water in the target, and the mass of projectile relics could not be found. However, projectile fragmentation seems to be enhanced if the target contains substantial amounts of water. Two experiments that were performed with 1 cm sized steel projectiles impacting at 3400 and 5300 m s?1 vertically onto dry Seeberger sandstone were investigated in detail. The recovered projectiles are intensely plastically deformed. Deformation mechanisms include dislocation glide and dislocation creep. The latter led to the formation of subgrains and micrometer‐sized dynamically recrystallized grains. In case of the 5300 m s?1 impact experiment, this deformation is followed by grain annealing. In addition, brittle fracturing and friction‐controlled melting at the surface along with melting and boiling of iron and silica were observed in both experiments. We estimated that heating and melting of the projectile impacting at 5300 m s?1 consumed 4.4% of the total impact energy and was converted into thermal energy and heat of fusion. Beside the formation of centimeter‐sized projectile relics, projectile matter is distributed in the ejecta as spherules, unmelted fragments, and intermingled iron‐silica aggregates.  相似文献   

17.
This paper presents the results of an experimental study on the geometric parameters of craters that originated at the impact interaction of polyethylene projectiles with a massive organic-glass target. The impactor speed ranged from 2.7 to 6.28 km/s. The shapes of the resulting craters are determined. Using statistical analysis and scaling theory, we obtained the dependence of the diameter and depth of the crater on defining parameters. The critical impact energy resulting in the catastrophic breakup of the target is estimated.  相似文献   

18.
S. Yamamoto 《Icarus》2002,158(1):87-97
This paper reports the results of experiments on projectile impact into regolith targets at various impact angles. Copper projectiles of 240 mg are accelerated to 197 to 272 m s−1 using an electromagnetic gun. The ejecta are detected by thin Al foil targets as secondary targets, and the resulting holes on the foil are measured to derive the spatial distribution of the ejecta. The ejecta that penetrated the foil are concentrated toward the downrange azimuths of impacting projectiles in oblique impacts. In order to investigate the ejecta velocity distribution, the nondimensional volume of ejecta with velocities higher than a given value is calculated from the spatial distribution. In the case of the vertical impact of the projectile, most ejecta have velocities lower than 24% of the projectile speed (∼50 m s−1), and there are only several ejecta with velocities higher than 72 m s−1. This result confirms the existence of an upper limit to the ejection velocity in the ejecta velocity distribution (Hartmann cutoff velocity) (W. K. Hartmann, 1985, Icarus63, 69-98). On the other hand, it is found that, in the oblique impacts, there are a large number of ejecta with velocities higher than the Hartmann cutoff velocity. The relative quantity of ejecta above the Hartmann cutoff velocity increases as the projectile impact angle decreases. Taking these results with the results of S. Yamamoto and A. M. Nakamura (1997, Icarus128, 160-170) from impact experiments using an impact angle of 30°, it can be concluded that the ejecta from these regolith targets exhibit a bimodal velocity distribution. Below a few tens of m s−1, we see the expected velocity distribution of ejecta, but above this velocity we see a separate group of high-velocity ejecta.  相似文献   

19.
We report on high-resolution three-dimensional calculations of oblique impacts into planetary atmospheres, specifically the atmosphere of Venus, extending the results of Korycansky et al. (2000, Icarus 146, 387-403; 2002, Icarus 157, 1-23). We have made calculations for impacts at 0°, 45°, and 60° from the vertical, different impactor velocities (10, 20, and 40 km s−1), and different impactor masses and orientations. We present results for porous impactors using a simple model of porosity. We have investigated the sensitivity to initial conditions of the calculations [as a follow-up to the results found in Korycansky et al. (2002)] and resolution effects. For use in cratering calculations, we fit simple functions to the numerical results for mass and momentum that penetrate to a given altitude (column mass) and investigate the behavior of the fit coefficients as functions of impactor parameters such as mass, velocity, and impact angle. Generally speaking, the mass and momentum (and hence resulting crater diameters) depend primarily on impactor mass and mass of atmosphere encountered and weakly or not at all on other parameters such as impactor velocity, impact angle, or porosity. The column mass to which the last portion of the impactor penetrates is approximately equal to the mass of impactor at the top of the atmosphere before the impact takes place. Finally, we present the beginnings of a simplified but physically based model for the impactor and its fragments to reproduce the mass and momentum fluxes as a function of height during the impact.  相似文献   

20.
Abstract— Metallic aluminum alloy foils exposed on the forward, comet‐facing surface of the aerogel tray on the Stardust spacecraft are likely to have been impacted by the same cometary particle population as the dedicated impact sensors and the aerogel collector. 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 μm to nearly 100 μm. 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.  相似文献   

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