Incoming Meteoroids Research Articles

Feasibility of meteor surveying from a Venus orbiter

Meteor and bolide phenomena caused by the atmospheric ablation of incoming meteoroids are predicted to occur at the planet Venus. Their systematic observation would allow to measure and compare the sub-mm to m meteoroid flux at different locations in the solar system. Using a physical model of atmospheric ablation, we demonstrate that Venus meteors would be brighter, shorter-lived, and appear higher in the atmosphere than Earth meteors. To investigate the feasibility of meteor detection at Venus from an orbiter, we apply the SWARMS survey simulator tool to sets of plausible meteoroid population parameters, atmospheric models and instrument designs suited to the task, such as the Mini-EUSO camera operational on the ISS since 2019. We find that such instrumentation would detect meteors at Venus with a 1.5× to 2.5× higher rate than at Earth. The estimated Venus–Earth detection ratio remains insensitive to variations in the chosen observation orbit and detector characteristics, implying that a meteor survey from Venus orbit is feasible, though contingent on the availability of suitable algorithms and methods for efficient on-board processing and downlinking of the meteor data to Earth. We further show that a hypothetical camera onboard the upcoming EnVision mission to Venus similar to the ISS instrument should detect many times more meteors than needed for an initial characterisation of the large meteoroid population at 0.7 au from the Sun.

The importance of acid-processed meteoric smoke relative to meteoric fragments for crystal nucleation in polar stratospheric clouds

Abstract. The crystal formation of nitric acid trihydrate (NAT) in the absence of water ice is important for a subset of polar stratospheric clouds (PSCs) and thereby ozone depletion. It has been suggested that either fragmented meteoroids or meteoric smoke particles (MSPs), or possibly both, are important as heterogeneous nuclei of these crystals. Previous work has focused on the nucleating ability of meteoric material in nitric acid in the absence of sulfuric acid. However, it is known that when immersed in stratospheric sulfuric acid droplets, metal-containing meteoric material particles partially dissolve and components can reprecipitate as silica and alumina that have different morphologies to the original meteoric material. Hence, in this study, we experimentally and theoretically explore the relative role that sulfuric acid-processed MSPs and meteoric fragments may play in NAT nucleation in PSCs. We compared meteoric fragments that had recently been prepared (by milling a meteorite sample) to a sample annealed under conditions designed to simulate heating during entry into the Earth's atmosphere. Whilst the addition of sulfuric acid decreased the nucleating ability of the recently milled meteoric material relative to nucleation in binary nitric acid-water solutions (at similar NAT saturation ratio), the annealed meteoric fragments nucleated NAT with a similar effectiveness in both solutions. However, combining our results with measured fluxes of meteoric material to the Earth, sedimentation modelling and recent experiments on fragmentation of incoming meteoroids suggests that it is unlikely for there to be sufficient fragments to contribute to the nucleation of crystalline NAT particles. We then considered silica formed from sulfuric acid-processed MSPs. Our previous work showed that nanoparticulate silica (radius ∼6 nm) is a relatively poor promoter of nucleation compared with micron-scaled silica particles, which were more effective. Both materials have similar chemical and structural (crystallographically amorphous) properties, indicating that size is critical. Here, we account for surface curvature of primary grains using the Classical Nucleation Theory (CNT) to explore this size dependence. This model is able to explain the discrepancy in nucleation effectiveness of fumed silica and fused quartz by treating their nucleating activity (contact angle) as equal but with differing particle size (or surface curvature), assuming interfacial energies that are physically reasonable. Here, we use this CNT model to present evidence that nucleation of NAT on acid-processed MSPs, where the primary grain size is tens of nanometres, is also effective enough to contribute to NAT crystals in early season PSCs where there is an absence of ice. This study demonstrates that the modelling of crystal nucleation in PSCs and resulting ozone depletion relies on an accurate understanding of the transport and chemical processing of MSPs. This will affect estimated sensitivity of stratospheric chemistry to rare events such as large volcanic eruptions and long-term forecasting of ozone recovery in a changing climate.

FRIPON: a worldwide network to track incoming meteoroids

Context.Until recently, camera networks designed for monitoring fireballs worldwide were not fully automated, implying that in case of a meteorite fall, the recovery campaign was rarely immediate. This was an important limiting factor as the most fragile – hence precious – meteorites must be recovered rapidly to avoid their alteration.Aims.The Fireball Recovery and InterPlanetary Observation Network (FRIPON) scientific project was designed to overcome this limitation. This network comprises a fully automated camera and radio network deployed over a significant fraction of western Europe and a small fraction of Canada. As of today, it consists of 150 cameras and 25 European radio receivers and covers an area of about 1.5 × 106km2.Methods.The FRIPON network, fully operational since 2018, has been monitoring meteoroid entries since 2016, thereby allowing the characterization of their dynamical and physical properties. In addition, the level of automation of the network makes it possible to trigger a meteorite recovery campaign only a few hours after it reaches the surface of the Earth. Recovery campaigns are only organized for meteorites with final masses estimated of at least 500 g, which is about one event per year in France. No recovery campaign is organized in the case of smaller final masses on the order of 50 to 100 g, which happens about three times a year; instead, the information is delivered to the local media so that it can reach the inhabitants living in the vicinity of the fall.Results.Nearly 4000 meteoroids have been detected so far and characterized by FRIPON. The distribution of their orbits appears to be bimodal, with a cometary population and a main belt population. Sporadic meteors amount to about 55% of all meteors. A first estimate of the absolute meteoroid flux (mag < –5; meteoroid size ≥~1 cm) amounts to 1250/yr/106km2. This value is compatible with previous estimates. Finally, the first meteorite was recovered in Italy (Cavezzo, January 2020) thanks to the PRISMA network, a component of the FRIPON science project.

A Comparative Modeling Study of the Seasonal, Temporal, and Spatial Distribution of Meteoroids in the Upper Atmospheres of Venus, Earth, and Mars

Abstract The meteoroid input function (MIF) describes the seasonal, diurnal and planetographic distribution of incoming meteoroids onto an atmosphere and/or surface of a solar system body. Utilizing state-of-the-art dynamical models of the main populations of meteoroids, we present a comparative study of the MIF on the atmospheres of Venus, Earth and Mars. Our modeling results show that, although a planet's axial tilt and orbital eccentricity introduce measurable important variability of the overall MIF, excursions from the ecliptic plane due to orbital inclination are responsible for the largest differences, producing variations of up to 40% with respect to the mean value in the overall mass fluxes of Venus and Mars. This is particularly true for meteoroid populations concentrated around the ecliptic plane, which are believed to be the dominant source of organics and metals on the atmospheres of these planets.

Recently Formed Crater Clusters on Mars

AbstractThis study maps and measures assorted properties of new dated crater clusters that formed recently when impactors fragmented in the atmosphere of Mars. We report these statistics for 77 clusters: number of craters, size of cluster, dispersion of cluster, direction (azimuth) from which the impactor approached, and an estimate of the angle from vertical of the impact. Clusters range from a few to hundreds of craters, with most containing tens of craters. They are most commonly dispersed over hundreds of meters, with extents ranging from a few meters to a few kilometers. We find that dispersion generally does not correlate with topographic elevation. However, when the highest elevations are disregarded, clusters are more dispersed at lower elevations, as expected. Impact azimuths are randomly distributed and do not express a clear directionality of incoming meteoroids. Results suggest impacts occur closer to horizontal than expected, which could be due to observational effects. The characteristics we report here provide important constraints for future work in understanding atmospheric fragmentation processes; properties of the impactors themselves, such as density and orbital parameters; and the seismic detectability of impacts. These are critical aspects to understand, as approximately half of current impacts are observed to be clusters.

Deconvoluting measurement uncertainty from the meteor speed distribution

AbstractDebiasing the velocity distribution of meteors observed by the Canadian Meteor Orbit Radar (CMOR) yields a distribution with large numbers of slow meteors. The distribution also contains significant numbers of hyperbolic meteors, in conflict with the expectation that interstellar meteors should be rare. In Moorhead et al. (2017a), we noted that measurement uncertainties were possibly smoothing the speed distribution and redistributing meteors to the extreme ends of the speed distribution. In this report, we use techniques analogous to image sharpening to remove the blurring caused by measurement uncertainties. The deconvolved speed distribution appears to have no meteors slower than 14 km s−1 and none faster than 74 km s−1. The result is to substantially raise the characteristic velocity of incoming meteoroids from 12.9 to 20.0 km s−1.

Kinetic studies of atmospherically relevant silicon chemistry. Part III: Reactions of Si+and SiO+with O3, and Si+with O2

Silicon ions are generated in the Earth's upper atmosphere by hyperthermal collisions of material ablated from incoming meteoroids with atmospheric molecules, and from charge transfer of silicon-bearing neutral species with major atmospheric ions. Reported Si(+) number density vs. height profiles show a sharp decrease below 95 km, which has been commonly attributed to the fast reaction with H(2)O. Here we report rate coefficients and branching ratios of the reactions of Si(+) and SiO(+) with O(3), measured using a flow tube with a laser ablation source and detection of ions by quadrupole mass spectrometry. The results obtained are (2σ uncertainty): k(Si(+) + O(3), 298 K) = (6.5 ± 2.1) × 10(-10) cm(3) molecule(-1) s(-1), with three product channels (branching ratios): SiO(+) + O(2) (0.52 ± 0.24), SiO + O(2)(+) (0.48 ± 0.24), and SiO(2)(+) + O (<0.1); k(SiO(+) + O(3), 298 K) = (6 ± 4) × 10(-10) cm(3) molecule(-1) s(-1), where the major products (branching ratio ≥ 0.95) are SiO(2) + O(2)(+). Reactions (1) and (2) therefore have the unusual ability to neutralise silicon directly, as well as forming molecular ions which can undergo dissociative recombination with electrons. These reactions, along with the recently reported reaction between Si(+) and O(2)((1)Δ(g)), largely explain the disappearance of Si(+) below 95 km in the atmosphere, relative to other major meteoric ions such as Fe(+) and Mg(+). The rate coefficient of the Si(+) + O(2) + He reaction was measured to be k(298 K) = (9.0±1.3) × 10(-30) cm(6) molecule(-2) s(-1), in agreement with previous measurements. The SiO(2)(+) species produced from this reaction, which could be vibrationally excited, is observed to charge transfer at a relatively slow rate with O(2), with a rate constant of k(298 K) = (1.5 ± 1.0) × 10(-13) cm(3) molecule(-1) s(-1).

Event and conditions that produced the iron meteorite Block Island on Mars

The Mars Exploration Rover Opportunity has discovered four large iron‐nickel meteorites that range in size from 50 to 240 kg dispersed over 10 km of Meridiani Planum, Mars. Because these meteorites are covered with hollows that resemble regmaglypts, their surfaces record their ablation through the atmosphere, and they must have landed at speeds below hypervelocity (&lt;2 km s−1) to survive. Slowing massive iron meteorites requires a minimum atmospheric density, which was quantified using a numerical model that integrates the equations of motion for incoming meteoroids through an atmosphere of a given surface density and scale height and records their outcomes as direct (generally hypervelocity impacts that form craters), longer over the horizon and fallback flight paths, and skip outs. The present atmosphere of Mars is sufficient to slow iron meteoroids as large as Block Island (the most massive meteorite) via drag and significant ablation on long flight paths, although for standard distributions of entering meteoroid masses, velocities, and entry angles, such events are rare (0.007% of incoming iron meteoroids). Such events require entry angles of 10°–13°, entry velocities of 6–18 km s−1, and entry masses of 225–710 kg. The absence of large stony meteorites is probably at least partially because they are much weaker and thus broken up into smaller fragments on impact. Although differential drag deceleration on long flight paths could disperse fragments of an entering meteoroid by tens of kilometers, dynamic pressures are too low to break up an iron meteorite, leaving the possibility that they are paired an open question.

Carbon in Meteoroids: Wild 2 Dust Analyses, IDPs and Cometary Dust Analogues

Assuming that similar organic components as in comet 81P/Wild 2 are present in incoming meteoroids, we try to anticipate the observable signatures they would produce for meteor detection techniques. In this analysis we consider the elemental and organic components in cometary aggregate interplanetary dust particles and laboratory analyses of inter- and circumstellar carbon dust analogues. On the basis of our analysis we submit that (semi) quantitative measurements of H, N and C produced during meteor ablation will open an entire new aspect to using meteoroids as tracers of these volatile element abundances in active comets and their contributions to the mesospheric metal layers.

Properties of meteoroids from different classes of parent bodies

AbstractMeteoroids observed to disintegrate in the terrestrial atmosphere can be directly linked to their parent bodies in case that they belong to certain meteor showers. We present a list of two dozens of parent bodies reliably associated with well recognized meteor showers. Among the parent bodies are long period comets, Halley-type comets, Jupiter family comets, comets of the inner solar system (such as 2P/Encke) and asteroids. Physical and chemical properties of meteoroids coming from various parents are compared on the basis of meteor heights, decelerations, light curves and spectra. Jupiter family comets produce meteoroids with the lowest strength, namely porous aggregates of dust grains with bulk densities of about 0.3 g cm−3or less. Halley type material is somewhat stronger and the material related to comet Encke is even stronger. In addition, small strong constituents, perhaps similar to carbonaceous chondrites, can be encountered within the normal cometary material. The strength of cometary material is also enhanced by long-term exposure to cosmic rays and by solar heating in the vicinity to the Sun (r&lt;0.2 AU). Both these processes lead to the loss of volatile sodium. Southern δ-Aquariids, Geminids and partly also Quadrantids were influenced by solar radiation. We argue that these showers, the asteroids associated with them ((3200) Phaethon and 2003 EH1), and the whole interplanetary complexes they belong to are of cometary origin. The argument is supported by lower than chondritic Fe/Mg ratio found in Geminids as well as in Halley type comets. The typical property of stony meteoroids of asteroidal origin is the presence of internal cracks which cause that the incoming meteoroids are much weaker than the recovered meteorites.

Impacts into Ice–Silicate Mixtures: Crater Morphologies, Volumes, Depth-to-Diameter Ratios, and Yield

In this and a companion paper, we analyze the strength-dominated impact process into ice–silicate mixtures via experimental techniques, which is important in understanding the evolution of icy satellite surfaces as well as the dynamics of planetary rings. We used the plasmadynamic accelerator (PDA) and the electrothermal accelerator (ET) of the Fachbereich Raumfahrt of the Technische Universität München to perform impact experiments. The projectile velocities were varied between 0.9 and 11.8 km/s and projectile masses were between 1.7·10 −11 kg and 7.2·10 −10 kg at the plasma accelerator (projectile material was glass); at the electrothermal accelerator, projectile velocities were between 1.1 to 3.3 km/s and projectile masses between 6·10 −6 kg and 3·10 −5 kg (projectile material: Nylon). The kinetic energies ranged over 6 orders of magnitude, from 8.8·10 −5 J to 70 J. Silicate contents of the target were varied from 5% to 20% (mass), the rest was water ice. The target temperature was 250K±5K. Typical crater diameters were in the order of 0.1 to 1 mm at the PDA and several cm at the ET. In general, the crater morphology can be described by a conical spallation zone, in which a central crater, at the electrothermal accelerator with raised rim, was observed. In the center, the craters were much brighter than the undisturbed target surface. At the ET experiments, we measured the silicate content in different regions of the crater. It does not change significantly; actually, there is a slight tendency for the silicate content to be higher in the center of the crater as compared to the undisturbed surface. Together with data from Frisch (1990, Dissertation, TU München; and 1992, Proceedings of the Workshop on Hypervelocity Impacts in Space) for pure ice and Moore et al. (1963, Trans. Min. Eng. 229, 258–262) for basalt, an empirical relationship for the crater volume depending on the target and projectile parameters is found. Typically, crater volumes in pure ice are about two orders of magnitude larger than craters in pure silicates, for identical projectile mass and velocity. The crater yield, defined as the ratio of ejected mass to projectile mass, was found to be in the order of 1 to 10 3. We derived an empirical relationship for the yield as a function of the target and projectile properties. This relationship was compared to the necessary yields found by Durisen et al. (1992, Icarus 100, 364–393) for the description of mass transfer in Saturn's A- and B-ring. We find that their required yields are about one to two orders of magnitude larger than our experiments showed and conclude that more knowledge of the flux of incoming meteoroids and the ring's viscosity are necessary.

Effects of the Venusian Atmosphere on Incoming Meteoroids and the Impact Crater Population

The dense atmosphere on Venus prevents craters smaller than about 2 km in diameter from forming and also causes formation of several crater fields and multiple-floored craters (collectively referred to as multiple impacts). A model has been constructed that simulates the behavior of a meteoroid in a dense planetary atmosphere. This model was then combined with an assumed flux of incoming meteoroids in an effort to reproduce the size-frequency distribution of impact craters and several aspects of the population of crater fields and multiple-floored craters on Venus. The modeling indicates that it is plausible that the observed rollover in the size-frequency curve for Venus is due entirely to atmospheric effects on incoming meteoroids. However, there must be substantial variation in the density and behavior of incoming meteoroids in the atmosphere. Lower-density meteoroids must be less likely to survive atmospheric passage than simple density differences can account for. Consequently, it is likely that the percentage of craters formed by high-density meteoroids is very high at small crater diameters, and this percentage decreases substantially with increasing crater diameter. Overall, high-density meteoroids created a disproportionately large percentage of the impact craters on Venus. Also, our results indicate that a process such as meteoroid flattening or atmospheric explosion of meteoroids must be invoked to prevent craters smaller than the observed minimum diameter (2 km) from forming. In terms of using the size-frequency distribution to age-date the surface, the model indicates that the observed population has at least 75% of the craters over 32 km in diameter that would be expected on an atmosphereless Venus; thus, this part of the curve is most suitable for comparison with the calibrated curves for the Moon. Separation of meteoroid fragments by aerodynamic drag alone is not adequate to explain either the number of multiple impacts or the dispersion of individual craters in multiple impacts. A large transverse velocity must be imparted on the fragments at breakup. This requires that meteoroids that form multiple impacts must have enough strength to resist breakup until sufficient pressure is built up on the leading edge of the meteoroid. It is likely that most multiple impacts were formed by asteroidal, and not cometary, meteoroids.

Impact Craters on Venus: Initial Analysis from Magellan

Magellan radar images of 15 percent of the planet show 135 craters of probable impact origin. Craters more than 15 km across tend to contain central peaks, multiple central peaks, and peak rings. Many craters smaller than 15 km exhibit multiple floors or appear in clusters; these phenomena are attributed to atmospheric breakup of incoming meteoroids. Additionally, the atmosphere appears to have prevented the formation of primary impact craters smaller than about 3 km and produced a deficiency in the number of craters smaller than about 25 km across. Ejecta is found at greater distances than that predicted by simple ballistic emplacement, and the distal ends of some ejecta deposits are lobate. These characteristics may represent surface flows of material initially entrained in the atmosphere. Many craters are surrounded by zones of low radar albedo whose origin may have been deformation of the surface by the shock or pressure wave associated with the incoming meteoroid. Craters are absent from several large areas such as a 5 million square kilometer region around Sappho Patera, where the most likely explanation for the dearth of craters is volcanic resurfacing. There is apparently a spectrum of surface ages on Venus ranging approximately from 0 to 800 million years, and therefore Venus must be a geologically active planet.

Bombardment of planetary rings by meteoroids: General formulation and effects of Oort cloud projectiles

We present a general solution for the angular distribution of the intensity and velocity of interplanetary projectiles as they impinge on a planetary ring system, given the original distribution in inertial space. Our solution lends itself immediately to three results of importance. First, we demonstrate a variation with orbital longitude of an impact-velocity-weighted impact rate of cometary meteoroids in planetary rings. The largest rate of energetic impacts occurs at orbital longitudes near solar midnight, consistent in location and form with observed creation rates of “spokes” in Saturn's rings. This provides support for spoke formation hypotheses which rely on meteroid impact. Second, we determine the angular distribution of the intensity of ejecta which result from the bombardment of a planetary ring composed of centimeter- to meter-sized particles by interplanetary meteroids in the subcentimeter-size range. We do this using a radiative transfer formalism. The angular distribution of ejecta resulting from the bombardment of a single target particle is first obtained as a function of angle from a single incident direction. In this step, we incorporate results from laboratory studies of nondisruptive hypervelocity impacts into granular and powdery surfaces. This single particle “phase function” is part of a standard expression for the net scattering function of the layer as a whole, which accounts for the escape probabilities of ejecta emerging from impacts occurring at different depths within the ring layer. We assume that multiple scattering terms resulting from impacts into nearby particles by the more slowly moving ejecta are negligible. Finally, the net scattering function of the layer is integrated over the angular distribution of the incoming meteoroids, which is determined in the frame of an orbiting ring particle by accounting for aberration effects arising from the orbital motion of the ring particle and its parent planet. Our calculated ejecta distributions are incorporated into evolutions of ring mass density and radial structure in a companion paper (Durisen et al. 1989, Icarus, 80 136–166). Third, we calculate the radial drift velocity of a planetary ring of arbitrary optical depth which results from two factors: simple mass loading, and aberration-induced asymmetry in the impact rate. Bombardment of ring systems at the currently accepted rate of interplanetary meteoroid flux leads to an inward radial drift of several cm yr −1 in regions of moderate optical depth. This rate is large enough for the Uranian α and β rings, and the entire C ring of Saturn, to fall into the atmosphere of the parent planet in about 10 8 years under only the known flux of projectiles on Oort cloud orbits. These effects can vary significantly with the orbital distribution of the projectile population. In this paper, we present results for projectiles with “Oort cloud” orbits. In a subsequent paper, we will present the results anticipated for projectiles in “local family” prograde, low inclination orbits.

Origin of the Goose Lake Meteorite

THE Goose Lake meteorite was sitting on the surface of the Earth when found1 and had no apparent crater associated with its impact. The absence of a crater undoubtedly means that the vertical component of velocity at the time of impact was extremely small. While a parabolic or hyperbolic orbit with grazing incidence is a theoretical possibility, the probability of such a meteoroid trajectory is relatively low. Furthermore, no impact scars are found1 on the meteorite, as might be expected if it had struck the Earth's surface with an appreciable horizontal component of velocity. Krinov2 indicates that those Sikhote–Alin fragments that had a mass about equal to the mass of the Goose Lake meteorite produced impact craters approximately 10 m in diameter. The Sikhote–Alin meteoroid entered the Earth's atmosphere with a velocity of 14.5 km/sec, a relatively low velocity for incoming meteoroids.