Free Astronomy Magazine May-June 2020

40 MAY-JUNE 2020 SMALL BODIES boiling plasma cylinder. In other words, the exceptionally high speed of the meteoroid would cause the column of air being passed through by the meteor to be instantly ionized along its entire length, but the surrounding pressure from the rest of the atmosphere would thermally isolate this column. There would, therefore, be no heat exchange with the gas outside the plasma cylinder, as is the case in ordinary meteors. Being much slower (20-30 km/s), ordinary meteors move slowly enough to allow cold air (ions and electrons again united) to reset behind them before the end of the glowing phenome- non. It is for this reason that we can appreciate the movement of the meteors through the sky. In the case of sub-relativistic meteors, how- ever, the speeds would be hundreds of times faster (thousands of km/s), the result being an instantaneous manifestation of the boil- ing plasma phenomenon along the entire meteor trajectory without the possibility of recognizing its beginning and end in the at- mosphere. According to Siraj and Loeb, the duration of the event should not exceed one-tenth millisecond, but on the other hand, the brightness would be very high, comparable at least to that of a typical fire- A swarm of Lyrids pho- tographed above some structures of the Las Cam- panas Observa- tory, with the dome of the Opti- cal Gravitational Lensing Experi- ment (OGLE) tele- scope in the fore- ground. [Y. Belet- sky, Carnegie, TWAN, 2017] Alongside, sev- eral Geminids captured at the Kitt Peak National Observatory. In the foreground, the open dome of the Bok Telescope; just behind the dome of the Mayall telescope. [David A. Harvey, 2010]