The Lunar Peaks
If the present trend of events in Europe continues we shall have to go far afield for our expeditions. This has led to the suggestion that the Mountains of the Moon be investigated. To be sure, the Duke of Abruzzi and others did magnificent work in the Ruwen- zori Range, but the peaks we are to discuss in this article remain, to our knowledge, virgin. These are the mountains of our own satellite—the Moon.
The first step in any exploration is a search for existing and available maps. Here is our first surprise. For no accurate map of the Moon exists.
From the time of Galileo astronomers, aided by the telescope, began a careful study of the Moon’s surface. As a result the geography, or selenography, of that portion of the Moon visible from the earth was thoroughly explored and is now well known. This known portion consists of a little more than half of the Moon’s surface. The rest remains unexplored. For the period of rotation of the Moon on its own axis is the same as that of its revolution about the Earth, with the result that the same side is always turned toward us. In past ages the Moon’s rotation was far more rapid, but its proximity to the Earth has enabled the inexorable pull of gravity to act as a brake upon this motion, slowing it down to its present period.
It is possible, however, to look around the edges a bit. This is because of what are known as the librations of the Moon. The axis of rotation of the Moon is inclined about 6.5° to the plane of its orbit about the Earth. As a consequence at one time during the month the Lunar North Pole is inclined 6.5° toward the Earth, and a fortnight later the South Pole is similarly inclined. This is known as the libration in latitude.
The libration in longitude is due to the fact that while the Moon’s period of rotation is uniform, its orbital speed is not. The orbit is an ellipse, and as the Moon approaches nearer the Earth its speed increases. The two motions, therefore, do not keep pace during the month and it is possible to see alternately a few degrees around the eastern and western edges of the Moon during the month. This amounts to about 7.75° each way.
Further, when the Moon is rising we look over its upper, which is then its northwestern edge, and in its setting see more of its northeastern edge. This is the diurnal libration, and permits seeing about 1° more of the lunar surface.
Yet another opportunity to add to the knowledge of the surface is given by the physical librations, or wobblings, of the Moon. The lunar equatorial diameter is about a mile greater than the polar, and the attraction of the Earth on this equatorial bulge, inclined 6.5° to the plane of the orbit, swings it sufficiently to bring a little more of the Moon’s surface into view.
The result of these various librations, geometrical and physical, is that 41 percent of the lunar surface is always visible, 18 percent is visible at times, and 41 percent remains invisible—terra, or rather luna incognita.
The existing lunar maps are merely plan or base maps, representing the spherical surface of the Moon projected on a plane surface, much as it appears when viewed through a telescope. The mountaineer, with his peculiar interest in the ups and downs of things, depends to a great extent upon a good topographic map, and would feel the need of it here. At present the Carnegie Institute is sponsoring a committee for the study of the surface features of the Moon. This committee has undertaken as one of the first of its projects the production of an accurate topographic map. Undoubtedly this map will be ready long before we do any climbing.
The next step is to examine what has been written on the region and to study such photographs as are available. Fortunately here we are no longer at a loss. There is no lack of literature and excellent photographs have been obtained. Examples of these are given in the plates which will be referred to from time to time.
The Moon is at a mean distance of 238,837 miles from the Earth. Due to the eccentricity of its orbit, this distance is variable between the limits of 221,463 and 252,710 miles. A magnifying power of 60 is sufficient to diminish this distance to 4000 miles and bring several hundred features into clear relief. With the largest telescopes it may be brought to within 200 or 300 miles and objects 500 feet apart distinguished under conditions of good seeing. The new 200-inch will reduce this to 25 miles. Skyscrapers, if they existed on the Moon’s surface, could clearly be seen.
With the aid of the photographs we may now proceed with a study of the region. Since the Moon shines by reflected light alone, and the reflected light is that of the sun, it is apparent that while the full Moon represents the phase of most brilliant illumination, it shows less detail. Objects on the Moon are seen at their best only as they are brought into clear relief by their shadows.
By means of their shadows the heights of the mountains and the depths of the craters may be determined with considerable accuracy, since this gives the base-line of a triangle. Another method, in the case of a lunar mountain, is to measure the distance between the summit and the terminator at the time when the summit first catches the light. At this instant it has the appearance of a point of light detached from the bright part of the Moon (Plate 4).
The terminator is the division line between light and darkness on the Moon’s surface. The advance of the terminator marks the approach of the lunar day. For a rapid survey of the more salient features of the Moon’s surface we will follow the sunrise across the Moon, looking briefly at the major physiographic features as the light strikes them.
First let us look at the Moon in the full light of the Sun, the full Moon (Plate 1). Here the image is right side up, just as seen through field-glasses and telescopes using a terrestrial eyepiece.
The darker areas are depressions on the Moon’s surface. Galileo called them “maria” or seas. Though they contain no water the name has been preserved. In reality they are large, low-lying plains, occasionally marked with ridges and small crater-like formations. The Sea of Conflicts is 280 miles long by 360 miles wide, covering an area of about 30,000 square miles.
Bordering the Sea of Showers are the Apennines, one of the largest and most important of the mountain ranges. Above these and across the straits connecting the Sea of Showers and the Sea of Serenity are the Caucasus Mountains, and to the left are the Alps.
Tycho is the most conspicuous of the great lunar craters. From it radiates the system of light streaks or light rays. These cross valleys, mountains and seas with no lessening of their definiteness until they fade out in the distance; the greater ones being as much as 100 miles in length and from 5 to 10 miles wide. It was early suggested that these were traces of volcanic dust and ash blown out from the crater and carried along by the jets of hot escaping gases. The fine material thus carried settled down along the paths of the gases. This view has been to a great extent corroborated in the light of recent investigations.
Following now the terminator let us study the lunar physiography in more detail and look at the Moon at four days, or shortly after new Moon (Plate 2). The image is now inverted as seen in a telescope equipped with an astronomical eyepiece. In the erect image of the Moon, as seen with the eye or through binoculars, N. and S. are the upper and lower poles respectively, E. is to the observer’s left as he faces the image and W. is to the right. In the inverted image all directions are reversed. N. and S. are transposed, E. is to the observer’s right and W. is to the left as on a terrestrial map. The upper right of the photograph becomes then S. E., and the Sea of Conflicts is in the lower left of the photograph instead of the upper right.
The central peak of the walled plain Langranus rises to a height of more than 3000 ft. The walls are 10,000 ft. high and the diameter of the plain is 90 miles. On the side of the smaller formation called Wrottesley the borders of Petavius rise 11,000 ft. above the floor. Cleomedes, just below the Sea of Conflicts, is about 80 miles long, with great walls rising 8000 to 10,000 ft. Below this the ramparts of Endymion rise to peaks of 10,000, 12,000 and 15,000 ft.
As the lunar day advances (Plate 3) the first rays of the Sun reach Aristotle and Eudoxus. These present their most striking aspect at this time, when the long shadows cover the crater floors and the whole E. walls are brilliantly illuminated in the sunrise. The three conspicuous craters bordering the Sea of Nectar are Theopolis, Cyrillus, and Catharina. The last is the largest, with a diameter of over 70 miles from N. to S. A great col leads into Cyrillus. The floor of Theopolis is 18,000 ft. below the highest points of its ramparts. The central mountain covers an area of 300 square miles and the peaks rise 6000 ft. above the floor. The first mountain range, the Pyrenees, now comes into the light. These rise to 12,000 ft., between the Sea of Fecundity and the Sea of Nectar. The Altai Mountains (13,000 ft.) lie to the S. of Catharina.
With the advance of the terminator, the more direct light of the Sun begins to obscure objects previously brought out in relief. Most conspicuous here (Plate 4) is Clavius, over which the Sun has just risen. This is one of the most magnificent of the lunar formations. Its walls are crowned with superb peaks 15,000 and 17,000 ft. high. On the floor, which covers an area of 15,000 square miles, five craters are visible. Below this is Tycho, whose rays are seen to best advantage in the first photograph. Above these, and on the southern limb of the Moon, so situated that they come into view only at times of favorable librations, are the highest of the known lunar ranges. These are the Doerful and Leibnitz Mountains. Their great peaks are seen nearly in profile when visible and attain heights of 26,000 and 30,000 ft. respectively. Another range at the edge of the S. E. limb, the Rook Mountains, contains a number of 25,000-ft. summits.
The sunlight has just struck the high peaks of the Carpathian Mountains, below Copernicus. In the early light of the lunar day rise the Apennines, the Caucasus and the Alps, sweeping in a great arc around the Sea of Showers. The ring plains, Aristillus, Autolycus and Archimedes, lie within this arc. One of the peaks of the crater Eratosthenes, at the eastern terminus of the Apennines, rises 16,000 ft. and Mt. Huygens, the highest peak in the Apennines, reaches an altitude of 21,000 ft.
The peaks of this vast composite “coast range,” it must be remembered, rise sheer from the floor of the plains. Even in comparison with our own mountains they more than rival the Himalayas. Yet the Moon is only one-quarter the size of the Earth. On the same scale our greatest peaks would crown ranges nearly 100,000 ft. high.
Plate 5 is an enlargement of the region of the Sea of Showers. In the center of the photograph is Mare Imbrium, bordered by the Caucasus, whose highest summits reach 19,000 ft., and below them are the Alps. To the S. E. of Plato lie a group of isolated peaks—the Teneriffe Mountains.
The smaller isolated peaks rising from the plains might well be counterparts of Shiprock. We might imagine Plate 6 to be a photograph of an expedition camped near the base of one of these. Only there would be no fire—sorry, no oxygen. In the accompanying photograph the plains of Mare Imbrium stretch away into the distance as the sunset lights up the rocks of the peak.
From the photographs the indications are that the lunar mountains are extremely rugged.1 This would necessarily be so since there are no agents of erosion at work to level down the results of the original cataclysm. The veiled clouds, so tenuous, so ethereal, yet with the power to bring the highest summits down to the level of the sea, are not here to melt down the solid lands. There is only the work of a lesser gravity to pull down the fragments broken off by the action of the extremes of heat and cold and the impacts of meteors.
Before further organizing our expedition let us look further into the physical conditions surrounding our objective.
The Moon is the fifth largest of the satellites of the Solar System and the largest in ratio of mass to its planet, being ?1 the mass of the Earth. The diameter of the Moon is 2160 miles. Its density is 3.3 that of water as compared to a value of 5.5 for that of the Earth. How will this affect our preparations ?
In the first place, one of the results of its smaller size and mass is a lowering of the value of surface gravity on the Moon. The surface attraction for bodies is about one-sixth that of the Earth. In other words, an object transported to the surface of the Moon would weigh only about one-sixth as much as it did on the Earth. The result of this in turn is a lowering of the “velocity of escape” for the Moon. This “velocity of escape” is the velocity which a particle must have to escape the gravitational attraction of its planet or satellite. A particle projected with a speed equal to or greater than this would fly off into space never to return. It is comparatively simple in celestial mechanics to calculate this velocity. This is done by determining the velocity which a body falling from rest at infinity would have on reaching the planet or satellite, and reversing it. The velocity of escape for the Earth is 11.8 km./sec., or approximately 7 miles a second. For the Moon it is 2.38 km./sec., or a little more than 1 mile a second.
According to the kinetic theory of gases, the molecules of gas are continually flying about in all directions with high velocities, colliding with one another and rebounding like perfectly elastic spheres. This is much the same situation as would exist in a closed tennis court, with an oversupply of tennis balls kept in continual motion. If, in their flying about and colliding, any of the molecules of the upper atmosphere reach the speed equal to the velocity of escape they fly off into space and are lost. If they have sufficient speed, or if the velocity of escape is low enough, the whole atmosphere dissipates away into space.
The mean velocities of the molecules of different gases depends upon the molecular weight of the gas and the temperature, and can be readily calculated. At 0° C. the value of the velocity is 1.84 km./sec. for hydrogen, 1.31 for helium, 0.62 for water vapor, 0.49 for nitrogen, 0.46 for oxygen, and 0.39 for carbon dioxide. These values increase by 17 percent at 100° C.
However, the velocity need not reach the critical value for escape. At the extreme upper limits of the atmosphere the free paths of the molecules are greater, they have less chance of colliding and being stopped, and thus have a greater chance of escape. Even if the mean molecular velocity is one-half that of the velocity of escape, Jeans has calculated that the atmosphere would be reduced to half its original amount in a few weeks. In the case of the Moon any atmosphere which it may have had has been dissipated away into space, for the simple reason that its gravitational force was not great enough to hold it.
The consequences following upon this lack of atmosphere are many. With the protective blanket of air removed the Sun beats down in undiminished fury upon the surface of the Moon. And during the lunar night, with nothing to withhold it, the heat is as suddenly withdrawn and the coldness of outer space creeps in. The temperature during the lunar day rises to 261° F., and at night drops to —243° F.
There is no dawn, no twilight. These are the results of the diffusive effects of an atmosphere. The Sun appears unheralded out of the blackness of night, and two weeks later is as suddenly swallowed up from a black sky.
There is no blue sky above; no colorful sunset. The blue of our own sky is the result of the scattering of the Sun’s light as it passes through the atmosphere. The shorter the wave length of light, the greater is its chance of being scattered as it travels through the molecules and dust particles of the atmosphere. The visible spectrum ranges through the colors of violet, indigo, blue, green, yellow, orange and red in the order of increasing wave length. Because of its short wave length blue light is scattered in all directions, giving the sky a blue color. At sunset and at dawn, when the light of the Sun must traverse a greater length of atmosphere, the longer wave lengths of light become scattered and the Sun and sky near it are red. At the higher altitudes, where a lesser depth of atmosphere is traversed, the color fades toward the violet, and ultimately toward the black.
There are no clouds, no water, no rivers, no glaciers or snow on the mountains; no sound except that transmitted through the rocks. The avalanche descends swiftly and ominously, with no warning save the ground vibrations set up before it. At the same time there is constant danger of bombardment from meteors falling in unchecked by the resistance of the atmosphere.
It is rather difficult to imagine the high mountains bare of all forest; with neither timber nor snow line. The topography too, is a strange one. There are no drainage patterns, no regular valleys, no ridges; no glacial cut or hanging valleys, no moraines, no terraces. In the wildness and desolation there is neither vegetation nor life. It is a barren desert.
Yet this Doreic scene would not be without its own beauty. As one sets out from the base camp in a lunar sunrise the jagged peaks and craters rise out of the cold in an unearthly quiet, their gleaming summits like beacons catching the first rays of the sun which flash instantly from peak to peak. There is no transition. All is light and darkness. Far below the vast white desert and the lesser craters are etched out in black and white with knife-edged shadows. Taking one’s eyes from the summit for a moment one looks out into the blackness of space at stars shining brilliantly, coldly, and without a twinkle, and with a clearness known only partially to those who have climbed in the great altitudes of our own planet.
In the shattering silence one can in fancy hear an almost audible hum of the planets as they swing by in their orbits.
Four times the size of the now visible Sun, the waning Earth adds its light to the scene, almost perceptibly spinning her blue seas and dark continents to light and shadow in turn beneath the covering of clouds.
Turning once more to the physical aspect, there is much that would invoke amazement at first, and a great deal that would require downright sound preparation if the summits of our goals are to be reached. The oxygen argument, for instance, would be settled once and for all.
It would be easy enough to call down to Camp V from 6000 ft. above: “Do you mind bringing the camp up here? There is a much better place for it.” Only the observer below could not hear, because sound waves must have an atmosphere to travel through. Presuming that he got the note thrown down to him (this would be easy, there would be no wind to carry it away, for wind is only air in motion), he could do it easily enough. That is, if Camp V didn’t weight over 300 lbs., or half a dozen 50-lb. loads. Furthermore, he could do it in an hour if the going were fairly good. A terrestrial 1000 ft. an hour is fairly steady going, and here you just divide everything having to do with gravity by six. A 30-ft. crevasse, for instance, would be no obstacle at all. You just jump across.
There would be two weeks of uninterrupted sunlight (save possibly for an eclipse) to make the summit in, though it would get extremely hot towards midday, or mid-fortnight. After sunset Earthlight lends sufficient light for continued work.
In addition to the bother of having to deal with oxygen (to say nothing of the disgrace) insulated clothes and special sleeping-bags would be in order. A range of temperature such as given above is apt to disconcert even the most hardy.
Face masks and special glasses are necessities too, for the whole range of the spectrum comes in undiminished, from the ultra-violet to the infra-red.
Of the actual rock climbing (for with no snow or ice it is to be all that) it is rather difficult to say just what the actual circumstances would be like. We can, however, make certain deductions.
The absence of an atmosphere and the ordinary terrestrial agencies of weathering and deposition precludes the possibility of sedimentary, and hence too of metamorphic rocks. Not much variety, for igneous is all that’s left. The Moon has a mean density of 3.3 that of water, as compared to the value of 5.5 for the Earth. Assuming the Earth’s rocky shell to be mainly dunite, if this body were formed from the outer layer of the Earth its density might be accounted for. This would be in accordance with the theory that the separation occurred due to the excessive rotational speed of the Earth, or that the material forming the satellite had been pulled out by the Sun shortly after the birth of the planet. In either case the heavier materials composing the Earth had sunk to its center, leaving the less dense, out of which the Moon was formed, at its surface. We are dealing then, with essentially the same type of materials.
Evidence of the composition of the Moon’s surface is given by the rate of cooling after an eclipse. As the shadow of the Earth passes over the Moon the temperature drops from 250° F. to —150° F. within an hour. This indicates that the lunar surface materials are excellent insulators; they have a small heat capacity, are poor conductors, and cannot, therefore, be massive rocks like granite or limestone, but rather light substance resembling in characteristics volcanic ash and pumice.
Further information regarding the composition of the lunar surface materials is obtained by photographing them in different lights. Near Aristarchus the rocks are very dark in a photograph taken with ultra-violet light, dark in one taken with violet, and invisible in one taken with orange light. The same phenomena can be simulated by photographing certain types of volcanic rock over which a thin layer of sulphur has been spread. It seems reasonable to infer, therefore, that the rocks near Aristarchus are probably volcanic and stained with sulphur, since sulphur is one of the more frequent constituents of vulcanism.
Being actually on the lunar surface, and able to gather more first-hand information, would assist greatly in solving the vexing problem of the lunar craters. This is fraught with interest, and their origin is still a matter of conjecture.
According to the meteoric theory the craters are the result of the impact of huge meteors, falling in with velocities of 20 to 40 km. a second and striking the surface with force sufficient to penetrate to some depth. The force of the impact, and the change of the residual kinetic energy into heat would be sufficient to melt the surrounding rock and produce the effect of the craters.
Objections to this theory are the fact that the Earth, too, would be subject to any bombardment of a magnitude sufficient to result in craters of such size, and there would be evidence of it at the surface, despite the lessened severity due to the blanket of atmosphere and the erasure of marks and traces by subsequent geologic agents. Again, all the lunar craters seem to be the result of direct hits; there are no glancing or side blows.
The other theory is that of lunar vulcanism. The lower value of gravity and lack of atmosphere are factors which must be taken into account. The effect on the one hand is to increase the range of the ejected materials, and on the other to augment this still further by the absence of a resisting medium. From observations of the volcano Cotopaxi, it has been calculated that the initial velocity of some of the ejected material has exceeded 2 km. a second. An eruption of the same force on the Moon would be sufficient to give this a range of over 1500 miles. The rays of Tycho extend to this distance. Furthermore, the ejected materials would be blown clear of the crater orifice and scattered so that the crater floor might even be lower than the surrounding plain. The same explosion scarcely blows the material clear of a terrestrial volcano, and a great deal of the ejected rock falls back into the crater mouth. The floors of the Earth craters are near the summit and well above the surrounding country.
Thus far we have considered the region from a mountaineer’s point of view, and will leave the design of means of transportation to more ingenious minds. The primary requirement for this is a speed sufficient to get us clear of the Earth. As we have seen, the velocity of escape is approximately 7 miles a second. Given this, it is possible to get clear of the Earth’s attraction. Unfortunately this means a speed of 25,200 miles an hour. Once clear of the attraction of this planet we could head for the Moon. However, this is a rather ticklish proposition. The Earth is rotating with an equatorial speed of 1000 miles an hour and moving through space at the rate of 18 miles a second; while the Moon revolves about the Earth with a velocity of 2000 miles an hour. This calls for accuracy and fine calculation in aiming. Then there is a rather troublesome difficulty connected with landing. Once within the attraction of the Moon the ship would be pulled toward its center. Now it is quite possible for a diver to guide himself once he hits the water, but impossible for him to effect a change of direction once in the air and headed for the pool; the medium he is in is not dense enough to permit effective control with the rudders at hands and feet, whereas the water is. An airplane maneuvers through the air because the air offers resistance to the tail and rudder, which give it change of direction. Without this they are useless.
Descending onto an atmosphereless satellite is much like diving into an empty pool. There is no way to check or guide one’s speed. Here the speed of impact would be over 60 miles a second. We had best wait until these details have been worked out.
The closest approach to lunar climbing conditions is exemplified in the ascent of Shiprock. See A.A.J. (1940), illustrations facing p. 56.