Météoroïde | EPFL Graph Search

thumb|Météoroïde, météore (étoile filante ou bolide) et météorite. Un météoroïde est un petit corps du Système solaire (astéroïde, noyau cométaire ou fragment d'iceux) intermédiaire entre les astéroïdes, plus grands, et la poussière interplanétaire. Le terme est inventé par l'astronome Hubert Anson Newton en 1864, Description La définition de l'Union astronomique internationale fournit une gamme de tailles, entre 30 micromètres et 1 mètre, tout en précisant que ces limites sont relativement arbitraires. En deçà, on parle de poussière interplanétaire (« IDP » en anglais, pour interplanetary dust particles) ; au-delà, on utilisera le terme d'astéroïde. Son errance et sa petite taille l'amènent en général à être capturé, le plus souvent en quelques millions à centaines de millions d'années, dans le champ gravitationnel d'une planète ou d'un satellite naturel, éventuellement à se consumer dans leur atmosphère ou à s’écraser sur leur surface solide. Le terme de météoroïde est

Vertical distribution of the different types of aerosols in the stratosphere: Detection of solid particles and analysis of their spatial variability

Quentin Bourgeois

Stratospheric aerosols play a significant role in stratospheric chemistry. In the past, it was assumed that only liquid droplets are present in the stratosphere. Nevertheless, a few lidar measurements have shown that sudden enhancement of aerosol content in the middle stratosphere could be due to meteoritic debris. Aircraft measurements have shown that solid particles can be found in the lower stratosphere; these particles are mainly soot, but also include some interplanetary material. In order to better document the various characteristics of aerosols in the unperturbed stratosphere (i.e., free of volcanic aerosols), we have performed observations using different balloon-borne instruments (Stratospheric and Tropospheric Aerosol Counter (STAC), Spectroscopie d'Absorption Lunaire pour l'Observation des Minoritaires Ozone et NOx (SALOMON), and Micro Radiometre Ballon (MicroRADIBAL)) and also some satellite data (Global ozone monitoring by occultation of stars Envisat (GOMOS-Envisat)). These instruments allow us to obtain the number of particles in different size classes, the wavelength dependence of aerosol extinction, and the radiance of the light scattered by aerosols. Combining all the data together, it appears that significant amounts of particles are ubiquitous in the middle stratosphere, above the canonical sulfate aerosol layer. "Background'' interplanetary dusts in low concentration are likely present in the stratosphere. Above 30 km, interplanetary dust and largest grains from meteoroid disintegration dominate. Although the disintegration of meteoroids occurs in the upper stratosphere or in the mesosphere at all latitudes, these solid aerosols can be transported to the polar regions by the general circulation and can descend into the middle and lower stratosphere during winter mesospheric descents. Between about 22 km and 30 km, soot particles contribute to the population of aerosols at all latitudes. These soot, likely originating from biomass burning at all latitudes, could be injected into the lower stratosphere by the pyroconvective effect and can then reach the middle stratosphere perhaps owing to the gravitophotophoresis effect as was theoretically proposed. In the lower unperturbed stratosphere, liquid sulfate aerosols dominate, although soot particles are still present. Local horizontal and vertical enhancements of solid aerosols have sometimes been detected, although their origin is not yet determined. The presence of these solid particles can strongly bias the interpretation of in situ and remote sensing measurements when only the presence of liquid aerosols is assumed. Therefore, a new strategy of measurement will be necessary in the future to better characterize the stratospheric aerosol content free of volcanic particles.

2008

Scaling analysis of meteorite shower mass distributions

Anders Meibom

Meteorite showers are the remains of extraterrestrial objects which are captivated by the gravitational field of the Earth. We have analyzed the mass distribution of fragments from 16 meteorite showers for scaling. The distributions exhibit distinct scaling behavior over several orders of magnitude; the observed scaling exponents vary from shower to shower. Half of the analyzed showers show a single scaling region while the other half show multiple scaling regimes. Such an analysis can provide knowledge about the fragmentation process and about the original meteoroid. We also suggest to compare the observed scaling exponents to exponents observed in laboratory experiments and discuss the possibility that one can derive insight into the original shapes of the meteoroids.

1998

Vertical distribution of the different types of aerosols in the stratosphere: Detection of solid particles and analysis of their spatial variability

Quentin Bourgeois

2008