The 1908 Tunguska air burst over a forested region of Russia released energy equivalent to up to 5 megatons of TNT, and is one of the largest such events in recorded history. Long attributed to the impact of an exraterrestrial body, the lack of large-scale meteorite material at the Tunguska site has made it difficult to determine whether the event was caused by a comet or a meteorite.
In a new study in the journal Planetary and Space Science, an international team of researchers has presented evidence that the Tunguska event was the result of a meteorite, and not a comet. Analyzing micro-samples taken from peat near the Tunguska epicenter, the researchers identified nano-inclusions of the minerals troilite (FeS), taenite (Fe-Ni, y-Fe and schreibersite ((FeNi)3P) within carbon fragments, and speculate that these inclusions are the result of intrusion of the molten minerals into carbon-rich material due to a meteorite impact, followed by rapid crystallization and cooling.
While a terrestrial origin for the samples can't be entirely ruled out, the identified minerals, as well as the samples' elevated Fe-Ni ratio, suggest that the Tunguska samples may be the remains of an iron meteorite.
You can read the study and view images of the Tunguska samples here!