Hoba Meteorite Namibia
The largest known of meteorite to crash to earth... but
no impact crater?
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The Hoba Meteorite:
Was discovered in 1920 on the Farm Hoba, near
Grootfontein in northern Namibia by, the farm owner, Jacobus
Hermanus Brits. The iron-nickel body was found partially buried in
calcrete and is the largest known meteorite on the Earth. Its approximate
measurements are 2.95 meters in length, 2.85 meters in width,
0.75 to 1.2 meter in height. It has three corners - the fourth being rounded
and weighs about 55 to 60 tons. The meteor is quite unusual in its shape
being somewhat cuboids. It is estimated at being between 200 and 400
million years old and that it fell to earth about 80,000 years ago.
The size of the Meteorite as
it entered the Earth's atmosphere would have been much larger and the
burn-out would have presented a most impressive sight to
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any living creature that may have witnessed
the event.
Amazingly, there
is no impact crater, and to this date there is no scientific explanation
for this mystery. It could be that it entered the
earth's atmosphere at a very low trajectory, impacted far away and
'bounced' to its' final resting place.
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Otjozondjupa Region |
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19º35S - 17º55'E |
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A National Heritage Site |
60 ton of iron / nickel |
Burn marks on surface |
Hoba Meteorite
- Astronomical Origin:
thought to be between 190 to 410 million years old
- Classification Ataxite: Iron alloy meteorite having a
high nickel content. Comprising of approximately 82.4% Iron, 16.4% Nickel,
with intergrowths of kamacite and taenite (see Widmanstatten Pattern
below). 0,76% Cobalt, 0,04% Phosphorus, with small amounts of Carbon, Sulphur, Chromium and Copper. Traces of Zinc, Gallium,
Germanium, and Iridium. There are also traces of rarer minerals that
do not exist on the Earth: Schreibersite [(FeNi)P3], Troilite [FeS]
and Draubreelite [FeCr2S4].
- Meteor Trajectory:
Low - direction unknown
- Collision with Earth:
Unknown, estimated - 80,000 years ago
- Location Of Landing:
Farm Hoba +- 20kms west of Grootfontein
- Size of Meteorite:
Length 2,95m x width 2,85m x depth of 0.75 to 1,2m
- Weight: about 60
tons
In 1955 the Hoba Meteorite was declared a National Monument. However, it was not until 1985 that Rossing Uranium Ltd. enabled the site
easily accessible for tourist viewing.
This could be your opportunity to get close up with an extra
terrestrial body that you can even touch. During the final
stage of its journey while burning through the Earth's atmosphere
the Hoba Meteorite's surface was thermally altered causing the
surface indentations. One corner of the meteorite bares a
lengthy cutting torch scar where samples for analysis were cut.
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Widmänstatten Pattern
Named
after Count Alois Von Beckh Widmänstatten (1753 to 1849) an Austrian
printer and scientist who noted that when the machined surface of an iron -
nickel meteorite was etched with acid a distinct cross-hatched pattern appeared
on the flat metal face. This crystalline structure is unique to metal bodies,
such as meteorites, that have formed in space, and happens |
when a molten metal meteorite
having a composition of about a 90% percent iron and 10% nickel
begins to cool. Calculations indicate that this cooling process,
which takes place under zero gravity conditions, is extremely slow,
being approximately 2°c per million years. As the temperature of the
metal alloy meteorite slowly lowers to about 700°c the meteorite
would still be in a liquid form, but within this approximate
temperature range, bands of crystals of the two associated metals kamacite and taenite would begin to be formed in a process know as
diffusion. (kamacite being formed in the low nickel phase while
taenite is formed during the high nickel phase). At this temperature
the composition of the kamacite would be about 4% nickel. Over a
period of some further 200 million years the meteor's temperature
would have cooled to about 600°c during which period the migration
of nickel atoms within the cooling molten metal mass would have
increased the nickel composition of the bands of kamacite to about
6% , Whereas the bands of taenite would have risen to have a
nickel content of approximately 19%. At approximately 500°c the
migration of the atoms ceases. The resultant crystalline structure
of the metal mass is of a cross-hatched formation now named as the
Widmänstatten Pattern. This condition is not found on any
metal bodies originating on planet earth.
Acknowledgements and further reading:
G1, G2, P1
The Hoba Meteorite is operated by the National
Heritage Council. There are camping areas near to the Hoba Meteorite. There
is no power and no hot water for showering, but the experience of sleeping
next to the meteorite is worth it.
Of Interest: In 1954 the curator of the American Museum of Natural
History in New York tried to purchase the Hoba Meteorite. It was
only owing to transport problems that the meteorite remained in
Namibia. Immediately following this matter a group of
responsible locals brought the 'near calamity' to light and the following year it was proclaimed a National
Monument.
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