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SMALL BODIESin their accuracy. The only thing known
with certainty is the effects produced on
the environment, of which there are many
images and some videos. Being able to
compare those effects with the aftermath
of an even smaller event, but for which we
have all the useful information to validate
the models applicable to the Tunguska
event, can get us a sufficiently precise idea
of the mass, volume, density and composi-
tion of the small asteroid that triggered
the disaster.
As we said at the beginning, the recent
Chelyabinsk event offered this opportu-
nity, becoming a sort of “Rosetta Stone” to
better interpret the Tunguska event. Un-
like previous studies that had taken into
consideration a small subset of cases based
on typical physical and dynamic properties,
the new research has greatly expanded the
series, including a new probabilistic aster-
oid impact risk model, to better evaluate
asteroid trajectory, explosion energy and
environmental effects. The model pro-
duced 50 million possible combinations,
able to cover the entire range of proper-
ties of the impactor. All possible scenarios
are sampled from probabilistic distribu-
tions representing our current knowledge
of asteroid properties, entry trajectories,
and size frequencies. The results show that
Tunguska-type events can be produced by
a wide range of impact scenarios and also
suggest that objects with diameters of 70 -
80 meters and initial energies of 20 - 30T
he illustration
on the right
shows the perime-
ter of the Siberian
area devastated
by the Tunguska
event with a red
outline. The same
perimeter was
then superim-
posed on the met-
ropolitan areas of
three major US
cities, to give an
idea of what could
happen if an
event like that of
1908 were re-
peated today in a
densely populated
region. The ani-
mation below also
extends the com-
parison to other
major cities
around the planet.
[Asteroidday.org]megatons are more likely to cause Tun-
guska-scale damage areas than objects at
the lower end of the potential size range.
Comparing these values to those previ-
ously considered closer to reality, it can beWashington, D.C.San FranciscoNew York CityTunguska 111 EN_l'Astrofilo 29/08/2019 15:43 Page 31