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Anghel, S., et al., The increase in detector sensitivity and availability in the past three decades has allowed us to derive knowledge of the meteoroid flux and impact energy into the Earth's atmosphere. We present the multi-instrument detected 2018 December 22 fireball over Western Pyrenees, and compare several techniques aiming to obtain a reliable method to be used when measuring impacts of similar scale. From trajectory data alone, we found a bulk density of 3.5 g cm-3 to be the most likely value for the Pyrenean meteoroid. This allowed to further constrain the dynamic mass, which translated into a kinetic energy of 1 ton TNT (4.184 × 109 J). For the second energy derivation, via the fireball's corrected optical radiation, we obtained a more accurate empirical relation measuring well-studied bolides. The result approximates to 1.1 ton TNT, which is notably close to the nominal dynamic result, and agrees with the lower margin of the seismic-based energy estimation, yet way lower than the infrasound estimate. Based on the relation derived in this study, we consider the nominal estimate from both the dynamic and photometric methods to be the most accurate value of deposited energy (1 ton TNT). We show that the combination of these two methods can be used to infer the meteoroid density. Among the methods presented in this paper, we found that the optical energy is the most reliable predictor of impact energy near the ton TNT-scale., S. Anghel and D. A. Nedelcu were supported by a grant of the Romanian Ministry of Research and Innovation, CCCDI - UEFISCDI, project number PN-III-P1-1.2-PCCDI-2017-0226/16PCCDI/2018, within PNCDI III. EP-A and JMT-R acknowledge funding from PGC2018-097374-B-I00 (MCI-AEI-FEDER, EU). M. Birlan work was partly supported by SEEING-IEA CNRS program. R. Hueso and A. Sánchez-Lavega were supported by Diputación Foral de Bizkaia and Gobierto Vasco IT1366-19.

Meteor physics can provide new clues about the size, structure, and density of cometary disintegration products, establishing a bridge between different research fields. From meteor magnitude data we have estimated the mass distribution of meteoroids from different cometary streams by using the relation between the luminosity and the mass obtained by Verniani. These mass distributions are in the range observed for dust particles released from comets 1P/Halley and 81P/Wild 2 as measured from spacecraft. From the derived mass distributions, we have integrated the incoming mass for the most significant meteor showers. By comparing the mass of the collected interplanetary dust particles (IDPs) with that derived for cometary meteoroids a gap of several orders of magnitude is encountered. The largest examples of fluffy particles are clusters of IDPs no larger than 100 μm in size (or 5 × 10–7 g in mass) while the largest cometary meteoroids are centimeter-sized objects. Such gaps can be explained by the fragmentation in the atmosphere of the original cometary particles. As an application of the mass distribution computations we describe the significance of the disruption of fragile comets in close approaches to Earth as a more efficient (and probably more frequent) way to deliver volatiles than direct impacts. We finally apply our model to quantify the flux of meteoroids from different meteoroid streams, and to describe the main physical processes contributing to the progressive decay of cometary meteoroids in the interplanetary medium., JMTR acknowledges financial support by the research project(PGC2018 097374-B-I00, funded by FEDER/Ministerio de Ciencia e Innovación – Agencia Estatal de Investigación. JB acknowledges the continuing support by the Deutsche Forschungsgemeinschaft and the Deutsches Zentrum für Luft- und Raumfahrt.

On February 16, 2021, an artificial object moving slowly over the Mediterranean was recorded by the Spanish Meteor Network (SPMN). Based on astrometric measurements, we identified this event as the reentry engine burn of a SpaceX Falcon 9 launch vehicle’s upper stage. To study this event in detail, we adapted the plane intersection method for near-straight meteoroid trajectories to analyze the slow and curved orbits associated with artificial objects. To corroborate our results, we approximated the orbital elements of the upper stage using four pieces of “debris” cataloged by the U.S. Government’s Combined Space Operations Center. Based on these calculations, we also estimated the possible deorbit hazard zone using the MSISE90 model atmosphere. We provide guidance regarding the interference that these artificial bolides may generate in fireball studies. Additionally, because artificial bolides will likely become more frequent in the future, we point out the new role that ground-based detection networks can play in the monitoring of potentially hazardous artificial objects in near-Earth space and in determining the strewn fields of artificial space debris. [Figure not available: see fulltext.], This research was supported by the research project (Grant No. PGC2018-097374-B-I00, PI: JMT-R), which is funded by FEDER/Ministerio de Ciencia e Innovación–Agencia Estatal de Investigación. This project has also received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme (Grant No. 865657) for the project “Quantum Chemistry on Interstellar Grains” (QUANTUMGRAIN).

Drolshagen, E., et al., [Context] In meteor physics, the luminous efficiency τ is used to convert the meteor's magnitude to the corresponding meteoroid's mass. However, a lack of sufficiently accurate verification methods or adequate laboratory tests mean that discussions around this parameter are a subject of controversy. [Aims] In this work, we aim to use meteor data obtained by the Fireball Recovery and InterPlanetary Observation to calculate the luminous efficiencies of the recorded meteors. We also show the limitations of the methods presented herein. [Methods] Deceleration-based formulas were used to calculate the masses of the pre-atmospheric meteoroids. These can in turn be compared to the meteor brightnesses to assess the luminous efficiencies of the recorded objects. Fragmentation of the meteoroids is not considered within this model. Good measurements of the meteor deceleration are required. [Results] We find τ-values, as well as the shape change coefficients, of 294 meteors and fireballs with determined masses in the range of 10-6-100 kg. The derived τ-values have a median of τmedian = 2.17%. Most of them are of the order of 0.1-10%. We present how our values are obtained, compare them with data reported in the literature, and discuss several methods. A dependence of τ on the pre-atmospheric velocity of the meteor, ve, is noticeable with a relation of τ = 0.0023 ve2.3. Furthermore, a dependence of τ on the initial meteoroid mass, Me, is found with negative linear behaviour in log-log space: τ = 0.48 Me-0.47. [Conclusions] The higher luminous efficiency of fast meteors could be explained by the higher amount of energy released. Fast meteoroids produce additional emission lines that radiate more efficiently in specific wavelengths due to the appearance of the so-called second component of higher temperature. Furthermore, the negative dependence of τ on Me implies that the radiation of smaller meteoroids is more efficient. The results of this study also show the limitations of the ablation-based model for the determination of the luminous efficiency.

In this study, we investigate the ablation properties of bolides capable of producing meteorites. The casual dashcam recordings from many locations of the Chelyabinsk superbolide associated with the atmospheric entry of an 18 m in diameter near-Earth object (NEO) have provided an excellent opportunity to reconstruct its atmospheric trajectory, deceleration, and heliocentric orbit. In this study, we focus on the study of the ablation properties of the Chelyabinsk bolide on the basis of its deceleration and fragmentation. We explore whether meteoroids exhibiting abrupt fragmentation can be studied by analyzing segments of the trajectory that do not include a disruption episode. We apply that approach to the lower part of the trajectory of the Chelyabinsk bolide to demonstrate that the obtained parameters are consistent. To do that, we implemented a numerical (Runge–Kutta) method appropriate for deriving the ablation properties of bolides based on observations. The method was successfully tested with the cases previously published in the literature. Our model yields fits that agree with observations reasonably well. It also produces a good fit to the main observed characteristics of Chelyabinsk superbolide and provides its averaged ablation coefficient σ = 0.034 s km. Our study also explores the main implications for impact hazard, concluding that tens of meters in diameter NEOs encountering the Earth in grazing trajectories and exhibiting low geocentric velocities are penetrating deeper into the atmosphere than previously thought and, as such, are capable of producing meteorites and even damage on the ground., This research was funded by the research project (PGC2018-097374-B-I00, P.I. J.M.T-R), funded by FEDER/Ministerio de Ciencia e Innovación–Agencia Estatal de Investigación. MG acknowledges support from the Academy of Finland (325806). Research at the Ural Federal University was supported by the Russian Foundation for Basic Research (18-08-00074 and 19-05-00028).

Aims. The existence of asteroid complexes produced by the disruption of these comets suggests that evolved comets could also produce high-strength materials able to survive as meteorites. We chose as an example comet 2P/Encke, one of the largest object of the so-called Taurid complex. We compare the reflectance spectrum of this comet with the laboratory spectra of some Antarctic ungrouped carbonaceous chondrites to investigate whether some of these meteorites could be associated with evolved comets. Methods. We compared the spectral behaviour of 2P/Encke with laboratory spectra of carbonaceous chondrites. Different specimens of the common carbonaceous chondrite groups do not match the overall features and slope of the comet 2P/Encke. By testing anomalous carbonaceous chondrites, we found two meteorites: Meteorite Hills 01017 and Grosvenor Mountains 95551, which could be good proxies for the dark materials that formed this short-period comet. We hypothesise that these two meteorites could be rare surviving samples, either from the Taurid complex or another compositionally similar body. In any case, it is difficult to get rid of the effects of terrestrial weathering in these Antarctic finds, and further studies are needed. A future sample return from the so-called dormant comets could also be useful to establish a ground truth on the materials forming evolved short-period comets. Results. As a natural outcome, we think that identifying good proxies of 2P/Encke-forming materials might have interesting implications for future sample-return missions to evolved, potentially dormant, or extinct comets. Understanding the compositional nature of evolved comets is particularly relevant in the context of the future mitigation of impact hazard from these dark and dangerous projectiles., J.M.T.R. and S.T. acknowledge financial support from the Spanish Ministry (PGC2018-097374-B-I00, PI: JMTR). J.L.L. is grateful to ICREA Academia program and funding from Generalitat de Catalunya (2017 SGR 128). US Antarctic meteorite samples are recovered by the Antarctic Search for Meteorites (ANSMET) program which has been funded by NSF and NASA, and characterized and curated by the Department of Mineral Sciences of the Smithsonian Institution and Astromaterials Acquisition and Curation Office at NASA Johnson Space Center.

(Topical Collection: Cosmic Dust from the Laboratory to the Stars, Edited by Rafael Rodrigo, Jürgen Blum, Hsiang-Wen Hsu, Detlef Koschny, Anny-Chantal Levasseur-Regourd, Jesús Martín-Pintado, Veerle Sterken and Andrew Westphal); International audience; Interplanetary dust particles and meteoroids mostly originate from comets and asteroids. Understanding their distribution in the Solar system, their dynamical behavior and their properties, sheds light on the current state and the dynamical behavior of the Solar system. Dust particles can endanger Earth-orbiting satellites and deep-space probes, and a good understanding of the spatial density and velocity distribution of dust and meteoroids in the Solar system is important for designing proper spacecraft shielding. The study of interplanetary dust and meteoroids provides clues to the formation of the Solar system. Particles having formed 4.5 billion years ago can survive planetary accretion and those that survived until now did not evolve significantly since then. Meteoroids and interplanetary dust can be observed by measuring the intensity and polarization of the zodiacal light, by observing meteors entering the Earth’s atmosphere, by collecting them in the upper atmosphere, polar ices and snow, and by detecting them with in-situ detectors on space probes.

Drolshagen, E., et al., [Context] The luminous efficiency, τ, can be used to compute the pre-Atmospheric masses of meteoroids from corresponding recorded meteor brightnesses. The derivation of the luminous efficiency is non-Trivial and is subject to biases and model assumptions. This has led to greatly varying results in the last decades of studies. [Aims] The present paper aims to investigate how a reduction in various observational biases can be achieved to derive (more) reliable values for the luminous efficiency. [Methods] A total of 281 meteors observed by the Fireball Recovery and InterPlanetary Observation Network (FRIPON) are studied. The luminous efficiencies of the events are computed using an ablation-based model. The relations of τ as a function of the pre-Atmospheric meteoroid velocity, ve, and mass, Me, are studied. Various aspects that could render the method less valid, cause inaccuracies, or bias the results are investigated. On this basis, the best suitable meteors were selected for luminous efficiency computations. [Results] The presented analysis shows the limits of the used method. The most influential characteristics that are necessary for reliable results for the τ computation were identified. We study the dependence of τ on the assumed meteoroid's density, ρ, and include improved ρ-values for objects with identified meteoroid stream association. Based on the discovered individual biases and constraints we create a pre-debiased subset of 54 well-recorded events with a relative velocity change >80%, a final height

Infrasound monitoring has proved to be effective in detection of the meteor generated shock waves. When combined with optical observations of meteors, this technique is also reliable for detecting centimeter-sized meteoroids that usually ablate at high altitudes, thus offering relevant clues that open the exploration of the meteoroid flight regimes. Since a shock wave is formed as a result of a passage of the meteoroid through the atmosphere, the knowledge of the physical parameters of the surrounding gas around the meteoroid surface can be used to determine the meteor flow regime. This study analyses the flow regimes of a data set of twenty-four centimeter-sized meteoroids for which well constrained infrasound and photometric information is available. This is the first time that the flow regimes for meteoroids in this size range are validated from observations. From our approach, the Knudsen and Reynolds numbers are calculated, and two different flow regime evaluation approaches are compared in order to validate the theoretical formulation. The results demonstrate that a combination of fluid dynamic dimensionless parameters is needed to allow a better inclusion of the local physical processes of the phenomena., 41 pages, 3 Figures and 3 Tables (in press in ApJ)

We analyse the outburst experienced by the September ∈-Perseid meteor shower on 2013 September 9. As a result of our monitoring, the atmospheric trajectory of 60 multistation events observed over Spain was obtained and accurate orbital data were derived from them. On the basis of these orbits, we have tried to determine the likely parent body of this meteoroid stream by employing orbital dissimilarity criteria. In addition, the emission spectra produced by two events belonging to this meteor shower were also recorded. The analysis of these spectra has provided information about the chemical nature of their progenitor meteoroids. We also present an estimation of the tensile strength for these particles.© 2018 The Author(s)., We acknowledge support from the Spanish Ministry of Science and Innovation (projects AYA2015-68646-P and AYA 2015-67175-P).

We describe the fall of Annama meteorite occurred in the remote Kola Peninsula (Russia) close to Finnish border on April 19, 2014 (local time). The fireball was instrumentally observed by the Finnish Fireball Network. From these observations the strewnfield was computed and two first meteorites were found only a few hundred meters from the predicted landing site on May 29th and May 30th 2014, so that the meteorite (an H4-5 chondrite) experienced only minimal terrestrial alteration. The accuracy of the observations allowed a precise geocentric radiant to be obtained, and the heliocentric orbit for the progenitor meteoroid to be calculated. Backward integrations of the orbits of selected near-Earth asteroids and the Annama meteoroid showed that they rapidly diverged so that the Annama meteorites are unlikely related to them. The only exception seems to be the recently discovered 2014UR116 that shows a plausible dynamic relationship. Instead, analysis of the heliocentric orbit of the meteoroid suggests that the delivery of Annama onto an Earth-crossing Apollo type orbit occurred via the 4:1 mean motion resonance with Jupiter or the nu6 secular resonance, dynamic mechanisms that are responsible for delivering to Earth most meteorites studied so far., Comment: 14 pages, 4 figures and 4 tables

Seven double-station α-Capricornid bolides with absolute magnitudes ranging from −6 to −10 are analyzed. These events were imaged between 2011 and 2013 in the framework of the continuous fireball monitoring and meteor spectroscopy campaign developed by the SPanish Meteor Network (SPMN). Their atmospheric trajectory is calculated, together with the orbit in the Solar System of the progenitor meteoroids and the tensile strength of these particles. Their emission spectra are also discussed, and the relative abundances of the main rock-forming chemical elements contained in these meteoroids are estimated. An overabundance of Mg with respect to the expected value for chondritic materials is inferred for most of these particles, although the spectra also reveal differences in the composition of α-Capricornid meteoroids that allow us to derive information about the parent body of this stream.

We analyze here two very bright fireballs produced by the ablation in the atmosphere of two large meteoroids in 2009 and 2010. These slow-moving and deep-penetrating events were observed over Spain in the framework of our Spanish Fireball Network continuous meteor monitoring campaign. The analysis of the emission spectrum imaged for one of these fireballs has provided the first clues about the chemical nature of the progenitor meteoroids. The orbital parameters of these particles suggests a likely association with the recently identified July rho-Herculid meteoroid stream. In addition, considerations about the likely parent body of this stream are also made on the basis of orbital dissimilarity criteria. This orbital analysis reveals that both meteoroids and PHA 2007LQ19 exhibit a similar evolution during a time period of almost 8,000 years, which suggests that either this NEO is the potential parent of these particles or that this NEO and both meteoroids had a common progenitor in the past., Accepted for publication in Monthly Notices of the Royal Astronomical Society(MNRAS) on 2014 June 23

When comet nuclei approach the Sun, the increasing energy flux through the surface layers leads to sublimation of the underlying ices and subsequent outgassing that promotes the observed emission of gas and dust. While the release of gas can be straightforwardly understood by solving the heat-transport equation and taking into account the finite permeability of the ice-free dust layer close to the surface of the comet nucleus, the ejection of dust additionally requires that the forces binding the dust particles to the comet nucleus must be overcome by the forces caused by the sublimation process. This relates to the question of how large the tensile strength of the overlying dust layer is. Homogeneous layers of micrometer-sized dust particles reach tensile strengths of typically 10 3 to 10 4 Pa . This exceeds by far the maximum sublimation pressure of water ice in comets. It is therefore unclear how cometary dust activity is driven. To solve this paradox, we used the model by Skorov and Blum (Skorov, Y.V., Blum, J. 2012. Icarus 221, 361–11), who assumed that cometesimals formed by gravitational instability of a cloud of dust and ice aggregates and calculated for the corresponding structure of comet nuclei tensile strength of the dust-aggregate layers on the order of 1 Pa. Here we present evidence that the emitted cometary dust particles are indeed aggregates with the right properties to fit the model by Skorov and Blum. Then we experimentally measure the tensile strengths of layers of laboratory dust aggregates and confirm the values derived by the model. To explain the comet activity driven by the evaporation of water ice, we derive a minimum size for the dust aggregates of ∼1 mm, in agreement with meteoroid observations and dust-agglomeration models in the solar nebula. Finally we conclude that cometesimals must have formed by gravitational instability, because all alternative formation models lead to higher tensile strengths of the surface layers.

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.

We present the analysis of five bright fireballs observed over Spain and France between 2010 and 2012. Their absolute magnitude ranged between −9.0 and −11.5. Radiant and orbital data indicate that these events were associated with the Taurid meteoroid stream. Their trajectory in the atmosphere is calculated and the heliocentric orbit of the meteoroids is obtained. The emission spectra produced by three of these fireballs are also discussed, and the chemical nature of the parent impactors is inferred, together with different physical parameters of these particles such as the meteoroid mass and tensile strength. On the basis of these results, the ability of Taurid meteoroids to produce meteorites is discussed.

The results of the atmospheric trajectory, radiant, heliocentric orbit, and preliminary strewn field calculations for an extremely bright slow-moving fireball are presented. In the evening hours of July 23, 2008, a bright object entered Earth's atmosphere over Tajikistan. The fireball had a −20.3 maximum absolute magnitude and a spectacularly long persistent dust trail remained visible over a widespread region of Tajikistan for about 28 minutes after sunset. The fireball was also recorded by a visible-light satellite system at 14 h 45 min 25 s UT, and the dust trail was imaged by video and photocameras. A unique aspect of this event is that it was detected by two infrasound and five seismic stations too. The bolide was first recorded at a height of 38.2 km, reached its maximum brightness at a height of 35.0 km, and finished at a height of 19.6 km. The first breakup occurred under an aerodynamic pressure of approximately 1.6 MPa, similar to the values derived for breakups of the scarcely reported meteorite-dropping bolides. The fireball's trajectory and dynamic results suggest that meteorite survival is likely. The meteoroid followed an Apollo-like asteroid orbit comparable to those derived for previously recovered meteorites with accurately known orbits.

We present new orbital data and dynamic results pointing towards the origin of the Northern χ-Orionid meteoroid stream, which is a part of the Taurid meteoroid complex. A new software package was developed to establish the potential parent bodies of meteoroid streams based on the similarity of their orbits. The analysis of a Northern χ-Orionid fireball observed on 2011 December 6 identified two potential parent bodies: the near-Earth object (NEO) 2002XM35 (previously proposed as the parent of this meteoroid stream) and the more recently discovered potentially hazardous asteroid 2008XM1. The calculation of the evolution of the orbital elements performed by using the Mercury 6 symplectic integrator supports the idea that 2008XM1 is a better parent body. Our data sample was expanded by including also in the calculations the mean orbit of the χ-Orionid stream. The results are consistent with the fragmentation of a larger body in the past that could give rise to both NEOs and the Northern χ-Orionid stream. To confirm this, further observations to improve the orbital elements of these asteroids should be attempted before the objects are lost. The analysis of the emission spectrum recorded for this fireball supports a primitive nature for these meteoroids., We acknowledge support from the Spanish Ministry of Science and Innovation (projects AYA2009-13227, AYA2009-14000-C03-01 and AYA2011-26522), CSIC (grant 201050I043) and Junta de Andalucia (project P09-FQM-4555).

Accurate orbital data obtained for the recently discovered γ -Ursae Minorids meteoroid stream during the 2010 and 2011 Spanish Meteor Network and Finnish Fireball Network observing ampaigns are presented. In particular, we focus on an outburst detected in 2010 and on the analysis of the first emission spectrum recorded for a member of this meteoroid stream. An array of high-sensitivity CCD video devices operating from different locations in Spain and Finland was used to perform this study. We have obtained precise trajectory, radiant and orbital information for seven members of this stream. Considerations about its likely parent body based on orbital dissimilarity criteria are made. We also present an estimation of the tensile strength for these meteoroids and a unique emission spectrum of a γ -Ursae inorid fireball that reveals that the main rocky components have chondritic abundances. Ministerio de Ciencia e Innovación AYA2009-13227, AYA2009-14000-C03-01, AYA2011-26522, AYA2011-30106-C02-01 CSIC #201050I043 Junta de Andalucía P09-FQM-4555

Multiple observational techniques are used to quantify the flux of meteoroids, asteroids and comets through near-Earth space. Telescopic CCD observations collect significant data of Earth-crossers being usually few hundreds of meters in diameter. These objects can be only observed during close approaches with Earth and are the most direct source of contemporary hazard to us. The 0.8 m Joan Oro Telescope located at Montsec Astronomical Observatory (Catalonia) allows a wide range of research in the minor bodies domain to be carried out. In this paper, two of its outstanding observational projects are described: (1) a follow-up of Near Earth Asteroids and Potentially Hazardous Asteroids during close approaches to our planet, and (2) a campaign collecting disk-integrated photometry of selected main belt asteroids which aims to enhance the Solar System science coming out from Gaia space mission. Additionally, a CCD-based all-sky camera together with video cameras from Catalonia stations record the appearance of large bolides that are linked with their parent asteroids using dissimilarity functions and backwards integrations of their respective orbits. With all these data it is expected to obtain not only a better understanding of the rate of meter- to tens of meters-sized asteroids impacting with Earth per unit of time, but also inferring new clues on the sources of these dangerous projectiles.

The extent of penetration into the Earth’s atmosphere of a meteoroid is defined by the point where its kinetic energy is no longer sufficient to produce luminosity. For most of the cases this is the point where the meteoroid disintegrates in the atmosphere due to ablation process and dynamic pressure during flight. However, some of these bodies have particular physical properties (bigger size, higher bulk strength, etc.) or favorable flight conditions (lower entry velocity or/and a convenient trajectory slope, etc.) that allow them to become a meteoritedropper and reach the ground. In both cases, we define the end of the luminous path of the trajectory as the terminal height or end height. Thus, the end point shows the amount of deceleration till the final braking. We thus assume that the ability of a fireball to produce meteorites is directly related to its terminal height. Previous studies have discussed the likely relationship between fireball atmospheric flight properties and the terminal height. Most of these studies require the knowledge of a set of properties and physical variables which cannot be determined with sufficient accuracy from ground-based observations. The recently validated dimensionless methodology offers a new approach to this problem. All the unknowns can be reduced to only two parameters which are easily derived from observations. Despite the calculation of the analytic solution of the equations of motion is not trivial, some simplifications are admitted. Here, we describe the best performance range and the errors associated with these simplifications. We discuss how terminal heights depend on two or three variables that are easily retrieved from the recordings, provided at least three trajectory (h, v) points. Additionally, we review the importance of terminal heights, and the way they have been estimated in previous studies. Finally we discuss a new approach for calculating terminal heights. © Springer International Publishing Switzerland 2017.

The Earth’s atmosphere is a good barrier for protecting the Earth from meter-sized interplanetary projectiles but it is not fullproof. Large meteoroids or small asteroids under certain entry geometries and slow geocentric velocities, can penetrate deep into the atmosphere, and become a source of hazard to humans. The energy deposited in the atmosphere causes these bodies to ablate and the hazard can take several forms: sonic booms, airbursts, hot plasma or even crater excavation. By understanding these sources of hazards, strategies can be produced to mitigate their effects. The historic records of such unusual events are highly biased because our ancestors were probably unable to identify and classify many of them. An example is the airburst that occurred on June 30, 1908 over the Tunguska region of Siberia where several hypotheses were proposed to explain it. The recent Chelyabinsk meteorite fall, renewed our interest in the problem. This work introduces the physics and describes the main mechanisms adopted by this. It is concluded that an early detection system, capable of identifying the main sources of contemporary hazard, is needed together with planning general scenarios and safety actions.

Ground-based observations of meteors and fireballs increase our data and statistics on meter-sized events entering the Earth’s atmosphere. Impacts by larger bodies are less frequent and telescopic surveys to find potentially hazardous objects are still crucial to infer the flux of these over long timescales. Telescopic surveys provide significant data on Near Earth Asteroids of few tens or hundreds of meters in diameter that can be only detected when these bodies are close to the Earth. Statistically, bodies with a diameter from a few meters up-to about a 100 m can be considered as the most direct source of contemporary hazard. Of course, larger bodies will do more damage, but impact less frequently. The behaviour of stony bodies interacting with the atmosphere is reasonably well known, but little is known about the either the flux or the behaviour of materials from dormant comets that are often associated with meteoroid streams and small Near Earth Objects. We will introduce some examples that meter-sized meteoroids following high-inclination, and eccentric orbits are not necessarily fragile, and can trace the existence of hazardous objects: dormant comets or Damocloids being an example. From all the available data, a better understanding of the rate at which asteroids impact the Earth can be derived. If meteoroids of cometary origin are included the flux of objects into the Earth’s atmosphere will be increased (Space Sci Rev 84(3/4): 327–471, 1998). However, the typical strengths of such meteoroids are too low to survive ablation in the upper atmosphere, so that they are unlikely to impact the ground. However, events such as that over Tunguska in 1908, where an air burst caused considerable damage over a large area, indicates that we should not underestimate fragile bodies as potentially hazardous sources. New missions aimed at returning samples of Near Earth Asteroids to Earth for analysis (Osiris-REx and Hayabusa 2) are very important because they will deliver to our laboratories materials probably non-sampled in meteorite collections. A better understanding of the composition of Near Earth Objects will allow the most efficient deflection techniques to be developed so that they present no hazard to human beings.

We have assembled data on thirteen 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 thirteen 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. 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 to 10 -2 times the tensile strengths of recovered samples.

–The fall of the Berduc meteorite took place on April 7, 2008, at 01 h 02 min 28 s ± 1 s UTC. A daylight fireball was witnessed by hundreds of people from Argentina and Uruguay, and also recorded by an infrasound array in Paraguay. From the available data, the fireball trajectory and radiant have been reconstructed with moderate accuracy. The modeled trajectory was tested to fit the infrasound and strewn field data. From the computed apparent radiant a = 87 ± 2 and d = )11 ± 2 and taking into account a range of plausible initial velocities, we obtained a range of orbital solutions. All of them suggest that the progenitor meteoroid originated from the main asteroid belt and followed an orbit of low inclination. Based on petrography, mineral chemistry, magnetic susceptibility, and bulk chemistry, the Berduc meteorite is classified as an L6 ordinary chondrite.

The fall of the Puerto Lapice eucrite occurred on May 10, 2007, at 17 h 57 m 30 ± 30 s UTC. Its daylight fireball was witnessed by hundreds of people from Spain, and produced a meteorite fall associated with a large strewn field of fragments. There were no direct pictures of the fireball, but several pictures of the fireballs train were taken from different locations in Spain. Additional theodolite calibrations of visual records were made in order to find the most probable fireball trajectory based on the available data. The shape of the meteorite strewn field was considered as well. Although the orbit of the Puerto Lapice meteoroid could not be computed due to the absence of velocity data, we assumed a likely range of geocentric velocities and computed a range of possible orbits. All solutions show that the body was in an Apollo-type orbit, with low inclination and perihelion distance just below 1 astronomical unit (AU). This is the first case that an orbit can be discussed for an HED meteorite fall.

10 pages, 6 figures, 5 tables, The fall of the Cali meteorite took place on 6 July 2007 at 16 h 32 ± 1 min local time (21 h 32 ± 1 min UTC). A daylight fireball was witnessed by hundreds of people in the Cauca Valley in Colombia from which 10 meteorite samples with a total mass of 478 g were recovered near 3°24.3'N, 76°30.6'W. The fireball trajectory and radiant have been reconstructed with moderate accuracy. From the computed radiant and from considering various plausible velocities, we obtained a range of orbital solutions that suggest that the Cali progenitor meteoroid probably originated in the main asteroid belt. Based on petrography, mineral chemistry, magnetic susceptibility, fhermoluminescence, and bulk chemistry, the Cali meteorite is classified as an H/L4 ordinary chondrite breccia, This work was partially supported by NASA Cosmochemistry grants NNH05AB65I to JNG and NNG06GF95G to AER and NASA Discovery Data Analysis grant NNX08G17G to DWGS. JMTR also thanks CSIC for a JAE-Doc research contract

The extremely porous structure and low strength of most comets and their fragments is opposed to the properties observed in relatively pristine chondritic asteroids, even although both are sharing important chemical similitude. Laboratory experiments and observational evidence suggest that the original extremely porous aggregates that were born from the protoplanetary-disk-forming materials were highly retentive of water and organic compounds present in their forming environment. After consolidation, many of them experienced a particular dynamic history. Some bodies, quickly scattered during the formation of the giant planets and later stored in the Kuiper Belt (KB) or the Oort Cloud (OC) regions, would have suffered a lower degree of impact processing than previously thought. In such category would be comet 81P/Wild 2, whose materials have not experienced aqueous alteration. Other bodies originally volatile-rich that were transiting other regions with higher impact rate were experiencing progressively significant compaction processing, together with subsequent aqueous alteration and loss of volatiles. The release of water from hydrated minerals or interior ices, participated in soaking the forming materials, and transforming their initial mineralogy and physical properties. As a consequence of the physico-chemical evolution promoted by impact processing of undifferentiated bodies, most of the bodies present in the inner solar system are not representative of the planetesimals. Thus, highly porous progenitors and their fragments are the preferential sources of water and organics to the early Earth, even in higher amounts than previously thought.

Aims. We carried out a continuous monitoring of comet 29P/Schwassmann-Wachmann 1 by using medium aperture telescopes with the aim of studying the activity and outburst mechanisms of this comet on the basis of photometric variations. Methods. We used a standardized method to obtain the coma photometry in the R filter of the Johnson-Kron-Cousins system. Some abrupt changes observed in the brightness of SW1 suggest important variations in surface activity with time. Results. During our 2002-2007 observational campaign we detected 28 outbursts (of 1 mag or larger) in 29P/Schwassmann-Wachmann 1. A typical outburst is characterized by a rapid increase towards maximum (in a few hours) and a slower decrease toward the quiescent level (in 3-4 days). Given the effective observing time, the average outburst rate is 7.3 events per year. Despite well-sampled data, no signs of a clear periodicity in the outburst occurrence has been found, thus confirming the unpredictability of the activity of this comet.

By using high-resolution, low-scan-rate, all-sky CCD cameras, the SPanish Meteor Network (SPMN) is currently monitoring meteor and fireball activity on a year round basis. Here are presented just a sampling of the accurate trajectory, radiant and orbital data obtained for meteors imaged simultaneously from two SPMN stations during the continuous 2006–2007 coverage of meteor and fireball monitoring. Typical astrometric uncertainty is 1–2 arc min, while velocity determination errors are of the order of 0.1–0.5 km/s, which is dependent on the distance of each event to the station and its particular viewing geometry. The cameras have demonstrated excellent performance for detecting meteor outbursts. The recent development of automatic detection software is also providing real-time information on the global meteor activity. Finally, some examples of the all-sky CCD cameras applications for detecting unexpected meteor activity are given.

Most meteorites are fragments from recent collisions experienced in the asteroid belt. In such a hypervelocity collision, the smaller collision partner is destroyed, whereas a crater on the asteroid is formed or it is entirely disrupted, too. The present size distribution of the asteroid belt suggests that an asteroid with a 100 km radius is encountered 1014 times during the lifetime of the solar system by objects larger than 10 cm in radius; the formed craters cover the surface of the asteroid about 100 times. We present a Monte Carlo code that takes into account the statistical bombardment of individual infinitesimally small surface elements, the subsequent compaction of the underlying material, and the formation of a crater and a regolith layer. For the entire asteroid, 10,000 individual surface elements are calculated. We compare the ejected material from the calculated craters with the shock stage of meteorites with low petrologic type and find that these most likely stem from smaller parent bodies that do not possess a significant regolith layer. For larger objects, which accrete a regolith layer, a prediction of the thickness depending on the largest visible crater can be made. Additionally, we compare the crater distribution of an object initially 100 km in radius with the shape model of the asteroid (21) Lutetia, assuming it to be initially formed spherical with a radius that is equal to its longest present ellipsoid length. Here we find the shapes of both objects to show resemblance to each other., Facultad de Ciencias Astronómicas y Geofísicas, Instituto Argentino de Radioastronomía

The activity of the Quadrantids in January during several years (2008, 2010, 2011 and 2012) has been investigated in the framework of the SPanish Meteor Network (SPMN). For this purpose, an array of high-sensitivity CCD video devices and CCD all-sky cameras have been used to obtain multi-station observations of these meteors. These allowed us to obtain precise radiant and orbital information about this meteoroid stream. This paper presents a large set of orbital data (namely, 85 orbits) of Quadrantid meteoroids. Most meteors produced by these particles were recorded during the activity peak of this shower. Besides, we discuss four Quadrantid emission spectra. The tensile strength of Quadrantid meteoroids has been also obtained., Comment: Accepted for publication in Icarus on 18 April 2016

During 2006 the SPanish Meteor Network (SPMN) set up three automated video stations in Andalusia for increasing the atmospheric coverage of the already existing low-scan-rate all-sky CCD systems. Despite their initially thought complementary nature, sensitive video cameras have been employed to setup an automatic meteor detection system that provides valuable real-time information on unusual meteor activity, and remarkable fireball events. In fact, during 2006 SPMN video stations participated in the detection of two unexpected meteor outbursts: Orionids and Comae Berenicids. The three new SPMN stations guarantee almost a continuous monitoring of meteor and fireball activity in Andalusia (Spain) and also increase the chance of future meteorite recoveries. A description of the main characteristics of these new observing video stations and some examples of the trajectory, radiant and orbital data obtained so far are presented here.

A daylight bolide was observed over Galicia (NW Spain) and Minho (N. Portugal) on March 1, 2005 at 15 h10 min ± 3 min UTC. We interviewed 23 eyewitnesses of the event in order to obtain the azimuth, altitude, and slope of the fireball’s trajectory. Reports suggest an atmospheric ending height below 20 km, indicating that meteorite survival was likely. From the reconstructed trajectory and the fireball’s duration, we obtained the approximate heliocentric orbits for the meteoroid. Assuming an entry velocity higher than 20 km s−1 which is consistent with its estimated duration, the meteoroid originated in the asteroid belt.

We present laboratory experiments on the formation of macroscopic dust aggregates. The centimeter-sized highly porous bodies are produced by random ballistic deposition from individual micrometer-sized dust particles. We find packing densities between 0.07 and 0.15 for uncompressed samples, dependent on the shape and size distribution of the constituent dust grains. Impacts into these bodies are simulated by uniaxial compression experiments. We find that the maximum compression, equivalent to the highest protoplanetary impact velocities of ~50 m s-1, increases the packing density to 0.20-0.33. Tensile strength measurements with our laboratory samples yield values in the range 200-1100 Pa for slightly compressed samples. We review packing densities and tensile strengths found for primitive solar system bodies, e.g., for comets, primitive meteorites, and meteoroids. We find a consistency between packing densities and tensile strengths of our laboratory samples with those from cometary origin.

Meteoroid behaviour during atmospheric interaction provides clues about the strength and density of cometary disintegration products, establishing a bridge between different research fields. We have estimated the strength of cometary meteoroids by studying meteor ablation light curves measured accurately from multiple-station meteor observation programmes. Our approach assumes that the typical height for meteoroid fragmentation is associated with the peak of meteor luminosity. The strength of cometary meteoroids is independent of the entry velocity and very similar for cometary streams with similar ages. Meteoroids from periodic comets have typical strength of ∼10 4 dyn cm -2 . The only exception among the studied comets is the extremely fluffy particles from 21P/Giacobini-Zinner that exhibit ∼4×10 2 dyn cm -2 . Finally, evolved bodies, e.g. 2P/Encke and 3200 Phaeton, release the toughest meteoroids. We suggest that the main physical difference between cometary particles reaching the Earth from several sources could be a different degree of compaction arising from different physical processing of cometary nuclei by collisional processes, thermal and, perhaps, aqueous alteration. Meteor data suggest that highly processed cometary nuclei produce the meteoroids with the largest tensile strength values while 'pristine comets' are producing meteoroids with the lowest strength values characteristic of bodies with a low degree of compaction.

We present the first redundant detection of sporadic impact flashes on the Moon from a systematic survey performed between 2001 and 2004. Our wide-field lunar monitoring allows us to estimate the impact rate of large meteoroids on the Moon as a function of the luminous energy received on Earth. It also shows that some historical well-documented mysterious lunar events fit in a clear impact context. Using these data and traditional values of the luminous efficiency for this kind of event we obtain that the impact rate on Earth of large meteoroids (0.1–10 m) would be at least one order of magnitude larger than currently thought. This discrepancy indicates that the luminous efficiency of the hypervelocity impacts is higher than 10−2, much larger than the common belief, or the latest impact fluxes are somewhat too low, or, most likely, a combination of both. Our nominal analysis implies that on Earth, collisions of bodies with masses larger than 1 kg can be as frequent as 80,000 per year and blasts larger than 15-kton could be as frequent as one per year, but this is highly dependent on the exact choice of the luminous efficiency value. As a direct application of our results, we expect that the impact flash of the SMART-1 spacecraft should be detectable from Earth with medium-sized telescopes.

A detailed analysis of a photographic spectrum of a Geminid fireball obtained in December 14, 1961 at the Ondrejov Observatory is presented. We have computed a synthetic spectrum for the fireball and compared it with the observed spectrum assuming chemical equilibrium in the meteor head. In this way we have determined relative chemical abundances in meteor vapors. Comparing the relative chemical abundances of this Geminid meteoroid with those obtained from meteoroids associated with comets 55P/Tempel-Tuttle and 109P/Swift-Tuttle we found no significant chemical differences in main rock-forming elements. Despite of this similarity, the deepest penetration of the Geminid meteoroids and their ability to reach high rotation rates in space without fragmentation suggest that thermal processing is affecting their physical properties. We suggest that as consequence of space weathering a high-strength envelope is produced around these particles. In this picture, heating processes of the mineral phases could result in the peculiar properties observed during atmospheric entry of the Geminid meteoroids, especially their strength, which is evidenced by its resistance to ablation. Finally, although one meteoroid cannot be obviously considered as representative of the composition of its parent body, we conclude that 3200 Phaethon is able to produce millimetre-size debris nearly chondritic in composition, but the measured slight overabundance of Na would support a cometary origin for this body.

An impressive daylight fireball was observed from Spain, Portugal, and the south of France at 16h46m45s UTC on January 4, 2004. The meteoroid penetrated into the atmosphere, generating shock waves that reached the ground and produced audible booms. The associated airwave was recorded at a seismic station located 90 km north of the fireball trajectory in Spain, and at an infrasound station in France located 750 km north-east of the fireball. The absolute magnitude of the bolide has been determined to be -18 ± 1 from a casual video record. The energy released in the atmosphere determined from photometric, seismic, and infrasound data was about 0.02 kilotons (kt). A massive fragmentation occurred at a height of 28 ± 0.2 km, resulting in a meteorite strewn field of 20 ± 6 km. The first meteorite specimen was found on January 11, 2004, near the village of Villalbeto de la Pena, in northern Palencia (Spain). To date, about 4.6 kg of meteorite mass have been recovered during several recovery campaigns. The meteorite is a moderately shocked (S4) L6 ordinary chondrite with a cosmic-ray-exposure age of 48 ± 5 Ma. Radioisotope analysis shows that the original body had a mass of 760 ± 150 kg, which is in agreement with the estimated mass obtained from photometric and seismic measurements.

In order to increase in Spain the social interest in the study of interplanetary matter (asteroids, comets and meteoroids) we created the Spanish Photographic Meteor Network (SPMN) in 1997. This network has been dedicated to studying interplanetary matter with participation of researchers from three universities (Universitat Jaume I, Universitat de Barcelona and Universitat de Valencia), the Institut d'Estudis Espacials de Catalunya (IEEC) and the Instituto de Astrofisica de Andalucia and it is also supported by the Atmospheric Sounding Station at El Arenosillo (INTA-CEDEA) and by the Experimental Station La Mayora (EELM-CSIC). In order to promote the participation of amateurs, our homepage (www.spmn.uji.es) presents public information about our research explains how amateur astronomers can participate in our network. In this paper we give some examples of the social role of a Fireball Network in order to give a coherent explanation to bright fireball events. Moreover, we also discuss the role of this kind of research project as a promoter of amateur participation and contribution to science. In fact, meteor astronomy can become an excellent area to form young researchers because systematic observation of meteors using photographic, video and CCD techniques has become one of the rare fields in astronomy in which amateurs can work together with professionals to make important contributions. We present here some results of the campaigns realized from the formation of the network. Finally, in a new step of development of our network, the all-sky CCD automatic cameras will be continuously detecting meteors and fireballs from four stations located in the Andalusia and Valencian communities by the end of 2005. Additionally, during important meteor showers we plan to develop fireball spectroscopy using medium field lenses.

We report here the observation of the first peak belonging to the 2002 Leonid meteor storm made during the night of November 18–19, 2002. This feature, produced by a 7-revolution dust trail, was observed from several photographic stations of the Spanish Photographic Meteor Network (SPMN) and one video station operated from the Instituto de Astrofisica de Andalucia (IAA) in an intensive campaign from the ground working in collaboration with the 2002 Leonid MAC mission. We used photography, slow-scan Charge Coupled Devices (CCD) and video CCD-imaging techniques to deduce the meteoroid flux density profiles in different ranges of masses. Additionally, we present multi-station work, developed during the storm, that allows us to deduce the orbital elements of ten meteoroids associated with this dust trail. We have found a clear similarity between their orbits and the one belonging to a theoretical orbit for particles ejected from 55P/Tempel–Tuttle in 1767.

Relative chemical abundances of 13 meteoroids were determined by averaging the composition of the radiating gas along the fireball path that originated during their penetration into the Earth's atmosphere. Mg, Fe, Ni, Cr, Mn, and Co abundances, relative to Si, are similar to those reported for CI and CM carbonaceous chondrites and interplanetary dust particles. In contrast, relative abundances of Ca and Ti in meteor spectra indicate that these elements suffer incomplete evaporation processes. The chemical composition of all meteoroids studied in this work differs from that of 1P/Halley dust.

Despite ablation and drag processes associated with atmospheric entry of meteoroids were a subject of intensive study over the last century, little attention was devoted to interpret the observed fireball terminal height. This is a key parameter because it not only depends on the initial mass, but also on the bulk physical properties of the meteoroids and hence of their ability to ablate in the atmosphere. In this work we have developed a new approach that is tested using the fireball terminal heights observed by the Meteorite Observation and Recovery Project operated in Canada between 1970-1985 (hereafter referred as MORP). We then compare them to the calculation made. Our results clearly show that the new methodology is able to forecast the degree of deepening of meteoroids in the Earth's atmosphere. Then, this approach has important applications in predicting the impact hazard from cm- to meter-sized bodies that are represented, in part, in the MORP bolide list., Comment: 26 pages, 5 figures, 1 table

We have analyzed the meteor activity associated with meteoroids of fresh dust trails of Comet 209P/LINEAR, which produced an outburst of the Camelopardalid meteor shower (IAU code #451, CAM) in May 2014. With this aim, we have employed an array of high-sensitivity CCD video devices and spectrographs deployed at 10 meteor observing stations in Spain in the framework of the Spanish Meteor Network (SPMN). Additional meteoroid flux data were obtained by means of two forward-scatter radio systems. The observed peak zenithal hourly rate (ZHR) was much lower than expected, of around 20 meteors h-1. Despite of the small meteor flux in the optical range, we have obtained precise atmospheric trajectory, radiant and orbital information for 11 meteor and fireball events associated with this stream. The ablation behaviour and low tensile strength calculated for these particles reveal that Camelopardalid meteoroids are very fragile, mostly pristine aggregates with strength similar to that of the Orionids and the Leonids. The mineral grains seem to be glued together by a volatile phase. We also present and discuss two unique emission spectra produced by two Camelopardalid bright meteors. These suggest a non-chondritic nature for these particles, which exhibit Fe depletion in their composition., Accepted for publication in Monthly Notices of the Royal Astronomical Society on Sept. 22, 2014

On April 13, 2013 a very bright fireball with an absolute magnitude of -13:0 ± 0:5 was recorded over the center of Spain. This sporadic event, which was witnessed by numerous casual observers throughout the whole country, was imaged from seven meteorobserving stations operated by the Spanish Meteor Network (SPMN), and its emission spectrum was also obtained in the framework of our meteor spectroscopy campaign. The atmospheric trajectory of the bolide and the heliocentric orbit of the parent meteoroid are analyzed here. The spectrum reveals a chondritic nature for this particle, which was following a Jupiter family comet orbit before its encounter with the Earth. In addition, the emission spectrum of the meteoric afterglow was recorded during about 0.8 s. The main emission lines appearing in this signal were identified and their evolution with time is also discussed. Afterglow spectra are not abundant in the literature, and these can provide important clues about the physical proceses taking place in meteoric persistent trains., Meteor stations at Sevilla, La Hita, Huelva and El Arenosillo have been funded by the first author. We acknowledge support from the Spanish Ministry of Science and Innovation (Projects AYA2009-13227 and AYA2011-26522). We also thank the AstroHita Foundation for its support in the establishment and operation of the automated meteor observing station located at La Hita Astronomical Observatory (La Puebla de Almoradiel, Toledo, Spain).

We analyze the likely link between the recently discovered Near Earth Object 2012XJ112 and a bright fireball observed over the south of Spain on December 27, 2012. The bolide, with an absolute magnitude of -9 +- 1, was simultaneously imaged during the morning twilight from two meteor stations operated by the SPanish Meteor Network (SPMN). It was also observed by several casual witnesses. The emission spectrum produced during the ablation of the meteoroid in the atmosphere was also recorded. From its analysis the chemical nature of this particle was inferred. Although our orbital association software identified several potential parent bodies for this meteoroid, the analysis of the evolution of the orbital elements performed with the Mercury 6 symplectic integrator supports the idea that NEO 2012XJ112 is the source of this meteoroid. The implications of this potential association are discussed here. In particular, the meteoroid bulk chemistry is consistent with a basaltic achondrite, and this emphasizes the importance to deduce from future Earth approaches the reflectance spectrum and taxonomic nature of 2012XJ112., Accepted for publication in Monthly Notices of the Royal Astronomical Society on Jan. 30, 2014

On October 8, 2011 the Earth crossed dust trails ejected from comet 21P/Giacobini-Zinner in the late 19th and early 20th Century. This gave rise to an outburst in the activity of the October Draconid meteor shower, and an international team was organized to analyze this event. The SPanish Meteor Network (SPMN) joined this initiative and recorded the October Draconids by means of low light level CCD cameras. In addition, spectroscopic observations were carried out. Tens of multi-station meteor trails were recorded, including an extraordinarily bright October Draconid fireball (absolute mag. -10.5) that was simultaneously imaged from three SPMN meteor ob-serving stations located in Andalusia. Its spectrum was obtained, showing a clear evolution in the relative intensity of emission lines as the fireball penetrated deeper into the atmosphere. Here we focus on the analysis of this remarkable spectrum, but also discuss the atmospheric trajectory, atmospheric penetration, and orbital data computed for this bolide which was probably released during 21P/Giacobini-Zinner return to perihelion in 1907. The spectrum is discussed together with the tensile strength for the October Draconid meteoroids. The chemical profile evolution of the main rocky elements for this extremely bright bolide is compared with the elemental abundances obtained for 5 October Draconid fireballs also recorded during our spectroscopic campaign but observed only at a single station. Significant chemical heterogeneity between the small meteoroids is found as we should expect for cometary aggregates being formed by diverse dust components., Manuscript in press in Monthly Notices of the Royal Astronomical Society. Accepted for publication in MNRAS on April 28th, 2013 Manuscript Pages: 28 Tables: 5 Figures: 12. Manuscript associated: "The 2011 October Draconids outburst. I. Orbital elements, meteoroid fluxes and 21P/Giacobini-Zinner delivered mass to Earth" by Trigo-Rodriguez et al. is also in press in the same journal

We present the analysis of the atmospheric trajectory and orbital data of four bright bolides observed over Spain, one of which is a potential meteorite dropping event. Their absolute magnitude ranges from -10 to -11. Two of these are of sporadic origin, although a Geminid and a kappa-Cygnid fireball are also considered. These events were recorded in the framework of the continuous fireball monitoring and spectroscopy campaigns developed by the SPanish Meteor Network (SPMN) between 2010 and 2012. The tensile strength of the parent meteoroids is estimated and the abundances of the main rock-forming elements in these particles are calculated from the emission spectrum obtained for three of these events. This analysis revealed a chondritic nature for these meteoroids., Comment: Manuscript in press in Monthly Notices of the Royal Astronomical Society

We present the observations of two fireballs that exhibit fast and quasi-periodic brightness variations along their atmospheric path. This phenomenon, which is known as “flickering”, is associated to the entry of spinning non-spherical meteoroids into the atmosphere. Both bolides were imaged in the framework of the continuous fireball monitoring and meteor spectroscopy campaigns organized by the SPanish Meteor Network (SPMN) in 2012. Their atmospheric trajectory, radiant, and orbit were calculated. The preatmospheric mass and tensile strength of the parent meteoroids were also estimated, and the rotation of these bodies analyzed on the basis of the photometric behavior of the bolides. Although small (less than 80 grams), a non-zero terminal mass was determined for both events. The emission spectra produced during the ablation of the meteoroids in the atmosphere are also discussed., We acknowledge support from the Spanish Ministry of Science and Innovation (project AYA2011-26522) and Junta de Andalucia (project P09-FQM-4555). We also thank the AstroHita Foundation for its support in the establishment and operation of the automated meteor observing station located at La Hita Astronomical Observatory (La Puebla de Almoradiel, Toledo, Spain).