[meteorite-list] Norway Meteorite Impact Site Believed to be Found

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Mon Jun 12 18:12:16 2006
Message-ID: <001e01c68e61$1307fba0$e242e146_at_ATARIENGINE>

Hi, All

http://www.aftenposten.no/english/local/article1348689.ece

    Great photo of the impact site. Very scenic. And absolutely
NOTHING to provide scale. Is that bleme in the rock 10 feet
across or 100 feet across? Well, there are some stunted arctic
bushes and part of a tree in the photo. Eyeballing it, I would say
it's about 10-20 meters across. Note that the "crater" is not just
that more regular circular feature, but is actually an elongated
ellipse stretching downslope.

http://www.lpl.arizona.edu/impacteffects/

    Race off to Melosh's on-line impact calculator, shamelessly
invent details: an iron (since it's small and a small rock would
be less likely to survive the atmosphere), a 25-degree angle of
incidence (it hit a semi-vertical surface; more likely at low angles),
hard crystalline rock as the target, of great depth (no-brainer),
an average-ish 25 km/sec entry velocity... Let's assume we're in
the Reisa Dale about 20 km away... skiing.

    Here's the results:

Distance from Impact: 20.00 km = 12.42 miles
Projectile Diameter: 1.00 m = 3.28 ft = 0.00 miles
Projectile Density: 8000 kg/m3
Impact Velocity: 25.00 km/s = 15.53 miles/s
Impact Angle: 25 degrees
Target Density: 2750 kg/m3
Target Type: Crystalline Rock
Energy before atmospheric entry: 1.31 x 1012 Joules = 0.31 x 10-3 MegaTons
TNT
The average interval between impacts of this size somewhere on Earth is 0.2
years
The projectile lands intact, with a velocity 0.719 km/s = 0.446 miles/s.
The energy lost in the atmosphere is 1.31 x 1012 Joules = 0.31 x 10-3
MegaTons.
Transient Crater Diameter: 13.6 m = 44.6 ft
Transient Crater Depth: 4.81 m = 15.8 ft
Final Crater Diameter: 17 m = 55.8 ft
Final Crater Depth: 3.63 m = 11.9 ft
The crater formed is a simple crater
The floor of the crater is underlain by a lens of broken rock debris
(breccia) with a maximum thickness of 1.68 m = 5.51 ft.
At this impact velocity ( < 12 km/s), little shock melting of the target
occurs.
Richter Scale Magnitude: 0.2
Mercalli Scale Intensity at a distance of 20 km:
Nothing would be felt. However, seismic equipment may still detect the
shaking
The air blast will arrive at approximately 60.6 seconds.
Peak Overpressure: 17.3 Pa = 0.000173 bars = 0.00246 psi
Max wind velocity: 0.0408 m/s = 0.0913 mph
Sound Intensity: 25 dB (Easily Heard) and barely audible up to 100
kilometers.

    Trying to check the consistency of this with the "story" we've gotten,
if we lower the size of the iron to 0.7 meters, we get only a 15-foot bleme,
and there is NO seismic trace, so it has to be bigger... Given the slope of
the mountain, the impact angle on the slope would be about 80 or 90
degrees, maximum for chunking out this shallow hole. If we reduce the
size of the iron to 0.95 meters, we get no seismic trace. At 1.05 meters,
Richter 0.3; at 1.0 meters, Richter 0.4; and so forth, so the seismic
numbers would really pin it down... Anybody know?

    The mass of a 1-meter iron sphere is 33,500 kilogrammes, or
34 English tonnes (or 34 American tons). That's about half-a-Hoba,
or about the mass of Cape York (Ahnighito). Dr. Hansen may think
?degaard was exaggerating, but if he thinks "it was a stone weighing
around 12 kilos (about 26 pounds)," that produced this impact
feature, he is much further off-the-mark than ?degaard. If this
reconstruction is vaguely correct, it lost much of its energy
passing through the atmosphere. The crater could be produced
by a kiloTon. I wonder if the two seismic traces:
http://www.astro.uio.no/ita/nyheter/ildkule06/ildkule06.html
have been calibrated on the Richter Scale?

   For comparison, a 1-meter hard stone fragments in a 15 kiloTon
airburst, and makes no crater. In fact, when you keep increasing the
size of the stone, you get up to a 100-meter stone with a 100 MegaTon
airburst with vast destruction and STILL no crater... Suggests it had to
be an iron to punch through to the ground if the input parameters are
even roughly correct (and the impact calculator model).
http://www.lpl.arizona.edu/~marcus/CollinsEtAl2005.pdf

    I opined that this was a terrible place to search for meteorites, but
IF it was an iron (only going about 1500 mph when it hit), I'd bet that
mountain slope down from that bleme is littered with -- guess what?
I could be dead wrong (as is most often the case). Right place for a
metal detector? CC: Mike Farmer. Wait a minute... if it was a 34
ton chunk of iron and it hit at "only" 1500-1700 mph, some of
those "fragments" might be really big. Look for 20 ton black rock
too, while you're at it... (Truth is, meteoritic iron, tough as it is, is
often quite brittle. Remember, inside it's only 50-100 deg K when
it hits, so maybe no big chunks.) Even if it was "only" a ton or two,
it would be worth looking for, obviously.

    Hey! It's summer in the Arctic, with sunshine 20-22 hours a day.
It's in the 50's F. (Take mosquito netting.)


Sterling K. Webb
------------------------------------------------------------------
----- Original Message -----
From: "Ron Baalke" <baalke_at_zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list_at_meteoritecentral.com>
Sent: Monday, June 12, 2006 12:52 PM
Subject: [meteorite-list] Norway Meteorite Impact Site Believed to be Found


>
> http://www.aftenposten.no/english/local/article1348689.ece
>
> Here's where the meteorite hit
> Aftenpoften (Norway)
> June 12, 2006
>
> Residents of the Norwegian county of Nord-Troms were shaken when a
> meteorite struck the valley of Reisadalen last week. Experts are
> debating its impact, but they've found the site where it hit the ground.
>
> [Photo]
> This is where last week's meteorite is believed to have hit Norway, at
> Reisadalen, east of Troms?.
>
> An astronomer at the University of Oslo, Knut J?rgen R?ed ?degaard, told
> Aftenposten.no last week that he thought the meteorite that was
> photographed streaking through the sky could have had the same impact as
> the atomic bomb that hit Hiroshima in 1945.
>
> "Of course the meteorite is not radioactive, but in explosive force we
> may be able to compare it to the (atomic) bomb," R?ed ?degaard said.
>
> Truls Lynne Hansen of the Northern Lights Observatory
> (Nordlysobservatoriet) in Troms? disputes R?ed ?degaard's description,
> calling it an exaggeration.
>
> "Our atmosphere is peppered with small stones from outer space all the
> time," Hansen told newspaper Aftenposten. "Most burn up and disappear,
> but some land here."
>
> He thinks that what hit northern Norway last week was a stone weighing
> around 12 kilos (about 26 pounds). "Out in space it generated enormous
> speed, but after entering our atmosphere its tempo eased," Hansen said.
> "This kind of meteorite isn't radioactive and it's not glowing when it
> hits the ground."
>
> The meteorite, whatever its size, created a stir nonetheless. Norway's
> Defense Ministry tries to track all flying objects and be prepared via
> radar on land, at sea and in the air.
>
> "We can observe such meteorites," said John Espen Lien of the northern
> military command in Bod?. "But everything happens so fast, and most of
> them disappear before they hit the ground."
>
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Received on Mon 12 Jun 2006 04:44:58 PM PDT