An investigation of the 27 July 2018 bolide and meteorite fall over Benenitra, southwestern Madagascar

Abstract

Several dozen stones of an ordinary chondrite meteorite fell in and around the town of Benenitra in southwestern Madagascar during the early evening of 27 July 2018, minutes after a widely observed meteor fireball (bolide) transit and detonation. The event was confirmed by low-frequency infrasound recordings received at ~17h15 UTC (Coordinated Universal Time; 19h15 local time) at the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO) infrasound station I33MG near Antananarivo, 542 km northnortheast of Benenitra. An energy release equivalent to 2.038 kt of TNT was calculated from the infrasound signals. Seismograph readings at the SKRH station 77 km north-northwest of Benenitra recorded a twostage signal consistent with the arrivals of an initial air-coupled ground wave at 16h48:08 UTC and a stronger pulse at 16h49:22 UTC linked directly to the atmospheric pressure wave. The infrasound and seismic signal arrival times suggest that the bolide entry and detonation occurred at approximately 18h46 local time (16h46 UTC), entry was from the northwest, and the detonation hypocentre was located within ~20 km of Benenitra. Despite meteorite debris being found among buildings within Benenitra, there was no damage to structures or injuries reported. Eyewitness accounts and photographic records indicate that approximately 75 mostly intact stones were collected; however, the remoteness of the area, the rugged nature of the terrain and sales of fragments to meteorite collectors have limited scientific analysis of the fall and the extent of the strewn field. The total mass of recovered stones is estimated at between 20 kg and 30 kg, with one fragment of 11.2 kg and several of ~1 kg. Petrographic and mineral chemical analyses indicate that the stones belong to the L6 class of ordinary chondrites. Cosmogenic radionuclide analysis confirms that the fall is linked to the bolide event. The name Benenitra has been officially accepted by the Meteoritical Bulletin Database.

New Evidence for Wet Accretion of Inner Solar System Planetesimals from Meteorites Chelyabinsk and Benenitra

“…In addition to the thermal metamorphism, heat can be locally produced by impacts and cause partial melting. Benenitra shows a low weak shock stage (S3; Gibson et al 2021), and Chelyabisk has been moderately shocked (Stage S4; Ozawa et al 2014), indicating that their parent bodies have experienced impact events. However, because the cooling rates of ordinary chondritic materials are high (200-600 K per 1000 yr; Ganguly et al 2016), the high post-shock temperatures (up to 1500 K) could not last long to drive water/hydrogen out and modify the D/H ratios of minerals.…”

New evidence for wet accretion of inner solar system planetesimals from meteorites Chelyabinsk andBenenitra

“…In addition to the thermal metamorphism, heat can be locally produced by impacts and cause partial melting. Benenitra shows low weak shock stage (S3, Gibson et al 2021) and Chelyabisk has been moderatly shocked (Stage S4, Ozawa et al 2014), indicating that their parent bodies have experienced impact events. However, because the cooling rates of ordinary chondritic materials are high (200-600K/thousand years, Ganguly et al 2016), the high post-shock temperatures (up to 1500 K) could not last long to drive water/hydrogen out and modify the D/H ratios of minerals.…”