Dmitry Vibe, Doctor of Physical and Mathematical Sciences, Researcher at the Institute of Astronomy
Night street lighting makes life more comfortable and safer, but, unfortunately, deprives citizens starry sky. The brightest stars from the city can still be seen, but the Milky Way is already completely inaccessible to many residents of the 21st century. But our ancestors had no problem admiring not only the Milky Way itself, but also the intricacies of its pattern. In particular, back in the 15th century, sailors sailing in the southern seas distinguished a distinct dark spot on the bright strip of the Milky Way. In those days, when the sky was not yet hopelessly spoiled by widespread illumination, a noticeable gap in the constellation of the Southern Cross was awarded its own name - it was called the Coal Sack.
Space dust captures the history of the solar systemComets contain the primordial dust from which our solar system was formed, and since these particles have remained very far from the Sun throughout their existence, they create the effect of deep freezing, thus preserving dust that is billions of years old.However, this did not mean that the stain was formed by some substance. Rather, on the contrary: in fact, until the beginning of the 20th century, these and other dark spots on the starry background were considered simply places where there were no stars. Legend has it that the greatest astronomer-observer William Herschel, seeing one of these spots through a telescope, shouted to his sister Caroline, his faithful assistant: “My God, there is a hole in the sky!”
The idea of voids in the distribution of stars has receded largely due to the painstaking work of Edward Barnard, who compiled a large-scale photographic atlas of the Milky Way. At first, in the descriptions of his photographs, he called dark spots “vacancies” or even “black holes” (not in the current sense of these words), but over time he came to the conclusion that in this case we are dealing with clouds of absorbing matter, which covers us some of the stars in the Milky Way.
Convincing evidence that the absorption of light in the Galaxy occurs not only in dark clouds, but generally everywhere, was first (in 1930) collected by another American, Robert Trumpler. He noted the following important facts. First, the light from a star is absorbed the stronger, the farther away from us the star is. Secondly, light passing through interstellar space is not only absorbed, but also turns red (like the Sun near the horizon), because blue rays are absorbed more than red ones. And the degree of this reddening also increases with the distance to the star. Trumpler concluded from this that absorbing matter is represented by particles (dust grains) scattered throughout the Galaxy with a size somewhat smaller than the wavelength of visible light. Dark clouds are particularly dense concentrations of these particles.
Initially, it was assumed that interstellar particles consist of ice - in the broad sense of the word, including not only water ice, but also other frozen gases (ammonia, carbon dioxide, etc.) - and condense in the same place where they are observed, that is, directly between the stars. This assumption seemed quite natural, taking into account the ideas of the middle of the 20th century about the content of atoms in the interstellar medium (ISM). However, already in the 1960s, these ideas had to be abandoned.
The fact is that the words "blue color is absorbed stronger than red" describe only the general dependence of absorption on the wavelength. Against the general background of an increase in absorption on going to shorter wavelengths, this dependence may have additional dips due to the fact that various substances have the ability to absorb light more efficiently in certain spectral ranges. For example, water ice is particularly good at absorbing infrared radiation with a wavelength of about 3 microns (µm). Therefore, if you look at a star through a cloud of ice particles, you can expect a dip near 3 microns in its spectrum. In addition, water ice strongly absorbs ultraviolet radiation with a wavelength shorter than 160 nm, which means that a dip in the ultraviolet (UV) range should also appear in the spectrum of the same star.
Both IR and UV observations require additional, sometimes very significant, efforts. As long as only the visible range was available to observers, the ice particle model did not encounter any particular inconsistencies. However, as soon as observations spread in both directions from the visible range, it became clear that traces of water ice are not observed either in the ultraviolet or in the IR, which means that the mixture of frozen gases, if included in the composition of cosmic dust particles, is not the main component . More precisely, a three-micron dip is observed, but only in those cases when the light of the background star passes through dense dust clouds, where water and other molecules can freeze in the form of ice mantles onto dust particles that are not ice themselves.
Other characteristics of absorption in the UV and IR ranges became an indication of the "true" composition of cosmic dust grains. It turned out that cosmic dust “steals” photons with wavelengths of about 200 nm and 10 microns from stellar spectra especially effectively. This selectivity reflects some features of the chemical and mineral composition of dust grains. In the late 1960s, absorption at 200 nm was associated with graphite, and absorption at 10 µm (and some other wavelengths) with minerals from the silicate group. On this basis, the idea was formed of interstellar dust as a mixture of graphite (or some other, but also containing carbon) and silicate particles. This idea has been preserved to this day, although, of course, in a repeatedly modified and supplemented form.
The graphite-silicate model is good in that it not only allows one to explain the nature of interstellar extinction, but also sheds some light on the origin of dust grains. Now, most experts believe that it is still impossible to condense stone dust particles in a cold rarefied interstellar gas in a reasonable period of time; you need to look for a place denser and hotter. Such a place turned out to be the extended atmospheres of stars in the last stages of evolution. While a Sun-like star is "in its prime," its atmosphere is too hot for solid matter to exist. However, at the end of a star's life path, its atmosphere swells and cools to such an extent that dust particles can already condense there, much like soot condenses in an insufficiently hot flame. Then the newly formed dust grains, together with the matter of the star, scatter through interstellar space.
For a long time, it was not clear why dust particles can collect into large clouds. However, in the 1960s and 1970s, it became clear that dust was in fact only a minor admixture (about 1% by mass) to the main ingredient in interstellar matter, gas, consisting mainly of hydrogen and helium. To estimate the scale of the gas content in the ISM, observations in the visible part of the spectrum are no longer enough: the gas almost does not absorb starlight, and itself glows only in the radio range. But there is so much of it that it completely entrains the dust with its movements. And the dark dust clouds are actually not even the tip of an iceberg, but just a tiny coating that betrays the presence of much more massive, but invisible clouds of interstellar gas.
This does not mean, of course, that dust can be neglected in the study of the Universe. First, its presence must be taken into account when studying stars, so as not to mistakenly attribute to a star the properties of dust grains that block its radiation. Second, dust plays an important role in the thermoregulation of the interstellar medium, acting as a powerful heat sink. Thirdly, it turns out to be a catalyst in interstellar chemical reactions allowing the formation of complex organic compounds. Fourthly, cosmic dust particles serve as the raw material for the formation of planets, on one of which - consisting of myriads of cosmic dust particles stuck together - we live. Finally, the carbon that we ourselves are made of could also have been part of interstellar carbon dust grains in the past.
Of course, the question of the role that cosmic dust plays in the emergence of life remains open. But in any case, we have to admit that the coal fantasy of medieval sailors turned out to be surprisingly visionary.
COSMIC MATTER ON THE EARTH'S SURFACE
Unfortunately, unambiguous criteria for differentiating spacechemical substance from formations close to it in shapeterrestrial origin has not yet been developed. That's whymost researchers prefer to search for spacecal particles in areas remote from industrial centers.For the same reason, the main object of research arespherical particles, and most of the material havingirregular shape, as a rule, falls out of sight.In many cases, only the magnetic fraction is analyzed.spherical particles, for which now there are the mostversatile information.
The most favorable objects for the search for spacewhich dust are deep-sea sediments / due to the low speedsedimentation /, as well as polar ice floes, excellentretaining all the matter settling from the atmosphere. Bothobjects are practically free from industrial pollutionand promising for the purpose of stratification, the study of the distributionof cosmic matter in time and space. Bythe conditions of sedimentation are close to them and the accumulation of salt, the latter are also convenient in that they make it easy to isolatedesired material.
Very promising may be the search for dispersedcosmic matter in peat deposits. It is known that the annual growth of high-moor peatlands isapproximately 3-4 mm per year, and the only sourcemineral nutrition for the vegetation of raised bogs ismatter that falls out of the atmosphere.
Spacedust from deep sea sediments
Peculiar red-colored clays and silts, composed of residualkami of siliceous radiolarians and diatoms, cover 82 million km 2ocean floor, which is one sixth of the surfaceour planet. Their composition according to S.S. Kuznetsov is as follows total:55% SiO 2 ;16% Al 2 O 3 ;9% F eO and 0.04% Ni and So, At a depth of 30-40 cm, teeth of fish, livingin the Tertiary era. This gives grounds to conclude thatsedimentation rate is approximately 4 cm pera million years. From the point of view of terrestrial origin, the compositionclays are difficult to interpret. High contentin them nickel and cobalt is the subject of numerousresearch and is considered to be associated with the introduction of spacematerial / 2,154,160,163,164,179/. Really,nickel clark is 0.008% for the upper horizons of the earthbark and 10 % for sea water /166/.
Extraterrestrial matter found in deep sea sedimentsfor the first time by Murray during the expedition on the Challenger/1873-1876/ /the so-called "Murray space balls"/.Somewhat later, Renard took up their study, as a resultthe result of which was the joint work on the description of the foundmaterial /141/. The discovered space balls belong topressed to two types: metal and silicate. Both typespossessed magnetic properties, which made it possible to applyto isolate them from the sediment magnet.
Spherulla had a regular round shape with an averagewith a diameter of 0.2 mm. In the center of the ball, malleablean iron core covered with an oxide film on top.balls, nickel and cobalt were found, which made it possible to expressassumption about their cosmic origin.
Silicate spherules are usually not have had strict sphereric form / they can be called spheroids /. Their size is somewhat larger than metal ones, the diameter reaches 1 mm . The surface has a scaly structure. mineralogicalcue composition is very uniform: they contain iron-magnesium silicates-olivines and pyroxenes.
Extensive material on the cosmic component of the deep sediments collected by a Swedish expedition on a vessel"Albatross" in 1947-1948. Its participants used the selectionsoil columns to a depth of 15 meters, the study of the obtainedA number of works are devoted to the material / 92,130,160,163,164,168/.The samples were very rich: Petterson points out that1 kg of sediment accounts for from several hundred to several thousand spheres.
All authors note a very uneven distributionballs both along the section of the ocean floor and along itsarea. For example, Hunter and Parkin /121/, having examined twodeep-sea samples from different places in the Atlantic Ocean,found that one of them contains almost 20 times morespherules than the other. They explained this difference by unequalsedimentation rates in different parts of the ocean.
In 1950-1952, the Danish deep-sea expedition usedNile to collect cosmic matter in bottom sediments ocean magnetic rake - oak board with reinforced onIt has 63 strong magnets. With the help of this device, about 45,000 m 2 of the surface of the ocean floor were combed.Among the magnetic particles that have a probable cosmicorigin, two groups are distinguished: black balls with metalwith or without personal nuclei and brown balls with crystalpersonal structure; the former are rarely larger than 0.2mm , they are shiny, with a smooth or rough surfaceness. Among them there are fused specimensunequal sizes. Nickel andcobalt, magnetite and schrei-bersite are common in the mineralogical composition.
Balls of the second group have a crystalline structureand are brown. Their average diameter is 0.5 mm . These spherules contain silicon, aluminum and magnesium andhave numerous transparent inclusions of olivine orpyroxenes /86/. The question of the presence of balls in bottom siltsThe Atlantic Ocean is also discussed in /172a/.
Spacedust from soils and sediments
Academician Vernadsky wrote that cosmic matter is continuously deposited on our planet.pial opportunity to find it anywhere in the worldsurfaces. This is connected, however, with certain difficulties,which can be led to the following main points:
1.
amount of matter deposited per unit areavery little;
2.
conditions for the preservation of spherules for a longtime is still insufficiently studied;
3.
there is the possibility of industrial and volcanic pollution;
4.
it is impossible to exclude the role of the redeposition of the already fallensubstances, as a result of which in some places there will beenrichment is observed, and in others - depletion of cosmic material.
Apparently optimal for the conservation of spacematerial is an oxygen-free environment, smoldering, in particularness, a place in deep-sea basins, in areas of accumuseparation of sedimentary material with rapid disposal of matter,as well as in swamps with a reducing environment. Mostprobably enrichment in cosmic matter as a result of redeposition in certain areas of river valleys, where a heavy fraction of mineral sediment is usually deposited/ obviously, only that part of the dropped out gets heresociety, specific gravity which is greater than 5/. It is possible thatenrichment with this substance also takes place in the finalmoraines of glaciers, at the bottom of tarns, in glacial pits,where melt water accumulates.
There is information in the literature about finds during the shlikhovspherules related to space /6,44,56/. in the atlasplacer minerals, published by the State Publishing House of Scientific and Technicalliterature in 1961, spherules of this kind are assigned tometeoritic. Of particular interest are the finds of spacesome dust in ancient rocks. The works of this direction arehave recently been very intensively investigated by a number oftel. So, spherical hour types, magnetic, metal
and glassy, the first with the appearance characteristic of meteoritesManstetten figures and high nickel content,described by Shkolnik in the Cretaceous, Miocene and Pleistocenerocks of California /177,176/. Later similar findswere made in the Triassic rocks of northern Germany /191/.Croisier, setting himself the goal of studying the spacecomponent of ancient sedimentary rocks, studied samplesfrom various locations / area of New York, New Mexico, Canada,Texas / and different ages / from Ordovician to Triassic inclusive/. Among the studied samples were limestones, dolomites, clays, shales. The author found spherules everywhere, which obviously cannot be attributed to indus-strial pollution, and most likely have a cosmic nature. Croisier claims that all sedimentary rocks contain cosmic material, and the number of spherules isranges from 28 to 240 per gram. Particle size in mostmost cases, it fits in the range from 3µ to 40µ , andtheir number is inversely proportional to the size /89/.Data on meteor dust in the Cambrian sandstones of Estoniainforms Wiiding /16a/.
As a rule, spherules accompany meteorites and they are foundat impact sites, along with meteorite debris. Previouslyall balls were found on the surface of the Braunau meteorite/3/ and in the craters of Hanbury and Vabar /3/, later similar formations along with a large number of particles of irregularforms found in the vicinity of the Arizona crater /146/.This type of finely dispersed substance, as already mentioned above, is usually referred to as meteorite dust. The latter has been subjected to detailed study in the works of many researchers.providers both in the USSR and abroad /31,34,36,39,77,91,138,146,147,170-171,206/. On the example of the Arizona spherulesit was found that these particles have an average size of 0.5 mmand consist either of kamacite intergrown with goethite, or ofalternating layers of goethite and magnetite covered with thina layer of silicate glass with small inclusions of quartz.The content of nickel and iron in these minerals is characteristicrepresented by the following numbers:
mineral iron nickel
kamacite 72-97%
0,2
- 25%
magnetite 60 - 67%
4 - 7%
goethite 52 - 60%
2-5%
Nininger /146/ found in the Arizona balls of a mineral-ly, characteristic of iron meteorites: cohenite, steatite,schreibersite, troilite. The nickel content was found to beon average,1 7%, which coincides, in general, with the numbers , received-nym Reinhard /171/. It should be noted that the distributionfine meteorite material in the vicinityArizona meteorite crater is very uneven. The probable cause of this is, apparently, either the wind,or an accompanying meteor shower. Mechanismformation of Arizona spherules, according to Reinhardt, consists ofsudden solidification of liquid fine meteoritesubstances. Other authors /135/, along with this, assign a definitiondivided place of condensation formed at the time of the fallvapors. Essentially similar results were obtained in the course of studyingvalues of finely dispersed meteoritic matter in the regionfallout of the Sikhote-Alin meteor shower. E.L. Krinov/35-37.39/ subdivides this substance into the following main categories:
1.
micrometeorites with a mass of 0.18 to 0.0003 g, havingregmaglypts and melting bark / should be strictly distinguishedmicrometeorites according to E.L. Krinov from micrometeorites in the understandingWhipple Institute, which was discussed above/;
2.
meteor dust - mostly hollow and porousmagnetite particles formed as a result of splashing of meteorite matter in the atmosphere;
3.
meteorite dust - a product of crushing falling meteorites, consisting of acute-angled fragments. In mineralogicalthe composition of the latter includes kamacite with an admixture of troilite, schreibersite, and chromite.As in the case of the Arizona meteorite crater, the distributionthe division of matter over the area is uneven.
Krinov considers spherules and other melted particles to be products of meteorite ablation and citesfinds of fragments of the latter with balls stuck to them.
Finds are also known at the site of the fall of a stone meteoriterain Kunashak /177/.
The issue of distribution deserves special discussion.cosmic dust in soils and other natural objectsarea of the fall of the Tunguska meteorite. Great work in thisdirection were carried out in 1958-65 by expeditionsCommittee on Meteorites of the Academy of Sciences of the USSR of the Siberian Branch of the Academy of Sciences of the USSR. It has been established thatin the soils of both the epicenter and places remote from it bydistances up to 400 km or more, are almost constantly detectedmetal and silicate balls ranging in size from 5 to 400 microns.Among them are shiny, matte and roughhour types, regular balls and hollow cones. In somecases, metallic and silicate particles are fused to each otherfriend. According to K.P. Florensky /72/, the soils of the epicentral region/ interfluve Khushma - Kimchu / contain these particles only ina small amount /1-2 per conventional unit of area/.Samples with a similar content of balls are found ondistance up to 70 km from the crash site. Relative povertyThe validity of these samples is explained by K.P. Florenskycircumstance that at the time of the explosion, the bulk of the weatherrita, having passed into a finely dispersed state, was thrown outinto the upper layers of the atmosphere and then drifted in the directionwind. Microscopic particles, settling according to the Stokes law,should have formed a scattering plume in this case.Florensky believes that the southern boundary of the plume is locatedapproximately 70 km to C Z from the meteorite lodge, in the poolChuni river / Mutorai trading post area / where the sample was foundwith the content of space balls up to 90 pieces per conditionalarea unit. In the future, according to the author, the traincontinues to stretch to the northwest, capturing the basin of the Taimura River.Works of the Siberian Branch of the USSR Academy of Sciences in 1964-65. it was found that relatively rich samples are found along the entire course R. Taimur, a also on N. Tunguska / see map-scheme /. The spherules isolated at the same time contain up to 19% nickel / according tomicrospectral analysis carried out at the Institute of Nuclearphysics of the Siberian Branch of the Academy of Sciences of the USSR /. This approximately coincides with the numbersobtained by P.N. Paley in the field on the modelricks isolated from the soils of the area of the Tunguska catastrophe.These data allow us to state that the found particlesare indeed of cosmic origin. The question isabout their relation to the Tunguska meteorite remainswhich is open due to the lack of similar studiesbackground regions, as well as the possible role of processesredeposition and secondary enrichment.
Interesting finds of spherules in the area of the crater on Patomskyhighlands. The origin of this formation, attributedHoop to volcanic, still debatablebecause the presence of a volcanic cone in an area remotemany thousands of kilometers from volcanic foci, ancientthem and modern ones, in many kilometers of sedimentary-metamorphicthicknesses of the Paleozoic, it seems at least strange. Studies of spherules from the crater could give an unambiguousanswer to the question and about its origin / 82,50,53 /.the removal of matter from soils can be carried out by walkinghovaniya. In this way, a fraction of hundreds ofmicron and specific gravity above 5. However, in this casethere is a danger of discarding all the small magnetic frocktion and most of the silicate. E.L. Krinov advisesremove magnetic sanding with a magnet suspended from the bottom tray / 37 /.
A more accurate method is magnetic separation, dryor wet, although it also has a significant drawback: induring processing, the silicate fraction is lost. One ofinstallations of dry magnetic separation are described by Reinhardt/171/.
As already mentioned, cosmic matter is often collectednear the surface of the earth, in areas free from industrial pollution. In their direction, these works are close to the search for cosmic matter in the upper horizons of the soil.Trays filled withwater or adhesive solution, and plates lubricatedglycerin. The exposure time can be measured in hours, days,weeks, depending on the purpose of the observations. At the Dunlap Observatory in Canada, the collection of space matter usingadhesive plates have been carried out since 1947 /123/. In lit-The literature describes several variants of methods of this kind.For example, Hodge and Wright /113/ used for a number of yearsfor this purpose, glass slides coated with slowly dryingemulsion and solidification forming a finished preparation of dust;Croisier /90/ used ethylene glycol poured onto trays,which was easily washed with distilled water; in the worksHunter and Parkin /158/ oiled nylon mesh was used.
In all cases, spherical particles were found in the sediment,metal and silicate, most often smaller in size 6 µ in diameter and rarely exceeding 40 µ.
Thus, the totality of the presented dataconfirms the assumption of the fundamental possibilitydetection of cosmic matter in the soil for almostany site earth's surface. At the same time, it shouldkeep in mind that the use of soil as an objectto identify the space component is associated with methodologicaldifficulties far greater than those forsnow, ice and, possibly, to bottom silts and peat.
spacesubstance in ice
According to Krinov /37/, the discovery of a cosmic substance in the polar regions is of significant scientific importance.ing, since in this way a sufficient amount of material can be obtained, the study of which will probably approximatesolution of some geophysical and geological issues.
The separation of cosmic matter from snow and ice canbe carried out by various methods, ranging from the collectionlarge fragments of meteorites and ending with the production of meltedwater mineral sediment containing mineral particles.
In 1959 Marshall /135/ suggested an ingenious waystudy of particles from ice, similar to the counting methodred blood cells in the bloodstream. Its essence isIt turns out that to the water obtained by melting the sampleice, an electrolyte is added and the solution is passed through a narrow hole with electrodes on both sides. Atthe passage of a particle, the resistance changes sharply in proportion to its volume. Changes are recorded using specialgod recording device.
It should be borne in mind that ice stratification is nowcarried out in several ways. It is possible thatcomparison of already stratified ice with distributioncosmic matter can open up new approaches tostratification in places where other methods cannot beapplied for one reason or another.
To collect space dust, American Antarcticexpeditions 1950-60 used cores obtained fromdetermination of the thickness of the ice cover by drilling. /1 S3/.Samples with a diameter of about 7 cm were sawn into segments along 30 cm long, melted and filtered. The resulting precipitate was carefully examined under a microscope. Were discoveredparticles of both spherical and irregular shapes, andthe former constituted an insignificant part of the sediment. Further research was limited to spherules, since theycould be more or less confidently attributed to spacecomponent. Among the balls in size from 15 to 180 / hbyparticles of two types were found: black, shiny, strictly spherical and brown transparent.
Detailed study of cosmic particles isolated fromice of Antarctica and Greenland, was undertaken by Hodgeand Wright /116/. In order to avoid industrial pollutionice was taken not from the surface, but from a certain depth -in Antarctica, a 55-year-old layer was used, and in Greenland,750 years ago. Particles were selected for comparison.from the air of Antarctica, which turned out to be similar to glacial ones. All particles fit into 10 classification groupswith a sharp division into spherical particles, metallicand silicate, with and without nickel.
An attempt to obtain space balls from a high mountainsnow was undertaken by Divari /23/. Having melted a significant amountsnow /85 buckets/ taken from the surface of 65 m 2 on the glacierTuyuk-Su in the Tien Shan, however, he did not get what he wantedresults that can be explained or unevencosmic dust falling on the earth's surface, orfeatures of the applied technique.
In general, apparently, the collection of cosmic matter inpolar regions and on high mountain glaciers is oneof the most promising areas of work on space dust.
Sources pollution
There are currently two main sources of materialla, which can imitate in its properties the spacedust: volcanic eruptions and industrial wasteenterprises and transport. It is known what volcanic dust,released into the atmosphere during eruptionsstay there in suspension for months and years.Due to structural features and a small specificweight, this material can be distributed globally, andduring the transfer process, particles are differentiated according toweight, composition and size, which must be taken into account whenspecific analysis of the situation. After the famous eruptionvolcano Krakatau in August 1883, the smallest dust thrown outshennaya to a height of up to 20 km. found in the airfor at least two years /162/. Similar observationsDenias were made during the periods of volcanic eruptions of Mont Pelee/1902/, Katmai /1912/, groups of volcanoes in the Cordillera /1932/,volcano Agung /1963/ /12/. Microscopic dust collectedfrom different areas of volcanic activity, looks likegrains of irregular shape, with curvilinear, broken,jagged contours and relatively rarely spheroidaland spherical with a size from 10µ to 100. The number of sphericalwater is only 0.0001% by weight of the total material/115/. Other authors raise this value to 0.002% /197/.
Particles of volcanic ash have black, red, greenlazy, gray or brown. Sometimes they are colorlesstransparent and glass-like. Generally speaking, in volcanicglass is an essential part of many products. itconfirmed by the data of Hodge and Wright, who found thatparticles with an amount of iron from 5% and above arenear volcanoes only 16% . It should be taken into account that in the processdust transfer occurs, it is differentiated by size andspecific gravity, and large dust particles are eliminated faster Total. As a result, in remote from volcaniccenters, areas are likely to detect only the smallest and light particles.
Spherical particles were subjected to special study.volcanic origin. It has been established that they havemost often eroded surface, shape, roughlyleaning to spherical, but never have elongatednecks, like particles of meteorite origin.It is very significant that they do not have a core composed of pureiron or nickel, like those balls that are consideredspace /115/.
In the mineralogical composition of volcanic balls,a significant role belongs to glass, which has a bubblystructure, and iron-magnesium silicates - olivine and pyroxene. A much smaller part of them is composed of ore minerals - pyri-volume and magnetite, which mostly form disseminatednicks in glass and frame structures.
As for the chemical composition of volcanic dust,an example is the composition of the ashes of Krakatoa.Murray /141/ found in it a high content of aluminum/up to 90%/ and low iron content /not exceeding 10%.It should be noted, however, that Hodge and Wright /115/ could notconfirm Morrey's data on aluminum. Question aboutspherules of volcanic origin are also discussed in/205a/.
Thus, the properties characteristic of volcanicmaterials can be summarized as follows:
1.
volcanic ash contains a high percentage of particlesirregular shape and low - spherical,
2.
balls of volcanic rock have certain structurestour features - eroded surfaces, the absence of hollow spherules, often blistering,
3.
spherules are dominated by porous glass,
4.
the percentage of magnetic particles is low,
5.
in most cases spherical particle shape imperfect
6.
acute-angled particles have sharply angular shapesrestrictions, which allows them to be used asabrasive material.
A very significant danger of imitation of space spheresroll with industrial balls, in large quantitiessteam locomotive, steamship, factory pipes, formed during electric welding, etc. Specialstudies of such objects have shown that a significanta percentage of the latter has the form of spherules. According to Shkolnik /177/,25% industrial products is composed of metal slag.He also gives the following classification of industrial dust:
1.
non-metallic balls, irregular shape,
2.
balls are hollow, very shiny,
3.
balls similar to space, folded metalcal material with the inclusion of glass. Among the latterhaving the greatest distribution, there are drop-shaped,cones, double spherules.
From our point of view, the chemical compositionindustrial dust was studied by Hodge and Wright /115/.updated that characteristic features its chemical compositionis a high content of iron and in most cases - the absence of nickel. It must be borne in mind, however, that neitherone of indicated signs cannot be absolutecriterion of difference, especially since the chemical composition of differenttypes of industrial dust can be varied, andforesee the appearance of one or another variety ofindustrial spherules is almost impossible. Therefore, the best a guarantee against confusion can serve at the modern levelknowledge is only sampling in remote "sterile" fromindustrial pollution areas. degree of industrialpollution, as shown by special studies, isin direct proportion to the distance to settlements.Parkin and Hunter in 1959 made observations as far as possible.transportability of industrial spherules with water /159/.Although balls with a diameter of more than 300µ flew out of the factory pipes, in water basin located 60 miles from the cityyes, in the direction of the prevailing winds, onlysingle copies of 30-60 in size, the number of copies isa ditch measuring 5-10µ was, however, significant. Hodge andWright /115/ showed that in the vicinity of the Yale observatory,near the city center, fell on 1cm 2 surfaces per dayup to 100 balls over 5µ in diameter. Them the amount doubleddecreased on Sundays and fell 4 times at a distance10 miles from the city. So in remote areasprobably industrial pollution only with balls of diameter rum less than 5 µ .
It must be taken into account that in recent20 years there is a real danger of food pollutionnuclear explosions" that can supply spherules to the globalnominal scale /90.115/. These products are different from yes like-ny radioactivity and the presence of specific isotopes -strontium - 89 and strontium - 90.
Finally, keep in mind that some pollutionatmosphere with products similar to meteor and meteoritedust, can be caused by combustion in the Earth's atmosphereartificial satellites and launch vehicles. Phenomena observedin this case, are very similar to what takes place whenfalling fireballs. Serious danger to scientific researchions of cosmic matter are irresponsibleexperiments implemented and planned abroad withlaunch into near-Earth spacePersian substance of artificial origin.
The formand physical properties of cosmic dust
Shape, specific gravity, color, luster, brittleness and other physicalThe cosmic properties of cosmic dust found in various objects have been studied by a number of authors. Some-ry researchers proposed schemes for the classification of spacecal dust based on its morphology and physical properties.Although a single unified system has not yet been developed,It seems, however, appropriate to cite some of them.
Baddhyu /1950/ /87/ on the basis of purely morphologicalsigns divided the terrestrial matter into the following 7 groups:
1.
irregular gray amorphous fragments of size 100-200µ.
2.
slag-like or ash-like particles,
3.
rounded grains, similar to fine black sand/magnetite/,
4.
smooth black shiny balls with an average diameter 20µ
.
5.
large black balls, less shiny, often roughrough, rarely exceeding 100 µ in diameter,
6.
silicate balls from white to black, sometimeswith gas inclusions
7.
dissimilar balls, consisting of metal and glass,20µ in size on average.
The whole variety of types of cosmic particles, however, is notis exhausted, apparently, by the listed groups.So, Hunter and Parkin /158/ found roundedflattened particles, apparently of cosmic origin which cannot be attributed to any of the transfersnumerical classes.
Of all the groups described above, the most accessible toidentification by appearance 4-7, having the form of correct balls.
E.L. Krinov, studying the dust collected in the Sikhote-Alinsky's fall, distinguished in its composition the wrongin the form of fragments, balls and hollow cones /39/.
Typical shapes of space balls are shown in Fig.2.
A number of authors classify cosmic matter according tosets of physical and morphological properties. By destinyto a certain weight, cosmic matter is usually divided into 3 groups/86/:
1.
metallic, consisting mainly of iron,with a specific gravity greater than 5 g/cm 3 .
2.
silicate - transparent glass particles with specificweighing approximately 3 g / cm 3
3.
heterogeneous: metal particles with glass inclusions and glass particles with magnetic inclusions.
Most researchers remain within thisrough classification, limited to only the most obviousfeatures of difference. However, those who deal withparticles extracted from the air, another group is distinguished -porous, brittle, with a density of about 0.1 g/cm 3 /129/. Toit includes particles of meteor showers and most bright sporadic meteors.
A rather thorough classification of the particles foundin the Antarctic and Greenland ice, as well as capturedfrom the air, given by Hodge and Wright and presented in the scheme / 205 /:
1.
black or dark gray dull metal balls,pitted, sometimes hollow;
2.
black, glassy, highly refractive balls;
3.
light, white or coral, glassy, smooth,sometimes translucent spherules;
4.
particles of irregular shape, black, shiny, brittle,granular, metallic;
5.
irregularly shaped reddish or orange, dull,uneven particles;
6.
irregular shape, pinkish-orange, dull;
7.
irregular shape, silvery, shiny and dull;
8.
irregular shape, multi-colored, brown, yellow, green, black;
9.
irregular shape, transparent, sometimes green orblue, glassy, smooth, with sharp edges;
10.
spheroids.
Although the classification of Hodge and Wright seems to be the most complete, there are still particles that, judging by the descriptions of various authors, are difficult to classifyback to one of the named groups. So, it is not uncommon to meetelongated particles, balls sticking together with each other, balls,having various growths on their surface /39/.
On the surface of some spherules in a detailed studyfigures are found that are similar to Widmanstätten, observedin iron-nickel meteorites / 176/.
The internal structure of the spherules does not differ greatlyimage. Based on this feature, the following 4 groups:
1.
hollow spherules / meet with meteorites /,
2.
metal spherules with a core and an oxidized shell/ in the core, as a rule, nickel and cobalt are concentrated,and in the shell - iron and magnesium /,
3.
oxidized balls of uniform composition,
4.
silicate balls, most often homogeneous, with flakythat surface, with metal and gas inclusions/ the latter give them the appearance of slag or even foam /.
As for particle sizes, there is no firmly established division on this basis, and each authoradheres to its classification depending on the specifics of the material available. The largest of the described spherules,found in deep-sea sediments by Brown and Pauli /86/ in 1955, hardly exceed 1.5 mm in diameter. itclose to the existing limit found by Epic /153/:
where r is the radius of the particle, σ - surface tensionmelt, ρ is the air density, and v is the speed of the drop. Radius
particle cannot exceed the known limit, otherwise the dropbreaks down into smaller ones.
The lower limit, in all likelihood, is not limited, which follows from the formula and is justified in practice, becauseas the techniques improve, the authors operate on allsmaller particles. Most researchers are limitedcheck the lower limit of 10-15µ /160-168,189/.At the same time, studies of particles with a diameter of up to 5 µ started /89/ and 3 µ /115-116/, and Hemenway, Fulman and Phillips operateparticles up to 0.2 / µ and less in diameter, highlighting them in particularthe former class of nanometeorites / 108 /.
The average diameter of cosmic dust particles is taken equal to 40-50 µ . As a result intensive study spacewhich substances from the atmosphere Japanese authors found that 70% of the entire material are particles less than 15 µ in diameter.
A number of works /27,89,130,189/ contain a statement aboutthat the distribution of balls depending on their massand the dimensions obey the following pattern:
V 1 N 1 \u003d V 2 N 2
where v - mass of the ball, N - number of balls in a given groupResults that agree satisfactorily with the theoretical ones were obtained by a number of researchers who worked with the spacematerial isolated from various objects / for example, Antarctic ice, deep sea sediments, materials,obtained as a result of satellite observations/.
Of fundamental interest is the question of whetherto what extent the properties of nyli changed over the course of geological history. Unfortunately, the currently accumulated material does not allow us to give an unambiguous answer, however,Shkolnik's message /176/ about the classification lives onspherules isolated from the Miocene sedimentary rocks of California. The author divided these particles into 4 categories:
1/ black, strongly and weakly magnetic, solid or with cores consisting of iron or nickel with an oxidized shellwhich is made of silica with an admixture of iron and titanium. These particles may be hollow. Their surface is intensely shiny, polished, in some cases rough or iridescent as a result of light reflection from saucer-shaped depressions on their surfaces
2/ gray-steel or bluish-gray, hollow, thinwall, very fragile spherules; contain nickel, havepolished or polished surface;
3/ brittle balls containing numerous inclusionsgray steel metallic and black non-metallicmaterial; microscopic bubbles in their walls ki / this group of particles is the most numerous /;
4/ brown or black silicate spherules, non-magnetic.
It is easy to replace that the first group according to Shkolnikcorresponds closely to Buddhue's 4 and 5 particle groups. Bamong these particles there are hollow spherules similar tothose found in meteorite impact areas.
Although these data do not contain exhaustive informationon the issue raised, it seems possible to expressin the first approximation, the opinion that morphology and physi-physical properties of at least some groups of particlesof cosmic origin, falling on the Earth, do notsang significant evolution over the availablegeological study of the period of the planet's development.
Chemicalcomposition of space dust.
The study of the chemical composition of cosmic dust occurswith certain difficulties of principle and technicalcharacter. Already on my own small size of the studied particles,the difficulty of obtaining in any significant quantitiesvakh create significant obstacles to the application of techniques that are widely used in analytical chemistry. Further,it must be borne in mind that the samples under study in the vast majority of cases may contain impurities, and sometimesvery significant, earthly material. Thus, the problem of studying the chemical composition of cosmic dust is intertwinedlurks with the question of its differentiation from terrestrial impurities.Finally, the very formulation of the question of the differentiation of the "terrestrial"and "cosmic" matter is to some extent conditional, because The earth and all its components, its constituents,represent, ultimately, also a cosmic object, andtherefore, strictly speaking, it would be more correct to pose the questionabout finding signs of difference between different categoriescosmic matter. It follows from this that the similarityentities of terrestrial and extraterrestrial origin can, in principle,extend very far, which creates additionaldifficulties for studying the chemical composition of cosmic dust.
However, in recent years, science has been enriched by a number ofmethodological techniques that allow, to a certain extent, to overcomeovercome or bypass obstacles that arise. Development but-the latest methods of radiation chemistry, X-ray diffractionmicroanalysis, the improvement of microspectral techniques now make it possible to investigate insignificant in their own waythe size of the objects. Currently quite affordableanalysis of the chemical composition of not only individual particles ofmic dust, but also the same particle in different its sections.
In the last decade, a significant numberworks devoted to the study of the chemical composition of spacedust from various sources. For reasonswhich we have already touched upon above, the study was mainly carried out by spherical particles related to magneticfraction of dust, As well as in relation to the characteristics of physicalproperties, our knowledge of the chemical composition of acute-angledmaterial is still quite scarce.
Analyzing the materials received in this direction by a wholea number of authors, one should come to the conclusion that, firstly,the same elements are found in cosmic dust as inother objects of terrestrial and cosmic origin, for example, it contains Fe, Si, Mg .In some cases - rarelyland elements and Ag the findings are doubtful /, in relation toThere are no reliable data in the literature. Secondly, allthe amount of cosmic dust that falls on Earthbe divided by chemical composition, at least for tri large groups of particles:
a) metal particles with a high content Fe
and N i ,
b) particles of predominantly silicate composition,
c) particles of mixed chemical nature.
It is easy to see that the three groups listedessentially coincide with the accepted classification of meteorites, whichrefers to a close, and perhaps a common source of origincirculation of both types of cosmic matter. It can be noted dFurther, there is a large variety of particles within each of the groups under consideration. This gives rise to a number of researchersher to divide cosmic dust by chemical composition by 5.6 andmore groups. Thus, Hodge and Wright single out the following eighttypes of basic particles that differ from each other as much as possiblerphological features, and chemical composition:
1.
iron balls containing nickel,
2.
iron spherules, in which nickel is not found,
3.
silica balls,
4.
other spheres,
5.
irregularly shaped particles with a high content of iron and nickel;
6.
the same without the presence of any significant quantities estv nickel,
7.
silicate particles of irregular shape,
8.
other particles of irregular shape.
From the above classification it follows, among other things,that circumstance that the presence of a high nickel content in the material under study cannot be recognized as a mandatory criterion for its cosmic origin. So, it meansThe main part of the material extracted from the ice of Antarctica and Greenland, collected from the air of the highlands of New Mexico, and even from the area where the Sikhote-Alin meteorite fell, did not contain quantities available for determination.nickel. At the same time, one has to take into account the well-founded opinion of Hodge and Wright that a high percentage of nickel (up to 20% in some cases) is the onlyreliable criterion of the cosmic origin of a particular particle. Obviously, in case of his absence, the researchershould not be guided by the search for "absolute" criteria"and on the assessment of the properties of the material under study, taken in their aggregates.
In many works, the heterogeneity of the chemical composition of even the same particle of space material in its different parts is noted. So it was established that nickel tends to the core of spherical particles, cobalt is also found there.The outer shell of the ball is composed of iron and its oxide.Some authors admit that nickel exists in the formindividual spots in the magnetite substrate. Below we presentdigital materials characterizing the average contentnickel in dust of cosmic and terrestrial origin.
From the table it follows that the analysis of the quantitative contentnickel can be useful in differentiatingspace dust from volcanic.
From the same point of view, the relations N i : Fe ; Ni : co, Ni : Cu , which are sufficientlyare constant for individual objects of the terrestrial and space origin.
igneous rocks-3,5 1,1
When differentiating cosmic dust from volcanicand industrial pollution can be of some benefitalso provide a study of the quantitative content Al and K , which are rich in volcanic products, and Ti and V being frequent companions Fe in industrial dust.It is significant that in some cases industrial dust may contain a high percentage of N i . Therefore, the criterion for distinguishing some types of cosmic dust fromterrestrial should serve not just a high content of N i , a high N content i together with Co and C u/88.121, 154.178.179/.
Information about the presence of radioactive products of cosmic dust is extremely scarce. Negative results are reportedtatah testing space dust for radioactivity, whichseems doubtful in view of the systematic bombingdust particles located in interplanetary spacesve, cosmic rays. Recall that the productscosmic radiation have been repeatedly detected in meteorites.
Dynamicscosmic dust fallout over time
According to the hypothesis Paneth /156/, fallout of meteoritesdid not take place in distant geological epochs / earlierQuaternary time /. If this view is correct, thenit should also extend to cosmic dust, or at leastwould be on that part of it, which we call meteorite dust.
The main argument in favor of the hypothesis was the absenceimpact of finds of meteorites in ancient rocks, at presenttime, however, there are a number of finds like meteorites,and the cosmic dust component in geologicalformations of rather ancient age / 44,92,122,134,176-177/, Many of the listed sources are citedabove, it should be added that March /142/ discovered balls,apparently of cosmic origin in the Siluriansalts, and Croisier /89/ found them even in the Ordovician.
The distribution of spherules along the section in deep-sea sediments was studied by Petterson and Rothschi /160/, who foundlived that nickel is unevenly distributed over the section, whichexplained, in their opinion, by cosmic causes. Laterfound to be richest in cosmic materialthe youngest layers of bottom silts, which, apparently, is associatedwith the gradual processes of destruction of spacewhom substances. In this regard, it is natural to assumethe idea of a gradual decrease in the concentration of cosmicsubstances down the cut. Unfortunately, in the literature available to us, we did not find sufficiently convincing data on suchkind, the available reports are fragmentary. So, Shkolnik /176/found an increased concentration of balls in the weathering zoneof Cretaceous deposits, from this fact he wasa reasonable conclusion was made that spherules, apparently,can withstand sufficiently harsh conditions if theycould survive lateritization.
Modern regular studies of space falloutdust show that its intensity varies significantly day by day /158/.
Apparently, there is a certain seasonal dynamics /128,135/, and the maximum intensity of precipitationfalls in August-September, which is associated with meteorstreams /78,139/,
It should be noted that meteor showers are not the onlynaya cause of massive fallout of cosmic dust.
There is a theory that meteor showers cause precipitation /82/, meteor particles in this case are condensation nuclei /129/. Some authors suggestThey claim to collect cosmic dust from rainwater and offer their devices for this purpose /194/.
Bowen /84/ found that the peak of precipitation is latefrom the maximum meteor activity by about 30 days, which can be seen from the following table.
These data, although not universally accepted, arethey deserve some attention. Bowen's findings confirmdata on the material of Western Siberia Lazarev /41/.
Although the question of the seasonal dynamics of cosmicdust and its connection with meteor showers is not completely clear.resolved, there are good reasons to believe that such a regularity takes place. So, Croisier / CO /, based onfive years of systematic observations, suggests that two maxima of cosmic dust fallout,that took place in the summer of 1957 and 1959 correlate with the meteormi streams. Summer high confirmed by Morikubo, seasonaldependence was also noted by Marshall and Craken /135,128/.It should be noted that not all authors are inclined to attribute theseasonal dependence due to meteor activity/for example, Brier, 85/.
With regard to the distribution curve of daily depositionmeteor dust, it is apparently strongly distorted by the influence of winds. This is reported, in particular, by Kizilermak andCroisier /126.90/. Good summary of materials on thisReinhardt has a question /169/.
Distributionspace dust on the earth's surface
The question of the distribution of cosmic matter on the surfaceof the Earth, like a number of others, was developed completely insufficientlyexactly. Opinions as well as factual material reportedby various researchers are very contradictory and incomplete.One of the leading experts in this field, Petterson,definitely expressed the opinion that cosmic matterdistributed on the surface of the Earth is extremely uneven / 163 /. Ethis, however, comes into conflict with a number of experimentaldata. In particular, de Jaeger /123/, based on feesof cosmic dust produced using sticky plates in the area of the Canadian Dunlap Observatory, claims that cosmic matter is distributed fairly evenly over large areas. A similar opinion was expressed by Hunter and Parkin /121/ on the basis of a study of cosmic matter in the bottom sediments of the Atlantic Ocean. Hodya /113/ carried out studies of cosmic dust at three remote points from each other. Observations were carried out for a long time, for a whole year. Analysis of the results obtained showed the same rate of accumulation of matter at all three points, and on average, about 1.1 spherules fell per 1 cm 2 per day.about three microns in size. Research in this direction were continued in 1956-56. Hodge and Wildt /114/. On thethis time the collection was carried out in areas separated from each otherfriend over very long distances: in California, Alaska,In Canada. Calculated the average number of spherules , fallen on a unit surface, which turned out to be 1.0 in California, 1.2 in Alaska and 1.1 spherical particles in Canada molds per 1 cm 2 per day. Size distribution of spheruleswas approximately the same for all three points, and 70% were formations with a diameter of less than 6 microns, the numberparticles larger than 9 microns in diameter were small.
It can be assumed that, apparently, the fallout of the cosmicdust reaches the Earth, in general, quite evenly, against this background, certain deviations from the general rule can be observed. So, one can expect the presence of a certain latitudinalthe effect of precipitation of magnetic particles with a tendency to concentrationtions of the latter in the polar regions. Further, it is known thatconcentration of finely dispersed cosmic matter canbe elevated in areas where large meteorite masses fall/ Arizona meteor crater, Sikhote-Alin meteorite,possibly the area where the Tunguska cosmic body fell.
Primary uniformity can, however, in the futuresignificantly disrupted as a result of the secondary redistributionfission of matter, and in some places it may have itaccumulation, and in others - a decrease in its concentration. In general, this issue has been developed very poorly, however, preliminarysolid data obtained by the expedition K M ET AS USSR /head K.P.Florensky/ / 72/ let's talk aboutthat, at least in a number of cases, the content of spacechemical substance in the soil can fluctuate over a wide range lah.
Migratzand Ispacesubstancesinbiogenosfere
No matter how contradictory estimates of the total number of spaceof the chemical substance that falls annually on the Earth, it is possible withcertainty to say one thing: it is measured by many hundredsthousand, and perhaps even millions of tons. Absolutelyit is obvious that this huge mass of matter is included in the farthe most complex chain of processes of the circulation of matter in nature, which constantly takes place within the framework of our planet.Cosmic matter will stop, thus the compositepart of our planet, in the literal sense - the substance of the earth,which is one of the possible channels of influence of spacesome environment on the biogenosphere. It is from these positions that the problemspace dust interested the founder of modernbiogeochemistry ac. Vernadsky. Unfortunately, work in thisdirection, in essence, has not yet begun in earnest. Thereforewe have to confine ourselves to stating a fewfacts that appear to be relevant to thequestion. There are a number of indications that deep-seasediments removed from sources of material drift and havinglow rate of accumulation, relatively rich, Co and Si.Many researchers attribute these elements to cosmicsome origin. Apparently, different types of particles are cos-The chemical dusts are included in the cycle of substances in nature at different rates. Some types of particles are very conservative in this regard, as evidenced by the findings of magnetite spherules in ancient sedimentary rocks.The number of particles can, obviously, depend not only on theirnature, but also on environmental conditions, in particular,its pH value. It is highly likely that the elementsfalling to Earth as part of cosmic dust, canfurther included in the composition of plant and animalorganisms that inhabit the earth. In favor of this assumptionsay, in particular, some data on the chemical compositionve vegetation in the area where the Tunguska meteorite fell.All this, however, is only the first outline,the first attempts at an approach not so much to a solution as toposing the question in this plane.
Recently there has been a trend towards more estimates of the probable mass of the falling cosmic dust. Fromefficient researchers estimate it at 2.4109 tons /107a/.
prospectsstudy of cosmic dust
Everything that has been said in the previous sections of the work,allows you to say with sufficient reason about two things:firstly, that the study of cosmic dust is seriouslyjust beginning and, secondly, that the work in this sectionscience turns out to be extremely fruitful for solvingmany questions of theory / in the future, maybe forpractices/. A researcher working in this area is attractedfirst of all, a huge variety of problems, one way or anotherotherwise related to the clarification of relationships in the system Earth is space.
How it seems to us that the further development of the doctrine ofcosmic dust should go mainly through the following main directions:
1.
The study of the near-Earth dust cloud, its spacenatural location, properties of dust particles enteringin its composition, sources and ways of its replenishment and loss,interaction with radiation belts. These studiescan be carried out in full with the help of missiles,artificial satellites, and later - interplanetaryships and automatic interplanetary stations.
2.
Of undoubted interest for geophysics is the spacechesky dust penetrating into the atmosphere at altitude 80-120 km, in
in particular, its role in the mechanism of emergence and developmentphenomena such as the glow of the night sky, the change in polaritydaylight fluctuations, transparency fluctuations atmosphere,
development of noctilucent clouds and bright Hoffmeister bands,dawn and twilight phenomena, meteor phenomena in atmosphere
Earth. Special of interest is the study of the degree of correlationlation between the phenomena listed. Unexpected Aspects
cosmic influences can be revealed, apparently, infurther study of the relationship of processes that haveplace in the lower layers of the atmosphere - the troposphere, with penetrationniem in the last cosmic matter. The most seriousAttention should be given to testing Bowen's conjecture aboutconnection of precipitation with meteor showers.
3.
Of undoubted interest to geochemists isstudy of the distribution of cosmic matter on the surfaceEarth, the influence on this process of specific geographical,climatic, geophysical and other conditions peculiar to
one or another region of the world. So far completelyinfluence has not been studied magnetic field Lands per processaccumulation of cosmic matter, meanwhile, in this area,likely to be interesting finds, especiallyif we build studies taking into account paleomagnetic data.
4.
Of fundamental interest for both astronomers and geophysicists, not to mention generalist cosmogonists,has a question about meteor activity in remote geologicalepochs. Materials that will be received during this
works, can probably be used in the futurein order to develop additional methods of stratificationbottom, glacial and silent sedimentary deposits.
5.
An important area of work is the studymorphological, physical, chemical properties of spacecomponent of terrestrial precipitation, development of methods for distinguishing braidsmic dust from volcanic and industrial, researchisotopic composition of cosmic dust.
6.Search for organic compounds in space dust.It seems likely that the study of cosmic dust will contribute to the solution of the following theoretical problems. questions:
1.
The study of the process of evolution of cosmic bodies, in particularness, the Earth and the solar system as a whole.
2.
The study of the movement, distribution and exchange of spacematter in the solar system and galaxy.
3. Elucidation of the role of galactic matter in the solar system.
4.
The study of orbits and velocities of space bodies.
5.
Development of the theory of interaction of cosmic bodies with the earth.
6.
Deciphering the mechanism of a number of geophysical processesin the Earth's atmosphere, undoubtedly associated with space phenomena.
7.
The study of possible ways of cosmic influences onbiogenosphere of the Earth and other planets.
It goes without saying that the development of even those problemswhich are listed above, but they are far from being exhausted.the whole complex of issues related to cosmic dust,is possible only under the condition of a broad integration and unificationthe efforts of specialists of various profiles.
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Interstellar dust is a product of various intensity processes occurring in all corners of the Universe, and its invisible particles even reach the surface of the Earth, flying in the atmosphere around us.
A repeatedly confirmed fact - nature does not like emptiness. Interstellar outer space, which seems to us to be vacuum, is actually filled with gas and microscopic dust particles, 0.01-0.2 microns in size. The combination of these invisible elements gives rise to objects of enormous size, a kind of clouds of the Universe, capable of absorbing some types of spectral radiation from stars, sometimes completely hiding them from earthly researchers.
What is interstellar dust made of?
These microscopic particles have a nucleus, which is formed in the gaseous envelope of stars and depends entirely on its composition. For example, graphite dust is formed from grains of carbon luminaries, and silicate dust is formed from oxygen ones. This is an interesting process that lasts for decades: when the stars cool down, they lose their molecules, which, flying into space, combine into groups and become the basis of the core of a dust grain. Further, a shell of hydrogen atoms and more complex molecules is formed. At low temperatures, interstellar dust is in the form of ice crystals. Wandering around the Galaxy, little travelers lose part of the gas when heated, but new molecules take the place of the departed molecules.
Location and properties
The main part of the dust that falls on our Galaxy is concentrated in the region of the Milky Way. It stands out against the background of stars in the form of black stripes and spots. Despite the fact that the weight of dust is negligible compared to the weight of gas and is only 1%, it is able to hide celestial bodies from us. Although the particles are separated from each other by tens of meters, but even in such an amount, the densest regions absorb up to 95% of the light emitted by stars. The sizes of gas and dust clouds in our system are really huge, they are measured in hundreds of light years.
Impact on observations
Thackeray globules obscure the region of the sky behind them
Interstellar dust absorbs most of the radiation from stars, especially in the blue spectrum, it distorts their light and polarity. Short waves from distant sources receive the greatest distortion. Microparticles mixed with gas are visible as dark spots on the Milky Way.
In connection with this factor, the core of our Galaxy is completely hidden and is available for observation only in infrared rays. Clouds with a high concentration of dust become almost opaque, so the particles inside do not lose their icy shell. Modern researchers and scientists believe that it is they who stick together to form the nuclei of new comets.
Science has proven the influence of dust granules on the processes of star formation. These particles contain various substances, including metals, which act as catalysts for numerous chemical processes.
Our planet increases its mass every year due to falling interstellar dust. Of course, these microscopic particles are invisible, and in order to find and study them, they explore the ocean floor and meteorites. The collection and delivery of interstellar dust has become one of the functions of spacecraft and missions.
When entering the Earth's atmosphere, large particles lose their shell, and small ones invisibly circle around us for years. Cosmic dust is ubiquitous and similar in all galaxies, astronomers regularly observe dark lines on the face of distant worlds.
COSMIC DUST, solid particles with characteristic sizes from about 0.001 microns to about 1 microns (and possibly up to 100 microns or more in the interplanetary medium and protoplanetary disks), found in almost all astronomical objects: from the solar system to very distant galaxies and quasars . Dust characteristics (particle concentration, chemical composition, particle size, etc.) vary significantly from one object to another, even for objects of the same type. Cosmic dust scatters and absorbs incident radiation. Scattered radiation with the same wavelength as the incident radiation propagates in all directions. The radiation absorbed by the dust grain is transformed into thermal energy, and the particle usually radiates in a longer wavelength region of the spectrum compared to the incident radiation. Both processes contribute to extinction - the attenuation of the radiation of celestial bodies by dust located on the line of sight between the object and the observer.
Dust objects are studied in almost the entire range of electromagnetic waves - from X-ray to millimeter. Electric dipole radiation from rapidly rotating ultrafine particles appears to make some contribution to microwave radiation at frequencies of 10-60 GHz. An important role is played by laboratory experiments in which they measure the refractive indices, as well as the absorption spectra and scattering matrices of particles - analogs of cosmic dust grains, simulate the processes of formation and growth of refractory dust grains in the atmospheres of stars and protoplanetary disks, study the formation of molecules and the evolution of volatile dust components under conditions similar to those found in dark interstellar clouds.
Cosmic dust, which is in various physical conditions, is directly studied in the composition of meteorites that have fallen to the Earth's surface, in upper layers Earth's atmosphere (interplanetary dust and remnants of small comets), during spacecraft flights to planets, asteroids and comets (near planetary and cometary dust) and outside the heliosphere (interstellar dust). Ground and space remote observations of cosmic dust cover the Solar System (interplanetary, circumplanetary and cometary dust, dust near the Sun), the interstellar medium of our Galaxy (interstellar, circumstellar and nebular dust) and other galaxies (extragalactic dust), as well as very distant objects (cosmological dust).
Cosmic dust particles mainly consist of carbonaceous substances (amorphous carbon, graphite) and magnesium-iron silicates (olivines, pyroxenes). They condense and grow in the atmospheres of stars of late spectral classes and in protoplanetary nebulae, and then are ejected into the interstellar medium by radiation pressure. In interstellar clouds, especially dense ones, refractory particles continue to grow as a result of the accretion of gas atoms, as well as when particles collide and stick together (coagulation). This leads to the appearance of shells of volatile substances (mainly ice) and to the formation of porous aggregate particles. The destruction of dust grains occurs as a result of dispersion in shock waves arising after supernova explosions, or evaporation in the process of star formation that began in the cloud. The remaining dust continues to evolve near the formed star and later manifests itself in the form of an interplanetary dust cloud or cometary nuclei. Paradoxically, dust around evolved (old) stars is “fresh” (recently formed in their atmosphere), and around young stars it is old (evolved as part of the interstellar medium). It is assumed that cosmological dust, possibly existing in distant galaxies, condensed in the ejecta of matter after the explosions of massive supernovae.
Lit. see at st. Interstellar dust.
During 2003–2008 a group of Russian and Austrian scientists with the participation of Heinz Kohlmann, a famous paleontologist, curator of the Eisenwurzen National Park, studied the catastrophe that happened 65 million years ago, when more than 75% of all organisms died out on Earth, including dinosaurs. Most researchers believe that the extinction was due to the fall of an asteroid, although there are other points of view.
Traces of this catastrophe in geological sections are represented by a thin layer of black clay with a thickness of 1 to 5 cm. One of these sections is located in Austria, in the Eastern Alps, in the National Park near the small town of Gams, located 200 km southwest of Vienna. As a result of the study of samples from this section using a scanning electron microscope, particles of unusual shape and composition were found, which are not formed under terrestrial conditions and belong to cosmic dust.
Space dust on earth
For the first time, traces of cosmic matter on Earth were discovered in red deep-sea clays by an English expedition that explored the bottom of the World Ocean on the Challenger ship (1872–1876). They were described by Murray and Renard in 1891. At two stations in the southern part Pacific Ocean during dredging from a depth of 4300 m, samples of ferromanganese nodules and magnetic microspheres with a diameter of up to 100 microns were raised, which later received the name "cosmic balls". However, iron microspheres recovered by the Challenger expedition have only been studied in detail in recent years. It turned out that the balls are 90% metallic iron, 10% nickel, and their surface is covered with a thin crust of iron oxide.
Rice. 1. Monolith from the Gams 1 section, prepared for sampling. Layers are marked in Latin letters different ages. The transitional clay layer between the Cretaceous and Paleogene periods (about 65 million years old), in which an accumulation of metal microspheres and plates was found, is marked with the letter "J". Photo by A.F. Grachev
With the discovery of mysterious balls in deep-sea clays, in fact, the beginning of the study of cosmic matter on Earth is connected. However, an explosion of researchers' interest in this problem occurred after the first launches of spacecraft, with the help of which it became possible to select lunar soil and samples of dust particles from different parts of the solar system. Importance also had works by K.P. Florensky (1963), who studied the traces of the Tunguska catastrophe, and E.L. Krinov (1971), who studied meteoric dust at the site of the fall of the Sikhote-Alin meteorite.
The interest of researchers in metallic microspheres has led to their discovery in sedimentary rocks of different ages and origins. Metal microspheres have been found in the ice of Antarctica and Greenland, in deep ocean sediments and manganese nodules, in the sands of deserts and coastal beaches. They are often found in meteorite craters and next to them.
In the last decade, metal microspheres of extraterrestrial origin have been found in sedimentary rocks of different ages: from the Lower Cambrian (about 500 million years ago) to modern formations.
Data on microspheres and other particles from ancient deposits make it possible to judge the volumes, as well as the uniformity or unevenness of the supply of cosmic matter to the Earth, the change in the composition of particles entering the Earth from space, and the primary sources of this matter. This is important because these processes affect the development of life on Earth. Many of these questions are still far from being resolved, but the accumulation of data and their comprehensive study will undoubtedly make it possible to answer them.
It is now known that the total mass of dust circulating inside the Earth's orbit is about 1015 tons. Every year, from 4 to 10 thousand tons of cosmic matter falls on the Earth's surface. 95% of the matter falling on the Earth's surface are particles with a size of 50-400 microns. The question of how the rate of arrival of cosmic matter to the Earth changes with time remains controversial until now, despite the many studies carried out in the past 10 years.
Based on the size of cosmic dust particles, interplanetary cosmic dust with a size of less than 30 microns and micrometeorites larger than 50 microns are currently isolated. Even earlier, E.L. Krinov suggested that the smallest fragments of a meteoroid melted from the surface be called micrometeorites.
Strict criteria for distinguishing between cosmic dust and meteorite particles have not yet been developed, and even using the example of the Hams section studied by us, it has been shown that metal particles and microspheres are more diverse in shape and composition than provided by the existing classifications. Almost perfect spherical shape, metallic luster and magnetic properties particles were considered as proof of their cosmic origin. According to geochemist E.V. Sobotovich, "the only morphological criterion for assessing the cosmogenicity of the material under study is the presence of melted balls, including magnetic ones." However, in addition to the extremely diverse form, the chemical composition of the substance is fundamentally important. The researchers found that along with microspheres of cosmic origin, there are a huge number of balls of a different genesis - associated with volcanic activity, the vital activity of bacteria or metamorphism. There is evidence that ferruginous microspheres of volcanic origin are much less likely to have an ideal spherical shape and, moreover, have an increased admixture of titanium (Ti) (more than 10%).
Russian-Austrian group of geologists and film crew of the Vienna Television on the Gams section in the Eastern Alps. In the foreground - A.F. Grachev
Origin of cosmic dust
The question of the origin of cosmic dust is still a subject of debate. Professor E.V. Sobotovich believed that cosmic dust could represent the remnants of the original protoplanetary cloud, which was objected to in 1973 by B.Yu. Levin and A.N. Simonenko, believing that a finely dispersed substance could not be preserved for a long time (Earth and Universe, 1980, No. 6).
There is another explanation: the formation of cosmic dust is associated with the destruction of asteroids and comets. As noted by E.V. Sobotovich, if the amount of cosmic dust entering the Earth does not change in time, then B.Yu. Levin and A.N. Simonenko.
Despite the large number of studies, the answer to this fundamental question cannot be given at present, because there are very few quantitative estimates, and their accuracy is debatable. Recently, data from NASA isotope studies of cosmic dust particles sampled in the stratosphere suggest the existence of particles of pre-solar origin. Minerals such as diamond, moissanite (silicon carbide) and corundum were found in this dust, which, using carbon and nitrogen isotopes, allow us to attribute their formation to the time before the formation of the solar system.
The importance of studying cosmic dust in the geological section is obvious. This article presents the first results of a study of cosmic matter in the transitional clay layer at the Cretaceous-Paleogene boundary (65 million years ago) from the Gams section, in the Eastern Alps (Austria).
General characteristics of the Gams section
Particles of cosmic origin were obtained from several sections of the transitional layers between the Cretaceous and Paleogene (in the German-language literature - the K / T boundary), located near the Alpine village of Gams, where the river of the same name in several places reveals this boundary.
In section Gams 1, a monolith was cut from the outcrop, in which the K/T boundary is very well expressed. Its height is 46 cm, width is 30 cm in the lower part and 22 cm in the upper part, thickness is 4 cm. ,C…W), and within each layer, the numbers (1, 2, 3, etc.) were also marked every 2 cm. The transition layer J at the K/T interface was studied in more detail, where six sublayers with a thickness of about 3 mm were identified.
The results of studies obtained in the Gams 1 section are largely repeated in the study of another section - Gams 2. The complex of studies included the study of thin sections and monomineral fractions, their chemical analysis, as well as X-ray fluorescence, neutron activation and X-ray structural analyzes, analysis of helium, carbon and oxygen, determination of the composition of minerals on a microprobe, magnetomineralogical analysis.
Variety of microparticles
Iron and nickel microspheres from the transitional layer between the Cretaceous and Paleogene in the Gams section: 1 – Fe microsphere with a rough reticulate-hummocky surface (upper part of the transitional layer J); 2 – Fe microsphere with a rough longitudinally parallel surface ( Bottom part transition layer J); 3 – Fe microsphere with elements of crystallographic faceting and coarse cellular-network surface texture (layer M); 4 – Fe microsphere with a thin network surface (upper part of transition layer J); 5 – Ni microsphere with crystallites on the surface (upper part of transition layer J); 6 – aggregate of sintered Ni microspheres with crystallites on the surface (upper part of transition layer J); 7 – aggregate of Ni microspheres with microdiamonds (C; upper part of the transition layer J); 8, 9—characteristic forms of metal particles from the transitional layer between the Cretaceous and Paleogene in the Gams section in the Eastern Alps.
In the transitional clay layer between the two geological boundaries - the Cretaceous and Paleogene, as well as at two levels in the overlying deposits of the Paleocene in the Gams section, many metal particles and microspheres of cosmic origin were found. They are much more diverse in form, surface texture, and chemical composition than all known so far in transitional clay layers of this age in other regions of the world.
In the Gams section, the cosmic matter is represented by finely dispersed particles of various shapes, among which the most common are magnetic microspheres ranging in size from 0.7 to 100 μm, consisting of 98% pure iron. Such particles in the form of spherules or microspherules are found in large quantities not only in layer J, but also higher, in clays of the Paleocene (layers K and M).
The microspheres are composed of pure iron or magnetite, some of them have impurities of chromium (Cr), an alloy of iron and nickel (avaruite), and pure nickel (Ni). Some Fe-Ni particles contain an admixture of molybdenum (Mo). In the transitional clay layer between the Cretaceous and Paleogene, all of them were discovered for the first time.
Never before have come across particles with a high nickel content and a significant admixture of molybdenum, microspheres with the presence of chromium and pieces of spiral iron. In addition to metallic microspheres and particles, Ni-spinel, microdiamonds with microspheres of pure Ni, as well as torn plates of Au and Cu, which were not found in the underlying and overlying deposits, were found in the transitional clay layer in Gams.
Characterization of microparticles
Metallic microspheres in the Gams section are present at three stratigraphic levels: ferruginous particles of various shapes are concentrated in the transitional clay layer, in the overlying fine-grained sandstones of layer K, and the third level is formed by siltstones of layer M.
Some spheres have a smooth surface, others have a reticulate-hilly surface, and others are covered with a network of small polygonal cracks or a system of parallel cracks extending from one main crack. They are hollow, shell-like, filled with a clay mineral, and may also have an internal concentric structure. Metal particles and Fe microspheres are found throughout the transitional clay layer, but are mainly concentrated in the lower and middle horizons.
Micrometeorites are melted particles of pure iron or Fe-Ni iron-nickel alloy (awaruite); their sizes are from 5 to 20 microns. Numerous awaruite particles are confined to the upper level of the transition layer J, while purely ferruginous particles are present in the lower and upper parts of the transition layer.
Particles in the form of plates with a transversely bumpy surface consist only of iron, their width is 10–20 µm, and their length is up to 150 µm. They are slightly arcuately curved and occur at the base of the transition layer J. In its lower part, there are also Fe-Ni plates with an admixture of Mo.
Plates made of an alloy of iron and nickel have an elongated shape, slightly curved, with longitudinal grooves on the surface, the dimensions vary in length from 70 to 150 microns with a width of about 20 microns. They are more common in the lower and middle parts of the transition layer.
Iron plates with longitudinal grooves are identical in shape and size to Ni-Fe alloy plates. They are confined to the lower and middle parts of the transition layer.
Of particular interest are particles of pure iron, having the shape of a regular spiral and bent in the form of a hook. They mainly consist of pure Fe, rarely it is an Fe-Ni-Mo alloy. Spiral iron particles occur in the upper part of the J layer and in the overlying sandstone layer (K layer). A spiral Fe-Ni-Mo particle was found at the base of the transition layer J.
In the upper part of the transition layer J, there were several grains of microdiamonds sintered with Ni microspheres. Microprobe studies of nickel balls carried out on two instruments (with wave and energy dispersive spectrometers) showed that these balls consist of almost pure nickel under a thin film of nickel oxide. The surface of all nickel balls is dotted with distinct crystallites with pronounced twins 1–2 µm in size. Such pure nickel in the form of balls with a well-crystallized surface is not found either in igneous rocks or in meteorites, where nickel necessarily contains a significant amount of impurities.
When studying a monolith from the Gams 1 section, pure Ni balls were found only in the uppermost part of the transition layer J (in its uppermost part, a very thin sedimentary layer J 6, whose thickness does not exceed 200 μm), and according to thermal magnetic analysis data, metallic nickel is present in transitional layer, starting from sublayer J4. Here, along with Ni balls, diamonds were also found. In a layer taken from a cube with an area of 1 cm2, the number of diamond grains found is in the tens (from fractions of microns to tens of microns in size), and hundreds of nickel balls of the same size.
In samples of the upper part of the transition layer, taken directly from the outcrop, diamonds were found with small particles of nickel on the grain surface. It is significant that the presence of the mineral moissanite was also revealed during the study of samples from this part of layer J. Previously, microdiamonds were found in the transitional layer at the Cretaceous-Paleogene boundary in Mexico.
Finds in other areas
Hams microspheres with concentric internal structure similar to those that were mined by the Challenger expedition in the deep-sea clays of the Pacific Ocean.
Iron particles of irregular shape with melted edges, as well as in the form of spirals and curved hooks and plates, are very similar to the destruction products of meteorites falling to the Earth, they can be considered as meteoric iron. Avaruite and pure nickel particles can be assigned to the same category.
Curved iron particles are close to the various forms of Pele's tears - lava drops (lapilli), which eject volcanoes from the vent during eruptions in a liquid state.
Thus, the transitional clay layer in Gams has a heterogeneous structure and is distinctly divided into two parts. Iron particles and microspheres predominate in the lower and middle parts, while the upper part of the layer is enriched in nickel: awaruite particles and nickel microspheres with diamonds. This is confirmed not only by the distribution of iron and nickel particles in the clay, but also by the data of chemical and thermomagnetic analyses.
Comparison of the data of thermomagnetic analysis and microprobe analysis indicates an extreme inhomogeneity in the distribution of nickel, iron, and their alloy within layer J; however, according to the results of thermomagnetic analysis, pure nickel is recorded only from layer J4. It is also noteworthy that helical iron occurs mainly in the upper part of layer J and continues to occur in the overlying layer K, where, however, there are few Fe, Fe-Ni particles of isometric or lamellar shape.
We emphasize that such a clear differentiation in terms of iron, nickel, and iridium, which is manifested in the transitional clay layer in Gamsa, also exists in other regions. For example, in the American state of New Jersey, in the transitional (6 cm) spherule layer, the iridium anomaly manifested itself sharply at its base, while impact minerals are concentrated only in the upper (1 cm) part of this layer. In Haiti, at the Cretaceous–Paleogene boundary and in the uppermost part of the spherule layer, there is a sharp enrichment in Ni and impact quartz.
Background phenomenon for the Earth
Many features of the found Fe and Fe-Ni spherules are similar to the balls discovered by the Challenger expedition in the deep-sea clays of the Pacific Ocean, in the area of the Tunguska catastrophe and the sites of the fall of the Sikhote-Alin meteorite and the Nio meteorite in Japan, as well as in sedimentary rocks of different ages from many regions of the world. Except for the areas of the Tunguska catastrophe and the fall of the Sikhote-Alin meteorite, in all other cases the formation of not only spherules, but also particles of various morphologies, consisting of pure iron (sometimes containing chromium) and nickel-iron alloy, has no connection with the impact event. We consider the appearance of such particles as a result of the fall of cosmic interplanetary dust onto the Earth's surface, a process that has been continuously ongoing since the formation of the Earth and is a kind of background phenomenon.
Many particles studied in the Gams section are close in composition to the bulk chemical composition of the meteorite substance at the site of the fall of the Sikhote-Alin meteorite (according to E.L. Krinov, these are 93.29% iron, 5.94% nickel, 0.38% cobalt).
The presence of molybdenum in some of the particles is not unexpected, as many types of meteorites include it. The content of molybdenum in meteorites (iron, stone and carbonaceous chondrites) ranges from 6 to 7 g/t. The most important was the discovery of molybdenite in the Allende meteorite as an inclusion in a metal alloy of the following composition (wt %): Fe—31.1, Ni—64.5, Co—2.0, Cr—0.3, V—0.5, P—0.1. It should be noted that native molybdenum and molybdenite were also found in the lunar dust sampled by the automatic stations Luna-16, Luna-20, and Luna-24.
The balls of pure nickel with a well-crystallized surface found for the first time are not known either in igneous rocks or in meteorites, where nickel necessarily contains a significant amount of impurities. Such a surface structure of nickel balls could have arisen in the event of an asteroid (meteorite) fall, which led to the release of energy, which made it possible not only to melt the material of the fallen body, but also to evaporate it. Metal vapors could be raised by the explosion to a great height (probably tens of kilometers), where crystallization took place.
Particles consisting of awaruite (Ni3Fe) are found together with metallic nickel balls. They belong to meteor dust, and melted iron particles (micrometeorites) should be considered as "meteorite dust" (according to the terminology of E.L. Krinov). The diamond crystals encountered together with the nickel balls probably arose as a result of the ablation (melting and evaporation) of the meteorite from the same vapor cloud during its subsequent cooling. It is known that synthetic diamonds are obtained by spontaneous crystallization from a carbon solution in a melt of metals (Ni, Fe) above the graphite–diamond phase equilibrium line in the form of single crystals, their intergrowths, twins, polycrystalline aggregates, framework crystals, needle-shaped crystals, and irregular grains. Almost all of the listed typomorphic features of diamond crystals were found in the studied sample.
This allows us to conclude that the processes of crystallization of diamond in a cloud of nickel-carbon vapor during its cooling and spontaneous crystallization from a carbon solution in a nickel melt in experiments are similar. However, the final conclusion about the nature of diamond can be made after detailed isotopic studies, for which it is necessary to obtain a sufficiently large amount of the substance.
Thus, the study of cosmic matter in the transitional clay layer at the Cretaceous–Paleogene boundary showed its presence in all parts (from layer J1 to layer J6), but signs of an impact event are recorded only from layer J4, which is 65 million years old. This layer of cosmic dust can be compared with the time of the death of dinosaurs.
A.F. GRACHEV Doctor of Geological and Mineralogical Sciences, V.A. TSELMOVICH Candidate of Physical and Mathematical Sciences, Institute of Physics of the Earth RAS (IFZ RAS), OA KORCHAGIN Candidate of Geological and Mineralogical Sciences, Geological Institute of the Russian Academy of Sciences (GIN RAS).
Magazine "Earth and Universe" № 5 2008.