Physical description of a large bright halo developing around a -3 magnitude Leonid meteor

Stenbaek-Nielsen and Jenniskens [Adv. Space Res. 33, 1459, 2004] reported a bright shock-like structure developing at ~110 km around a -3 magnitude Leonid meteor. The authors speculated that it is unrealistic to assume that the structure is similar to the shock observed around re-entry vehicles as it would result in a 100 m meteor size. Although thermalization of sputtered particles has been satisfactorily employed in explaining the luminosity of high altitude meteors [Hill et al., Earth, Moon, and Planets, 95, 403, 2004; Rogers et al., Planetary and Space Sci., 53, 1341, 2005; Vinkovic, Adv. Space Res., 39, 574, 2007], here in agreement with [Stenbaek-Nielsen and Jenniskens, 2004] we argue that at 110 km altitude the mean-free path for sputtered particles is much smaller than the ~500 m structure observed. Specifically, we calculate the mean free path [e.g., Opik, Physics of Meteor Flight in the Atmosphere, 1958, p. 117] for sputtered particles with energy distributions provided in [Guttormsen et al., JGR, 125, e2020JA028229, 2020] to demonstrate that sputtered particles quickly thermalize in a short distance from the meteoroid. On the other hand, we demonstrate that UV photons from atmospheric molecular nitrogen excited by collisions with meteoric atoms are efficiently absorbed on spatial scales comparable to the structure’s dimensions [e.g., Zheleznyak et al., High Temp., 20, 357, 1982; Janalizadeh and Pasko, Plasma Sources Sci. Technol., 28, 105006, 2019]. This is broadly consistent with original suggestion of Stenbaek-Nielsen and Jenniskens [2004] that photo-chemical processes should be a root cause of the dramatic increase in size and brightness of the ablating meteor having only ~1 g mass. In this work we investigate these processes driven by absorption of the intense UV radiation from the hot plasma immediately surrounding the meteor.