Call that a meteorite?

As reported by Uncertain Principles and Bad Astronomy, there was a meteorite impact in Northern Norway – Tromsø area.

Initial reports were “impact compared to atomic bomb”…
here is the proper report, including seismic signal – really did impact.

Current reports suggest it was a ~ 10kg rocky meteorite.
Meteors hit at 10-40 km/sec, typically, or 108-9 J/kg of energy.

Now there are 4.2 GigaJoules per ton of TNT. So the impact energy was actually about the same as a few hundred pounds of explosive, comparable, say, to a couple of 500pound USAF bombs.
Consistent with the eyewitness accounts. Not a nuclear bomb level impact. Largest impact on historical record in Norway, ie recovered rock, was 90kg in 1904.
There is a reward (100,000 Nkr!) for finding this one.

Still interesting, it did some damage to the ground, and fortunately hit a sparsely populated area (well, actually that is not particularly fortunate, most of the Earth is sparsely populated, still).

But, we’ve done better up in the arctic in recent years

NASA GOES imagery of actual atom bomb level impact on Greenland 1997

Watch the plume on the lower right, that is the impact of a large meteorite that came across the North Atlantic (seen by fishing fleets). Impact site was covered in several meters of snow over the winter and never recovered, original crater would have been pretty impressive.

There were a couple of significant ground strikes in the 20th century, Tunguska 1908, of course and another in Brazil in the 1930s. General feeling now is that there were actual casualties in Tunguska, and possibly also Brazil.

NORAD list of major events over a decade

The USAF tracks atmospheric impacts, and used to send them out, that appears to have stopped a couple of years ago, but the Canadians kept the list (above).

There are some interesting events on that list, including two that, according to rumours, lead to Pres Clinton being woken up, and in one case started on the path to the ready helicopter (looked like a over-the-south-pole sneak launch designed to blind radars).

this one was a 40 Ton TNT equivalent airburst, over Washington DC! In 1995

These are not complete, but clearly show there are multiple impacts on the Earth with impact comparable to a large (multi ton – hundreds of ton explosive) conventional bomb. Most are airbursts at high altitude, or over ocean or uninhabited areas.

Very roughly, the probability of an impactor declines as a power law with the energy. The index of the power law is not terribly well constrained, but you can’t go far wrong with a -2 index, in which case we expect several kiloton impacts per century, consistent with the two we know about, given that both the current set is somewhat incomplete, and there were probably several ocean impacts in the 20thC we never knew about.

Comments

  1. #1 thorsett
    June 13, 2006

    Looks like it might have zipped right over the old family farm…

  2. #2 Karmen
    June 13, 2006

    While I’d never dispute the fact that meteorites strike us all the time, I’m not certain Tunguska was one of these events. I’ve always leaned towards the geothermal theories, but it might be wishful thinking on my part. I’m quite curious about new information that has been coming out on the event… would you blog more on this? :)

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