Recent observations through the new big telescopes upset scientists’ old belief that the moon is dead and stimulate speculation about what forms of life exist there
By Isabel M. Lewis (Connected with the Nautical Almanac Office of the US Naval Observatory, Washington.)
Is the moon a barren, desolate waste, devoid of air and water, a dead world, as we have been taught for so many years, or do the observations of Professor W. H. Pickering, who has made a long-continued and systematic study of lunar markings under particularly favorable observing conditions at Arequlpa, Peru, and in Jamaica, and the observations of many other astronomers, in the past as well as today, indicate that the pulse of life still stirs within our satellite?
There is no doubt that water in the form of lakes, rivers or oceans cannot exist on the moon owing to its excessively rare atmosphere. No banks of clouds drift over areas of many square miles and temporally conceal the surface markings from view as In the case with our own planet. If extensive sheets of water existed on the surface of the moon or clouds temporarily obscured portions of its surface the telescope would reveal them.
The possibility that snow and ice may exist on the moon has long been recognized, however, and there is absolutely no reason why certain portions of the moon’s surface may not be clothed in a permanent mantle of white. The dazzling radiance of some parts of it, particularly in the south west quadrant, which is the highest and most rugged portion of the lunar surface, suggests the presence of snow and ice.
Now we know that the lunar day equals the period of the moon’s revolution around the earth, and it is for that reason equal in length to twenty-eight and a half of our own days. For more than fourteen days the sun beats down with merciless intensity upon a surface unprotected by the presence of a blanketing atmosphere. It has been estimated that at the lunar mid-day the temperature approaches close to the boiling point of water, while during the lunar night of over fourteen days’ length the temperature falls nearly to the absolute zero of space, several hundred degrees below zero of the Fahrenheit scale.
How is it, then, that ice and snow on the moon would be able to withstand the in tensity of the sun’s rays that raises the surface to a temperature of nearly 212 degrees Fahrenheit during the long day of two weeks’ duration? Would not large bodies of water take the place of the canopy of snow and ice that would exist under the frigid temperature of the long lunar night?
Let us consider for a moment conditions on our own planet. There is no place on the earth’s surface where the amount of heat received from the sun is not more than sufficient to melt whatever ice and snow falls upon it. Yet we know that the loftiest peaks of the Himalayas and Andes are covered with a snow that never melts. It may evaporate or change into hoar frost directly, but it will not first melt.
On our loftiest mountains conditions somewhat approach the conditions that exist on the moon’s surface. The air is extremely rare and “dry;” that is, it is lacking in water vapor and carbon dioxide, the two substances in the earth’s atmosphere that give it its heat-retaining power and make our planet inhabitable and which are to be found in considerable quantities only at low altitudes. If these two substances were absent from our atmosphere, the heat received from the sun would be radiated so rapidly back to space that it would not serve to warm us, and life would be impossible.
The Moon’s Ice Unmelted
The surrounding air on our loftiest mountains contains such small quantities of these heat-absorbing substances that the heat received from the sun is not stored up to an extent that will raise the ice and snow to the melting point, and though the rays of the sun fall on such surfaces for countless ages with great intensity the snow remains unmelted. Such are the conditions on the surface of the moon, only the atmosphere is much rarer there than It is on our mountain peaks, and so the surrounding space is still colder and conditions even more unfavorable for the formation of water.
Some astronomers have expressed the belief that far beneath the snow melting may take place as a result of the internal heat of the moon, but this is improbable, for however hot the interior may be, the surface as a whole will be kept at the temperature of surrounding space or. If the body possesses an atmosphere, at the temperature of the surrounding atmosphere. It is, therefore, very probable that water exists extensively beneath a lunar mantle of snow and ice.
It is very unlikely that all of the lunar surface is covered with ice and snow, how ever. There are all gradations of color tune on the moon, from the brilliant white of snow and ice to the deepest black. The peculiar darkness or the floor of the crater Plato caused it to be called Lacus Niger Major, “The Greater Back Lake,” by the astronomers of the seventeenth century, and one of the roost indisputable signs that periodic change does occur on the moon is the mysterious increase in darkness of the floor of Plato with the advance of the lunar day.
No satisfactory explanation of this change has ever been given. Professor Pickering’s most recent observations show a progressive darkening of the floors of certain craters; for example, of Eratos thenes, a crater about forty miles in diameter at the termination of the lunar mountain range called the Apennines.
Professor Pickering takes this to be due to a rapid vegetational growth during the lunar day of two weeks’ duration.
The possibility of life on the moon is attributed by those who believe in it to the existence of a certain low-lying gaseous medium close to the surface, permeating its crack and crevices and crater pits in sufficient quantities to permit the development of the life process, which’ does not necessarily imply the existence of human life as we are all to prone to believe, but simply the development of certain organisms peculiarly adapted to their environment. We know, for instance, that there are organisms to which oxygen is poison, and it is true that there are to be found in the Valley of Ten Thousand Smokes in Alaska certain forms of vegetation growing on the edge of volcanic vents which are emitting vapors at a temperature of 212 degrees Fahrenheit.
The maria, or so-called “seas,” on the moon are dark patches so familiar to ail of us. They are, in contrast to the elevated plateaus of the southwest quadrant, at a very low level. They were called seas by the early observers because their grayish appearance on the whole was such as might be attributed to the presence of extensive bodies of water.
The better telescopes of modern times show that these regions resemble, rather, dried-up ocean beds or extensive sheets of volcanic overflow.
They show in the telescope a wealth of detail. They are covered with ripples and ridges such as might be seen on exposed ocean floors, and they also show a variety of color-tone as if, possibly, they were covered with a form of vegetal growth or with volcanic rocks of different shades. In these low lying regions, where heavy gases may collect or where certain exhalations from the surface may arise, there is a possibility that certain forms of life may exist. The life-supporting elements in our own atmosphere — water vapor and carbon dioxide — are to be found only within a limit of a very few miles of the surface. Above an elevation of three or four miles, the human race cannot exist for any length of time in safety.
Close to the surface and in the cracks and crevices of the moon it is conceivable that there may exist a gaseous medium to which the life process might adapt itself.
There appears now to be abundant evidence of the existence of numberless crater cones on the moon, minute objects similar to active volcanic vents or fumaroles on our own planet that are in constant eruption. The existence of such vents on the moon implies the existence of heat in the interior similar to terrestrial heat and of ejected steam and vapors of many gases.
After their ejection, many of these gases would rapidly solidify and settle upon the surrounding surface, producing the light streaks and spots that are always associated with these minute markings. The steam would rapidly be transformed to clouds of hoar frost and at the time of eruption would temporarily obliterate these small markings.
Haze Hampers Observation
Records of observations show the gathering of haze around such markings, the temporary disappearance of many crate: cones and changes in their form and extent from time to time. Since the crater cones are at best the most difficult to observe of all lunar markings, and since all lunar markings vary greatly with the phases of the moon and observing conditions on the earth, it is easy to dispute the actuality of these changes or attribute them to changes in illumination or lunar phases. It is in this way that the evidences of change advanced by a number of selenographers of the past century have been explained away.
In the Mare Serenitatis, one of the lunar “seas,” there is a small object known as Linne, which has been the subject of much controversy in the past owing to the fact that many observers maintained that it changed greatly in appearance within the last century. Probably no object on the lunar surface has been more carefully examined with the possible exception of the floor of the crater Plato, which is covered with numerous crater-cones and light spots that unmistakably show signs of change.
Linne was described by the selenographer Madler in the earlier part of the nineteenth century as a deep crater six miles in diameter very conspicuous under a low sun. This did not flt the description of Schroter, who spoke of it in 1788 as a small, round, brilliant, white spot, with a somewhat uncertain depression. Neither did it agree with the observations of Schmidt in 1866, who found it only a hazy patch of light, though a number of years before he had seen it as it appeared to Madler. At the present time, it is a small crater less than a mile in diameter, and it is by no means an easy object to observe.
A conspicuous feature of the lunar surface is the network of rills, or clefts, that are visible in all parts of the surface, though they are met with less frequently on the maria, or seas, than elsewhere.
There is nothing on the surface of our own planet that corresponds in any way to these lunar rills. They range from a few hundred yards to a mile or two in width and from ten to several hundred miles in length. Their depth is uncertain, but is estimated to be less than a thousand feet. They extend, in some instances, in nearly straight lines for many miles, passing in their course through many obstacles, such as crater walls and ridges, though they frequently end in a small mound. The interior of craters are often intersected by them and they constantly appear near the border of mountain ranges and crater rims. They have been compared to inverted river beds because they usually become broader and deeper as they approach higher altitudes. They have in some in stances a decidedly artificial appearance, though it is generally believed that they are simply huge cracks in the brittle surface of the moon, produced possibly by terrific “moonquakes” or violent internal disturbances.
Here, too, we find evidence that changes have taken place. New clefts have appeared. Old clefts have temporarily disappeared or been temporarily obliterated haze. More than a thousand clefts have been mapped and new ones are constantly being added as the lunar surface is scanned with telescopes of increasingly greater power. More than forty delicate rills have been seen In a single lunar crater. So to find evidence of change among such indicate systems of delicate markings that aia seen with difficulty at best is no easy matter, and to convince others that change has taken place in them is still more difficult.
There is abundant evidence, however, that changes have frequently taken place in the visibility of the coarser rill systems. Rills that are at times easy objects with telescopes of small size are searched for in vain at other times, according to reliable observers, although the condition under which the observations have been made were in all respects the same. It is expected that here, too, a low-lying gaseous medium hovers over the lunar surface, filling certain of these cracks or crevices with the vapors from active volcanic vents, which in time clear away more or less, leaving the clefts beneath more clearly exposed to view.
If, then, forms of life are existent on the moon they are to be found only in the vicinity of active vents and fumaroles or in deep depressions of the surface, the low lying “seas,” the floors of craters or the interiors of clefts and rills, where the gases and vapors arising from the surface would tend to collect. The most authentic instances of change are found on the low lying seas in rill systems and crater cones and on the floors of craters, and not on the lofty plateaus or mountain ridges or the lofty walls of craters covered, we suspect, with a permanent mantle of snow and ice. Here no signs of change have been discovered.
Should Study Moon More
Most astronomers devote comparatively little time to systematic study of lunar markings. It is so generally believed that the moon is a dead world, whose evolution is practically finished, that it is hardly considered worth while to search here for new discoveries. Yet there is no body in the heavens concerning which we know less in some respects or that furnishes a more fertile field for discovery.
The cause of the formation of the mysterious lunar craters is not definitely known; the cause of the peculiar radiating streaks from Tycho has never been satisfactorily explained; the nature of the clefts and rills is in doubt. It cannot be definitely proven whether or not change has taken place in minute lunar markings owing to the absence of accurate photo graphic records of lunar markings taken with powerful telescopes, since it has not been considered worth while to make a systematic record of the markings of a “dead” world. It is easier to prove from photographic records that change is taking place tn a spiral nebula at the other end of the universe than to disprove the evidence that the pulse of life stirs within our own satellite only a celestial stone’s throw away.
At the present time, most astronomers consider the moon chiefly as a “show” object for visitors’ nights at our great observatories, or as a suitable object for testing the power of telescopes that must be devoted to more important work among the stars.
Not until the moon is considered to be worthy of careful and systematic observations with the best of telescopes will the controversy over the evidence that change is taking place on the moon be settled beyond dispute.