ALL-SOVIET UNION SOCIETY FOR THE SPREAD OF POLITICAL AND SCIENTIFIC KNOWLEDGE

Corresponding Member of the USSR Academy of Sciences G. A. TIKHOV

LATEST RESEARCH
ON THE QUESTION OF VEGETATION
ON THE PLANET MARS

Transcript of a public lecture given at the Central Lecture Hall of the Society in Moscow

MOSCOW * 1948.

TABLE OF CONTENTS

Preface

In his lecture on vegetation on Mars, our famous astrophysicist G. A. Tikhov, who founded a new science, astrobotany, in 1945, takes the point of view of the so-called geomorphic hypothesis, according to which all phenomena observed on the planet Mars should be similar to any terrestrial phenomena. Back in the last century, some observers called the planet Mars “an undersized lookalike of the Earth”. Indeed, the phenomena have been discovered on the disk of Mars, which seem to be completely analogous to those on Earth. So, for example, back in the XVIII century, first Maraldi (in Paris), and then the famous W. Herschel often saw some white, bright segments at the poles of the planet. Now, without exception, astronomers believe that these bright white spots are something like snow or frost, representing ice-covered areas. The same is observed here on the Earth.
From the point of view of the geomorphic hypothesis, G. A. Tikhov also approaches the question of vegetation on Mars. He approaches this issue very consistently and logically. Perhaps, in some places, we even see some exaggerations in G. A. Tikhov[’s work], but this is completely permissible for a scientist who is a pioneer in a new interesting field, which he called astrobotany.
The lecture of corresponding member of the Academy of Sciences of the USSR G. A. Tikhov will, as one might think, be especially valuable in its content to all those lecturers who give lectures about Mars. Regarding the climatic conditions on Mars, one must, of course, be restrained, but hardly anyone will deny the existence of vegetation on this distant planet in our time, since the emerald, greenish and blue-green colors of its “seas” undoubtedly indicate that there is some kind of vegetation on this planet, in general, green in color, subject to clearly expressed seasonal changes.

K. L. BAEV, Doctor of Physical and Mathematical Sciences, Professor.

§ 1. Visual observations of Mars made by the author in Pulkovo and in Tashkent

In 1918-1920, I observed Mars visually in Pulkovo using a 15-inch refractor¹, and in 1948 I made observations in Tashkent using a 10-inch refractor.
In all cases, light filters placed between the eyepiece and the eye were used. The color of the filters was red, yellow, green and blue.

The use of light filters allows you to distinguish clearly the colored formations. So, green, cyan and blue places become very dark through a red light filter.
On the contrary, through a green light filter, these places become light and stand out very little against the general orange background of Mars. At the same time, white places, polar caps and clouds, become markedly bright and eye-catching.

This emphasis is further enhanced through a blue light filter.
Here, on pages 5, 6 and 7, we give 10 typical drawings of Mars, representing good copies from our original drawings made in Pulkovo and in Tashkent.
In Figure 1, taken through a red light filter, a chain of southern “seas” is visible from above and a large dark formation called Mare Acidalium is visible below.
In Figure 2, long channels with thickenings in several places are particularly clearly visible.
In Figure 3, the channels and the thickening on them are even better visible.
Figure 4 is interesting in two ways: firstly, no details are visible on the entire left edge of the disk (it is recorded in the observation journal that there is a green haze here), and secondly, when observed through a green filter, the place outlined with a dotted line was much lighter than all other places on the disk, except for the northern polar cap.
Figure 5, taken through a green filter, shows four light bands of clouds. They are very high, as it can be seen by the light cusps B and D, protruding against the dark background of the waning part of the disk. In addition, a particularly bright place A, circled with a dotted line, is interesting.

In Figure 6, the “seas”, the northern polar cap A and the bright spot B on the morning edge of the disk are clearly visible.
Figure 7 clearly shows the northern polar cap A and the southern seas. At the same time, light spots C and B on the morning and evening edges of the disk were clearly visible through the green filter.
In Figure 8, made through a red filter, the “seas” and the northern polar cap are clearly visible, and through a green filter, a bright spot B on the evening edge of the disk is visible.
Figure 9 is interesting because here a light oval spot, well known to Mars observers, was visible through a green filter. It is outlined in the figure with a dotted line. It is interesting to note that after 20 hours this spot was located just at the very edge of the disk (Figure 10) and had the appearance of a very small bright point in B. Apparently, this is a mountain or a plateau.

Figure 10 shows two more bright areas C and D on the morning and evening edges of the disk.
From my observations in Tashkent, it should also be noted that the “seas”, being on the edges of the disk, clearly showed a greenish tint that disappeared when they moved to the middle meridian of the disk. It is interesting to compare this phenomenon with the green haze, which we talked about when describing Figure 4.

§ 2. Climate on Mars

Before considering the question of vegetation on Mars, it is necessary to know what the climate is there, whether vegetation can exist there at all.
As we know, Mars is 1.52 times farther from the Sun than the Earth, and, therefore, receives a 2.3 times lesser heat flux from the Sun.
This ratio will become more clear from the following example: under the latitude of 43 degrees, for example, in Alma-Ata, on the day of the winter solstice (December 22), a unit of the earth’s surface, for example, one square meter, receives at noon the light and heat flux from the Sun just 2.3 times less than at noon during the summer solstice (June 22).
Distracting from the atmosphere of both planets, we can say that summer on Mars at a latitude of 43 degrees corresponds in temperature to winter on Earth at the same latitude.
What is the influence of the atmosphere? It is known that the atmosphere of Mars is much thinner and more transparent than the Earth’s.
Therefore, the same heat flow at the boundary of the atmosphere causes much greater heating on the surface of Mars itself than on the surface of the Earth. It follows that in summer, daytime heating on Mars is much greater than daytime heating in winter on Earth, but nighttime cooling on Mars is stronger than on Earth. In other words, the daily temperature fluctuations on Mars are much greater than on Earth. These are the theoretical conclusions.
What do direct observations show? The temperature of different places on Mars has been studied by astronomers. For this purpose, powerful telescopes and small, very sensitive thermoelements were used, on the receiving platform of which selected locations on the surface of Mars were projected. All observers come to the same conclusion that in the equatorial places of the planet, the temperature in the afternoon can rise to +20 degrees Celsius. Dark places are somewhat warmer than reddish ones. Even at the equator, at sunrise and sunset, the temperature is much below zero, and the nights should be very cold. On the polar caps, the temperature drops to -70 degrees Celsius; but in late summer, after the disappearance of the southern polar cap, the surface here becomes almost as warm as at the equator. In the winter hemisphere, the temperature is kept from -70 degrees to -80 degrees. Definitions of the average annual temperature of Mars vary greatly from one researcher to another. One thing is for sure: the average annual temperature of Mars is significantly below zero and, according to some observers, does not exceed -23 degrees Celsius, whereas on Earth the average temperature is +15 degrees Celsius.
We will make not quite accurate, obviously simplified, but at least an approximate calculation. The hottest places on Earth (Sudan, some places in India, etc.) have an average annual temperature of about +30 degrees, – 15 degrees more than the average annual for the whole Earth. Adding +15 degrees to -23 degrees, we get that the warmest places on Mars have an average annual temperature of -8 degrees. Are there places with such a temperature on Earth? Yes, there are. These are, for example, the western shores of Novaya Zemlya, Turukhansk (on the Yenisei), some places in Yakutia, etc. It is even colder in Yakutsk itself and Verkhoyansk; there the average annual temperatures are 11 and 16 degrees below zero.

§ 3. Seasonal changes on Mars

There are very distinct seasonal changes on Mars. Let’s start with spring. In the corresponding hemisphere, spring begins with the melting of the polar cap from the equator. In place of the melted snow, a dark ring appears surrounding the part of the cap that has not yet melted. At the same time, in the spring hemisphere, the seas, lakes and channels begin to appear clearer and clearer, acquiring a greenish or bluish color. This is noticeable not only by direct impressions when observed without a light filter. These formations stand out especially well and become dark when they are observed through a red light filter. On the contrary, through the green and especially through the blue light filter, they blur and almost do not differ from the continents.
The hue and depth of the color of the seas, and in some cases their area and shape change with the Martian seasons and from year to year. The main formations are fairly constant in their shape and position, but vary greatly in brightness. In general, they are shown up better in spring, during the melting of the polar cap, and gradually decrease or fade in autumn, and in addition some places change their color from green to yellow or brown and yellow islands appear on some ones. These seasonal phenomena reach the equator and even beyond.
All these changes are mostly repeated with sufficient accuracy during successive orbits of the planet around the Sun. In some cases, there were more permanent changes in the contours of the formations.
According to Lowell’s long-term observations, the improvement in the visibility of channels in spring also occurs due to the melting of the polar cap and spreads to the equator and beyond. The color of the channels is either green or blue. It can be assumed that we do not see the channels themselves, but the vegetation developing along them.

§ 4. Adaptability of terrestrial plants to cold and dryness

As it was shown above, the phenomena on Mars resemble seasonal changes in terrestrial vegetation. Let’s try to understand this issue in more detail. First of all, let’s consider whether the harsh climate of Mars excludes the possibility of the existence of Earth-like vegetation on it. The term “earth-like” vegetation has to be applied because to talk about any other one would simply mean to fantasize. Here is what is said about the adaptability of plants to cold in the book of Professor V. V. Alyokhin “Geography of Plants” (Moscow. 1938.): “We can say that on the earth’s surface there is almost no such a place, where plants could not exist because of the lack of heat; if in some Arctic regions, there are no plants, it depends on the fact that there is no land, free from snow and ice, but on each piece of land some plants develop, at least for a short time” (p. 78).
“...The deserts caused by cold and ethernal snows, are, first, Alpine deserts, and second, the Arctic and Antarctic ones.
We cannot speak about spring or autumn here, since the growing period is very short. Plants cling to the ground: it heats up better than air. We cannot have a continuous vegetation cover here, since only a few more favorable habitats carry as if oases of vegetation, and otherwise they are almost lifeless deserts with rare individual specimens.
An example of cold deserts is also the Pamir, located at an altitude of 3-4 thousand meters and representing desert plateaus. In winter, there is no snow cover that could protect vegetation.
In winter, the temperature drops to -46.7 degrees, and in summer it can rise to +30 degrees, during the growing season the temperature can drop to 0 degrees and below. The temperature of the soil on its surface can reach +33.5 degrees, and in general the role of the soil in terms of thermal regime is very great.
Such a situation is extremely unfavorable for the growth of plants: they cling to the soil, finding a more favorable environment here.
The crowding of plants with exceptional sparsity of the herbaceous cover is extremely interesting: so, sometimes a cushion of a certain species is grown through with several species: plants cling not only to the soil, but also to each other” (pp. 252-254).
“...Another very interesting feature of alpine plants attracts attention: this is an extreme resistance against freezing. Even at summer night, due to strong emission, the temperature drops below 0 degrees; the corollas of some flowers freeze and become brittle like glass, but under the influence of the Sun beams they quickly thaw out, and the flowers continue to bloom” (p. 228).
«...Even on the rocks and in the snowfields of inland Greenland, some plants are still found: for example, quite a significant number of higher plants can be found on the rocks, and some algae can be found on the ice. Thus, the alga Anabaena Nordenskioeldi turns purple-brown significant areas of the glacial fields of inland Greenland.
In general, we can think that low temperature conditions do not pose obstacles to the existence of plants anywhere on the earth’s surface” (pp. 255-256).
“...The life span of plants is very diverse... while some tropical plants are damaged from the cold at +2 degrees or even at +5, in the north plants freely withstand very low temperatures, and, for example, in Verkhoyansk (Eastern Siberia), forests grow at an average temperature of -48.4 degrees in December, -51.5 degrees in January, -46.2 degrees in February (minimum temperature -70 degrees, -76 degrees), and the flora numbers more than 200 species.
It has long been known that the spoonwort (Cochlearia arctica) on the northern coast of Siberia when having leaves and buds tolerates a harsh winter with temperatures up to -46 degrees and continues its development in the spring (Chilman). So do many of our plants (daisy – Bellix perennis, chickweed – Stellaria media, wild pansy – Viola tricolor, etc.), appearing from under the snow with green leaves and buds that did not have time to bloom in autumn. Many of our herbaceous plants do not lose leaves for the winter, being winter-green, for example, yellow archangel – Galeobdolon luteum, hazelwort – Asarum europaeum” (p. 78).
So, in the conditions of the most severe frosts on Earth, plants live. From this we can conclude that the temperature conditions on Mars do not exclude the possibility of vegetation development at all. Let the climate on this planet be drier and colder. But don’t plants have the ability to adapt? And if terrestrial plants, having got into the Martian climate, died, it does not mean at all that Martian plants, maybe adapting to the environment for millions of years, cannot exist.

§ 5. The difference between the optical properties of Martian vegetation and the properties of the Earth one

First of all, this applies to infrared rays. Terrestrial plants scatter infrared rays very strongly, and deciduous plants scatter them much more strongly than winter-green ones. This is clearly seen in photos 11 and 12 of the Asian spruce, obtained near Alma-Ata at an altitude of 2400 meters: photo 11 is ordinary, photo 12 is in infrared rays.
One might have thought that the Martian vegetation also had all these properties. But in 1924, the American astronomer Wright, photographing Mars in various rays, including infrared ones, did not find this phenomenon on the vegetation of Mars. On the contrary, it turned out that as the wavelength increases, the seas become darker and darker, and in infrared rays they are darker than, for example, in yellow ones.
In 1939, N. N. Sytinskaya determined at the Tashkent Observatory the reflectivity of the seas of Mars in various rays – from ultraviolet to edge red – and found no increase in reflectivity in the latter. Thus, it seemed that the question of vegetation on Mars had reached a dead end, and there is no longer a reason to talk about Earth-like vegetation on Mars.
But in 1945, the Alma-Ata agrometeorologist A. P. Kutyreva made an interesting assumption that, adapting to the harsh and dry climate of Mars, plants on it could gradually decrease and lose their reflectivity in infrared rays. This is fully confirmed by the observations of A. P. Kutyreva, indicating changes in the radiation properties of plants depending on changes in the meteorological conditions of their growth. In fact, it is very unprofitable for a plant in a harsh climate to reflect strongly the infrared rays that carry half of the solar heat.

Fig. 11. Schrenk's spruce, Tian Shan subspecies, common photo.	Fig. 12. Schrenk's spruce, Tian Shan subspecies, photo in infrared light.

Agreeing with this opinion, I came up with the idea to compare the reflection of infrared rays by deciduous and coniferous plants, using handwritten data from the observations of E. L. Krinov. It could be expected that the reflectivity in infrared rays is significantly less in conifers than in deciduous plants. This expectation was fully confirmed.
Thus, with the same values for birch and spruce in blue rays, the reflectivity of birch in infrared rays is more than three times higher than the reflectivity of spruce.
With the same values for oats and tundra juniper in green rays, the reflectivity of oats in edge red rays is more than three times higher than the reflectivity of juniper.
The following phenomenon discovered by E. L. Krinov and confirmed by my observations is also interesting: the reflectivity of coniferous trees in infrared rays is significantly less in winter than in summer.
Another difference between Martian vegetation and terrestrial vegetation is as follows. Terrestrial vegetation is mostly green in color. The situation is different with those places on Mars that are considered vegetation. Many observers see them now green, then cyan, then blue.
Further, the earth’s greenery strongly absorbs the edge red rays, giving the famous red absorption band of chlorophyll in the spectrum. This was not found in Martian plants: strong absorption was found there in the entire long-wavelength part of the visible spectrum, i.e. in the rays of red, orange, yellow and green. In all likelihood, this is due to the evolutionary adaptation of Martian vegetation to the harsh climate. In fact, if for the decomposition of carbon dioxide into carbon and oxygen and the formation of organic compounds, the so-called photosynthesis, it is enough for terrestrial plants to absorb relatively little sunlight, then for Martian plants living in a harsh climate, it is necessary to absorb more long-wave rays, in which mainly solar heat is concentrated. This is what gives the Martian vegetation cyan and blue colors.
The blue shade is also visible on some terrestrial plants living in northern countries and in high mountains. Such are fir and Canadian pine, for example. In the high Alma-Ata mountains – for example, on the Tuyuk-Su moraine (altitude 3400 meters) – locoweed (Oxytropis chionobia) lives in form of cushions, and its leaves, being mostly green, have a distinct blue coating.
In this regard, the message I received from the scientist-forester from Kiev, Georgy Andreevich Stoyanov, is of great interest: “Young seedlings of our European red pine very often acquire rich purple shade on their needles before winter. Sometimes this color completely overlays the green color, especially on the upper needles. This is observed only in young seedlings.
When visiting (before the war) a nursery in Germany by one of our foresters, the German forester asked to pay attention to young pine trees raised from Russian seeds, as they stood out sharply from their southwestern peers in lilac (violet) shade. He thought it was a disease, although the pine trees looked healthy. The Russian forester had to explain that this is a common phenomenon in the north, and the seeds have retained this property by inheritance, having moved to other conditions and environments where native forms do not possess this property”.
Thus, we have found a natural explanation for the blue and cyan colors of Martian vegetation. To understand what is observed on the vegetation of Mars, it is necessary to study the optical properties of terrestrial plants in possibly harsh climatic conditions – in the Arctic and especially in high mountains, where the atmospheric pressure approaches to some extent the atmospheric pressure on Mars. These studies constitute the content of a new science – astrobotany, founded in 1945 in the Soviet Union.

§ 6. Deciduous and winter-green plants on Mars

Subjecting my old Pulkovo observations of 1920 to a new study, in 1945 I drew attention to some records that at first seemed to me very strange or even erroneous. So, on May 13, 1920, it was recorded that through a yellow filter, the southern vegetation covers appear greenish, and the northern ones are brownish. The same is recorded when observing without a light filter. Finally, this is also confirmed by the fact that on the same day, when observed through a green filter, the vegetation cover in the northern hemisphere was darker than in the southern hemisphere. It was midwinter in the southern hemisphere of Mars at that time, and midsummer in the northern hemisphere. Thus, it became clear that winter-green plants exist on Mars along with plants that turn brown already in the middle of summer.
This can be confirmed by other data: the most noticeable formation, which has the shape of a funnel, is called Syrtis Major. Its color was noted by very many observers. Professor N. P. Barabashev¹ collected observations of the color of the Syrtis Major from 1858 to 1939. Professor Barabashev writes that the color of the Syrtis Major changes dramatically and, apparently, periodically. If we compare the color marks collected by Professor Barabashev with the seasonal ones in the northern part of the Syrtis Major, it is not difficult to establish the following. In all seasons, except the second half of autumn and the first half of winter, the Syrtis Major is blue, cyan or green. As for the second half of autumn and the first half of winter, its color is mottled: some observers call it blue, others – green and most – brown.

This can again be explained by the fact that both winter-green plants and deciduous ones, turning brown or losing their foliage by the second half of autumn grow interspersed on the Syrtis Major.
Numerous confirmations of the existence on Mars of vegetation that changes its color depending on the season are also available in foreign literature.
According to the observations of Mars in March 1918 Phillips writes:
“The most interesting in colour is a contrast between the northern and southern spots: the last ones are greenish-blue in refractor and bluish-grey in reflector; northern spots, for example, Mare Acidalium, seem to me to be a neutral color in both instruments”.¹

In March 24, 1918 there was the winter solstice in the southern hemisphere and the summer solstice in the northern hemisphere. Thus, in the southern hemisphere winter-green plants were observed.
Summing up his observations over several years, Thomson (N. Thomson) writes: “Portus Sigeus (latitude – 5 degrees) seems to me changing its appearance very little from year to year, in marked contrast with the areas to the south of it, such as the Pandorae Fretum, which varies greatly both in its appearance and intensity.
Maybe, it is interesting to make an assumption whether this is an indication of some kind of evergreen tropical vegetation that changes little with the Martian seasons”.¹

Everything is fine here, except for the word “tropical”. Tropical vegetation is completely incompatible with the harsh climate of Mars. Here we can only talk about winter-green vegetation of the terrestrial polar type.
In the book “Earth, Moon and Planets”¹ we find the following places: “The famous French Mars observer Antoniadi saw color changes in the south polar region in 1924. He writes: “Not only green areas, but also grayish or blue areas turned into brown, into brownish-purple or pink, while other green or bluish areas remained unchanged. The colors were almost exactly like the colors of leaves that fall from trees in summer or autumn in our latitudes. But the brown color appeared sometimes early, sometimes late in the Martian year and remained only for a short time, in proportion to the duration of the brown leaves in our vegetation”. (Translated from “La Planete Mars”, p. 18).

“The darkening of the polar regions with the melting of the caps and the gradual darkening towards the equator with accompanying color changes indicate with overwhelming evidence the growth and withering of some types of vegetation on the planet Mars”.
In “L’Astronomie” magazine from January 1925, Antoniadi writes: “It is possible that places that remain green all the time, such as parts of Mare Sirenum and Mare Erythraeum, represent vast grass steppes or shallow lakes with algae at the bottom, although this seems less likely”.
In the same journal, another French astronomer, Baldet, based on his observations through the large refractor of the Meudon Observatory, writes: “It is possible that along with the continental vegetation on Mars, there is aquatic and marsh vegetation, or vast expanses like the Saragasso Sea (a sea of floating algae in the Atlantic Ocean)”.
In the before-mentioned book “Earth, Moon and Planets” there is a table with observations of the color of the Mare Erythraeum made in 1903 by the famous American explorer of Mars Lowell. Here I give this table. In it, Martian dates are presented in the terrestrial sense for the northern hemisphere.
The observations are given in this book without any explanation. They are decyphered by me in the remarks given in the last column of the table.

Mare Erythraeum (Lowell 1903)

From this table it is clearly seen that Lowell’s observations make the hypothesis of the existence of both deciduous and winter-green vegetation on Mars perfectly natural.

§ 7. The hypothesis about flowers on Mars

In 1925, Antoniadi published a very interesting map of Mars¹, where the color properties of different places on this planet are indicated by different hatching (according to observations during the 1924 opposition): changed from green or gray to brown; from green, gray or blue to brown-purple; took a chestnut shade; changed color from gray to carmine, remained invariably green or invariably blue, cobalt.

According to Antoniadi’s observations, a significant part of the Ethiopia* desert, located between the latitudes of +30 degrees and -5 degrees, has changed gray to pink, and according to Baldet’s observations, to purple-violet.
Are there any similarities in the changes in the color of the Ethiopia desert observed by Antoniadi and Baldet with the phenomena occurring on Earth? “The end of March-April is the period of spring flowering of the desert. At this time, the deserts seem to be as if drenched in blood. This is a mass flowering of poppies, which leaves an indelible impression. At this time, poppies are found literally everywhere, even on the clay roofs of houses and sheds, along fences on the streets of Tashkent and Samarkand”.¹

§ 8. Places on Mars that are most favorable for life, at least for plant life

The climatic conditions on Mars are not so unfavorable for plant life. However, in those places of the planet where the Sun rises and sets daily, even at the equator, the temperature ranges from 20 degrees above zero to 50 degrees below zero during the day. Of course, vegetation could have adapted evolutionarily even to such conditions, but in the polar countries of Mars, where the Sun does not set for more or less of the Martian half-year, almost equal in duration to the Earth year, the temperature changes very little during this period, remaining continuously above zero. These are the places that are most favorable for plant life. For such a long period of time, the plants in the field can have time to turn green, bloom, wither and disseminate.
The seeds are hidden in the soil, under the protection of the foliage of previous years. With the onset of autumn, the Sun begins to set, and nights begin, at first very short, and then gradually lengthening, until the day when night falls for almost the entire Martian half-year. Thus, the transition from the warm season to the harsh Martian winter is very slow and very consistent.

§ 9. What kind of vegetation can be imagined on Mars

First of all, it should be undersized, clinging to the soil. These are mainly grasses and procumbent shrubs of a green-blue color. Some of them turn brown and dry out by the middle of summer; others retain their green-blue leaves in winter.
These plants live interspersed with each other. Our juniper, locoweed, cloudberry, lingonberry, mosses, lichens and other northern and alpine plants may have some similarities with Martian plants.

§ 10. Carbon dioxide in the atmosphere of Mars

In connection with our topic, the discovery made in 1947 by the American astronomer Kuiper¹ acquires exceptional importance. Using the powerful instruments of the Yerkes Observatory, he found that the atmosphere of Mars contains at least as much carbon dioxide as the Earth’s atmosphere. Moreover, it turned out that on Mars such poisonous gases as ammonia and methane, which are abundant in the atmospheres of large planets, are absent at all.

So, on this planet, despite its harsh climate compared to Earth, plant life is quite possible. Hence, the possibility that there may be an animal world on Mars is not excluded.
There are no boundaries for human cognition. Sooner or later, this question will be clarified one way or another, and the science of vegetation on other planets – astrobotany – will play a significant role in it.

§ 11. Further observations for studying vegetation on Mars

First of all, it should be visual and photographic observations of Mars with the help of powerful telescopes using different light filters.
Such observations will provide objective information about the color of different formations on Mars and about the change of this color with the seasons.
Then it is extremely important to obtain spectrograms of a small dispersion for various places on Mars.
Terrestrial vegetation should be studied spectrally in different seasons, mainly in places with a harsh climate. Especially significant is the penetration possible further into the infrared rays.

POPULAR LITERATURE ABOUT MARS

1. Lowell, Professor “Mars as the Adobe of Life”. Translated from English. Edited by A. R. Orbinsky. Ed. “Mathesis”. Odessa. 1912.
2. Arrhenius Svante “The destinies of the Stars”. Translated from the German, GIz. 1933.
3. Stovichek B. V. – Mysterious planet Mars. [Russian edition] Translated and edited by Professor S. N. Blazhko. Ed. “Puchina”. 1925.
4. Polak I. F., Professor “The planet Mars and the question of life on it”. 3rd ed. ONTY. 1939. (There is also a new edition.)
5. Baev K. L., Professor “Are the planets inhabited?”. Moscow. Gaiz.1936.
6. Vorontsov-Velyaminov “Universe” Ogiz 1947.
7. F. Whipple “Earth, Moon and planets”. Ogiz - Gostekhizdat. 1948.

Translated by Pavel Volkov, 2021
The original article in Russian is here