Small Impactor Research Articles

The Impact of Cometary “Impacts” on the Chemistry, Climate, and Spectra of Hot Jupiter Atmospheres

Impacts from icy and rocky bodies have helped shape the composition of Solar System objects; for example, the Earth–Moon system, or the recent impact of comet Shoemaker–Levy 9 with Jupiter. It is likely that such impacts also shape the composition of exoplanetary systems. Here, we investigate how cometary impacts might affect the atmospheric composition/chemistry of hot Jupiters, which are prime targets for characterization. We introduce a parameterized cometary impact model that includes thermal ablation and pressure driven breakup, which we couple with the 1D “radiative-convective” atmospheric model ATMO, including disequilibrium chemistry. We use this model to investigate a wide range of impactor masses and compositions, including those based on observations of Solar System comets, and interstellar ices (with JWST). We find that even a small impactor (R = 2.5 km) can lead to significant short-term changes in the atmospheric chemistry, including a factor >10 enhancement in H2O, CO, and CO2 abundances, as well as atmospheric opacity more generally, and the near-complete removal of observable hydrocarbons, such as CH4, from the upper atmosphere. These effects scale with the change in atmospheric C/O ratio and metallicity. Potentially observable changes are possible for a body that has undergone significant/continuous bombardment, such that the global atmospheric chemistry has been impacted. Our works reveals that cometary impacts can significantly alter or pollute the atmospheric composition/chemistry of hot Jupiters. These changes have the potential to mute/break the proposed link between atmospheric C/O ratio and planet formation location relative to key snowlines in the natal protoplanetary disk.

Volatiles Detection in Lunar Polar Region

In lunar science, volatiles are defined as chemical elements and unstable compounds, evaporating, sublimating, or flowing in other ways at low temperature. At moderate temperature, volatiles transfers its flowing elements from solid materials to coexisting gas phases. Such substances include S, Cu, Zn, As, Se, Ag, Cd, In, Te, Hg, Ti, Pb, Bi, and halogens (F, C L, Br, and I). These volatile substances are mainly added by small impactors, so they should be uniformly deposited in lunar regolith. In the permanently shaded regions (PSRs) of the lunar polar region, the extremely low temperature may allow the solar activity record to be kept longer. When the lunar soil is heated, it will release volatile elements in the form of gas, especially the particles injected into the lunar soil by the solar wind. In deeper lunar soil, it means that these particles were implanted in different periods of solar evolution. The study of regolith in polar PSRs may help to solve this problem, because it has not been widely heated and therefore may not be subjected to postimplantation modification. The research on volatiles detection in lunar polar region can help us confirm the content and distribution of water ice in the permanent shadow region of the lunar polar region, and the composition, distribution, source, transport and loss mechanism of other volatiles in this region, as well as the relationship between lunar soil in the polar region and the ancient solar wind environment, and the environment and mineral resources in the region. Chandrayaan-3 provided important assistance to the conceptualization of this project. At the end of the article, we discussed the lunar orbit.

Mantle fragmentation and incomplete core merging of colliding planetesimals as evidenced by pallasites

Main group pallasites were likely formed by the collision of their parent body with a smaller impactor that caused a mixing of mantle and core material from the target and impactor, respectively. In order to better constrain the collision, we present particle size distribution (PSD) analyses of olivines in seven main group pallasites and of the Eagle station pallasite. The PSDs of two fragmental pallasites (Admire and Huckitta) contain linear segments in bi-logarithmic particle number versus size diagrams that are similar to terrestrial cataclasites or impact-related rocks. On the other hand, the PSDs of four angular pallasites only display linear segments above their respective average grain sizes. We argue that fragmental pallasites record brittle rock deformation close to the impact site of the collision, while angular pallasites represent deeper-lying mantle rocks of the target body that were disintegrated by the downward percolation of core metal from the impactor. High strain-rate deformation experiments with the system olivine – FeS melt ± Au melt produced microstructures and PSDs that are broadly similar to these two textural groups. The experiments also suggest that de-localized metal melt percolation and concomitant mantle disintegration as evidenced in angular pallasites is facilitated by weak grain boundaries caused by a small fraction of previously present metal melt in the mantle as opposed to localized diking that is dominant in a melt-free mantle. The former mechanism is expected to prevent efficient core-merging and instead causes mantle-impregnation with metal melt, which could be active when planetesimal mantles were still warm due to short-lived radiogenic heating. In addition to the parent body of the PMG, asteroid 16 Psyche may be an example of this inefficient core-merging mechanism.

Degradation of the Lunar Surface by Small Impacts

The surfaces of airless bodies like the Moon are bombarded by a steady stream of small impactors that lead to erosion of the topography over time. However, the rate of degradation from small impacts, a key parameter in interpreting the ages of present-day lunar surface features, is not well constrained. Here we demonstrate, using a numerical mass transport model, that impact erosion is a nonlinear diffusion process, in contrast to past studies of crater degradation that have assumed that the downslope mass flux of ejecta is linearly proportional to hillslope gradient. Nonlinearity is a consequence of the asymmetric shape of ejecta blankets on sloped surfaces, and as a result, the degradation rate on steep slopes is over 40% greater than on nearly flat surfaces. Using measurements of the morphology and formation rate of small primary and secondary craters, the kilometer-scale lunar landscape diffusivity is computed and compared to the value inferred from topographic profiles of degraded craters. We show that the abundance of decameter-scale craters forming on the Moon over the past decade is consistent with small impacts dominating the erosion of the lunar landscape, but only if the primary size−frequency distribution remains steep down to the submillimeter scale.

Numerical simulations of hypervelocity collisions scenarios against a large satellite

This paper describes a set of numerical simulations of hypervelocity collisions involving the ESA LOFT spacecraft, with CubeSat impactors ranging from 1 U to 48 U and diverse collision scenarios. The study was done with the purpose to investigate (1) the transition between sub-catastrophic and catastrophic collision with increasing impactor's kinetic energy, and (2) the effect of impact point and encounter configuration on the collision severity.The simulations were performed with the new semi-empirical Collision Simulation Tool developed by CISAS-University of Padova (prime contractor) and etamax GmbH in the framework of an ESA contract recently completed. The CST makes possible to model a large variety of collision scenarios with spacecraft design details included, and is capable to provide statistically accurate impact fragments distributions with low computational expense. It is shown that (1) the ratio between the kinetic energy of the impactor and the mass of the target (Energy-to-Mass Ratio, EMR) is not sufficient to discriminate between sub-catastrophic and catastrophic impacts, and (2) the damage suffered by the target and the number of collision fragments are limited when impacts are not central and the ratio between impactor size and target size is small. In particular, results suggest that the NASA Standard Breakup Model overpredicts the fragments for glancing impacts and/or small impactors, showing that both the impact point and the size of the impactor at a given energy play a significant role to determine the severity of the event.

Pluto and Charon Impact Crater Populations: Reconciling Different Results

Abstract The size–frequency distribution (SFD) of objects across the solar system is influenced by their formation and dynamic evolution. Bodies in different areas of the solar system—especially the inner versus outer—have likely experienced different histories, so measuring that SFD across orders of magnitude of solar distance can elucidate those different pasts. Accurate measurement of the SFD is greatly assisted by impact craters, formed from the smaller bodies that strike much larger ones, and it is often easier to measure impact craters’ SFDs than the smaller impactors themselves. One of the main results from New Horizons’ Pluto–Charon encounter was the crater SFD measurement, which illustrated an unexpected SFD with a distinct change in slope near ≈10–15 km diameter features. However, different methods of reporting these impact craters have resulted in some questions in the community about what the SFD actually is of Pluto's and Charon's crater population and therefore what the SFD is of the impactors that formed them. We have performed new crater population studies on both bodies, compared them with previously published work, and demonstrated that there is no ambiguity with respect to whether there is a transition to a shallower SFD population near ≈10–15 km. We find that this shallower slope is approximately −1.7 ± 0.2, while the steeper slope for larger craters is approximately −3.8 ± 0.6, though both of these uncertainties must be considered absolute minima based on fit sensitivity to the exact parameters and craters used. These values are consistent with previously reported results.

Scientific results obtained from the operation of Hayabusa2 Small Carry-on Impactor

Scientific results obtained from the operation of Hayabusa2 Small Carry-on Impactor

Application of electromagnetic induction for impact load measurement

In this paper, a small impact testing machine was developed as an application of the method for measuring impact load based on electromagnetic induction phenomena. The experimental results were shown to determine the effectiveness of the method. The electromotive forces generated in two coils near a specimen were measured when a small impactor containing a neodymium magnet, having a mass of 0.36 g, was dropped freely onto a 1.2-mm-thick glass plate. The histories of the impact load and the relation between the impact load and specimen deflection were evaluated from the measured electromotive forces because the electromotive force per impactor velocity is dependent on only the position of the impactor. The method and developed machine with the measurement system were determined to be effective by considering the experimental impact test results for the glass plates.

Blowing a crater in asteroid Ryugu

Asteroids The Hayabusa2 spacecraft was designed to collect samples from the nearby asteroid (162173) Ryugu and return them to Earth for laboratory analysis. Arakawa et al. describe how the spacecraft's Small Carry-on Impactor was fired into the asteroid's surface, producing an artificial impact crater. Analysis of the resulting plume of ejecta, recorded by a remote camera, sets an upper limit on the strength of the rubble-pile surface. The crater has a semicircular shape, probably due to a large boulder buried close to the impact location. The crater exposed material from Ryugu's subsurface, which has not been subjected to space weathering, that is suitable for collection by Hayabusa2. Science , this issue p. [67][1] [1]: /lookup/doi/10.1126/science.aaz1701

Impact History and Regolith Evolution on the Moon: Geochemistry and Ages of Glasses from the Apollo 16 Site

AbstractLunar impact glasses are quenched droplets of melt that carry geochemical records of their target compositions, formation ages, and time‐integrated exposure in the upper layers of the lunar regolith. Here we present the first study to obtain major element, trace element, and Ar isotopic data for impact glasses from the Apollo 16 regolith sample 66031. Thirty particles were analysed with 27 of them yielding useable age information. The glasses have a wide range of major and trace element compositions, similar to that observed in lunar meteorites. Half of these glasses have compositions similar to Apollo 16 soils and are considered to be “locally derived”, whereas the others represent diverse source regions and are considered to be “exotic” particles that were delivered from a considerable distance to the landing site.Almost 40% of the samples analysed for this study have formation ages younger than 500 Ma. Duplicate particles produced in single impact events contribute minimally to the age distribution, and diurnal or transient heating of the regolith does not appear to have had a significant effect on the 40Ar/39Ar ages. Rather, the ages reflect primarily the formation of these glasses by impact melting, with the distribution modified to some degree by preservation bias. As most of these glasses are likely formed by relatively small impactors, their age distribution cannot be compared directly with the crystalline lunar melt rocks to constrain the impact mass flux through time.

Temperatures of lunar impact flashes: mass and size distribution of small impactors hitting the Moon

Lunar impact flashes have been monitored over the last 20 years for determining the mass frequency distribution of near-Earth objects in the cm-dm size range. In this work, using telescopic observations in R and I band from the NELIOTA database, impact flash temperatures are derived. They are found to range between approximately 1,300 and 5,800 K. In addition, it is also found that temperature values appear to have a distribution significantly broader than a Gaussian function, therefore making it difficult to estimate the impact flash luminous energy by assigning an average temperature. By measuring the flash temperatures and assuming a black body emission, here we derive the energy of the impacts. We also study the potential link of each event to individual meteoroid streams, which allows us to assign an impact velocity and therefore constrain the projectile mass. Impactor masses are found to range between a few to hundreds of grams, while their sizes are just of few centimetres following a size frequency distribution similar to other studies.

Inversion of Meteor Rayleigh Waves on Earth and Modeling of Air Coupled Rayleigh Waves on Mars

Meteor impacts and/or meteor events generate body and surface seismic waves on the surface of a planet. When meteoroids burst in the atmosphere, they generate shock waves that subsequently convert into acoustic waves in the atmosphere and seismic waves in the ground. This effect can be modeled as the amplitude of Rayleigh and other Spheroidal modes excitation, due to atmospheric/ground coupling effects. First, an inversion of the seismic source of Chelyabinsk superbolide is performed. We develop an approach in order to model a line source in the atmosphere, corresponding to the consecutive generation of shock waves by the interaction with the atmosphere. The model is based on the known trajectory. We calculate the synthetic seismograms of Rayleigh waves associated with the event by the summation of normal modes of a model of the solid part and the atmosphere of the planet. Through an inversion technique based on singular value decomposition, we perform a full Rayleigh wave inversion and we provide solutions for the moment magnitude. SEIS will likely detect seismic waves generated by impacts and the later might be further located by remote sensing differential processing. In the case of Mars, we use the same method to obtain waveforms associated with impacts on the planetary surface or in low altitudes in the Martian atmosphere. We show that the contribution of the fundamental spheroidal solid mode is dominating the waveforms, compared to that of the first two overtones. We perform an amplitude comparison and we show that small impactors (diameter of 0.5 to 2 m), can be detected by the SEIS VBB seismometer of InSight mission, even in short epicentral distances, in the higher frequencies of the Rayleigh waves. We perform an analysis based on impact rate estimations and we calculate the number of detectable events of 1 meter diameter meteor impacts to be 6.7 to 13.4 per 1 Martian year for a $Q=500$ .

New diagnostic method for evaluating penetration strength of rubber sheet by measuring electromagnetic induction

This paper presents a new diagnostic method for evaluating the penetration strength of a rubber sheet based on electromagnetic induction phenomena. This method was established on the basis of the experimental results of impact tests of specimens when small impactors collided with rubber sheets. The impactor behavior, impact force, and specimen deflection were analyzed based on the electromotive force generated in a coil near the specimens when the impactors containing a neodymium magnet collided with the specimens because the intensity of the electromotive force is proportional to the impactor velocity and because its variation is solely dependent on the position of the impactor. The validity of the analyzed impact force and specimen deflection was confirmed by considering the impactor behavior, which was observed using a high-speed camera, and the external work of the impactors evaluated from the analyzed results. The penetration strength of the rubber sheet was determined from the impact-force history and the impact force-specimen deformation curve based on the analyzed impactor behavior during the collision.

Geochemical Constraints on the Size of the Moon‐Forming Giant Impact

AbstractRecent models involving the Moon‐forming giant impact hypothesis have managed to reproduce the striking isotopic similarity between the two bodies, albeit using two extreme models: one involves a high‐energy small impactor that makes the Moon out of Earth's proto‐mantle; the other supposes a gigantic collision between two half‐Earths creating the Earth‐Moon system from both bodies. Here we modeled the geochemical influence of the giant impact on Earth's mantle and found that impactors larger than 15% of Earth mass result in mantles always violating the present‐day concentrations of four refractory moderately siderophile trace elements (Ni, Co, Cr, and V). In the aftermath of the impact, our models cannot further discriminate between a fully and a partially molten bulk silicate Earth. Then, the preservation of primordial geochemical reservoirs predating the Moon remains the sole argument against a fully molten mantle after the Moon‐forming impact.

Testing models for the formation of the equatorial ridge on Iapetus via crater counting

Iapetus's equatorial ridge, visible in global views of the moon, is unique in the Solar System. The formation of this feature is likely attributed to a key event in the evolution of Iapetus, and various models have been proposed as the source of the ridge. By surveying imagery from the Cassini and Voyager missions, this study aims to compile a database of the impact crater population on and around Iapetus's equatorial ridge, assess the relative age of the ridge from differences in cratering between on ridge and off ridge, and test the various models of ridge formation. This work presents a database that contains 7748 craters ranging from 0.83 km to 591 km in diameter. The database includes the study area in which the crater is located, the latitude and longitude of the crater, the major and minor axis lengths, and the azimuthal angle of orientation of the major axis. Analysis of crater orientation over the entire study area reveals that there is no preference for long-axis orientation, particularly in the area with the highest resolution. Comparison of the crater size-frequency distributions show that the crater distribution on the ridge appears to be depleted in craters larger than 16 km with an abruptly enhanced crater population less than 16 km in diameter up to saturation. One possible interpretation is that the ridge is a relatively younger surface with an enhanced small impactor population. Finally, the compiled results are used to examine each ridge formation hypothesis. Based on these results, a model of ridge formation via a tidally disrupted sub-satellite appears most consistent with our interpretation of a younger ridge with an enhanced small impactor population.

Sedimentary laminations in the Isheyevo (CH/CBb) carbonaceous chondrite formed by gentle impact-plume sweep-up

Prominent macroscopic sedimentary laminations, consisting of mm- to cm-thick alternating well-sorted but poorly mixed silicate and metal-rich layers cut by faults and downward penetrating load structures, are prevalent in the Isheyevo (CH/CBb) carbonaceous chondrite. The load structures give the up direction of this sedimentary rock that accumulated from in-falling metal- and silicate-rich grains under near vacuum conditions onto the surface of an accreting planetesimal. The Isheyevo meteorite is the end result of a combination of events and processes that we suggest was initiated by the glancing blow impact of two planetesimals. The smaller impactor was disrupted forming an impact plume downrange of the impact. The components within the plume were aerodynamically size sorted by the nebular gas and swept up by the impacted planetesimal before turbulent mixing within the plume could blur the effects of the sorting. This plume would have contained a range of materials including elementally zoned Fe-Ni metal grains that condensed in the plume to disrupted unaltered material from the crust of the impactor, such as the hydrated matrix lumps. The juxtaposition of hydrated matrix lumps, some of which have not been heated above 150 °C, together with components that formed above 1000 °C, is compelling evidence that they were swept up together. Sweep-up would have occurred as the rotating impactor moved through the plume producing layers of material: the Isheyevo sample thus represents material accumulated while that part of the rotating planetesimal moved into the plume. Vibrations from subsequent impacts helped to form the load structures and induced weak grading within the layers via kinetic sieving. Following sweep-up, the particles were compacted under low static temperatures as evidenced by the preservation of elementally zoned Fe-Ni metal grains with preserved martensite α2 cores, distinct metal-metal grain boundaries, and metal-deformation microstructures. This meteorite provides evidence of gentle layer-by-layer accretion in the early Solar System, and also extends the terrestrial sedimentary source-to-sink paradigm to a near vacuum environment where neither fluvial nor aeolian processes operate.

Rotational and translational considerations in kinetic impact deflection of potentially hazardous asteroids

Kinetic impact may be the most reliable and easily implemented method to deflect hazardous asteroids using current technology. Depending on warning time, it can be effective on asteroids with diameters of a few hundred meters. Current impact deflection research often focuses on the orbital dynamics of asteroids. In this paper, we use the ejection outcome of a general oblique impact to calculate how an asteroid’s rotational and translational state changes after impact. The results demonstrate how small impactors affect the dynamical state of small asteroids having a diameter of about 100m. According to these consequences, we propose using several small impactors to hit an asteroid continuously and gently, making the deflection mission relatively flexible. After calculating the rotational variation, we find that the rotational state, especially of slender non-porous asteroids, can be changed significantly. This gives the possibility of using multiple small impactors to mitigate a potentially hazardous asteroid by spinning it up into pieces, or to despin one for future in-situ investigation (e.g., asteroid retrieval or mining).

PLANETESIMAL COLLISIONS AS A CHONDRULE FORMING EVENT

ABSTRACT Chondritic meteorites contain unique spherical materials named chondrules: sub-mm sized silicate grains once melted in a high temperature condition in the solar nebula. We numerically explore one of the chondrule forming processes—planetesimal collisions. Previous studies have found that impact jetting via protoplanet–planetesimal collisions can make chondrules with 1% of the impactors’ mass, when the impact velocity exceeds 2.5 km s−1. Based on the mineralogical data of chondrules, undifferentiated planetesimals would be more suitable for chondrule-forming collisions than potentially differentiated protoplanets. We examine planetesimal–planetesimal collisions using a shock physics code and find two things: one is that planetesimal–planetesimal collisions produce nearly the same amount of chondrules as protoplanet–planetesimal collisions (∼1%). The other is that the amount of produced chondrules becomes larger as the impact velocity increases when two planetesimals collide with each other. We also find that progenitors of chondrules can originate from deeper regions of large targets (planetesimals or protoplanets) than small impactors (planetesimals). The composition of targets is therefore important, to fully account for the mineralogical data of currently sampled chondrules.

Measuring Method of Impact Load in Collision of Small Impactor Based on Electromagnetic Induction

Measuring Method of Impact Load in Collision of Small Impactor Based on Electromagnetic Induction

An investigation of Crater Diameter on Plain Slab Foamed Concrete Rice Husk Ash (FCRHA) Exposed to Low Impact Loading

As sustainable material building and construction, the foamed concrete (FC) in this investigation was modified by adding the Rice Husk Ash (RHA) as sand replacement to increase its strength. Furthermore, this modification material (is called FCRHA) treated on impact loading. This investigation was motivated when the plain slab of FCRHA subjected to small impactor, then the nose impactor over all would penetrate into slab target due to porosity of FCRHA. The experimental produced plain slabs FCRHA and FC (as a control) with 1400 kg/m 3 and 1600 Kg/m 3 of densities. In impact test all plain slabs exposed by 40 mm steel blunt nose impactor with various impact velocities. The result showed the crater which produced by impact loading was not found spalling, scabbing, radial crack and widely cratering. This local damage occurred when porosity of FCRHA took over the impact loading. The nose impactor over all considered have been successful penetrated into slab of FCRHA and FC. Therefore, the diameter of crater equals to diameter of impactor. With this certainty, the prediction penetration depth on plain slab FCRHA (also FC) can be determined in future investigation. In addition, the penetration of impactor on FCRHA with low impact velocity give the same impression on penetration impactor with high impact velocity on FC.