THE PLANET MARS
Through the works of Schiaparelli, Flammarion, and Lowell the vivid
interest of the general public has been directed toward our neighbour
planet Mars. Several investigators, Flammarion and Lowell among them,
assert with full confidence that Mars has intelligent inhabitants, who
have built and maintain the curious “canals,” which, it is stated,
could not have been created except by intelligent beings far superior
to man.
Air, water, and sunshine exist there, says Flammarion in his well-known
great work, _La Planète Mars_ (1902, page 515). “It appears incongruous
to us to condemn a world like Mars, where all the conditions for life
exist, to such a fate” (to be a dry desert). No doubt sentiment and the
desired result play a part in all such deductions, as indeed the words
chosen by Flammarion would indicate.
As contrasted to the Earth, Mars is, on the other hand, considerably
further removed from the Sun, whose radiation therefore on Mars
possesses only 43 per cent. of its intensity on Earth. Judging by this
fact, the mean temperature of Mars should fall far below that of the
Earth and considerably below the freezing point of water and under such
conditions it is hard to imagine a vegetation near the poles of Mars
as Lowell does in his volume, _Mars as the Abode of Life_ (1909), or
even in the neighbourhood of the canals anywhere on the surface of the
planet as assumed by Flammarion.
With such ideas in vogue we can well understand that the astronomers
would point their lately extremely sharpened instruments toward our
ruby-coloured neighbour in the sky when, in 1909, it passed very close
to the earth under conditions particularly favourable to accurate
observations, more so in fact than they had been during the seventeen
preceding years.
Numerous astro-physicists, among them the world’s foremost
representatives of their discipline, have repeatedly turned their
spectroscopes toward Mars in order to ascertain whether water vapour
was present there or not. In the spectrum of the Sun we find several
so-called “rain-bands” due to the fact that the light before it reaches
the apparatus has passed through the moisture of the air. The more
humid the air the more strongly developed these rain-bands are. If we
direct the instrument first on the Moon, which lacks an atmosphere
and therefore also moisture, and then on Mars, which for the sake of
simplicity we assume standing close to the Moon-disk, a difference
should appear in the spectra of these two bodies, provided moisture
is present in the atmosphere of Mars. The rain-bands ought to be more
pronounced in sunlight that has passed the atmosphere of Mars (passed
it twice as the light is reflected by the surface of the planet) than
in light reflected from the naked Moon. The bands appear of course
in both spectra as the light on its final stage to the spectroscope
passes the atmosphere of the Earth, which never is free from moisture.
In this manner Huggins and Janssen, scientists of world-wide fame,
believed that they had demonstrated the presence of water vapour on
Mars. Campbell, on the other hand, the prominent director of the
Lick Observatory, made similar investigations of the planet in 1894,
and so did a French astronomer, Marchand, in 1896 and 1898, both
under unusually favourable circumstances as the former installed
his instrument 1283 m. (5200 ft.) and the latter 2860 m. (9370 ft.)
above sea level, but neither found any indication of moisture in the
atmosphere of Mars.
It is evident that the observations would be far more accurate if we
could eliminate the moisture from the atmosphere of the Earth, in which
case no rain-bands would appear in the spectrum of the Moon. It would
then be unnecessary to compare the two spectra; we would only have to
determine whether rain-bands were present in the spectrum of Mars or
not. We can never entirely avoid the water vapour of the air, but its
influence may be greatly reduced by making our observations from high
mountains or in desert climates where the air is comparatively dry,
that is free from water vapour. Investigations undertaken where the
air is dry deserve therefore more confidence than those handicapped by
greater humidity. The observations by Campbell and Marchand fall in the
former category, and it would, therefore, appear that the presence of
water vapour on Mars to any extent worth mentioning is highly doubtful.
In later trials, Campbell and Keeler have employed an improved method,
using photographs of the spectra on sensitive plates, but neither has
succeeded in discovering any water vapour in the atmosphere of Mars.
Obviously photography offers a great advantage over direct ocular
observation. The two pictures may be placed side by side and very
accurate measurements may be made at leisure. We may also choose the
moments for exposure when the two stellar bodies stand equally high
over the horizon so that the sunlight reflected from them traverses
equal distances in the humid atmosphere of the earth.
It now devolved upon Lowell to test his theories by means of the
magnificent resources at his disposal in Flagstaff observatory in the
desert of Arizona 2200 m. (7200 ft.) above sea level. In the months of
January and February the dew-point there is about -7° C. (+19.4° F.)
_i. e._, each cubic meter (1.3 cu. yds.) of air contains 2.8 grammes
(43.25 grains) of water vapour while saturated air at zero temperature
(32° F.) holds nearly twice this amount or 4.8 grammes (74 grains)
per cubic meter (1.3 cu. yds.). Slipher, working in this observatory,
pushed the sensitiveness of his plates to the utmost then obtainable,
and photographed the spectrum of Mars in January and February, 1908.
He found that the most important rain-band always was more prominent
in the spectrum of Mars than in the spectrum of the Moon photographed
later during the same night. Peculiarly enough, it was only the
rain-band designated “A,” and located in the red spectral field, that
was of a marked difference in the two spectra. Other bands gave no
indication of the presence of water vapour on Mars. This result did not
directly contradict the conclusions reached by Campbell and Keeler,
also by means of photography; they had investigated other bands than
“A.” The “A”-line might therefore possibly be more sensitive to water
vapour than the others.
Slipher’s discovery was considered so valuable that it must be employed
to the limit. The well-known physicist Very was therefore called in
consultation; he made careful measurements of the intensity of the
“A”-lines on the various plates and calculated that the atmosphere of
Mars contained 1.75 times as much water vapour as that of the Earth at
the point of observation. If we desire to determine the proportion
of water vapour in the air at the surface of Mars from this statement
we may figure in the following manner. The amount of water vapour in
a vertical column of air one square meter (1.2 sq. yds.) in section
is, according to Hann, 2500 times the amount in a cubic meter (1.3 cu.
yds.) at the surface of the earth. At the time of the observation, the
latter amount was 2.29 grammes (35.4 grains); on each square meter (1.2
sq. yds.) of the ground rested therefore 5725 grammes (12 lbs. 11 oz.)
of water vapour. That the quantity of water is not larger, although
the depth of the atmosphere far exceeds 2500 m. (1.5 miles), is due
to the fact that the temperature rapidly decreases with distance from
the ground. On Mars, the temperature ought not to fall so quickly with
change in height because the intensity of gravity there is 2.68 times
smaller than on the Earth. The temperature drops there 2.68 times
slower with ascent in the atmosphere, and a column of air on Mars one
square meter (1.2 sq. yds.) in section should therefore contain 6680
times as much water vapour as a cubic meter (1.3 cu. yds.) at its
surface. As Mars did not stand in zenith, the distance traversed by the
light-ray in the atmosphere was greater--in fact 1.43 times greater
than if such had been the case. A column of air in the direction of
the light-ray, one square meter (1.2 sq. yds.) in section contained
therefore 8175 grammes (18 lbs. 3 oz.) water vapour. In the atmosphere
of Mars which the light passed in a vertical direction there was, if
we are to believe Very, 1.75 times as much, or 14,300 grammes (31
lbs. 8 oz.) and in a cubic meter (1.3 cu. yds.) at the surface of the
planet, consequently 6680 times less, or 2.14 grammes (33.1 grains).
The corresponding dew-point is then, according to this determination,
-10.3° C. (+13.5° F.). It is agreed upon that a desert climate
prevails on Mars. It might at the time of the observation conform to
the extremely dry climate at Salt Lake City in the height of summer
when the humidity there is only 31 per cent. of saturation. Under
such conditions saturated air at noon in the equatorial belt on Mars
should contain 7 grammes (108 grains) per cubic meter (1.3 cu. yds.)
corresponding to a temperature of 5.3° C. (41.5° F.).
It must be admitted that this was not very encouraging to Lowell. If
the temperature in the middle of the day, when the sunlight falls
perpendicularly on the surface of the planet, rises only to about 5° C.
(41° F.), the mean temperature for twenty-four hours, even in the midst
of the summer, must in this entirely clear, light air be far below
freezing and vegetation on Mars is therefore not very well conceivable.
In spite of this, Lowell saw in Slipher’s measurements a confirmation
of his theory that Mars is the abode of an intelligent race that
utilizes, in their wrestle with existence, a verdant vegetation pushed
even into the polar regions.
Campbell, however, went one step further than Slipher. In August and
September, 1909, Mars occupied a position in the sky particularly
favourable to observations. Campbell decided to benefit thereby.
With the support of a rich patron of science, a Mr. Crocker, who
on several occasions has made magnificent contributions toward
astronomical research, Campbell equipped an expedition to Mount Whitney
in California, 4425 m. (14,502 ft.) high and the loftiest peak in the
United States. He was accompanied by an able scientific staff, the most
prominent of which were Dr. Abbot, head of the observatory belonging
to the Smithsonian Institution, and a well-known German astronomer,
Albrecht. The members of the expedition were affected by mountain
sickness and suffered many severe hardships when the wind was high,
reaching about 25 m. per sec. (56 miles per hour), and at the same time
cold, falling below zero (freezing) during the night. The barometric
pressure was only 447 mm. (17.6 inches). During the nights, when the
observations were made, the water content of the air fell to between
0.5 and 0.9 grammes (7.7 grains to 13.9 grains) per cubic meter (1.3
cu. yd.) or 2.5 to 4 times less than Slipher had to contend with. The
spectra of the Moon and of Mars were photographed in close succession,
two exposures being made in each case. The band “A” was plainly visible
on several plates. No indication of greater prominence of this band
in the spectrum of Mars could be found. Other rain-bands were also
investigated with the same result. Neither were the characteristic
bands of oxygen stronger in the spectrum of Mars, than in that of the
Moon. Slipher believed that he had discerned a difference, although of
a hair’s breadth, which would indicate the presence of oxygen in the
atmosphere of Mars. The conclusion itself is not improbable, but the
amount of oxygen there is in any case considerably smaller than in the
Earth’s atmosphere.
Several statements by Campbell, as well as Slipher’s observations,
indicate that a difference ought to have appeared between the spectrum
of Mars and that of the Moon if the water content in Mars’ atmosphere
had been the same as in the Earth’s at the time of the observation.
This content, as stated before, was about 3 times smaller on Mount
Whitney than at Flagstaff. At the latter place, the measurements gave
1.75 as the ratio of water vapour on Mars to that on the Earth. The
amount of water vapour with the Sun in zenith on Mars should therefore,
according to Campbell’s observations, only reach 0.4 gramme (6.1
grains) per cubic meter (1.3 cu. yds.) corresponding to a dew-point of
-28° C. (-18.4° F.) or to an actual temperature of -17° C. (+1.4° F.)
allowing also for a desert climate with only 31 per cent. saturation.
This temperature is probably higher than the mean for a summer day as
the observations were made at noon on Mars.
It must now be evident that we should consider Mars as unfit to
harbour living beings. There is possibly a slight amount of oxygen in
the thin air but the extremely low temperature and the scant supply
of water vapour form insurmountable obstacles to the subsistence of
even the simplest forms of life in the equatorial regions on Mars.
The temperature difference between day and night must be enormous on
account of the desert climate. Even if life could develop during the
day, which has nearly the same duration as with us--Lowell fixed it at
24 hours, 37 minutes, 22.6 seconds--and during which the temperature
possibly might rise above the freezing point, it would nevertheless be
destroyed without mercy by the bitter frost at night.
Campbell has offered an explanation of the indications of water vapour
on Mars, apparent on Slipher’s photographs. An analysis of the latter’s
observations shows that the Moon was photographed about four hours
later in the night than was Mars. On all occasions except one, clouds
appeared in the sky. This indicates the presence of moisture in the
air, so that the humidity should change with the temperature which
latter rapidly falls in the course of the night. Campbell, himself,
found during the clear nights, when he made his observations, that
the humidity in the hours of the night up to midnight falls to a
fraction--a half or a third--of its original value an hour or so after
sunset. This rapid temperature drop is probably confined to the strata
immediately above the observation point but the moisture is strongly
concentrated downward so that this change in humidity undoubtedly
should have been taken into account. Or better, observations should
be avoided in the beginning of the night and the Moon and Mars
photographed as soon after each other as possible, precautions taken
by Campbell but not by Slipher. That the latter found less traces of
water on the lunar photos than on the martian ones is, therefore,
probably due to the fact that the former were taken about midnight but
the latter not long after sunset, when the atmosphere contained much
more water vapour. Thus, we learn how a small slip, more obvious to the
meteorologist than to the astronomer, may spoil a labour otherwise done
with extraordinary care.
To Campbell’s critique Very answered by the suggestion that the
meteorological conditions during the Mount Whitney observations should
have been exceptionally unfavourable. The entire south-west of the
United States and the north of Mexico were visited at that time by
cloudy weather and heavy downpours. Very contends that this humidity
should partly have extended to the high strata above Mount Whitney and
therefore rendered the calculation of the moisture content of the air
entirely unreliable.
Simultaneously (August, 1910) new measurements were published of
Slipher’s photo-plates from February, 1908, which Very had examined.
The result was now that the rain-band “A” was 2.5 times more pronounced
in the spectrum of Mars than in that of the Moon. Furthermore, the
oxygen absorption-band “B” was 1.5 times stronger for Mars than for the
Moon. Great quantities of water vapour and oxygen should, therefore,
undoubtedly exist in the atmosphere of Mars.
In the meantime Campbell had not been idle. The difficulty with the
older measurements consisted in the fact that the absorption line
of water vapour in the atmosphere of Mars occupies the identical
place of the line due to vapour in the Earth’s atmosphere. There
exists, however, a method, as already pointed out by Campbell in 1896,
of separating the two, which method is available when Mars either
approaches or departs from the Earth with sufficient velocity. The
latter could be determined both from the known motions of the two
planets and from the displacement of certain spectral lines of the Sun.
These two determinations were in almost perfect agreement; for instance
January 26–27, 1910, astronomical calculations gave a relative velocity
of 19.1 km. (11.86 miles) per second and spectroscopical measurements
19.2 km. (11.93 miles) per second, while on February 3–4 the relative
velocity was 18.1 km. (11.24 miles) a difference of 1 km. (.62 miles)
per second. This trial shows the accuracy of the method. Among the
absorption lines of water vapour and of oxygen there was, however, none
due to the atmosphere of Mars. Campbell assumes that such lines would
certainly have been visible if they had been only one-fifth as strong
as the so-called tellurian lines. The advantage of this method is
evidently that the “martian” and the “tellurian” lines lie close beside
each other on the same plate so that differences in sensitiveness,
exposure, and atmospheric conditions are entirely eliminated.
From these and the following data we may calculate water content and
temperature of the atmosphere on Mars anew: water vapour at the point
of observation was 1.9 grammes (29.3 grains) per cubic meter (1.3 cu.
yds.), zenith-distance of Mars 55° and incident as well as reflected
sun-rays formed an angle of 70° with the surface of Mars; hence, the
amount of moisture at the surface was only 0.12 gramme (1.85 grains)
per cubic meter (1.3 cu. yds.), corresponding to -38° C. (-36.4°
F.) for saturated air and to -27° C. (-16.6° F.) for air of 31 per
cent. saturation. Oxygen content per cubic meter (1.3 cu. yds.) at
the surface of Mars would be only a sixteenth part of corresponding
numerical value on the Earth. This determination is more accurate
than any of the previous ones and reduces the temperature another
10° C. (18° F.) below the lowest value derived earlier in this chapter.
We should remember, however, that, during the trial of September,
1909, the sun stood practically in zenith on Mars, while in January
and February, 1910, we are concerned with a point where sunrise had
occurred about four and a half hours previously. The latter observation
should give a value close to, but slightly above, the mean diurnal
temperature on Mars.
No determination comparable in precision with this one by Campbell
appears to have been made. We must therefore recognize it as conclusive.
We may easily calculate the surface temperature of a planet from the
intensity of the solar radiation received, or insolation, provided
the surrounding vapour shell contains no heat retarding gas. The most
important gases of this kind are water vapour, which, as we just have
seen, is very sparse in the atmosphere of Mars, and carbon dioxide,
of which there probably also, for reasons stated below, is only a
scant supply in the martian gas shell. Such calculations were first
performed by Christiansen of Copenhagen, who assumed 2.5 calories as
the solar constant on Earth, _i. e._, the amount of energy received
through insolation per minute by each square centimeter (.15 sq. in.)
of the Earth’s surface when at right angle to the radiation and on
mean distance from the Sun. On Mars, the radiating energy received
under similar conditions is only about 1.1 calories. The surface of
the planet is heated until it radiates as much energy into space as it
receives from the Sun. In this way we obtain an average temperature
of -37° C. (-34.6° F.) for the entire surface of Mars. The regions,
exposed to the Sun in zenith at noon, might, if heat were not conveyed
therefrom, possibly reach a daily mean temperature of +8° C. (46.4° F.)
and perhaps slightly more at noon. Probably not even the freezing
point is reached, as the heat is rapidly carried away by the freely
circulating air. The above-mentioned mean temperature of -37° C.
(-34.6° F.) seems on the whole to agree well with the observations by
Campbell on Mount Whitney.
Recent accurate determinations of the intensity of the solar radiation
by Abbot, K. Ångström and others, indicate that it has been estimated
about 20 per cent. too high. If we take the solar constant to an even
2.0 calories, which is a trifle high, we reach the conclusion that the
mean temperature on Mars would fall about 50 degrees below freezing.
Equatorial regions might then reach an average of -8° C. (+17.6° F.)
and at noon the temperature might possibly rise slightly above zero
(32° F.). A higher temperature yet might be attained at the pole where
the Sun during the summer remains for months above the horizon or a
high mark of +8° C. (46.4° F.) provided no heat were carried away by
air currents. Such losses naturally must occur, and the temperature
probably hovers around freezing. At the martian poles we might possibly
imagine the existence of some low forms of vegetation (snow-algæ,
etc.) during the height of the short summer.
When we hitherto on the authority of Lowell, Very, and others, have
assumed an average temperature of +10° C. (50° F.) on Mars, we have
done so on the supposition that the atmosphere of the planet contained
great quantities of heat-conserving gases. This assumption appears
to be no more tenable than the belief in the high temperature on
Mars. After all, the temperature is probably about 10° C. (18° F.)
higher than our last calculation would indicate--or about -40° C.
(-40° F.)--because the air on Mars is very clear and admits, therefore,
all sun-rays, retaining also a fraction by virtue of what little water
vapour, carbon dioxide, and other heat-conserving gases there may be
present in the atmosphere. The mean summer temperature at the martian
equator (-27° C. or -16.6° F. acc. to Campbell’s data) would then lie
about 13° C. (23.4° F.) above the mean for the planet. This agrees
closely with conditions on the Earth where the highest mean in July
at the equator is 27° C. (80.6° F.) and the mean for the earth 16° C.
(60.8° F.).
We are consequently obliged to revise in their entirety our ideas about
Mars. The belief that organic life (green vegetation) causes the colour
of the so-called seas on Mars, as assumed by Lowell, or that the red
tints belong to the gorgeous dress in which autumn arrays the plants
before their leaves are shed under the attacks of frost, as intimated
by Flammarion, must nowadays take its place in the shadowy realm of
dreams.
Those who do not believe that the so-called canals are real
waterways, devoted to freight carrying and irrigation, or illusions,
which conception the photographs contradict (for example Fig. 18),
generally consider that they signify cracks or fissures. As in the
crust of the Earth, they generally run in nearly straight lines or
in regularly bent curves (Fig. 17 and 17a). Flammarion mentions that
the renowned physicist Fizeau looked upon the “canals” as cracks in
the ice-coverings of the oceans on Mars. Penard, in 1888, expressed
the more likely opinion that they correspond to the fissures in the
crust of the Earth. Flammarion contends that such fissures do not have
the rectilinear configuration of the “canals.” This is completely in
error, as shown on the map here reproduced (Fig. 16). It is also stated
that they are so inexplicably long, for instance the canal Phison is
2250 English miles (Lowell) or 3620 km. in length. The longest known
earthquake crack along the entire length of which a dislocation has
taken place _at one time_ is 600 km. (373 miles) in extension; the
violent earthquake in California, 1906, originated from this crack.
There is no doubt, moreover, that a great fissure in the Earth follows
the coast of Chile from Arica to the Strait of Magellan in a nearly
north and south direction for a distance of about 32 parallels or 3560
km. (2210 miles). This fissure is almost as long as Phison on Mars.
Such cracks exist along the entire coast of the Pacific Ocean. As yet,
we do not know their position in much detail, because long stretches
run below the sea or through territories not yet occupied by civilized
people. As an example of a small fissure, a picture taken by Sederholm
from Segelskär, east of Hangö in the Baltic, may serve (see Fig. 15).
As the studies of earthquakes are prosecuted with increasing interest
in later years, fissures of all dimensions will undoubtedly soon be
discovered. The solid crust on Mars is, furthermore, somewhat thicker
than that of the Earth as the cooling of that planet has progressed
further. The sections broken off at the bursting of the Martian crust
ought therefore to be much larger both in breadth and in length.
No doubt, the facts that the intensity of gravity on Mars is only
three-eights of its intensity on the Earth and that the curvature of
the Martian surface is twice as sharp as the Earth’s contribute to
this result. Imagine two vaults, one built with higher and broader
wedge-shaped stones than the other and with half the radius and
furthermore loaded only one-third as heavily as the other, and it
will become evident that we can permit a much larger span in the former
than in the latter case without fear of collapse. In other words, it
requires a much more extensive caving or shrinkage of the molten mass
beneath the crust of Mars to cause a rupture than under the terrestrial
crust.
[Illustration:
Fig. 15. Narrow bay on the left side of Segelskar, east of
Hango in Finland. The bay owes its existence to the fact
that the ice has laid bare a territory coursed through by
fissures. Photo by I. I. Sederholm.
]
[Illustration:
Fig. 16. Earthquake centres in Calabria and in Sicily. On the
larger map the damaged localities are indicated, on the
smaller the most prominent tremor lines. Drawn by I. I.
Sederholm.
]
As a consequence, the fissures on Mars ought to be longer than the
corresponding formations on the Earth. A thorough study of the large
fissure in Calabria shows that it consists of a veritable network of
smaller straight cracks (as is apparent on Figure 16, which is taken
from a work by the well-known Finnish geologist Sederholm). On this
map the radial cracks (see _Worlds in the Making_, Fig. 16), charted
by Suess, are also shown, and their direction under the sea designated
by dotted lines. The sketch in the upper left corner of Fig. 16 is in
striking similarity to a picture drawn by Schiaparelli in Mercator’s
projection of the planet Mars (see map at the end of book). We notice
on both, the numerous equidistant lines corresponding to parallel
cracks and duplex canals. Not every fissure has its parallel and not
every canal its mate--generally only one of the latter is visible and
sometimes both disappear.
As the radial cracks in the drawing by Suess if extended meet in the
Lipari Islands, so also several canals on Mars run together in a
so-called lake (Lowell called them “groves” or “oases”) which evidently
is a centre of collapse (many appear on Fig. 17). It is plain that all
crossings of the “canals” are not necessarily such centres of collapse.
(See maps Figs. 17 and 17a at end of book).
We shall consequently assume that the canals on Mars correspond to the
geological dislocation fissures on the Earth. Along these fissures
emerge the gases liberated in the cooling process on both planets;
which are similar gases to those which escape through the volcanoes.
These vapours are primarily water, next carbon dioxide and, in
considerably smaller quantities, sulphuretted gases and hydrochloric
acid. They discharge through cracks in regions which, geologically
speaking, not so long ago were the scene of volcanic activity. In the
dislocation-grooves, lakes, and water courses are often formed, as we
may observe in several places in Sweden, for instance near Stockholm.
Assume now a gradual cooling of our earth. Most territories are covered
by stratified, comparatively light rocks. To the dislocation fissures
water gathers from the surrounding strata and occasionally from the
interior, partly washes away the loose material and transforms the
fissures into furrows, generally with flat bottoms. Dissolved salts
are carried to the sea. As cooling proceeds, the ocean commences to
freeze. Each summer the surface melts to a certain extent, as is the
case now in our polar regions. Finally, the entire ocean freezes to the
bottom, the ice is now to be considered as a kind of rock, flexures and
dislocations cease and the ice assumes a smooth surface. In the strong
sunlight during the summer this surface thaws, as do the water-courses
on the mainland, and these continue to carry their salts to the open
surface water. At the approach of winter the latter solidifies again
but not as the water in our inland lakes from the top but from the
bottom, as ordinary sea-water possesses its greatest density below
the freezing point while the opposite is true of fresh water. The
consequence is that the ice foundation grows upward and as the surface
water becomes increasingly shallow it is turned into a concentrated
salt solution. With a further drop in temperature the ice formation is
accompanied by crystallization of the salts.
Something similar takes place on the Martian mainland in its flat river
basins, which correspond to the salt lakes in our deserts. On account
of the bitter cold and the consumption of the water in the process of
disintegration (the carbon dioxide has been largely used up in the
same manner), precipitation has almost ceased on Mars and most of the
water in circulation emerges from the interior of the planet along
the fissures. As it contains hydrochloric acid and carbon dioxide it
extracts from the soil salts, such as the chlorides of sodium (common
salt), of calcium and of magnesium, all present in common sea-water
to which it was brought by the rivers. The compounds of calcium and
magnesium are not precipitated as carbonated salts through the medium
of crustacea as is the case on earth. The strong solar radiation during
the summer partly evaporates the water into the thin air, leaving the
salts behind. On account of the low temperature, this vaporization on
Mars is probably slower than on the Earth. Along the cracks in the
crust, a kind of dry salt-lakes are formed similar to the generally
shallow and occasionally dry lakes common in the deserts of Central
Asia as described by Hedin. We know that Mars possesses a pronounced
desert climate. There finally remains in the lowest sections of the
water courses a concentrated salt solution, which parts with its water
more and more reluctantly, so that the salts which most strongly hold
the water crystallize at the deepest points. If the winter’s cold is
sufficiently severe (below -55° C. or -67° F.) ice is extracted even
from the most concentrated solutions, which mainly contain chloride of
calcium. In spite of such extreme temperatures, evaporation into the
rare atmosphere is not negligible and the ice crystals partly vanish,
to reappear in the coldest regions of the planet, that is, around the
pole which at the time is turned away from the sun. On the ocean, now
frozen solid throughout, a polar-cap of snow and hoar-frost is formed
which finally reaches as far as the 38th parallel on the southern
hemisphere (see Figs. 18 and 19), where winter occurs when Mars is most
removed from the sun, and to the 58th parallel (see Fig. 19) on the
northern hemisphere where winter reigns while Mars is nearest to the
Sun and consequently not quite so cold. Similar conditions obtain on
the Earth although not to such a marked degree.
[Illustration:
Fig. 18. Photograph of Mars, enlarged and retouched; taken by
Lampland
]
[Illustration:
Fig. 19. Appearance of Mars April 8, 1907, as observed by
Quénisset. Below one pole a dark line is plainly visible.
]
[Illustration:
Fig. 20. The south pole spot on Mars observed by Jarry-Desloges
July 10, 1909.
]
[Illustration:
Fig. 21. The appearance of Mars during an observation by
Antoniadi in 1909. The whole disk is somewhat hazy; below,
the details are hidden by clouds of sand.
]
In the vicinity of the snow-white polar cap, whether there be continent
or sea, bodies of water occur with solidly frozen surface covered by
crystals of very hygroscopic salts, such as the chlorides of calcium,
magnesium, and sodium. When the summer warmth returns and the polar
cap is heated, the hoar-frost evaporates, and the now comparatively
humid air spreads over the surrounding territory. We observe also
frequent mist-formations in these places. The ground near the edge
of the polar snow assumes then often a dark hue on account of the
moisture (Fig. 19). Occasionally canals and lakes appear in the polar
cap (see Fig. 20). This is evidently due to hot emanations along the
cracks. The moist air sweeps over the salts, which then absorb water
and dissolve into concentrated solutions. New quantities of water
vapour are supplied from the pole as they distill over toward the
other pole, where winter now exists, and push on toward the equator
which they finally pass. In their course they dissolve the salts
in the depressions along the fissures and particularly at the deep
crossings where the centres of collapse or the so-called “oases” are
located. Lowell has observed that the “canals” in this manner gradually
“liquify” from 78° N. Lat. to the equator in fifty-two days.
The canal theory presents great difficulties to the explanation of this
curious phenomenon. In order to make the water flow it must be assumed
that the surface of Mars is entirely smooth or at least very nearly so
and that the inhabitants convey the water melted at the poles through
pumping stations. The canals vary in width; according to Lowell, their
mean is 16 km. (10 miles), according to Flammarion between 300 and 60
km. (185 and 37 miles) which latter estimate probably is too high. The
same canal differs widely in breadth in successive years and sometime
disappears altogether. When the supply of water vapour is scant, only
the most hygroscopic salts are dissolved, _i. e._, those deposited in
the deepest furrow of the canal, but when the moisture sweeping over
the canal is more abundant the broader portions absorb water, darken
and thus become visible. The same holds true in regard to the inland
lakes (“oases”). As the water vapour diffuses in the air, the canal
becomes liquid along its entire length independent of the altitude of
its various parts.
All agree upon the desert climate of the mainland on Mars. Like most
deserts on the Earth, it is, therefore, probably a table-land, where
one plateau mounts above the other, each one nearly level. By the
action of the wind, the upper layers have been transformed into fine
sand. On the dead planet no further sediments are deposited by the
sea. The only accretions to the planet are meteorites and cosmic dust
which slowly rains down. It contains among other substances iron,
partly metallic and partly in the form of protoxides (which have a
light green colour).[5] The oxygen in the atmosphere of Mars transforms
these compounds to ferro-oxide which has different colours according
to its coarseness, but generally is ochre. The surface of Mars is also
described as possessing this colour. Dross has, therefore, assumed
that the Martian soil is mingled with ferro-oxide. The finest dust,
however, is yellow while larger crystals tend toward violet. We often
observe on Mars that the details are covered by a yellow veil. This is
of course finely powdered ferro-oxide probably mixed with less coloured
sand which the desert wind whirls up over large portions of Mars. Vast
sections of the planet bore such wrappings in the autumn of 1909, as
observed and described by Antoniadi in Paris (see Fig. 21). Similar
observations have previously been made by W. H. Pickering and others.
[5] In the deepest portions of the oceans on the Earth where
no sediments from the coasts are deposited, large
accumulations containing iron compounds have been found
and the presence of certain minerals therein points to
their meteoric origin.
As a rule, only the central and the polar regions of the surface of
Mars can be seen. Territories near the equator more than 40 to 50
degrees removed from the point in line with the Sun and the centre of
the planet are generally hidden behind a thin, white veil of mist. As
soon as the Sun leaves the zenith and reaches half-way to the horizon
the moisture of the air is precipitated near the ground. This shows
that the planet does not possess any quantities of heat-conserving
vapours in its gas shell. The mist does not extend to the poles, whose
white caps always appear distinctly, because the Sun cannot greatly
affect the evaporation in regions where the Sun’s altitude is neither
very high nor very variable. The same holds true for other snow-covered
tracts, even if they are not located in the immediate vicinity of the
pole.
When the supply of water vapour is scant, only the most salient canals
come into view. As a rule they do not then appear double, as one of the
mates is always less prominent. Lowell showed, he believed, that it
always is the same canal out of a pair which first comes to sight and
that its position always remains unchanged in contrast to Schiaparelli
who has reached the opposite conclusion. This, of course, is quite
natural.
On account of the small amount of water vapour in the atmosphere of
Mars true clouds are rare. Figure 22 shows such a cloud at the edge
of the planet. The aforementioned mists are often called clouds, for
instance by Pickering.
[Illustration:
Fig. 22. Cloud at the upper right edge of Mars observed by
Molesworth, March 7, 1901
]
[Illustration:
Fig. 23. Mars as observed by Lowell, July 11, 1907. Even the
dark portions appear coursed through by “canals.”
]
[Illustration:
Fig. 24. Mars, as observed by E. M. Antoniadi, October 6, 1909.
]
That elevations really may be found on Mars is evident from the fact
that snow or hoar-frost often remains in patches near the pole and
occasionally quite far therefrom, for instance on the large island
Hellas (40° S. Lat.), while it disappears from the surroundings and
sometimes from the pole itself (the south pole). Such a highland
covered by ice exists near the south pole, and is shown near the
upper edge of Fig. 24. In places where snow always remains, a feeble
glacier formation may occur. Most investigators assume that mountains
and plateaus exist on Mars, although of modest altitude (Campbell
believes that he has observed peaks 3000 m. (9800 ft.) high). Lowell
who diligently has looked for mountains at the edge of the illuminated
part of Mars, has reached the conclusion that they, if present,
cannot rise more than 600 to 900 m. (2000 to 3000 ft.) above the
surrounding plains. It were indeed improbable that all inequalities
of the Martian surface should have been removed in the process of
disintegration, which although at work for enormous extensions of time,
has long been extremely feeble and is unassisted by torrents of rain
which might rapidly wash the products into the valleys. At present, it
is mainly the sand carried by the desert wind that slowly reduces the
roughnesses and in this process extensive highlands are hardly touched.
But, without the assumption, in itself very unlikely, of a nearly level
surface on Mars it becomes difficult to comprehend how the canals, if
filled with pure water, can proceed in straight lines without reference
to existing differences in altitude. Like the rivers on the Earth they
ought to bend according to the topography, even if constructed by
engineers.
When the canals freeze at the approach of winter, they invariably
have been observed to disappear in company with the lakes or oases
at their crossings. They are then all covered by the reddish-yellow
dust carried by wind from the surroundings. When a canal is about to
reappear it frequently first comes to sight as a dark streak evidently
the result of moistened ferro-oxide. Occasionally a mist formation
precedes the appearance of the canal. It is plain that the cold, misty
air settles in the valleys, there as here, and gives up its moisture to
the salts on their bottom and the canal is thus brought out as a dark
line. Sometimes the vicinity also assumes a darker shade indicating
the absorption of some moisture. On the sides of the canals the less
hygroscopic salts are deposited. Possibly the green colour of the
canals is partly a contrast-effect due to the red surrounding, possibly
also the result of finely divided matter in the liquid. It is also
conceivable that the cause is the reducing influence on the ferro-oxide
of the sulphuric gases emerging from the fissures; an exceedingly
small quantity accomplishes in this case large results. F. le Coultre
describes the colour as being sometimes a dead black.
Something similar applies to the seas. When these freeze, especially in
shallow places, yellowish-red dust from the continent settles on their
surface and lends it hues between the original dark green and the light
yellowish-red. When the ice subsequently melts this dust sinks in the
water which latter resumes its dark green colour.
Chloride solutions, if concentrated, freeze at the following
temperatures; that of calcium at -55° C. (-67° F.) that of magnesium
at -44° C. (-48.2° F.) and that of sodium at -22° C. (-7.6° F.). If
now, as we previously have seen, the mean temperature of Mars as
a whole is about -40° C. (-40° F.), of the equatorial belt about
-10° C. (+14° F.), and of the pole in the height of summer about 0° C.
(32° F.), it is evident that a liquefaction of the ocean surface and of
the canals, particularly where salts are deposited, very readily may
take place. We should in this connection remember that the ice on Mars
is stationary while on Earth it is in motion. The consequence is that
sand and dust in the course of thousands of years have accumulated on
the bottom of the shallow basins in the polar ice. These seas appear
therefore dark in spite of their exceedingly small depth and the white
salt and ice-crystals remaining undissolved are unable to display
their light colour. Even in the “ocean,” Lowell was persuaded that he
had observed canals (see Fig. 23), and it may be possible that cracks
are in evidence there, particularly in the most shallow sections, as
is the case in the Tyrrhenian sea north of Sicily. It is significant
that Flammarion has reached the conclusion, which at first appears
highly hazardous, that the freezing point of water is lower on Mars
than on Earth. This is entirely correct, if we let water stand for salt
solutions.
It is customary to point to the strictly uniform breadth and the
rectilinear appearance of the canals as clear evidence of their being
artificial, _i. e._, the work of engineers. The Italian astronomer
Cerulli strongly objected to this conception. “In the exceedingly
rare cases when both sides of the canal plainly may be seen,” states
Schiaparelli, “I have observed curves and notches in the borders.”
This occurred with the canals Euphrates and Triton in 1879, and with
the Ganges in 1888. And it would seem obvious that watercourses
produced in old furrows would not, as a rule, be of uniform breadth.
Antoniadi, by his observations in the autumn of 1909 (see Fig. 17a and
24), has confirmed this opinion, as has le Coultre, who found twice
as many irregular canals as rectilinear ones. Antoniadi remarks that
some canals appear to be collections of lakes strung out in a certain
direction while others are narrow lines which bend and twist. “The
complicated network of straight lines is probably illusory.” The spots
on Mars, he continues, are very irregular, and “present by no means
any geometrical form” (on which the belief largely is founded that
they are the product of intelligent beings). “The appearance of the
planet reminds one of that of the Moon (except that the latter is dead,
_i. e._, unchangeable) or of a terrestrial landscape viewed from a
balloon.”--“In a word, the ‘geometry’ of Mars is revealed as a pure
illusion.” Exceedingly instructive is a comparison between the two maps
of Mars drawn by Schiaparelli (1886) and by Antoniadi (1909) reproduced
here and found at the end of the volume. While Schiaparelli as a rule
represents the canals as narrow, straight, or slightly curved bands
of uniform width, these formations on the Antoniadi chart frequently
dissolve into a series of dark spots joined by less obscure sections
(see for example the canals Nectar and Oeroe at the Sunlake). The
same is true about several of the so-called “seas,” particularly the
Tyrrhenian (Mare Tyrrhenum), and the Sunlake (Lacus Solis); also about
the “Ocean-bays” such as the well-known Syrtis major which with the
Sunlake form the most conspicuous objects on the surface of Mars. These
maps are, moreover, of great interest because several canals and other
features present on one are absent on the other and vice versa. In this
way, we obtain a vivid conception of the remarkable changeableness of
the Martian surface as contrasted with the exterior of the Earth. The
latter, if viewed from Mars, would not have presented any noticeable
change in historical time except for the seasonal variation of the snow
fields. This peculiarity of Mars is only explained by the fact that the
geographical features of that planet as a rule are surface formations
of a slight depth and therefore subject to rapid transformations.
Frequently, large white spots suddenly appear, especially near the
lakes, such as the spot at Lake Phœnix near the centre of Fig. 24 which
represents Mars on October 6, 1909, according to Antoniadi. These
white spots disappear as suddenly as they show forth. The white colour
is probably due to a very thin snow or hoar-frost, which is easily
condensed in the vicinity of the lakes but which as readily vanishes at
the approach of a warm draft or of sunshine.
Occasionally, dark spots on Mars are described as dissolving under
strong enlargement into dark and light squares giving the appearance
of a chessboard. This reminds one of the bayirs in Turkestan (see Fig.
9).
The collections of lakes along the cracks on Mars which appear to
us as “canals” are repeatedly filled up by sand and dried out. They
are revived through new depressions along the dislocation fissures,
corresponding to our earthquakes, when vapours of water and other
gases pour forth and condense to lakes in the deepest pockets of the
fissures. Canals are therefore created rather rapidly, sometimes over
night, and vanish occasionally as suddenly. The most remarkable case of
“new” canals was made known through a communication by Lowell. Two new
canals, at the time the most conspicuous on the surface of Mars, were
observed east of “Syrtis magna” on September 30, 1909, from Flagstaff
observatory, when they also were photographed, which precludes an
illusion. (On the other hand there was no sign of the great canal
Amenthes, shown on the map Fig. 17, a short distance to the left,
_i. e._, east of Syrtis in the very section where the new canals were
observed.) Also two new oases through which the new slightly curved
canals passed were observed for the first time, as were also a few
minor canals in the neighbourhood.
In 1913, the double canal Æthiops (see map at Long. 240°; the canal is
there single) was rediscovered from the Lowell observatory after an
absence of fifteen years.
These data make it evident that one or possibly several rather strong
earthquakes took place east of Syrtis major just prior to September
30, 1909 with the two oases as centres of collapse. The fissures now
made visible have probably existed before but filled with sand and have
now reappeared as a result of the condensation of water vapour when it
emerged into the cold Martian air.
This fact, that the most prominent canals in such manner now suddenly
appear and now as rapidly vanish, ought to convince us beyond doubt
that they are not magnificent products of engineering skill, for the
construction of which we should require centuries on the Earth.
The theory that intelligent men exist on Mars is very popular. With
its help everything may be explained, particularly if we attribute an
intelligence vastly superior to our own to these beings, so that we
not always are able to fathom the wisdom with which their canals are
constructed. The crossings of the latter are said to be cities (Lowell)
fifty times greater than London. The trouble with these “explanations”
is that they explain anything, and therefore in fact nothing. If we
would endeavour to understand the phenomena on Mars, we must in the
first place avoid the formerly so popular principle of “purposiveness”
which led even the most prominent scientists into so many amusing
errors. Neither may we base our conceptions, as does Flammarion, on the
assumption of natural forces unknown to us, no matter how much such a
course may appeal to mystics. Only forces with which we are familiar
can be resorted to, if we really are to understand nature. It seems to
me that such method of research might with good results be applied also
to the planet Mars.