References

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Rha

Classification of meteorites hierarchy of sub-divisions into groups and classes. There is not always a clear cut distinction between types e.g., there are many iron meteorites that contain silicate inclusions related to chondritic meteorites. Both melted and unmelted stony meteorites are made from the same elements as terrestrial rocks Si, O, Fe, Mg, Ca and Al. Like terrestrial rocks, these meteorites are assemblages of silicate minerals pyroxene, olivine and plagioclase, but unlike...

Update on new developments of the Advanced Meteor Orbit Radar AMOR

Bennetta, S.H. Marsha, G.E. Planka and D.P. Galligana aDepartment of Physics and Astronomy, University of Canterbury, Private Bag 4800, New Zealand. AMOR is a continuously operating radar facility for measuring the heliocentric orbits of Earth-impacting grains down to sizes of about 40 im. Recent developments including additional extensive antenna arrays and multi-antenna independent phase measurements are providing an expanded sky coverage and increased meteoroid...

Oblique reflection

In this geometry the radar transmitter and receiver have a ground separation large compared to the meteor target height so that the specular condition results in a large scattering angle (the angle between the normal to the meteor train and the incident wave propagation direction, cf> , where 4> 0 for transverse, backscattering case). In effect the Fresnel zone length for such a forward scatter configuration is increased by a factor (cos < f)) 2 and the radar wavelength is effectively...

Numerical Simulations

Forced elements are the component of a dust particle's osculating (or instantaneous) orbital elements imposed by the presence of the planets. These forced elements vary with heliocentric distance, time and particle diameter, and are responsible for the large-scale asymmetries observed in the distribution of dust particles in the zodiacal cloud. To calculate the current distributions of these forced elements, we employed the new dissipative code discussed above to evolve representative samples...

Magnetic Dust Aggregation Experiments

Magnetic dust aggregation has been studied numerically 16,13,14 , In order to have a means for calibrating and validating these simulations, we investigated the effects of magnetic interactions on the preplanetary grain growth process in analogous laboratory experiments. To this end, we used single domain (SD) ferritic (Ba,Sr)-Fei20i9 powder in the levitation drum setup described by Blum et al. 17 . SD ferritic grains are used as a raw material for the industrial production of sintered...

Doppler Filtering Of Extrasolar Planetarydustnoise

DRVS also faces new challenges in detecting and characterizing extrasolar planets embedded in dust clouds. There is a significant excess of the orbital mean velocity of the scatterers surrounding the Earth's orbit, over the terrestrial velocity, of the order of +25 to +30 9 . A similar difference in the mean orbital velocity of the extrasolar-planetary-dust with respect to the extrasolar planet would lead to a periodically varying difference in their radial velocities. For a circular orbit the...

Ldef And The Flux Model

As stated above, LDEF offers the most useful retrieved surface dataset. Foil penetrations and crater data span the fim to mm size regime, thus the data are self consistent over a very large particle mass range. Furthermore, the geometry of LDEF is also of great benefit for statistically resolving meteoroid fluxes from debris contaminants. LDEF was gravity gradient stabilised, such that it maintained a fixed orientation with respect to Earth. The satellite was an elongated cylinder with 12 side...

Acknowledgements

The Colloquium was sponsored by IAU Commission 22 Meteors, Meteorites and Interplanetary Dust and supported by Commission 15 Physical Study of Comets and Minor Planets , Commission 20 Positions and motions of Mnor Planets, Comets and Satellites , Commission 21 Light of the Night Sky and Commission 51 Bioastronomy search for Extraterrestrial Life and also by COSPAR. We are indebted to several organisations for financial support The International Astronomical Union, COSPAR, The Royal Astronomical...

Thermal gradients in micrometeoroids during atmospheric entry M J Genge and M M Grady

Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, UK. Melted rims found on micrometeorites recovered from Antarctic ice indicate that micrometeoroids as small as 50 J.m in diameter can maintain temperature differences of at least 600 K between their surfaces and cores. We present the results of finite element simulations of the thermal evolution of micrometeoroids during entry heating that indicate that large thermal gradients cannot arise simply as a result...

Introduction

A large number of asteroids are categorized into S-type based on their reflectance spectra. Those S-type asteroids are believed to be parent bodies of ordinary chondrites 1 , However, the steep reddened slope of their reflectance spectra and the derived mineralogies of S-type asteroids are different from those of ordinary chondrites. The mismatch between spectra of ordinary chondrites and S-type asteroids is considered to be caused by so-calledspace weathering, where high-velocity impacts of...

The Life Of A Meteoroid Stream

The basic physics behind the process of ejecting meteoroids from a cometary nucleus became straightforward as soon as a reasonably correct model for the cometary nucleus became available. Such a model for the nucleus was proposed in 1950 by Whipple 11 , the so called dirty snowball model, in which dust grains were embedded in an icy matrix. As the comet approaches the Sun, the nucleus heats up until some of the ices sublime and become gaseous. The heliocentric distance at which this occurs will...