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The successful application of modern observing techniques for Leonid storm observations show that meteor (shower) detections will have a bright future if the field will pursue difficult but important questions. How to forecast a satellite threatening meteor storm? What happens to the organic matter in meteors and can this be an important source of prebiotic molecules? What range of variations in composition and morphology exists among cometary grains and what does this tell us about the origin of the solar system? What long-period comets approach Earth orbit and can meteoroid streams provide early warning for giant impacts? What are the sources of interstellar and interplanetary grains? Just to mention a few. To answer these questions will need new technologies and facilities, some of which are being developed for other use. This may include NASA’s Stratospheric Observatory For Infrared and sub-millimeter Astronomy (SOFIA). In addition, big-science space missions can drive the field if meteor detections are an integral part. Special events, such as meteor outbursts and the “artificial meteor” from the reentry of sample return capsules from interplanetary space, can mobilize observing and theoretical efforts. These and other future opportunities are briefly discussed. [ABSTRACT FROM AUTHOR]

The Canadian Meteor Orbit Radar (CMOR) is used to look at the distribution of meteoroids which encounter the Earth. As a single-station operation, it is capable of determining radiant distributions on a statistical basis and the position and speed of individual meteors. The addition of two outlying receiving stations allows the determination of the orientation in space of the meteor leading to an estimate of the orbital parameters of the individual meteor and an independent additional estimate of its speed. Comparison is made of the effectiveness of the two modes of operation using observations on the Geminid and Sextantid meteor streams. [ABSTRACT FROM AUTHOR]

The recent systematic monitoring of the skies has led to the discovery of an increasingly large number of objects on Earth approaching orbits. Not surprisingly, an increasing number of this population have also been associated with meteoroid streams in the literature. We will review the history of this topic. We have also conducted our own search for asteroids moving on orbits that are similar to the orbits of known fireball streams. As NEOs are moving in prograde orbits with low geocentric velocities, any potential streams will have large radiant areas and in consequence, may have been identified as several “sub-streams”. This greatly hampers both their detection and their recognition as single meteoroid streams. With the large number of Near Earth Asteroids detected, the probability of two orbits being similar at the present time by coincidence is high. We have therefore also investigated the evolution of the orbits and only include as real asteroid-stream pairs those where the evolution is also similar over 5000 years. We have identified nine pairs, including the well known pair of the Geminid meteoroid stream and asteroid 3200 Phaethon. Currently there are a number of papers being published on the pairing of asteroid 2003 EH1 and the Quadrantid meteoroid stream. Because of the newness of the research and the fact that this is a high inclination pair, we have excluded this pair from our discussions. [ABSTRACT FROM AUTHOR]

The theoretical model of a range distribution of overdense radar echoes together with its application to two day-time showers of the Taurid complex is presented. This model provides us with possibility of the estimate of four parameters connected with an the structure of meteor showers and physical features of meteoroids. These are: the mass-distribution index, the shower flux density, the ionization probability and the product of the shape-density parameter and the ablation coefficient. We publish here their values computed from radar data recorded during observations of ζ Perseids and β Taurids in 2003. [ABSTRACT FROM AUTHOR]

Results of Ondřejov radar observation of Taurid complex meteor showers, i.e. ζ Perseids, β Taurids, S and N Taurids, performed in 2003, are presented. We have found some mass segregation within ζ Perseid, β Taurid and S Taurid showers. We have also established conspicuous lack of long duration echoes (with T ≥ 3 s resp. T ≥ 5 s) in S and N Taurid showers. The lack within remaining showers is not so pronounced but still persists. [ABSTRACT FROM AUTHOR]

At altitudes above 93 km in the atmosphere, magnetic and electric fields can affect the modes and rates of non-turbulent diffusion of ionized meteor trails. Anisotropic diffusion is expected. Most theories of anisotropic diffusion, and indeed most experimental studies, have concentrated on the effects of the magnetic field in producing this anisotropy, and different rates of expansion are expected in directions parallel to and perpendicular to the magnetic field lines. In this study, we use interferometric meteor radars to investigate the dependence of the ambipolar diffusion coefficient on viewing direction relative to the magnetic field, and show that the dependence is at best weak when daily averages are used. We then demonstrate that the reason for this effect is that the positions of maximum and minimum diffusion rates varies as a function of time of day, and that daily averaging masks the anisotropy. One possibility to account for the observations is that this strong diurnal variation is a consequence of the electric fields in the upper atmosphere, which are often tidally driven. An alternative possibility is a diurnal cycle in mean meteor entrance speeds. We lean towards the first hypothesis, but both possibilities are discussed. We demonstrate our results with data from several sites, but particularly using the Clovar radar near London, Ontario, Canada. [ABSTRACT FROM AUTHOR]

Experimental and theoretical work on the transverse dimensions of meteoric plasma trains have not converged to provide generally accepted values: especially uncertain is the dependence of the train radii on meteor speeds. The roles of the meteoroid structure, fragmentation and plasma processes such as ion-electron instabilities need establishing. Knowledge of the quantitative spatial distribution of plasma in meteor trains is essential for a correct interpretation of fluxes and orbital characteristics. A current project is described which employs the AMOR 26 MHz radar facility in conjunction with a frequency managed radar operating at longer wavelengths designed to measure the ionization train radii, heights, atmospheric speeds and orbits of individual meteors. [ABSTRACT FROM AUTHOR]

Fragmentation of an ablating meteoroid is a process that depends on the physical constitution of the body and the internal structure. These parameters are thought to control temperature gradients within the body. Phase signatures from the University of Canterbury’s AMOR facility are shown to be able to resolve instances in which meteors are subject to gross macro-fragmentation where the meteoroid body disrupts into a few discrete components. [ABSTRACT FROM AUTHOR]

Measurements of meteoroid velocities and decelerations have been obtained from post-t0 diffraction patterns present in echo signatures obtained from the multi-site AMOR radar operated at the University of Canterbury’s research facility. The system allows the sampling of a meteoroid’s velocity at separated points along the body’s trajectory to yield decelerations. The technique has potential value in providing data on the relation between trajectory behaviour, drag characteristics, the physical structure of meteoroids and stream membership or orbit type. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present observations and preliminary results from a meteor experiment carried out with the 224 MHz EISCAT VHF radar in Tromsø, Norway, which was run for 6 h on November 26, 2003. The data set contains echoes with peculiar pulsations in received power in the frequency range 20–200 Hz, limited by instrumental parameters. The process causing the echo power pulsations has not yet been identified. Plasma effects are the most likely cause, a possible mechanism is for instance asymmetrical dust grains in rotation causing a modulation of the ionization rate. [ABSTRACT FROM AUTHOR]

High Power Large Aperture (HPLA) radars generally observe very high meteor velocities averaging over 50 km s−1. There are only a few events recorded around 30 km s−1, while meteors at 20 km s−1 or slower are very rare. This is a clear and debated contradiction to specular meteor radar results. A high plasma density condition contributes, but the dominating phenomenon is the hyperthermal ionization mechanism due to chemical dynamics of the ionization process. The observed high velocities can be explained in terms of high hyperthermal ionization cross-sections for collisions between ablated meteoroid metal atoms such as Na and/or Fe and atmospheric species. [ABSTRACT FROM AUTHOR]

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

We compare the results from the application of four different methods to determine the speed of meteoroids from single station radar data. The methods used are the pre-t0 amplitude, post-t0 amplitude, pre-t0 phase and the Fresnel transform (FT) methods. Speeds from the first three methods are compared to the FT method since, requiring the use of the entire records of both the amplitude and phase data, this method is the most accurate of the four. [ABSTRACT FROM AUTHOR]

We have carried out multi-station TV observations since 1994 in order to determine the orbit of the Arietid daytime meteor stream. In 1999, one possible Arietid meteor was recorded by our simultaneous observations and its orbit was determined. In 2003, two Arietid meteors were observed from two stations of our observing site, those orbits were determined precisely, the orbital elements were in good agreement with each other. This is the first time that determination of the precise orbit of the Arietids has been made from optical observations. The orbit of these Arietid meteors, and comparison with the orbit obtained from radar observations are discussed. [ABSTRACT FROM AUTHOR]

A digital image intensified CCD camera with an electronically gated image intensifier was used to produce very short duration images of meteors. The observational system employed a 0.40 m F/4.5 Newtonian telescope to obtain high spatial resolution. A second intensified CCD camera was used to yield height information using parallax. At a typical meteor height one pixel (for the vertically oriented system) corresponded to about 1.1 m. A sampling of 59 mainly sporadic meteors was analyzed. There is clear variability from meteor to meteor, with many meteors (nearly 50%) showing only a small amount of wake, while some meteors (approximately 20%) have the off segments completely filled in. [ABSTRACT FROM AUTHOR]

We report results from two station, short-baseline (<100 m) high resolution measurements of faint meteors (limiting meteor magnitude +9) with the goal of measuring their optical trail widths. Meteors were observed using two 0.40 m Newtonian telescopes (field of view ∼0.4 degrees) equipped with image intensifiers. Both telescopes were vertically oriented in a fixed mount and pointed to the same field of view. One system used a gated image intensified camera allowing the transverse velocity component to be measured. The widest trail captured, out of a total of 34 common events measured by both optical systems, had a full-width to half-maximum of 1.37±0.71 m. The widest trail overall was captured by the gated system only, and was found to have a full-width of ∼10 m. The brightness variation across this trail was found to be best represented by a Lorentzian. Most trails were smaller than our resolution limit and hence we could only place upper limits on their optical width. These were generally less than 1 m after correction for instrumental effects. Four meteors were found to have heights near 65 km and very low transverse velocities. These may be indicative of a largely unreported high density asteroidal component at these faint meteor magnitudes. [ABSTRACT FROM AUTHOR]

We present detailed data on 8 bright meteors recorded simultaneously by different observational techniques. All meteors were recorded by all-sky cameras at the Czech stations of the European Fireball Network and by image intensified TV cameras placed at Ondrejov and Kunzak observatories. As well as direct photographic and LLLTV recordings, most of meteors were recorded also by the spectral TV camera and some also by photographic spectral cameras. For 6 cases, lightcurves from radiometers with very high time resolution (1200 s−1) are also available. From all these detections we found a significant difference between TV and photographic beginning heights. TV beginnings are in average about 40 km higher than the photographic ones. We found that meteor brightness is up to 2 magnitudes higher in the photographic system than in the TV system. This difference for high velocity meteors is mainly caused by the presence of strong Ca+ lines in the blue part of the spectrum, where the image intensifier is only marginally sensitive. At heights above 110 km, the Na line is usually brighter than the Mg line, while at lower heights both lines have comparable brightness. In one of two captured spectra of short duration luminous trains, a small initial brightening of the Mg and Na lines caused by recombination processes was observed. [ABSTRACT FROM AUTHOR]

We have developed an all-sky charge coupled devices (CCD) automatic system for detecting meteors and fireballs that will be operative in four stations in Spain during 2005. The cameras were developed following the BOOTES-1 prototype installed at the El Arenosillo Observatory in 2002, which is based on a CCD detector of 4096 × 4096 pixels with a fish-eye lens that provides an all-sky image with enough resolution to make accurate astrometric measurements. Since late 2004, a couple of cameras at two of the four stations operate for 30 s in alternate exposures, allowing 100% time coverage. The stellar limiting magnitude of the images is +10 in the zenith, and +8 below ∼65° of zenithal angle. As a result, the images provide enough comparison stars to make astrometric measurements of faint meteors and fireballs with an accuracy of ∼2 arcminutes. Using this prototype, four automatic all-sky CCD stations have been developed, two in Andalusia and two in the Valencian Community, to start full operation of the Spanish Fireball Network. In addition to all-sky coverage, we are developing a fireball spectroscopy program using medium field lenses with additional CCD cameras. Here we present the first images obtained from the El Arenosillo and La Mayora stations in Andalusia during their first months of activity. The detection of the Jan 27, 2003 superbolide of −17 ± 1 absolute magnitude that overflew Algeria and Morocco is an example of the detection capability of our prototype. [ABSTRACT FROM AUTHOR]

The recent development and data collection results of the Astrobiology Instrumentation for Meteor Imaging and Tracking (AIM-IT) system, has demonstrated an ability to point narrow field-of-view instruments at transient events such as meteors. AIM-IT uses the principle of tracking moving objects via a paired set of relay mirrors along with an integrated hardware/software solution, to acquire and track meteors in real-time. Development of the instrument has progressed from a prototype rocker-box system through more recent use of a fast response mirror system during several meteor shower campaigns. Several narrow field of view instruments have been deployed using AIM-IT including high spatial resolution video, high frame rate video, and meteor spectrographic equipment. Analysis of the imagery shows evidence for meteor fragmentation in as many as 20% of the meteors tracked thus far. The success of the AIM-IT technology in tracking meteors during their luminous flight provides a new tool in enhancing the capabilities and data volume that can be obtained with existing narrow field of view instruments. [ABSTRACT FROM AUTHOR]

Meteor44 is a software system developed at MSFC for the calibration and analysis of video meteor data. The photometric range of the (8 bit) video data is extended from a visual magnitude range of from 8 to 3 to from 8 to −8 for both meteors and stellar images using saturation compensation. Camera and lens specific saturation compensation coefficients are derived from artificial variable star laboratory measurements. Saturation compensation significantly increases the number of meteors with measured intensity and improves the estimation of meteoroid mass distribution. Astrometry is automated to determine each image’s plate coefficient using appropriate star catalogs. The images are simultaneously intensity calibrated from the contained stars to determine the photon sensitivity and the saturation level referenced above the atmosphere. The camera’s spectral response is used to compensate for stellar color index and typical meteor spectra in order to report meteor light curves in traditional visual magnitude units. Recent efforts include improved camera calibration procedures and long focal length “treak” meteor photometry. Meteor44 has been used to analyze data from the 2001, 2002 and 2003 MSFC Leonid observational campaigns as well as several lesser showers. [ABSTRACT FROM AUTHOR]

Optical observations remain the most widely used method for studying meteors, even though they are limited by daylight and weather conditions. Visual observations have been used throughout history. They lack the precision of other methods, since they rely on the judgment of observers for trajectory information. However, since no special equipment is required, visual observations are widespread, and can give valuable information on the activity profile of showers. Photographic observations are much more precise. Rotating shutters allow velocities to be determined, and networks of cameras permit the height and trajectory of a meteor to be calculated. Except for the Super-Schmidt observations at Harvard, most photographic observations record only meteors brighter than 0 magnitude. Video observations, using image intensifiers, can record much fainter meteors down to +7 magnitude. Processing is becoming very automated, so that large quantities of data can be reduced relatively easily. Most video cameras have much lower precision than photographic cameras, but new technologies are changing this. Spectral observations of meteors, using video or photographic techniques, can be used to investigate the chemistry of meteoroids, while telescopic observations allow measurements to be extended to much fainter meteors (+10 or fainter). [ABSTRACT FROM AUTHOR]

The phenomenon of terminal thermal explosions of bolides is considered and mathematically modeled, using the mechanisms of ablation and fragmentation due to mechanical and thermal stresses. The definition and criterion of thermal explosions are given. An analytical solution is obtained for the model of ablating and mechanically fragmenting meteoroid motion in the atmosphere. Numerical calculations including the terminal stage of the motion are fulfilled for the Tunguska parameters. They demonstrated a very rapid energy loss, corresponding to the terminal flare and full mass loss, explaining the absence meteorites. [ABSTRACT FROM AUTHOR]

The acoustic amplitude-yield relationships, including formal errors, for a population of energetic (>0.05 kt) and well-observed bolide events have been investigated. Using various infrasonic signal measurements as a function of range, these data have been calibrated against optical yield estimates from satellite measurements. Correction for the presence of stratospheric winds has also been applied to the observations and is found to be small, suggesting that either scatter is dominated by other variations amongst the fireball population such as differing burst altitudes and greater or lesser amounts of fragmentation or the magnitude of the variability in the stratospheric winds, which can be comparable to or even exceed the strength of the winds themselves. Comparison to similar point source, ground-level nuclear and high explosive airwave data shows that bolide infrasound is consistently lower in amplitude. This downward shift relative to nuclear and HE data is interpreted as due in part to increased weak non-linearity during signal propagation from higher altitudes. This is a likely explanation, since mean estimates of the altitude of maximum energy deposition along the bolide trajectory was found to be between 20 and 30 km altitude for this fireball population. [ABSTRACT FROM AUTHOR]

Sixty fireball cameras operated in Western Canada from 1971 to 1985. Over one thousand (1016) fireballs were recorded at more than one station, but only 367 were reduced, of which 285 have been published, including that of the Innisfree meteorite. Digitization of all the data is underway, and procedures are being developed which will allow the automatic reduction of events not previously examined. The results of the analysis of 80 fireballs reduced but not previously published are presented. When the new analysis is complete, the MORP archive will be a valuable source of information on meteoroid orbits. [ABSTRACT FROM AUTHOR]

We present results on the MFM analysis (Meteor fragmentation model recently proposed by Ceplecha and ReVelle, 2005) of EN270200, a type-I fireball of maximum absolute magnitude −10 from February 27, 2000, 19 h 22 m 57 s UT, based on observational data from four Czech stations of the European Fireball Network equipped with fish-eye cameras. Radiometer record of the light curve with time resolution of 1200 records per second is also available. Two grating spectra point to composition of an ordinary chondrite. Data on height and stellar magnitude were available at 73 individual trajectory points. The standard deviation of our fit was ±28 m for height as function of time and ±0.11 magnitude for the light curve. Ablation coefficient was found to be constant during the entire trajectory (0.004 s2 km−2). The shape-density coefficient varied in a wide range of values (1.65 and 0.12 c.g.s.). We found 17 fragmentation events during the entire photographic light curve, 7 of them larger than 1% of the main body mass. All fragmentation occurred in a form of clusters of tiny fragments. The initial mass resulted as 3.6 ± 0.2 kg at a height of 80.144 km with velocity of 18.790 km s−1, and the terminal mass was 0.27 ± 0.02 kg at a height of 31.62 km with velocity of 6.64 ± 0.12 km s−1. We were able to explain the very short millisecond flare by the MFM model. [ABSTRACT FROM AUTHOR]

In this paper, we will review recent research on numerous aspects of bolide entry into a planetary atmosphere, including such topics as the entry dynamics, energetics, ablation, deceleration, fragmentation, luminosity, mechanical wave generation processes, a total (panchromatic) power budget including differential and integral efficiencies versus time, etc. Fragmentation, triggered by stagnation pressures exceeding the bolide breaking strength, has been subsequently included in either a collective or non-collective wake behavior limit. We have also utilized the differential panchromatic luminous efficiency of ReVelle and Ceplecha (2002) to compute bolide luminosity. In addition we also introduce the concept of the differential and integral acoustic/infrasonic efficiency and generalized it to the case of mechanical wave efficiency including internal atmospheric gravity waves generated during entry. Unlike the other efficiencies which are assumed to be a constant multiple of the luminous efficiency, the acoustic efficiency is calculated independently using a “first principles” approach. All of these topics have been pursued using either a homogeneous or a porous meteoroid model with great success. As a direct result, porosity seems to be a rather good possibility for explaining anomalous meteoroid behavior in the atmosphere. [ABSTRACT FROM AUTHOR]

The conservation of the ablation parameter is one of the main assumptions of the classical physical theory of meteors (PTM). But this value does vary dramatically on meteoroids trajectories for the most part of them. The drag and heat-transfer coefficients in the basic equations of PTM are considered from the gasdynamical point of view and mathematically modeled in the present paper. Analytical approximations of the drag and heat transfer coefficients valid for any flow regimes and separate approximation of the drag coefficient for free-molecule regime are offered and discussed. They use the Reynolds number as the main parameter characterizing flow regimes. The variations of coefficients result in the variation of the ablation parameter by 100% for meteoroids, passing all the flow regimes. The importance of correct calculation of the coefficients for meteoroids motion modeling was demonstrated by the numerical examples. [ABSTRACT FROM AUTHOR]

Based on the number of planet-approaching cometary orbits at Mars and Venus relative to the Earth, there should be ample opportunities for observing meteor activity at those two planets. The ratio of planet-approaching Jupiter family comets (JFCs) at Mars, Earth, and Venus is 4:2:1 indicating that JFC-related outbursts would be more frequent at Mars than the Earth. The relative numbers of planet-approaching Halley-type comets (HTCs) implies that the respective levels of annual meteor activity at those three planets are similar. We identify several instances where near-comet outbursts (Jenniskens, P.: 1995, Astron. Astrophys.295, 206–235) may occur. A possible double outburst of this type at Venus related to 45P/Honda-Mrkos-Padjusakova may be observable by the ESA Venus Express spacecraft in the summer of 2006. Similarly, the Japanese Planet-C Venus orbiter may observe an outburst related to 27P/Crommelin’s perihelion passage in July 2011. Several additional opportunities exist to observe such outbursts at Mars from 2019 to 2026 associated with comets 38P/Stephan-Oterma, 13P/Olbers and 114P/Wiseman-Skiff. [ABSTRACT FROM AUTHOR]

We modeled equilibrium vaporization of chondritic and achondritic materials using the MAGMA code. We calculated both instantaneous and integrated element abundances of Na, Mg, Ca, Al, Fe, Si, Ti, and K in chondritic and achondritic meteors. Our results are qualitatively consistent with observations of meteor spectra. [ABSTRACT FROM AUTHOR]

Conventional ablation theory assumes that a meteoroid undergoes intensive heating during atmospheric flight and surface atoms are liberated through thermal processes. Our research has indicated that physical sputtering could play a significant role in meteoroid mass loss. Using a 4th order Runge-Kutta numerical integration technique, we tabulated the mass loss due to the two ablation mechanisms and computed the fraction of total mass lost due to sputtering. We modeled cometary structure meteoroids with masses ranging from 10−13 to 10−3 kg and velocities ranging from 11.2 to 71 km s−1. Our results indicate that a significant fraction of the mass loss for small, fast meteors is due to sputtering, particularly in the early portion of the light curve. In the past 6 years evidence has emerged for meteor luminosity at heights greater than can be explained by conventional ablation theory. We have applied our sputtering model and find excellent agreement with these observations, and therefore suggest that sputtered material accounts for the new type of radiation found at great heights. [ABSTRACT FROM AUTHOR]