The Utility of Infrasound in Global Monitoring of Extraterrestrial Impacts: A Case Study of the 2008 July 23 Tajikistan Bolide

Among various observational techniques used for detection of large bolides on a global scale is a low frequency sound known as infrasound. Infrasound, which is also one of the four sensing modalities used by the International Monitoring System (IMS), offers continuous global monitoring, and can be leveraged for planetary defense. Infrasonic records can provide an additional dimension for event characterization and a distinct perspective that might not be available through any other observational method. This paper describes infrasonic detection and characterization of the bolide that disintegrated over Tajikistan on 23 July 2008. This event was detected by two infrasound stations at distances of 1530 and 2130 km. Propagation paths to one of the stations were not predicted by the model despite being clearly detected. The presence of the signal is attributed to the acoustic energy being trapped in a weak but leaky stratospheric AtmoSOFAR channel. The infrasound signal analysis indicates that the shock originated at the point of the main breakup at an altitude of 35 km. The primary mode of shock production of the signal detected at the two stations was a spherical blast resulting from the main gross fragmentation episode. The energy estimate, based on the signal period, is 0.17-0.51 kt of TNT equivalent, suggesting a mass of 6.6-23.5 tons. The corresponding object radius, assuming the chondritic origin, was 0.78-1.18 m.