The parent of the Quadrantid meteoroid stream

The Quadrantid meteor shower is one of the major showers that produces reliable displays every January. However, it is unique amongst the major showers in still not having its parent uniquely identified. One of the reasons for this may be because the stream, and presumably the parent, lies in a region of the Solar system where near-resonant motion with Jupiter, coupled with potential close encounters, is possible. Such a combination can lead to a rapid dynamical evolution of an orbit. In particular, it may be possible that the orbit of the parent both satisfies the condition for a close encounter and is in resonant motion, while most of the meteoroids cannot satisfy both conditions. This results in the parent evolving away from the bulk of the stream.
To date, two suggestions have been made regarding possible parents for the Quadrantid stream, these being Comet 1491 I and Comet 96P/Machholz. The argument in favour of the first named being the parent is because of the general similarity between the orbits around 1491. The argument for comet 96P/Machholz being the parent is based on the similarity in orbital evolution coupled with a similarity in orbits phase-shifted by 2000 yr. In this paper we suggest that on both counts asteroid 5496 (1973 NA) is more similar to the Quadrantids, and that even if 5496 is not the actual parent in the strict sense that meteoroids are currently being ejected, it is either likely to be a fragment of the parent or the dormant remains of the parent.     

A new octuple Earth-crossing meteoroid stream

It was shown that the orbit of Virginid meteors is an octuple Earth-crosser so that the stream can produce eight related meteor showers. Of these eight theoretical showers five are identified in the catalogues; one of these is the Cygnids.     

Radar surveys of meteoroid orbits

Summary Radar facilities providing routine measurements of the heliocentric orbits of meteoroids are valuable in providing a data-base of the orbital characteristics of the solar system small body population in the mass range about 10^–2 down to 10^–6 g. Such an orbital information background is essential for an understanding of the evolutionary processes of this component.An outline is presented of orbit-finding systems; their inherent limitations and associated selection effects with some emphasis given to the on-going southern hemisphere routine survey provided by the AMOR facility which provides orbits down to a limiting magnitude +13.     

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.     

The activity of the 2004 Geminid meteor shower from global visual observations

A comprehensive set of 612 h of visual meteor observations with a total of 29 077 Geminid meteors detected was analysed. The shower activity is measured in terms of the Zenithal Hourly Rate (ZHR). Two peaks are found at solar longitudes     and     with  ZHR = 126 ± 4  and  ZHR = 134 ± 4  , respectively. The physical quantities of the Geminid meteoroid stream are the mass index and the spatial number density of particles. We find a mass index of   s ≈ 1.7  and two peaks of spatial number density  234 ± 36  and  220 ± 31  particles causing meteors of magnitude +6.5 and brighter in a volume of 10⁹ km³, for the two corresponding ZHR maxima. There were  0.88 ± 0.08  and  0.98 ± 0.08  particles with masses of 1 g or more in the same volume during the two ZHR peaks. The second of the two maxima was populated by larger particles than the first one. We compare the activity and mass index profiles with recent Geminid stream modelling. The comparison may be useful to calibrate the numerical models.     

Filaments within the Perseid meteoroid stream and their coincidence with the location of mean-motion resonances

Positions of 17 filaments found inside the Perseid meteoroid stream by method of indices are compared with those of low-order mean-motion resonances with Jupiter and Saturn. By this comparing, the Jupiter and Saturn branches of the Perseid stream were identified. The existence of gaps in the distribution of the semi-major axes of the Perseids is confirmed using the more numerous material of a new version of the IAU Meteor Data Center Catalogue. Our integrations of the motion of particles in the Perseid stream lead to an extraordinary important fact. The found filaments are located in close proximity of strong resonances. They represent, with a high probability, increased numbers of particles gravitationally expelled from a resonant gap and (temporary) settled down in its close proximity.     

The effects of meteoroid stream enhanced activity on human space flight: an overview

The origin, dispersion mechanisms and evolution of particle streams producing enhanced activity (outburst or storm) of meteoroids are discussed in relation to their effects on artificial satellites and space platforms. A review of the active meteoroids suggests that at least five streams may undergo outburst or storm activity in the next few years. Modern radio techniques not affected by illumination conditions and cloud coverage, improve significantly the detectability of meteor streams. The impact probabilities of storm meteoroids on space platforms in Earth orbit can increase by factors in excess of 10²–10⁴ over the sporadic background.     

Radar observations of apollo

Radar observations of the asteroid Apollo, at 3.5 cm wavelength, indicate a radius of 600 m and a rotation period of 3.0 hr. The data are consistent with a rough surface of either hard ice or of regolith softened rock.     

The use of the distribution of the orbital energy to investigate the evolution of the Perseid meteoroid stream

Numerical integration of a meteor stream over a long period is a very time consuming process, especially if a number of different models have to be investigated. In this paper we demonstrate that using the distribution of orbital energy as a vector in a Markov process can be a useful tool and that meaningful results can be obtained with far less computation than is normally required.     

Radar observations of the icy Galilean satellites

We report 12.6-cm-wavelength radar observations of Europa, Ganymede, and Callisto made at the Arecibo Observatory in November 1977 and February 1979. When combined with previous observations, our results establish firmly the distinguishing radar properties of these satellites: (i) high geometric albedos, α; (ii) circular polarization ratios, μ_C, which anomalously exceed unity; (iii) linear polarization ratios, μ_L, which are approximately 0.5; and (iv) diffuse scattering which varies as cosⁿθ, where θ is angle of incidence and 1 ? n ? 2. We tabulate weighted-mean values of α, μ_C, μ_L, and n derived from observations between 1975 and 1979. The values of μ_C for Ganymede and Europa are nearly identical and significantly larger than that for Callisto. The values of n for Ganymede and Callisto are nearly identical and significantly smaller than that for Europa. Although significant albedo and/or polarization features are common in the radar spectra, the fractional rms fluctuation in disk-integrated properties is only ～10%. No time variation in the radar properties has been evident during 1976–1979.