A meteorite crater on Earth formed on September 15, 2007: The Carancas hypervelocity impact

Abstract— On September 15, 2007, a bright fireball was observed and a big explosion was heard by many inhabitants near the southern shore of Lake Titicaca. In the community of Carancas (Peru), a 13.5 m crater and several fragments of a stony meteorite were found close to the site of the impact. The Carancas event is the first impact crater whose formation was directly observed by several witnesses as well as the first unambiguous seismic recording of a crater‐forming meteorite impact on Earth. We present several lines of evidence that suggest that the Carancas crater was a hypervelocity impact. An event like this should have not occurred according to the accepted picture of stony meteoroids ablating in the Earth's atmosphere, therefore it challenges our present models of entry dynamics. We discuss alternatives to explain this particular event. This emphasizes the weakness in the pervasive use of “average” parameters (such as tensile strength, fragmentation behavior and ablation behavior) in current modeling efforts. This underscores the need to examine a full range of possible values for these parameters when drawing general conclusions from models about impact processes.     

Effects of atmospheric breakup on crater field formation

This paper investigates the physics of meteoroid breakup in the atmosphere and its implications for the observed features of strewn fields. There are several effects which cause dispersion of the meteoroid fragments: gravity, differential lift of the fragments, bow shock interaction just after breakup, centripetal separation by a rotating meteoroid, and possibly a dynamical transverse separation resulting from the crushing deceleration in the atmosphere. Of these, we show that gravity alone can produce the common pattern in which the largest crater occurs at the downrange end of the scatter ellipse. The average lift-to-drag ratio of the tumbling fragments must be less than about 10^?3, otherwise small fragments would produce small craters downrange of the main crater, and this is not generally observed. The cross-range dispersion is probably due to the combined effects of bow shock interaction, crushing deceleration, and possibly spinning of the meteoroid. A number of terrestrial strewn fields are discussed in the light of these ideas, which are formulated quantitatively for a range of meteoroid velocities, entry angles, and crushing strengths. It is found that when the crater size exceeds about 1 km, the separation between the fragments upon landing is a fraction of their own diameter, so that the crater formed by such a fragmented meteoroid is almost indistinguishable from that formed by a solid body of the same total mass and velocity.     

The Whitecourt meteorite impact crater,Alberta, Canada

Abstract– The <1,100 yr old Whitecourt meteorite impact crater, located south of Whitecourt, Alberta, Canada, is a well‐preserved bowl‐shaped structure having a depth and diameter of approximately 6 and 36 m, respectively. There are fewer than a dozen known terrestrial sites of similar size and age. Unlike most of these sites, however, the Whitecourt crater contains nearly all of the features associated with small impact craters including meteorites, ejecta blanket, observable transient crater boundary, raised rim, and associated shock indicators. This study indicates that the crater formed from the impact of an approximately 1 m diameter type IIIAB iron meteoroid traveling east‐northeast at less than approximately 10 km s^?1, striking the surface at an angle between 40° and 55° to horizontal. It appears that the main mass survived atmospheric transit relatively intact, with fragmentation and partial melting during impact. Most meteoritic material has a jagged, shrapnel‐like morphology and is distributed downrange of the crater.     

Physical mechanism of Chelyabinsk superbolide explosion

The work presents modern ideas on the physical mechanism of explosion of large meteoroids (superbolides) in the Earth’s atmosphere at the end of their trajectories. As a result of our work, the values of following parameters were obtained: the altitude of the beginning of the aerodynamic destruction of a meteoroid like the Chelyabinsk superbolide; the altitude of a relatively very thin layer, characterized by sharp aerodynamic deceleration of a fragmenting and laterally expanding space object, accompanied by an impulse transformation of kinetic energy into thermal energy with plasma generation which results in intense electromagnetic radiation and an explosive shock wave; and, the initial temperature of such a plasma.     

Reconstruction of the Morasko meteoroid impact—Insight from numerical modeling

The Morasko strewn field located near Poznań, Poland comprises seven impact craters with diameters ranging from 20 to 90 m, all of which were formed in glacial sediments around 5000 yr ago. Numerous iron meteorites have been recovered in the area and their distribution suggests a projectile with the trajectory from NE to SW. Similar impact events producing crater strewn fields on average happen every 500 yr and pose a serious risk for modern civilization, which is why it is of utmost importance to study terrestrial strewn fields in detail. In this work, we investigate the Morasko meteoroid passage through the atmosphere, the distribution of its fragments on the ground, and the process of forming individual craters by means of numerical modeling. By combining atmospheric entry modeling, Pi‐group scaling of transient crater size and hydrocode simulations of impact processes, we constructed a comprehensive model of the Morasko strewn field formation. We determined the preatmospheric parameters of the Morasko meteoroid. The entry mass is between 600 and 1100 tons, the velocity range is between 16 and 18 km s^?1, and the trajectory angle is 30–40^°. Such entry velocities and trajectory angles do not deviate from typical values for near‐Earth asteroids, although the initial mass we determined can be considered as small. Our studies on velocities and masses of crater‐forming fragments showed that the biggest Morasko crater was formed by a projectile about 1.5 m in diameter with the impact velocity ~10 km s^?1. Environmental consequences of the Morasko impact event are very localized.     

Martian cratering 12. Utilizing primary crater clusters to study crater populations and meteoroid properties

Images from Mars Global Surveyor and later images from Mars Reconnaissance Orbiter reveal that roughly half of the meteoroids striking Mars (at meter to few decameter crater diameters) fragment in the Martian atmosphere, producing small clusters of primary impact craters. Statistics of these “primary clusters” yield valuable information about important Martian phenomena and properties of interplanetary bodies, including meteoroid behavior in the Martian atmosphere, bulk strengths of bodies striking Mars, and the fraction of Martian “field secondary” craters, a datum that would improve crater count chronometry. Many Martian impactors fragment at altitudes significantly higher than 18 km above the mean surface of Mars, and we find that most bodies striking Mars and Earth have low bulk strengths, consistent with crumbly or highly fractured objects. Applying statistics of primary clusters at various elevations and independent diameter bins, we describe a technique to estimate the percentage of semirandomly scattered “field secondary” craters. Our provisional estimate of this percentage, in the diameter range ~250 m down to ~22 m, is ~40% to ~80% of the total impacts, with the higher percentages at smaller diameters. Our data argue against earlier suggestions of overwhelming dominance by either primaries or secondaries in this diameter range.     

Very low strengths of interplanetary meteoroids and small asteroids

Abstract– We have assembled data on 13 cases of meteorite falls with accurate tracking data on atmospheric passage. In all cases, we estimate the bulk strength of the object corresponding to its earliest observed or inferred fragmentation in the high atmosphere, and can compare these values with measured strengths of meteorites in the taxonomic class for that fall. In all 13 cases, the strength corresponding to earliest observed or inferred fragmentation is much less than the compressive or tensile strength reported for that class of stony meteorites. Bulk strengths upon atmospheric entry of these bodies are shown to be very low, 0.1 to approximately 1 MPa on first breakup, and maximal strength on breakup as 1–10 MPa corresponding to weak and “crumbly” objects, whereas measured average tensile strength of the similar meteorite classes is about 30 MPa. We find a more random relation between bulk sample strength and sample mass than is suggested by a commonly used empirical power law. We estimate bulk strengths on entry being characteristically of the order of 10^?1–10^?2 times the tensile strengths of recovered samples. We conclude that pre‐entry, meter‐scale interplanetary meteoroids are typically highly fractured or in some cases rubbly in texture, presumably as a result of their parent bodies’ collisional history, and can break up under stresses of a few megapascals. The weakness of some carbonaceous objects may result from very porous primordial accretional structures, more than fractures. These conclusions have implications for future asteroid missions, sample extraction, and asteroid hazard mitigation.     

Aerial bursts in the terrestrial atmosphere

Impacts of cosmic bodies (stony and comet-like) are considered that “burn out” (or, more strictly, totally evaporate) in the atmosphere, which do not form craters but cause fires and destruction on the Earth’s surface. The heights of fragmentation, total evaporation, and deceleration of stony and comet-like meteoroids of different sizes, initial velocities, and impact angles are found from numerical simulations. The possible consequences of such falls are considered. The possible parameters of the Tunguska cosmic body are estimated.     

The rate of small impacts on Earth

Abstract— Asteroids tens to hundreds of meters in diameter constitute the most immediate impact hazard to human populations, yet the rate at which they arrive at Earth's surface is poorly known. Astronomic observations are still incomplete in this size range; impactors are subjected to disruption in Earth's atmosphere, and unlike the Moon, small craters on Earth are rapidly eroded. In this paper, we first model the atmospheric behavior of iron and stony bodies over the mass range 1–10¹² kg (size range 6 cm‐1 km) taking into account deceleration, ablation, and fragmentation. Previous models in meteoritics deal with rather small masses (<10⁵–10⁶ kg) with the aim of interpreting registered fireballs in atmosphere, or with substantially larger objects without taking into account asteroid disruption to model cratering processes. A few earlier attempts to model terrestrial crater strewn fields did not take into account possible cascade fragmentation. We have performed large numbers of simulations in a wide mass range, using both the earlier “pancake” models and also the separated fragments model to develop a statistical picture of atmosphere‐bolide interaction for both iron and stony impactors with initial diameters up to ?1 km. Second, using a compilation of data for the flux at the upper atmosphere, we have derived a cumulative size‐frequency distribution (SFD) for upper atmosphere impactors. This curve is a close fit to virtually all of the upper atmosphere data over 16 orders of magnitude. Third, we have applied our model results to scale the upper atmosphere curve to a flux at the Earth's surface, elucidating the impact rate of objects <1 km diameter on Earth. We find that iron meteorites >5 times 10⁴ kg (2.5 m) arrive at the Earth's surface approximately once every 50 years. Iron bodies a few meters in diameter (10⁵–10⁶ kg), which form craters ?100 m in diameter, will strike the Earth's land area every 500 years. Larger bodies will form craters 0.5 km in diameter every 20,000 years, and craters 1 km in diameter will be formed on the Earth's land area every 50,000 years. Tunguska events (low‐level atmospheric disruption of stony bolides >10⁸ kg) may occur every 500 years. Bodies capable of producing hazardous tsunami (?200 m diameter projectiles) should strike the Earth's surface every ?100,000 years. This data also allows us to assess the completeness of the terrestrial crater record for a given area over a given time interval.     

The Canyon Diablo impact event: Projectile motion through the atmosphere

Abstract— Meteor Crater is one of the first impact structures systematically studied on Earth. Its location in arid northern Arizona has been ideal for the preservation of the structure and the surviving meteoric material. The recovery of a large amount of meteoritic material in and around the crater has allowed a rough reconstruction of the impact event: an iron object 50 m in diameter impacted the Earth's surface after breaking up in the atmosphere. The details of the disruption, however, are still debated. The final crater morphology (deep, bowl‐shaped crater) rules out the formation of the crater by an open or dispersed swarm of fragments, in which the ratio of swarm radius to initial projectile radius C_d is larger than 3 (the final crater results from the sum of the craters formed by individual fragments). On the other hand, the lack of significant impact melt in the crater has been used to suggest that the impactor was slowed down to 12 km/s by the atmosphere, implying significant fragmentation and fragments' separation up to 4 initial radii. This paper focuses on the problem of entry and motion through the atmosphere for a possible Canyon Diablo impactor as a first but necessary step for constraining the initial conditions of the impact event which created Meteor Crater. After evaluating typical models used to investigate meteoroid disruption, such as the pancake and separated fragment models, we have carried out a series of hydrodynamic simulations using the 3D code SOVA to model the impactor flight through the atmosphere, both as a continuum object and a disrupted swarm. Our results indicate that the most probable pre‐atmospheric mass of the Meteor Crater projectile was in the range of 4.10⁸to 1.2.10⁹kg (equivalent to a sphere 46–66 m in diameter). During the entry process the projectile lost probably 30% to 70% of its mass, mainly because of mechanical ablation and gross fragmentation. Even in the case of a tight swarm of particles (C_d < 3), small fragments can separate from the crater‐forming swarm and land on the plains (tens of km away from the crater) as individual meteorites. Starting from an impactor pre‐atmospheric velocity of ?18 km/s, which represents an average value for Earth‐crossing asteroids, we find that after disruption, the most probable impact velocity at the Earth's surface for a tight swarm is around 15 km/s or higher. A highly dispersed swarm would result in a much stronger deceleration of the fragments but would produce a final crater much shallower than observed at Meteor Crater.     

Asteroid Apophis: Evaluating the impact hazards of such bodies

Soon after the discovery of asteroid 99942 Apophis, it was classified as a potentially hazardous object with a high probability of an impact on the Earth in 2029. Although subsequent observations have substantially reduced the probability of a collision, it has not been ruled out; moreover, similar-sized asteroids in orbits intersecting the Earth’s orbit may well be discovered in the near future. We conduct a numerical simulation of an atmospheric passage and an impact on the Earth’s surface of a stony cosmic body with a diameter of 300 m and kinetic energy of about 1000 Mt, which roughly corresponds to the parameters of the asteroid Apophis, at atmospheric entry angles of 90° (vertical stroke), 45°, and 30°. The simulation is performed by solving three-dimensional equations of hydrodynamics and radiative transfer equations in the approximations of radiative heat conduction and volume emission. The following hazards are considered: an air shock wave, ejecta from the crater, thermal radiation, and ionospheric disturbances. Our calculations of the overpressure and wind speed on the Earth’s surface show that the zone of destruction of the weakest structures can be as large as 700–1000 km in diameter; a decrease in the flight path angle to the surface leads to a marked increase in the area affected by the shock wave. The ionospheric disturbances are global in nature and continue for hours: at distances of several thousand kilometers at altitudes of more than 100 km, air density disturbances are tens of percent and the vertical and horizontal velocity components reach hundreds of meters per second. The impact of radiation on objects on the Earth’s surface is estimated by solving the equation of radiative transfer along rays passing through a luminous area. In clear weather, the size of the zone where thermal heating may ignite wood can be as large as 200 km, and the zone of individual fire outbreaks associated with the ignition of flammable materials can be twice as large. In the 100-km central area, which is characterized by very strong thermal damage, there is ignition of structures, roofs, clothes, etc. The human hazardous area increases with the decrease in the trajectory angle, and people may experience thermal effects at distances of up to 250–400 km from the crater.     

Gebel Kamil: The iron meteorite that formed the Kamil crater (Egypt)

Abstract– The 45 m in diameter Kamil impact crater was formed <5000 yr ago in the eastern Sahara, close to the southern border of modern Egypt. The original features of this structure, including thousands of fragments of the meteorite impactor, are extremely well preserved. With the exception of a single 83 kg regmaglypted individual, all specimens of Gebel Kamil (the iron meteorite that formed the Kamil crater) are explosion fragments weighing from <1 g to 34 kg. Gebel Kamil is an ungrouped Ni‐rich (about 20 wt% Ni) ataxite characterized by high Ge and Ga contents (approximately 120 μg g^?1 and approximately 50 μg g^?1, respectively) and by a very fine‐grained duplex plessite metal matrix. Accessory mineral phases in Gebel Kamil are schreibersite, troilite, daubréelite, and native copper. Meteorite fragments are cross‐cut by curvilinear shear bands formed during the explosive terrestrial impact. A systematic search around the crater revealed that meteorite fragments have a highly asymmetric distribution, with greater concentrations in the southeast sector and a broad maximum in meteorite concentration in the 125–160° N sector at about 200 m from the crater rim. The total mass of shrapnel specimens >10 g, inferred from the density map compiled in this study is 3400 kg. Field data indicate that the iron bolide approached the Earth’s crust from the northwest (305–340° N), travelling along a moderately oblique trajectory. Upon hypervelocity impact, the projectile was disrupted into thousands of fragments. Shattering was accompanied by some melting of the projectile and of the quartz‐arenite target rocks, which also suffered shock metamorphism.     

A meteoroid stream survey using the Canadian Meteor Orbit Radar: I. Methodology and radiant catalogue

Using a meteor orbit radar, a total of more than 2.5 million meteoroids with masses ∼10⁻⁷ kg have had orbits measured in the interval 2002-2006. From these data, a total of 45 meteoroid streams have been identified using a wavelet transform approach to isolate enhancements in radiant density in geocentric coordinates. Of the recorded streams, 12 are previously unreported or unrecognized. The survey finds >90% of all meteoroids at this size range are part of the sporadic meteoroid background. A large fraction of the radar detected streams have q<0.15 AU suggestive of a strong contribution from sungrazing comets to the meteoroid stream population currently intersecting the Earth. We find a remarkably long period of activity for the Taurid shower (almost half the year as a clearly definable radiant) and several streams notable for a high proportion of small meteoroids only, among these a strong new shower in January at the time of the Quadrantids (January Leonids). A new shower (Epsilon Perseids) has also been identified with orbital elements almost identical to Comet 96P/Machholz.     

Analysis of a Low Density Meteoroid with Enhanced Sodium

We present an analysis of sporadic meteor number 07406018, observed by image intensified video cameras at two stations, which showed a pronounced deceleration along its trajectory. We have applied the erosion model to analyze simultaneously the deceleration and light curve. We have found that the meteoroid had a low density of about 500 kg m⁻³, consistent with its cometary orbit. The meteoroid structure was, nevertheless, markedly different from the Draconid meteoroids, studied recently with the same model. The size of the constituent grains was larger and the erosion energy was higher than in Draconids. The meteor spectrum was also different from Draconid spectra and showed very bright Na lines. The meteoroid composition was probably different from normal cometary composition.     

Determining meteoroid bulk densities using a plasma scattering model with high-power large-aperture radar data

We present an improved technique for calculating bulk densities of low-mass (<1 g) meteoroids using a scattering model applied to the high-density plasma formed around the meteoroid as it enters Earth’s atmosphere. These plasmas, referred to as head echoes, travel at or near the speed of the meteoroid, thereby allowing the determination of the ballistic coefficient (mass divided by physical cross-section), which depends upon speed and deceleration. Concurrently, we apply a scattering model to the returned signal strength of the head echo in order to correlate radar-cross-section (RCS) to plasma density and meteoroid mass. In this way, we can uniquely solve for the meteoroid mass, radius and bulk density independently. We have applied this new technique to head echo data collected in 2007 and 2008 simultaneously at VHF (160 MHz) and UHF (422 MHz) at ALTAIR, which is a high-power large-aperture radar located on the Kwajalein Atoll. These data include approximately 20,000 detections with dual-frequency, dual-polarization, and monopulse (i.e. angle) returns. From 2000 detections with the smallest monopulse errors, we find a mean meteoroid bulk density of 0.9 g/cm³ with observations spanning almost three orders of magnitude from 0.01 g/cm³ to 8 g/cm³. Our results show a clear dependence between meteoroid bulk density and altitude of head echo formation, as well as dependence between meteoroid bulk density and 3D speed. The highest bulk densities are detected at the lowest altitudes and lowest speeds. Additionally, we stipulate that the approximations used to derive the ballistic parameter, in addition to neglecting fragmentation, suggest that the traditional ballistic parameter must be used with caution when determining meteoroid parameters.     

Evidence for a meteoritic origin of the September 15, 2007, Carancas crater

Abstract— On September 15th, 2007, around 11:45 local time in Peru, near the Bolivian border, the atmospheric entry of a meteoroid produced bright lights in the sky and intense detonations. Soon after, a crater was discovered south of Lake Titicaca. These events have been detected by the Bolivian seismic network and two infrasound arrays operating for the Comprehensive Nuclear‐Test‐Ban Treaty Organization, situated at about 80 and 1620 km from the crater. The localization and origin time computed with the seismic records are consistent with the reported impact. The entry elevation and azimuthal angles of the trajectory are estimated from the observed signal time sequences and back‐azimuths. From the crater diameter and the airwave amplitudes, the kinetic energy, mass and explosive energy are calculated. Using the estimated velocity of the meteoroid and similarity criteria between orbital elements, an association with possible parent asteroids is attempted. The favorable setting of this event provides a unique opportunity to evaluate physical and kinematic parameters of the object that generated the first actual terrestrial meteorite impact seismically recorded.     

The Maribo CM2 meteorite fall—Survival of weak material at high entry speed

High entry speed (>25 km s^?1) and low density (<2500 kg m^?3) are the two factors that lower the chance of a meteoroid to drop meteorites. The 26 g carbonaceous (CM2) meteorite Maribo recovered in Denmark in 2009 was delivered by a bright bolide observed by several instruments across northern and central Europe. By reanalyzing the available data, we confirmed the previously reported high entry speed of (28.3 ± 0.3) km s^?1 and trajectory with slope of 31° to the horizontal. In order to understand how such a fragile material survived, we applied three different models of meteoroid atmospheric fragmentation to the detailed bolide light curve obtained by radiometers located in Czech Republic. The Maribo meteoroid was found to be quite inhomogeneous with different parts fragmenting at different dynamic pressures. While 30–40% of the (2000 ± 1000) kg entry mass was destroyed already at 0.02 MPa, another 25–40%, according to different models, survived without fragmentation up to the relatively large dynamic pressures of 3–5 MPa. These pressures are only slightly lower than the measured tensile strengths of hydrated carbonaceous chondrite (CC) meteorites and are comparable with usual atmospheric fragmentation pressures of ordinary chondritic (OC) meteoroids. While internal cracks weaken OC meteoroids in comparison with meteorites, this effect seems to be absent in CC, enabling meteorite delivery even at high speeds, though in the form of only small fragments.     

Bolides in the present and past martian atmosphere and effects on cratering processes

Abstract— We investigate the action of the martian atmosphere on entering meteoroids for present and past atmospheres with various surface pressures to predict the smallest observable craters, and to understand the implications for the size distributions of craters on Mars and meteoroids in space. We assume different strengths appropriate to icy, stone, and iron bodies and test the results against available data on terrestrial bolides. Deceleration, ablation, and fragmentation effects are included. We find that the smallest icy, stone, and iron meteoroids to hit the martian ground at crater forming speeds of ≥500 m/s have diameters of about 2 m, 0.03‐0.9 m (depending on strength), and 0.01 m, respectively, in the current atmosphere. For hypothetical denser past atmospheres, the cutoff diameters rise. At a surface pressure of 100 mb, the cutoff diameters are about 24 m, 5–12 m, and 0.14 m for the 3 classes. The weaker stony bodies in the size range of about 1–30 m may explode at altitudes of about 10–20 km above the ground. These figures imply that under the present atmosphere, the smallest craters made by these objects would be as follows: by ice bodies, craters of diameter (D) ?8 m, by stones about 0.5–6 m, and by irons, about 0.3 m. A strong depletion of craters should, thus, occur at diameters below about 0.3 m to 5 m. Predicted fragmentation and ablation effects on weak meteoroids in the present atmosphere may also produce a milder depletion below D ?500 m, relative to the lunar population. But, this effect may be difficult to detect in present data because of additional losses of small craters due to sedimentation, dunes, and other obliteration effects. Craters in strewn fields, caused by meteoroid fragmentation, will be near or below present‐day resolution limits, but examples have been found. These phenomena have significant consequences. Under the present atmosphere, the smallest (decimeter‐scale) craters in sands and soils could be quickly obliterated but might still be preserved on rock surfaces, as noted by Hörz et al. (1999). Ancient crater populations, if preserved, could yield diagnostic signatures of earlier atmospheric conditions. Surfaces formed under past denser atmospheres (few hundred mbar), if preserved by burial and later exposed by exhumation, could show: a) striking depletions of small craters (few meter sizes up to as much as 200 m), relative to modern surfaces; b) more clustered craters due to atmospheric breakup; and c) different distributions of meteorite types, with 4 m to 200 m craters formed primarily by irons instead of by stones as on present‐day Mars. Megaregolith gardening of the early crust would be significant but coarser than the gardening of the ancient lunar uplands.     

Comparison of four meteorite penetration funnels in the Campo del Cielo crater field,Argentina

Abstract– More craters may be discovered in the future, but as it is currently known, the Campo del Cielo crater field is 18 km long by 4 km at its widest point. Such a distribution of craters suggests that the parent meteoroid entered and traversed the atmosphere at a very low angle relative to horizontal. The crater field contains at least 20 small craters produced by the larger fragments of the parent meteoroid. Four of these are explosion analog craters and the rest are penetration funnels. During four field seasons, we have constructed topographic and magnetic maps of four of the penetration funnels as found, and then dug trenches across them to learn their original structures and recover meteorites preserved within them. Structures of these penetration funnels indicate very low angles of impact, i.e., 9–16° relative to horizontal. This supports the idea that the parent meteoroid traversed the atmosphere at a low angle. Data given here for the four penetration funnels include projectile masses, lengths, widths, depths, and estimates of impact angles and azimuths. One of the penetration funnels described here (No. 6) can almost be classified as an explosion analog crater.     

The Velocity Distribution of Meteoroids at the Earth as Measured by the Canadian Meteor Orbit Radar (CMOR)

The velocity distribution of meteoroids at the Earth is measured using a time-of-flight measurement technique applied to data collected by the CMOR radar (29.85 MHz). Comparison to earlier velocity measurements from the Harvard Radio Meteor Project suggests that HRMP suffered from biases which underestimated the number of fragmenting meteoroids. This bias results in a systematic underestimation of the numbers of higher velocity meteoroids. Other works (cf. Taylor and Elford, 1998) have also found additional biases in the HRMP which suggest the original HRMP meteoroid velocity analysis may have underestimated the fraction of high velocity meteors by factors up to 10⁴.