IS ANIMAL LIFE POSSIBLE ON MARS?
Having now shown, that, even admitting the accuracy of all Mr. Lowell's
observations, and provisionally accepting all his chief conclusions as
to the climate, the nature of the snow-caps, the vegetation, and the
animal life of Mars, yet his interpretation of the lines on its surface
as being veritably 'canals,' constructed by intelligent beings for the
special purpose of carrying water to the more arid regions, is wholly
erroneous and rationally inconceivable. I now proceed to discuss his
more fundamental position as to the actual habitability of Mars by a
highly organised and intellectual race of material organic beings.
_Water and Air essential to Life._
Here, fortunately, the issue is rendered very simple, because Mr. Lowell
fully recognises the identity of the constitution of matter and of
physical laws throughout the solar-system, and that for any high form of
organic life certain conditions which are absolutely essential on our
earth must also exist in Mars. He admits, for example, that water is
essential, that an atmosphere containing oxygen, nitrogen, aqueous
vapour, and carbonic acid gas is essential, and that an abundant
vegetation is essential; and these of course involve a
surface-temperature through a considerable portion of the year that
renders the existence of these--especially of water--possible and
available for the purposes of a high and abundant animal life.
_Blue Colour the only Evidence of Water._
In attempting to show that these essentials actually exist on Mars he is
not very successful. He adduces evidence of an atmosphere, but of an
exceedingly scanty one, since the greatest amount he can give to it is--
"not more than about four inches of barometric pressure as we reckon
it";[7] and he assumes, as he has a fair right to do till disproved,
that it consists of oxygen and nitrogen, with carbon-dioxide and
water-vapour, in approximately the same proportions as with us. With
regard to the last item--the water-vapour--there are however many
serious difficulties. The water-vapour of our atmosphere is derived from
the enormous area of our seas, oceans, lakes, and rivers, as well as
from the evaporation from heated lands and tropical forests of much of
the moisture produced by frequent and abundant rains. All these sources
of supply are admittedly absent from Mars, which has no permanent bodies
of water, no rain, and tropical regions which are almost entirely
desert. Many writers have therefore doubted the existence of water in
any form upon this planet, supposing that the snow-caps are not formed
of frozen water but of carbon-dioxide, or some other heavy gas, in a
frozen state; and Mr. Lowell evidently feels this to be a difficulty,
since the only fact he is able to adduce in favour of the melting snows
of the polar caps producing water is, that at the time they are melting
a marginal blue band appears which accompanies them in their retreat,
and this blue colour is said to prove conclusively that the liquid is
not carbonic acid but water. This point he dwells upon repeatedly,
stating, of these blue borders: "This excludes the possibility of their
being formed by carbon-dioxide, and shows that of all the substances we
know the material composing them must be water."
[Footnote 7: In a paper written since the book appeared the density of
air at the surface of Mars is said to be 1/12 of the earth's.]
This is the only proof of the existence of _water_ he adduces, and it is
certainly a most extraordinary and futile one. For it is perfectly well
known that although water, in large masses and by transmitted light, is
of a blue colour, yet shallow water by reflected light is not so; and in
the case of the liquid produced by the snow-caps of Mars, which the
whole conditions of the planet show must be shallow, and also be more or
less turbid, it cannot possibly be the cause of the 'deep blue' tint
said to result from the melting of the snow.
But there is a very weighty argument depending on the molecular theory
of gases against the polar caps of Mars being composed of frozen water
at all. The mass and elastic force of the several gases is due to the
greater or less rapidity of the vibratory motion of their molecules
under identical conditions. The speed of these molecular motions has
been ascertained for all the chief gases, and it is found to be so great
as in certain cases to enable them to overcome the force of gravity and
escape from a planet's surface into space. Dr. G. Johnstone Stoney has
specially investigated this subject, and he finds that the force of
gravity on the earth is sufficient to retain all the gases composing its
atmosphere, but not sufficient to retain hydrogen; and as a consequence,
although this gas is produced in small quantities by volcanoes and by
decomposing vegetation, yet no trace of it is found in our atmosphere.
The moon however, having only one-eightieth the mass of the earth,
cannot retain any gas, hence its airless and waterless condition.
_Water Vapour cannot exist on Mars._
Now, Dr. Stoney finds that in order to retain water vapour permanently a
planet must have a mass at least a quarter that of the earth. But the
mass of Mars is only one-ninth that of the earth; therefore, unless
there are some special conditions that prevent its loss, this gas cannot
be present in the atmosphere. Mr. Lowell does not refer to this argument
against his view, neither does he claim the evidence of spectroscopy in
his favour. This was alleged more than thirty years ago to show the
existence of water-vapour in the atmosphere of Mars, but of late years
it has been doubted, and Mr. Lowell's complete silence on the subject,
while laying stress on such a very weak and inconclusive argument as
that from the tinge of colour that is observed a little distance from
the edge of the diminishing snow-caps, shows that he himself does not
think the fact to be thus proved. If he did he would hardly adduce such
an argument for its presence as the following: "The melting of the caps
on the one hand and their re-forming on the other affirm the presence of
water-vapour in the Martian atmosphere, of whatever else that air
consists" (p. 162). Yet absolutely the only proof he gives that the caps
are frozen water is the almost frivolous colour-argument above referred
to!
_No Spectroscopic Evidence of Water Vapour._
As Sir William Huggins is the chief authority quoted for this fact, and
is referred to as being almost conclusive in the third edition of Miss
Clerke's _History of Astronomy_ in 1893, I have ascertained that his
opinion at the present time is that "there is no conclusive proof of the
presence of aqueous vapour in the atmosphere of Mars, and that
observations at the Lick Observatory (in 1895), where the conditions and
instruments are of the highest order, were negative." He also informs me
that Marchand at the Pic du Midi Observatory was unable to obtain lines
of aqueous vapour in the spectrum of Mars; and that in 1905, Slipher, at
Mr. Lowell's observatory, was unable to detect any indications of
aqueous vapour in the spectrum of Mars.
It thus appears that spectroscopic observations are quite accordant with
the calculations founded on the molecular theory of gases as to the
absence of aqueous vapour, and therefore presumably of liquid water,
from Mars. It is true that the spectroscopic argument is purely
negative, and this may be due to the extreme delicacy of the
observations required; but that dependent on the inability of the force
of gravity to retain it is positive scientific evidence against its
presence, and, till shown to be erroneous, must be held to be
conclusive.
This absence of water is of itself conclusive against the existence of
animal life, unless we enter the regions of pure conjecture as to the
possibility of some other liquid being able to take its place, and that
liquid being as omnipresent there as water is here. Mr. Lowell however
never takes this ground, but bases his whole theory on the fundamental
identity of the substance of the bodies of living organisms wherever
they may exist in the solar system. In the next two chapters I shall
discuss an equally essential condition, that of temperature, which
affords a still more conclusive and even crushing argument against the
suitability of Mars for the existence of organic life.