Physical characteristics and occurrence rates of meteoric plasma layers detected in the Martian ionosphere by the Mars Global Surveyor Radio Science Experiment

Low-altitude plasma layers are present in 71 of 5600 electron density profiles from the Martian ionosphere obtained by the Mars Global Surveyor Radio Science experiment. These layers are produced by the ablation of meteoroids and subsequent ionization of meteoric atoms. The mean altitude of the meteoric layer is 91.7 +/- 4.8 km. The mean peak electron density in the meteoric layer is (1.33 +/- 0.25) x 10(10) m(-3). The mean width of the meteoric layer is 10.3 +/- 5.2 km. The occurrence rate of meteoric layers varies with season, solar zenith angle, and latitude. Seasonal variations in occurrence rate are particularly strong, often exceeding an order of magnitude. Meteoric layer altitude, peak electron density, and width are all positively correlated, with correlation coefficients of 0.3-0.4. Other correlation coefficients between the physical characteristics of meteoric layers and atmospheric or observational properties, such as scale height, solar zenith angle, and solar flux, have absolute values that are significantly smaller, indicating lack of correlation. The photochemical lifetime of plasma in meteoric layers is similar to 12 days and depends on altitude.