(meteorobs) Meteorites on The Ground! (Was: To Dirk)
Meteorites USA
eric at meteoritesusa.com
Sat Mar 26 15:38:02 EDT 2011
Even though this is the BEST data we have on a body before it enters our
atmosphere and impacts our planet, it still estimates the original size
of the asteroid while still in space. The variables are not accurate
enough for a control even in the case of TC3. Sorry, but "guessing" the
weight of an object before entry is no more accurate than assuming that
all the pieces that fell were recovered.
Please don't get me wrong. TC3 is perhaps still the best documented
meteorite fall in the history of human kind, and an extremely important
event to the science of meteoritics. It's unprecedented and spectacular.
However, I don't think, based on what I described above, that it can be
used to determine ablation rates, how much of the body actually survived
to the ground because there are such large variables, the most important
of course being weight. The size of the object before entry is only an
estimate. The difference between 2 and 5 meters is more than double at
2.5 times, so therefore the weight wouldn't be accurate. Would you use
this in your calculations? Sure, you could use the weight range
estimate, but then your ablation calculation would not be accurate
because the "reported" amount of material recovered varies and so would
your results.
I tend to give more credit to the Meteoritical Bulletin over Wikipedia.
Though Wikipedia has great information, one must still research other
sources and compare the data to have any semblance of accuracy. (NASA
ADS has it at a "3 to 4 meter sized asteroid")
The other major variable which needs more accurate data is recovery. To
be accurate you need the complete recovery of all specimens. Don't take
this wrong. Peter Jenniskins did a superb job along with his colleagues
and students to record the data. What I'm referring to is the massive
size of the known strewnfield and the fact that not all specimens were
recovered. Yes many tens of students searched this strewnfield but only
a few kilos of specimens were found in the strewnfield which stretched
some 28 km long by 5km wide. That's a HUGE area to search by
inexperienced student/hunters. Not to mention there are many human
variables such as fatigue, eyesight, inexperience, and greed. I'm simply
pointing out that it's data which cannot be determined complete, nor can
it be used as a control.
The entire known meteorite strewnfield area is 140 square kilometers.
Did they find 10.5 kilos? The Meteoritical Bulletin has the TKW 3.95kg.
NASA ADS has the weight at 10.5 kgs recovered.
http://adsabs.harvard.edu/abs/2010DPS....42.6008J
It goes further to say "Based on the density of fallen meteorites, the
total fallen mass is estimated as 39 +/- 6 kg" Even that number, 39
kilos, is an estimate of what's still on the ground. Is that accurate? I
don't know... Do you?
One has to realize that not all the specimens the fell to Earth have
been recovered, and the original size of the asteroid is only an
estimate, therefore as much as we'd like the hang our hat on this
unprecedented and certainly historical event, it's just not enough data
to determine ablation rates empirically.
At least in my opinion.
Regards,
Eric
On 3/25/2011 11:06 PM, Wayne Hally wrote:
> "2008 TC3 was a meteoroid 2 to 5 meters (7 to 16 ft) in diameter and
> weighting 80 tons that entered Earth's atmosphere on October 7, 2008, at
> 02:46 UTC (05:46 local time). The meteoroid was notable as the first such
> body to be observed and tracked prior to reaching Earth. It exploded an
> estimated 37 kilometers (23 mi) above the Nubian Desert in Sudan. A search
> of the impact zone that began on December 2008 turned up 10.5 kilograms (23
> lb) of meteorites in 600 fragments, which are surviving pieces of the
> meteoroid. The meteorites are of a rare type known as ureilites."
>
> > From Wiki, references there:
>
> http://en.wikipedia.org/wiki/2008_TC3
>
>
>
>
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