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Ionized gas and fast electrons in the vicinity of the earth and in interplanetary space
ARTIFICIAL EARTH SATELLITES U.S.S.R.
(LSKUSSTVENNYE SPUTNIKI ZEMLI) (PUBLISHED BY THE U.S.S.R. ACADEMY MOSCOW)
OF SCIENCES
Translations of any papers abstracted here may be obtained from Pergamon Institute at a reasonable cost. Enquiries should be addressed to the Administrative Secretary, Pergamon Institute, at either Headington Hill Hall, Oxford, England, or 122 East 55th Street, New York, N.Y., U.S.A.
IONIZED GAS AND FAST ELECTRONS IN THE VICINITY OF THE EAR.TH AND IN INTERPLANETARY SPACE* K. I. GRINGAWZ, V. G. KURT, V. I. MOROZ and I. S. SI-IKLQVSKIL @ranslated by R. kI~?-x'ww9 from Z~~~~~~ye
Spmtiki Zedi, No. 6, p. 108 (1961).
A study of experimental material obtained during the flight of the second Soviet space rocket(l) has shown that the first half of its trajectory can be split up into four sections: 1. The section up to R = 22,000 km (R being the distance from the earth% s&ace), where in all the traps with negative and zero potential, appreciable positive collector currents were recorded whilst in the trap with a potential + 15 V relative to the body there are either small negative currents or currents equal to zero; 2. A section 22,000 km < R < 50,000 km where the collector currents of all the traps flu~uate between zero and certain negative values (I&< 6 x 10-10A); 3. A section 50,000 km c R < 70,000 km where in all the traps there are simultaneously negative currents, the largest recorded in absolute value being 10-gA and the smallest 3 x w*A; 4. The section R > 70,000 km where the currents of all the traps fluctuate between zero values and values around -(5-6) x lW1*A, which evidently determine the maximum photocurrent from the inner grid to the collector. The overall picture of the results agrees for all three flights of the Soviet space rockets. For evaluating ion concentration from the collector-current measurement-data of the traps, substantial importance attaches to a knowledge of the electrical potential of the container relative to the medium, depending on a number of factors including the highenergy electron flux N, in the second radiation belt, the radiation maximum of which is located, of course, at distances from the earth corresponding to our first section. Important conclusions regarding the value N, can be drawn from the current-measurement data in three-electrode traps. From this standpoint particular interest is afforded by an analysis of current variations in the “f15 V”’trap. If the plasma temperature is not too high (2’ I 105OK)then positive ions obviously cannot hit the trap. However, electron fluxes with energy E ;b 200 eV must be recorded in this trap. Assuming evaluations of electron fluxes with energy E > 20 keV in the zone of the outer radiation belt maximum in the order of W-1011 cm-s/s(B-a)then the currents in the “+S V” trap must be in the order of 5 x 10-S-5 x 10-s A. At the same time on the Grst section the negative currents in this trap (after deducting the photocurrent from the inner grid) do not exceed 1 x lo-X*A. It thus follows that the upper electron-flux limit with energy E > 200 eV in the zone of the outer radiation belt must be N, 5: 2 x 10’ cm-*/s (N, being the flux per 1 ems in the hemisphere). The attempt may be made to attribute the absence of large negative currents in the “+ 15 V’”trap in the outer radiation belt maximum by assuming a considerable secondary electron emission from the collector under the action of bombardment of the collector by electrons of the radiation belt. However, secondary electrons cannot possess suffioient * F&atpublished in Dokl. Akad. Mtuk SSSR, 132,1062 (1960). 21
22
K. I. GRINGAUZ,
V. G. KURT, V. I. MOROZ AND I. S. SHKLOVSKII
energy for overcoming the retarding field existing between the inner grid of the trap and the collector. In the same way the small negative currents in the “+ 15 v” trap on passing through the outer radiation belt maximum cannot be explained on the basis of “radiation” electron current compensation by the positive-ion current of the plasma at the high negative potential of the container body. This could be subject to the considerable radiation electron current on the container body. However a study of the relationship of the “+ 15 V” trap current to N, for any plasma density shows that such compensation is impossible for the given trap. Fig. 1 shows an example of this relationship for n, = 108cm -s. For N, --+ 00 the negative trap current ZR+ &S, where ie is the photocurrent density from the container surface, and S is the cross-section of the trap. The photocurrent density assumed je = 2.5 x lo-lo A cm-s is rather underestimated than exaggerated. For the “0 V” traps (in addition to the “-5 V”) compensation is possible, as seen in Fig. 1, only for some completely determinate relationship n, and N, that is to say only over a small section of the trajectory, since the characteristics of the plasma and radiation electron flux (determining the container potential) vary over wide ranges and independently. In actual fact the current readings for all the traps are practically insensitive to entry into the zone of the outer radiation belt.
IO’
IO’
IO’
N,, FlQ. 1. CoLLmzmll v Cp(mm
10’0
IO”
cmw2/src
Ia OF TRAPS WlTH pg, = o(cuRw1),~~*= 3) A!3A FUNcnoN OF RADIATION BLSCI’RDN FLJJX N, Jr, = 10’ cm-a.
t2uRRmm
+15v(cuRvE2)ANDcoNTAINER WITH PLASMA ION CONCLWIXU~ON
The small “+I5 V” trap currents on the first section of the trajectory yield only one conclusion: the electron fluxes with energy greater than 200 eV in the zone of the outer radiation belt do not exceed 2 x 107cm-*/s. This result substantially contradicts the concept of large electron fluxes with E w 20-30 keV in the outer radiation belt maximum. The observed counting rate in the experiments(&6) was explained, by the authors, on the basis of the X-ray emission flux, occurring in the container body and in the counter screens under the action of relatively soft electrons (E RSJ20-30 kev). As proposed by us, the observed counting rate must be due to the considerably smaller fluxes of substantially
IoNlzED
GAS AND FAST ELECTRONS
23
with this the eiedrm kinetic energydensity in the outer harder eiectrm. (Ibmmtd radiathn belt maximum mustbe sewrd orders of magnitu& iess than the ge tic
Bald enemy density whilst the ~~ &ld strength ~~ observed at the altitude 14,000kssP is obviously not associated with diamagnetism of high-energy electrous in the radiation belt. In the range 50,000 < R < 70,000km the negative currents of all the traps, ~oun~g to IO-@ A, can be due only to electron fluxes witb energy E > 200 eV N, M W-2 x 108cm-s/s. Since in the zone of the second radiation belt N, < 2 x 10Tcm-*/s we arrive at the concept of a third ou~ost belt (or blanket), consisting of relatively low-energy electrons. The fact that earlier ex~~e~~ did not detect this outermost belt may be due to its very small content of relatively high-energy electrons (E ;rr 100 kev).
b.
2. EhAW
SHOWlNi3 THB PCSMlON OF TH3 RADXATION EELTS. I--“~” %--THIRD BELT; h-G3KMAWEllC JiQUAWXt.
BELT;
2-"OU'IlZR" BELT;
Figure 2 illustrates the space distribution of the radiation belts su~o~~g the earth as proposed by us, taking account of the recent results set out above. The outer limit of the third belt is drawn along the lines of force of the ma~etic Beld, as was done for the fhst and second belt&@. Measurement results obtained on the first Soviet space rocket (coming less i~$ormation) give grounds to assume that the inner limit of the third belt was lower (R w 30,000km) on the 2 Jamrary 1959. It is observed that according to exigent carried out on the third Soviet artificial satellite at relatively low altitudes (R = 1800km) above the temperate geomagnetic latitudes, electron fiuxes with energy E cw10keV were directly recorded amounting to 3 x 10scm-* s-l. This may sign@ that the so~-el~~ ~on~en~tion has a turn in the zone of the radiation belts. However, account has to be taken of the fact that the experimentc8)was not performed piteously with that described in the present communication. It can be shown that, with such small electron fluxes in the radiation belts as indicated above, they do not exert any influence on the potential of the body of the rocket, which is determ@d by the photo-effect from ultra-violet solar radiation and plasma currents. Calculations show that under t&se argons the potential of the body dBbrs from zero by not more then a few volts if the plasma ion concentration n, zr 10 cm4 and its temperature are not too high (fm example, T = I@ “IQ.
24
K. 1.GRINGAUZ, V. Gi. KURT, V. I. MOROZ AND I. S, SHKLOVSKII
The plasma ion concentration can be evaluated q~nti~tively from the indications of the trap with zero potential on the Brst section of the tmjeetory. The wide dispersion ~~~u~tion”) of the current indications of traps with zero and negative potential is due mainly to the effect of variation in the orientation of the traps with respect to the velocity vector of the container during its rotation. IO’
10
IO’
-r
i
!b
I
IO’ -1
I I
IO
I 0
/
t
20000
10,000 R.
6
3oc)oo
km
FIGS. 3. ION CXhN CBNTRATlON IQ AS A FUNOF DISTANCE R TO THE BARTH% SURFACIL l-th~reti~l distribution for T = 1.8 x 10’ OK; 2,3,4-results of exprimanta with 2’ ual respectively to 1.8 x lo*, 10‘; 5 x 10” OK; points Q and b correapd to meaauremen taataltitudea4 1 @andWkm (third artifkial earth satellite).
Assuming the plasma ions to be protons (for which there are sound bases) then their thermal velocities are near to the container velocity. The results of calculations depend on the plasma temperature assumed. Fig. 3 shows nt as a function of R for plasma ~m~ratures T = 14 x 10s; lo” and 5 x 104“K (higher ~rn~rat~es are excluded in any case for R < 10,000km since they contradict the observed modulation depth). These eval~tions were carried out for maximum currents in order as far as possible to be free from the effect of variation in trap orientation. However, as can be deducted from a study of the curves of Fig. 3 in the paper of, the errors in ~on~n~tion associated with insutlicient regard for this e&t can reach a considerable value; an error with a factor of 2, for example, is quite possible. It follows from Fig. 3 that the ~vestiga~d plasma is not ~~~e~y ionized gas. This is an extensive blanket being an ionized component of the outermost section of the earth’s atmosphere, the so-called geocorona. Attention is drawn to the marked increase in the density gradient of the “geocorona” plasma starting from R w 15,000km, whilst at smaller distances the &n&y varies only stightly. It is significant that the current drop in all the traps points to a sharp “break” in density and therefore it cannot be due to errors on account of orientation. It is quite natural that the currents firlloff diRerently in the different traps &XX,to the effect associated with the actual ~n~n~~on variation, there is added the effect of orientation and of the outer grid potential. Figure 3 shows the theoretical curve (1) for the relative ~~bution of hydrogen plasma
IONIZED GAS AND FAST ELBCI-RONS
25
T = 1800°K obtained from the barometric equation taking into account of the layers, Comparison of the theoretical curve with experimental results shows that the observed slight gradient of the “geocorona” plasma concentration (for R < 15,000 km) can be readily explained whilst the “break” in the concentration n,, starting in the vicinity of R a~15,000 km, requires special analysis. This question will be considered separately. If the geocorona plasma is considered nitrogen-oxygen, then the concentration would vary slightly as compared with Fig. 3. To explain the section of the curve with small gradient requires a temperature T PW15,OOO”K. It is observed that the phenomenon of the increased gradient would remain also for a higher assumed photocurrent density from the container (for example j, w 2 x lO_@A cm-*) and only at a distance in the order of 20,~22,~ km would the concentration evaluation rise to R$M 100 cm*. For distances R > 22,000 km only the upper limit n, can be evalusted. This is within assumed for the medium. the range 30-60 cm A depending on the different chara&risti~ This value is certainly below the upper limit {600 cm+) found from rn~~rnen~ of zodiacal light polarization (for examplefl*)). Hence it can be concluded that the polarixed component of zodiacal light is due to the scattering of sunlight on dust particles and not on free electrons as proposed by Bebr and Si~entopf(lo). V. G. Fesenkovor) and Van de HukMs) have shown that polarkation of the dust component can be quite high.
concentration with
curvature
REPERENCES 1. K. I. GRINAUZ, V. V. B~UK~KH, V. D. OZEROV,and R. E. R131, 1301 (1960). Isk. Sput. ZemZi, present issue. p. 101.
mr, Dokl. Akc-td.N&c. SSSR.,
2. S. N. VBRNOV,A. E. Cmmicov, P. V. VAKULOV,Yu. I. bGACHEW, Doki. Akad. Nauk. SSSR. 125, 304 (1959). 3. J. A. VAN ALJ..KN and L. A. ERANK,Nature (Land.), 183,430 (1959). 4. C. N. VERNOV,A. E. CHUCUKOV, Dokl. Akad. N&. SSSR., 130,517 (1960). 5. J. A. VAN ALLZNand L. A. FRANK,Nature &wad.). 184,219 (1959). 6. J. A. VAN AL=, C. E. Mc1~w.m; G. H. L&WI& J. t%oph.‘Res.~ 64,271 (1959). 7. S. SH. DCXGINOVand N. V. Pusmcov. Dokl. Akad. Nauk SSSR.. 129.77 0959). 8. iC I. KRASOWWI, I. S. SHKLOVSKU, Y<. I. GAL’P~UNand E. M. &J&T&, Doicr. Akad. Nauk. SSSR., 127,78 (1959). 9. K. I. GRINOAUZ,Dokl. Akad. N&t&. SSSR, 120, 1234 (1958); Isk. Spur. Zemii, No. 1, p. 62 (1958). 10. A. BBHRand H. SJEDBNTOPF, 2. Astrophys., 32, 19 (1953). 11. V. G. PBsBNRov,Astron. Z/I., 35, 513 (1958). 12. H. C. VAN DE HUIAT,Light Scattering by Small Particles, London (1957).
(LSKUSSTVENNYE SPUTNIKI ZEMLI) (PUBLISHED BY THE U.S.S.R. ACADEMY MOSCOW)
OF SCIENCES
Translations of any papers abstracted here may be obtained from Pergamon Institute at a reasonable cost. Enquiries should be addressed to the Administrative Secretary, Pergamon Institute, at either Headington Hill Hall, Oxford, England, or 122 East 55th Street, New York, N.Y., U.S.A.
IONIZED GAS AND FAST ELECTRONS IN THE VICINITY OF THE EAR.TH AND IN INTERPLANETARY SPACE* K. I. GRINGAWZ, V. G. KURT, V. I. MOROZ and I. S. SI-IKLQVSKIL @ranslated by R. kI~?-x'ww9 from Z~~~~~~ye
Spmtiki Zedi, No. 6, p. 108 (1961).
A study of experimental material obtained during the flight of the second Soviet space rocket(l) has shown that the first half of its trajectory can be split up into four sections: 1. The section up to R = 22,000 km (R being the distance from the earth% s&ace), where in all the traps with negative and zero potential, appreciable positive collector currents were recorded whilst in the trap with a potential + 15 V relative to the body there are either small negative currents or currents equal to zero; 2. A section 22,000 km < R < 50,000 km where the collector currents of all the traps flu~uate between zero and certain negative values (I&< 6 x 10-10A); 3. A section 50,000 km c R < 70,000 km where in all the traps there are simultaneously negative currents, the largest recorded in absolute value being 10-gA and the smallest 3 x w*A; 4. The section R > 70,000 km where the currents of all the traps fluctuate between zero values and values around -(5-6) x lW1*A, which evidently determine the maximum photocurrent from the inner grid to the collector. The overall picture of the results agrees for all three flights of the Soviet space rockets. For evaluating ion concentration from the collector-current measurement-data of the traps, substantial importance attaches to a knowledge of the electrical potential of the container relative to the medium, depending on a number of factors including the highenergy electron flux N, in the second radiation belt, the radiation maximum of which is located, of course, at distances from the earth corresponding to our first section. Important conclusions regarding the value N, can be drawn from the current-measurement data in three-electrode traps. From this standpoint particular interest is afforded by an analysis of current variations in the “f15 V”’trap. If the plasma temperature is not too high (2’ I 105OK)then positive ions obviously cannot hit the trap. However, electron fluxes with energy E ;b 200 eV must be recorded in this trap. Assuming evaluations of electron fluxes with energy E > 20 keV in the zone of the outer radiation belt maximum in the order of W-1011 cm-s/s(B-a)then the currents in the “+S V” trap must be in the order of 5 x 10-S-5 x 10-s A. At the same time on the Grst section the negative currents in this trap (after deducting the photocurrent from the inner grid) do not exceed 1 x lo-X*A. It thus follows that the upper electron-flux limit with energy E > 200 eV in the zone of the outer radiation belt must be N, 5: 2 x 10’ cm-*/s (N, being the flux per 1 ems in the hemisphere). The attempt may be made to attribute the absence of large negative currents in the “+ 15 V’”trap in the outer radiation belt maximum by assuming a considerable secondary electron emission from the collector under the action of bombardment of the collector by electrons of the radiation belt. However, secondary electrons cannot possess suffioient * F&atpublished in Dokl. Akad. Mtuk SSSR, 132,1062 (1960). 21
22
K. I. GRINGAUZ,
V. G. KURT, V. I. MOROZ AND I. S. SHKLOVSKII
energy for overcoming the retarding field existing between the inner grid of the trap and the collector. In the same way the small negative currents in the “+ 15 v” trap on passing through the outer radiation belt maximum cannot be explained on the basis of “radiation” electron current compensation by the positive-ion current of the plasma at the high negative potential of the container body. This could be subject to the considerable radiation electron current on the container body. However a study of the relationship of the “+ 15 V” trap current to N, for any plasma density shows that such compensation is impossible for the given trap. Fig. 1 shows an example of this relationship for n, = 108cm -s. For N, --+ 00 the negative trap current ZR+ &S, where ie is the photocurrent density from the container surface, and S is the cross-section of the trap. The photocurrent density assumed je = 2.5 x lo-lo A cm-s is rather underestimated than exaggerated. For the “0 V” traps (in addition to the “-5 V”) compensation is possible, as seen in Fig. 1, only for some completely determinate relationship n, and N, that is to say only over a small section of the trajectory, since the characteristics of the plasma and radiation electron flux (determining the container potential) vary over wide ranges and independently. In actual fact the current readings for all the traps are practically insensitive to entry into the zone of the outer radiation belt.
IO’
IO’
IO’
N,, FlQ. 1. CoLLmzmll v Cp(mm
10’0
IO”
cmw2/src
Ia OF TRAPS WlTH pg, = o(cuRw1),~~*= 3) A!3A FUNcnoN OF RADIATION BLSCI’RDN FLJJX N, Jr, = 10’ cm-a.
t2uRRmm
+15v(cuRvE2)ANDcoNTAINER WITH PLASMA ION CONCLWIXU~ON
The small “+I5 V” trap currents on the first section of the trajectory yield only one conclusion: the electron fluxes with energy greater than 200 eV in the zone of the outer radiation belt do not exceed 2 x 107cm-*/s. This result substantially contradicts the concept of large electron fluxes with E w 20-30 keV in the outer radiation belt maximum. The observed counting rate in the experiments(&6) was explained, by the authors, on the basis of the X-ray emission flux, occurring in the container body and in the counter screens under the action of relatively soft electrons (E RSJ20-30 kev). As proposed by us, the observed counting rate must be due to the considerably smaller fluxes of substantially
IoNlzED
GAS AND FAST ELECTRONS
23
with this the eiedrm kinetic energydensity in the outer harder eiectrm. (Ibmmtd radiathn belt maximum mustbe sewrd orders of magnitu& iess than the ge tic
Bald enemy density whilst the ~~ &ld strength ~~ observed at the altitude 14,000kssP is obviously not associated with diamagnetism of high-energy electrous in the radiation belt. In the range 50,000 < R < 70,000km the negative currents of all the traps, ~oun~g to IO-@ A, can be due only to electron fluxes witb energy E > 200 eV N, M W-2 x 108cm-s/s. Since in the zone of the second radiation belt N, < 2 x 10Tcm-*/s we arrive at the concept of a third ou~ost belt (or blanket), consisting of relatively low-energy electrons. The fact that earlier ex~~e~~ did not detect this outermost belt may be due to its very small content of relatively high-energy electrons (E ;rr 100 kev).
b.
2. EhAW
SHOWlNi3 THB PCSMlON OF TH3 RADXATION EELTS. I--“~” %--THIRD BELT; h-G3KMAWEllC JiQUAWXt.
BELT;
2-"OU'IlZR" BELT;
Figure 2 illustrates the space distribution of the radiation belts su~o~~g the earth as proposed by us, taking account of the recent results set out above. The outer limit of the third belt is drawn along the lines of force of the ma~etic Beld, as was done for the fhst and second belt&@. Measurement results obtained on the first Soviet space rocket (coming less i~$ormation) give grounds to assume that the inner limit of the third belt was lower (R w 30,000km) on the 2 Jamrary 1959. It is observed that according to exigent carried out on the third Soviet artificial satellite at relatively low altitudes (R = 1800km) above the temperate geomagnetic latitudes, electron fiuxes with energy E cw10keV were directly recorded amounting to 3 x 10scm-* s-l. This may sign@ that the so~-el~~ ~on~en~tion has a turn in the zone of the radiation belts. However, account has to be taken of the fact that the experimentc8)was not performed piteously with that described in the present communication. It can be shown that, with such small electron fluxes in the radiation belts as indicated above, they do not exert any influence on the potential of the body of the rocket, which is determ@d by the photo-effect from ultra-violet solar radiation and plasma currents. Calculations show that under t&se argons the potential of the body dBbrs from zero by not more then a few volts if the plasma ion concentration n, zr 10 cm4 and its temperature are not too high (fm example, T = I@ “IQ.
24
K. 1.GRINGAUZ, V. Gi. KURT, V. I. MOROZ AND I. S, SHKLOVSKII
The plasma ion concentration can be evaluated q~nti~tively from the indications of the trap with zero potential on the Brst section of the tmjeetory. The wide dispersion ~~~u~tion”) of the current indications of traps with zero and negative potential is due mainly to the effect of variation in the orientation of the traps with respect to the velocity vector of the container during its rotation. IO’
10
IO’
-r
i
!b
I
IO’ -1
I I
IO
I 0
/
t
20000
10,000 R.
6
3oc)oo
km
FIGS. 3. ION CXhN CBNTRATlON IQ AS A FUNOF DISTANCE R TO THE BARTH% SURFACIL l-th~reti~l distribution for T = 1.8 x 10’ OK; 2,3,4-results of exprimanta with 2’ ual respectively to 1.8 x lo*, 10‘; 5 x 10” OK; points Q and b correapd to meaauremen taataltitudea4 1 @andWkm (third artifkial earth satellite).
Assuming the plasma ions to be protons (for which there are sound bases) then their thermal velocities are near to the container velocity. The results of calculations depend on the plasma temperature assumed. Fig. 3 shows nt as a function of R for plasma ~m~ratures T = 14 x 10s; lo” and 5 x 104“K (higher ~rn~rat~es are excluded in any case for R < 10,000km since they contradict the observed modulation depth). These eval~tions were carried out for maximum currents in order as far as possible to be free from the effect of variation in trap orientation. However, as can be deducted from a study of the curves of Fig. 3 in the paper of, the errors in ~on~n~tion associated with insutlicient regard for this e&t can reach a considerable value; an error with a factor of 2, for example, is quite possible. It follows from Fig. 3 that the ~vestiga~d plasma is not ~~~e~y ionized gas. This is an extensive blanket being an ionized component of the outermost section of the earth’s atmosphere, the so-called geocorona. Attention is drawn to the marked increase in the density gradient of the “geocorona” plasma starting from R w 15,000km, whilst at smaller distances the &n&y varies only stightly. It is significant that the current drop in all the traps points to a sharp “break” in density and therefore it cannot be due to errors on account of orientation. It is quite natural that the currents firlloff diRerently in the different traps &XX,to the effect associated with the actual ~n~n~~on variation, there is added the effect of orientation and of the outer grid potential. Figure 3 shows the theoretical curve (1) for the relative ~~bution of hydrogen plasma
IONIZED GAS AND FAST ELBCI-RONS
25
T = 1800°K obtained from the barometric equation taking into account of the layers, Comparison of the theoretical curve with experimental results shows that the observed slight gradient of the “geocorona” plasma concentration (for R < 15,000 km) can be readily explained whilst the “break” in the concentration n,, starting in the vicinity of R a~15,000 km, requires special analysis. This question will be considered separately. If the geocorona plasma is considered nitrogen-oxygen, then the concentration would vary slightly as compared with Fig. 3. To explain the section of the curve with small gradient requires a temperature T PW15,OOO”K. It is observed that the phenomenon of the increased gradient would remain also for a higher assumed photocurrent density from the container (for example j, w 2 x lO_@A cm-*) and only at a distance in the order of 20,~22,~ km would the concentration evaluation rise to R$M 100 cm*. For distances R > 22,000 km only the upper limit n, can be evalusted. This is within assumed for the medium. the range 30-60 cm A depending on the different chara&risti~ This value is certainly below the upper limit {600 cm+) found from rn~~rnen~ of zodiacal light polarization (for examplefl*)). Hence it can be concluded that the polarixed component of zodiacal light is due to the scattering of sunlight on dust particles and not on free electrons as proposed by Bebr and Si~entopf(lo). V. G. Fesenkovor) and Van de HukMs) have shown that polarkation of the dust component can be quite high.
concentration with
curvature
REPERENCES 1. K. I. GRINAUZ, V. V. B~UK~KH, V. D. OZEROV,and R. E. R131, 1301 (1960). Isk. Sput. ZemZi, present issue. p. 101.
mr, Dokl. Akc-td.N&c. SSSR.,
2. S. N. VBRNOV,A. E. Cmmicov, P. V. VAKULOV,Yu. I. bGACHEW, Doki. Akad. Nauk. SSSR. 125, 304 (1959). 3. J. A. VAN ALJ..KN and L. A. ERANK,Nature (Land.), 183,430 (1959). 4. C. N. VERNOV,A. E. CHUCUKOV, Dokl. Akad. N&. SSSR., 130,517 (1960). 5. J. A. VAN ALLZNand L. A. FRANK,Nature &wad.). 184,219 (1959). 6. J. A. VAN AL=, C. E. Mc1~w.m; G. H. L&WI& J. t%oph.‘Res.~ 64,271 (1959). 7. S. SH. DCXGINOVand N. V. Pusmcov. Dokl. Akad. Nauk SSSR.. 129.77 0959). 8. iC I. KRASOWWI, I. S. SHKLOVSKU, Y<. I. GAL’P~UNand E. M. &J&T&, Doicr. Akad. Nauk. SSSR., 127,78 (1959). 9. K. I. GRINOAUZ,Dokl. Akad. N&t&. SSSR, 120, 1234 (1958); Isk. Spur. Zemii, No. 1, p. 62 (1958). 10. A. BBHRand H. SJEDBNTOPF, 2. Astrophys., 32, 19 (1953). 11. V. G. PBsBNRov,Astron. Z/I., 35, 513 (1958). 12. H. C. VAN DE HUIAT,Light Scattering by Small Particles, London (1957).