Leonid Meteor Research Articles

Quantitative meteor spectroscopy: Elemental abundances

Procedures are outlined to derive from a meteor spectrum the elemental abundances of its meteoroid, with particular application to observations obtained by an unintensified cooled-CCD slit-less spectrograph. Results are given for two Leonid meteors observed during the 2001 encounter of Earth with dust ejected by comet 55P/Tempel-Tuttle in 1767. The spectra contain air plasma lines of N and O, and meteoric metal atom lines of Fe, Mg, Na, Ca, Si, Mn, Al, and Cr. Excitation conditions are investigated from the relative line intensity of Fe and N + lines. The elemental abundances, normalized to solar system abundances, show a striking correlation with condensation temperature, defined as the temperature at which 50% of elements in a cooling gas mixture with chondritic abundance have condensed into a solid phase. Iron is depleted by a factor of 3, magnesium, calcium, and aluminum by a factor of 8. I conclude that rapid evaporation keeps the mineral surface temperature at ∼1150 K. Much of the refractory elements in these fast 71.6 km/s Leonid meteoroids are deposited in the form of solid meteoric debris rich in Mg, Ca, and Al.

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.

First 0.96–1.46 micron near-IR spectra of meteors

During the 2002 Leonid Multi-Instrument Aircraft Campaign, spectra were obtained of two Leonid meteors in the near-IR wavelength range of an InGaAs camera (0.96–1.46 micron). The spectrum contains atomic oxygen and nitrogen lines that are well-described by a typical warm 4400 K meteoric plasma emitting in local thermodynamic equilibrium, but the First Positive Δ ν = 0 band of N 2 is weaker than expected. A quite bright continuum is also present, with a blackbody temperature of ∼4400 K, much higher than that expected from hot debris. The cause of the continuum blackbody emission is a puzzle, as are several unidentified features.

The beginning heights and light curves of high-altitude meteors

Abstract— In this paper, we provide an overview of meteors with high beginning height. During the recent Leonid meteor storms, as well as within the regular double station video observations of other meteor showers, we recorded 164 meteors with a beginning height above 130 km. We found that beginning heights between 130 and 150 km are quite usual, especially for the Leonid meteor shower. Conversely, meteors with beginning heights above 160 km are very rare even among Leonids. From the meteor light curves, we are able to distinguish two different processes that govern radiation of the meteors at different altitudes. Light curves vary greatly above 130 km and exhibit sudden changes in meteor brightness. Sputtering from the meteoroid surface is the dominating process during this phase of the meteor luminous trajectory. Around 130 km, the process switches to ablation and the light curves become similar to the light curves of standard meteors. The sputtering model was successfully applied to explain the difference in the beginning heights of high-altitude Leonid and Perseid meteors. We show also that this process in connection with high altitude fragmentation could explain the anomalously high beginning heights of several relatively faint meteors.

On the sodium overabundance in cometary meteoroids

Relative chemical abundances and physical properties of cometary meteoroids can be deduced from meteor spectroscopy. The study of moderately volatile elements like Na can provide clues on the structure of cometary particles and processes suffered by these particles. Recent studies of spectra of photographic fireballs (produced by cm-sized meteoroids) suggest that Na is enhanced in a 1.5 factor relative to the chondritic value. The observed features in the ablation of Perseid and Leonid meteoroids suggest that the particle fragmentation behavior of an important part of the large meteoroids fits well with a dustball model where Na would be associated with an interstitial material joining mineral grains. We suggest that aqueous alteration in the parent bodies of these meteoroids can promote chemical redistribution of Na as has been widely observed in carbonaceous chondrites. Then, this element is mobilised towards interstitial fine-grain materials that are joining large mineral grains. These more friable materials (rich in Na) can be ablated preferentially in the first stages of ablation. Finally, we discuss briefly the interest in the development of meteor spectroscopy in UV and IR in order to improve our knowledge of the ablation of volatile and moderately volatile phases of meteoroids.

The origin of the Ca(II) emission, in one of two plasma components, and the metallic abundances in a 2002 Leonid meteor spectrum

Fast-moving meteors such as Leonid meteors have two types of spectra. One is the main component composed of neutral atomic lines having low excitation temperature (∼5000 K) and the other is the hot component composed of singly ionized lines such as Mg(II) and Ca(II) having high excitation temperature (∼10,000 K). We observed the brightest fireball which appeared at, 03 h 47 m 54 s UT of November 19, 2002 in the 2002 Leonid aircraft campaign. The neutral atoms composing the main component such as Mg(I), Fe(I), Ca(I) and Na(I) were identified in the wavelength range of 300–650 nm. The singly ionized atomic emissions of Ca(II) and Mg(II) were also detected in this Leonid spectra during the temporal series of brightness of the fireball flight. So far, these emissions were considered to originate from the hot component. However, we found in several frames taken at the bright fireball during the period of the observation that the Ca(II) lines do not satisfy the hot-component condition even if the hot-component Mg(II) (448 nm) emission was observed. This indicates that the Ca(II) lines do not always satisfy the hot-component condition.

A synthetical index of the potential threats about intense activities of meteors

In the present age, several techniques for the application to the observation of meteors and meteor showers have been developed in modern meteor astronomy. The initial definition for a meteor storm based on the visual observation with a Zenithal Hourly Rate of above 1000 seems insufficient now, since it only means a storm or burst of meteors in numbers and means that an eyewitness could have a chance to see a spectacular meteor show. Up to now, peoples have also recorded the meteoric flashes on the Moon during the Leonid meteor showers. Especially, the increasing activities of mankind in space for scientific, commercial and military purposes, have led to an increase in the problems concerning the safety of the satellites, space stations and astronauts. How the intense activity of a meteor storm is defined and forecast, some new points of view are needed. In this paper, several aspects about the intensity of the meteor storm are analyzed, including the number, mass, impulse, energy, electric charge, different purposes and different physical meanings. Finally, a synthetical index denoting the activity and potential threat of an intense meteor shower is suggested.

Observations of seismic electromagnetic phenomena in VHF band by dual frequency method

AbstractSeismic electromagnetic (EM) phenomena have been observed at many laboratories with specially designed systems. Recently we can utilize radio receivers, personal computers, and communication systems with higher performances and reasonable cost. It is possible to observe seismic EM phenomena not only by specially designed systems but also by a simple observation system integrated by these devices and systems. We have created an observation system for seismic EM phenomena with them in the very high frequency (VHF) band, from 76 MHz to 90 MHz, assigned for FM broadcasting exclusive use in Japan. We are surrounded by many EM waves, such as broadcasting, communication usage, and man‐made noises. Thus, we have newly developed the dual frequency observation method. In this paper, we describe an observation method that can identify whether a received signal is a broadband EM wave or an artificial FM radio wave. Next, the observation results for broadband EM waves from galactic noise and solar flares are presented. Then, the observation results for FM radio waves reflected from sporadic E layer and the Leonid meteors are shown. Finally, the observation results for the detected broadband EM waves associated with the Geiyo earthquake are described. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(4): 36–44, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20350

Metallic Abundances of 2002 Leonid Meteoroids in Two Dust Trails Formed in Different Epochs: No Evidence of Solar Heating Effect

High-definition TV spectra in the ultraviolet to visible region were obtained during the 2002 Leonid aircraft campaign. We analyzed 20 meteor spectra obtained from the 1767 (seven revolution) and 1866 (four revolution) trails on 2002 November 19 and identified neutral atoms, mainly Mg I, Fe I, Ca I, and Na I, in the observed wavelengths between 300 and 650 nm. The singly ionized atomic emissions, Ca II and Mg II lines, also appeared in the spectrum. The abundances of the metallic atoms, the electronic excitation temperature, and the electron density are obtained for each spectrum, assuming the Boltzmann distribution for the number at each energy level. The metallic abundances of Fe, Ca, and Na relative to Mg are slightly lower than solar abundances on average. We could not find any evidence of the solar heating effect on Leonid meteoroids between the 1767 and 1866 trails on orbit with their perihelion (q ~ 1 AU). We can support the idea that silicate and carbon-mixed silicate are preserved in interplanetary space for at least several hundred years. Bands of CHON-related molecules, such as OH and CN, are not detected in this study.

Mass loss due to sputtering and thermal processes in meteoroid ablation

Conventional meteoroid theory assumes that the dominant mode of ablation (which we will refer to as thermal ablation) is by evaporation following intense heating during atmospheric flight. Light production results from excitation of ablated meteoroid atoms following collisions with atmospheric constituents. In this paper, we consider the question of whether sputtering may provide an alternative disintegration process of some importance. For meteoroids in the mass range from 10 - 3 to 10 - 13 kg and covering a meteor velocity range from 11 to 71 km / s , we numerically modeled both thermal ablation and sputtering ablation during atmospheric flight. We considered three meteoroid models believed to be representative of asteroidal ( 3300 kg / m 3 mass density), cometary ( 1000 kg / m 3 ) and porous cometary ( 300 kg / m 3 ) meteoroid structures. Atmospheric profiles which considered the molecular compositions at different heights were use in the sputtering calculations. We find that while in many cases (particularly at low velocities and for relatively large meteoroid masses) sputtering contributes only a small amount of mass loss during atmospheric flight, in some cases sputtering is very important. For example, a 10 - 10 kg porous meteoroid at 40 km / s will lose nearly 51% of its mass by sputtering, while a 10 - 13 kg asteroidal meteoroid at 60 km / s will lose nearly 83% of its mass by sputtering. We argue that sputtering may explain the light production observed at very great heights in some Leonid meteors. We discuss methods to observationally test the predictions of these computations. A search for early gradual tails on meteor light curves prior to the commencement of intense thermal ablation possibly represents the most promising approach. The impact of this work will be most dramatic for very small meteoroids such as those observed with large aperture radars. The heights of ablation and decelerations observed using these systems may provide evidence for the importance of sputtering.

Results from 2002 Leonid meteor storm TV observations in Kyiv

Results are presented from double-station TV observations of the 2002 Leonids meteor storm as seen from Kyiv (Ukraine). The observations were carried out from two observational stations 54 km apart. The total observation time was five hours: from 23:30 till 4:30 UT on 18/19 November, 2002. The total number of two-station meteors was 38, 28 of which allowed for precise processing. The trajectories of the meteors in Earth’s atmosphere, their radiant coordinates, heliocentric orbital elements, etc., were calculated. The highest beginning height observed was 151.53 ± 2.79 km, and distributions of beginning and end heights are presented. Leonids registered during the onset of the storm between 3:00 and 4:00 UT had geocentric radiants (J2000.0) concentrated into a compact group with mean RA = 154°.43 ± 0°.55 and Decl. = 21°.91 ± 0°.58. The corresponding mean inclination and argument of perihelion of the orbit are i = 162°.62 ± 0°.61 and ω = 175°.13 ± 1°.37, respectively. The initial masses of meteoroids were calculated from photometry, from which a mass distribution index s = 1.43 ± 0.02 was derived. We determined that the number of meteors brighter than 4 m (1.54 × 10 −4 g) that crossed a horizontal circular area of radius 100 km at an altitude of 100 km, for an assumed radiant in zenith, changed during the observations from 350/h to 1400/h. The corresponding spatial density of Leonid stream particles was 4.3 × 10 −8–1.7 × 10 −7 km −3.

A new method to predict meteor showers

Our model of meteor shower forecasting (described in Paper I) is applied to the Leonid shower. This model is based on the dirty snowball model of comets, and on heavy numerical simulation of the generation and evolution of meteoroid streams. The amount of dust emitted by comet 55P/Tempel-Tuttle is computed. A statistical weight is associated to each simulated particle. This weight represents the real amount of meteoroids released by the comet. Particles close to the Earth are examined. There is no unique set of initial conditions (velocity and angle of ejection) for them to reach the Earth at the time of the shower. The shape of the metoroid stream projected on the ecliptic is not elliptical, due to non-gravitational forces and ejection processes. The mixing of particles is revealed to be very efficient. A comparison between observations and predictions of Leonid meteor showers is done. The time of maximum is found to be very accurate, except for certain years (1999 in particular). This problem is common to all models. The level of the predicted shower is obtained through a fit of the size distribution index s = 2.4±0.1. This model provides a unique opportunity to derive cometary parameters from meteor shower observations. Leonid meteor shower forecasts are provided for years up to 2100. The next storm is expected in 2034.

A new method to predict meteor showers

Observations of meteor showers allow us to constrain several cometary parameter and to retrieve useful parameters on cometary dust grains, for instance the dust size distribution index s. In this first paper, we describe new model to compute the time and level of meteor shower whose parent body is known periodic comet. The aim of our work was to use all the available knowledge on cometary dust to avoid most of the a priori hypotheses of previous meteoroid stream models. The ejection velocity is based on hydrodynamic model. Because of the large amount of particles released by the comet, it is impossible to compute the orbits of all of them. Instead, we link each computed particle with the real number of meteoroids ejected in the same conditions, through dirty snowball cometary model calibrated with the [A f ρ] parameter. We used massive numerical integration for all the particles without hypotheses about size distribution. The time of maximum is evaluated from the position of the nodes of impacting meteoroids. The model allows us to compute ephemerides of meteors showers and the spatial density of meteors streams, from which ZHR can be estimated. At the end fit of our predictions with observations allows us to compute the dust size distribution index. We used 2002 and 2003 leonid meteor showers to illustrate our method. The application of our model to the Leonid meteor shower from 1833 to 2100 is given in Paper II.

Temporal evolution of the vertical content of metallic ion and neutral species

Temporal changes in the vertical column contents of the meteoric metals Mg +, Mg, Fe +, and Fe have been measured at ∼1030 LT for all longitudes in the latitude zone of 10°N–30°N during November 1996, encompassing the period of the Leonid meteor shower. The column contents were obtained using UV radiances measured by the GOME instrument on the ERS-2 satellite. Throughout the month there are several interesting prominent content enhancements of all species. After the Leonid shower peak on 17 November the ion species contents increase before the contents of the neutrals. However, it is difficult to confirm that this is a shower effect given the other similar variations seen earlier in the contents and in the sporadic meteor flux enhancements. The peaks in visual meteors on 17 November are not observed in the total metal column amounts. The GOME instrument has been in continuous operation since April 1995 and is an excellent resource for studying the temporal behavior of meteoric metals on a global scale.

The relationship between the semi-major axis, mass index and age of the Leonid meteor shower

Owing to sublimation of ice, comet nuclei eject dust particles when they are near to the sun. Those particles assume velocities and then vary their orbits to ones similar to that of the comet. The most notable difference between the orbit of the parent comet and those of the particles is their semi-major axes. This difference (Δa) has been widely used in modern meteor shower predictions. Observational evidence of the distribution showed that it is a function of Δa, and the age of the dust trail. However, the relation is not well known. In this paper, a simplified relation between Δa, the mass index (s) and the age of the dust trail is presented, taking the instance of a recent Leonid meteor shower.

Metallic abundances of the 2002 Leonid meteor deduced from high-definition TV spectra

High-definition TV spectra in the ultraviolet-visible region were obtained during the 2002 Leonid aircraft campaign. We analyze the spectra of the brightest fireball that appeared at 03 h 47 m 54 s UT on Nov. 19, 2002 and identify the neutral atoms, mainly MgI, FeI, CaI, and NaI in the observed wavelengths between 300-650 nm. The singly ionized atomic emissions, CaII and MgII lines, also appeared in the spectrum in several epochs during the series of video frames. From analysis of the spectra, time variation in the abundances of metallic atoms, along with their electronic excitation and blackbody temperatures, were obtained assuming the Local Thermal Equilibrium (LTE) condition. Both Fe and Ca abundances relative to Mg are lower than the solar abundance, while Na is slightly higher. We found correlation between the excitation temperature and the abundance of Ca, which suggests incomplete evaporation of the Ca due to intrinsic refractoriness. A search for bands of CHON-related molecules, such as OH and CN, is not successful in the brightest fireball in this study.

Observations of persistent Leonid meteor trails: 4. Buoyant rise/vortex formation as mechanism for creation of parallel meteor train pairs

In this paper we present numerical computations designed to demonstrate effects associated with the buoyant rise of persistent trails produced by large Leonid meteors in cases where the meteor velocity vector has a large horizontal component. We model the meteor trail as a hot cylindrical volume in an equilibrium atmosphere. The computed results show the hot cylinder first expanding radially and then rising because of buoyancy, while evolving into a pair of counterrotating linear vortices. These line vortex phenomena are offered as an explanation for the otherwise mysterious parallel pairs of trails that are often observed. We also show some high‐resolution images of double meteor trails observed during the high Leonid meteor activity of 1998–2002. For the case of the Diamond Ring event we compare computed and measured luminosity profiles for the sodium 589 nm emission and for the red–near IR O2 atmospheric band (O2(b1Σg+) – O2(X3Σg−)) emission.

Leonid Meteoroid Orbits Perturbed by Collisions with Interplanetary Dust

By analyzing high-accuracy Leonid orbits obtained from multiple-station meteor observations during the 1998 outburst and 1999 storm, we have detected the presence of meteoroids with peculiar orbits. These meteoroids are characterized by having a geocentric radiant nearly identical to the members of the storm that appeared with them but showing different orbital elements owing to their lower geocentric velocities. The changes in some orbital elements are significant and allow us to interpret the cause of such differences. Mainly, the semimajor axis and the eccentricity of these anomalous orbits are lower than expected for members of the dust trail or members coming from the background component linked to the annual stream. From these characteristics it is likely that these peculiar meteoroids suffered some perturbations on very short timescales. We have investigated several causes, including planetary perturbations, collisions, and radiative effects in order to explain the observed orbital changes. We conclude that these orbital changes can be explained by the loss of orbital energy close to the ecliptic plane. Such an effect can only be explained clearly by collisions of the original meteoroids with dust particles associated with the zodiacal dust cloud. We have applied this hypothesis in order to constrain some physical properties of 55P/Tempel-Tuttle cometary meteoroids.

二周波法によるVHF帯地震電磁現象の観測

Seismic electromagnetic (EM) phenomena have been observed at many laboratories with specially designed systems. Recently we can utilize radio receivers, personal computers, and communication systems with higher performances and reasonable cost. It is possible to observe seismic EM phenomena not only by specially designed systems but also by a simple observation system integrated by these devices and systems. We have created an observation system for seismic EM phenomena with them in the very high frequency (VHF) band, from 76 MHz to 90 MHz, assigned for FM broadcasting exclusive use in Japan. We are surrounded by many EM waves, such as broadcasting, communication usage, and man-made noises. Thus, we have newly developed the dual frequency observation method. In this paper, we describe an observation method that can identify whether a received signal is a broadband EM wave or an artificial FM radio wave. Next, the observation results for broadband EM waves from galactic noise and solar flares are presented. Then, the observation results for FM radio waves reflected from sporadic E layer and the Leonid meteors are shown. Finally, the observation results for the detected broadband EM waves associated with the Geiyo earthquake are described. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(4): 36–44, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20350

Detection of the [FORMULA][F][RM]N[/RM][SUP]+[/SUP][INF]2[/INF][/F][/FORMULA] First Negative System in a Bright Leonid Fireball

An ultraviolet-visible spectrum between 300 and 450 nm of a cometary meteoroid that originated from 55P/Tempel-Tuttle was investigated, and its new molecules, induced by atmospheric interaction, were discovered. The spectroscopy was carried out using an intensified high-definition TV camera with a slitless reflection grating during the 2001 Leonid meteor shower over Japan. A best-fit calculation mixed with atoms and molecules confirmed the first discovery of N B 2Σ → X 2Σ bands in the UV meteor spectrum. The N temperature was estimated to be 10,000 K with a low number density of 1.55 × 105 cm-3. Such unexpectedly strong ultraviolet emission, in particular for N (1, 0) at 353.4 nm, is supposed to be formed through the wide dimensions of high-temperature regions caused by a large meteoroid. Spectroscopic observations of reentry capsules will provide us with good opportunities for confirming the discovered N.