After 31 years during which the Japanese antarctic meteorite program has existed, 25 years of the ANSMET program, and three or four field seasons by European consortia, we have a collection of around 30 000 meteorite specimens from Antarctica. Is there anything we can learn from this massive group of specimens that we could not have learned by patiently waiting for falls to occur during the normal course of events, in more convenient regions of the world? We have seen already that one martian meteorite from Antarctica has had an important role in establishing Mars as the planet of origin of the SNC meteorites. Our first lunar meteorite, also found in Antarctica, has provided proof that rocks can be lofted into space, at least from smaller planetary bodies. The antarctic collection has added significantly to the numbers of available specimens of some of the rarer meteorite groups. But all this would have occurred sooner or later over the careers of successive generations of planetologists, patiently waiting for new falls to arrive. So the question is, ‘Is there anything unique about the antarctic collection to justify all the effort that has been expended in amassing it?’

I have given a lot of thought to this question, and I believe the answer is yes, for the following reasons.

• There is much to be said in favor of systematic collection and controlled curation of large numbers of meteorites in a frozen environment such as that of Antarctica. We can get an independent estimate of the proportions of the different groups of meteorites reaching Earth.

• […]

This wonderful tale of physical and intellectual adventure details the development of the ANSMET (Antarctic Search for Meteorites) program of meteorite collection in Antarctica and its importance for planetary science. Starting from the chance discovery by Japanese glaciologists of several different types of meteorites in a limited field area of Antarctica, Cassidy describes the flash of insight that led to his conviction that Antarctica must be a place where many meteorites could be found. His basic idea was that it was wildly improbable to find different meteorites in a limited area unless there was a concentration mechanism at work. The subsequent discovery of several hundred meteorite samples by another Japanese team proved the point.

Alas, insights are not always easily shared. The initial rejection of his proposal to test his idea serves as a most useful lesson to young scientists everywhere – don't be discouraged by initial rejection of your new ideas, persist!

Initially undertaken as a joint Japanese–American effort, the national programs eventually diverged. The work directed by Cassidy matured into the highly successful ANSMET program that has become an integral part of the NSF's (National Science Foundation) polar research program.

I had the good fortune to participate in two ANSMET field seasons and believe that ANSMET is organized in just the right way. It need not have been thus.

INTRODUCTION

A mountain, a mesa, a cliff and, in fact, any major outcropping of rock normally has an accumulation of weathering products piled up around its base. Such an accumulation of rocks is commonly called talus. When these rocks are carried away from their site of origin by river or glacial transport, they become float deposits. As geologists, we prefer to collect our samples directly off the outcrop because we can precisely locate where on the outcrop they originated. If the outcrop is a steep cliff that we cannot climb, we may settle for a collection of rocks from the talus. Rocks collected from float deposits, however, may have been sorted during transport and may derive from many different sites along the path of the transporting agent. These contain the least information value and are generally ignored in favor of the other two sources. But suppose the original outcrop had been destroyed and its talus carried away, or for some reason was inaccessible? By now, geologists would have figured out all sorts of clever ways to extract information from the float about the inaccessible outcrop from which it came. This, of course, is the situation faced by meteoriticists: a meteorite is a sample of the detritus from an outcrop that either is inaccessible to us, or that no longer exists.

INTRODUCTION

It may be impossible to overestimate the importance of the moon to us earth-dwellers. The moon likely provided our first correct intimation of the idea that one body can orbit another. Eratosthenes showed us how to measure the diameter of the earth in the second century (bc), and made a pretty good estimate of it himself. With a refined measurement of the earth's diameter, we could use that number as a baseline to measure the distance from the earth to the moon. Knowing this distance, we did not find the numbers so incredible when we then measured the distances to nearby asteroids; then to Apollo's Chariot and to all the planets of the solar system, using essentially the same method with simple geometry. Knowing the distance to the sun allowed us to calculate distances to nearby stars, using the diameter of the earth's orbit as a measuring stick. It all started with measuring the distance to the moon.

But much more recently, the moon served as a stepping-stone of another kind. It was a nearby body. We might aspire one day to stand on the moon, because it was so close. We did so aspire, and brought it about. With the astronauts standing there, we thought many previously unthinkable things: among them, the long jump to Mars suddenly seemed within our capabilities. We will certainly accomplish that visit also, and this will lead us ever farther. Who can say how far?

The Yamato Mountain Range wraps the ice sheet around its shoulders like an old man with a shawl. Ice coming from high off the ice plateau of East Antarctica, arriving from as far away as a subice ridge 600 km to the south, finds this mountain range is the first barrier to its flow. The ice has piled its substance up against the mountains in a titanic contest that pits billions of tons of advancing ice against immovable rock, whose roots extend at least to a depth of 30 km. The ice is moving because billions of tons of ice are behind it, pushing it off the continent and into the sea. Ultimately it yields, diverging to flow around the mountains. On the upstream side the rocks have been almost completely overwhelmed – only pink granite peaks protrude above the ice, which spills down between and around them in tremendous frozen streams and eddies, lobes, and deeply crevassed icefalls. The change in elevation of some 1100 m between the high plateau upstream of the mountains and the lower ice flowing away from the downstream slopes creates a spectacular view of this giant downward step in the ice surface. Almost constant howling winds from the interior blow streamers of ice crystals off the mountain peaks and “snow snakes” dance down the slopes in sinuous trains, as if somehow connected to each other. The scale of the scene is such that people become mere specks in an awesome, frigid emptiness.

Under certain circumstances, being completely alone can get to one. Being alone in Antarctica can get to one pretty fast. Admiral Byrd wrote a book entitled, Alone. Even being part of a small group, one experiences a sort of group aloneness, leading to a sense of awe, perhaps, at the total isolation of this small nucleus of humanity whose individuals are completely dependent upon one another, not only for intellectual stimulation but even for nourishing the basic need of the mind to feel that it is still a part of the fundamental structure of human society. We deal with the sense of isolation through conversation, clowning around (Figure 5.1), and seizing upon the arrival of holidays to hold parties. But it is definitely an abnormal existence, during which strange and memorable things sometimes happen. Following are some events that seem to fall into that category.

EVENT 1: WORKING ALONE

In the field we try never to be alone, usually working in pairs or as a complete party. The practical rationale for this rule is that one person, alone, can get into a lot more trouble with crevasses, or stranding due to mechanical breakdowns, than would two people. Traversing between campsites is potentially the most hazardous operation if we are taking a path for the first time. There may be crevasses. At such times the field party travels as a unit. To deal with the question of crevasses we have a “crevasse expert.”

Antarctica is the best place in the world to find meteorites, but it is also a singular place in many other ways. In Part I, while I outline the manner in which the Antarctic Search for Meteorites (ANSMET) project came into being, I also describe our field experiences as untested beginners, discovering the hardships and dangers of this special place in theworld, aswell as our slowly growing awareness and appreciation of its alien beauty. Antarctica is a presence in any scientific research conducted there, imposing its own rules upon what can and cannot be done, how things can be done, and what the cost is for doing those things. At the same time, it rewards the dedicated field person, not only in yielding scientific results not available anywhere else in the world, but with a headful of wonderful memories, startling in their clarity, of snow plumes swept horizontally off rocky peaks like chimney smoke in a strong wind; of poking a hole through a snowbridge and marveling at the clusters of platy six-sided ice crystals that have grown in the special environment of a crevasse below the fragile protection of a few centimeters of snow; of emerging from one's tent after a six-day storm to find the delicate snow structures randomly sculpted by a wind which, while it was churning furiously through camp, seemed to have no shred of decency about it, much less any hint of an artistic impulse; of returning late one evening after a 12-hour traverse to a campsite occupied earlier in the season, when the sun makes a low angle to the horizon and we camp beneath a tremendous tidal wave of ice with its downsun side in shadow and displaying every imaginable shade of blue, and, having been there before, learning again the pleasant feeling of having come home.

ANTARCTICA AS A PLACE TO SEARCH FOR METEORITES? YOU MUST BE KIDDING!

The concept followed no evolutionary path. It was suddenly there, as bright as the comic-strip light bulb that signifies a new idea: meteorites are concentrated on the ice in Antarctica! The occasion was the thirty-sixth annual meeting of the Meteoritical Society, which took place during the last week of August 1973 in Davos, Switzerland. I was listening to a paper by Makoto and Masako Shima, a Japanese husband and wife team who are both chemists. He was describing their analyses of some stony meteorites. These specimens were interesting to me because they had been recovered in Antarctica. The pre-meeting abstract of the paper mentioned four meteorites that had been found within a 5 × 10 km area, lying on the ice at the Yamato Mountains (see Figure 1.1). I was quite aware of how rare meteorites really are, and as far as I knew, when meteorites are found near each other, as these had been, they are invariably fragments of a single fall. This was my assumption in the present case, and I had attended this presentation because of a long-standing, general interest in Antarctica, rather than a specific interest in the meteorites to be described. Actually, the abstract made it clear that these specimens were of distinctly different types, but I had been skimming and had not read that far. The key word, so far as I was concerned, had been Antarctica.

INTRODUCTION

Asteroidal meteorites form the bulk of the collection. The fact that we can find lunar and martian samples in Antarctica has been a very nice dividend for the ANSMET project and has helped significantly in ensuring a continuation of its funding over many years. But these samples are isolated faces in an enormous crowd – memorable and important, true, but very few in number. Almost all antarctic meteorites (and also meteorites fallen in the rest of the world) are believed to be asteroidal meteorites. By this we mean that they are fragments of larger bodies whose abode is (or was) the asteroid belt. The asteroid belt is a region between the orbits of Mars and Jupiter within which we have telescopic evidence of the existence of thousands of bodies in orbit about the sun. All the bodies we have detected telescopically, of course, are larger than the bodies we have collected on the earth as meteorites. If there are thousands of asteroids large enough to see from Earth with a telescope, there must be millions or billions of meteoroid-size particles there, too small to be seen, but each following its individual path in orbit about the sun. What we have in our meteorite collections is a tiny sample of all the meteorites whose orbits have, for one reason or another, become earth-crossing. These earth-crossers, in turn, are only a small fraction of the numbers of meteoroids that must remain in the asteroid belt.

METEORITES AND BLUE ICE

The well known rock cycle describes the ways in which natural processes degrade and disperse geological materials, sorting their components and converting them into the raw materials of new, and often very different, rocks. At the earth's surface, meteorites are further from chemical equilibrium than most terrestrial rocks and therefore are more susceptible to destruction by weathering and dispersal of their components. They are also very rare among the overwhelming background of terrestrial materials. This is not true of the meteorites we find in Antarctica – they resist weathering for long periods of time and are often found in high concentrations on exposed patches of bluish ice at, or above, about 2000 m elevation. If a patch of blue ice contains a concentration of meteorites we call it a meteorite stranding surface. To a meteoriticist, the levels of concentration are almost unbelievable: as of December, 1999, Japanese, US and European field teams had searched only about 3500 km2 of blue ice and recovered around 17 800 meteorite specimens.

Until recently, much emphasis had been put on the “treasure trove” aspect of the meteorite finds and their demonstrated value as scientific specimens, while very little attention had been given to the “treasure chests,” i.e., the sites where they are found. These sites and the meteorites found on them are linked to the history of the ice sheet and to climate change.

FIELD LOGISTICS

If field work is to be carried out within 100 nautical miles (=185 km) of McMurdo Station the preferred mode of travel is by helicopter, but we had begun prospecting for meteorites at sites that were out of helicopter range. For a while, it was sufficient to be put in at Allan Hills by helicopter and travel from there by snowmobile, towing everything on sledges. Our snowmobiles were geared-down machines made by Bombardier Corp. of Canada and were designed for heavy pulling. We found we could tow three fully loaded nansen sledges about as easily as one, so our cargo transport capacity gave us self-sufficiency for long oversnow traverses and long stays at remote sites (Figure 4.1). In this way, we were able to work effectively at the Reckling Peak, Elephant Moraine and Allan Hills Far Western icefields (see Frontispiece). But existing satellite photos gave us the ability to identify ice patches in all parts of the continent, and there were more-distant places that we aspired to visit. Camps at these sites are often referred to as deep-field camps.

Longer lifts are carried out by LC-130s, which actually can reach any part of the antarctic continent. For extreme distances, there is a trade-off between cargo weight and distance flown, but that limitation has not yet affected our field operations. The LC-130s (Figure 4.2) have been fitted with aluminum skis. These are very large, commensurate with the size of the airplane, and have been coated with Teflon®.

INTRODUCTION

Around 4.57 billion years ago, our part of the Galaxy was approaching a cusp in time and space that, once passed, would see the beginning of an irreversible process of star and planet formation. Our solar system would result. Just before it happened, our cloud of gas and dust had a past but no future – it wasn't quite dense enough on its own to begin gravitational contractions that would result in the birth of a star and associated planets. With no external stimulus it probably would just remain a cloud – formless, highly diffuse and without apparent purpose. But in a very intimate sense it was our cloud – we were all there, represented unknowingly by the atoms of which we are today composed.

A cusp is a point defined by the tangential convergence of two curves. The time line of our cloud was converging with the time line of a nearby giant star that had become unstable and was set to collapse inward with unimaginable intensity. This would initiate a supernova and splash part of itself out into space in an ejaculation of cosmic violence. Part of this giant splash was directed toward us (to be). The first signal of the nearby supernova was a flash of electromagnetic radiation, of which the part we call visible light is a tiny segment, washing into and through our cloud; perhaps for the first time illuminating its murky interior for no one to see.