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HARPER'S LIBRARY of LIVING THOUGHT
ARE THE PLANETS INHABITED?
BY E. WALTER MAUNDER, F.R.A.S.
SUPERINTENDENT OF THE SOLAR DEPARTMENT,
ROYAL OBSERVATORY GREENWICH
AUTHOR OF "ASTRONOMY WITHOUT A TELESCOPE"
"THE ROYAL OBSERVATORY, GREENWICH, ITS HISTORY AND WORK"
"THE ASTRONOMY OF THE BIBLE," "THE HEAVENS AND THEIR STORY"
ETC.
HARPER & BROTHERS
LONDON AND NEW YORK
45 ALBEMARLE STREET, W.
1913
_Published March, 1913_
CONTENTS
CHAPTER PAGE
I. THE QUESTION STATED 1
II. THE LIVING ORGANISM 6
III. THE SUN 20
IV. THE DISTRIBUTION OF THE ELEMENTS IN SPACE 33
V. THE MOON 43
VI. THE CANALS OF MARS 57
VII. THE CONDITION OF MARS 71
VIII. THE ILLUSIONS OF MARS 96
IX. VENUS, MERCURY AND THE ASTEROIDS 111
X. THE MAJOR PLANETS 122
XI. WHEN THE MAJOR PLANETS COOL 133
XII. THE FINAL QUESTION 143
INDEX 163
ARE THE PLANETS INHABITED?
CHAPTER I
THE QUESTION STATED
The first thought that men had concerning the heavenly bodies was an
obvious one: they were lights. There was a greater light to rule the day;
a lesser light to rule the night; and there were the stars also.
In those days there seemed an immense difference between the earth upon
which men stood, and the bright objects that shone down upon it from the
heavens above. The earth seemed to be vast, dark, and motionless; the
celestial lights seemed to be small, and moved, and shone. The earth was
then regarded as the fixed centre of the universe, but the Copernican
theory has since deprived it of this pride of place. Yet from another
point of view the new conception of its position involves a promotion,
since the earth itself is now regarded as a heavenly body of the same
order as some of those which shine down upon us. It is amongst them, and
it too moves and shines--shines, as some of them do, by reflecting the
light of the sun. Could we transport ourselves to a neighbouring world,
the earth would seem a star, not distinguishable in kind from the rest.
But as men realized this, they began to ask: "Since this world from a
distant standpoint must appear as a star, would not a star, if we could
get near enough to it, show itself also as a world? This world teems with
life; above all, it is the home of human life. Men and women, gifted with
feeling, intelligence, and character, look upward from its surface and
watch the shining members of the heavenly host. Are none of these the home
of beings gifted with like powers, who watch in their turn the movements
of that shining point which is our world?"
This is the meaning of the controversy on the Plurality of Worlds which
excited so much interest some sixty years ago, and has been with us more
or less ever since. It is the desire to recognize the presence in the orbs
around us of beings like ourselves, possessed of personality and
intelligence, lodged in an organic body.
This is what is meant when we speak of a world being "inhabited." It would
not, for example, at all content us if we could ascertain that Jupiter was
covered by a shoreless ocean, rich in every variety of fish; or that the
hard rocks of the Moon were delicately veiled by lichens. Just as no
richness of vegetation and no fulness and complexity of animal life would
justify an explorer in describing some land that he had discovered as
being "inhabited" if no men were there, so we cannot rightly speak of any
other world as being "inhabited" if it is not the home of intelligent
life. If the life did not rise above the level of algae or oysters, the
globe on which they flourish would be uninhabited in our estimation, and
its chief interest would lie in the possibility that in the course of ages
life might change its forms and develop hereafter into manifestations with
which we could claim a nearer kinship.
On the other hand, of necessity we are precluded from extending our
enquiry to the case of disembodied intelligences, if such be conceived
possible. All created existences must be conditioned, but if we have no
knowledge of what those conditions may be, or means for attaining such
knowledge, we cannot discuss them. Nothing can be affirmed, nothing
denied, concerning the possibility of intelligences existing on the Moon
or even in the Sun if we are unable to ascertain under what limitations
those particular intelligences subsist. Gnomes, sylphs, elves, and
fairies, and all similar conceptions, escape the possibility of discussion
by our ignorance of their properties. As nothing can be asserted of them
they remain beyond investigation, as they are beyond sight and touch.
The only beings, then, the presence of which would justify us in regarding
another world as "inhabited" are such as would justify us in applying that
term to a part of our own world. They must possess intelligence and
consciousness on the one hand; on the other, they must likewise have
corporeal form. True, the form might be imagined as different from that we
possess; but, as with ourselves, the intelligent spirit must be lodged in
and expressed by a living material body. Our enquiry is thus rendered a
physical one; it is the necessities of the living body that must guide us
in it; a world unsuited for living organisms is not, in the sense of this
enquiry, a "habitable" world.
The discussion, as it was carried on sixty years ago by Dr. Whewell and
Sir David Brewster, was essentially a metaphysical, almost a theological
one, and it was chiefly considered in its supposed relationship to certain
religious conceptions. It was urged that it was derogatory to the wisdom
and goodness of the Creator to suppose that He would have created so many
great and glorious orbs without having a definite purpose in so doing, and
that the only purpose for which a world could be made was that it might be
inhabited. So, again, when Dr. A. R. Wallace revived the discussion in
1903, he clearly had a theological purpose in his opening paper, though he
was taking the opposite view from that held by Brewster half a century
earlier.
For myself, if there be any theological significance attaching to the
solving of this problem, I do not know what it is. If we decide that there
are very many inhabited worlds, or that there are few, or that there is
but one--our own--I fail to see how it should modify our religious
beliefs. For example: explorers have made their way across the Antarctic
continent to the South Pole but have found no "inhabitant" there. Has this
fact any theological bearing? or if, on the contrary, a race of men had
been discovered there, what change would it have made in the theological
position of anyone? And if this be so with regard to a new continent on
this earth, why should it be different with regard to the continents of
another planet?
The problem therefore seems not to be theological or metaphysical, but
purely physical. We have simply to ask with regard to each heavenly body
which we pass in review: "Are its physical conditions, so far as we can
ascertain them, such as would render the maintenance of life possible upon
it?" The question is not at all as to how life is generated on a world,
but as to whether, if once in action on a particular world, its activities
could be carried on.