Lunar caustic

“ At the time when it was believed that the moon might be the source of meteorites, there was thought to be good reason for the supposition that some of the lunar volcanoes retained their igneous energy. Modern research has, however, demonstrated that the lunar volcanoes are absolutely silent and ineffective. ”

“ But in another instant the commotion was over, and the world whose curious spectacles had been enacted as if on the other side of a window, seemed to retreat swiftly into space, until at last, emerging from a fleecy cloud, it reappeared in the form of the full moon hanging in the sky, but larger than is its wont, with its dry ocean-beds, its keen-spired peaks, its ragged mountain ranges, its gaping chasms, its immense crater rings, and Tycho, the chief of them all, shooting raylike streaks across the scarred face of the abandoned lunar globe. ”

“ Ten thousand artemisium mills shot their etheric rays upon the moon, and our unfortunate satellite’s metal ribs were stripped by atomic force. Some of the great white rays that had been one of the telescopic wonders of the lunar landscapes disappeared, and the face of the moon, which had remained unchanged before the eyes of the children of Adam from the beginning of their race, now looked as if the blast of a furnace had swept it. At night, on the moonward side, the earth was studded with brilliant spikes, all pointed at the heart of its child in the sky. ”

“ We have just observed that the moon is characterized by vast mountain rings, attaining in many cases a diameter exceeding fifty miles. If these are volcanic craters, it is evident, at a glance, that the mightiest volcanoes of the earth fall into insignificance beside them. Now, the slight force of gravity on the moon has been appealed to as a reason why volcanic explosions on the lunar globe should produce incomparably greater effects than upon the earth, where the ejected materials are so much heavier. ”

“ In fact, if the invisible disc had any atmosphere, the shooting stars would be seen passing through it. If the projectile itself passed through the fluid strata, might it not hear some noise echoed—a storm, for instance, an avalanche, or a volcano in activity? Should they not see the intense fulgurations of a burning mountain? Such facts, carefully recorded, would have singularly elucidated the obscure question of the lunar constitution. Thus Barbicane and Nicholl, standing like astronomers at their port-lights, watched with scrupulous patience. ”

“ As I drew near it, in the vast realms of space, I loosened my car from the meteor, and then, restoring the power of gravitation, dashed on into the lunar sphere of gravitation towards the southern mountain-region that surrounds the lunar South Pole. It was a wondrously grand, and yet an awful, spectacle,–those vast and desolate rings of lunar mountains. Chain beyond chain, circle beyond circle, ring beyond ring, of extinct volcanoes opened up to my vision,–all glistening in the bright sunlight. To man, the heat would have been fatal. ”

“ In the relatively near future, men will certainly land on the surface of the moon. We know from radiometric studies that some degree of radioactivity is induced in meteorites by the full-intensity cosmic radiation to which they have been exposed during their motion through space. The nearly airless moon, like the meteorites, has also been exposed to very intense cosmic radiation for a long time. So those who are planning to land on our satellite are concerned about the radioactivities they will encounter when they begin their explorations of the lunar surface. ”

“ First, when the moon is occulted by the earth it is believed to be devoured by some evil demon, or by wolves or dogs. This is the superstitious vagary of the Hindoos, the Chinese, Asiatics generally, Europeans, Africans, Americans, and Polynesians. Secondly, a lunar eclipse is the precursor of some dreadful calamity to the inhabitants of the earth. This notion is also traceable in every quarter of the globe. And thirdly, during the obscuration the light of the moon is reddened, and at last extinguished, by the blood which flows from its wounds ”

“ The far greater effects of lunar vulcanicity, as compared with those of our globe, may be accounted for to some extent by the consideration that the force of gravity on the surface of the moon is only one-sixth of that on the surface of the earth. Hence the eruptive forces of the interior of our satellite have had less resistance to overcome than in the case of our planet; and the erupted materials have been shot forth to greater distances, and piled up in greater magnitude, than with us. ”

“ An undoubted case of combustion lies before us. Therefore, this part of the Moon must have an atmosphere!"
"Perhaps so," observed Barbican, "but not necessarily so. The volcano, by decomposing certain substances, gunpowder for instance, may be able to furnish its own oxygen, and thus explode in a vacuum. That blaze, in fact, seems to me to possess the intensity and the blinding glare of objects burning in pure oxygen. Let us therefore be not over hasty in jumping at the conclusion of the existence of a lunar atmosphere." ”

“ Many have fallen on our earth at various times, some being tons in weight. Usually, however, they are so small that on entering our atmosphere they become fused by the friction and changed to dust. Larger ones are partially fused, and often split into fragments in the upper air. The moon, having no atmosphere, is quite unprotected in this respect; and meteorites moving at enormous speeds, probably over forty miles in a second, travel unchecked and unaltered in character until they strike the lunar surface. It is estimated that immense numbers constantly enter our atmosphere and are destroyed ”

“ The absence of air and of water from the moon explains the sublime ruggedness of the lunar scenery. We know that on the earth the action of wind and of rain, of frost and of snow, is constantly tending to wear down our mountains and reduce their asperities. No such agents are at work on the moon. Volcanoes sculptured the surface into its present condition, and, though they have ceased to operate for ages, the traces of their handiwork seem nearly as fresh to-day as they were when the mighty fires were extinguished. ”

“ Having a much larger surface in proportion to her bulk than the earth, the oxidation of the moon has, he thinks, extended much deeper than that of the earth, and her atmosphere and oceans have been exhausted in the process. Both the earth and the moon, he maintains, have metallic nuclei, and the streaks about Tycho and Copernicus, and some other lunar craters, may be dikes of pure and shining metal, which have escaped oxidation owing to the comparatively small supply of lunar oxygen. ”

“ These streaks are cracks, made in the Moon's surface by cooling or by shrinkage, through which volcanic matter has been forced up by internal pressure. The sinking ice of a frozen lake, when meeting with some sharp pointed rock, cracks in a radiating manner: every one of its fissures then admits the water, which immediately spreads laterally over the ice pretty much as the lava spreads itself over the lunar surface. ”

“ Thus we see that an intense but extremely confined explosion, for instance, beneath the moon’s crust must disturb a circular area of its surface, if the intervening material be homogeneous. If this be not homogeneous there would be, where it offered less than the average resistance to the disturbance, an outward distortion of the circle; and an opposite interruption to circularity if it offers more than the average resistance. This assumed homogeneity may possibly be the explanation of the general circularity of the lunar surface features, small and great. ”

“ But changes such as these are not volcanic; they attest no lunar vitality. They are antecedently so probable, indeed, while volcanic changes are antecedently so unlikely, that when any change is clearly recognised in the moon's surface, nothing but the most convincing evidence could be accepted as demonstrating that the change was of volcanic origin and not due to the continued expansion and contraction of the lunar crust. ”

“ The oxygen was supposed to have entered into combination with the cooling rocks and minerals, thus being withdrawn from the atmosphere, and the nitrogen was imagined to have disappeared also [Pg 233] within the lunar crust. For it seems to have always been tacitly assumed that the phenomenon to be accounted for was not so much the absence of a lunar atmosphere as its disappearance. But disappearance, of course, implies previous existence. In like manner it has always been a commonly accepted view that the moon probably once had enough water to form lakes and seas. ”

“ But the rays which pass back to earth after their impact on the moon's surface are profoundly changed. The spectroscope shows that they lose practically all the slower vibrations we call red and infra-red, while the extremely rapid vibrations we call the violet and ultra-violet are accelerated and altered. Many scientists hold that there is an unknown element in the moon—perhaps that which makes the gigantic luminous trails that radiate in all directions—from the lunar crater Tycho—whose energies are absorbed by and carried on the moon rays. ”

“ It however calls up another interesting theory, which has not met with much acceptance, to the effect that such lunar volcanoes as Copernicus may have been powerful enough to eject masses of lava and rocks with a velocity sufficient to enable them to escape from the attraction of the moon, whereupon they became meteorites traveling in independent orbits around the sun. Some of these, the theory suggests, may be among those that have fallen upon the earth. A velocity of a mile and a half per second would be sufficient to overcome the gravitation of the moon. ”

“ Many theoretical efforts, some of considerable violence, have been made to reconcile the supposed physical contradiction presented by the great magnitude and area of former volcanic activity of the Moon, and the present absence of water on its surface. So long as we accept the generally received belief that water is a necessary agent in the evolution of volcanic forces, the difficulties presented by the lunar surface are rather increased than diminished by further examination and speculation. ”

“ This regolith may vary its thickness between 2 to 20 meters, so every time a mission land on the Moon, it leaves a record of that event. Even though the Moon is covered in this dust, most of its surface (under this layer) has basalt, a volcanic rock, or, in this case, from a lunar core rock that resurfaced after meteors impacts.
The Moon, unlike stars like the Sun, but like the planets, doesn’t emit light itself but reflects the light that comes from the Sun, which happens due to the lack of mass to produce energy in its core. ”

“ In earlier days, most scientists believed that the craters on the moon had all been formed by volcanic action. Now the pendulum of scientific opinion seems to have swung toward the view that all the thousands of lunar craters are the result of meteorite impacts that took place in the long distant past. Both views are better examples of how scientific “fashions” control men’s minds than they are of explanations that really account for all of the observed facts—as any acceptable explanation must do. ”

“ We are, therefore, forced to discard the lunar theory of meteorites altogether, for the simple reason that if the moon ever did project meteoritic masses, they must have tumbled down on the earth ages ago, at the time when the lunar volcanoes were still active. ”

“ When and where will the next crater-producing fall occur? Perhaps on the earth, perhaps on the moon, for our nearest neighbor in space has also been the target of meteorites of huge size. The effects of this meteoritic bombardment are shown by the rarest and most striking type of lunar crater: that which exhibits long, bright rays extending outward from the crater itself as the spokes of a wheel radiate from its hub. These so-called ray-craters show to best advantage at or near the time of full moon, when they become one of the most remarkable features visible on our satellite. ”

“ And these same points, when seen in the dim reflection of the Earth, will still predominate in intensity over the neighbouring regions. In this way Arago and others explain the observations of Herschel, without admitting the existence of active volcanoes in the Moon. That volcanoes there are, is a familiar fact; but they would seem to have exhausted their activity in long-past ages. The lunar surface is now a dreary waste of rugged lava and ashes, covered with the matter ejected from craters once in a state of furious eruption. The Moon, in fact, is a world which has burned itself out. ”

“ The lunar Caucasus is the broader, but shorter, range of mountains at the northeastern corner of the Mare Serenitatis, and the Alps extend eastward from the Caucasus to a conspicuous dark oval close to the terminator, which is one of the most remarkable formations on the moon, and which, when we come to study it in one of the larger photographs, will probably interest you deeply because it is one of the places where recent studies have discovered indications of what may possibly be some form of lunar life. I wish now to direct your attention to the central and upper parts of the photograph. ”