Mars
Mars was called by the ancients "the vanishing star," owing to the long
periods during which it is practically invisible from the earth.[98] It
was also called [Greek: puroeis] and Hercules.
I have seen it stated in a book on the "Solar System" by a well-known
astronomer that the _axis_ of Mars "is inclined to the plane of the orbit"
at an angle of 24° 50'! But this is quite erroneous. The angle given is
the angle between _the plane of the planet's equator_ and the plane of its
orbit, which is quite a different thing. This angle, which may be called
the obliquity of Mars' ecliptic, does not differ much from that of the
earth. Lowell finds it 23° 13' from observations in 1907.[99]
The late Mr. Proctor thought that Mars is "far the reddest star in the
heavens; Aldebaran and Antares are pale beside him."[100] But this does
not agree with my experience. Antares is to my eye quite as red as Mars.
Its name is derived from two Greek words implying "redder than Mars." The
colour of Aldebaran is, I think, quite comparable with that of the "ruddy
planet." In the telescope the colour of Mars is, I believe, more yellow
than red, but I have not seen the planet very often in a telescope. Sir
John Herschel suggested that the reddish colour of Mars may possibly be
due to red rocks, like those of the Old Red Sandstone, and the red soil
often associated with such rocks, as I have myself noticed near Torquay
and other places in Devonshire.
The ruddy colour of Mars was formerly thought to be due to the great
density of its atmosphere. But modern observations seem to show that the
planet's atmosphere is, on the contrary, much rarer than that of the
earth. The persistent visibility of the markings on its surface shows that
its atmosphere cannot be cloud-laden like ours; and the spectroscope shows
that the water vapour present is--although perceptible--less than that of
our terrestrial envelope.
The existence of water vapour is clearly shown by photographs of the
planet's spectrum taken by Mr. Slipher at the Lowell Observatory in 1908.
These show that the water vapour bands _a_ and near D are stronger in the
spectrum of Mars than in that of the moon at the same altitude.[101]
The dark markings on Mars were formerly supposed to represent water and
the light parts land. But this idea has now been abandoned. Light
reflected from a water surface is polarized at certain angles. Prof. W. H.
Pickering, in his observations on Mars, finds no trace of polarization in
the light reflected from the dark parts of the planet. But under the same
conditions he finds that the bluish-black ring surrounding the white polar
cap shows a well-marked polarization of light, thus indicating that this
dark ring is probably water.[102]
Projections on the limb of the planet have frequently been observed in
America. These are known _not_ to be mountains, as they do not reappear
under similar conditions. They are supposed to be clouds, and one seen in
December, 1900, has been explained as a cloud lying at a height of some 13
miles above the planet's surface and drifting at the rate of about 27
miles an hour. If there are any mountains on Mars they have not yet been
discovered.
The existence of the so-called "canals" of Mars is supposed to be
confirmed by Lowell's photographs of the planet. But what these "canals"
really represent, that is the question. They have certainly an artificial
look about them, and they form one of the most curious and interesting
problems in the heavens. Prof. Lowell says--
"Most suggestive of all Martian phenomena are the canals. Were they
more generally observable the world would have been spared much
scepticism and more theory. They may of course not be artificial, but
observations here [Flagstaff] indicate that they are; as will, I
think, appear from the drawings. For it is one thing to see two or
three canals and quite another to have the planet's disc mapped with
them on a most elaborate system of triangulation. In the first place
they are this season (August, 1894) bluish-green, of the same colour
as the seas into which the longer ones all eventually debouch. In the
next place they are almost without exception geodetically straight,
supernaturally so, and this in spite of their leading in every
possible direction. Then they are of apparently nearly uniform width
throughout their length. What they are is another matter. Their mere
aspect, however, is enough to cause all theories about glaciation
fissures or surface cracks to die an instant and natural death."[103]
Some of the observed colour-changes on Mars are very curious. In April,
1905, Mr. Lowell observed that the marking known as Mare Erythræum, just
above Syrtis, had "changed from a blue-green to a chocolate-brown colour."
The season on Mars corresponded with our February.
Signor V. Cerulli says that, having observed Mars regularly for ten years,
he has come to the conclusion that the actual existence of the "canals" is
as much a subject for physiological as for astronomical investigation. He
states that "the phenomena observed are so near the limit of the range of
the human eye that in observing them one really experiences an effect
accompanying the 'birth of vision.' That is to say, the eye sees more and
more as it becomes accustomed, or strained, to the delicate markings, and
thus the joining up of spots to form 'canals' and the gemination of the
latter follow as a physiological effect, and need not necessarily be
subjective phenomena seen by the unaccustomed eye."[104]
The possibility of life on Mars has been recently much discussed; some
denying, others asserting. M. E. Rogovsky says--
"As free oxygen and carbonic dioxide may exist in the atmosphere of
_Mars_, vegetable and animal life is quite possible. If the
temperature which prevails upon _Mars_ is nearer to -36° C. than to
-73° C., the existence of living beings like ourselves is possible. In
fact, the ice of some Greenland and Alpine glaciers is covered by red
algæ (_Sphærella nivalis_); we find there also different species of
rotaloria, variegated spiders, and other animals on the snow fields
illuminated by the sun; at the edges of glacier snows in the Tyrol we
see violet bells of _Soldanella pusilla_, the stalks of which make
their way through the snow by producing heat which melts it round
about them. Finally the Siberian town Verkhociansk, near Yakutsk,
exists, though the temperature there falls to -69°·8 C. and the mean
temperature of January to -51°·2, and the mean pressure of the vapour
of water is less than 0·05mm. It is possible, therefore, that living
beings have become adapted to the conditions now prevailing upon
_Mars_ after the lapse of many ages, and live at an even lower
temperature than upon the earth, developing the necessary heat
themselves."
M. Rogovsky adds, "Water in organisms is mainly a liquid or solvent, and
many other liquids may be the same. We have no reason to believe that life
is possible only under the same conditions and with the same chemical
composition of organisms as upon the earth, although indeed we cannot
affirm that they actually exist on Mars."[105] With the above views the
present writer fully concurs.
Prof. Lowell thinks that the polar regions of Mars, both north and south,
are actually warmer than the corresponding regions of the earth, although
the mean temperature of the planet is probably twelve degrees lower than
the earth's mean temperature.[106]
A writer in _Astronomy and Astrophysics_ (1892, p. 748) says--
"Whether the planet Mars is inhabited or not seems to be the
all-absorbing question with the ordinary reader. With the astronomer
this query is almost the last thing about the planet that he would
think of when he has an opportunity to study its surface markings ...
no astronomer claims to know whether the planet is inhabited or not."
Several suggestions have been made with reference to the possibility of
signalling to Mars. But, as Mr. Larkin of Mount Lowe (U.S.A.) points out,
all writers on this subject seem to forget the fact that the night side of
two planets are never turned towards each other. "When the sun is between
them it is day on the side of Mars which is towards us, and also day on
the side of the earth which is towards Mars. When they are on the same
side of the sun, it is day on Mars when night on the earth, and for this
reason they could never see our signals. This should make it apparent that
the task of signalling to Mars is a more difficult one than the most
hopeful theorist has probably considered. All this is under the
supposition that the Martians (if there are such) are beings like
ourselves. If they are not like us, we cannot guess what they are
like."[107] These views seem to me to be undoubtedly correct, and show the
futility of visual signals. Electricity might, however, be conceivably
used for the purpose; but even this seems highly improbable.
Prof. Newcomb, in his work _Astronomy for Everybody_, says with reference
to this question, "The reader will excuse me from saying nothing in this
chapter about the possible inhabitants of Mars. He knows just as much
about the subject as I do, and that is nothing at all."
It is, however, quite possible that life _in some form_ may exist on Mars.
As Lowell well says, "Life but waits in the wings of existence for its cue
to enter the scene the moment the stage is set."[108] With reference to
the "canals" he says--
"It is certainly no exaggeration to say that they are the most
astonishing objects to be viewed in the heavens. There are celestial
sights more dazzling, spectacles that inspire more awe, but to the
thoughtful observer who is privileged to see them well, there is
nothing in the sky so profoundly impressive as these canals of
Mars."[109]
The eminent Swedish physicist Arrhenius thinks that the mean annual
temperature on Mars may possibly be as high as 50° F. He says, "Sometimes
the snow-caps on the poles of Mars disappear entirely during the Mars
summer; this never happens on our terrestrial poles. The mean temperature
of Mars must therefore be above zero, probably about +10° [Centigrade =
50° Fahrenheit]. Organic life may very probably thrive, therefore, on
Mars."[110] He thinks that this excess of mean temperature above the
calculated temperature may be due to an increased amount of carbonic acid
in the planet's atmosphere, and says "any doubling of the percentage of
carbon dioxide in the air would raise the temperature of the earth's
surface by 4°; and if the carbon dioxide were increased fourfold, the
temperature would rise by 8°."[111]
Denning says,--[112]
"A few years ago, when christening celestial formations was more in
fashion than it is now, a man simply had to use a telescope for an
evening or two on Mars or the moon, and spice the relation of his
seeings with something in the way of novelty, when his name would be
pretty certainly attached to an object and hung in the heavens for all
time! A writer in the _Astronomical Register_ for January, 1879,
humorously suggested that 'the matter should be put into the hands of
an advertising agent,' and 'made the means of raising a revenue for
astronomical purposes.' Some men would not object to pay handsomely
for the distinction of having their names applied to the seas and
continents of Mars or the craters of the moon."
An occultation of Mars by the moon is recorded by Aristotle as having
occurred on April 4, 357 B.C.[113]
Seen from Mars the maximum apparent distance between the earth and moon
would vary from 3-1/2' to nearly 17'.[114]