A Fine Structure of the Perseid Meteoroid Stream

A fine structure of the Perseid stream in the range of photographic magnitudes is studied using the method of indices. A new completed 2003 version of the IAU Meteor Data Center Catalogue of 4581 photographic orbits is used. The method of indices is used to acquire a basic data set for the Perseids. Subsequently, the method is applied on the chosen Perseids to study their structure. Sixty four percent of chosen Perseids taken into account are attached to one of the 17 determined filaments of orbits. The filaments are not distributed in the space accidentally, but they form a higher structure consisting of at least four well-defined and distinguished “branches”.     

Lunar Gravitational Focusing of Meteoroid Streams and Sporadic Sources

Recent work on the gravitational focusing of meteoroid streams and their threat to satellites and astronauts in the near-Earth environment has concentrated on Earth acting as the gravitational attractor, totally ignoring the Moon. Though the Moon is twelve-thousandths the mass of the Earth, it too can focus meteors, albeit at a much greater distance downstream from its orbital position in space. At the Earth–Moon distance during particular phases of the Moon, slower speed meteoroid streams with very compact radiant diameters can show meteoroid flux enhancements in Earth’s immediate neighborhood. When the right geometric alignment occurs, this arises as a narrowed beam of particles of approximately 1,000 km width. For a narrow radiant of one-tenth degree diameter there is a 10-fold increase in the level of flux passing through the near-Earth environment. Meteoroid streams with more typical radiant sizes of 1° show at most two times enhancement. For sporadic sources, the enhancement is found to be insignificant due to the wide angular spread of the diffuse radiant and thus may be considered of little importance.     

Updates to the MSFC Meteoroid Stream Model

The Marshall Space Flight Center (MSFC) Meteoroid Stream Model simulates particle ejection and subsequent evolution from comets in order to provide meteor shower forecasts to spacecraft operators for hazard mitigation and planning purposes. The model, previously detailed in Moser and Cooke (Earth Moon Planets 95, 141 (2004)), has recently been updated; the changes include the implementation of the RADAU integrator, an improved planetary treatment, and the inclusion of general relativistic effects in the force function. The results of these updates are investigated with respect to various meteoroid streams and the outcome presented.     

On the Substantial Spatial Spread of the Quadrantid Meteoroid Stream

We explored the substantial spatial spread of the Quadrantid stream, based on the backward integration of orbital motions of the Quadrantids, impulsively perturbed by Jupiter. We found that the Jovian impulses can widely spread out them in the early twentieth century, especially their perihelia extended by a factor of ∼90 than those at the observed epoch. We regarded the spread as the intrinsic one of the Quadrantid stream itself.     

Meteoroid Stream Searching: The Use of the Vectorial Elements

In this initial study, we propose a new distance function D _V involving heliocentric vectorial orbital elements. The function measures differences between: the orbital energies, the angular momentums vectors and the Laplace vectors. In comparison with the widely used D _SH criterion of Southworth and Hawkins, D _D criterion of Drummond and their hybrid D _H by Jopek, the new function contains one invariant with respect to the principal secular perturbation: the orbital energy. The new function proved to be useful in the classification amongst the IAU2003 meteoroids which we searched for streams by D _V function and also using D _SH and D _N -function given by Valsecchi et al. For major streams, the results agree very well. For minor, and near-ecliptical streams the results sometimes differ markedly.     

MSFC Stream Model Preliminary Results: Modeling Recent Leonid and Perseid Encounters

The cometary meteoroid ejection model of Jones and Brown [Physics, Chemistry, and Dynamics of Interplanetary Dust, ASP Conference Series 104 (1996b) 137] was used to simulate ejection from comets 55P/Tempel-Tuttle during the last 12 revolutions, and the last 9 apparitions of 109P/Swift-Tuttle. Using cometary ephemerides generated by the Jet Propulsion Laboratory’s (JPL) HORIZONS Solar System Data and Ephemeris Computation Service, two independent ejection schemes were simulated. In the first case, ejection was simulated in 1 h time steps along the comet’s orbit while it was within 2.5 AU of the Sun. In the second case, ejection was simulated to occur at the hour the comet reached perihelion. A 4th order variable step-size Runge–Kutta integrator was then used to integrate meteoroid position and velocity forward in time, accounting for the effects of radiation pressure, Poynting–Robertson drag, and the gravitational forces of the planets, which were computed using JPL’s DE406 planetary ephemerides. An impact parameter (IP) was computed for each particle approaching the Earth to create a flux profile, and the results compared to observations of the 1998 and 1999 Leonid showers, and the 1993 and 2004 Perseids.     

Mass distribution of Perseid meteoroids

An analysis of the Perseid meteoroid mass distribution is given. It is shown that particle mass distributions are qualitatively the same along the entire orbit of the stream. The extra minima in the cross sections of the stream at the ascending and descending branches of the curve of the parameter S indicate a jetlike nature of the stream. The variations of the nodal longitudes of maximum stream activity versus the minimum observed mass of meteoroids are found along the entire orbit of the stream. The positions of maximum activity for particles with minimum detectable masses larger than 1 and 10^?3 g are shifted by 1.4 degrees in solar longitude, with larger longitudes for smaller particles.     

Meteoroid streams and the sporadic background

Summary There is a general agreement that meteoroid streams form through the ejection of dust grains, or meteoroids, up to a few centimeters in size from comets and possibly asteroids. After ejection these meteoroids are subject to forces arising from Solar radiation and the gravitational fields of the planets. Meteoroids may also break up into smaller ones through collisions and other effects. In many cases meteor showers have been observed for millennia, with material being fed into the stream throughout this period from the parent and material lost through the external effects mentioned. Much of the lost material forms the general sporadic background. This paper will review our state of knowledge of the processes involved above and will also aim to give some insight into the structure of the sporadic background     

Meteoroid impacts on the gemini windows

Fourteen windows of the Gemini spacecraft were closely examined after return from space flight for evidence of meteoroid impact. Although a number of microscopic pits were found on each window, only one of these pits appears to have been caused by a meteoroid impact. A meteoroid flux-mass relation calculated from this single hit is found to be in close agreement with Naumann's (1966) analysis of the Explorer and Pegasus meteoroid penetration experiments. Particle, mass, and area distribution curves are derived from the flux-mass relation and are presented in graphical form. Problems in interpreting the data because of contaminants on the windows are also discussed.     

TVZHR profile for the 1991 Perseid shower

Image intensified video detection systems were used to observe the 1991 Perseid meteor shower from two locations in eastern Canada. In 29.6 hours of total observing time a total of 668 meteors were detected, of which 403 were Perseids. We derived a profile of TVZHR (television zenithal hourly rate) values for the 1991 Perseid shower over the solar longitude (epoch 2000) interval 138°51 to 141°01. The apparent limiting stellar magnitudes of the observing systems were +9.4 and +8.8 (corresponding to limiting meteor magnitudes for our geometry ranging from +8.7 to +7.0). Within the observing period, the maximum TVZHR rate was approximately 1600, and occurred at solar longitude 139.9°. This is in good agreement with the second peak observed by visual observers. The data suggest that TVZHR values should be divided by a factor of approximately 5 to compare TVZHR and ZHR values.     

Radiant ephemeris and radiant area of the Perseid meteoroid stream

More than 600 double-station photographic recordings of Perseid meteor trails have been obtained at various stations in the period 1937–1985. This large data sample has recently been used to determine the activity profile and mean orbit of the Perseid meteoroid stream (Lindblad and Poruban, 1994). In the present paper the radiant of the Perseid meteoroid stream is studied based on a sample of 592 double-station photographic recordings. The daily motion of the radiant and the change of the size of the radiant area with date is investigated. A daily motion of 1.40° in right ascension and 0.20° in declination is derived. These values are slightly larger than those previously found by other researchers. The contraction of the radiant area at shower maximum previously reported from visual observations is confirmed. In a further study radiant areas derived for the dates of the new and the old Perseid maxima are compared. It is found that the radiant area of the new maximum is smaller than that of the old maximum.     

Extraterrestrial Technogenic Component of the Meteoroid Flux

It is shown that the Earth is a natural collector of extraterrestrial nonsterile artefacts that could impact our planet. Artefacts from 1.2 × 106 nearby stars could have reached the Earth over its history, and could be agents for spontaneous interstellar panspermia, even if alien civilizations pollute space only at the current terrestrial rate.     

Elemental Abundances in Leonid and Perseid Meteoroids

High dispersion photographic spectra of three Leonid and five Perseid meteors are used to derive relative abundances of nine chemical elements in the radiating meteoric vapors and in the meteoroids. Al and Ca were found to be incompletely evaporated in the main spectral component at 5000 K but completely evaporated in the second component at 10,000 K. Si lines are present in both components which enhances the reliability of determination of the Si abundance. The composition of the meteoroids was found to be more similar to comet Halley than to chondritic meteoroids. Fe, Cr, and Mn are depleted and Si, Na, and H are enhanced relative to Mg in comparison with CI chondrites.     

The Dynamics of Meteoroid streams

Meteors are streaks of light seen in the upper atmosphere when particles from the inter-planetary dust complex collide with the Earth. Meteor showers originate from the impact of a coherent stream of such dust particles, generally assumed to have been recently ejected from a parent comet. The parent comets of these dust particles, or meteoroids, fortunately, for us tend not to collide with the Earth. Hence there has been orbital changes from one to the other so as to cause a relative movement of the nodes of the meteor orbits and that of the comet, implying changes in the energy and/or angular momentum. In this review, we will discuss these changes and their causes and through this place limits on the ejection process. Other forces also come into play in the longer term, for example perturbations from the planets, and the effects of radiation pressure and Poynting–Robertson drag. The effect of these will also be discussed with a view to understanding both the observed evolution in some meteor streams. Finally we will consider the final fate of meteor streams as contributors to the interplanetary dust complex.     

The luminosity functions of the 1969 Perseid and Orionid meteor showers

Visual counts of the 1969 Perseid and Orionid meteor showers are presented, comprising 288 Perseids and 56 Orionids. On the basis of the maximum-likelihood method of determining the power law luminosity function index, we derive s ≡ 1 + 2.5 log(r) = 1.56 ± 0.06 for the Perseids with m_v = +1 to ?5, and s ≈ 1.85 ± 0.1 for the Orionids with m_v = +2 to ?3. These values are somewhat lower than those found by other observers, but we confirm the approximate power law nature of the luminosity functions. Under the assumption that the masses of visual meteors are proportional to a power law function of the luminosities, this implies power law mass functions. If mass is directly proportional to luminosity, we have power law mass functions with the indices s given above.     

Semimajor axes of the orbits and ejection velocities of Perseid meteoroids

Photographic orbits of meteors are combined with modeling of the ejection of Perseids during the perihelion passage of comet Swift-Tuttle in 1862 to analyze the most likely ejection velocities of particles from the comet nucleus. Given the scatter of the semimajor axes of observed Perseids with masses greater than 10^–4 g, the most likely interval of ejection velocities spans 0 to 300 m/s for particles ejected in the plane of the comet orbit in the retrograde direction and in the direction of the comets anomalous tail.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 2, 2005, pp. 184–190.Original Russian Text Copyright © 2005 by Ishmukhametova, Kondrateva.     

Associations Between Asteroids and Meteoroid Streams

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.     

A search for large meteoroids in the Perseid stream

Abstract— We report on two surveys conducted during the times of Perseid shower maximum in 1997 and 1998. The first survey entailed the video monitoring of the Moon's disk with the intent of recording the optical flashes that should result when large meteoroids strike the lunar surface. The second survey consisted of a combination video camera and very low frequency (VLF) radiowave receiver system capable of detecting electrophonic meteors during their ablation in the Earth's atmosphere. Using standard ablation theory, we find that for a Perseid meteoroid to be capable of generating electrophonic sounds, it must have an initial mass in excess of 495 kg. We also find, as a result of the surveys, an upper limit of 2 × 10^?17 m^?2 s^?1 to the flux of electrophonic Perseid meteors entering the Earth's atmosphere. Although our study indicates that large, meter-sized meteoroids must, at best, be sparsely distributed within the Perseid stream, we briefly discuss some tantalizing lines of evidence, found from within the astronomical literature, that hint at their true existence.     

The Dynamics of Low-Perihelion Meteoroid Streams

The Canadian Meteor Orbit Radar (CMOR) has collected information on a number of weak meteor showers that have not been well characterized in the literature. A subsample of these showers (1) do not show a strong orbital resemblance to any known comets or asteroids, (2) have highly inclined orbits, (3) are at low perihelion distances ( AU) and (4) are at small semimajor axes (<2 AU). Though one might conclude that the absence of a parent object could be the result of its disruption, it is unclear how this relatively inaccessible (dynamically speaking) region of phase space might have been populated by parents in the first place. It will be shown that the Kozai secular resonance and/or Poynting–Robertson drag can modify meteor stream orbits rapidly (on time scales comparable to a precession cycle) and may be responsible for placing some of these streams into their current locations. These same effects are also argued to act on these streams so as to contribute to the high-ecliptic latitude north and south toroidal sporadic meteor sources. There remain some differences between the simple model results presented here and observations, but there may be no need to invoke a substantial population of high-inclination parents for the observed high-inclination meteoroid streams with small perihelion distances.     

Orbital Elements of 2004 Perseid Meteoroids Perturbed by Jupiter

Jupiter and Saturn produce important gravitational impulses on meteoroids released by comet 109P/Swift-Tuttle. The meteoroids from this comet once released follow retrograde orbits that during their periodic approaches to these planets (within 1.6 and 0.9 A.U., respectively) are impulsed gaining orbital energy. This perturbation effect is translated into a net inward shift in the node of the perturbed meteoroids. Such geometry with Jupiter occurred in 2004 over a meteoroid trail ejected by this comet during the 1862 A.D. return of the comet to perihelion. In order to study the predicted outburst produced by one-revolution meteoroids, the Spanish Photographic Meteor Network (SPMN) performed an extensive campaign. As a part of this observational effort here are presented 10 accurate meteoroid orbits. We discuss their origin by comparing them with the theoretical orbital elements of the dust trails intercepting the Earth during the 2004 Perseid return.