Mario Di Martino | Searcharxiv

arXiv2023

Computation of a possible Tunguska's strewn field

On June 30, 1908, at about 0h 14.5m UTC, the Tunguska Event (TE) occurred, most likely caused by the fall of a small stony asteroid of about 50-80 meters in diameter over the basin of the Tunguska River (Central Siberia). This paper will establish whether stony macroscopic fragments could have survived the TCB's airburst (Tunguska Cosmic Body) and where they might have fallen. For this purpose, we have implemented a fall model to describe the mass ablation, pancake expansion, airburst and fragments's dark flight. In our scenario, the fragments have a higher mean strength than the main body due to Weibull's law. The results, for a TCB with a kinetic energy of 15 Mt, atmospheric speed in the range of 11-20 km/s, trajectory inclination of $35^\circ$ and average strength in the range of 3-70 MPa, tell us that for a macroscopic fragment with a mean strength between 14-85 MPa would be possible to survive the high pressure and temperature airburst to reach the ground. The falling speed of the fragments is in the range of 0.8-0.5 km/s, favouring their burial in the permafrost. The range of mean strength values for the TCB's macroscopic fragment appears physically plausible if we consider the falls of Carancas in 2007, with an estimated strength in the range of 20-40 MPa. So our possible strewn field, computed for a typical fall speed of $10 \pm 3 $ km/s, is located about 11 km northwest from the epicentre, with an area of about $140~\textrm{km}^2$. Finally, Cheko Lake, which by some authors is considered an impact crater, falls about 3.5 km outside the strewn fields at 3 sigma level and it is unlikely that it could be a real impact crater: only if the TCB's trajectory had an azimuth in the range $150^\circ - 180^\circ$ would be in the strewn field area, but this is not consistent with the most likely trajectory azimuth.

astro-ph.EP↗

arXiv2020

Luminous efficiency based on FRIPON meteors

In meteor physics the luminous efficiency $τ$ is used to convert the meteor's magnitude to the corresponding meteoroid's mass. However, lack of sufficiently accurate verification methods or adequate laboratory tests leave this parameter to be controversially discussed. In this work meteor/fireball data obtained by the Fireball Recovery and InterPlanetary Observation Network (FRIPON) was used to calculate the masses of the pre-atmospheric meteoroids which could in turn be compared to the meteor brightnesses to assess their luminous efficiencies. For that, deceleration-based formulas for the mass computation were used. We have found $τ$-values, as well as the shape change coefficients, of 294 fireballs with determined masses in the range of $10^{-6}$ kg - $100$ kg. The derived $τ$-values have a median of $τ_{median}$ = 2.17 %. Most of them are on the order of 0.1 % - 10 %. We present how our values were obtained, compare them with data reported in the literature, and discuss several methods. A dependence of $τ$ on the pre-atmospheric velocity of the meteor, $v_e$, is noticeable with a relation of $τ=0.0023 \cdot v_e^{2.3}$. The higher luminous efficiency of fast meteors could be explained by the higher energy released. Fast meteoroids produce additional emission lines that radiate more efficiently in specific wavelengths due to the appearance of the so-called second component of higher temperature. Furthermore, a dependence of $τ$ on the initial meteoroid mass, $M_e$, was found, with negative linear behaviour in log-log space: $τ=0.48 \cdot M_e^{-0.47}$. This implies that the radiation of smaller meteoroids is more efficient.

astro-ph.EP↗