Niger Meteorite Recon

www.niger-meteorite-recon.de
Rub' al-Khali Expedition 2008
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Text: Svend Buhl, Photos: Svend Buhl and Thomas Kurtz

Coincidences and other improbabilities

Later, I was just about to calculate our drinking water reserve, Thomas called me over to the vehicle. He had discovered a praying mantis on one of the rear wheels. It was an Arabian Devils Flower, Blepharopsis mendica. A male as could be seen by the feathery split antennae. We were still wondering why the insect of all things had chosen to land on the tire when I discovered a second mantis on one of the front tires. This time it was an adult female specimen measuring seven or eight centimeters, also of the Blepharopsis species.

Arabian devil's flower, Blepharopsis mendica (Fabricius 1775). The adult female measures approximately 7.5cm

When gently blown at, the beautiful animal will slowly rock from side to side. This is typical behavior of most cryptic species. This swaying is mimicking a dried leaf or branch moving in the wind.

We stood and watched the confiding animals quite some time in the hope to observe the catch of a locust or moth but both insects were simply occupied with personal hygiene. Particularly the barbed triple folded forelegs received a thorough cleaning from dust and plant fibers.

In the morning both animals were still there. Before we stowed away our gear we took the insects from the tires which they put up with unopposed, although the species can fly for short distances. When brought together on the ground they showed no aggressiveness among each other. Although Blepharopsis mendica is commonly known for cannibalism I presume this is rather the case in captivity and when in lack of food. In the present habitat and with a decent population of prey there would be no cause for this.

The female is rather interested in our camera than in the male specimen which is visible in the background

The morning was hot and remarkably clear. But already a short time after sunrise the scenery had changed. Where had been a distinct horizon only minutes ago now only multiple looming bewildered the eye. We had just climbed in the Land Cruiser and were about to start when we became witnesses of a rare form of the Fata Morgana. Low above the horizon, apparently in a distance of barely four kilometers, a flat building emerged from the flickering heat that quickly gained focus and plasticity. Beside it and out of nothing an elongated bronze colored object materialized that seemed to crawl alongside the building. By binoculars we could see that this was a large semi trailer. The illusion presented itself in such a way that the building as well as the truck could both be seen twice. The first reflection showed the scene according to the common rules of gravity upright while the second mirroring produced the objects upside down.

With the field glass we were able to make out single persons wrapped in white dischdaschas that went inside and out of the building. We consulted our maps and GPS and found out that the nearest asphalt road suitable for larger trucks let alone buildings was at least eighty miles from our position as the crow flies.

‚Perhaps an image from the future?' Thomas suggested eerily. 'You watching too much TV pal' I replied raising a brow. 'Don't watch no TV at all' it came back neutrally from behind the binoculars while he stared at where the mirage loomed in the distant haze. 'Then maybe that is the problem' I settled the matter after a pause which I needed to figure whether we both might have had too much of sun.

After ten minutes the construct dissolved, but not before the semi trailer evaporated a black plume of smoke and slowly rolled away. Like a steamer on a calm sea, half a degree above the horizon, the vehicle silently floated into the monochrome lead grey of the desert sky. Much too late, when the image was already about to disappear, I snapped the camera and shot a photo. We had been spellbound watching the spectacle without even thinking of documenting it. Fine explorers we were.

Fata Morgana

The only find we made that day was a very small and beyond recognition weathered fragment that was almost completely embedded in the soil. It was impossible to see from the car. Fortunately Thomas had stepped on it when we stopped to empty ourselves after we had searched the complete noon without success. It was the only halt we made until dusk. And exactly at this spot, right below where he stepped off the car, Thomas had found the meteorite that hardly weighed twenty grams.

This find triggered a stimulated discussion on coincidence versus determinism that continued for the best part of the afternoon. While I argued that the probability of us finding a miniature meteorite where quite high, pretty much regardless where we would step out of the car, my team mate defended the powers of destiny which he believed had led us to stop at the very spot of the find. My appeals to my companion's self-concept of rational thought were to no avail. He repeatedly claimed that now 'it was proven', that he was chosen as an 'instrument of divine providence'. We had a lot of fun that day.

The afternoon went by without further incidents, presumably the divine providence had lost its interest in the 'chosen one' as we made no further finds. We camped between the tracks of our search loops next to a narrow milk weed bush (Calotropis procera) which we had used as a landmark for our bearing the last few hours. Even after dusk we continued prospecting on foot for another hour until we sat down at the campfire.

Found by accident, 'Rub' al-Khali 012', a 68.5g ordinary chondrite

The next morning we got up long before sunrise. When the first rays of the new sun immersed the eastern sky in a fiery glow we had already completed a brief breakfast and stowed away our belongings in the car. I intended to start early today, to compensate for yesterdays meager finds.

But I had not reckoned on Thomas, who sat on the co driver's seat and was still occupied entrusting his journal entries in epic dimensions. This could take a little longer as I knew from experience and so I grabbed my toothbrush to promenade the gravel bed within range of sight of the vehicle. Automatically I focused the ground.

What could there be more contemplative than strolling the gravel beds of the Rub' al-Khali in the early morning light, tooth brushing and studying the manifold forms of desert weathering on the surface? I didn't make it far though, because only a few paces from the car a stone attracted my attention. In the shadows this particular pebble seemed just a fraction darker than the others. 'You wanted to take care of this one already yesterday evening' I remembered. For some mysterious reason my footprints had wandered off just three meters ahead of it, I noticed bemused.

As I stood directly above the minute rock I still didn't know what to make of it. A scallop shaped fracture irritated me. This type of fracture is common rather for cryptocrystalline minerals like flint stone or chert while meteorites tend to break rather irregular due to a coarser grain size. Otherwise everything made sense: color, texture and shape pointed to a meteorite. I continued brushing my teeth. Still far from being wide awake in this early morning hour and still without a coffee the situation slightly overstrained my. 'Maybe I should get to the car and get the magnet' I thought. While I searched for the device Thomas obviously was still busy composing what seemed to be a significant literary opus comparable in dimension to the Encyclopedia Britannica at least. He was so submerged in his creative outpour, not even my admittedly diffuse declaration, 'believe I got something', was able to disturb him.

Finder Thomas Kurtz (left) and author together with 'Rub' al-Khali 017'

The stone attracted the magnet with considerable force. As I could see on closer inspection the edges of the fracture had been smoothened by sand abrasion. What I had taken for a scallop shaped flaking was in fact a true weathering fracture on the surface of a genuine meteorite. A deep contraction crack and a flank that showed remnants of flow lines clearly confirmed the meteoritic nature of the walnut sized rock.

'Scored' I called out in the direction of the car, whereupon Thomas darted up in his seat like a greased lightning thereby catapulting his ball pen out of the window. With three huge paces he hurried over to where I was lying on the ground, inspecting the meteorite. 'Impossible' he protested. ‚I walked along here three times yesterday'. 'Sure' I needled him, 'but you wouldn't even find the Hoba mass if it lay here'. We both could get a laugh out of it for in fact as our footprints showed to us, 'the chosen one' and I had walked past the meteorite quite close at least two times without noticing it on the previous day. Today had started out great, things could go on like this.

Sand abrasion and desert pavement

In fact it went on like this. Distributed throughout the day we found five more masses, which we assigned to two different fall events. While brushing my teeth I had in fact discovered a new strewn field. Remarkably we had combed the same area the previous day and hadn't found a single mass. The terrain was ideal. Absolutely void of any cover, no grain sizes above 50mm and the borderless plains were big enough to land a A-380 Airbus on them without even kicking the trust reversion. We drove dead straight parallel search tracks three to five kilometers in length and with intervals of fifty meters. In the late afternoon when checking our GPS we discovered a gap in our search pattern located at the northern end of the strewn field we were working on. We would have good light for at least one more hour. So we decided to go there and turned.

Because the course into that particular search area would lead us driving directly against the sun prospecting from the car along the way was not an option. I kicked down pedal to metal which was a novelty on that trip. Against the deep standing sun there was not much to bee seen of what was ahead of us. But because we hadn't seen any potential obstacle on the dead flat plain during the last two days of driving the risk of colliding with anything more hazardous than camel droppings was negligible.

'Rub' al-Khali 018', in situ photo in back light

Generally the driving on the even terrain through the desert had a somnambulistic touch to it. Wile searching for meteorites from the car and provided that the visibility is good and the vehicle is kept at jogging speed, a glance ahead every ten minutes or so is completely sufficient, to guide the vehicle safely. Occasionally it may happen that the driver is so lost in his task of scanning the surface at his side for meteorites that he completely forgets to look ahead at all. In this case a too easy going attitude to driving may admittedly lead to sudden and unexpected perspectives.

Meanwhile we were driving for five or six minutes with accelerated speed when I spotted a larger object on the plain ahead of us. Against the blinding sun one could not determine if bright or dark let alone what it was. Therefore I adjusted our course a little towards the spot and decelerated to catch a quick glimpse while I would pass the object close at the driver's side. I didn't pay much attention because whatever it was it seemed too obvious on the plain and too big to be a meteorite. In the light of the sinking sun there wasn't much to be seen anyhow. But in the moment of passing for a second an image of the rock flashed in my mirror that triggered me to slam on the brakes instantly.

Adherent patches of caliche preserved on the lee side of the meteorite mark the level of a previous sedimentation

In my enthusiasm I had forgotten that, as always, we were driving with our windows down. This minor but decisive fact brought about that the humungous dust cloud which trailed us like a pyroclastic flow, now also distributed itself unhindered in the interior of our car. Coughing and exclaiming fierce maledictions we rescued ourselves into the open.

It must have triggered a quick reaction because the questioned rock rested in a distance of not even forty meters from where the Land Cruiser had come to a halt. Now, with the sun from the back and already from this distance it was obvious that we were dealing with the genuine thing. On approaching the new find we mutually congratulated us. Instead of walking straight to the meteorite we circled the mass in a distance like Tibetan pilgrims a holy mountain, because the sight of the large mass in the light of the evening sun on the bright gravel pavement was simply to awe inspiring.

Studio image of 'Rub' al-Khali 018'. Note the distinct abrasion through wind borne sand ('corrasion') in the upper third of the meteorite

On closer inspection we figured that the meteorite showed strong signs of abrasion towards a single side, more precisely towards 55° North by Northeast. On the flank pointing into this direction sand abrasion had erased several centimeters of the original material. Over the millennia the wind that on increasing speed carries grains of sand and silt works like a steady sandblaster on the meteorite. This way it had molded deep tunnels and cavities into the meteoritic stone. Even in the surfacing side of the rock deep channels and hollows had formed, originating from the North by Northeast pointing side. This process called abrasion was only visible on the windward side but not on the lee side, that still showed remnants of heavily weathered fusion rind.

Top view with indication of the prominent wind abrasion originating from 55° North by Northeast

The distinct one sided abrasion indicated that the meteorite during his terrestrial lifetime had never been moved in his relative position. It was also a proof for the steadiness of the trade wind for at least the last fifteen to twenty thousand years. Most probably the meteorite had been covered by the accumulated sediments before and was uncovered successively by the increasing wind erosion. Thus after climate changes have led to a disappearance of the natural plant cover that prevented the top soil from eolian deflation. This was obvious from the fact, that the grade of destruction was much heavier in the upper third of the meteorite while the lower portions which currently suffered most of the sandblast, showed a much lesser abrasion ratio.

Although it is true that silt and finer grained dust particles commonly move up to heights of one to two meters above the surface their destructive capacity when impacting on meteorites and other rocks is negligible due to their low mass and small grain size. The abrasion that was visible on our meteorite rather resulted from sand grains with a grain size of 0.1 to 1mm. These sand grains are transported by the wind rolling and bouncing and arely reach heights above two centimeters. In this range close above the surface the mechanical abrasion through sand is most harmful.

Because our recent find displayed the strongest abrasion in the upper third, five to seven centimeters above the resting surface, this pointed towards a considerable period of time which the mass must have spent embedded in the ground up to the lower level of the mentioned destruction zone. During this period the main body of the mass must have been protected from the sand abrasion.

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