STUDY OF THE SOLID COMPONENT OF INTERPLANETARY MATTER USING ROCKETS AND ARTIFICIAL EARTH SATELLITES

S. M. Poloskov, T. N. Nazarova

The study of meteoric matter entering the Earth’s atmosphere from interplanetary space was formerly always regarded as an astronomical problem. At present it has become clear that investigation of this question is of great interest for geophysics (clarifying the role of meteoric particles in physical processes occurring in the atmosphere, in particular in the formation of the sporadic layer \(E\), noctilucent clouds, atmospheric luminescence, etc.), and also for certain problems of an applied nature, in particular for problems connected with studying the conditions of motion, in the high layers of the atmosphere, of rockets and artificial Earth satellites. The most urgent problems that must be solved at the first stage of research are the following:

1. Determination of the flux of meteoric particles.
2. Study of the spectrum of their energies. It would be very important to decode the energy spectrum of particles in the flux, determining separately the mass spectrum and the velocity spectrum.

Investigation of the solid component of interplanetary matter is carried out by direct methods (with the aid of rockets) and by indirect methods. Among the indirect methods we shall include astronomical methods of studying meteoric bodies entering the Earth’s atmosphere from interplanetary space, as well as various methods of studying meteoric matter falling onto the surface of the Earth.

The information on the solid component of interplanetary matter that we currently possess has been obtained by indirect methods. It must be said in advance, however, that at present there are no data that are in any way satisfactory. Data obtained by different methods and by different authors agree poorly with one another. Reliable data, apparently, can be obtained only by direct methods: with the aid of rockets, and especially with the aid of artificial Earth satellites remaining for a long time in the upper atmosphere. At present, however, only isolated data have been obtained by direct methods. The available information cannot answer the questions posed above, which gives rise to the urgent necessity of formulating this problem as one of the scientific tasks for rocket research.

1. DETERMINATION OF THE FLUX OF METEORIC PARTICLES

Data on the solid component of interplanetary matter may be obtained by: a) observations of the outer corona of the Sun (the so-called Fraunhofer component of the outer corona), the gegenschein, and zodiacal light; b) observations of meteors; c) study of meteoric matter falling onto the surface of the Earth.

a) Study of the Fraunhofer component
of the outer solar corona, counterglow
and zodiacal light

The data obtained from these observations have the common shortcoming that they do not make it possible to draw reliable conclusions about the concentration of interplanetary dust in the Earth’s orbit. For example, it is very difficult to separate, in the zodiacal glow, the component introduced by scattering on solid particles from the component due to scattering on free electrons.

Earlier it was assumed that only electrons are responsible for the polarization, and the electron concentration was determined from the degree of polarization. However, Van de Hulst showed^1 that the polarization due to solid particles will be of the same order (about 20%) as the polarization produced by electrons.

On the basis of study of the outer corona and zodiacal light, the density of the solid component at a distance from the Sun equal to the radius of the Earth’s orbit is estimated as \(10^{-23} \leqslant \rho \leqslant 10^{-21}\ \mathrm{g/cm^3}\), and this estimate, as has already been said, is very uncertain.

A number of researchers^1,2 obtained contradictory data on the spatial density of dusty matter in the neighborhood of the Earth’s orbit on the basis of photometric studies of the \(F\)-component of the solar corona. Thus, Van de Hulst^1 estimated the volume density of the meteoric cloud surrounding the Sun, \(\rho\), at \(5\cdot 10^{-21}\ \mathrm{g/cm^3}\), assuming that the density of the particles is \(5\ \mathrm{g/cm^3}\). On the basis of photometric data and the theory of light scattering by dust, Van de Hulst found the distribution function of particles in the cloud according to their sizes. This function has the form

\[ n(a)=Ca^{-2,6}, \tag{1} \]

where \(a\) is the particle radius, \(C\) is a constant. It is assumed here that the albedo of the particles is 0.1, that there are fewer particles with sizes greater than \(1\ \mathrm{mm}\) than follows from formula (1), and that \(C \sim 10^{-20}\) at \(r=1\) astronomical unit (the Earth’s orbit) and \(C \sim 5\cdot 10^{-20}\) at \(r=\tfrac12\) a.u.

Table I

The mean free path, according to Van de Hulst, for interplanetary particles is \(10^6\) a.u. The thickness of the meteoric cloud in a direction perpendicular to the ecliptic is 0.1 a.u., and therefore the mass of particles within the Earth’s orbit amounts to only \(5\cdot 10^{18}\ \mathrm{g}\), i.e. is equal to the mass of a large comet and is a billion times smaller than the mass of the Earth.

According to Van Rijn’s estimate^2 the volume density of the meteoric cloud is \(\rho = 5\cdot 10^{-18}\ \mathrm{g/cm^3}\), i.e. three orders of magnitude greater than Van de Hulst’s. This discrepancy, in Van de Hulst’s opinion, is explained by a difference in determining the size of the particles that effectively scatter zodiacal light. According to Van Rijn these particles have a mean radius of \(50\ \mathrm{cm}\), whereas Van de Hulst considers their radius to be 1000 times smaller.

A critical review of the results concerning data on the spatial density of dusty matter in the neighborhood of the Earth’s orbit, obtained by a number of researchers on the basis of photometric studies of the \(F\)-component of the solar corona, is contained in the monograph of B. Yu. Levin.^3 These results are brought together in Table I.

b) Observation of meteors

At first glance it seems that precisely the observations of meteors by optical and radar methods are the most reliable means of studying the questions posed above. These methods undoubtedly are of great value, in particular for solving a number of geophysical problems, such as the formation of the sporadic layer \(E\), the determination of the structural parameters of the atmosphere, etc. At present, however, they do not make it possible to obtain the data of interest to us on the flux of meteoric particles and their energy.

Indeed, in studying the motion of meteors in the Earth’s atmosphere, one should remember that there exist a number of factors distorting the true picture of the motion of meteoric bodies outside the Earth’s atmosphere. The chief of these are: distortion of the motion connected with the passage of particles through the dense terrestrial atmosphere, and observational selection.

The smallest meteoric particles, having an initial velocity of \(11—70\) km/sec relative to the Earth, may be completely decelerated in the atmosphere, and their further motion will take place under the action of gravity. For particles of dimensions of the order of a micron and less, the motion apparently acquires such a character already from heights \(\sim 80—90\) km. At the same time, only comparatively large particles, which produce meteor phenomena in passing through the atmosphere, are accessible to astronomical and radar observations. To judge smaller particles one must resort to extrapolations, more or less well founded.

At present, only meteors whose brightness lies in the interval of stellar magnitudes \(+4 < m < -4\) for naked-eye observations and \(+4 < m < 11\) for telescopic observations are subject to optical (visual and photographic) registration.

Owing to the short duration of the phenomenon and, consequently, the necessarily short exposures, only very bright meteors can be detected photographically. The radar method makes it possible to register meteors that have a brightness down to \(+12^m\). In this case meteors are detected by the electron trail they create, i.e., a column of ions with a concentration several orders of magnitude greater than the ionospheric background.

In meteor astronomy a formula has been obtained that relates the brightness of a meteor to the mass of the particle and its velocity. For a meteoric body moving with velocity \(v = 56\) km/sec, this formula has the following form:

\[ \lg M = -1.1 - 0.4\,m_z, \tag{2} \]

where \(M\) is the mass of the meteor, and \(m_z\) is the brightness reduced to the zenith. Consequently, a meteor of the second magnitude will have a mass of about \(0.01\) g.

If one assumes some value for the mean density of the meteoric body, then its dimensions may be determined from this formula. For example, for \(\rho_{\text{part}} = 5\) g/cm\(^3\) we have

\[ \lg a = -0.8 - 0.133\,m_z. \]

Table II (columns 1, 2, and 3) gives the apparent brightnesses of meteors and the corresponding masses of meteoric bodies and their radii, calculated from formula (2).

Consideration of Table II shows that the size of the particles producing telescopic meteors is such that it approaches the dimensions of the largest particles of zodiacal light.

Table II

c) Estimation of the total flux of meteoric particles and of the mass of meteoric matter falling on the Earth

Attempts have repeatedly been made to determine the total flux of meteoric particles on the basis of data obtained from observations of meteors, and in this way to estimate the mass of meteoric matter falling per unit area of the Earth’s surface (or over the entire surface of the Earth) per unit time (usually per day). This, evidently, can be done if it proves possible to pass from the observed distribution of meteoric bodies to their true distribution beyond the limits of the Earth’s atmosphere (taking micrometeorites into account).

In 1955 S. V. Orlov reviewed earlier attempts to estimate the mass of meteoric matter falling on the surface of the Earth. He based himself on data from visual observations of meteors covering the range of brightnesses from \(+3^{m}\) to \(-3^{m}\), since visual estimates of meteors brighter than \(-3^{m}\) are already unreliable (\(-4^{m}\) is the brightness of Venus during periods of greatest brightness), while meteors fainter than \(+3^{m}\) will not all be recorded, since the sky background, the observer’s visual acuity, and his experience will strongly affect the observational results.

In the fourth column of Table II are given data on the number of meteors used by S. V. Orlov. Using these data, he found the values of the total mass of meteoric bodies falling within a unit interval of stellar magnitudes. For all intervals from \(-3^{m}\) to \(+3^{m}\) (i.e., for particles with sizes from 0.68 cm to 0.14 cm), a mass of about 100 kg (110 kg) was obtained. On this basis S. V. Orlov assumes (and this assumption is completely arbitrary) that the total mass of particles of any sizes, including the very smallest, is constant within a unit interval of stellar magnitudes and is equal to \(\simeq 110\) kg. There are no sufficient physical grounds for such an assumption. One might suppose, for example, that in any processes of formation of solid particles there should be some normal distribution by masses (and sizes):

\[ n(m)=f(m)\,dm \quad \text{or} \quad n(a)=F(a)\,da. \]

In this case the number of meteoric particles with some definite mass (with some definite size) would be maximal.

S. V. Orlov believes that the series given in column 4 of Table II is a geometric progression with ratio 2.5, and by extrapolation he finds the number of micrometeors in various intervals of stellar magnitudes (Table III).

Table III

If, further, it is assumed that particles with radius \(a<0.25\cdot 10^{-4}\ \mathrm{cm}\) will not be present in the dust cloud because they are subject to the action of radiation pressure (the Poynting–Robertson effect), then the above assumption makes it possible easily to calculate \(M\)—the total mass of matter falling on the Earth per day. S. V. Orlov takes the range from \(-40^m\) to \(+30^m\) and considers that for each interval of one stellar magnitude there are \(\sim 100\ \mathrm{kg}\) of meteoric matter; in this case the total mass is obtained as \(\approx 10\ \mathrm{t/day}\). Thus, on \(1\ m^2\) per day there falls a flux of micrometeorites equal to \(10^3\) particles \((a\approx 10^{-4}\ \mathrm{cm})\).

This calculation is, of course, extremely uncertain, but in essence it agrees with Watson’s well-known estimate.

Watson’s estimate, like S. V. Orlov’s estimate, is based on data from observations of the number of meteors entering the Earth’s atmosphere daily. Watson assumes that for meteors with velocity \(v=56\ \mathrm{km/sec}\) the interval of stellar magnitudes is equal to 40 (from \(-10\) to \(+30\)), and the daily mass of meteoric matter falling on the Earth is \(4.4\ \mathrm{t/day}\).

The shortcomings of calculations of this kind are considered in the work of B. Yu. Levin \(^{3}\). Let us compare the results obtained on the basis of meteor observations with the results of observations of the Fraunhofer component of the solar corona. If \(N\) is the number of meteoric bodies in one cubic centimeter, \(\Delta N\) is the number of meteoric bodies having masses, sizes, and stellar magnitudes in a specified interval, and \(a\) is the radius of the meteoric bodies, then according to Watson (on the basis of meteor observations)

\[ \frac{dN}{da}=10^{-28.2}a^{-5.2}, \tag{3} \]

and according to van de Hulst (from observations of the \(F\)-component of the solar corona)

\[ \frac{dN}{da}=10^{-19.5}a^{-2.6}. \tag{4} \]

In Table IV a comparison is given of the results obtained by the two methods indicated above, for the number of particles of several sizes in 1 cubic parsec.

Table IV

The discrepancy, as we see from Table IV, is very large. The number of particles with sizes from 1 to 0.1 mm according to Van de Hulst is approximately 10,000 times greater than can be judged from the number of telescopic meteors.

Van de Hulst gave an explanation\(^1\) of this contradiction, proceeding from a definite assumption about the character of the motion of meteoric bodies in interplanetary space, and in this case the results of both authors may be considered correct. Some investigators, however, express doubt as to the reliability of both these and other data\(^3\).

In conclusion we shall present estimates of the increase in the Earth’s mass due to meteoric matter falling on its surface. These estimates are also very contradictory.

An estimate based on the study of the number of meteors is founded on the application of the elementary formula

\[ \frac{dM}{dt}=86400\pi R^2\overline{\sigma v_g}\rho, \tag{5} \]

where \(\sigma\) is the effective cross section for collision of a meteor with the Earth \((\mathrm{cm}^2)\), \(v_g\) is the geocentric velocity of the meteor, and \(\rho\) is the density of the meteoric matter. The use of formula (5) leads to the values

\[ 4 < M < 15\ \text{t/day} \]

(\(4.4\ \text{t/day}\) according to Watson\(^4\), \(15\ \text{t/day}\) according to Levin\(^3\), under the assumption that \(\rho=10^{-23}\ \mathrm{g/cm^3}\)). If \(\rho=10^{-21}\ \mathrm{g/cm^3}\), as follows from Van de Hulst’s results, then \(\Delta M \approx 100—500\ \text{t}\) of meteoric matter per day.

Estimates of the quantity of cosmic dust falling on the Earth, according to data from various investigators, range from 1500\(^5\) to 4000—6000 t/day\(^6,7\). These estimates, based on the results of collecting cosmic dust and on investigations of silt samples raised from the ocean floor far from the shores, possess great uncertainty, and the error here may exceed an order of magnitude.

2. DETERMINATION OF THE KINETIC ENERGY

(OR MOMENTUM) OF METEORIC PARTICLES

At the present time it is considered established that meteors with hyperbolic orbits in the planetary system are practically absent. Therefore the relative velocities of meteoric particles outside the Earth’s atmosphere with respect to a satellite or rocket will lie within the limits \(70 \geq v \geq 11\ \mathrm{km/sec}\). Thus, it may be asserted,

that at very great altitudes meteoric particles of various masses (and, consequently, sizes) can, upon impact with a rocket or satellite,

a)

b)

Fig. 1. Traces of collisions of micrometeors with a polished bronze plate:
a) 1—crater with a diameter of 0.8 mm, 2—colors of tempering, 3—corrosion spot; b) crater with a diameter of 3 mm.

transfer the kinetic energies or momenta indicated in Table V.

Table V

From Table V it is seen that the kinetic energy for particles of the sizes of interest to us lies within the limits

\[ 10 < E_{\rm kin} < 10^{11}\ {\rm erg}. \]

These quantities are quite accessible to measurement, provided there are no interferences in the form of other impacting particles (not cosmic dust) or any other disturbing factors.

a) Some possible methods for investigating micrometeorites by means of rockets

Micrometeorites were detected during rocket ascents from the traces of particle collisions with polished plates, by recording the acoustic energy arising in collisions, and also with the aid of photomultipliers recording the light pulse that appears when particles strike a receiver.

Traces from the collision of micrometeors with a polished bronze plate at an altitude of approximately 100 km are shown in Fig. 1. The traces are small craters several microns deep, with a diameter in some cases reaching two or more millimeters. Temper colors are observed along the edges of the crater. As is evident from the photographs, small particles can seriously damage optical surfaces and disrupt the normal operation of optical and other equipment during flights of an artificial Earth satellite remaining in the upper atmosphere for a long time.

In December 1949 and August 1950, under the direction of Professor Bohne, the first acoustic measurements were carried out⁸. During the flights of the V-2 rocket, pulses were recorded that were apparently caused by impacts of micrometeorites. The number of micrometeorites colliding with the rocket body was studied by means of a crystal microphone and an amplifier in the range 30–60 kc/s with a bandwidth of 10 kc/s.

Fig. 2. Probable meteor collisions recorded during the launch of the V-2 rocket on December 8, 1949. 1 — meteor collisions; 2 — calibration voltage (telemetry not operating).

On December 8, 1949, between the 70th and 214th seconds of the rocket flight, 66 collisions were recorded, which amounted to 1 impact in 2.2 seconds (Fig. 2). This agrees in order of magnitude with Whipple’s calculation⁷, according to which the probable number of collisions with particles,

possessing an energy above \(10^{-2}\) erg (which could be detected by a microphone), is equal to 10 collisions in 1 sec per 1 sq. m. Whipple’s calculation is based on Watson’s results cited above, which, as was shown, cannot be regarded as reliably established.

During the flight on August 31, 1950, at altitudes from 90 to 150 km, a total of 14 collisions were recorded. This difference is explained by the different sensitivity of the receiving-amplifying device.

To detect collisions with micrometeorites, in the Aerobee rocket experiment of September 14, 1955, a crystal microphone made of ammonium dihydrogen phosphate with a stainless-steel diaphragm 0.017 inch thick and an area of 25 sq. inches was installed. The microphone and amplifier had a natural frequency in the region of 70 kc/s, with a passband of 10 kc/s, and had a telemetry output. The sensitivity of the apparatus was calibrated as follows: sand sorted by diameter within the limits from 4000 microns to less than 100 microns was dropped onto the diaphragm, and the readings of the system were recorded. The sensitivity of the entire system was such that particles about 200 microns in diameter, falling from a height of 2 cm, produced an amplifier output signal of about 2 V. For a rocket moving at a speed equal to 1 M, the equivalent sensitivity in the case of a collision with a particle 2 microns in diameter and of stellar magnitude \(+15\) will be obtained. At relative impact velocities of the order of 20 km/sec, a two-volt deflection at the amplifier output will be produced by particles of \(+20\)—\(+25\) stellar magnitude.

Experiments were also carried out to determine the response of the acoustic system to collisions of the entire rocket body with micrometeors. For given pulses, the signal decreased exponentially with distance from the microphone; however, all impacts on the rocket surface could be recorded.

The experiments described above give data on the flux of meteoric particles per unit surface area. To determine the energy and momentum of the particles, it is necessary to isolate the receiving surface from the entire body of the rocket. Then, having calibration curves

\[ V = P\left(mv,\frac{mv^{2}}{2}\right), \]

one can determine the value \(P\) from the response of the system to an impact.

At present it cannot be said with certainty what determines the readings of a piezoelectric transducer when particles flying at cosmic velocities strike it—momentum or kinetic energy, or some function of both. A piezoelectric transducer ought to register the quantity of motion. However, an experiment investigating its response to collisions lasting microseconds shows, as is evident from the graph shown in Fig. 3, that the piezoelectric element responds not only to the quantity of motion, but also to kinetic energy.

Fig. 3. Response of the piezoelectric transducer to an impact with a duration of 1 microsecond.

To separate mass and velocity, it is necessary on the rocket or satellite to have a frequency discriminator, and to carry out calibration separately for mass and for velocity, but no longer by dropping sand onto the diaphragm, rather by accelerating particles in an electric field.

A crystal microphone with an amplifier and a telemetric system makes it possible to record impacts of meteor particles with energies from 1 to \(10^6\) ergs.

In 1955 a new instrument was developed for the investigation of micrometeors[^9]. This instrument consists of a Plexiglas cone coated with an aluminum layer \(8 \cdot 10^{-6}\) cm thick and connected to a photomultiplier. Figure 4 shows a cross-section of the receiver and its position relative to the rocket. When micrometeors collide with the receiver, a glow arises, which is recorded by the photomultiplier, with subsequent transmission of the signal by telemetry to the Earth. The apparatus has high sensitivity. It makes it possible to register a light pulse of \(0.0001\) lm·sec/m.

Fig. 4. Aluminized Plexiglas cone 2 with a transparent exit window adjacent to photomultiplier 3. 1 — rocket skin.

It is known that when micrometeorites collide with an obstacle, kinetic energy is expended on heating, visible glow, and partial ionization. If it is assumed that the energy released in this process is distributed in the same way as for meteorites moving in a rarefied atmosphere, then the ratio (theoretically) between the corresponding fractions of energy will be as follows: \(10^4\) (heat) : \(10^2\) (light) : \(10^0\) (ionization). Taking this into account, it was found that this receiver can record collisions with micrometeorites possessing an energy of only \(0.005\) erg, which corresponds, for example, to the energy of an iron meteorite with a diameter of one micron and a speed of approximately \(0.5\) km/sec.

Fig. 5. Meteor impacts recorded during the flight of “Aerobee” on November 17, 1955. 1 — meteor impacts, 2 — end of telemetry operation.

Figure 5 gives the data from investigations of micrometeorites during the launch of the “Aerobee” rocket in 1955. The altitude reached was 103 km. On the graph, the recorded impacts are superposed on the rocket trajectory. A receiver with an area of \(75\ \text{cm}^2\) registered 114 collisions with micrometeorites; of these, 101 occurred over the course of 84 sec, when the rocket was above 85 km—the altitude above which no visible increase in the frequency of collisions was detected. Thus, per \(1\ \text{cm}^2\) of receiver area there is 1 impact in 57 sec.

Analyzing the data obtained, it should be noted that the marks of collisions of the receiver with micrometeorites were registered (both during ascent and during descent) only above a certain definite altitude, and they are arranged symmetrically with respect to the maximum alt—

moments of the rocket’s ascent. In the marks of the impacts there is no cyclicity, despite the five-second period of rotation of the rocket in flight. The latter indicates the absence of any radiant from which the meteorites come. At the time when the rocket’s axis of rotation was parallel to the Earth, the receiver registered collisions with micrometeors only when it was turned upward.

In the present experiment only the particle flux was recorded. However, by the method described one can also obtain data on the spectrum of energies and momenta, provided that a preliminary calibration is made establishing a correspondence between the kinetic energy or the amount of motion of the moving particles and the light pulse they produce.

For the investigation of the solid component of interplanetary matter by means of rockets and artificial Earth satellites, some other methods may also be applied.

b) Interfering factors

In setting up investigations of micrometeorites on rockets, it is useful to discuss possible interference and other factors that may affect the results of applying the method described above.

Table VI

In addition to meteoric particles, corpuscles emitted by the Sun and cosmic particles constituting the primary cosmic rays may strike the body of a rocket or an artificial Earth satellite during their flight in the upper atmosphere. It is known that solar corpuscles (with the exception of a certain part of them emitted only during chromospheric flares) have velocities $\sim 1.5\cdot 10^3\ \mathrm{km/sec}$. Assuming that these particles are electrons, protons, alpha-particles, and Ca ions, we obtain the energy values given in Table VI.

Table VII

For helium nuclei entering into the composition of cosmic radiation, respectively, the values obtained are those indicated in Table VII.

From Tables VI and VII given above it is evident that solar corpuscles possess energies many orders of magnitude smaller than those that can be registered by the receiving apparatus. As for cosmic $\alpha$-particles, their energy is sufficient to be recorded; however, the microphones used are transparent to cosmic particles.

c) Electrical and magnetic effects

In the initial formulation of the problem we considered meteoric matter to be electrically neutral. Let us now consider what must be changed, in experimental and theoretical respects, in the formulation of our problem if it is assumed that cosmic dust has some electric charge.

If the problem is posed of studying meteor activity not only at a given place on the earth’s surface, but the latitudinal effect is studied and one has in view the solution of the astronomical problem of the distribution of meteoric matter near the earth’s orbit or in the solar system, then, if the dust is charged, the problem, on the one hand, becomes more complicated, but, on the other hand, a number of new possibilities arise. Indeed, if dust particles have a positive charge, then, in addition to the forces of gravitation and radiation pressure, they will be acted upon by the magnetic fields of the solar system and of the Earth. Moreover, as is explained below, the motion will be affected by the change with time of the particle’s charge, if such a change occurs.

Let us briefly consider by what the charge of a dust particle should be determined and what geophysical consequences should be caused by its presence.

Basically, the magnitude of the charge must be determined by the influence of two effects acting in opposite directions: electrification and neutralization. Electrification is caused by photoelectric emission (as a result of the direct photoelectric effect) and by impacts of protons, which also release electrons. Neutralization occurs by the absorption of electrons from the surrounding space under the action of the particle’s Coulomb field. The charge of a dust particle must therefore vary as a function of time: it must be different for particles located at a given instant in the daytime and nighttime parts of the atmosphere; the state of the solar envelope must be reflected in its magnitude (for example, the charge must increase sharply during chromospheric flares).

Having determined the charge, we can estimate the order of the ratio \(\frac{Q}{mv}\), where \(Q\) is the particle charge, \(m\) its mass, and \(v\) its velocity. This quantity \(\frac{Q}{mv}\), called the magnetic rigidity, plays the principal role in estimating various geophysical effects, in particular latitudinal changes of meteor activity and its changes caused by magnetic storms. At the same time, the character of the motion of a charged particle may serve as an indicator of the Earth’s magnetic field.

Under the conditions of experiments on rockets and artificial Earth satellites, the circumstance that meteoric particles are charged may have an adverse effect because of induction phenomena. Therefore, to shield the receivers one should use metallic diaphragms. If polished metallic plates are used as such diaphragms, then, simultaneously with the recording of ultrasonic vibrations arising when micrometeors strike, it is possible to record meteor impacts as traces on the polished plates.

All the features associated with the impact of a rapidly moving charged particle on a membrane are very difficult to take into account in advance. Therefore the question arises of the necessity of laboratory modeling. A preliminary (order-of-magnitude) calculation shows that charged dust grains of the sizes of interest to us can be accelerated to the required velocities in fields of \(\sim 100\text{--}200\ \mathrm{kv}\).

The arrangement of such an experiment should be recognized as highly desirable, since it is necessary to determine the difference in the results of slow and fast impacts of particles on an obstacle. Probably only in this case will it be possible, for example, to clarify fully for fast particles the relative role of kinetic energy and momentum in the resulting piezoelectric effect.

References

1. H. C. van de Hulst, Ap. J. 105, 471 (1947).
2. P. J. van Rhijn, Pub. Astr. Lab. Groningen 31 (1921).
3. B. Yu. Levin, Physical Theory of Meteors and Meteoritic Matter in the Solar System, Publishing House of the Academy of Sciences of the USSR, 1956.
4. F. Watson, Between the Planets, Philadelphia, 1940 (Russian translation: Gostekhizdat, Moscow, 1947).
5. C. de Jager, Colloque a Liege 174 (1954).
6. H. Pettersson and H. Potschi, Nature 166, 308 (1950).
7. H. Pettersson and H. Potschi, Geochim. et Cosmochim. Acta 2, 84 (1952).
8. M. Dubin, Meteor Impacts by Acoustical Techniques Rocket Exploration of the Atmosphere, 1954.
9. O. E. Berg, L. H. Meredith, Meteorite impacts to altitude of 103 kilometers, J. of Geoph. Res. 61, No. 4 (1956).