MARS
The Red Planet is our nearest neighbour on the further, as Venus is on
the hither side. He is also in some ways the planet best situated for
our observation; for while the greatest apparent diameter of his disc
is considerably less than that of Venus, he does not hide close to the
sun's rays like the inferior planets, but may be seen all night
when in opposition.[*] Not all oppositions, however, are equally
favourable. Under the best circumstances he may come as near to us as
35,000,000 miles; when less favourably situated, he may come no nearer
than 61,000,000. This very considerable variation in his distance
arises from the eccentricity of the planet's orbit, which amounts to
nearly one-tenth, and, so far as we are concerned, it means that his
disc is three times larger when he comes to opposition at his least
distance from the sun than it is when the conditions are reversed.
Under the most favourable circumstances--_i.e._, when opposition and
perihelion[†] occur together, he presents, it has been calculated, a
disc of the same diameter as a half sovereign held up 2,000 yards from
the spectator. Periods of opposition recur at intervals of about 780
days, and at the more favourable ones the planet's brilliancy is very
striking. The 1877 opposition was very notable in this respect, and in
others connected with the study of Mars, and that which preceded the
Crimean War was also marked by great brilliancy. Readers of Tennyson
will remember how Maud
'Seem'd to divide in a dream from a band of the blest,
And spoke of a hope for the world in the coming wars--
... and pointed to Mars
As he glow'd like a ruddy shield on the Lion's breast.'
Ancient records tell us of his brightness having been so great on
some occasions as to create a panic. Panics were evidently more easily
created by celestial phenomena then than they are now; but possibly
such statements have to be taken with a small grain of salt.
The diameter of Mars is 4,200 miles. In volume he is equal to
one-seventh of the world; but his density is somewhat smaller, so that
nine globes such as Mars would be required to balance the earth. He
turns upon his axis in twenty-four hours thirty-seven minutes, and as
the inclination of the axis is not much different from that of our
own world he will experience seasonal effects somewhat similar to
the changes of our own seasons. The Martian seasons, however, will be
considerably longer than ours, as the year of Mars occupies 687 days,
and they will be further modified by the large variation which
his distance from the sun undergoes in the course of his year--the
difference between his greatest and least distances being no less than
26,500,000 miles.
The telescopic view of Mars at once reveals features of considerable
interest. We are no longer presented with anything like the beautiful
phases of Venus, though Mars does show a slight phase when his
position makes a right angle with the sun and the earth. This phase,
however, never amounts to more than a dull gibbosity, like that of the
moon two or three days before or after full--the most uninteresting of
phases. But the other details which are visible much more than atone
for any deficiency in this respect. The brilliant ruddy star expands
under telescopic power into a broad disc whose ground tint is a warm
ochre. This tint is diversified in two ways. At the poles there are
brilliant patches of white, larger or smaller according to the Martian
season; while the whole surface of the remaining orange-tinted portion
is broken up by patches and lines of a dark greenish-grey tone.
The analogy with Arctic and Antarctic ice and snow-fields, and with
terrestrial continents and seas, is at once and almost irresistibly
suggested, although, as will be seen, there are strong reasons for not
pressing it too far.
The dark markings, though by no means so sharply defined as the
outlines of lunar objects, are yet evidently permanent features; at
least this may be confidently affirmed of the more prominent among
them. Some of these can be readily recognised on drawings dating from
200 years back, and have served to determine with very satisfactory
accuracy the planet's rotation period. In accordance with the almost
irresistible evidence which the telescope was held to present, these
features were assumed to be seas, straits and bays, while the general
ochre-tinted portion of the planet's surface was considered to be dry
land. On this supposition the land area of Mars amounts to 5/7 of the
planet's surface, water being confined to the remaining 2/7. But it
is by no means to be taken as an accepted fact that the dark and light
areas do represent water and land. One fact most embarrassing to those
who hold this traditional view is that in the great wealth of detail
which observation with the huge telescopes of to-day has accumulated
the bulk belongs to the dark areas. Gradations of shade are seen
constantly in them; delicate details are far more commonly to be
observed upon them than upon the bright portions of the surface, and
several of the 'canals' have been traced clear through the so-called
seas. Speaking of his observations of Mars in 1894 with the 36-inch
refractor of the Lick observatory, Professor Barnard says: 'Though
much detail was shown on the bright "continental" regions, the
greater amount was visible on the so-called "seas."... During these
observations the impression seemed to force itself upon me that I was
actually looking down from a great altitude upon just such a surface
as that in which our observatory was placed. At these times there was
no suggestion that the view was one of far-away seas and oceans, but
exactly the reverse.' Such observations are somewhat disconcerting
to the old belief, which, nevertheless, continues to maintain itself,
though in somewhat modified form.
It is indeed difficult, if not impossible, to explain the observed
facts with regard, for instance, to the white polar caps, on any other
supposition than that of the existence of at least a considerable
amount of water upon the planet. These caps are observed to be large
after the Martian winter has passed over each particular hemisphere.
As the season progresses, the polar cap diminishes, and has even been
seen to melt away altogether. In one of the fine drawings by the Rev.
T. E. R. Phillips, which illustrate this chapter (Plate XX.), the
north polar snow will be seen accompanied by a dark circular line,
concerning which the author of the sketch says: 'The _melting_ cap is
always girdled by a narrow and intensely dark line. This is not seen
when the cap is forming.' It is hard to believe that this is anything
else than the result of the melting of polar snows, and where there
is melting snow there must be water. Such results as those obtained by
Professor Pickering by photography point in the same direction. In one
of his photographs the polar cap was shown much shrunken; in another,
taken a few days later, it had very considerably increased in
dimensions--as one would naturally conclude, from a fall of snow in
the interval. The quantity of water may not be anything like so
great as was at one time imagined; still, to give any evidence of
its presence at all at a distance of 40,000,000 miles it must be very
considerable, and must play an important part in the economy of the
planet.
[Illustration: PLATE XX.
Mars: Drawing 1, January 30, 1899--12 hours. [lambda] = 301°, [phi] =
+10°.
Drawing 2, April 22, 1903--10 hours. [lambda] = 200°, [phi] = +24°.
Rev. T. E. R. Phillips.]
In 1877 Schiaparelli of Milan announced that he had discovered that
the surface of Mars was covered with a network of lines running with
perfect straightness often for hundreds of miles across the surface,
and invariably connecting two of the dark areas. To these markings
he gave the name of 'canali,' a word which has been responsible for
a good deal of misunderstanding. Translated into our language by
'canals,' it suggested the work of intelligent beings, and imagination
was allowed to run riot over the idea of a globe peopled by Martians
of superhuman intelligence and vast engineering skill. The title
'canals' is still retained; but it should be noted that the term is
not meant to imply artificial construction any more than the term
'rill' on the moon implies the presence of water.
At the next opposition of Mars, Schiaparelli not only rediscovered his
canals, but made the astonishing announcement that many of them were
double, a second streak running exactly parallel to the first at some
distance from it. His observations were received with a considerable
amount of doubt and hesitation. Skilled observers declared that
they could see nothing in the heavens the least corresponding to the
network of hard lines which the Italian observer drew across the globe
of Mars; and therein to some extent they were right, for the canals
are not seen with that hardness of definition with which they
are sometimes represented. But, at the same time, each successive
opposition has added fresh proof of the fact that Schiaparelli was
essentially right in his statement of what was seen. The question
of the doubling of the canals is still under dispute, and it seems
probable that it is not a real objective fact existing upon the
planet, but is merely an optical effect due to contrast. There can be
no question, however, about the positive reality of a great number
of the canals themselves; their existence is too well attested by
observers of the highest skill and experience. 'There is really no
doubt whatever,' says Mr. Denning, 'about the streaked or striated
configuration of the Northern hemisphere of Mars. The canals do not
appear as narrow straight deep lines in my telescope, but as soft
streams of dusky material with frequent condensations.' The drawings
by Mr. Phillips well represent the surface of the planet as seen with
an instrument of considerable power; and the reader will notice that
his representation of the canals agrees remarkably well with Denning's
description. The 'soft streams with frequent condensations' are
particularly well shown on the drawing of April 22, 1903, which
represents the region of 200° longitude (see Chart, Plate XXI.) on
the centre of the disc. 'The main results of Professor Schiaparelli's
work,' remarks Mr. Phillips, 'are imperishable and beyond question.
During recent years some observers have given to the so-called
"canals" a hardness and an artificiality which they do not possess,
with the result that discredit has been brought upon the whole canal
system.... But of the substantial accuracy and truthfulness (as a
basis on which to work) of the planet's configuration as charted by
the great Italian in 1877 and subsequent years, there is in my mind no
doubt.' The question of the reality of the canal system may almost
be said to have received a definite answer from the remarkable
photographs of Mars secured in May, 1905, by Mr. Lampland at the
Flagstaff Observatory, which prove that, whatever may be the nature
of the canals, the principal ones at all events are actual features of
the planet's surface.
Much attention has been directed within the last few years to the
observations of Lowell, made with a fine 24-inch refractor at the same
observatory, which is situated at an elevation of over 7,000 feet. His
conclusion as to the reality of the canals is most positive; but in
addition to his confirmation of their existence, he has put forward
other views with regard to Mars which as yet have found comparatively
few supporters. He has pointed out that in almost all instances the
canals radiate from certain round spots which dot the surface of the
planet. These spots, which have been seen to a certain extent by
other observers, he calls 'oases,' using the term in its ordinary
terrestrial significance. His conclusions are, briefly, as follows:
That Mars has an atmosphere; that the dark regions are not seas, but
marshy tracts of vegetation; that the polar caps are snow and ice, and
the reddish portions of the surface desert land. The canals he holds
to be waterways, lined on either bank by vegetation, so that we see,
not the actual canal, but the green strip of fertilized land through
which it passes, while the round dark spots or 'oases' he believes to
be the actual population centres of the planet, where the inhabitants
cluster to profit by the fertility created by the canals. In support
of this view he adduces the observed fact that the canals and oases
begin to darken as the polar caps melt, and reasons that this implies
that the water set free by the melting of the polar snows is conveyed
by artificial means to make the wilderness rejoice.
Lowell's theories may seem, very likely are, somewhat fanciful. It
must be remembered, however, that the ground facts of his argument are
at least unquestionable, whatever may be thought of his inferences.
The melting of the polar caps is matter of direct observation; nor
can it be questioned that it is followed by the darkening of the canal
system. It is probably wiser not to dogmatize upon the reasons and
purposes of these phenomena, for the very sufficient reason that we
have no means of arriving at any certitude. Terrestrial analogies
cannot safely be used in connection with a globe whose conditions are
so different from those of our own earth. The matter is well summed up
by Miss Agnes Clerke: 'Evidently the relations of solid and liquid in
that remote orb are abnormal; they cannot be completely explained by
terrestrial analogies. Yet a series of well-authenticated phenomena
are intelligible only on the supposition that Mars is, in some real
sense a terraqueous globe. Where snows melt there must be water; and
the origin of the Rhone from a great glacier is scarcely more evident
to our senses than the dissolution of the Martian ice-caps into pools
and streams.'
[Illustration:
PLATE XXI.
Chart of Mars. 'Memoirs of the British Astronomical Association,' Vol.
XI., Part III., Plate VI.]
Closely linked with the question of the existence of water on the
planet, and indeed a fundamental point in the settlement of it, is the
further question of whether there is any aqueous vapour in the Martian
atmosphere. The evidence is somewhat conflicting. It is quite apparent
that in the atmosphere of Mars there is nothing like the volume of
water vapour which is present in that of the earth, for if there were,
his features would be much more frequently obscured by cloud than
is found to be the case. Still there are many observations on record
which seem quite unaccountable unless the occasional presence of
clouds is allowed. Thus on May 21, 1903, Mr. Denning records that the
Syrtis Major (see Chart, Plate XXI.) being then very dark and sharply
outlined, a very bright region crossed its southern extremity. By May
23, the Syrtis Major, 'usually the most conspicuous object in Mars,
had become extremely feeble, as if covered with highly reflective
vapours.' On May 24, Mr. Phillips observed the region of Zephyria and
Aeolis to be also whitened, while the Syrtis Major was very faint; and
on the 25th, Mr. Denning observed the striking whiteness of the same
region observed by Mr. Phillips the day before. Illusion, so often
invoked to explain away inconvenient observations, seems here
impossible, in view of the prominence of the markings obscured, and
the experience of the observers; and the evidence seems strongly in
favour of real obscuration by cloud. It might have been expected that
the evidence of the spectroscope would in such a case be decisive, but
Campbell's negative conclusion is balanced by the affirmative result
reached by Huggins and Vogel. It is safe to say, however, that
whatever be the constitution of the Martian atmosphere, it is
considerably less dense than our own air mantle.
During the last few years the public mind has been unusually exercised
over Mars, largely by reason of a misapprehension of the terms
employed in the discussion about his physical features. The talk of
'canals' has suggested human, or at all events intelligent, agency,
and the expectation arose that it might not be quite impossible to
establish communication between our world and its nearest neighbour on
the further side. The idea is, of course, only an old one furbished up
again, for early in last century it was suggested that a huge triangle
or ellipse should be erected on the Siberian steppes to show the
Lunarians or the Martians that we were intelligent creatures who
knew geometry. In these circumstances curiosity was whetted by the
announcement, first made in 1890, and since frequently repeated, of
the appearance of bright projections on the terminator of Mars. These
were construed, by people with vivid imaginations, as signals from
the Martians to us; while a popular novelist suggested a more sinister
interpretation, and harrowed our feelings with weird descriptions of
the invasion of our world by Martian beings of uncouth appearance and
superhuman intelligence, who were shot to our globe by an immense gun
whose flashes occasioned the bright projections seen. The projections
were, however, prosaically referred by Campbell to snow-covered
mountains, while Lowell believed that one very large one observed at
Flagstaff in May, 1903, was due to sunlight striking on a great cloud,
not of water-vapour, but of dust.
As a matter of fact, Mars is somewhat disappointing to those who
approach the study of his surface with the hope of finding traces of
anything which might favour the idea of human habitation. He presents
an apparently enticing general resemblance to the earth, with his
polar caps and his bright and dark markings; and his curious network
of canals may suggest intelligent agency. But the resemblances are
not nearly so striking when examined in detail. The polar caps are
the only features that seem to hold their own beside their terrestrial
analogues, and even their resemblance is not unquestioned; the dark
areas, so long thought to be seas, are now proved to be certainly not
seas, whatever else they may be; and the canal system presents nothing
but the name of similarity to anything that we know upon earth. It is
quite probable that were Mars to come as near to us as our own moon,
the fancied resemblances would disappear almost entirely, and we
should find that the red planet is only another instance of the
infinite variety which seems to prevail among celestial bodies. That
being so, it need scarcely be remarked that any talk about Martian
inhabitants is, to say the least of it, premature. There may be such
creatures, and they may be anything you like to imagine. There is no
restraint upon the fancy, for no one knows anything about them, and no
one is in the least likely to know anything.
The moons of Mars are among the most curious finds of modern
astronomy. When the ingenious Dr. Jonathan Swift, in editing the
travels of Mr. Lemuel Gulliver, of Wapping, wrote that the astronomers
of Laputa had discovered 'two lesser stars, or satellites, which
revolve about Mars,' the suggestion was, no doubt, put in merely
because some detail of their skill had to be given, and as well
one unlikely thing as another. Probably no one would have been more
surprised than the Dean of St. Patrick's, had he lived long enough,
or cared sixpence about the matter, to hear that his bow drawn at a
venture had hit the mark, and that Professor Asaph Hall had detected
two satellites of Mars. The discovery was one of the first-fruits of
the 26-inch Washington refractor, and was made in 1877, the year from
which the new interest in Mars may be said to date. The two moons
have been called Deimos and Phobos, or Fear and Panic, and are, in
all probability, among the very tiniest bodies of our system, as their
diameter can scarcely be greater than ten miles. Deimos revolves in an
orbit which takes him thirty hours eighteen minutes to complete, at
a distance of 14,600 miles from the centre of Mars. Phobos is much
nearer the planet, his distance from its centre being 5,800, while
from its surface he is distant only 3,700 miles. In consequence of
this nearness, he can never be seen by an observer on Mars from any
latitude higher than 69°, the bulge of the globe permanently shutting
him out from view. His period of revolution is only seven hours
thirty-nine minutes, so that to the Martian inhabitants, if there are
any, the nearer of the planet's moons must appear to rise in the west
and set in the east. By the combination of its own revolution and the
opposite rotation of Mars it will take about eleven hours to cross the
heavens; and during that period it will go through all its phases and
half through a second display.
These little moons are certainly among the most curious and
interesting bodies of the solar system; but, unfortunately, the sight
of them is denied to most observers. That they were not seen by Sir
William Herschel with his great 4-foot reflector probably only points
to the superior defining power of the 26-inch Washington refractor as
compared with Herschel's celebrated but cumbrous instrument. Still,
they were missed by many telescopes quite competent to show them, and
of as good defining quality as the Washington instrument--a fact which
goes to add proof, if proof were needed, that the power which makes
discoveries is the product of telescope × observer, and that of the
two factors concerned the latter is the more important. It is said
that the moons have been seen by Dr. Wentworth Erck with a 7-1/3-inch
refractor. The ordinary observer is not likely to catch even a glimpse
of them with anything much smaller than a 12-inch instrument, and even
then must use precautions to exclude the glare of the planet, and may
count himself lucky if he succeed in the observation.
A word or two may be said as to what a beginner may expect to see with
a small instrument. It has been stated that nothing under 6 inches can
make much of Mars; but this is a somewhat exaggerated statement of the
case. It is quite certain that the bulk of the more prominent markings
can be seen with telescopes of much smaller aperture. Some detail
has been seen with only 1-3/4-inch, while Grover has, with a 2-inch,
executed drawings which show how much can be done with but little
telescopic power. The fact is, that observers who are only in the
habit of using large telescopes are apt to be unduly sceptical of the
powers of small ones, which are often wonderfully efficient. The fine
detail of the canal system is, of course, altogether beyond small
instruments; and, generally speaking, it will take at least a 4-inch
to show even the more strongly marked of these strange features. At
the 1894 opposition, the writer, using a 3-7/8-inch Dollond of good
quality, was able to detect several of the more prominent canals,
but only on occasions of the best definition. The accompanying rough
sketch (Fig. 24) gives an idea of what may be expected to be seen,
under favourable conditions, with an instrument of between 2 and 3
inches. It represents Mars as seen with a glass of 2-5/8-inch aperture
and fair quality. The main marking in the centre of the disc is
that formerly known as the Kaiser or Hour-glass Sea. Its name in
Schiaparelli's nomenclature, now universally used, is the Syrtis
Major. The same marking will also be seen in Mr. Phillips's drawing of
1899, January 30, in which it is separated by a curious bright bridge
from the Nilosyrtis to the North. The observer need scarcely expect to
see much more than is depicted in Fig. 24, with an instrument of
the class mentioned, but Plate XX. will give a very good idea of the
appearance of the planet when viewed with a telescope of considerable
power. The polar caps will be within reach, and sometimes present the
effect of projecting above the general level of the planet's surface,
owing, no doubt, to irradiation.
[Illustration: FIG. 24.
MARS, June 25, 1890, 10 hours 15 minutes; 2-5/8-inch, power 120.]
To the intending observer one important caution may be suggested. In
observing and sketching the surface of Mars, do so _independently_.
The chart which accompanies this chapter is given for the purpose of
identifying markings which have been already seen, not for that of
enabling the observer to see details which are beyond the power of his
glass. No planet has been the cause of more illusion than Mars, and
drawings of him are extant which resemble nothing so much as the
photograph of an umbrella which has been turned inside out by a gust
of wind. In such cases it may reasonably be concluded that there is
something wrong, and that, unconsciously, 'the vision and the faculty
divine' have been exercised at the expense of the more prosaic, but
in this case more useful, quality of accuracy. By prolonged study of
a modern chart of Mars, and a little gentle stretching of the
imagination, the most unskilled observer with the smallest instrument
will detect a multitude of canals upon the planet, to which there is
but one objection, that they do not exist. There is enough genuine
interest about Mars, even when viewed with a small glass, without the
importation of anything spurious. In observation it will be noticed
that as the rotation period of Mars nearly coincides with that of the
earth, the change in the aspect presented from night to night will
be comparatively small, the same object coming to the meridian
thirty-seven minutes later each successive evening. Generally
speaking, Mars is an easier object to define than either Venus or
Jupiter, though perhaps scarcely bearing high powers so well as
Saturn. There is no planet more certain to repay study and to maintain
interest. He and Jupiter may be said to be at present the 'live'
planets of the solar system in an astronomical sense.
[Footnote *: The opposition of a planet occurs 'whenever
the sun, the earth, and the planet, as represented in their
projected orbits, are in a straight line, with the earth in
the middle.']
[Footnote †: That point in the orbit of a planet or comet
which is nearest to the sun.]