If this had happened over Melbourne or Sydney, or any major world city, it would still be making headlines.

On October 8, a mini-asteroid screamed into the upper atmosphere over the Indonesian coastal town of Bone, in the South Sulawesi region, and exploded with the force equivalent to two to three times that of the atom bombs that incinerated Hiroshima and Nagasaki.

It is now estimated to have been about 10 metres across and travelling at more than 20 kilometres per second.

Atmospheric pressure fiercely decelerated more than 1000 tonnes of stone to a near standstill almost instantly, converting its kinetic energy, or mass times velocity squared, into a briefly dazzling fireball.

By the time video cameras were pointed towards it, all that remained was a very high altitude trail of debris and the twisted expansion of the compressed air the object punched through the sky ahead of its disintegration.

The blast was detected by a network of infrasound monitoring stations maintained by the Comprehensive Nuclear test Ban Treaty Organisation at distances of up to 18,000 kilometres.

The Bone object wasn’t seen coming. It was well below the minimum 200-300 metres diameter range that the killer comet and asteroid warning observatories are likely to pick up, although objects this “small” have been found and tracked in the past.

As NASA and the authors of a detailed Canadian analysis of the event point out, the most common types of stony asteroids would not be expected to cause ground damage unless their diameters were about 25 meters wide or larger.

Objects the size of the Bone meteorite are currently estimated to collide with the outer atmosphere once every 2-12 years.

The Bone fireball is a sharp reminder of an often-made prediction by astronomers studying earth crossing objects.

That is: some time this century, as the human species expands into a larger target across the surface of the earth, a dangerously large rock or comet shard will burn a city, instead of explode over a wilderness such as the Tunguska meteorite of 1908, and millions will die.

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Peter Fray
Peter Fray
Editor-in-chief of Crikey
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