The Lost Planet
“Metallic meteorites, says N. J. BERRILL,have long puzzled mankind. Stony ones have not always been recognized. Now we can add a third hind, the small glass meteorites known as tektites found scattered over wide areas of the Australian desert and various other naked regions of the earth. What are they made of, and by what means could they have become what they are? The answer seems to point to a planet that once existed not too far away but no longer exists.” Professor of Zoology at McGill University, Mr. Berrill is the author of several books, including Journey Into Wonder, Sex and the Nature of Things, and Man’s Emerging Mind.
by N. J. BERRILL
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A FEW years ago, having seen some aerial photos of a craterlike rim showing through the snow in the Ungava region of northern Quebec, Arctic prospector Fred Chubb and Ben Meen of the Royal Ontario Museum flew north to look it over. Within a year, in 1951, they returned to Quebec as part of an expedition sent jointly by the Museum and the National Geographic Society of the U.S. Their findings are now history. The crater is 11,500 feet from rim to rim, and the depth from the rim to the bottom of the lake more than 1300 feet, but the exciting find was evidence of a great metallic meteorite possibly a mile in diameter lying shattered deep beneath the surface. Until the Chubb crater was discovered, the famous meteoritic crater in Arizona, less than half the diameter and depth of Chubb, was the largest known. In both cases the meteorite struck the earth’s surface at a sharp angle, blasting a circular hole but coming to rest in rock below the rim of one side. Some idea of the impact is given by the granite ridges which spread like ripples away from the crater rim, and scientists have estimated that the meteorite struck at a speed somewhere between 30,000 and 150,000 miles all hour.
A Very large lump of metal evidently descended from other space at a very considerable speed. The question is, Where did it come from? Where have they all come from, the large and the small, the metallic meteorites and the stony ones, not to mention the shooting stars that flare through the upper atmosphere but never reach the earth’s surface? And the comets that give us a near miss once in a while? Space, at least in our neighborhood, seems a little cluttered up with small odds and ends. Are they leftovers from something or are they the result of a celestial smashup not too far away? Put them all together and we get a story.
Metallic meteorites have long puzzled mankind. Stony ones have not always been recognized. Now we can add a third kind, the small glass meteorites known as tektites found scattered over wide areas of the Australian desert and various other naked regions of the earth. All of them are of interest, for they are the only samples of matter which we can touch and investigate in the laboratory that are not part of our own planet. They are fragments, to be sure, but they are fragments with a history that can to some extent be deciphered, just as we can find meaning in a clay tablet from Mesopotamia or in a fossil skull of subhuman shape. For each kind of meteorite the first questions are, What are they made of, and by what means could they have become what they are? The answer in each case seems to point to a planet that once existed not too far away but no longer exists. In fact there is room for one bet ween Mars and Jupiter, and that is where it may well have been.
Mars, the only planet, besides the earth with any visible sign of life, has been the brightest object in the sky apart from the moon during recent months. The earth, traveling faster on its inner track, has bypassed the smaller planet at a distance of about 35 million miles, which it does after every sixteen years. Working out from the sun, the distances between the planets increase wilh each step. The rule was stated as long ago as 1772, by Johann Bode, and assigns the following numbers as closely representing the distances from the sun: Mercury
4, Venus 7, Earth 10, Mars 10,—28, Jupiter 52, Saturn 100,— 196. Within ten years the outer of the two vacant places was discovered to be occupied by Uranus; and within another ten years, in 1801, a tiny planet less than 500 miles across and only one fifth the diameter of the moon was found circling in the inner of the two vacant orbits, between Mars and Jupiter. Such a minute planet, which was called Ceres, was too little to make sense among its larger neighbors and yet too big to be ignored.
Others soon turned up, none of them as large as the first but in astonishing numbers. By 1942 as many as 1539 had been plotted and numbered, while the number seen now is close to 2000. We may call them planets out of courtesy, but they are remarkable in several ways. Only 4 exceed one hundred miles in diameter; 195 are between twenty-five and sixty; 193 are between ten and twenty-five miles across; while the vast majority are of even smaller dimensions. Moreover, most of them have queer irregular shapes. One of them, Eros, is fourteen miles long and four in diameter. Put them all together — all those that are known and the host that probably exist but are too small to see — and you still have a collection amounting to no more than one five-hundredth of the bulk of the earth. The majority circle the sun in the orbit between Mars and Jupiter, but many are decidedly erratic and swing all the way across the paths of the earth and Venus as well. In recent years two of these, about a mile across, have come within one million miles of the earth, which is just a little close for comfort. The Arizona and Chubb craters with their buried meteorites show that once in a while they do collide, for these meteorites are similar in size to those that have been spotted passing by. The wonder is that we have as little traffic trouble as we do.
What happened out there beyond Mars to account for the multitude of fragments that are flying about? Either a planet in the making failed to be put together properly or else a well-made planet exploded or in some other way smashed up. Could such a planet have supported living beings intelligent enough, though dumb enough, to have started an atomic bomb chain reaction powerful enough to have blown their planet apart? It is extremely unlikely, but considering our own recent and continuing state of jitters it is natural to ask the question. If the planet belonged where we think it did — roughly 100 million miles further from the sun than Mars—the answer is no. At that distance water would never be liquid; and as we cannot imagine life in any other terms, such an explanation appears to be ruled out. What then?
The answer, such as it is, lies at our feet. The several kinds of meteorites scattered over the earth’s surface have been carefully examined and analyzed, particularly during the last few years, and the facts seem to fit together remarkably well. The heavy metallic meteorites have naturally received attention for the longest time, for their weight and circumstance make them rather obviously out of place. Whenever they land, the general story is that of a fiery mass suddenly appearing in the sky and accompanied by sound like the thunder of guns. Throughout the ages the larger ones have usually been worshiped as having been sent by the gods, and even primitive man seems to have recognized their celestial origin. The “Black Stone" of the Kaaba, the holiest of holies of the Mohammedans, is undoubtedly a meteorite with its strange black crust.
The likelihood that meteorites are fragments of one or more planets has opened up the exciting opportunity to find out just how planets are made, quite apart from curiosity concerning what happened to break one into small pieces. We know a lot about the earth, it is true, but mostly by indirect measurement and calculation. Even the deepest mines are but scratches in the crust, and we have no chance of exploring the deep interior, let alone taking it all apart and still being around after the event to look at the bits.
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THE largest metcorite on display weighs thirtythree tons, was found in Greenland by Robert Peary in 1897, and may be seen in the Hayden Planetarium in New York City. In general the metallic meteorites are composed of iron and nickel. This in itself is significant, for it shows that matter in space is similar to matter on earth. The iron-nickel lumps, however, are peculiar. When a meteorite is cut and polished, and the cut surface etched, crystal structures appear which alternate between nickel-rich and nickel-poor bands of a special kind. The same kind of pattern has been produced by Dr. H. H. Uhlig in his laboratory at Massachusetts Inst itufe of Technology, though on a much smaller scale, by very slow cooling of a hot mixture of the two metals. The size and pattern of the crystals in the meteorites, however, show that the cooling process must have taken millions of years and that they were produced under pressures of many thousand atmospheres. So what can we think except that the crystalline metallic meteorites were formed from the liquid metal deep in the interior of a fairly large planet? For only there would pressures be great enough and the cooling process slow enough to produce the particular structure that we see. As a matter of fact metallurgists who have examined meteorilic crystals microscopically have found evidence of a sudden release of the tremendous pressure, as if there had been an explosive disruption.
So much for the chemist. Now the nuclear physicist enters the picture. Iron meteorites contain extremely small amounts of uranium; and as we all know, uranium is a radioactive element. As such it not only is a basis for bombs and atomic power but serves as a clock for timing events as old as the universe itself. The uranium breaks down into a special form of lead and produces helium in the process, but at an astonishingly low rate. The rate of decay is so slow and at the same time so constant that if the proportions of these substances are determined, the age of the rock containing them can be stated with a certain amount of accuracy. Some of the oldest rock in Canada, for instance, which even shows traces of microscopic fossil plants, is found by this method to be two billion years old, or about half as old as the planet itself is thought to be. Employing the same method, in particular the proportion of uranium to lead, Dr. Harrison Brown of the University of Chicago has estimated that uranium in the Bethany meteorite now at Harvard University has been decaying for about 4.5 billion years. In other words, the meteoritic metal solidified from the liquid state as long ago as that, presumably during the early days of the planet of which it was a part. Accordingly the planet of the meteorites came into existence at much the same time as the earth and by much the same sort of process.
That was the beginning, but there was also an end, and here again the meteorites tell their own story. Not all the helium produced within the meteorites comes from the decay of uranium. Much of it comes, apparently, as the result of bombardment of the iron by cosmic rays. When the quantity of helium present is known, the length of time the meteorites have been flying about, as fragments incessantly subjected to the action of high-energy cosmic rays, can be calculated. According to Dr. Fred Singer of the University of Maryland this period, for the four meteorites analyzed, turns out to be about 300 million years — a long time, to be sure, but pretty recent compared with the 4500 million years the meteorite substance has existed in solid form. It comes to this: that the planet which first congealed 4.5 billion years ago broke up with a bang a few hundred million years ago at the most, sometime during the great age of reptiles on the earth.
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WHAT kind of planet was it and how did it come to get smashed? According to Dr. G. P. Kuiper of Yerkes Observatory it never really became a planet, but remained half put together right from the first. His theory is that four to five billion years ago a group of small planets 30 to 500 miles in diameter formed from collections of dust, between Mars and Jupiter. Internal radioactivity caused them to heat up and melt, only to solidify again, and during this process of solidification the stony and metallic materials separated into stony crusts and metallic cores. Eventually they collided and broke into smaller pieces, to give us meteorites on earth, asteroids in their orbits, and comets that travel on the wildest courses. Yet other scientists believe that at least one planet must have been almost as large as the earth. For even a planet as large as Mars, with a diameter of over 4000 miles, or more than half the diameter of the earth, appears to have no core of heavy metal and is little heavier than stone throughout.
A planet apparently must be almost as large as the earth before its own pull of gravity is great enough to cause the original mixture of heavy and light materials to separate out to form a stony crust and metallic center. Yet this is what the various kinds of meteorites forcibly suggest. Some are nickel-iron similar to what we believe the central core of the earth to be; some are stony like our oldest rocks; and some are glassy, the lightest of all. So the odds are in favor of a fairly large planet, although one is not enough. It takes at least two planets to make a collision, though not necessarily two planets of the same size.
All we know is that, there is planetary debris flying around that looks as though it had been part of a large planet which somehow had a smashup. Supposing a pair of planets, one of them something like the earth and the other perhaps not much larger than the moon, had been born within the bell between Jupiter and Mars, why should they have had such an accident? Planets are not likely to collide unless there is interference from a third party. Here lies the answer; for whether or not we are right in thinking there must have been two planets traveling much the same circuit, the giant Jupiter circling near by like a great magnet would have made its presence felt. Jupiter would have continually changed their individual orbits, and differently in the two cases. Sooner or later their paths would cross, and it was later rather than sooner when they did. For more than four billion years they kept apart, with how many near misses no one will ever know, only to crash together In relatively recent solar system times.
Supposing this combination of facts and conjecture is reasonably correct, what, kind of planet came to its premature end? The several kinds of meteorites combine to fill in some detail. Meteorites may be iron, stony-iron, or stone, a series which grade one into the other and all with certain complex minerals which are not found on the earth. It certainly seems that they have come from one source despite their obvious differences. According to Dr. Paneth the three kinds—iron, iron and stone mixtures, and stone — probably separated from an originally homogeneous mixture when the planet was first forming, just as in the case of the earth with its metallic core and stony crust. For if the earth should blow up or otherwise come apart at its seams in an explosive fashion, it would strew the space it travels in with stony, stony-iron, and iron meteorites just as surely. The lost planet therefore most likely had a more or less metallic core, a stony crust, and a mixture in between. Unless a planet is large enough the power of gravity within it is not strong enough to bring about such a separation. The earth is big enough, as we know, but Mars is not, for Mars has been weighed by astrophysicists, by their own peculiar methods, and found wanting. The missing planet accordingly was considerably larger than Mars but smaller than the earth, for the shape and mechanical strength of the iron meteorites are such that the core they came from was not a single spherical mass of metal but was intermingled with stone.
Apart from this question of size, we know something about its crust. In the firsl place the minerals which are peculiar to the meteorites, especially in the stony kind, do not exist on earth for the reason that in the presence of water and oxygen they would soon be changed to other kinds. So water and oxygen almost certainly were absent Irom the crust and surface of the planet.
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IN ADDITION to stone and iron meteorites, another kind lies widely scattered and shattered on the face of the earth. They are the small and glassy tektites which are strewn over the Australian desert, over an area of more than two million square miles, far from any volcanoes that might possibly have produced them. Only their descent from space seems to fit all the facts, and it seems reasonable to suppose they came from the same general region as the rest of the meteorites. If so, then in all probability they represent the glassy surface of the broken planet. For just as metal sinks toward the center of a large planet in the making, and stone is left as the crust, so the lightest material, which is glass, spills onto the surface to form a brittle skin. There is little doubt that the earth itself possessed such a glistening surface at a very early stage in its career, but water erosion has long since destroyed it. but without water as such, the lost planet retained its original coat until the time of its destruction. How such showers of meteoritic glass reached the earth is another question, though one that carries us one step further in reconstructing the planet.
The tiny meteors that burn out as shooting stars as they enter our atmosphere and the larger meteorites that land with much of their substance still intact are not the only wanderers in near-by space. There are also the comets, more than 100,000 of them, each showing its tail as it nears the sun on its wild flight from far outer space and back. They are considered to have had their origin within the solar system no matter how far into the void they travel before they return again. At the same time the orbits of the comets are so fantastic it seems impossible that they were born at the same time as the planets swinging their orderly way around the sun. What is more likely than that they are pieces of the outer frozen envelope of our lost planet, like the icy crust of Jupiter, sent violently out of the original course by the great collision?
The spectrum of comets seems to confirm this view, for they are now known to consist largely of frozen gaseous matter such as ammonia, carbon dioxide, carbon monoxide, and nitrogen. Each time a comet approaches the sun, much of this material is heated up and swept away by the sun’s rays, to form the comet’s tail. So perhaps with every passing comet we actually see what might have been a planet’s atmosphere had the planet survived and had it spun in its course a little nearer to the sun. It would have been an atmosphere that could not have supported life as we know it, but it would have been an atmosphere similar to what the earth most likely started with. Given a somewhat different place in the solar system and no companion to get in its way, the lost planet might well have flowered in its time and produced a living world to match the earth. As it was, it was born in sterility and died in catastrophe.
