3-D reconstruction (viewpoint from S) of the morphology of the Lake Cheko based on real topographic /bathymetric data. The water level has been placed 40 m below the actual level to enhance underwater morphological features. This small lake (500 m diameter; 50 m maximum depth) is located 8 km NW of the inferred epicentre of the explosion.
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A possible crater
An accurate analysis of the data collected by our 1999 expedition together with the results of field researches performed in 2002, 2008 and 2009 have lead to the formulation of the hypothesis that the Tunguska bolide underwent fragmentation or was one of the 20% of NEAs that are double bodies. In this picture, the disintegration in the atmosphere of the main body was the cause of the known devastations, while a secondary body has originated a crater now filled by Lake Cheko.
This hypothesis was presented in a series of four papers (2007-2011):
Our papers have stimulated an intense scientific debate
(See: some citations), as well as a diffuse interest in local media of many countries.
Some of the evidence in favour of the impact hypothedis is: 1) the unusual, funnel-like morphology of the lake, different from that of common thermokarst Siberian lakes, but compatible with a “soft” low-velocity (<1 km/s) impact crater of a m-size projectile in a swampy ground with permafrost; 2) the lake appears to be not older than 1908, as suggested by radiometric dating of the lacustrine sediments and by the absence of aquatic plant pollens in sediments older than 1908; 3) a clear magnetic/density anomaly is present at the lake centre, about 10m below the bottom; 4) the patterns of growth ring in trees surviving the 1908 event and in trees born after the event.
These data suggest that Lake Cheko was probably formed in 1908 as a consequence of an impact, and that below its bottom we could find markers of the “impactor” that could tell us whether the Tunguska cosmic object was an asteroid or a comet. Our findings are in line with the ideas of Leonid Kulik, who first explored the devastated area. In fact, Kulik spent long a time searching for multiple craters left by the impact with the ground, possibly caused by fragments of a cosmic body that he believed was an asteroid. It is remarkable that his interpretation of the Tunguska Event could be re-evaluated almost a century later.
The crater hypothesis has been illustrated in