Density Of Meteoroids Research Articles

Observation of meteors from space with the Mini-EUSO detector on board the International Space Station

Context. Observations of meteors in the Earth’s atmosphere offer a unique tool for determining the flux of meteoroids that are too small to be detected by direct telescopic observations. Although these objects are routinely observed from ground-based facilities, such as meteor and fireball networks, space-based instruments come with notable advantages and have the potential to achieve a broad and uniform exposure. Aims. In this paper, we describe the first observations of meteor events with Mini-EUSO, a very wide field-of-view telescope launched in August 2019 from the Baikonur cosmodrome and installed on board the Russian Zvezda module of the International Space Station. Mini-EUSO can map the night-time Earth in the near-UV range (290-130 nm) with a field of view equal to 44° × 44° and a spatial resolution of about 4.7 km at an altitude of 100 km from the ground. The detector saves triggered transient phenomena with a sampling frequency of 2.5 µs and 320 µs, as well as a continuous acquisition at 40.96 ms scale that is suitable for meteor observations. Methods. We designed two dedicated and complementary trigger methods, together with an analysis pipeline able to estimate the main physical parameters of the observed population of meteors, such as the duration, horizontal speed, azimuth, and absolute magnitude. To compute the absolute flux of meteors from Mini-EUSO observations, we implemented a simulation framework able to estimate the detection efficiency as a function of the meteor magnitude and the background illumination conditions. Results. The instrument detected 24 thousand meteors within the first 40 data-taking sessions from November 2019 to August 2021, for a total observation time of approximately 6 days with a limiting absolute magnitude of +6. Our estimation of the absolute flux density of meteoroids in the range of mass between 10−5 kg to 10−1 kg was found to be comparable to other results available in the literature. Conclusions. The results of this work prove the potential for space-based observations to increase the statistics of meteor observations achievable with instruments operating on the ground. The slope of the mass distribution of meteoroids sampled with Mini-EUSO suggests a mass index of either s = 2.09 ± 0.02 or s = 2.31 ± 0.03, according to two different methodologies for the computation of the pre-atmospheric mass starting from the luminosity of each event.

Observations of the new meteor shower from comet 46P/Wirtanen

Context. A new meteor shower λ-Sculptorids produced by the comet 46P/Wirtanen was forecast for December 12, 2023. The predicted activity was highly uncertain, but generally considered to be low. Observations in Australia, New Zealand, and Oceania were solicited to help constrain the size distribution of meteoroids in the shower. Aims. This work aims to characterize the new meteor shower, by comparing the observed and predicted radiants and orbits, and to provide a calibration for future predictions. Methods. Global Meteor Network video cameras were used to observe the meteor shower. Multi-station observations were used to compute trajectories and orbits, while single-station observations were used to measure the flux profile. Results. A total of 23 λ-Sculptorid orbits have been measured. The shower peaked at a zenithal hourly rate (ZHR) of 0.65−0.20+0.24 meteors per hour at λ⊙ = 259.988° ±0.042°. Due to the low in-atmosphere speed of 15 km s−1, the mean mass of observed meteoroids was 0.5 g (∼10 mm diameter), an order of magnitude higher than predicted. The dynamical simulations of the meteoroid stream can only produce such large meteoroids arriving at Earth in 2023 with correct radiants when a very low meteoroid density of ∼100 kg m−3 is assumed. However, this assumption cannot reproduce the activity profile. It may be reproduced by considering higher density meteoroids in a larger ecliptic plane-crossing time window (ΔT = 20 days) and trails ejected prior to 1908, but then the observed radiant structure is not reproduced.

A physical survey of meteoroid streams: Comparing cometary reservoirs

In this work, we present an optical survey of mm-sized meteoroids using the Canadian Automated Meteor Observatory’s (CAMO) mirror tracking system. The system tracks meteors to magnitude +7.5 through an image-intensified telescopic system which has a spatial accuracy of ∼1m and a temporal resolution of 10ms. We analyse 41 meteors from 13 showers with known parent bodies, recorded between 2016 and 2022. We fit a numerical ablation and fragmentation model to our data which models meteoroid fragmentation as erosion into 10µm to 500µm constituent grains and used the observed wake as a hard constraint on the model parameters. We measure average bulk meteoroid densities which are consistent with in situ measurements: 602 ±155kgm−3 for Jupiter-family and 345 ±48kgm−3 for Halley-type showers. The Geminids had the highest measured bulk density of 1387 ±240kgm−3, consistent with carbonaceous material. We fail to reproduce the high bulk density (>3000kgm−3) for Jupiter-family meteoroids previously reported in the literature derived using fragmentation models on data sets with fewer observational constraints. We also provide estimates of the meteoroid grain sizes, grain mass distributions, and energy necessary to trigger the erosion for meteoroids in the analysed showers.

On the question of constructing the distribution of the flux density of meteoroids over the celestial sphere in ground-based single-position radar measurements of meteor activity and velocity: The experience of past years

The construction of the distribution of the flux density of meteor bodies over the celestial sphere is necessary for solving problems of meteor astronomy and others. To construct such distributions, experimental data on the coordinates of meteor radiants are needed. Meteor radars provide determination of the coordinates of the radiant in the presence of one transmitter and three spaced receivers. In this research, we are talking about ground-based meteor observations of the number of meteors using single-station meteor back-skatter radars as simpler than measurements of meteor radiants. In the 1950–80s in Kharkiv (Ukraine), active meteor radar research was carried out, both simple single-station and complex with remote points. The authors in the 1980s were participants in the meteor international program GLOBMET (Kashcheev, 1982; Roper, 1990). At that time, they modified an algorithm for calculating the flux density of meteor bodies over the heliocentric celestial sphere by number, range and velocity for radar observations with using single-station meteor backscatter. An algorithm was developed for dividing the celestial sphere into regions with a combination of “celestial” and “antenna” regions with a binding of a meteor to the antenna region in radar observations with a narrowly directed antenna without goniometr. This algorithm was applied to specific equipment for measuring the number of meteors by the Kharkiv Meteor Automated Radar System (MARS), 31.1 MHz. The correctness of the algorithm was confirmed by constructing the density distribution of the incident flux over the celestial sphere based on measurements in October-December 1989. The distributions are constructed using two methods for approximating the amplitude-time characteristics of signals. The results represent the experience of past years, which may be of interest as a scientific and technical solution.

Абляция мелких метеорных тел: сравнение модели сплошного и пористого тела

An ablation model is used to describe the interaction of small meteoroids with the Earth’s atmosphere. In this model, the mass loss of a meteoroid is determined using the saturated vapor pressure of the assumed meteoroid substance. The meteoroid is considered in two modifications as a solid and a porous object. An automated method for estimating the parameters of meteoroids (mass, size, and density) from light curves is developed based on the model of small meteor body ablation, which has been used to estimate the parameters of the Perseid meteors with a brightness of -2m to +2m. The effect of the dependence for saturated vapor pressure and the residual on the parameters of the meteoric body is analyzed. It is shown that for the same meteor, the use of different dependences for pressure or different residuals leads to the dispersion of the meteor mass estimate of not more than 10-15% of the average value, and for the meteor size not more than 35-40%. The difference between the maximum and minimum density estimates can be up to five times. The selected dependence for the saturation vapor pressure strongly affects the shape of the light curve, the quality of its approximation, and the density estimate. The average porosity for all meteoroids is 86±5%, which is close to the values for IDP. The density of meteoroids is determined with a large error. The selected model better describes meteoroids with the degree of skewness of the light curve in the range of 0.4 - 0.5. The use of the porous body model has little effect on the mass estimate, while the density estimates increase by up to 2 times.

Velocity and distribution velocity of meteoroids and space debris in near-earth space

The problems of assessing a risk of damaging a spacecraft by meteoroids and space debris are fairly important. The probability of not damaging a SC depends on the properties of its structural elements, particle flux density and velocity of hypervelocity meteoroids and/or space debris. This article offers an analytical review of papers (primarily foreign ones) assessing velocity of meteoroids based on the experimental evidence. Stated are general requirements for experimental data acceptable for acquiring reliable meteoroid velocity data. Compared are meteoroid velocity values obtained from different models, including the data presented in the current national domestic standards. Based on the analysis of experimental data accumulated so far, the most probable values of meteoroid and space debris velocities to be used in ballistic limit equations have been proposed. Key words: meteoroid, space debris, spacecraft shielding against meteoroids, meteoroid environment, meteoroid flux density and velocity.

Meteorite hazard model for a space mission to Mars

Currently, for the world’s space agencies, the robotic exploration of Mars is one of the most important tasks. One of the necessary stages for the implementation of this mission is the development and addition of new information to the State standard “Meteoric substance, spatial distribution model”. Until now, the State Standard has been more detailed in comparison with the American analogue (developed by NASA) and the European one. The standard is a mandatory document in the design of spacecraft. It should be noted that modeling of meteor hazard at a distance from Earth to Mars is a complex problem, since the analysis of the meteor population in near-Earth space does not give a complete picture of the propagation of meteoroids along the Earth-Mars route. Moreover, the further the trajectory of the spacecraft from the Earth’s orbit is, the less the number of near-Earth meteorites becomes. That is, objects that have the same orbital parameters with small bodies crossing the Earth’s orbit. The only way to solve this problem is to build an interpolation regression model, which is based on measurements from the Earth’s surface and observations of space missions. For this purpose, the density of sporadic meteoroids was transformed from the space mission coordinate system to the ground one. This was done in order to analyze meteorite observations by the Mariner 4 and Pioneer 10 spacecrafts. The results of the work made it possible to obtain new data for the spatial distribution of meteoroids on the Earth-Mars path. According to a comparison of our data with the data on the density of space debris in the previous works the most safe for space flights are normalization conditions of distributions of the elements of the orbits of meteoric bodies P(Z, e, i) < 60.

Energy signature of ton TNT-class impacts: analysis of the 2018 December 22 fireball over Western Pyrenees

ABSTRACT 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.

Dual frequency measurements of meteor head echoes simultaneously detected with the MAARSY and EISCAT radar systems

We present dual frequency measurements of common meteor head echoes, conducted with the VHF radar MAARSY (53.5 MHz) and the UHF EISCAT (930 MHz) radar located in Northern Norway. With temporal resolutions of 1ms, we find most head echoes show a continuous increase/decrease in radar cross section (RCS) with time at both frequencies. In some cases a sudden drop of several dBsm is detected by both radars, which we interpret as direct evidence for gross fragmentation. The mean difference of the RCS between both frequencies is about 17 dBsm at an average altitude of 100 km. We find a clear positive correlation between both RCS’s as well as a trend of RCS increasing with altitude, as expected (Close et al. 2002b). We were not able to find physically allowable fits to our dual frequency measurements for plasma radial distributions following either a 1r or 1r2 fall-off around the ablating meteoroid (Marshall et al. 2017). Assuming an overdense Gaussian plasma distribution, we estimated our typical meteoroid masses as ≈100 micrograms and a mean meteoroid density of ∼600kgm3. Two other plasma distribution functions (exponential and parabolic exponential) lead to slightly larger meteoroid densities of about ∼800kgm3. All of our meteor head echoes followed cometary-type orbits prior to Earth impact.

Modeling meteoroid densities for spacecraft risk assessment

This report describes the methodologies and algorithms that NASA’s Meteoroid Environment Office (MEO) currently utilizes to measure meteoroid densities. We discuss the needs for an accurate model for the meteoroid density distribution in its Meteoroid Engineering Model (MEM), and its potential implications for spacecraft design. The recently developed process is heavily derived from that of previous work [4], although subtle differences exist. A thorough comparison of the best-fit densities derived for sixty meteoroids in [4] and with the process described here shows that discrepancies in final densities larger than a factor of two are measured for ~ 20% of our test events. Such a level of discrepancy suggests that any density calculated using similar methods cannot be assumed to represent a unique fit to the data. Additional observational data for meteoroids beyond those utilized in this work will be essential for producing more reliable and repeatable density measurements.

Dynamical and physical features of Perseid meteoroids from Tajikistan fireball network observations

ABSTRACTWe present the results of a study of the dynamical and physical properties of large-sized Perseid meteoroids based on optical observations. Photographic observations of the Perseid meteor shower were carried out during the maximum of its activity in 2007–2011 using the Tajikistan fireball network. Multistation images of 29 Perseids recorded during this period were processed. The atmospheric trajectories, velocities, radiants, orbits, photometric masses and densities of the meteoroids were determined using the astrometric and photometric reduction of fireball images. The initial masses of meteoroids that produced fireballs range from several to 20 g. The observed light-curves of the Perseids and the mean bulk density of most meteoroids of ~0.4 g cm−3 are typical for cometary matter. According to the radiants, velocities and orbits, the captured Perseids are related both to the annual component of the stream and to the dust trail ejected by the parent comet 109P/Swift–Tuttle during its last perihelion passage in 1992.

Interplanetary Dust, Meteoroids, Meteors and Meteorites

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.

Physical properties of the meteoroids using simultaneous radar and optical observations

The calculation results of photographic and radar meteoroid mass of simultaneous radio - TV and radio-photographic observations of meteors in 1977–1980 in Hissar Astronomical Observatory of the Institute of Astrophysics, Academy of Sciences of Tajikistan. The analyses' results of the shape of light curves of meteors within the theory of evaporation and the theory of the quasi-continuous fragmentation are presented.The photographic meteoroid mass from the light curve were defined: a) by the value of maximum luminous intensity at a height hm and b) by the integration light curve. Based on analysis of the data of the photographic mass were obtained correction factor that takes into account the effect of fragmentation and other factors to determine the mass of meteoroids first method. Average value of the mass of meteoroids calculated from the light curve for meteors with magnitude M ≤ 1 is 19∗10−3g, and the average value of the mass found on magnitude of the luminous intensity at the height the maximum brightness consist 18.2∗10−3g, that is in satisfactory agreement between. Masses of the meteoroids was calculated also radio method by value of maximum linear electron density at the height of maximum ionization.In the framework of the classical theory and the theory quasi-continuous fragmentation, we analyzed the shape of the light curves of simultaneous radio - optical meteors. It is shown that the main mechanism of ablation approximately 60% of simultaneous radio - optical meteors is a quasi-continuous fragmentation. The bulk density and porosity of showers and sporadic meteoroids were determined. Found that the Geminids meteoroids and S.δ-Aquariids have the largest bulk densities (δ0=3.6g/cm3), and have not porosity (K = 0). A meteoroids of the showers Orionids and Leonids have the lowest bulk density (δ0≤0.6g/cm3), and the highest value of the porosity (60≤K≤80%). The mass fragments of shower and sporadic meteoroids lie in the range of 5∗10−8÷10−5g.

A Monte Carlo-type simulation toolbox for Solar System small body dynamics: Application to the October Draconids

We present the current status and first results from a Monte Carlo-type simulation toolbox for Solar System small body dynamics. We also present fundamental methods for evaluating the results of this type of simulations using convergence criteria. The calculations consider a body in the Solar System with a mass loss mechanism that generates smaller particles. In our application the body, or parent body, is a comet and the mass loss mechanism is a sublimation process. In order to study mass propagation from parent bodies to Earth, we use the toolbox to sample the uncertainty distributions of relevant comet parameters and to find the resulting Earth influx distributions. The initial distributions considered represent orbital elements, sublimation distance, cometary and meteoroid densities, comet and meteoroid sizes and cometary surface activity. Simulations include perturbations from all major planets, radiation pressure and the Poynting-Robertson effect. In this paper we present the results of an initial software validation performed by producing synthetic versions of the 1933, 1946, 2011 and 2012 October Draconids meteor outbursts and comparing them with observational data and previous models. The synthetic meteor showers were generated by ejecting and propagating material from the recognized parent body of the October Draconids; the comet 21P/Giacobini-Zinner. Material was ejected during 17 perihelion passages between 1866 and 1972. Each perihelion passage was sampled with 50 clones of the parent body, all producing meteoroid streams. The clones were drawn from a multidimensional Gaussian distribution on the orbital elements, with distribution variances proportional to observational uncertainties. In the simulations, each clone ejected 8000 particles. Each particle was assigned an individual weight proportional to the mass loss it represented. This generated a total of 6.7 million test particles, out of which 43 thousand entered the Earth's Hill sphere during 1900–2020 and were considered encounters. The simulation reproduces the predictions and observations of the 1933, 1946, 2011 and 2012 October Draconids, including the unexpected but measured deviation of the meteoroid mass index from a power law in 2012 as compared to 2011. We show that when convergence is sufficient in the simulation, the fraction between two encountered mass distributions is independent of the assumed input mass distribution. Finally, we predict an outburst for the 2018 October Draconids with a peak on October 8–9 that could be up to twice as large as the 2011 and 2012 outbursts.

Bulk density of small meteoroids

Aims. Here we report on precise metric and photometric observations of 107 optical meteors, which were simultaneously recorded at multiple stations using three different intensified video camera systems. The purpose is to estimate bulk meteoroid density, link small meteoroids to their parent bodies based on dynamical and physical density values expected for different small body populations, to better understand and explain the dynamical evolution of meteoroids after release from their parent bodies. Methods. The video systems used had image sizes ranging from 640 × 480 to 1360 × 1036 pixels, with pixel scales from 0.01 ◦ per pixel to 0.05 ◦ per pixel, and limiting meteor magnitudes ranging from Mv =+ 2.5 to +6.0. We find that 78% of our sample show noticeable deceleration, allowing more robust constraints to be placed on density estimates. The density of each meteoroid is estimated by simultaneously fitting the observed deceleration and lightcurve using a model based on thermal fragmentation, conservation of energy and momentum. The entire phase space of the model free parameters is explored for each event to find ranges of parameters which fit the observations within the measurement uncertainty. Results. (a) We have analysed our data by first associating each of our events with one of the five meteoroid classes. The average density of meteoroids whose orbits are asteroidal and chondritic (AC) is 4200 kg m −3 suggesting an asteroidal parentage, possibly related to the high-iron content population. Meteoroids with orbits belonging to Jupiter family comets (JFCs) have an average density of 3100 ± 300 kg m −3 . This high density is found for all meteoroids with JFC-like orbits and supports the notion that the refractory material reported from the Stardust measurements of 81P/Wild 2 dust is common among the broader JFC population. This high density is also the average bulk density for the 4 meteoroids with orbits belonging to the Ecliptic shower-type class (ES) also related to JFCs. Both categories we suggest are chondritic based on their high bulk density. Meteoroids of HT (Halley type) orbits have a minimum bulk density value of 360 +400 −900 kg m −3 . This is consistent with many previous works which suggest bulk cometary meteoroid density is low. SA (Sun-approaching)-type meteoroids show a density spread from 1000 kg m −3 to 4000 kg m −3 , reflecting multiple origins. (b) We found two different meteor showers in our sample: Perseids (10 meteoroids, ∼11% of our sample) with an average bulk density of 620 kg m −3 and Northern Iota Aquariids (4 meteoroids) with an average bulk density of 3200 kg m −3 , consistent with the notion that the NIA derive from 2P/Encke.

Physical characteristics of very small meteoroids

We have optically recorded faint meteors using a large aperture LLLTV (low light level television) system based on second generation image intensifiers. These data consist of 42 two-station meteors of which 13 were captured during an observing campaign near London, Ontario (Canada) in May 2004, and 29 during a campaign near Kiruna (Sweden) in October 2007. Among 13 meteors recorded in the London campaign, where the baseline between the two sites was 5 km, only four meteors satisfied our requirement for complete lightcurves and deceleration profiles by starting in the field of view, of at least one station and also ending in the field of view of at least one station. From the second set of 29 meteors captured in Sweden, with a baseline of 117.7 km, only two satisfied these criteria. The cameras used in both campaigns had fields of view of 6 degrees, which with an assumed range of 100 km, gives a scale of 13 m/pixel at ∼60 interlaced fields per second. This resolution allows precise measurement of the deceleration of very faint meteors. The limiting magnitude for meteors on these systems is near V =+ 8, while +11th magnitude stars are visible in the individual fields. The meteors detected in these two campaigns have peak brightnesses between absolute magnitude +6.2 and +7.4. Their photometric masses range from 4.2 mg to 0.35 mg. An ablation model was applied to fit each complete two-station event using the high-precision metric and photometric data as a constraint, in an attempt to compute bulk meteoroid densities. Interestingly, a large proportion of our faint meteor events were found to ablate at low altitudes, a result partly of our observing biases. The orbits of these events are consistent with either asteroidal or a Jupiter-family comet origin. The meteoroids’ physical properties, as determined through model fits, suggest high densities, which favors an asteroidal interpretation. The high percentage of apparently dense asteroidal meteoroids at these small sizes may call into question earlier findings that only ∼1% of meteoroids at these masses are asteroidal in origin. Our results are similar to others that find ∼15% of faint TV meteors had spectra consistent with pure iron meteoroids. We find that many of these apparently asteroidal objects also undergo extensive fragmentation, which may reflect melting and spraying of droplets rather than mechanical fragmentation. Some individual cases in our small dataset will be highlighted where high bulk densities (approaching that of iron) are required to adequately match the end height, peak brightness, and observed deceleration. We speculate that these meteoroids may represent metallic condensates from impact-processed asteroid regolith.

Validity of the photometric formula for estimating the mass of a fireball projectile

The extraterrestrial mass of a meteoroid is conventionally determined using a photometric formula, by integrating the brightness along the entire luminous segment of the trajectory. The extraterrestrial mass can also be estimated using the altitude and rate of meteor deceleration in the atmosphere. The discrepancy of the estimates obtained using these two techniques is usually diminished by selecting “appropriate” values of the meteoroid density. However, this leads to obviously underestimated values of ~0.25 g/cm 3 for this density [1, 2]. In order to eliminate these discrepancies, it was proposed to consider a swarm of similar-size fragments instead of a single meteoroid. In this case, it is the photometric-to-dynamic mass ratio that determines the number of such fragments [3, 4]. In the present paper, the extraterrestrial mass is calculated using the data of actual observations, by selecting the parameters describing deceleration and ablation of meteoroids along the luminous segment of the trajectory. The model is based on the best fitting of the observational data by an analytical solution of the equations of meteor physics. Cases will be presented where the discrepancy between the dynamic and photometric estimates cannot be explained by the above-mentioned reasons. In particular, large fireballs with dynamic masses exceeding the photometric mass by more than an order of magnitude were observed. Photometric observations are conventionally processed within the framework of the commonly accepted assumption that a certain fraction of the kinetic-energy losses of a meteoroid is converted into its brightness, I τ ˜ dM V 2 /2

Geminid Meteor shower activity 2003–2005 as observed by Gadanki radar

The distribution of meteor signals reflected from a backscatter radar is considered according to their duration. This duration time ( T) is used to classify the meteor echoes and to calculate the mass index ( S) of different meteoroids of shower plus sporadic background. Observational data on particle size distribution of the Geminid meteor shower are very scarce, particularly at low latitudes. In this paper the observational data from Gadanki radar (13.46°N, 79.18°E) have been used to determine the particle size distribution and the number density of meteoroids inside the stream of the Geminid meteor shower. The mean variation of meteor number density across the stream has been determined for three echo duration classes, T<0.4, T=0.4–1 and T>1 s. We are more interested in the appearance of echoes of various durations and therefore meteors of various masses in order to understand more on the filamentary structure of the stream. It is observed that the faint particle flux peaks earlier than the larger particles. We found a decreasing trend in the mass index values from the day of peak activity to the next observation days. The mass index profile was found to be U-shaped with a minimum value near the time of peak activity. The observed minimum s values are 1.64±0.05 and 1.65±0.04 in the years 2003 and 2005, respectively. The activity of the shower indicates the mass segregation of meteoroids inside the stream. Our results are best comparable with the “scissors” structure model of the meteoroid stream formation of Ryabova [2007. Mathematical modeling of the Geminid meteoroid stream. Mon. Not. R. Astron. Soc. 375, 1371–1380] by considering the asteroid 3200 Phaethon as an extinct comet.

Radar Observations of Leonid Meteor Shower 2003

Observations carried out during Leonid meteor shower 2003, by using Indian MST radar (13.46^N, 79.18^E; dip 12.5^N) are used to determine the number density of meteoroids through the cross section of the meteor streams. Cross sections are calculated for a number of classes of echo duration (particle size). They are also used to determine the relative flux of the shower in particle size ranges producing radar meteor echoes having durations 1 s. Mean activity profiles along the Earth's passage through the stream show a systematic change of the peak activity and the width of the stream depending on the distribution of echo durations across the stream. The patterns of mass distribution index s are presented and discussed.

Meteoroid Bulk Density Determination Using Radar Head Echo Observations

We present the results of a study of meteoroid bulk densities determined from meteor head echoes observed by radar. Meteor observations were made using the Advanced Research Projects Agency Long-Range Tracking And Instrumentation Radar (ALTAIR). ALTAIR is particularly well suited to the detection of meteor head echoes, being capable of detecting upwards of 1000 meteor head echoes per hour. Data were collected for 19 beam pointings and are comprised of approximately 70 min. of VHF observations. During these observations the ALTAIR beam was directed largely at the north apex sporadic source. Densities are calculated using the classical physical theory of meteors. Meteoroid masses are determined by applying a full wave scattering theory to the observed radar cross-section. Observed meteoroids are predominantly in the 10−10 to 10−6 kg mass range. We find that the vast majority of meteoroid densities are consistent with low density, highly porous objects as would be expected from cometary sources. The median calculated bulk density was found to be 900 kg/m3. The orbital distribution of this population of meteoroids was found to be highly inclined.