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

At five p.m. the whirling dust had darkened the sky in a way that no longer admitted searching. We steered the jeep towards a group of precipices to see whether we could find a campground among them that would protect us from the blowing dust storm. Around us the wind was howling and dark clouds of dust chased over the crests of escarps we were walking. We were shouting with croaky throats to each other to make us heard. Temperatures had sunken below 60°F.

'Rub al Khali 008' (field name) in situ. The 80.10g fragment has the shape of a ship's bow

I folded the chech around my head leaving only a narrow slit for the eyes over which I draw the dust goggles. Between the escarpments protection from wind and the blowing sand was to be found only near the surface. Our tents would be blown away in a minute if we dared to erect them here. Finally we manage to find a horse shoe shaped dell that was encircled by the eroded remnants of limestone bedrock. From one of these walls a narrow black socket gaped at us, bleached bones littered around its maw. Thomas suspected a mighty reptile lives in the cave. Therefore we named the location 'Djebel Abu al-Khaaf', 'The Father of the Cave'.

Camp between the inselbergs at 'Djebel Abu al-Khaaf'

The mother of all stoves

Completely exhausted we let ourselves drop to the ground. Through the open gap in the dell we gaze upon a blurred lunar landscape the color of dried blood, contours fading in the dim light. Dante Alighieri, the great Italian 14th century poet must have visited this place when he wrote his description of the eighth circle of hell: 'Lodged in hell is a place called Malebolge, all made of stone the color of iron ore, as is the cliff wall that encloses it."

Before we pitch our tents I bring myself to shoot a number of photos which I plan to combine in a panoramic view of our camp site after the trip. I do not get that far, because the reflex camera swallows a truckload of dust, grits a last time and is down for the rest of the tour. Killed in action. I am now left with my Nikon Coolpix 5400.

After nightfall it got lousily cold in our camp. Out of large limestone plates we therefore erect an oven that is closed at the sides and on top and emits warmth and light only to front. Crouched in front of the 'mother of all stoves", that is how we proudly refer to our invention, we eat a meager dinner of canned tuna. The rest of the evening we spent drinking hot tea. Throughout the whole cold night the tents crackled in the wind.

In fact the wind had not weakened the next morning but the visibility had improved and was sufficient for meteorite prospecting. The area was hard to drive but rich on finds. While Thomas searched on foot I skirted most of the forenoon along a chain of cliffs that separated us from the next plain in order to find a drivable passage through them. Frequently I got off the car to probe the ground on foot. But each time only to sink in knee deep in the fine silt that had accumulated at the leeward faces of the escarps. This won't work. On top of a narrow ridge barely the width of the car I bring the Land Cruiser dangerously wallowing close to the edge of a steep slope. From its foot merely fifty meters of deep sand separate me from the limestone bank on the fringe of the plain which is my target.

Sunrise at 'Djebel Abu al-Khaaf'

Repeatedly I walk the route back and forth to probe the surface condition. Later from the car I would check for a safe passage by reading the depth of my footprints. Indeed fine sand had collected at the foot of the steep slope as well but now I'm determined. I buckle up, start the car, speed up down the arduous scarp, kick in the second gear and moments later I dash amidst a humongous cloud of dust through the deep sand towards the limestone bank. The vehicle looses momentum rapidly but with the very last push I reach the safe ground. 'Piece of cake' I convince myself.

Already twenty minutes later I come across the first meteorite of the day. It seemed to appear from nowhere on the grey gravel bed. I could have sworn it had not been there ten seconds before. A large heavily weathered chondrite, perhaps a pound or bigger. Unfortunately and definitively not paired with our fresh finds from the previous day.

'Rub' al-Khali 006' in situ, a heavily weathered 488g chondrite

It is the sixth meteorite and the tenth single mass we find. While I begin documenting the specimen by shooting in situ photos lying flat on the ground Thomas approaches. He has seen my performance from the edge of the cliff and decided it might be a better idea to join me in the car before the sun rises higher and the temperatures become uncomfortable. We agree to continue in the car and plan to cover the vast plain with parallel search tracks in the next two days.

We spent four days in the area around the Abwaab as-Sabr and in average we found four individual meteorites per day. Often they have fragmented into five to ten single masses through weathering. It is here where we made the experience that meteorites can be spotted on great distances by binoculars. Initially to observe the terrain and the wildlife I had a 8 x 50 Hensoldt-Wetzlar German army issue binoculars in my baggage.

On our second search day near at the 'Djebel Abu al-Khaaf' in the early afternoon I had spotted a minute black object among a group of roots slightly brighter, which I had actually focused. As we later measured, the distance was 85 meters. We drove up to the object and could not believe our eyes when it indeed turned out to be a meteorite. It was a mass of slightly conical shape and weighed 90 grams. Only a third of the meteorite protruded from the fine grained gravel. A beautiful find indeed.

From now on the binoculars came into operation more frequently. In the end we should find seven out of a total of 27 meteorite finds with the Hensoldt binoculars. In the process we would increase the identification distances from 85 meters in the beginning up to 500 meters on ideal terrain at the end of the expedition. Whenever a new perspective onto the landscape or an elevated outlook was offered we searched the surfaces in front of us for suspicious signs of extraterrestrial presence with the field glass.

The 8 x 50 Hensoldt-Wetzlar field glass

With the sun in the back we stood for minutes scanning the ground square meter-wise, sharing the field glass and discussing potential targets. Most could be ruled out visually from the distance but every now and then we had to change course and drive by a particular candidate to have a closer look.

Generally we worked continually on improving our search techniques. We always drove in a way that kept the sun in our nine o'clock position. We surveyed an angle from our twelve o'clock position to our three o'clock position. Like on the bridge of a surfaced U-boat the sectors to be monitored were accurately assigned. We worked as a well rehearsed team and everybody knew exactly what his job was. While the driver kept an eye on the area in front of the vehicle and to the angular left, the co-driver scanned the surface diagonally in front of him to 90° on his right. To maintain an ideal course relative to the moving position of the sun the driver constantly checked the exact shadow casting, usually by stretching the arm out of his window. Later we attached a small vertical pole to the hood for that purpose.

Driving rarely exceeded walking speed and every 300 meters we searched the terrain by binoculars. This way we made slow progress, but the area we crossed this way was pretty much clear of larger finds.

'Rub' al-Khali 23', a chondrite of 210g, pictured in back light from a distance of 25 meters

The technique to identify a meteorite across a certain distance on the desert surface is relatively simple in theory. The most crucial factor is the altitude and position of the sun. The more an object is lighted from the side relative to ones own position the less sharp are the color contrasts. Only direct sunlight from behind your position will bring out ideal color contrasts. Only this way the prospector can distinguish between a dark green or dark brown flint stone and a desert varnished chondrite.

Also, in direct light the problems resulting from irritating cast shadows is omitted. In contrast in back light a fist sized meteorite can not be distinguished from a cast shadow even if the viewer looks at it from a distance of ten paces. Aside from the angle of the sun light the altitude of the sun plays an important role. The best light conditions are given two to three hours after sunrise and three to two hours before sundown.

Directly after sunrise every thumb sized pebble will cast a shadow of thirty centimeters length and more. Only gradually the patchwork of bright and dark stripes will dissolve and merge into a well arranged pattern of single dark objects on a bright background. This ideal light will remain for two brief hours and will become too bright towards midday. When the sun reaches its zenith all colors disappear until there are only variations of white left and the complete landscape morphs into a blurring and blinding haze. This state remains for the best of three hours. Continually searching this blaze of white is painful even for the sun goggle protected eye.

'Rub' al-Khali 23', pictured from the same distance, this time in direct light

Now the art of desert prospecting in The Rub al-Khali and pretty much elsewhere lies within the ability to assign objects to certain categories. To be more precise, within the ability to recognize every object darker than the natural surface, of which there are more than one would believe, as a pseudo meteorite. This is easier said than done. Depending on the character of the respective soil there are hundreds of darker patches and spots in ones field of vision. On closer inspection minute differences in color shade, contours and contrast become visible, demanding interpretation. All forms of natural cover, be it lumps of dry camel grass, be it the root stumps of died Shakr bushes, give away by their soft contours. In nine out of ten they can be excluded by binoculars up to 300 meters.

Shadows cast by stones projecting from the gravel bed are often to be identified by comparison of the surrounding ground texture for they rarely occur solitary. Usually they mark the crests and ridges of shallow elevations because those larger boulders represent remnants of the bedrock that forms the basements of the gravel plains. Due to their mineral composition some of these sediment rocks resist erosion better than others and therefore protrude further out of the top soil.

Fresh camel dung often displays a color shading and texture very similar to meteorites. Due to its relatively low specific density and in contrast to meteorites it bears on top of the soil with a very small resting surface. Sometimes the droppings are distributed by the wind solitary but usually they appear in groups of several, which is a further knock out criterion.

Every once in a while the eye catches the mummified carcasses of birds or larger insects. In contrast to inorganic objects and similar like in the case of plants mentioned above, they provide a contrast to the background which is characterized by soft contours. The mortal coils of life it seems have little to resist against the abrasive forces of chemical and mechanical weathering. They fray out easily once life has deserted them and this leads to frayed silhouettes.

Darker stones imply yet another degree of difficulty. An intimate familiarity with the occurring foreign minerals and inclusions common in the search area is necessary. Otherwise every alien looking piece of debris would have to be inspected closer to go sure no meteorite stays overlooked. No matter how dark these pseudo meteorites are, they never reach the ultimate blackness of a chondrite or iron meteorite coated with fusion crust or desert varnish. For the expert eye, as every prospector can tell, there is always a degree of separation that tells the ordinary dark rock from the ordinary chondrite.

The hardest temptation to abandon the course and to view a given object from a closer range originates from tins and cans. Although it is common for parts of the Rub' al-Khali that no remains of civilization at all are to be found there are some parts where cans are quite abundant. Particularly in the areas frequented by the petrol prospecting parties of Saudi Aramco cans are spread massively throughout the desert.

Visibility at noon

Often these vestiges from the pioneer ages of the Empty Quarter have been sandblasted for decades. Some of them carry stamping from the 1950ies and 60ies. Because they stand out from the bright soil in a near perfect black it is only by their tell tale oval and elongated shapes that they can be distinguished from genuine space rocks from a distance. But if these cans are rumpled or dented it may happen, that in the harsh light even from a couple of paces there is no way to tell whether it is the real McCoy or an antique repository for sardines in oil.

These hardly distinguishable objects are passing by in countless numbers and variations. In the blurring of the desert haze the prospector's eye has to identify them over distances the human eye can barely cope with. Nevertheless they have to be sorted permanently into the right categories. In the long run this sort of occupation affords an enormous amount of concentration and is physically exhausting. To get an idea one may imagine staring on a flickering wide screen monitor for ten hours a day in search of single black pixels that may or may not appear.

In the meantime we had replenished our provisions from the storage dump we had disposed on our way to the Gates of Patience. After three more days of permanent searching the exhaustion made itself noticeable. Despite well toned goggles our work lead to a habitual squinting particularly towards noon. The scrunched up eyes persisted longer each day and the time came, when I could no longer focus my left eye on a black spot the size of a walnut some fifty meters away. When I rubbed my aching eyes and Thomas inquired what was wrong I told him of the alarming sign. 'Makes no odds Svend', he replied, 'we got a total of three eyes left for prospecting, that will certainly do'.

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