Deepest ever photographed Geminid with small but not negligible terminal mass

Abstract

We report an instrumental observation of the very exceptional Geminid fireball which was observed in scope of the Czech part of the European Fireball Network (EN) on 13 December 2012 at 4h12m59.4s UT. The uniqueness of this Geminid fireball consists of the record depth of its penetration in the atmosphere (to the height of 32.5 km) and in the fact that most likely a very small fraction of its initial mass survived severe deceleration in the atmosphere and landed on the ground. Such deeply penetrating Geminid with so precise and reliable data has not yet been observed. From a comparison with a large number of Geminids observed by the European Fireball Network and all brightest Geminids from the Prairie Fireball Network in USA and the Canadian MORP Network, we have shown that for Geminids with an entry mass greater than approximately 10 grams, the terminal altitude limit does not decrease further as it does for smaller Geminids, but remains constant at around 38 km. In this comparison, we have shown that there is only one exception, and that is the Geminid presented here. This one penetrated nearly 6 km deeper with very low terminal speed for Geminids. During the atmospheric flight this Geminid meteoroid slowed down from its original speed of 35.75 km/s to 6.8 km/s. This small meteoroid with initial mass of only 0.25 kg is probably the fastest candidate for a meteorite dropping event ever observed. This solid meteoroid belonging to the meteor shower survived a significant dynamic pressure of almost 2 MPa and thus ranks among the interplanetary bodies of asteroidal origin that caused the observed meteorite fall. Although a similar Geminid event has been previously presented in the literature, we demonstrate here that this claim was flawed.

Figures (11)

• Figure 1: All-sky and detailed images of the EN131212_041258 Geminid fireball from both stations. (a) Left - station Přimda, (b) Right - station Churáňov.
• Figure 2: Radiometric curve obtained by AFO at the Přimda station. The marked heights (dashed lines) delimit the area of regular brightness fluctuations (see section 3.3) and also heights of two consecutive flares, which correspond to fragmentation events described in section 3.4.
• Figure 3: Ground projection of the recorded atmospheric trajectory (yellow arrow) of the EN131212_041258 Geminid fireball and location of the Czech stations Přimda and Churáňov where its records were taken. The average slope of the atmospheric trajectory was 54.7 and its length was 81.9 km. (source of the map: Google Earth)
• Figure 4: Detailed section of the radiometric light curve of the EN131212_041259 Geminid fireball recorded independently at both stations, showing the area of periodic fluctuations corresponding to altitudes between 73.2 and 61.3 km, as indicated in Figure \ref{['LCint_11fin']}
• Figure 5: Frequency of periodic fluctuations as a function of fireball time. The range of values corresponds to heights from 73.2 km to 61.3 km. It is evident that the frequency increases with time, and this trend is approximately exponential.