Meteor Physics Research Articles

Machine learning for the prediction of local asteroid damages

Risk assessment studies of local asteroid hazards traditionally simulate the physics of meteors with engineering models tailored to analyze tens-of-millions of scenarios. However, these simplified approaches still need to solve time-dependent ODEs to model the entry process and the resulting ground damage. With a computational cost of O(0.01 CPU.s) per scenario, simulating these large numbers of potential entry conditions can take several days on local computers. To improve computational efficiency, we propose in this paper an orthogonal approach based on machine learning models to predict the size of damaged areas given a list of entry parameters. We train 5 machine learning methods and compare the predictions to the outputs of NASA’s state-of-the-art Probabilistic Asteroid Impact Risk (PAIR) model. PAIR’s remarkable capability to handle a broad spectrum of entry conditions and a high volume of scenarios establishes it as our reference model, with PAIR estimates assumed ground truth and used to train, test, and validate the machine learning models. The ML models, initially trained with PAIR’s primitive input variables, are then further enhanced with engineered features to improve the performance of interpretable models. We find that complex models like neural networks are well-suited to estimate blast hazards, while simpler, interpretable linear models can accurately assess thermal damage. For both types of hazards, the radii of damaged areas can be predicted with less than 10% average relative errors for radii greater than 100 km. The CPU time is decreased by a factor O(103) compared to the PAIR model, enabling the simulation of millions of scenarios within minutes on a local computer. Beyond serving as surrogate models, we incorporate the machine learning models into a comprehensive Shapley sensitivity analysis, yielding a ranking of entry parameters based on their contributions to ground damages. These results offer valuable insights for prioritizing observation missions.

Differential Ablation of Organic Coatings From Micrometeoroids Simulated in the Laboratory

AbstractMicrometeoroids contain organic material that may undergo differential ablation during atmospheric entry, potentially depositing organic material into Earth's atmosphere and affecting the radar detectability of meteors. To investigate the differential ablation of organics, we used a dust accelerator to shoot submicron polypyrrole‐coated olivine particles at speeds of 10–20 km/s into a gas target containing air. A set of biased electrodes placed along the path of the particles measured the charges generated when the particles ablated and the ablated molecules collided with gas molecules. We observed that the particles differentially ablate their organic polypyrrole coatings prior to their inorganic olivine cores, producing spikes in charge production, with charge yields of 104–105 C/kg even at relatively low speeds. These measurements suggest that large organic molecules survived ablation and are responsible for the observed charge production since small molecules either do not produce ions at those speeds or produce them in much lower quantities than observed. We modeled the ablation using basic meteor physics by assuming that the polypyrrole coating decomposes into pyrrole monomer. Extending these results to the ablation of micrometeoroids in the atmosphere indicates that organic coatings should ablate at high altitudes within relatively narrow altitude ranges, which has consequences for the detectability of meteors by radar. Since the ablated coatings generate relatively large molecules, the results also suggest that micrometeoroids can deliver complex organic material into planetary atmospheres by ablating them during entry, potentially serving as a source of prebiotic organics.

On the uncertainty factor in approximation of the heat transfer coefficient in the problem of modelling the interaction of meteor body with the atmosphere

The problem of modelling the interaction of meteor body with the Earth’s atmosphere is considered. The motion, ablation, and energy deposition of the meteoroid and its fragments moving as a single body are modelled by numerically solving the meteor physics equations. For the heat transfer coefficient, which is a governing parameter in these equations, the proposed approximate expression is used, depending on the meteoroid velocity and size and the atmospheric density, as well as a constant value accepted in the literature. An uncertainty parameter is introduced into the formula for the heat transfer coefficient to make allowance for the existing uncertainty in the radiative heat flux computations in the meteoric range of flow parameters. The influence of uncertainty of the heat transfer coefficient on the meteoroid mass loss, velocity, trajectory, and energy deposition is evaluated.

Effect of the heat transfer coefficient on modelling the energy deposition of destructed meteoroid

Models of meteoroid destruction into the cloud of fragments moving with a common shock wave are considered: the two-parameter model that takes into account changes of the shape and density of the cloud, and simple models that leave these factors out of account, including those used in the literature. Models differ in equations governing the lateral expansion of the cloud. We numerically simulate the interaction of the Chelyabinsk asteroid with the Earth’s atmosphere by solving the meteor physics equations using fragment cloud models, and study the models abilities to reproduce the observational energy deposition curve. Heat transfer coefficient effect on simulating energy deposition using different models is estimated. For simple fragment cloud models, the optimal coefficient in the cloud lateral expansion equation is proposed as a function of the heat transfer coefficient (ablation parameter) to match the observational altitude of the bolide peak brightness. The optimal value of the uncertainty parameter in the expression for the heat transfer coefficient is found to match also a shape of the observational energy deposition curve. It is shown that the optimal simple and the two-parameter models give results of modelling the energy deposition of the Chelyabinsk asteroid and estimates of its entry mass, which are very close to each other and are consistent with the observational data.

Luminous efficiency based on FRIPON meteors and limitations of ablation models

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.

Fragmentation and ablation of the planetesimals in the protoplanetary disks of Jupiter and Saturn

In this study we discuss the capture of bodies into the gaseous disks around young Jupiter and Saturn due to gas drag in the disks. We suppose that solution of the problem will allow estimation of the masses and composition of bodies that fell on the growing icy moons. This would provide explanation of the differences in the mean density and internal structure of giant icy moons of Jupiter and Saturn. The multiparameter problem of braking, fragmentation and ablation of planetesimals (a comet substance) in the gas medium of the circumplanetary disk is solved by a modified approach of the meteor physics. Our research shows that a significant masses of protosatellite material falling on the circumplanetary disks of Jupiter and Saturn are captured in the disks. At the same time the masses captured in the formation region of different moons are very different. The braking and fragmentation of planetesimals can be the main parameter in the mechanism of capture mass of planetesimals by the accretion disks of giant planets. There is a significant difference in the mass of material captured by the aerodynamic braking and ablation in the formation regions of Ganymede, Callisto, and Titan (up to 30-40%). For a material strength of 2* 104 Pa <σ* <2*105 Pa, a significant difference in the amount of matter captured by the disk in the feeding region of the regular ice satellites of Ganymede, Callisto and Titan is possible. The presence of fragmentation is perhaps one of the reasons for the difference in the internal structure of Ganymede, Callisto and Titan.

Radio meteor physics – a comparison between techniques from 1945 to the mid-1970's

A description of the physics of radar meteors from 1945 to the mid-1970s is presented. Concrete designs of various radars in different countries are presented. Harvard project is the best documented of these early radars, and we will focus on that radar. Application of multi-receiver stations for orbit determination became relatively common, especially with the advent of the IGY in 1957. Canada also built the Springhill Observatory around the time of the IGY, but of special note was the construction of several meteor radars in the USSR. The contribution of Kashcheyev and his scientific group to the development of radar meteor technologies was emphasized. A discussion of some equipment options of Balakleya geophysical complex in different years was held. Problems of meteor radar technologies in solving problems of astronomy and geophysics are noted. Meteor became a mainstay of upper atmospheric research into dynamical processes after 1960's. Such research was undertaken at multiple sites all over the Western global arena as well as in the USSR. In attention is paid to the history of changes in the methods of obtaining, processing and storage of meteor information. Some aspects of the application of innovative technologies in meteor radar systems were discussed, primarily in the study of winds and atmospheric circulation in the meteor zone. The advent of personal computers, plus the somewhat simultaneous development of digitizers in the early 1970's, was a major breakthrough for many areas of scientific research and studies. This work is the first part of a planned review of radar meteor physics and related technologies from 1945 to 2020.

On models of meteoroid disruption into the cloud of fragments

The meteoroid disruption into a large number of fragments when they move with a common shock wave before dispersion to a sufficient distance to move independently is considered. Disrupted meteoroid under the action of pressure forces is deformed: it is compressed in a flight direction and expands in a lateral one. Four models of the meteoroid disruption into a cloud of fragments moving as a single body are considered: two models developed by the authors and two models used in the literature (Grigoryan, 1979; Hills and Goda, 1993). The principal differences between the proposed and accepted models are shown. Numerical solutions of the meteor physics equations are obtained using the above models to simulate the interaction of the Chelyabinsk meteoroid with the atmosphere. To model the meteoroid ablation, an approximate formula is used for the radiative heat transfer coefficient as a function of the meteoroid velocity and size and the atmospheric density. The influence of the heat transfer coefficient uncertainty (including its constant value) on the meteoroid mass loss, energy deposition and initial mass estimate is studied. Solutions using different fragmentation models are compared with each other and with observational data and the results of comparisons are discussed.

Luminosity calculation of meteor entry based on detailed flow simulations in the continuum regime

Context. Composition, mass, and trajectory parameters of meteors can be derived by combining observations with the meteor physics equations. The fidelity of these equations, which rely on heuristic coefficients, significantly affects the accuracy of the properties inferred. Aims. Our objective is to present a methodology that can be used to compute the luminosity of meteor entry based on detailed flow simulations in the continuum regime. Methods. The methodology consists in solving the Navier–Stokes equations using state-of-the-art physico-chemical models for hypersonic flows. It includes accurate boundary conditions to simulate the surface evaporation of the molten material and coupled flow-radiation effects. Such detailed simulations allow for the calculation of heat-transfer coefficients and luminous efficiency, which can be incorporated into the meteor physics equations. Finally, we integrate the radiative transfer equation over a line of sight from the ground to the meteor to derive the luminosity magnitude. Results. We use the developed methodology to simulate the Lost City bolide and to derive the luminosity magnitude, obtaining good agreement between numerical results and observations. The computed color index is more prominent than the observations. This is attributed to a lack of refractory elements such as Ca in the modeled flow that might originate from the vaporization of droplets in the trail, a phenomenon currently not included in the model.

A comparison of ELF/VLF signals generated by different types of meteor showers

Understanding the meteoroids environment and their properties are important for several fields such as solar system evolution and space science. The investigation of their emissions helps to a better understanding of the physics of meteors and their interactions with the atmosphere. We have compared the ELF/VLF signals generated by Perseids-2016, Leonids-2018 and Geminids-2018 meteors. The results show that a typical meteor generated by small meteoroids, can produce ELF/VLF signals just like brighter fireballs but with lower amplitude and time duration. Also, the results show that the ELF/VLF waves which are generated by Leonids meteors are signals with the most during the effective time and maximum signals per minutes. The results also show that the PER’s and GEM’s signals are a combination of several separated smaller signals. The typical meteor signals have the frequency ranges below 2 kHz but GEM’s meteors generated signals in 3 minutes which have the frequency range up to 4.5 kHz.

Secondary cameras onboard the Mini-EUSO experiment: Control software and calibration

Mini-EUSO is a space experiment selected to be installed inside the International Space Station. It has a compact telescope with a large field of view (44 × 44 sq. deg.) focusing light on an array of photo-multipliers tubes in order to observe UV emission coming from Earth’s atmosphere. Observations will be complemented with data recorded by some ancillary detectors. In particular, the Mini-EUSO Additional Data Acquisition System (ADS) is composed by two cameras, which will allow us to obtain data in the near infrared, and in the visible range. These will be used to monitor the observation conditions, and to acquire useful information on several scientific topics to be studied with the main instrument, such as the physics of atmosphere, meteors, and strange quark matter. Here we present the ADS control software developed to stream cameras together with the UV main instrument, in order to grab images in an automated and independent way, and we also describe the calibration activities performed on these two ancillary cameras before flight.

Meteor Observations at Kazan Federal University (Russia)

SummaryThis poster paper described initial results of recent meteor observations in Kazan obtained with a new meteor radar, SKiYMET. Significant improvements in the number of registrations are being recorded, enabling better statistics.Radar observations of meteors have been carried out and archived since the mid-20th Century; at Kazan University (56°N, 49°E) they commenced in 1956, and have continued with only a few interruptions. A quasi-tomographic method (developed in-house in 2000) has been used to determine the coordinates of radiants of meteor showers, and to derive the orbital elements of small showers (microshowers).The observations provide valuable information about the distribution of meteoric matter near the Earth’s orbit. That information supports studies of stratospheric temperatures. A new radar, SKiYMET, was deployed in 2015 and measured parameters such as meteor speeds, but in 2016 its software was supplemented by an in-house package which performed more efficient pre-filtering of the primary data to eliminate non-meteor reflections from various sources. The new filtering algorithm has reduced substantially the threshold S/N ratio for detecting meteors (so fainter meteors can now be recorded), while the package also enables meteor velocities to be calculated much more efficiently than with SKiYMET, improving significantly the quality and statistical indicators of the processed data. By detecting a much larger number of meteors, it enables more detailed studies of the distribution of meteor velocities per day and per season.Daily meteor counts for 2016–2017, extracted from the observations by the KFU programme, yielded significantly higher rates than with SKiYMET. These results support much better statistics, and also enable much finer details to be discerned. In particular, plots of meteor rates against speed are found to exhibit two maxima, one near 30 km s−1 and one near 55 km s−1. This bifurcation in the relationship can also be discerned in the seasonal dependences of the speed distribution.Improvements in the measurements of the speeds of meteor particles entering the atmosphere reveal an increase in the numbers with higher speeds (&gt; 50 km s−1). The distributions of speeds and heights show a rather strong dependence of the meteor speed upon altitude; as predicted by meteor physics, those with higher speeds begin to burn at higher altitudes. A local increase in the number of meteors that have speeds of about 55 km s−1 has also been reported in the literature. The increase could be associated with heterogeneities in the distribution of meteoric matter in the vicinity of the Earth’s orbit.

Determination of Meteorite Trajectories: Observations and Modeling

We construct the complete trajectory of a meteorite from observations on the visible (“bright”) section of the trajectory. Mathematically, this is a minimization problem for a functional defined as the deviation of the observed trajectory from the trajectory calculated using the system of meteor physics equations. This differential system has been solved numerically, and the minimization problem has been solved by the Nelder–Mead method. The solution makes it possible to determine the physical parameters of the body entering the Earth’s atmosphere and to complete its trajectory on the unobservable (“dark”) section until its collision with the Earth’s surface.

The mass index and mass of the Geminid meteoroid stream as determined with radar, optical and lunar impact data

The Geminid meteor shower was observed in 2015 using the Western Meteor Physics Group's Canadian Meteor Orbit Radar (CMOR), Marshall Space Flight Center's (MSFC) eight wide-field optical cameras, and telescopes of MSFC's lunar impact monitoring program. These observations allowed Geminid fluxes to be calculated in three unique mass-ranges, from 1.8×10−4g to 30g. From these fluxes, a mass index of 1.68±0.04 was measured. The quantities derived here, along with a profile of the Geminid meteor shower activity in 2015 from CMOR, were used to find a total Geminid mass of 3.5×107g the Earth encountered in 2015, along with a minimum total mass for the Geminid meteoroid stream of 1.6×1016g. Attempts have been made in the past to measure the mass of meteoroid streams using ZHR profiles, but this new and improved treatment uses empirically derived fluxes and measured mass indices for the 2015 encounter with the meteoroid stream. These results are compared to meteoroid stream mass estimate measured for the Perseids of 3.3×1017g. Instead of three flux values, a single flux value and an assumed mass index of 1.78 was used in Perseid analysis.

Women in radio science

This time, I present Margaret Campbell-Brown, Associate Professor of Physics and Astronomy at the University of Western Ontario, and a member of the very successful Western Meteor Physics Group in Canada.

Destruction mechanisms of meteoroids and heat transfer to their surfaces

The phenomena of the movement and destruction of celestial bodies in the Earth’s atmosphere are investigated based on the advanced equations of meteor physics. The movement of meteorites in Kunya-Urgench (1998) and Chelyabinsk (2013) is analyzed as an example taking into account changes in the ablation along the trajectory. Different mechanisms of destruction of these meteorites are described.

Approximating the solution of meteor physics equations through the use of elementary functions

In this paper we examine the possibility of using approximations of elementary functions for the analytical solution of meteor physics equations, used to describe the trajectory and to evaluate the defining parameters of meteoroids entering the Earth’s atmosphere. We show the possibility of replacing the analytical solution with the combination of two elementary functions along one parameter. We provide estimates for the error of the proposed replacement. We investigate the magnitude of error in the function which arises in the approximation of meteoric observational data.

DETECTION OF RADIO EMISSION FROM FIREBALLS

We present the findings from the Prototype All-Sky Imager (PASI), a backend correlator of the first station of the Long Wavelength Array (LWA1), which has recorded over 11,000 hours of all-sky images at frequencies between 25 and 75 MHz. In a search of this data for radio transients, we have found 49 long (10s of seconds) duration transients. Ten of these transients correlate both spatially and temporally with large meteors (fireballs), and their signatures suggest that fireballs emit a previously undiscovered low frequency, non-thermal pulse. This emission provides a new probe into the physics of meteors and identifies a new form of naturally occurring radio transient foreground.

Consequences of collisions of natural cosmic bodies with the Earth’s atmosphere and surface

Possible consequences of collisions of natural cosmic bodies with the Earth’s atmosphere and surface are described. The methodological basis of classification of consequences is the solution of meteor physics equations characterizing the trajectory of a body in the atmosphere, namely, the dependence of the body’s velocity and mass on the flight altitude. The solution depends on two dimensionless parameters characterizing the drag altitude and the role of mass loss by a meteoroid during its motion in the atmosphere. Depending on values of these parameters, the degree of effect on the planetary surface considerably changes. In particular, the conditions of cratering and meteorite fall on the planetary surface are obtained. The results are presented in a simple analytical form. They quite match to the real events considered in the paper. Recommendations are given on further investigations into the important problem of interaction of cosmic bodies with planetary atmospheres.

Orbital observations of meteors in the Martian atmosphere using the SPOSH camera

We investigate the expected performance of a wide-angle camera in Martian orbit, which, unlike previous cameras that have flown to Mars, is capable of recording meteor activity in that planet's atmosphere. We show that, based on our current understanding of meteor physics and the interplanetary meteoroid population, several meteors will be detected by this instrument during a single nightside pass on a low Martian orbit. The instrument will also record the signatures of meteor showers expected to occur every Martian year (1.88 Earth years). The results of this investigation will test models of the flux of “large” (mm-cm) meteoroids at the orbit of Mars and their interaction with the Martian atmosphere.