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NASA TT F-9898
STUDY OF THE EARTH- TIPE PLANETS
I. K. Koval'
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IPACfesI
(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.
1^
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.
6
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).
7
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.
