I'm sure many readers will have heard of the explosion that took place high over Indonesia earlier this month. For those who missed it, New Scientist reports:
On 8 October an asteroid detonated high in the atmosphere above South Sulawesi, Indonesia, releasing about as much energy as 50,000 tons of TNT, according to a NASA estimate released on Friday. That's about three times more powerful than the atomic bomb that levelled Hiroshima, making it one of the largest asteroid explosions ever observed.
However, the blast caused no damage on the ground because of the high altitude, 15 to 20 kilometres above Earth's surface, says astronomer Peter Brown of the University of Western Ontario (UWO), Canada.
Brown and Elizabeth Silber, also of UWO, estimated the explosion energy from infrasound waves that rippled halfway around the world and were recorded by an international network of instruments that listens for nuclear explosions.
The explosion was heard by witnesses in Indonesia. Video images of the sky following the event show a dust trail characteristic of an exploding asteroid.
The amount of energy released suggests the object was about 10 metres across, the researchers say. Such objects are thought to hit Earth about once per decade.
No telescope spotted the asteroid ahead of its impact. That is not surprising, given that only a tiny fraction of asteroids smaller than 100 metres across have been catalogued, says Tim Spahr, director of the Minor Planet Center in Cambridge, Massachusetts. Yet objects as small as 20 or 30 metres across may be capable of doing damage on the ground, he says.
There's more at the link.
Here's a video clip from an Indonesian news broadcast, showing the trail left high in the sky by the asteroid and its explosion.
However, I'm puzzled. I've always understood that an explosion of that force, that high in the atmosphere, would produce some form of electromagnetic pulse or EMP. The recent EMPACT Conference examined the danger, and the vulnerability of the US electrical grid to an EMP attack or incident is well known. However, this explosion - certainly as large or larger than many nuclear and/or thermonuclear warheads - doesn't seem to have produced any disabling EMP, either directly or as a side-effect.
I don't understand this. Is EMP, perhaps, solely a by-product of a nuclear explosion? That doesn't make sense to me, because militaries all over the world are working on EMP weapons using conventional explosives and technologies. It seems to me that an asteroid explosion of this magnitude, at this altitude, should produce massive radiation in at least parts of the electromagnetic spectrum. I'd have thought that would produce EMP as a side-effect. Am I wrong? Can any scientifically-minded readers explain? If so, I'd be grateful.