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Some problems in chemical evolution of matter in space


HomepageINSTITUTE of Physico-Chemical Problems of EvolutionPhysical Chemistry of Evolution of Planetary SystemsSome problems in chemical evolution of matter in space

The translation of the parts of the book by G.P.Gladyshev
"Thermodynamics and Macrokinetics of Natural Hierarchic Processes", Nauka, Moscow, 1988.
Zhurnal Vses. Khim. Ob-va im. D.I.Mendeleeva, Vol. 35, No. 5, pp. 625-631, 1990
G.P.Gladyshev and D.Kh.Kitaeva
UDC 523-52:523.4-36

Physicochemical processes taking place in space are characterized by a number of specific features that distinguish them from conditions in the terrestrial atmosphere. They are generally effected in ultrahigh vacuum at extremal temperatures in ultrastrong or ultraweak fields (electrical, magnetic, or gravitational). The range of problems pertaining to the chemical evolution of matter in space is extremely broad [1-6], and it is impossible to discuss more than a small portion of them in a single paper. The present article is devoted to individual aspects of the course of chemical processes under the extremal conditions that might have obtained during formation of the Solar System and other planetary systems. Particular attention will be given to problems of the spatially periodic condensation of matter under the conditions of the protosolar system, which bad not previously been taken into account by evolutionary theories.

We will follow the published general schema of the processes involved [1] and consider the stages in the evolution of the Solar System. The first stage was the development of the Protosun, which was formed as a result of accretion from the original Solar System cloud; the second was disposition of the gas and dust forming the atmosphere in the vicinity of the magnetized central body, the third was transfer of momentum from the Protosun to the surrounding atmosphere, so that the gas and dust particles began to move in Keplerian orbits relative to the Sun. The decisive role during these stages was played by magnetohydrodynamic effects, since the gas falling toward the sun was quite rarified and constituted a plasma. As the matter became concentrated around the Sun, the density of the cloud increased and the influence of magnetohydrodynamic effects diminished. When the protocloud coalesced and became a disk, these effects became small. The stages described above were completed relatively rapidly, within 107-108 years.

According to the theory elaborated in [7-13], there then ensued a protracted fourth evolutionary stage, formation of the primary Solar System rings, which ended relatively recently. It was associated with diffusion (mass transfer) of the solar material to the evolving disk, in which spatially periodic condensation of material from the supersaturated state took place to form rings of condensed matter (the latter subsequently accumulated into the planets as system development progressed). It was shown in these studies that the matter concentration in the protoclouds could have remained quite high for some time, so that the role of the magnetohydrodynamic effects discussed in monograph [1] would not have been as substantial in the stage under consideration. The decisive role was apparently played by diffusion of material from the central bodies into the corresponding protoclouds and chemical reactions leading to condensation from the supersaturated state. It can be assumed with some measure of approximation that Ficke's law:

(1)

is satisfied starting at some distance rn' from the surface of the Protosun, where the are the average concentrations of material diffusing from the central body S and cloud material N, while DS,N is the average diffusion coefficient. An expression relating the location (rn) of the n-th ring and the time of its formation (tn) is easily obtained from (1):

(2)

Liesegang's theory of periodic condensation can be used to explain the empirical Titius-Bode rule of planetary distances, according to which the distance of the n-th planet from the Sun (rn) satisfies the relation [4]:

Table I
Some Planetary Parameters [1] and Characteristic Durations of Stages in Evolution of Solar System

Planet Planetary mass,
m0·10-27, g
Major semiaxis, rn·10-13, cm Planetary radius,
Rm·10-9, cm
Formation time of primary ring,
tp.r·10-6, years
Planetary age,
t·10-9, cm
Jet formation time
tj, years
Planetary nucleus formation time,
tp.n·10-6, years
Accretion time,
tac·10-6, years
 
Mercury0.3330.5790.2430.374.520130.78
Venus4.871.080.6051.24.550140.63
Earth5.971.50.6382.54.575352.0
Mars0.6422.280.3405.84.4911042082
Jupiter1899.07.787.16674.43390382.2
Saturn568.014.36.02304.2772033061
Uranus87.228.72.549103.61.4·103>104**8.8·103
Neptune102.045.02.472.25·1032.252.3·103>104**>104**
Pluto *0.6659.00.323.9·1030.63.0· 103----

*Calculations made for regular planet in far reaches of Pluto's orbit.
**Characteristic times tac and tp.n for outer planets are comparatively long, since flattening of torus was not taken into account in this approximation.


(3)

where rn, is the greater semiaxis of the orbit of the n-th planet and r, and r0 are empirical constants.

After specifying physically reasonable values for the parameters [1,14], we can obtain the values of tn from expression (2), i.e., estimate the times at which the primary rings were formed (tnє tp.r):

(4)

where m and V are the mass and volume of the protoplanetary disk, s and M are the average diameter and molecular mass of the diffusing particles, g is a constant (g =6), T is the absolute temperature, and R is the universal gas constant.

The results of these estimates are given in Table 1. The age of a planet is estimated as the difference between the total age of the Solar System (assumed to be ~ 4.5• 10-9 years) and the corresponding tp.r. According to the concepts elaborated here, the further a planet is located from the Sun, the younger it is. The theory predicts the existence of ring systems and satellites in an active evolutionary stage for young planets.

As the primary rings initially formed near the Sun developed, the next stage of evolution proceeded. A ring of condensed matter was formed in the jets, consisting of solid grains and gas. The accretive evolution of the jets of each protoplanetary ring led to development of a planetesimal and then of a planetary core, consisting basically of compounds of heavy elements. During formation of large planets, gravitational capture of uncondensed substances (H2, He, etc.) occurred when the core reached sufficient size. As the planetary cores grew and a magnetic field appeared, magnetohydrodynamic effects became perceptible in their initial protosatellite clouds. As in the case of the Sun, gas and dust were distributed around each planet, forming an protodoud; transfer of momentum occurred, and the cloud particles began to move in Keplerian orbits. As concentration of the material progressed, the magnetohydrodynamic effects became weaker again. Gravitational compression led to warming of the protoplanet and to ejection (diffusion) of its material into the gas "shells" of the protocloud, which was apparently accompanied by spatially periodic condensation and formation of the primary rings of regular protosatellites and then of planetary satellites. The fourth and final evolutionary stages proceeded in parallel.

Thus, the general premises of the magnetohydrodynamic theory of Solar System evolution [1] are in good qualitative agreement with the theory of spatially periodic condensation. Quantitative assessment of the electromagnetic effects [7] shows that their role might actually have diminished as the protodisks developed and constricted and again increased in those regions where matter condensed and the gases became incandescent. The criterion in gas dynamics that justifies neglecting electromagnetic effects is the characteristic magnetohydrodynamic parameter L, which should, according to [1], be far less than one:

(5)

where B is the magnetic induction, l is the linear extent of the medium, sE is the medium electrical conductivity, PB is the magnetic permeability, r is the medium density, and c is the speed of light.

We know that L>>1 and usually equals 1015—1020 for a number of stellar and interplanetary regions. In the E layer of planetary ionosphere, L~1; for planetary atmospheres and hydrospheres, L<<1. It is thought [1] that LЈ 106 in the interior of cold dark clouds.

The parameter L was estimated for the central regions of forming protodisks in [7], proceeding from the average parameters of the solar disk and utilizing data on the planetary atmospheres of the Earth and Mars. Assuming that the inner layers of the disk must be screened from ionizing-radiation by a layer of material h<1, r2 (where r1 and r2 are the radius and average thickness of the disk) in order for criterion (5) to be satisfied, it was shown that this condition is fulfilled not only in the case of Earth and Mars but also over the series comprising the Solar System and the satellite systems of Jupiter, Saturn, Uranus, and Neptune (and more strictly so on moving toward the outer planets).

The final stage in protoplanet formation is gas capture by the jets, or planetary nuclei. The basic mechanism of the process is treated by utilizing the model of gas molecule 'adhesion' to a cold solid surface [1]. Moreover, according to [7], gas apparently accumulates as a result of 'apparent attraction,' i.e., multiple collisions of gas molecules with jet grains. Some of the gas is not retained by the jet and diffuses out of it, forming a jet atmosphere. If we assume the rate at which gas mass is absorbed (dm/dt) to be proportional to the nucleus surface area (A) and the gas mass (m) in the volume from which diffusion takes place, i.e.,

(6)

where g ' is a proportionality factor, we find that, when A=const, the loss of gas cloud mass as a result of gas absorption by jet particles is described by the relation:

(7)

When A varies (for gas absorption by a planetary nucleus), we have in the general case:

(8)

where R0 and M are the initial size and mass of the nucleus, q is the density of the nucleus, r is the density of the growing layer during gas condensation, nig is the gas cloud mass at the starting time, and m is the cloud gas mass at time t.

Equation (7) and the solution of Eq. (8) can be used to calculate the times tj, and tp.n, which characterize the decrease in gas mass (e.g., by a factor of 10) during formation of a jet and planetary nucleus respectively. The results of such estimates are given in Table 1. The accretion times tac are also listed, for purposes of comparison [1]. It can be seen that tp.n differs from tac by a factor of 2-10 and that tj<<tp.n, tac. It can thus be assumed in first approximation that the limiting stages of the formation of large planets in the Solar System is diffusion, which leads to condensation of material from the supersaturated state and formation of primary rings, as well as hydrogen and helium accretion by planetary nuclei.

Periodic condensation should inevitably be detected in the deep atmospheric layers of planets, comets, and other bodies; the process in cometary atmospheres can serve as a model of the condensation that occurred during formation of the Solar System. There is reason to believe [15-17] that L<<1 and that magnetohydrodynamic effects are not decisive in the inner atmospheric layers of comets that are not very close to the sun and extend for several thousand kilometers. Cometary nuclei generally contain a number of comparatively volatile compounds, such as H2O, CO2, CO, HCN, etc. As comets approach the Sun, these substances begin to evaporate at high rates [15,16]. The vapor tension of substances at the surface of the nucleus is approximately equal to the equilibrium value defined by the Clausius-Clapeyron equation:

Table 2
Known Interstellar Molecules and Ions [22]

Consisting solely of C and H Containing O Containing N Containing O and N Containing S and Si
CH
CH+
CH4
CєC
CєCH
HCєCH
H2C=CH2
Cє CCH
H3CCєCH
(CєC)2H
H3C(CєC)2H


OH
H2O
CO
HCO
HCO+
HOC+
H2CO
CH2CO
CH3CHO
CH3OH
CH3CH2OH
HCO2H
CH3CO2H
CH3OCH3
HOCO+
CєCCO
CN
HCN
HNC
N2H+
NH3
H2CN+NH2CN
CH2NH
CH3NH2
CH3CN
CH3CH2CN
H2C=CHCN
HCє CCN
H(CєC)2CN
H(CєC)3CN
H(CєC)4CN
H(CєC)5CN
CєCCN
H3CCєCCN
H3C(CєC)2CN
NO
HNO
HNCO
HOCN
NH2CHO
SO
SN
CS
H2S
SO2
OCS
HCS+
H2CS
CH3SH
HNCS
SiO
SiS
SiC2
SiH4

Fig. 1. Photograph of regular spatially periodic condensation of NH4Cl. Annular deposit structures produced during two-dimensional diffusion of NH3 in HCl vapor.


(9)

where p and T with appropriate indices are the initial and final equilibrium pressure and temperature, and ; DH is the change in enthalpy on sublunation and R is the universal gas constant.

Rapid sublimation of material begins at some distance from the Sun, and it then expands adiabatically. Adiabatic expansion is accompanied by cooling of the gas; the latter is supercooled in this case. Published relations for the adiabatic process were used in [7] to estimate the characteristic dimensions of the material condensation zones:

(10)

where Vad is the volume and is the heat capacity ratio.

If one solves Eqs. (9) and (10) jointly and specifies the supersaturation , one can estimate the ratio r2/r1 where r1 and r2, are the radii of successive zones of spherical (annular, etc.) structure formation. The process by which successive condensation zones are formed can be repeated so long as turbulent magnetohydrodynamic effects do not disturb the structure. It has been shown, for example, that only one or two condensed CO2 structures can be formed for s = 40 in a cometary atmosphere. Periodic structures consisting of H20 ice fogs can be formed in cometary atmospheres near the sun. The values of s for water in cometary atmospheres should apparently vary over the range 1-5, and instances in which several condensation zones develop are therefore possible. Comet Donati provides an example supporting the approximate model under consideration [15]. The comet put out five envelopes over the period covering 4 and 5 October 1858. Then-formation mechanism did not preclude condensation of material from the supersaturated state. The model under discussion can in principle be validated by putting artificial comets containing volatile components into earth orbits.

Figure I is a photograph of a system of periodic NH4Cl deposits produced (according to the data of (18]) during two-dimensional diffusion of NH3 in HCl vapor. The pattern depicted in this figure does not differ in its fundamentals from the phenomenon that should be observed on a large scale during formation of planetary and satellite systems, since there is no reason to believe that the classical mass transfer laws and concepts of condensation from the supersaturated state established under terrestrial conditions (12,19-21] are not satisfied over long time cycles and vast distances.

We will now turn to probable models of the chemical transformations that occur in different stages of planetary system formation. There can be many such models, since conditions for formation of such systems differ substantially in different parts of the universe. One illustration of the foregoing is the great variety of interstellar molecules that have now been detected and are present under different conditions in different systems. Thus, besides H2, He, and other inert gases, diffuse clouds, cold dense clouds, and stellar envelopes have been found to contain about 70 molecular and ionic species, extending through atomic number 13 [3,22,28] (see. e.g., Table 2). It should also be remarked that, as is well known, various hydrocarbons (CH4, C2H2, C2H6, etc.) have been detected in the planetary atmospheres of the Solar System, together with H2, He, NH3, PH3, CO, CO2, H2O, HCN, and so forth. The present survey will not attempt to cover all the multiplicity of chemical processes that occurred in material condensation during the early stages of formation of the Solar System [3 -5,23-28]. We will merely touch upon those reactions that probably could have been responsible for transport of heavy elements from the central Solar System to the periphery and formation of rings of condensed matter, followed by planets.

According to the theory being discussed here, appearance of primary rings is a consequence of chemical reaction of the substances in the cloud (N) and those from the central body (S) that diffuse into the cloud surrounding the planet. One necessary condition for condensation is supersaturation. This planetary formation mechanism should apparently bold for stars embedded in dark nebulae and going through the T body stage (there is reason to suppose that our Sun went through this stage at some point). It is not at all necessary for periodic condensation that the chemical composition of the central body gas phase and cloud differ: periodic condensation can also take place when there is a temperature gradient in the cloud. However, it is difficult to conceive of a case in which the compositions of the protostar gas envelope and cloud would be identical Thus, if we assume that stars of the Sun's type are formed as a result of gravitational compression of interstellar clouds, then gravitational separation of elements is possible during the collapse. The star formed can contain more heavy elements than the-surrounding cloud. In addition, the occurrence of nuclear reactions in stars can cause their composition to differ significantly from that of the clouds around them. As a consequence of the low cloud temperature, most of the heavy elements in the cloud can be in solid (dust) form even when the central body and cloud have the same overall composition.

As was noted above, many reported dense clouds contain such molecules as H2, He, CO, HCN, NH3, H2O, H2CO, SiO, H2S, etc., as well as a variety of ions and radicals; the principal cloud components are often H2, He, CO, and H2O. The CO concentration is far lower than the H2 or He concentration, but it is, as a rule, relatively high in comparison with that of other components. It can therefore be supposed that H2 and CO (or H2, CO, and H2O) play the major role in reactions. The H2 and CO in a cloud can be responsible for transporting virtually all heavy elements to the peripheral regions of a planetary system, in the form of hydrides and carbonyls. Elements emanating from a protostar react with one another in its vicinity to form volatile molecules [e.g., H2, CO, SiO, FeH, CH, SiH, FeHx(CO)y, etc.], which diffuse into the cloud. As diffusion proceeds in low-temperature zones, these molecules can react with the cloud material and be converted to new volatile particles, which diffuse further. Individual molecules that are thermodynamically stable under given conditions may not enter into further reactions with the cloud matter and, after attaining "supersaturation", condense to form primary rings. Diffusion of protostar material as a result of tandem transport reactions can thus be accompanied by a change in its nature. Despite the formation of various substances that are apparently characterized by different diffusion and supersaturation coefficients, the Titius-Bode rule is relatively well satisfied. This can probably be attributed to the fact that formation of primary rings is due primarily to reactions of several of the most common elements in the universe, e.g., Fe, Mg, S, Si, O, N, C, and H [23 -29] (see Table 3), to the fact that the change in the nature of the condensed material can be neglected, and to the fact that condensation zones with greater mass "absorb" small zones as they undergo conversion to planets (satellites).

Table 3
Abundance of Elements in the Cosmos

Element Relative abundance (by number of atoms)
H 1
He 0.14
C 3.75· 10-4
N 8.7· 10-5
O 4.4· 10-4
Ne 2.6· 10-5
Si 3.2· 10-5
S 1.4· 10-5
Fe 3.2· 10-5

It thus seems sensible to suppose that the basic initial processes might be formation of volatile hydrides, carbonyls, and carbonyl hydrides of iron- and magnesium-group elements, such as FeH and FeHn, (CO)m, type, together with carbonyl halohydrides and carbonyl halides of the Fe(CO)mF and Fe(CO)mCl type and compounds of the FeHn(CO)m(SiO)pHalr type, where the sum of n, m, p, and r can vary from 1 to 5. Formation of these substances is accompanied by evolution of heat (i.e., their synthesis at the low temperatures observed in the neighborhood of the Sun and in clouds is thermodynamically advantageous) and are stable in a hydrogen atmosphere. The same assumption can be made regarding similar compounds of other heavy elements (Cu, Ag, Au, Ca, Zn, Hg, etc.). If the concentrations of H, C, and Si in a cloud are sufficiently high, these compounds do not interact with O, since they react primarily with C, Si and H to form CO, SiO, OH(H2O), etc..

If the H2O content in a cloud is elevated (for example, it is believed [27,49] that H2O can be formed in space from H2 and CO by reactions of the Fisher-Tropsch type, nCO + (n + m/2)H2 ® CnHm + nH2O, which take place at high temperatures at catalysts, i.e., magnetite and hydrated silicates), then the compounds being transported can react with the water molecules to produce substances capable of condensing from the supersaturated state. If the cloud has a CO content higher than that in the protostar atmosphere and contains little H2O, then volatile hydrides, carbonyl hydrides, and carbonyl halohydrides of the FeH, FeHn(CO)m and Fe(CO)mHal types formed in the neighborhood of the protostar are converted to comparatively low-volatility carbonyls of the Fe(CO)mSiO type, which are capable for forming condensation zones. In clouds containing high concentrations of NO, NH3 and SiO, hydrides and carbonyl hydrides can be converted to compounds such as Fe(CO)3NO, Fe(CO)3NH3, FeH(CO)mSiO, etc. The model is thus applicable not only to actual cases where H2, CO, and H2O molecules predominate in the cloud, but also to hypothetical cases, when there is an excess of NH3 or NO molecules.

The model of heavy element transport that presumes formation of hydrides and carbonyl hydrides agrees with our conceptions of the composition of planetary and satellite cores. For example, reaction of compounds of the FeHn(CO)mSiO type with water leads to silicate formation. Moreover, after such substances condense and accumulate in solid form, they are converted to iron, silicates, and CO as a result of even slight warming. The hypothesis that metal carbonyls have played a substantial part in the chemical evolution of the Solar System [10] is supported by the results of [30] and [31], where one model of Triton was developed. The author of the latter study showed that this satellite of Neptune may consist of Fe2(CO)9 (91%) and CH4 (9%). It should be noted that one significant fact supporting the model under consideration for formation of the Solar System and other planetary systems is the existence of SNC meteorites, whose age is only 109 years.

The reactions of ions formed under the action of cosmic rays play an essential role in periodic condensation in cold dense clouds consisting basically of H2 He, CO, and SiO, since these are exothermal reactions with low activation energy [22,28]. If we assume the composition of the protostar to differ from that of the protocloud primarily in the amount of He (which is formed in the protostar as hydrogen is burned), this can lead to various reactions. Since the He+ ions formed under the action of cosmic rays (He + cosmic ray protons ® He+ + e- + protons') react slowly with H2, they are present in significant amounts in the cloud. As it has a strong affinity for electrons, He+ is capable of reacting with neutral particles, e.g. [22,29,32]:

He++CO® C++O+He

He++O2® O++O+He

He++N2® N++N+He

He++CN® C++N+He

He++N2® N2++He

He++SiO® Si++O+He

The active C+ and O particles formed can react with the cloud components to produce condensed compounds.

The general mechanisms of spatially periodic condensation can in principle extend to formation of galaxies, assuming that hydrogen and helium synthesis is possible not only in stars, but also from the "supersaturated" state in outer space by reactions of the type [13]:

We cannot preclude the possibility that the following reactions of gaseous compounds also played an important role under terrestrial conditions:

SiH4+2H2O® SiO2Ї +4H2

SiF4+2H2O® SiO2Ї +4HF

SiCl4+2H2O® SiO2Ї +4HCl

AlCl6+3H2O® Al2O3Ї +6HCl

Fe(CO)5+O2® Fe2O3Ї , CO, CO2

There is thus reason to believe that the cores of all the protoplanets in the Solar System (and certain other planetary systems) consist of metal/silicate material. If we assume typical temperatures in the perisolar disk to be in the range 100-200 K at a distance of 1 AU and 10-20K at a distance of 10 AU, we can draw the following conclusion [33]: compounds of metals and silicon condense in the regions of space where the terrestrial-group planets are located, while all substances except hydrogen and helium condense in the regions occupied by the outer planets. The hydrogen and helium subsequently undergo gravitational capture, mostly by the Jupiter-group planets. Gravitational warming of the planets, which leads to development of satellite systems, as in the case of the Sun, later promotes changes in protoplanet chemical composition.

The model of the physicochemical processes that have played a significant role at definite stages in the evolution of the Solar System considered here is undoubtedly oversimplified. Nevertheless, it makes it possible to determine the age of the planets and account for the Titius-Bode rule. According to our theories, the further a planet is from the sun, the younger it is. The model in question made it possible to predict the existence of rings in the satellite systems of young planets (Uranus, Neptune, and Jupiter) long before they were discovered, as well as individual features of the rings and satellite systems of Uranus, Neptune, and Triton that have been confirmed by data obtained with spacecraft [7].

Another interesting aspect of the evolution of chemicals in space is related to the development of chirality (optical activity). One important feature of chemical reactions in ultrararefied molecular protoclouds in space is the far stronger dependence of reaction mechanism on the presence of force fields (electrical, magnetic, and gravitational) than is the case under the conditions of the terrestrial lithosphere, which can promote formation of excesses of optically active substances having a definite orientation. We cannot preclude the possibility that optically active substances might have been generated during formation of the Solar System.

The optical activity of substances of biological origin is an inseparable property of life and is due to inclusion in biomolecules of only amino acid L-isomers and sugar D-isomers (or fragments). Many theories have been advanced to explain this phenomenon [34-47]. Evolutionary concepts assume gradual deracemization under the influence of some asymmetric advantage factor promoting accumulation of one isomer. The concept of spontaneous deracemization was advanced comparatively recently [43,44] and holds that chiral purity arose as a result of a spontaneous transition to the prebiological (chemical) stage of evolution. Spontaneous racemization subsequently occurred in inorganic nature, while chirality persisted in living organisms as a consequence of self-replication and survived as a memory of the state of the environment during the birth of life on Earth. It has been shown that polynucleotide self-replication can occur only in a chirally pure medium [45,46]. It has been hypothesized that life originates in cold dense interstellar clouds [47,48]. The effect of various asymmetric agents, including natural physical fields, radiations, and combinations thereof, and nonconservation of parity in weak interactions, has been discussed. It was shown in. [7,10] that the stereospecific action of such fields can be manifested to a far greater extent in ultrararified molecular clouds than under terrestrial conditions, since the energy of atomic and molecular thermal motion at ordinary temperatures (t ~ 300 K) is far greater than that of the orienting effect of natural asymmetric fields. Thus, the interaction with the relict radiation having a temperature T0=2.7K becomes decisive in dark clouds (the kinetic temperature characteristic of interstellar clouds can be quite high, Tk=100-200K). The low-temperature residual radiation is sometimes not capable of 'masking' the stereospecific action of sufficiently strong asymmetric fields.

The occupancy of molecular energy levels in ultrararified gases, where the pressure is extremely low, does not follow Boltzmann's law:

(11)

where nu and nl are the concentrations of molecules in the upper and lower levels of a given transition respectively, gu and gl are the statistical weights of the levels, n 0 is the transition frequency, h and k are the Planck and Boltzmann constants respectively, and Ts is the excitation temperature, which equals the kinetic temperature Tk of the ambient medium under conditions of thermodynamic equilibrium for all levels.

These deviations from local thermodynamic equilibrium are due to low medium density, with collision frequency being very small in comparison with the rate of spontaneous transitions. This causes the higher energy levels to be underpopulated. Moreover, conditions such that molecules react with one another not only in the electronic and vibrational ground states but even in rotational states are created in interstellar clouds [49].

According to the calculations made in [7], the Earth's magnetic field can have a perceptible effect only on nonrotating molecules. The proportion of nonrotating molecules oriented by the Earth's magnetic field is determined by the expression

(12)

where n(l) and n(2) are the concentrations of molecules oriented parallel and perpendicular to the field respectively, n is the total molecular concentration. A, B, and C are the molecular rotational constants, s ' is the number of physically indistinguishable molecular orientations, W is the orientation energy of a paramagnetic molecule in the Earth's field, and T is the molecular excitation temperature.

If we substitute T=300K into (12), we obtain [n(l)-n(2)]/n@ 10-9, so that the molecules are almost randomly oriented. When , the orientation becomes quite perceptible. A graphic example of the formation of optically active RCH(OH)CN molecules is the process

RCHO+HCN RCH(OH)CN,

which can occur in space.

Similar reactions in which L- or D-forms are generated can in principle take place not only when the reactant partides are oriented in collisions in the gaseous state, but also when one of the reactants is absorbed on an oriented solid particle and the other is in the gas phase. Moreover, interaction of two appropriate molecules adsorbed on oriented solid particles is possible in rarified clouds. However, the relative role of these mechanisms in the evolution of matter is unclear from the standpoint of the chirality problem. Neither can we overlook the influence exerted by electromagnetic fields in combination with the gravitational fields of sufficiently massive oriented structures on selection or differentiation of chemical substances during the course of evolution [7,50].

REFERENCES

  1. H.Alfven and G.Arrhenius, Evolution of the Solar System [Russian translation], Mir, Moscow, 1979.
  2. V.S.Safronov and A.V.Vitjazev, in: Chemistry and Physics of Terrestrial Planets, Springer-Verlag, N.Y., Berlin, Heidelberg, 1986, pp. 1-29.
  3. B.E.Turner and L.M.Zurus, in: Galactic and Extragalactic Radio Astronomy, Springer-Verlag, Berlin, Heidelberg, N.Y., 1988, pp. 200-254.
  4. H.Reeves (Editor), Origin of the Solar System [Russian translation], Mir, Moscow, 1976.
  5. A.G.W.Cameron, Space Sd. Revs., vol. 15, no. 1, pp. 121-146, 1973.
  6. L.Grossman and J.W.Larimer, Rev.Geophys. Space Phys., vol. 12, no. I, pp. 71-101, 1974.
  7. G.P.Gladyshev, Thermodynamics and Macrokinetics of Natural Hierarchic Processes [in Russian], Nauka, Moscow, 1988.
  8. G.P.Gladyshev, The Role of Physicochemical Processes in Formation of Planetary Systems [in Russian], IKhF AN SSSR, Chernogolovka, 1977.
  9. G.P.Gladyshev, Moon and Planets, vol. 18, no. 2, pp. 217-221, 1978.
  10. G.P.Gladyshev, Ibid., vol. 19, no. I, pp. 89-98.
  11. V.P.Budtov and G. P. Gladyshev, Ibid., vol. 20, no. 3, pp. 213-218, 1979.
  12. G.P.Gladyshev and V. P. Budtov, Ibid., voL 25, no. 4, pp. 413-425, 1981.
  13. G.P.Gladyshev, Condensation of Matter in the Universe [in Russian], Bash. fit AN SSSR, Ufa, 1982.
  14. J.Hirschfelder, C.Curtis, and R.Byrd, Molecular Theory of Gases and Liquids [Russian translation], Mir, Moscow, 1961.
  15. F.L.Whipple, in: Comets and the Origin of Life [Russian translation], Mir, Moscow, 1984, pp. 9—28.
  16. See [15], pp. 96-108.
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  18. V.N.Gorshenev and G. P. Gladyshev, Zh. fiz. khirnii, voL 55, no. II, pp. 2897-2903, 1981.
  19. R.R.Rogers, Short Course in Cloud Physics [Russian translation], Gidrometeoizdat, Leningrad, 1979.
  20. A.M.Borovikov, I.I.Gaivoronskii, E. G. Zak, et al„ Cloud Physics [m Russian], Gidrometeoizdat, Leningrad, 1961.
  21. A.G.Amelin, Theoretical Principles of Nebula Formation [in Russian], Khimiya, Moscow, 1972.
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  23. J.S.Lewis, Icarus, vol. 16, no. 2, pp. 241-253, 1972.
  24. J.S.Lewis, Annu. Rev. Phys. Chem., vol. 24, pp. 339-351, 1973.
  25. S.K.Saxena and G. Eriksson, see [2], pp. 30-105.
  26. G.V.Voitkevich, Problems in Cosmochemistry [in Russian], lzd-vo Rost. u-ta, Rostov, 1987.
  27. G.V.Voitkevich, Foundations of a Theory of the Origin of Earth [in Russian], Nedra, Moscow, 1988.
  28. H.E.Suess, Chemistry of the Solar System: an Elementary Introduction to Cosmochemistry, Wiley, N.Y., 1987.
  29. E.Herbst and W.Klemperer, Astrophys. J„ vol. 185, pp. 505-533, 1973.
  30. G.H.A.Cole, Geophys. J. Roy. Soc. Astron. Soc., vol. 77, pp. 549-557, 1984.
  31. V.Celebonovic, Earth, Moon and Planets, vol. 34, no. I, pp. 59-63, 1984.
  32. J.L.Turner and A.Dalgarno, Astrophys. J„ vol. 213, pp. 386-389, 1977.
  33. See [4], pp. 107-115.
  34. I.Idsumi and A.Tai, Stereodifferentiating Reactions [Russian translation], Mir, Moscow, 1979.
  35. M.Calvin, Chemical Evolution [Russian translation], Mir, Moscow, 1971.
  36. M.Rutten, Origin of Life [Russian translation], Mir, Moscow, 1973.
  37. S.Fox and K.Dose, Molecular Evolution and the Origins of Life [Russian translation], Mir, Moscow,
  38. E.Broda, Evolution of Bioenergetic Processes [Russian translation], Mir, Moscow, 1978.
  39. W.Thiemann, Naturwissenshaften, voL 61, pp. 476-483, 1974.
  40. W.Thiemann. Orig. Life, voL II, no. I, pp. 187-190, 1981.
  41. W.L.Keszthelyi, Ibid., p. 191.
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  43. L.L.Morozov, Orig. Life, voL 9, no. 3, pp. 187-217, 1979.
  44. V.I.Gol'danskii and V.V.Kuz'min, Uspekhi fiz. nauk, voL 157, no. I, pp. 3-50, 1989.
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  46. V.I.Gol'danskii, V.A.Avetisov, and V.V.Kuz'min, Ibid., vol. 190, no. 3, pp. 734-738, 1986.
  47. F.Hoyle and N.C.Wickramasinghe, Lifedoud. The Origin of Life in the Universe, J. M. Dent and Sons LTD, London, Toronto, Melbourne, 1978.
  48. V.I.Gol'danskii, Nature, voL 279, no. 5709, pp. 109-115, 1979.
  49. B.E.Turner, in: Galactic and Extragalactic Radio Astronomy, Springer-Verlag, Berlin, Heidelberg, N.Y., 1974, pp. 303-399.
  50. G.P.Gladyshev, Yu.B.Monakov, A.A.Berg, and V.P.Grigor'eva, On Radical Initiator Decay in an Ultracentrifuge Field [in Russian], Bash. filial AN SSSR, Ufa, 1981.

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