Devastation caused by the explosion of a meteroid at low altitude in the Tunguska region of Siberia in 1908. (Imge: Wikipedia)

Every Thursday lunchtime here at the Open University, a small band of enthusiasts meet up to discuss, well, just about anything really, but mainly meteorites. Of course, the group has a nice official title: the Cosmochemistry Research Group or CRG. Sounds very techie, but it’s not really like that. We bring our own sandwiches, and cakes are generally provided. Actually, the cake is amazingly good. The chocolate brownies are out of this world, as you would expect.

So, what’s on today’s agenda? Well, due to a last minute change of plan (we have lots of those), we are going to be talking about Asteroid 2008 TC3 and its meteorite Almahata Sitta. I have been delegated to give a short slide presentation. I’m sure our discussions will touch all the main aspects of the event (see previous two blog entries): how Asteroid 2008 TC3 was detected, tracked and samples recovered. The implications of Almahata Sitta’s unusual composition is sure to be a key area of discussion.

But, after the more technical stuff, there will be the “what ifs”. Almahata Sitta exploded harmlessly at high altitude over a remote desert region. But what if it had been bigger and a little stronger? Would it have penetrated further into the atmosphere before exploding? What if such a meteoroid came down over a populated area? What if it had been like Tunguska and exploded at a much lower altitude? Ah yes! When it comes to talking about the destructive potential of a meteoroid, the Tunguska event always comes into the frame.

The Tunguska incident took place in 1908 in central Siberia. A massive explosion knocked over 80 million trees covering an area of 2,150 square kilometres. The energy from the blast is estimated to have been equivalent to 1000 times that of the Hiroshima atomic bomb. The event is generally believed to be the result of the explosive destruction of a meteoroid at low altitude, perhaps as little as 5000 metres above the ground. One unresolved issue is whether the Tunguska meteoroid was an asteroid or a comet. The suggestion that the Tunguska meteoroid was a cometry body, and hence composed of ice and dust, was first proposed by the British scientist Francis Whipple in 1930. It has remained a popular explanation for the event ever since. However, the possibility that it was asteroidal, i.e. more stony in composition, has also been suggested. The problem with a stony body is that it should have hit the ground and produced a crater. But perhaps Almahata Sitta changes all that. Here was a stony meteorite, which was so porous and friable, that it exploded high in the atmosphere. Could the Tunguska body have been similar in composition to Almahata Sitta?

So, back to the Sci-Fi movie script where we began these entries on Almahata Sitta. Perhaps in order to improve the dramatic effect, we should merge Almahata Sitta with the Tunguska incident and have the action take place over a populated area. Of course, we will need to give Bruce Willis a call.