Ken Tapping, April 1, 2009

Scientists are very interested in meteors and meteorites. Firstly these objects are samples of material from beyond our world. They might be bits knocked off the Moon, Mars or other planets, or from construction material left over from building the Sun and planets. There is a chance they are ambassadors from the Outer Solar System, or even from interstellar space.

What these objects can tell us goes far beyond what we learn from holding them in our hands and from testing them in the laboratory. We want to know their track through the atmosphere on their way to the ground, not only because we want to work out where they came down so that we can recover them; what we would really like to do is calculate their orbits: their path through space up to the time our planet got in the way. If we can estimate the orbit we can get a much better idea of where that rock or piece of nickel iron came from. What scientists dream about detecting the object well before it ploughs into our atmosphere. That doesn't happen very often. However, on October 7, 2008, that's exactly what happened.

On October 6, a small object was detected approaching Earth. Designated 2008 TC3 it was estimated to be a few metres in diameter. On the basis of the observations, its discoverers calculated it would hit the atmosphere at 02:46 Greenwich Mean Time on October 7. It would enter the atmosphere over the Sudan, and being quite large, was expected to form a very spectacular fireball. The spectacle was seen from an airliner, from satellites and by many people on the ground. One curiosity was that it exploded into many fragments quite early in its descent through the atmosphere, some 37 kilometres above the ground. With the precise tracking information it was possible to make a good estimate as to where the fragments landed on the ground. NASA provided the information, and a professor and some students from the University of Khartoum set out to find them, which they did.

That the object disintegrated so high up suggests it was made of relatively weak material, formed under circumstances where it was not compressed by strong gravity. This is especially interesting because this event resembles what happened when an object exploded in the atmosphere over Tagish Lake, BC, in January, 2000. This event produced a fireball seen all over the Yukon and Northwest Territories. Some of the fragments contained organic (carbon-based) molecules. The presence of these does not prove there is life elsewhere in the universe, but it's encouraging.

These events may teach us something more about what happened at Tunguska in Siberia in 1908, when an object exploded high in the atmosphere with an explosion large enough to flatten trees for many miles. Luckily, the Khartoum and Tagish Lake objects were too small to be a serious threat, but the Tunguska object was much larger. We detected 2008 TC3 20 hours before it entered the atmosphere, which was too late for us to do much about it. How soon could we detect another Tunguska object, and what could we do about that?

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Ken Tapping is an astronomer at the National Research Council Herzberg Institute of Astrophysics (NRC-HIA), and is based at the Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9 Tel (250) 493-2277, Fax (250) 493-7767,
E-mail: ken.tapping@nrc-cnrc.gc.ca