100 years ago today in Tunguska, Siberia something happened.

[GabonX]

But I don't understand why a meteor / comet / heavenly body explodes in the air, rather than slamming into the ground.
I'm no scientist, but why the air burst, instead of an impact?

A comet is basically a big object of dirty ice. rentry puts a lot of heat stress on an object. Most metals will simply go molten since they are good heat conductors, but water ice is actually a good insulator so the stresses on the comet from the heat gradients can cause the object to massively break up, much like an ice cube can suddenly explode with a crack sometimes in liquid. Of course since the object is traveling at supersonic speeds a significant change to its aerodynamics will cause such breakups to explode violently.

Sort of like the space shuttle.

The idea that this was a piece of ice doesn't hold up as there were miles upon miles of charred trees.

[Iliad]

It was the last time my civilisation visited our base here on Earth

I thought no drinking and travelling in space?

[muy_thaiguy]

It was the last time my civilisation visited our base here on Earth

I thought no drinking and travelling in space?

Apparently, it's legal in this solar system.

[Minister Masket]

I've got one word to say to you, just one word:

Aliens

What? Whose wife?

PS. No, you don't get this joke, unless you know Latin and are on my wavelength...

I know a bit of Latin (see my sig), but I highly doubt you're on my wavelength.

[heavycola]

When something happens in Tunguska, Siberia, nothing happens, it's just another russian dead.

[tzor]

The idea that this was a piece of ice doesn't hold up as there were miles upon miles of charred trees.

Wiki states, "Comet nuclei are in a range from 1/2 kilometer to 50 kilometers across and are composed of rock, dust, water ice, and frozen gases such as carbon monoxide, carbon dioxide, methane and ammonia." Methane and ammonia could easily be the fuel to start a fire. Moreover who is to say that when a comet goes through the atmosphere it might also cause a lightning strike?

[Nickbaldwin]

The idea that this was a piece of ice doesn't hold up as there were miles upon miles of charred trees.

Wiki states, "Comet nuclei are in a range from 1/2 kilometer to 50 kilometers across and are composed of rock, dust, water ice, and frozen gases such as carbon monoxide, carbon dioxide, methane and ammonia." Methane and ammonia could easily be the fuel to start a fire. Moreover who is to say that when a comet goes through the atmosphere it might also cause a lightning strike?

The heat from re-entry would be enough to break apart the ice and rock and ignite the gases.