Free Astronomy Magazine September-October 2019

SEPTEMBER-OCTOBER 2019 SMALL BODIES be associated with the asteroid have ever been found. Even if a sin- gle crater unequivocally attributa- ble to the ground impact of an asteroid is never identified, studies from a decade ago propose Lake Cheko, located 8 km north of the epicenter, as a probable site of fall of a secondary fragment. This lake, half a kilometer long and about 300 meters wide, does not seem to have existed before 1908. The very approximate knowledge of the physical parameters of the asteroid has never allowed for an accurate description of the dynam- ics of the Tunguska event; conse- quently, all the forecasts made in the past on the possible repetition of such an occurrence were suspect S atellite views of the vast area affected by the transit and final explosion of the Tunguska as- teroid. Vanavara, North-Northwest of Lake Baikal, was in 1908 the nearest town to the epicenter. [Google Maps] has undergone some significant updates. The object that exploded in flight had to be a small rocky asteroid (although the cometary nucleus hypothesis has not been entirely ruled out), with an initial diameter between 30 and 60 meters, which traveled at least 15 km/s and which produced an en- ergy of 5-20 megatons, exploding at a height between 5 and 10 km above the ground. The explosion devastated a sur- face are of over 2000 km 2 , destroying up- to 80 million trees. No fragments that could