Monday, October 26, 2009

A question for scientifically-minded readers


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.





Impressive!

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.

Peter

10 comments:

Brad J (Kazrak) said...

My understanding is that it's specific to nuclear weapons - the gamma-ray burst from the weapon causes atmospheric interactions that cause the EMP.

Federation of American Scientists has some info.

Old NFO said...

Brad is correct. You can "tune" for an EMP with certain airbursts...

Anonymous said...

From Joe-ex-PNG:
There's a great write up here: http://www.projectrho.com/rocket/rocket3x.html#nuke

Just scroll down a bit.

Stingray said...

As stated, EMP is basically nuclear only (that, or specifically designed circuits involving magnets and such). Since this meteor's explosion was a kinetic-only event, I'd imagine the only magnetic field involved would be the one created by big chunks of iron usually found in meteors moving through earth's natural magnetic field, which would probably be dwarfed by your local power lines. It did technically produce electromagnetic radiation, but it was all (or almost all) in the visible and infrared portion of the spectrum in the light & heat from the burst.

PresterSean said...

Until recently, atomic/nuclear detonations were the only ways to create an EMP effect. There has been much research into non-nuclear ways to create such an effect- see this article; http://www.howstuffworks.com/e-bomb3.htm

Popular Science did an excellent cover article on this a number of years ago as well. In short, there would be no EMP from a normal, conventional explosion, no matter the magnitude or altitude.

Anonymous said...

Non-nuclear EMP devices have been demonstrated, but as Stingray said, they involve explosion causing other effects via electro-mechanical internal devices. I wonder the basis for comparison of the energy of this explosion with a 50KT nuke. It certainly doesn't sound like the shock caused any damage, although the ground was only about 65,000 feet away.

Leatherneck

geekWithA.45 said...

Note that wide ranging EMP effects are the interaction of the nuke detonation and the ionosphere.

All nuke detonations have an area of EMP effect, it's just that normally, this area is about the same size as the fireball, which corresponds to the the area in which steel vaporizes. This means that your ipod will cease functioning about 20 nanoseconds before it ceases existing.

Stranger said...

The problem is the "rise time" of the pulse. A rise time of a few microseconds would do little more damage than a hefty lightning strike.

Drop the rise time to a few picoseconds - essentially zero rise time - and even a small trigger event can raise unshirted hades with anything susceptible.

It does not take a great deal of energy to wipe out electronics over a wide area. In theory, the amount of energy in a couple of truck batteries could destroy the power grid over a 25-30 mile radius.

A nuke certainly creates a sufficiently short rise time event to create a massive EMP field. An even larger one can be created by a solar flare.

Look up the "Carrington Event" for details on what the Sun is capable of doing.

Stranger

Diamond Mair said...

Y'all know those folks who seem determined to "share" their taste {or lack thereof! ;-) } in music with the entire world as they're driving along? Ye-eah, I've been kicking around an idea for something along the lines of a wireless Taser, utilizing a targeted EMP capability, to fry their entire electrical systems ................. betcha they would KEEP their "music" down to a dull roar once they had to have their ENTIRE vehicular circuitry re-done .......................

Semper Fi'
DM

Thor said...

The primary method of delivering an EMP is a nuclear device, for all the reasons mentioned above.

It is possible to generate a Non Nuclear EMP, and it many facilities do this as a testing service. The keys here though are:

1. Nuclear detonations have their own "organic" EMP that is enhanced by the actual energy of the detontation.

2. Non Nuclear EMP has to find a method to generate the EMP and then enhance it using an energy source.