Free Astronomy Magazine May-June 2020

39 SMALL BODIES Siraj and Loeb have applied their model to hypothetical sub-relativistic meteoroids with diameters between 1 mm and 100 mm, which enter the atmosphere perpendicular to the surface and produce effects essen- tially starting from a height of 10 km. The researchers’ goal was to track the evolution of the plasma generated by sub-relativistic meteors in order to determine what type of signal they might produce, then provide as- tronomers with information on what to look for. The results indicate that a large part of a meteoroid’s energy would be re- leased into the upper atmosphere and would feed the adiabatic expansion of a A Perseid shower in the sky over the Na- tional Astronomical Observatory of Japan, the sum of images taken with the Moon illuminating the horizon. [NAOJ, 2017]