High Altitude Meteors Explained by Thermalization of Sputtered Particles
Abstract
High altitude meteors are characterized by anomalous beginning heights of more than 130 km. They appear as diffuse structures, which transform into comet-like structures while approaching the 130 km altitude. Since the standard theory of meteor ablation is not applicable at these altitudes, the nature of these meteors has remained unexplained. Here we describe a theoretical model that successfully addresses all aspects of this phenomenon. The diffuse radiation is produced by fast particles sputtered from the meteoroid surface through collisions with the atmosphere. Each sputtered particle produces a cascade of atmospheric collisions during thermalization on the spatial and temporal scale dictated by the atmospheric mean free path. This creates a coma due to radiation from a large number of excited atmospheric particles. The shape of the coma is changing as the meteoroid reaches lower altitudes. The exact structural appearance of this coma depends on the relative position between the observer and the meteor path and on the resolution and sensitivity of the detector. We performed direct simulation Monte Carlo calculations and reproduced typical observational signatures of high altitude meteors. In the context of this theoretical picture, the phenomenon of jets from meteors can be interpreted simply as a modulation in the ejection properties of sputtered particles. However, the size of meteors below 130 km still remains a mystery. Transverse sizes of 1 km are reported for Leonids at altitudes as low as 100 km. The interaction with the atmosphere is still molecular at these altitudes and no particle can reach that distance from the meteoroid body on the timescale of a meteor event. Explanations based on dustball models can also be ruled out by the imaging data. The only remaining explanation is that at these altitudes the atmosphere becomes dense enough to glow under the light produced by the meteor.
- Publication:
-
35th COSPAR Scientific Assembly
- Pub Date:
- 2004
- Bibcode:
- 2004cosp...35.2094V