Natural Hazards and Earth System Science www.nat-hazards-earth-syst-sci.net 1561-8633 1684-9981 4 5/6 2004 10.5194/nhess-4-793-2004 http://www.nat-hazards-earth-syst-sci.net/4/793/2004/ http://www.nat-hazards-earth-syst-sci.net/4/793/2004/nhess-4-793-2004.html http://www.nat-hazards-earth-syst-sci.net/4/793/2004/nhess-4-793-2004.pdf 793 798 2004-11-30 Interpretation of the microwave non-thermal radiation of the Moon during impact events V. Grimalsky A. Berezhnoy A. Kotsarenko N. Makarets S. Koshevaya R. Pérez Enríquez Instituto Nacional de Astrofisica, Optica y Electronica (INAOE), Puebla, Mexico Advanced Research Institute for Science and Engineering, Waseda University, Tokyo, Japan Now at: Sternberg Astronomical Institute, Moscow University, Moscow, Russia Centro de Geociencias, Juriquilla, UNAM, Querétaro, Mexico Kyiv National Shevchenko University, Faculty of Physics, Kyiv, Ukraine Universidad Autonoma del Estado de Morelos (UAEM), CIICAp, Cuernavaca, Mexico The results of recent observations of the non-thermal electromagnetic (EM) emission at wavelengths of 2.5cm, 13cm, and 21cm are summarized. After strong impacts of meteorites or spacecrafts (Lunar Prospector) with the Moon's surface, the radio emissions in various frequency ranges were recorded. The most distinctive phenomenon is the appearance of quasi-periodic oscillations with amplitudes of 3–10K during several hours. The mechanism concerning the EM emission from a propagating crack within a piezoactive dielectric medium is considered. The impact may cause the global acoustic oscillations of the Moon. These oscillations lead to the crackening of the Moon's surface. The propagation of a crack within a piezoactive medium is accompanied by the excitation of an alternative current source. It is revealed that the source of the EM emission is the effective transient magnetization that appears in the case of a moving crack in piezoelectrics. The moving crack creates additional non-stationary local mechanical stresses around the apex of the crack, which generate the non-stationary electromagnetic field. For the cracks with a length of 0.1–1µm, the maximum of the EM emission may be in the 1–10GHz range.