An ET Origin for Stratospheric Particles Collected during the 1998 Leonids Meteor Shower

Abstract

On 17 November 1998, a helium-filled weather balloon was launched into the stratosphere, equipped with a xerogel microparticle collector. The three-hour flight was designed to sample the dust environment in the stratosphere during the Leonid meteor shower, and possibly to capture Leonid meteoroids. Environmental Scanning Electron Microscope analyses of the returned collectors revealed the capture of a $\sim$30-$μ$m particle, with a smooth, multigranular shape, and partially melted, translucent rims; similar to known Antarctic micrometeorites. Energy-dispersive X-ray Mass Spectroscopy shows enriched concentrations of the non-volatile elements, Mg, Al, and Fe. The particle possesses a high magnesium to iron ratio of 2.96, similar to that observed in 1998 Leonids meteors (Borovicka, {\it et al.} 1999) and sharply higher than the ratio expected for typical material from the earth's crust. A statistical nearest-neighbor analysis of the abundance ratios Mg/Si, Al/Si, and Fe/Si demonstrates that the particle is most similar in composition to cosmic spherules captured during airplane flights through the stratosphere. The mineralogical class is consistent with a stony (S) type of silicates, olivine [(Mg,Fe)$_{2}$SiO$_{4}$] and pyroxene [(Mg,Fe)SiO$_{3}$]--or oxides, herecynite [(Fe, Mg) Al$_{2}$O$_{4}$]. Attribution to the debris stream of the Leonids' parent body, comet Tempel-Tuttle, would make it the first such material from beyond the orbit of Uranus positively identified on Earth.