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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.09.007 Byline: S. Close (a), P. Brown (b), M. Campbell-Brown (b), M. Oppenheim (c), P. Colestock (a) Keywords: Meteors; Radio observations Abstract: High-power, large-aperture (HPLA) radars detect the plasma that forms in the vicinity of a meteoroid and moves approximately at its velocity; reflections from these plasmas are called head echoes. For over a decade, HPLA radars have been detecting head echoes with peak velocity distributions >50 km/s. These results have created some controversy within the field of meteor physics because previous data, including spacecraft impact cratering studies, optical and specular meteor data, indicate that the peak of the velocity distribution to a set limiting mass should be Author Affiliation: (a) Los Alamos National Laboratory, Space and Remote Sensing Sciences, Mail Stop D436, Los Alamos, NM 87545, USA (b) Department of Physics and Astronomy, University of Western Ontario, London, ON N6A 3K7, Canada (c) Center for Space Physics, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA Article History: Received 8 June 2006; Revised 12 September 2006

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 resonance's. They represent, with a high probability, increased numbers of particles gravitationally expelled from a resonant gap and (temporary) settled down in its close proximity. Keywords: Meteoroids; Orbits; Resonances

Zagami, a well characterized SNC meteorite, represents a reference sample to verify the feasibility of the non-destructive infrared micro-spectroscopy technique to extract spectral signatures from individual mineral phases in a meteorite sample. For the first time individual infrared spectra of the major mineral phases, in the 6000-600 [cm.sup.-1] (1.67-16.7 [micro]n) spectral interval, whose identification is confirmed by energy dispersive X-ray analysis and backscattered imaging, are measured. The signatures of the main mineral phases we identified in the Zagami chip are: (1) maskelynite characterized by broad and smooth Si-O vibrational bands in the 1000 [cm.sup.-1] spectral region; (2) crystalline pyroxenes showing well defined fine structures; and (3) an oxide mineral phase with an almost featureless and flat spectrum. In the part of the spectrum centered around 2 [micro]m, by analyzing the different positions of the [Fe.sup.2+] bands, we were able to discern the high-Ca from the low-Ca pyroxene phases. This result demonstrates that by means of the infrared micro-spectroscopy technique it is possible to retrieve directly the composition of pyroxenes in the En-Fs-Wo system, without relying on the use of deconvolution techniques. In addition IR signatures due to water and aliphatic hydrocarbons were observed to be more abundant in the pyroxenes than in maskelynite. This could be an indication that the organic and water signatures are due to indigenous compounds in Zagami rather than laboratory contamination, however, further investigations are necessary before this conclusion can be confirmed. Keywords: Mars; Meteorites; Spectroscopy; Mineralogy; Experimental techniques

We present a survey of 97 spectra of mainly sporadic meteors in the magnitude range +3 to -1, corresponding to meteoroid sizes 1-10 mm. For the majority of the meteors, heliocentric orbits are known as well. We classified the spectra according to relative intensities of the lines of Mg, Na, and Fe. Theoretical intensities of these lines for a chondritic composition of the meteoroid and a wide range of excitation and ionization conditions were computed. We found that only a minority of the meteoroids show chondritic composition. Three distinct populations of Na-free meteoroids, each comprising ~ 10% of sporadic meteoroids in the studied size range, were identified. The first population are meteoroids on asteroidal orbits containing only Fe lines in their spectra and possibly related to iron-nickel meteorites. The second population are meteoroids on orbits with small perihelia (q [less than or equal to] 0.2 AU), where Na was lost by thermal desorption. The third population of Na-free meteoroids resides on Halley type cometary orbits. This material was possibly formed by irradiation of cometary surfaces by cosmic rays in the Oort cloud. The composition of meteoroids on Halley type orbits is diverse, probably reflecting internal inhomogeneity of comets. On average, cometary dust has lower than chondritic Fe/Mg ratio. Surprisingly, iron meteoroids prevail among millimeter-sized meteoroids on typical Apollo-asteroid orbits. We have also found varying content of Na in the members of the Geminid meteoroid stream, suggesting that Geminid meteoroids were not released from their parent body at the same time. Keywords: Meteors; Meteoroids; Spectroscopy; Comets, composition; Asteroids, composition

We report here the observation of the first peak belonging to the 2002 Leonid meteor storm made during the night of November 18-19, 2002. This feature, produced by a 7-revolution dust trail, was observed from several photographic stations of the Spanish Photographic Meteor Network (SPMN) and one video station operated from the Instituto de Astrofisica de Andalucia (IAA) in an intensive campaign from the ground working in collaboration with the 2002 Leonid MAC mission. We used photography, slow-scan Charge Coupled Devices (CCD) and video CCD-imaging techniques to deduce the meteoroid flax density profiles in different ranges of masses. Additionally. we present multi-station work, developed during the storm, that allows us to deduce the orbital elements of ten meteoroids associated with this dust trail. We have found a clear similarity between their orbits and the one belonging to a theoretical orbit for particles ejected from 55P/Tempel-Tuttle in 1767. Keywords: Meteors; Meteoroids; Orbits; Comets: Leonids; 55P/TempeI-Tuttle