Spaceborne ultraviolet 251-384 nm spectroscopy of a meteor during the 1997 Leonid shower

Abstract

We used the ultraviolet to visible spectrometers onboard the midcourse space experiment to obtain the first ultraviolet spectral measurements of a bright meteor during the 1997 Leonid shower. The meteor was most likely a Leonid with a brightness of about -2 magnitute at 100 km altitude. In the region between 251 and 310 nm, the two strongest emission lines are from neutral and ionized magnesium. Ionized Ca lines, indicative of a hot T roughly equal to 10 000 K plasma, are not detected. The Mg and Mg+ line intensity ratio alone does not yield the ionization temperature, which can be determined only by assuming the electron density. A typical air plasma temperature of T = 4400 K would imply a very high electron density: ne = 2.2 x 10^18 m-3, but at chondritic abundances of Fe/Mg and Si/Mg which equals approximately 1. For a more reasonable local-thermodynamic-equilibrium (LTE) air plasma electron density, the Mg and Mg+ line ratio implies a less than chondritic Fe/Mg = 0.06 abundance ratio and a cool non-LTE T = 2830 K ionization temperature for the ablation vapor plasma. The present observations do not permit a choice between these two alternatives. The new data provide also the first spectral confirmation of the presence of molecular OH and NO emission in meteor spectra.