Johannesburg Centre, Astronomical Society of Southern Africa

Meteorite Recovery in Southern Africa

We have all seen and enjoyed watching meteors rushing dramatically across the night sky. If we have been fortunate and observant [I haven’t], we may have seen a daylight meteor.

Once a small chunk of interplanetary rock reaches the surface of the Earth it ceases to be a meteor and becomes a meteorite.

The recovery, preservation and study of meteorites is an important prelude to assembling the early the history of the Solar System.

I’m not going to write about meteors, because Tim Cooper does that excellently.

I’m also not going to write about the history of the Solar System, despite it being one of my major interests.

I intend to write to write about the recovery of meteorites in Southern Africa, but if I wander off the subject a little, I hope you will forgive me.

In July 1999, South Africa hosted the 62nd Annual Meeting of the Meteoritical Society, an international inter-disciplinary body [see my other article in MNASSA] dedicated to a fairly range of planetary sciences, including the recovery and study of meteorites.

Up to now, the recovery of meteorites has been either a serendipitous process, resulting from seeing a fall, finding a large and unmistakable meteorite, or a short term project to find anything that may have fallen in a likely spot.

Following the 62nd Meeting of the Meteoritical Society at University of the Witwatersrand in July 1999, I got to thinking about the role of amateurs and the recovery of meteorites.

I also did some initial enquiries and put together an informal proposal which I sent off to Professor Wolf Uwe Reimold at the Department of Geology, U Wits. I considerd that this could be an ideal activity for amateurs to be involved in, and that the Johannesburg Centre would be an ideal body to run with the concept.

The initial proposal, rushed off before the results of the first enquiries were available was a little off the mark, but, nevertheless, here it is:

 

Notes on Proposed Meteorite Recovery Program for Southern Africa

Abstract Meteorites have been recovered in Southern Africa chiefly in those rare instances where they were seen to fall, or where the size of the meteorite was such that it was difficult to overlook.

No concerted effort has been directed to study the feasibility of recovering less obvious falls.

Obviously the viability of recovery varies inversely with rainfall and vegetation and in Southern Africa, this means an increasing recovery probability as one travels westwards.

The recovery exercise is an ideal project for amateurs to contribute directly to planetary science.

All recoveries will be handed in to Professor W U Reimold of the Geology Department of the University of the Witwatersrand, in accordance with the provisions of the National Monuments Act.

 

Scope This project intends to recover meteorites from:

[1] seasonal playa lakes, which dry up in the low rainfall months;

[2] erg surfaces in sandy deserts, where the meteorite impacts a sand dune, and settles with sand movement to a basal layer. The basal layer is exposed as the dune migrates.

Exclusions:

[a] The project does not have resources to follow up legends of falls;

[b] micrometeorite recoveries; i.e. rain gauge collections

[c] witnessed falls; [through triangulation].

[d] fossil meteorite recoveries [magnetic recovery of material from mining operations].

 

Recovery Strategy

Playa Lakes

 Playa lakes represent an opportunity to test recoveries strategies and in particular offer a monochrome surface, against some fresh falls will stand out in contrast.

However, older falls will assume the monochromaticity of the lake bed, owing to deposits of clay minerals stirred up during seasonal filling of the lake. These older falls MAY be found as a bump on the dry lake surface. Since the bed is usually one of very low relief, these items should also stand out.

Target sites will be obtained from progressively smaller scale maps. Ownership of the farms will be provided through the auspices of the Geology Department, University of the Witwatersrand. Owners will be contacted in advance for permission to conduct a research and recovery operation from the lake beds on their farms.

Once permission has been received, detailed mapping, preferably from aerial mapping, will be done. Grids will be set up along easy compass directions and team members will each be given one grid line [separated from the next by 10m] to walk.

A collector will walk behind the team with a cart. Once a likely piece has been found, the collector will bag and document it and place it on the cart.

A small team will test the viability of the procedures in advance of a full operation.

It is proposed to collect all suitable material using tongs [untouched by human hands], place them in plastic bags and seal them on the spot. A sticker on the bag will identify the collector, the lake bed name, the date and a gps location and a sample number.

In due course each sample number will be plotted on the map.

 

Recovery Strategy

Erg surfaces

 Owing to the temporary nature of these surfaces, maps will provide only limited use: to identify areas where these surfaces exist.

Recent aerial maps, or local knowledge must be used to pinpoint suitable candidates.

As meteorites fall into sand dunes, the impact is cushioned to some degree. As saltation proceeds, the meteorites are left behind and gradually fall to a hard surface, where they accumulate together with other rock fragments.

Each field officer will be given one erg to walk along. For each recovery [estimated at a few per day] , the officer places a stick in the ground. A sticker is stuck to the stick to identify the sample number, which is bagged and labelled. Later, A GPS co-ordinate is obtained for each stick and noted on the sample bag.

It is estimated that erg surfaces [Namib Desert] will lie further afield than playa lakes [Karoo] and therefore playa lakes will enjoy priority, purely as a function of logistics.

 

Formal Approval Process Initial concept approval will be obtained from Professor W U Reimold of the Geology Department of the University of the Witwatersrand.

On modification, a pilot plan will be set up. The results of the pilot will ultimately further modify the concept.

Approval includes acceptance of recoveries by the Department of Geology, together with an assurance of communication of research papers to the team i.r.o. their recoveries.

The Department of Geology will be free to disseminate recoveries to any person doing research in this area, regardless of which country the research will be conducted in.

 

 

Pilot Project- Silver Streams

Professor Reimold accepted the proposal, and we set up a pilot project to test the concept feasibility.

Without using anything more high tech than a road map which showed a pan close to the road near Silver Streams, I managed to obtain the names and contact details for farmers who owned pieces of pan, and obtained permission to conduct a recovery operation on those parts [one farmer refused to grant permission over the weekend, another two accepted and one of those offered overnight accommodation].

Brian and Val Fraser and I conducted a search in September. We had considered that the chief problem may be heat and sun and we were indeed fortunate not to have to deal with that problem at all, as it had snowed in the vicinity overnight and the temperature was, taking wind chill into account, only just above freezing.

Just as I had hoped, a fair area of pan was free of vegetation, although much was covered with a short grass. Additionally, the bare area consisted of a light coloured calcrete, against which it was hoped that the black fusion crusts of meteorites would stand out in profusion.

Sure enough, a large number of black objects did stand out in profusion, but they all turned out to be the weathered remains of loose pieces of the underlying Transvaal Dolomite, which weathers to a black colour.

With such a low signal to noise ratio, no meteorites were recovered.

Subsequent Progress

A number of meteoriticists have provided useful information:

Dr Mike Zolensky [JSC, NASA] has advised that many meteorites in the Namib weather to a red/brown, not black.

Dr Sara Russell of the Natural History museum in London has also advised on legalities of collecting in Namibia, and also likely areas.

Dr Alex Bevan, curator of meteorites in Western Australia, has also helped with information on the 15 years of recovery operations he conducted in the deserts of Western Australia. In addition, he advised that in Australia searches are successfully conducted amongst the piles of stones farmers gather at the edge of fields.

They all wish us well.

Professor Reimold is concerned that we need to be less random in the selection of likely locations and to this end has suggested a meeting with a sedimentologist, Dion Brandt, of Wits Geology. This meeting identified bare areas of low sedimentation and high ablation that should multiply our chances of recovery.

The low sedimentation principle means that meteorite falls will not be covered rapidly by sand/ mud etc., and will remain exposed longer. The high ablation principle suggests that if a meteorite did become buried [and some meteorite are quite capable of digging holes!] the covering material will be blown away by wind [or washed away] to expose the underlying meteorite. The longer the time interval [the Kalahari is some 80 million years old], the more meteorites it will have soaked up, and the better the chances of recovering one or more.

The improved chances are however, offset by the high rate of weathering of meteorites, which, for stony meteorites makes them unidentifiable within a year.

Professor Reimold is also willing to conduct a training course for interested people who do not know how to identify a meteorite.

Team Members

Initially, we will restrict recovery team members to members of the Johannesburg Centre, but hopefully as the operation grows, we can include members of other centres, students and interested members of the general public.

If the operation does take off, it may provide a source of new members.

There are some costs, and these can be quite considerable. The first cost is transportation to the remote site [ meteorites seldom fall conveniently close to home], and the second is accommodation [we cannot rely on the goodwill of farmers].

Basic equipment is more than likely to hand anyway.

Team member functions include organisation [setting up an expedition], site selection, obtaining the names of owners of the site and obtaining permission from them to recover meteorites, photography of the meteorite before it is recovered, administration [assigning an initial unique identifier to the recovery], provision of transport, finding accommodation locally, handing the finds over to the University for study, obtaining feedback etc., catering on site, etc. We also need someone with knowledge of first aid. Whatever you can contribute will be used in some way and will be most welcomed. Here is another unusual opportunity for we amateurs to contribute to science.

If anyone would like the opportunity to get out of the city into the country for, probably, a weekend [the distance one can go is limited by the length of the weekend and the balance between search time and travel time], please contact:

 

Trevor Gould

Home:      011-886-5602
Mobile:    083-212-8945
E-mail:     trevorgo@tnet.co.za

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