Large Meteoroids Research Articles

Nonspecular meteor trails from non‐field‐aligned irregularities: Can they be explained by presence of charged meteor dust?

AbstractNonspecular meteor echoes have been associated with field‐aligned irregularities and have been observed at low‐latitude and midlatitude sites. We present observations obtained at high latitudes with range‐time features that resemble those at lower latitudes. However, these echoes cannot come from field‐aligned irregularities, since the radar‐pointing angles are almost parallel to the magnetic field. Using interferometry, we have been able to discriminate space and time features. Our echoes could be qualitatively explained by the presence of charged dust forming from the meteoric material immersed in a turbulent flow. This can lead to a high Schmidt number plasma that can sustain meter‐scale turbulence just as it does for the polar mesospheric summer echoes. These rare events require relatively large meteoroids. The result emphasizes the importance of charged dust in understanding all long‐duration nonspecular meteor echoes. This dust will extend their diffusion times and will affect temperature estimations from specular echoes.

A large lunar impact blast on 2013 September 11

On 2013 September 11 at 20h07m28.68 $\pm$ 0.01 s UTC, two telescopes operated in the framework of our lunar impact flashes monitoring project recorded an extraordinary flash produced by the impact on the Moon of a large meteoroid at selenographic coordinates 17.2 $\pm$ 0.2 $^{\circ}$ S, 20.5 $\pm$ 0.2 $^{\circ}$ W. The peak brightness of this flash reached 2.9 $\pm$ 0.2 mag in V and it lasted over 8 seconds. The estimated energy released during the impact of the meteoroid was 15.6 $\pm$ 2.5 tons of TNT under the assumption of a luminous efficiency of 0.002. This event, which is the longest and brightest confirmed impact flash recorded on the Moon thus far, is analyzed here. The likely origin of the impactor is discussed. Considerations in relation to the impact flux on Earth are also made.

Analysis of two superbolides with a cometary origin observed over the Iberian Peninsula

Among the most astonishing astronomical phenomena are the extremely bright bolides produced by the entry of large meteoroids into the Earth’s atmosphere. These events are rare and unexpected because current telescopic surveys are still missing meter-sized meteoroids, particularly those of dark nature and presumably cometary origin. In this work we present the analysis of two very bright fireballs of such origin recently observed over Spain. The first of these was recorded on September 25, 2010, while the second one took place on August 23, 2012. With an absolute magnitude of −18 and −17, respectively, these sporadic events fall within the superbolide category. Their atmospheric trajectory is calculated, together with the heliocentric orbit of the parent meteoroids. Other physical properties of these particles are estimated, such as their preatmospheric mass and tensile strength. The emission spectrum recorded for one of these events is also discussed. Our analysis indicates that none of these superbolides was a meteorite-dropping event. From their orbital parameters, a cometary nature for the parent meteoroids is inferred.

Atom & cosmos: Large meteor strikes underestimated: Chelyabinsk‐sized rocks may hit Earth once every 30 years

Atom & cosmos: Large meteor strikes underestimated: Chelyabinsk‐sized rocks may hit Earth once every 30 years

Seismic Characterization of the Chelyabinsk Meteor's Terminal Explosion

Online Material: Figures of waveform fit, apparent source time functions, and video of impact of shock wave at factory. Impacts with our planet cause seismic shaking by a variety of mechanisms. Catastrophic ground motion, even at antipodal distances, can be generated by the extremely infrequent, hypersonic collisions with large asteroids or comets (Meschede et al. , 2011). Fortunately, the atmosphere effectively shields the smaller (and far more common) meteoroids, greatly reducing their initial kinetic energy at high altitude, causing them to slow down, break up, and even vaporize, producing a meteor (Ceplecha and Revelle, 2005). In most instances, the ground shaking is triggered by the atmospheric shock wave of a meteor, not by the impact of the surviving meteorites (Edwards et al. , 2008). A particularly strong shock wave can be generated by explosive fragmentation of the meteoroid in one or several final airbursts (Ceplecha and Revelle, 2005; Edwards et al. , 2008). Such disruptions are triggered when the pressure (ram pressure) caused by atmospheric drag exceeds the internal strength of a meteoroid. They are accompanied by a sudden increase in the meteor luminosity (a flare), because they imply a sharp increase in the surface area being subject to ablation. On 15 February 2013 at 03:20 UTC, an exceptionally large meteor in the region of Chelyabinsk, Russia, produced a powerful shock wave, which caused unprecedented damage to people and property. According to official news reports, glass windows were shattered in over 7300 buildings (some of these even experienced slight structural damage), and falling debris hurt more than 1600 people. The meteorite fragments that survived the atmospheric entry hit the ground at subsonic terminal velocity (Schiermeier, 2013), and did not cause any seismic shaking detectable at regional distances. However, the meteor produced the strongest atmospheric infrasound signal ever recorded (Stone, 2013) and …

Earth-viewing satellite perspectives on the Chelyabinsk meteor event

Large meteors (or superbolides [Ceplecha Z, et al. (1999) Meteoroids 1998:37-54]), although rare in recorded history, give sobering testimony to civilization's inherent vulnerability. A not-so-subtle reminder came on the morning of February 15, 2013, when a large meteoroid hurtled into the Earth's atmosphere, forming a superbolide near the city of Chelyabinsnk, Russia, ∼1,500 km east of Moscow, Russia [Ivanova MA, et al. (2013) Abstracts of the 76th Annual Meeting of the Meteoritical Society, 5366]. The object exploded in the stratosphere, and the ensuing shock wave blasted the city of Chelyabinsk, damaging structures and injuring hundreds. Details of trajectory are important for determining its specific source, the likelihood of future events, and potential mitigation measures. Earth-viewing environmental satellites can assist in these assessments. Here we examine satellite observations of the Chelyabinsk superbolide debris trail, collected within minutes of its entry. Estimates of trajectory are derived from differential views of the significantly parallax-displaced [e.g., Hasler AF (1981) Bull Am Meteor Soc 52:194-212] debris trail. The 282.7 ± 2.3° azimuth of trajectory, 18.5 ± 3.8° slope to the horizontal, and 17.7 ± 0.5 km/s velocity derived from these satellites agree well with parameters inferred from the wealth of surface-based photographs and amateur videos. More importantly, the results demonstrate the general ability of Earth-viewing satellites to provide valuable insight on trajectory reconstruction in the more likely scenario of sparse or nonexistent surface observations.

The meteoroid environment and impacts on Phobos

We review current knowledge of the flux of meteoroids on Phobos, a key to interpreting its cratering record and understanding the origin of the Martian satellite system. Past observational attempts to estimate the flux of small (mm to cm) meteoroids as meteors in the Martian atmosphere highlight the need for customised instrumentation onboard future missions bound for Mars. The temporal distribution of cometary meteoroid streams as predicted by recent work is non-uniform; we advocate emplacing seismic stations on Phobos or cameras optimised to monitor the Martian atmosphere for meteors as a means to elucidate this and other features of the meteoroid population. We construct a model of the sporadic flux of metre-sized or larger meteoroids and use it to predict a leading/trailing ratio in crater density of ~4 if crater production by asteroidal meteoroids dominates over that by cometary ones. It is found that the observed distribution of craters ≥100m as determined from spacecraft images is consistent with a 50/50 contribution from the two meteoroid populations in our model. A need for more complete models of the meteoroid flux is identified. Finally, the prospects for new observational constraints on the meteoroid environment are reviewed.

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.

Ionospheric effects induced by the Chelyabinsk meteor

The data, obtained for the first time, permit the conclusion to be drawn, with a high degree of probability, that large meteors similar to the Chelyabinsk meteor, while entering the Earth’s atmosphere, are able to cause perturbations within the whole ionospheric stratum, rather than only at the sporadic Es layer altitudes, as previously thought.

The present-day flux of large meteoroids on the lunar surface—A synthesis of models and observational techniques

Monitoring the lunar surface for impacts is a highly rewarding approach to study small asteroids and large meteoroids encountering the Earth–Moon System. The various effects of meteoroids impacting the Moon are described and results from different detection and study techniques are compared. While the traditional statistics of impact craters allow us to determine the cumulative meteoroid flux on the lunar surface, the recent successful identification of fresh craters in orbital imagery has the potential to directly measure the cratering rate of today. Time-resolved recordings, e.g., seismic data of impacts and impact flash detections clearly demonstrate variations of the impact flux during the lunar day. From the temporal/spatial distribution of impact events, constraints can be obtained on the meteoroid approach trajectories and velocities. The current monitoring allows us to identify temporal clustering of impacts and to study the different meteoroid showers encountering the Earth–Moon system. Though observational biases and deficiencies in our knowledge of the scaling laws are severe, there appears to be an order-of-magnitude agreement in the observed flux within the error limits. Selenographic asymmetries in the impact flux (e.g., for equatorial vs. polar areas) have been predicted. An excess of impacts on the lunar leading hemisphere can be demonstrated in current data. We expect that future missions will allow simultaneous detections of seismic events and impact flashes. The known locations and times of the flashes will allow us to constrain the seismic solutions. While the numbers of flash detections are still limited, coordinated world-wide observations hold great potential for exploiting this observation technique. The potential for identification of fresh craters in high-resolution orbital image data has just barely been tapped, but should improve significantly with the LRO extended mission.

Fireball on 6 July 2002 over the Mediterranean Sea is a fragment of the comet's nucleus

AbstractToday has been known for a considerable number of cases, the explosion of large meteoroids in Earth's atmosphere. This is confirmed by the data of registrations of fireballs by devices and the results of measurements in the atmosphere of bright light flashes by photodiodes Corporation “Sandia Laboratories", which were installed on geostationary satellites of the United States, and also by data of measurements of acoustic-gravitational waves from the thermal explosions of meteoroids [ReVelle D.O. Historical detection of atmospheric impacts by large bolides using acoustic-gravity waves, Near-Earth Objects, Ed. Remo J. Annals of the New York Academy of Sciences 882, 284-302, 1997]. The work [Brown P., Spalding R.E., ReVelle D.O. et al. The flux of small near-Earth objects colliding with the Earth, Nature 420, 314-316, 2002.] shows the results of processing the observations of flashes of large meteoroids in Earth's atmosphere, obtained with the help of geostationary satellites of the United States. Over 8.5 years (from February 1994 to September 2002) 300 such events were registered. On July 6, 2002 r over the Mediterranean Sea a bright fireball was registered. The energy of the meteoroid explosion that caused the phenomenon of the car, was 26 kilotons of TNT [Brown et al., 2002]. We believe that this energy refers to the height of the full bracking of the meteoroid. At a speed of 20.3 km/s adopted by the authors, body mass at this height is 5 × 108 g, and when entering the Earth's atmosphere, it was about 7 × 108 g. Based on the obtained values of the mass, we conclude that the exploded meteoroid, causing a phenomenon of the fireball was a fragment of the comet nucleus. In processing the density of the body were taken 1 g/cm3 and the initial velocity (~30 km/s).

Explosion of a comet nucleus fragment in the earth’s atmosphere

This paper analyzes data on thermal explosions of large meteoroids in the earth’s atmosphere. The cumulative function of flux of space bodies is corrected with regard to the explosion height, which is determined, according to our approach, by maximum braking. As a result, the integral function of flux in the work [Brown, P., Spalding, R.E., ReVelle, D.O., et al., The Flux of Small Near-Earth Objects Colliding with the Earth, Nature, 2002, vol. 420, pp. 314–316] is consistent with the one we derived earlier. It is found that at least one phenomenon of those discussed in the paper by Brown et al. is a result of explosion of a comet nucleus fragment. It is shown that the Tunguska phenomenon cannot be explained within a monolithic body model.

Relationship between iron-meteorite composition and size: Compositional distribution of irons from North Africa

During the past three decades many iron meteorites have been collected from the deserts of North Africa. Almost all are now characterized, and the distribution among classes is found to be very different from those that were in museums prior to the collection of meteorites from hot and cold (Antarctica) deserts. Similar to the iron meteorites from Antarctica, the irons from Northwest Africa include a high fraction of ungrouped irons and of minor subgroups of group IAB. The different distribution is attributed to the small median size of the desert meteorites (∼1.3 kg in North African irons, ∼30 kg in non-desert irons). It appears that a sizable fraction of these small (several centimeter) masses constitute melt pockets produced by impacts in chondritic regoliths; they were never part of a large (meter-to-kilometer) magma bodies. As a result, a meter-size fragment ejected from the regolith of the asteroid may contain several of these small metallic masses. It may be that such stochastic sampling effects enhanced the fraction of IAB-sHL irons among the irons from Northwest Africa. The variety observed in small meteoroids is also enhanced because (relative to large) small fragments are more efficiently ejected from asteroids and because the orbital parameters of small meteoroids are more strongly affected by collisions and drag effects, they evolve to have Earth-crossing perihelia more rapidly than large meteoroids; as a result, the set of small meteoroids tends to sample a larger number of parent asteroids than does the set of larger meteoroids.

Formation of molecules in bright meteors

We calculated equilibrium chemical composition of a mixture of meteoritic vapor and air during fireball events, i.e. during penetration of large meteoroids into terrestrial atmosphere. Different types of fireballs were considered, and calculations were performed for wide ranges of temperatures and pressures. Chemical composition at the quenching point was estimated by comparison of hydrodynamic and chemical reaction time scales. For the typical fireball temperatures of 4000–5000 K, most elements are expected to be in the form of atoms and ions. Notable exceptions are Si and C, which are expected to be mainly in the form of SiO and CO. Other molecules abundant at these temperatures are N 2 and NO. Metal monoxides are most abundant at 2000–2500 K and are formed during the cooling phase. Conditions for formation of other molecules such as N 2 + , CN, C 2 and OH were also considered. The composition of freshly ablated meteoroid material was studied using the MAGMA code.

A new variant of saponite‐rich micrometeorites recovered from recent Antarctic snowfall

Abstract– Eight saponite‐rich micrometeorites with very similar mineralogy were found from the recent surface snow in Antarctica. They might have come to Earth as a larger meteoroid and broke up into pieces on Earth, because they were recovered from the same layer and the same location of the snow. Synchrotron X‐ray diffraction (XRD) analysis indicates that saponite, Mg‐Fe carbonate, and pyrrhotite are major phases and serpentine, magnetite, and pentlandite are minor phases. Anhydrous silicates are entirely absent from all micrometeorites, suggesting that their parental object has undergone heavy aqueous alteration. Saponite/serpentine ratios are higher than in the Orgueil CI chondrite and are similar to the Tagish Lake carbonaceous chondrite. Transmission electron microscope (TEM) observation indicates that serpentine occupies core regions of fine‐grained saponite, pyrrhotite has a low‐Ni concentration, and Mg‐Fe carbonate shows unique concentric ring structures and has a mean molar Mg/(Mg + Fe) ratio of 0.7. Comparison of the mineralogy to hydrated chondrites and interplanetary dust particles (IDPs) suggests that the micrometeorites are most similar to the carbonate‐poor lithology of the Tagish Lake carbonaceous chondrite and some hydrous IDPs, but they show a carbonate mineralogy dissimilar to any primitive chondritic materials. Therefore, they are a new variant of saponite‐rich micrometeorite extracted from a primitive hydrous asteroid and recently accreted to Antarctica.

The optical properties of vapors of matter of cosmic bodies invading the Earth atmosphere

The procedure is described of the calculation of the optical properties of vapors of matter of cosmic bodies invading the Earth atmosphere. The calculations are performed for a mixture of 16 elements, namely, Fe-O-Mg-Si-C-N-H-S-Al-Ca-Na-K-Ti-Cr-Mn-Ni, for bodies of different chemical compositions such as H-, LL-, and C-chondrites, comet matter, and ice in the temperature range from 3 to 40 kK. Examples of calculations are given. The results make it possible to demonstrate that, in the case of large meteoroids (10 m and more) moving at velocities of 15–20 km/s and higher, the effect of screening of their surface by the emerging vapor layer at altitudes of 30 km and lower is significant. This considerably reduces the ablation by thermal radiation and promotes deeper penetration of cosmic bodies into the atmosphere.

Meteosat observation of the atmospheric entry of 2008 TC$\mathsf{_{3}}$ over Sudan and the associated dust cloud

We analyzed serendipitous observations by the Meteosat 8 weather satellite of the fireball caused by the entry of the small asteroid (or large meteoroid) 2008 TC3 over northern Sudan on October 7, 2008. Meteosat 8 scans the Earth in 5 min cycles. The fireball was captured in the 2:45 UT images in four visible-near infrared channels (0.6–1.6 μm) at a height of 45 km, and in eight mid infrared channels (3.9–13.4 μm) at a height of 33 km. The latter channels also detected at least two dust clouds deposited in the atmosphere at the heights of about 44 and 36 km. The dust deposition was a result of severe atmospheric fragmentation of the asteroid, accompanied by fireball flares, which could be detected in the light scattered by the Earth’s surface. The fireball brightness was measured at two random heights, 45 and 37.5 km, where it reached −18. 8a nd−19.7 mag, respectively. The peak brightness was probably higher than −20 mag. The color temperature of the fireball at 45 km was 3650 ± 100 K. Infrared spectra of the fresh dust clouds were dominated by the 10 μm Si-O band caused by recondensed amorphous silicates. Five minutes later, the dust clouds were detected in absorption of thermal radiation of the Earth. At that time, the silicates were largely crystalline, suggesting silicate smoke temperatures exceeding 1000 K. The total mass of the silicate smoke was estimated to be 3100 ± 600 kg. More mass was probably contained in larger, micron sized, and colder dust particles resulting from incomplete sublimation of the asteroidal material and detected later by Meteosat 8 and 9 in scattered sunlight. Based on the heights of asteroid fragmentations, we guess that the bulk porosity of 2008 TC3 was of the order of 50%, i.e. higher than the porosity of the recovered meteorite Almahata Sitta.

An estimate of the terrestrial influx of large meteoroids from infrasonic measurements

The influx rate of meteoroids hitting the Earth is most uncertain at sizes of ∼10 m. Here we make use of historical data of large bolides recorded infrasonically over a period of 13 years by the U.S. Air Force Technical Applications Center (AFTAC) to refine the terrestrial influx rate at these sizes. Several independent techniques were applied to these airwave data to calculate bolide kinetic energies. At low energies our flux results are within a factor of two in agreement with previous estimates. For 5–20‐m diameter objects, however, our measurements of the cumulative number of Earth‐impacting meteoroids are as much as an order of magnitude higher than estimates from telescopic surveys of near‐Earth objects and satellite‐detected bolides impacting the Earth. The precise cause of this disagreement is unclear, though we propose several possible explanations. From our infrasound study, our best estimate for the cumulative annual flux of impactors with energy equal to or greater than E (in kilotons of TNT equivalent) is N = 4.5 E−0.6.

A dynamical model of the sporadic meteoroid complex

Sporadic meteoroids are the most abundant yet least understood component of the Earth's meteoroid complex. This paper aims to build a physics-based model of this complex calibrated with five years of radar observations. The model of the sporadic meteoroid complex presented here includes the effects of the Sun and all eight planets, radiation forces and collisions. The model uses the observed meteor patrol radar strengths of the sporadic meteors to solve for the dust production rates of the populations of comets modeled, as well as the mass index. The model can explain some of the differences between the meteor velocity distributions seen by transverse versus radial scatter radars. The different ionization limits of the two techniques result in their looking at different populations with different velocity distributions. Radial scatter radars see primarily meteors from 55P/Tempel–Tuttle (or an orbitally similar lost comet), while transverse scatter radars are dominated by larger meteoroids from the Jupiter-family comets. In fact, our results suggest that the sporadic complex is better understood as originating from a small number of comets which transfer material to near-Earth space quite efficiently, rather than as a product of the cometary population as a whole. The model also sheds light on variations in the mass index reported by different radars, revealing it to be a result of their sampling different portions of the meteoroid population. In addition, we find that a mass index of s = 2.34 as observed at Earth requires a shallower index ( s = 2.2 ) at the time of meteoroid production because of size-dependent processes in the evolution of meteoroids. The model also reveals the origin of the 55° radius ring seen centered on the Earth's apex (a result of high-inclination meteoroids undergoing Kozai oscillation) and the central condensations seen in the apex sources, as well as providing insight into the strength asymmetry of the helion and anti-helion sources.

Estimating the terminal mass of large meteoroids

Estimating the terminal mass of large meteoroids