Satellite observation of the dust trail of a major bolide event over the Bering Sea on December 18, 2018

Abstract

One of the most energetic bolide events in recent decades was detected by the US Government sensors (USGS) over remote areas of the Bering Sea on December 18, 2018, 23:48 UT. No ground-based optical observations exist. Using the satellite imagery of the dust trail left behind by the bolide, we tried to reconstruct the bolide trajectory. In combination with the bolide speed reported by the USGS, we computed the pre-atmospheric orbit. Observations in various spectral bands from 0.4 to 13.3 microns enabled us to study the dust properties. Images of the dust trail and its shadow obtained from various angles by the MISR instrument on board the Terra satellite and geostationary satellites Himawari-8 and GOES-17 were used. The initial position and orientation of the trail was varied, and its projections into the geoid coordinate grid were computed and compared with real data. Trail motion due to atmospheric wind was taken into account. Radiances and reflectances of selected parts of the dust trail were taken from the MODIS instrument. Reflectance spectra were compared with asteroid spectra. The bolide radiant was found to be 13 +/- 9 degrees from that reported by the USGS, at azimuth 130\degr\ (from south to west) and zenith distance 14\degr. The bolide position was confirmed, including the height of maximum dust deposition around 25 km. The incoming asteroid had to be quite strong to maintain a high speed down to this height. The speed of 32 km/s, reported by the USGS, was found to be plausible. The orbit had a high inclination of about 50\degr\ and a perihelion distance between 0.95-1 AU. The semimajor axis could not be restricted well but was most probably between 1-3 AU. The dust reflectance was much lower in the blue than in the red, consistent with the material of A- or L-type asteroid. The absorption at 11 microns confirms the presence of crystalline silicates in the dust.