Theory on gas adsorption by lunar surface to explain loss of lunar atmospher

Gutkin, A. M.

Markov, M. S.

Raitbrud, Ts. M.

Slonimskaya, M. V.

English

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- 1;
National Aeronautics and Space Administration
Goddard Space Flight Center
Contract No.NAS-5-12487
ST-ACH-LS-10778
ADSORPTION WAY OF THE LOSS OF MOON'S ATMOSPHERE
By
A.M. Gutkin
M. S. Karkov
Ts.M. -laitbrud
M.V. Slonimskaya
(USSR)
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25 NOVEMBER 1968
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ST-ACH-LS-10778
ADSORPTION WAY OF THE LOSS OF MOON'S ATMOSPHERE
Doklady Akademii Nauk SSSR 	 By
Tom 182, No.6, pp 1294-1295	 A.M. Gutkin, M.S. Markov
Izd-vo "NAUKA", Moscow 1968	 Ts.M. Raitbrud & M.V. Slonimskaya
The Earth's hydrosphere and atmosphere are considered at present as a
result of its geological development and their formation is linked with the
fusion and degassing of mantle matter [1]. In recent years Ye.K. Markhinin
[4] succeeded to evaluate the amount of water vapors and other gases ejected
into the atmosphere. These data have shown that during the Earth's geological
history, the ejection of volatile constituents by volcanoes (admitting the
intensity of volcanic action as being close to contemporary) is quite suf-
ficient for the formation of hydrosphere and atmosphere. One may think that
analogous processes of volatile ejections are also inherent to the Moon.
This is attested by direct observations of the Moon [2,3].
Recently American investigators [11] systematized all the "non-stationary''
points of the visible part of the Moon, which are evidence of endogenic activity
on the lunar surface. At the same time, =he data on lunar geology, accumulated
to date, confirm conclusively the duratiu.. of its superficial structures' for-
mation and consequently the period of its geological history [6, 9, 121. The
various age structures being monotypic, we are led to assume also the duration
of volcanic activity on the Moon. Furthermore, one may assume the presence on
the Moon of other processes, resulting in the generation of gases. In the first
place, one should attribute to them the meteorite impacts against the surface
of the Moon. The corresponding computations, indicating the role of these
processes in local heating of its surface and in evaporation of its matter,
were carried out by K.P. Stanyukevich and V.V. Fedynskiy [7]. The decay of
radioactive elements entering into the composition of lunar crust could also
play a certain role. However, the results of optical and radioastronomical
observations indicate that the concentration ofases in the lunar atmosphere
is at present vanishingly low (it is at least 10 2 times lower than the air
concentration at sea level of Earth's surface). In order to explain the absence
of atmosphere on the Moon, recourse is generally made to the escape mechanism
of thermal gas from the lunar surface. Because of small mass of the Moon, the
critical velocity is comparatively low (vk = 2.38 km/sec). The mean velocity
of thermal motion of gas molecules with small molecular weight at temperatures
that occur on the lunar surface in daytime (300-400°K), has the magnitude of
the same order as the critical one, and the dissipation time on the Moon of
such gases as H29 He, is very short. However, for such typical gas of the Earth's
atmosphere as N 2 , the thermal dissipation time is of the order of 10 7 years,
provided it is estimated according to Jean's formula. Using the more precise
Shklovskiy's formula, the obtained dissipation time is still greater [10]. For
such gases as SO 2 , the dissipation time is greater than the age of the Moon.
Thus, the thermal dissipation of gases cannot practically explain the
2total absence of atmosphere on the Moon. This is why other mechanisms are
involved for the explanation of dissipation such as: the ionizing action
of solar ultraviolet radiation, the energy transfer :o molecules of lunar
atmosphere by particles o : solar corpuscu;ar radiation (solar wind), for-
mation at certain altitude above the Moon of an ionized layer, analog ous to
that of the Earth's exosphere, with a 1000-1500°C temperature. No mathema-
tical analysis of the action of these mechanisms is available in literature.
Qualitative estimates have an insufficiently well founded character. Thus,
for example, the scattering cross-section for the process of energy transfer
to molecules by protons with energy of 2 kev, is taken equal to 10 -15 cm.
For these energies, greatly exceeding the energy of ionization and disso iation,
the molecule scattering cross-section is by many orders smaller.
It appears, that in order to explain the absence of atmosphere on the
Moon, it is necessary to take into account the gas adsorption process by lunar
surface. Because of its high porosity, the capability of adsorption by lunar
surface should be substantial [5, 8]. The settling of cosmic dust, the fresh
lava sheets, the new surfaces forming after settling on the lunar surface of
particles arising from meteorite impacts, all this should restore the adsorption
capability of the lunar surface. However, the most important aspect of gas
absorption process by porous matter of lunar surface, is the thermal diffusion
of the adsorbed molecules into the depth of the porous layer under the action
of temperature gradient. During the day, the temperature decreases in depth
from 300-400°K at the very surface and to 200-250°K at the depth of 0.5-2 m [8].
Inasmuch as the surface diffusion coefficient of the adsorbed atoms is sharply
dependent on the temperature, this should induce a diffusion stream inside the
porous layer. One may neglect the reverse stream which, generally speaking,
will take place during the nighttime, while the temperature gradient is directed
outward, as the low temperature at the surface layer will lead to a nearly
complete cessation of diffusion processes. If the adsorption heat of gas mole-
cules exceeds the activation energy of diffusion of the gas along the adsorbent's
surface, the probability of molecule dsorption is smaller than the pr bability
of their migration into the porous layer. The adsorptive escape of such gases
will prevail over the dissipation. The investigates phenomenon should result in
that the numerous chemical substances should accumulate at a small depth inside
the surface layer of lunar crust.
Geological Institute	 Manuscript received
Akademy of Sciences SSSR
	
13 February, 1968
* * * THE END * * *
R E F E R E N C E S
1. A.P. VINOGRADOV, Izv. AN SSSR, eer. g:ol., No.4, (1967).
2. N.A. KOZYREV, Sborn. Novoe o Lune, I.d-vo AN SSSR, 1963.
3. Yu.N. LIPSKIY, M.M. POSPERGELIS, Byuro astr. soobsch., Astr. tsirkulyar,
No.389, 1-2 (1966)
4. E.K. MARKHINI, Rol' vulkanizma v formirovanii zemnoy kory. "NAUKA", 1967.
(The vulcanic role in the formation of Earth's crust)
3R E F E R E N C E S
(continued)
5. PERVYYE PANORAMY LUNNOY POVERKHNOSTI, "NAUKA", 1966.
(First Panoramas of the Lunar Surface)
6. A.L. SUKHANOV, B.G. TRIFONOV, Geotektonika, No.4, (1967)
7. K.P. STANYUKOVICH, V.V. FEDYNSKIY, DAN, 57 No.2, (1947).
8. V.S. TROITSKIY, Izv. vyssh. uchebn. zaved., ser. Radiofizika, 9, No.10,
(1967).
9. A.V. KHABAKOV, Sborn. LUNA, M., 1960.
10. I.S. SHKLOVSKIY, DAN, 76, NO.2 (1951).
11. B.M. MIDDELCHURST, P.A. MOOR, Sci., 155, No.3761 (1967).
12. J.E. SPURR, Geology Applied to Selenology, 1945.
CONTRACT No.NAS-5-12487
	
Translated by
Volt Information Sciences, Inc.,	 Ludmilla D. Fedine
1145 - 19th Street, N.W.	 22 November, 1968
Washington, D.C. 20036	 Revised by
Tel: 223-6700 (X-36,37) 	 Dr. Andre L. Brichant
25 November, 1968


Adsorption Way of the Loss of Moon's Atmosphere

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