LIFE ON THE PLANETS?

Gisborne Times, Volume LXXXIV, Issue 12905, 4 July 1936, Page 9

LIFE ON THE PLANETS?

Lot us consider some of these factors : Tlio planets in the solar system range in size from .Mercury, one-six-teenth of the sizo of the earth, to Jupiter, • 3300 times the size of the earth. The moon and the satellites fit other planets are mostly much smaller than .Mercury. We cannot expect, to line! Jife on cither a very small or a very largo planet. -Dead Worlds.” A small planet is unable to support life because it cannot retain any atmosphere. Our atmosphere would rapidly dissipate away into space were it not for the gravitational pitil of the earth that prevents it from escaping. But the grip of a..small planet on its atmosphere is too weak to prevent this dissipation. So we line! that the small bodies, like the moon and tin- planet Mercury, have entirely lost their atmospheres. There is consequently neither oxygen nor water on them. We cannot conceive that under these circumstances life of any sort can exist. 'They are dead worlds. Conditions are just the. opposite co a large planet. It exerts so strong e. pull that, it has a very dense and extensive atmosphere. Even hydrogen, the lightest, of all substances and the one that can escape most easily, js held hound. The hydrogen that was once abundant in the earth’s atmosphere has been almost entirely lost. though oxygen and nitrogen have been io a large extent retained. But the ehane.es for the development of life are much reduced when hydrogen is unable to escape. Hydrogen is by far the most abundant element in tho sun and in all other stars. As the planets were formed of vapours drawn out from the parcur sun by the gravitational pull of t: star that passed near by, they must all at first have consisted predominantly of hydrogen. When they rind cooled sufficiently for a. solid crust to form, (ho atmosphere outside the crust must have contained more hydrogen than ail the other gases together.

This hydrogen soon escaped from the small planets. Init it was unable to escape from the large planets. A lime came when all the oxygen combined with a portion of the hydrogen to form water-vapour; the nitrogen also combined with some of the hydrogen to form ammonia, the pungent gas used in many refrigerating plants; more of the hydrogen combined with carbon to form marsh-gas, the gas known to the miner as the dangerous fire-damp, that is given oil by decaying vegetable matter. On a Large Planet. Fk> we may expect to find on a largo planet an atmosphere consisting largely of hydrogen, wat'er-vaponr, ammonia and marsh-gas, but entirely devoid of oxygen and nitrogen—the principal constituents ol our own atmosphere. It the planet cools sufficiently, the water-vapour freezes out. io form a thick glacier coating surrounding the planet. This is just what we find on Mm large pianists in the solar system, Jupiter, Saturn, Uranus and Neptune. Knell nf these planets has a glacier coating thousands of mi Us thick, surrounded by a dense atmosphere several thousand miles in depth, in which both ammonia and marsh-gas nro prominent constituents. At tho surface of the planet the pressure of tho atmosphere amounts t<~ many thousands of tons to tho square inch, so that oven the most refractory of gases to liquefy, helium and hydrogen, become liquid. No Ido can possibly exist under these, conditions. Wo cannot expect, therefore. co find any life on either the very small O- the very largo planets. Those ot medium size stand the best chance of becoming a home of life. But there is another important factor. None of tho planets in the solar system has any store of heat of us own. They are warmed by the sun, and there is an exact balance between the heat that each receives from, the son and the heat that it, in turn, gives out into space. Extremes of Temperature. Hence the nearer the planet to the sun, the warmer it will he. Thus we find that, while Mercury is at hot as molten zinc, the outermost planets aro so cold that the Antarctic regions of our earth are extremely hot by comparison. It is difficult to conceive that life can possibly exist under either of those extreme conditions of temperature. Looking at other stars, we find that some give out many thousands or even hundreds of thousands of Jimes as much heat as our sun. If

NONE ON SMALLER SPHERES. IF MARS JS INHABITED. DO ITS PEOPLE LIVE IN DUG-OUTS? \yiIAT IS THE POSSIBILITY Hint life exists elsewhere in the universe limn on our enrtli ? Though tliero may he many stars, in addition to the sun, with jilnnets circlnig l round them, we are able to say with certainty that not more than a very small jmijiortion of these planets rim, have life on them. For a very delicate balance is needed in order that, conditions suitable- for the support of: life .may exist.

such a star has any planets life could not possibly exist on them unless they were much farther away from if than the planets in the solar system are Jrom our sun. Other stars, again, give out only a. small fraction o! tho heat given out by tho sun; there can be no life on a, planet belonging to such a s|ar unless it Lcomparatively near. There is a. limited region around a. star within which a planet, must he found if it. is to ho neither too hot nor too cold tor life to exist.

This condition very much reduces the expectation of finding life on any planet elsewhere in the universe; the additional condition that the planet must he neither too small nor too large still further reduces the expectation.

In the solar system, we can definitely rule but of consideration all the jilnnets except Venus and Mars. Venus is the twin sister of the earth, or nearly the same size and nearly tho same weight.

It. is rather warmer than the earth, because it is nearer the sun. It is always covered with a den,t> layer of cloud and evidently has. as we should expect, a considerable armosphere. There is little, if any oxygen ;u this atmosphere, but there is an abundance of carbon dioxide, at least several hundred times as much ns our own atmosphere.

What is the reason for this difference? The. abundance of oxygen Li our atmosphere is due to the extensive vegetation that * covers the earth. This is continually extracting carbon dioxide from the air and returning oxygen in its stead. The

fcrcnco is that there is not as yet much vegetation on Venus. If is probable that when life first appeared. on the earth there was not much oxygen. The first life would be primitive vegetation; as this developed, li gradually brought about an increase in the supply of oxygen until conditions became suitable for animal life. is There Life on Venus? Tho conditions now prevailing on Venus are probably not unlike those rialt prevailed on the earth millions of years ago, when the earth had a warmer and more humid climate than it has now and when it was covered with vast swamps.

If animal life exists at all on VV~ lins, it is probably somewhat akin u the swamp-dwelling mammoths that, onco lived on the earth. We have left Mars for brief final consideration. Professor Lowell pictures Arars as an arid world, inhabited by a race of intelligent beings engaged in a desperate struggle tor existence. They had constructed canals, extending for thousands *>f miles, to carry water from the polar ice caps, as they melted in the summer, to the drought-stricken equatorial regions. but there seems little doubt that the canals have no real existence, their appearance being due to a subjective tendency for the human -ye t., connect by straight lines markings that are almost aL the limit of vision. What, of Mars? Rejecting, therefore, Lowell's graphic picture, what do we know about Mur.s? ]t is a smaller world than the earth and lias largely lost its atmosphere. A thin atmosphere there certainly is, extending for fully 50 miles above the surface. Water vapour is undoubtedly present in tins atmosphere, and probably - oxygen also. Mars is farther away from the sun and therefore rather colder than the earth. In tho equatorial regions tho noon temperature is about dOdog. U. But fhe thin atmosphere is a poor blanket, and, as the sun gets lower m tlio heavens, tho temperature rapidly falls. The cold becomes intense, and tho minimum temperature at night is about 150 deg. F. below zero. Tho difference between the noon and midnight temperatures is about equal to tho difference between the boiling point and the freezing point of water.

These extreme changes of temperature must be very trying for any form of life that may exist on Mars. Life has a wonderful facility for adaptation, and any life on Mars will have developed by evolution to types suited to the prevailing conditions. I imagine that the Martians must live in dugouts, well below the surface, of the 'ground, - in which they will-take refuge at night from the bitter cold. Wo compared the conditions m Venus with those that existed on the earth , many millions jof years ago. Those on Mars may be not unlike the conditions that will prevail on the eartli many millions of years lienee, when the sun is cooler than it ij now. and when the earth will have lost much of its present atmosphere.