¹Masahisa Yanagisawa, ¹Yuki Uchida, ¹Seiya Kurihara, ²Shinsuke Abe, ²Ryota Fuse, ³Satoshi Tanaka, ⁴Keisuke Onodera, ⁵Taichi Kawamura, ⁶Ryuhei Yamada
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2025.11648]
¹Department of Engineering Science, The University of Electro-Communications, Japan
²Department of Aerospace Engineering, Nihon Univ., Japan
³Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Japan
⁴Earthquake Research Institute, The University of Tokyo, Japan
⁵Institut de Physique du Globe de Paris, University of Paris Diderot, France
⁶School of Computer Science and Engineering, The University of Aizu, Japan
Copyright Elsevier

Lunar impact flashes are observed at collisions of meteoroids against the non-sunlit lunar surface. They appear suddenly and usually last only 0.1 s or less in visible light. Using our spectral video cameras, we made observations to obtain their low dispersion spectra from Oct. 2017 to Dec. 13, 2018. We detected five flashes confirmed by multiple site observations and eight unconfirmed flashes. The spectra of the confirmed flashes in the 400–800 nm wavelengths are continuous and red. The best-fitted single blackbody spectra to these spectra show temperatures of 2200–4000 K. The spectrum at the beginning of the brightest confirmed flash may show the optical radiation from the impact-generated vapor plume. The rapid cooling of the impact-generated fine droplets could explain the decrease in brightness and temperature between the subsequent two video frames. The temperature of this flash remained above 2300 K, even 80 ms (milliseconds) after the flash appearance, indicating the existence of coarse incandescent ejecta that cools slowly. This flash’s spectral evolution would show the following three processes of meteoroids’ impact phenomena on the moon: vapor plume generation, rapid cooling of fine droplets that would be later the lunar spherical glasses, and the ejection of incandescent coarse particles probably melt and solid particle aggregates.