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NASA TT F-9898 



STUDY OF THE EARTH- TIPE PLANETS 



I. K. Koval' 



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(NASA CR OR TMX OH AD NUMBER) 



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(CATEGORY) 



Translation of "Izucheniye planet tipa Zemli" 

Zetnlya i Vselennaya, 

Vo. 1, No. 6, pp. 53-55. 1965 



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f? 653 July 65 



NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON MARCH I966 



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NASA TT F-9898 



STUDY OF THE EARTH- TYPE PLANETS 



I. K, Koval' 



ABSTRACT ^ J^ 



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The article discusses work by the USSR Academy of Sciences 
Commission on Planetary Physics in \^G\ and 1965. Atmospheric 
pressure Investigations by photometric and polarimetric means 
were conducted. Aerosol influence is considered. Values for 
the Mars and Venus atmospheres are presented. Various individ- 
ual studies were presented by their authors. 

Great interest in earth-type planets — Mars and Venus-- has been gen- /53* 
erated recently by great progress in the fields of space investigation. Many 
observations of these planets have already been perfomied by instiiiments on 
rockets and space stations^ and interesting results have been obtained. 

Thorough study of Mars and Venus is necessary to permit landing automatic 
stations on their surfaces. 

In the USSR a Work Group for study of earth-type planets was established by 
the Astronomic Council of the USSR Academy of Sciences for coordinating investi- 
gations within the framework of the Commission on Planetary Physics. At the 
Group's yearly meetings, scientists learn of recent accomplishments and plan 



*Wumbers given in margin indicate pagination in original foreign text. 



NASA TT F-9898 

future studies. Such a meeting of the Group took place in Kiev in 1964 and at 
the Crimean Astrophysical Observatory in 1965- 

Spectroscopic, photometric and polarimetric investigation methods yielding 
new data concerning physico chemical characteristics of the Martian and Venusian 
atmospheres received most attention at these meetings. 

Atmospheric Pressure 

Determining atmospheric pressure on the Martian surface by photometric 
observation leads to calculating optical density of the atmosphere by formulas 
for the theory of light- scattering in planetary atmospheres. 

The Soviet astronomers N. N. Sytinskaya, V. V. Sharonov, W. P, Barabashov, 
et al. at different times arrived at agreeing results of relative values of 
optical thickness of the Martian atmosphere. Atmospheric density at the sur- 
face was equal to 60 mm Hg. Such a value was also obtained by polarization 
observations . 

However^ now spectroscopists have worked on determining atmospheric pres- 
sure on Mars. Using bands of molecular absorption (belts of carbonic gas), 
many American astronomers, as well as the Soviet V. I. Moroz, have found that 
pressure on Mars is approximately one third that anticipated from photometric 
and polarimetric measurements. 

What is wrong? Which value should be given preference? 

At the Kiev conference V. I. Moroz, N. N. Sytinskaya and E. G. Yanovitskiy 
presented the opinion that pressure determination using optical atmospheric 



Here and later the value for pressure is given in mm Hg, calculated by aneroid 
barometer. The mercury barometer here is not suitable, because its indications 
depend on gravity, which varies for different planets. Ed. 



thickness leads to values known to be increased. The problem is that these very- 
photometric and polarimetric observations of Mars, by which atmospheric optical 
thickness was obtained, indicate the constant presence in the Martian atmosphere 
of hard (aerosol) particles--dust and Ice crystals. This contamination of the 
Martian atmosphere considerably increases its optical thickness. In other 
words, we can never determine the optical thickness of only the gaseous atmos- 
phere of Mars, although the true gas component must enter into the formulas for 
determining atmospheric pressure. What is important about the spectroscopic JS^ 
method is that it is free of the influence of aerosol particles and yields in- 
formation on the strictly gaseous atmosphere. 

E. G. Yanovitskiy has conducted quite indicative calculations for evalu- 
ating the influence of aerosols on results of determinations of atmospheric 
pressure by optical thickness. He used measurements of optical thickness of 
the earth's atmosphere for calculating atmospheric pressure at the earth's 
surface. Instead of the 760 mm Hg, he obtained values of ± I7OO mm, which 
definitely is explained by the contamination of earth's atmosphere by very 
small hard particles with radii of ± 10" cm. Their presence in the background 
of molecular mixtures can almost not be shown, because they disperse solar light 
by almost the same law as gas molecules. 

Thus, the spectroscopic method of determining atmospheric pressure for 
planets with atmospheres containing aerosols apparently is more basic, and we 
must take 15-20 mm Hg as the more probable values of atmospheric pressure on 
the Martian surface. 

Recently A. V. Morozhenko concluded an extensive series of measurements of 
Martian polarization by photoelectrical means. These measurements allowed him 
to determine atmospheric pressure using polarization properties of the Martian 



atmosphere in various regions of the spectrum. Pressure at the surface did not 
exceed I5 mm Hg. 

We must assume that even these pressure values are exaggerated; in parti- 
cular, measurement results depend on the optical properties of the Martian 
surface . 

Thus, if we verify information on the roughness of the Martian surface, 
this leads to decrease in calculated values of the optical thickness of its 
atmosphere and simultaneously to decrease in evaluation of the amount of aero- 
sol particles. In this respect we should note that data from Mariner IV showed 
Martian surface atmospheric pressure as equal to ± 10 mm Hg. 

V. I. Moroz considers the atmospheric pressure on the surface of Venus 
equal to 10 atm. Observations give the value for pressure only for the upper 
limits of the cloud layer--20 mm Hg, and pressure for a determined model at- 
mosphere can be found by calculation. 

Chemical Composition and Some Properties of the 
Atmospheres of Venus and Mars 

The thorough reports by V. K. Prokof 'yev "Analysis and Perspectives of 
Spectroscopic Investigations of Venus and Mars" and V. I. Moroz "Eeview of 
Infrared Spectroscopy of Venus and Mars" preceded discussion of this question. 

The presence of carbon dioxide, oxygen and water vapor is now reliably es- 
tablished, and on Mars that of carbon dioxide and water vapor. 

Recently variations in intensity of carbon dioxide belts in the atmosphere 
of Venus were observed. Moreover, observers reported the appearance of dark 
and light formations on the disk of Venus in the shortwave region of the spec- 
trum. The majority of dark spots are unstable and only 2 or 3 days after ap- 
pearance lose contrast and disappear on the bright background of the planet. 

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However, stable spots with long duration, visible for several days, also appear. 
Unfortunately, as a result of the instability of the terrestrial atmosphere, we 
have not yet succeeded in obtaining the spectrum of the dark spots, thus reducing 
the number of hypotheses on their origin. Meanwhile there are no polarimetric 
observations of individual spots, although as a whole the study of polarization 
of Venus correctly shows the presence of clear particles--small crystals ( of 
ice ? ) or water droplets with 2 |X diameters. 

The light spots also observed in the ultraviolet rays near the limits of 
the terminator lines (borders of light and dark) almost always occupy large ISS^ 
areas and can be observed for several weeks. Some observers believe that these 
spots are at the poles. Light spots considerably smaller than "polar" are some- 
times observed near medium- temperature zones. As a rule, the spots are weakly 
defined and endure briefly. No one doubts their reality, but sometimes reports 
appear in the literature on the appearance of small, rather bright spots in 
various parts of the illuminated portion of the disk of Venus, Their existence 
is all the more questionable, because the observers themselves sometimes equate 
these spots with flares. 

V. I. Moroz briefly considered infrared radiation reception presently 
extant for various regions of the infrared spectrum, and he presented basic 
physical characteristics of the atmospheres of Venus and Mars (chemical compo- 
sition, pressure, temperature, aerosol particle dimensions, etc.). He empha- 
sized the importance of resolving such problems as study of variations in carbon 
dioxide amounts with phase and by the disk of Venus, 1*0 give accuracy of its 
content in the atmospheres of Venus and Mars by intensity of unsaturated belts, 
pursuing spectral observations of Venus and Mars with high solution in the in- 
frrared window of earth's atmosphere clearness for 8-13 M- waves. 




Photograph of Venus obtained 
by Slayfer at Flagstaff Ob- 
servatory. 

The 1965 Work Group meeting decided to conduct future systematic coopera- 
tive observations of Venus and Mars, the necessity of which was discussed in 
many reports . 

A. V. Morozhenko and M. M. Pospergelis discussed polarimetric studies of 
Venus and Mars. A. V. Morozhenko reported new results of investigations of 
the dependence of the degree of polarization of Mars on wavelength and phase 
angle obtained at the Main Astronomical Observatory of the Uk.SSR Academy of 
Sciences. These studies provided evaluation of atmospheric pressure at the 
surface of Mars (I5 mm Hg), which we have already discussed. He also indicated 
the need for further polarimetric studies of the planets in various spectral 
regions parallel with photometric studies. Such material will be quite valuable 
from the point of view of the application of the theory for determining physi- 
cal characteristics of the planets' atmospheres, 

M. M. Pospergelis described an instrument he devised, an automatic polari- 
meter, and discussed perspectives for its application. 

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Photograph of Mars obtained with 
blue rays In 195^ (above) and I956 
(below), indicating "blue layer" 
structure variability. 



Members of the conference attentively listened to the report by L. A. 
Mitrofanova on laboratory investigation of molecular spectra for absorption 
of various gases performed at the USSR Academy of Sciences Main Astronomical 
Observatory at Pulkova. These works are most important in interpretation of 
spectral observations of the atmospheres of the planets, and the Work Group 
recommended their continuation. 

I. N. Minin spoke on theoretical works in the laboratory of the Leningrad 
University which will later permit interpretation of polarimetric observations 
of Mars from the Main Astronomical Observatory of the Uk.SSR Academy of 
Sciences. The Work Group approved these studies and recommended broadening 
them, including photometric and spectrophotometric observations. 

N. A. Kozyrev emphasized the impor Lance of systematic observations of 
the nocturnal side of Venus (obtaining spectra and photographs to discover 
sources of information related to lower layers of cloud cover). 

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NASA TT F-9898 

New methods of observing Venus and Mars- -photoelectric scanning, obtaining 
short-exposure photographs by television, received great attention. A report on 
developing new types of Infrared receivers at the Uk.SSR Academy of Sciences 
Institute of Physics received great attention. 

Because terrestrial observations allow us to resolve only limiting 
questions, the necessity for broader development of extraterrestrial observa- 
tions of planets was noted at the conference.