In early summer 1908, something blew up -- quite impressively -- over a remote location in Siberia near the Podkamennaya Tunguska river. Trees were flattened for hundreds of square kilometers, the pressure from the air blast registered all over the world, and witnesses saw a huge fireball trailing smoke.
Yet there was no crater.
This set scientists to thinking that whatever it was blew up high in the atmosphere, disintegrating the object. The blast downward felled the trees, and since it didn't hit the ground, no crater was created. There has been no trace of the object ever found, either; no meteorites of any kind.
Now some scientists have claimed to have found a crater. A 500 meter long and 50 meter deep lake sits in the flight path of the object, and the bottom of the lake is funnel shaped, very unusual for a lake in the area. They surmise a ten meter chunk of the object survived the explosion and landed in the swampy area, carving out the depression.
I'm not sure I am all that swayed by their evidence as reported in the article, though. The shape of the crater isn't consistent with an impact crater, for one. For another, a ten meter chunk is big, and you'd expect to see many smaller fragments... millions of them, in fact. Yet none has been found. Another explosion over Russia four decades later created the Sikhote Alin meteorite fragments, and thousands of them have been found (I own several, in fact). So we have precedent for assuming we'd see lots of smaller fragments. Where are they?
A rocky asteroid would have left fragments, but solid ice would have vaporized completely. Maybe the impactor was a solid block of ice with little or no rock, but that seems mighty unusual.
Mysteries still abound (though we're pretty sure it wasn't a UFO or black hole, as some kooks have claimed). But the scientists who looked at the lake said they're going back to do a more thorough investigation. I'm all for that! After all these years it's time we put this event to bed. We know a lot more about impact physics than we did 100 years ago, so I'd like to see a detailed examination by experts of the area.