5. A new analysis of the Tunguska event
By means of Eq. (6) we can replace Table 1 with a new table for the breakup speeds of different types of cosmic body (see Table 2). Note that now the inferred speed for an iron body would be too high, and stony bodies provide the most plausible solution. This is consistent with the results of a detailed analysis of several hundreds meteors carried out by Ceplecha & McCrosky (1976) and Ceplecha (1994), who found that a height around 10 km is fairly typical for stony objects.
Table 2. Speed of the Tunguska cosmic body vs. strength according to Eq. (6)
We can now calculate other data for the Tunguska event solving the equations of motion and the luminosity equation, according to the procedure described in Foschini (1998). The results are summarized in Table 3. The following assumptions have been made: (i) the luminous efficiency is ; (ii) the diameter of the object is calculated assuming a spherical shape and a density of 3500 kg/m3, typical for a stony object.
Table 3. Summary on the properties of the Tunguska Cosmic Body a From Ben-Menahem (1975). b Over the horizon. c Clockwise from North.
Comparing these results to previous ones and to the available data (for a review see Vasilyev 1998), we note a generally good agreement, except for the trajectory inclination over the horizon. The value obtained here is about , while Vasilyev reported that the most likely inclination angle was about . However, he also noted the possibility of a good aerodynamic shape of the Tunguska cosmic body, that may have decreased the inclination angle. Moreover, we have neglected the lift effects, following Chyba et al. (1993).
Among the authors quoted by Vasilyev, only Sekanina derived an angle lower than . Interestingly, it was just Sekanina (1998) who strongly favoured the conclusion of an asteroidal origin for the Tunguska cosmic body. The results obtained here provide additional support for Sekanina's conclusion.
© European Southern Observatory (ESO) 1999
Online publication: December 22, 1998