Extraterrestrial Objects Research Articles

Formation of spinels in cosmic objects during atmospheric entry: a clue to the Cretaceous-Tertiary boundary event

Magnetic spinels produced by oxidation of extraterrestrial objects in the atmosphere have a composition distinct from terrestrial spinels. They are characterized by a high iron oxidation state, arising from crystallization under high oxygen fugacities, and a high nickel concentration due to the relatively high abundance of this element in extraterrestrial material. The iron oxidation state increases from micrometeorites, to meteoroid ablation material and to impact-generated products. This reflects a progressive increase of the oxygen fugacity, corresponding to decreasing altitudes of crystallization. Spinels found at the Cretaceous-Tertiary boundary are similar to those that crystallized from meteoroid ablation material and impact-generated products, supporting the view that a collisional event did occur at the end of the Cretaceous.

Endogenous production, exogenous delivery and impact-shock synthesis of organic molecules: an inventory for the origins of life.

Sources of organic molecules on the early Earth divide into three categories: delivery by extraterrestrial objects; organic synthesis driven by impact shocks; and organic synthesis by other energy sources (such as ultraviolet light or electrical discharges). Estimates of these sources for plausible end-member oxidation states of the early terrestrial atmosphere suggest that the heavy bombardment before 3.5 Gyr ago either produced or delivered quantities of organics comparable to those produced by other energy sources. Which sources of prebiotic organics were quantitatively dominant depends strongly on the composition of the early terrestrial atmosphere. In the event of an early strongly reducing atmosphere, production by atmospheric shocks seems to have dominated that due to electrical discharges. Organic synthesis by ultraviolet light may, in turn, have dominated shock production, but only if a long-wavelength absorber such as H2S were supplied to the atmosphere at a rate sufficient for synthesis to have been limited by ultraviolet flux, rather than by reactant abundance. In the apparently more likely case of an early terrestrial atmosphere of intermediate oxidation state, atmospheric shocks were probably of little importance for direct organic production. For [H2]/[CO2] ratios of approximately 0.1, net organic production was some three orders of magnitude lower than for reducing atmospheres, with delivery of intact exogenous organics in interplanetary dust particles (IDPs) and ultraviolet production being the most important sources. At still lower [H2]/[CO2] ratios, IDPs may have been the dominant source of prebiotic organics on the early Earth. Endogenous, exogenous and impact-shock sources of organics could each have made a significant contribution to the origins of life.

The oceanic impact of large objects

The impact of large extraterrestrial objects upon the ocean is expected to produce a strong wave system forced by oscillations (“sloshing”) of the ensuing water crater. A 0.2 km object impacting at about 20 km/sec produces a crater with diameter D c ∼ 2.5 km with a natural period on the order of 55 seconds which is the forcing period for the wave system. The crater “slosh” period is consistent with the estimated phase velocity across the crater. The wavelength is comparable to the ocean depth and is thus very short. For wavelengths much greater than this the far field progresses as gravity waves to great distance. Both vertical gun experiments and numerical calculations using the SALE program confirm the general morphology of the wave field. An initial surge is produced from the excavation of the water crater which is fundamentally different from subsequent waves generated by crater slosh. This surge is augmented in velocity compared with the other waves which travel at the predicted phase velocity. In addition, the initial surge is immediately followed by a bore resulting from the collapsing crater, analogous to the ‘dam breaking’ problem. Shoaling eventually terminates the wave system. The short wavelength means that forward momentum is strongly dispersed shoreward, decreasing the depth of a shoreward invasion of water and thus decreasing the intensity of a consequent geological record.

Absence of shock-metamorphic effects in the Bushveld Complex, South Africa: results of an intensive search

An extensive search was made for distinctive shock-metamorphic effects in order to test the theory that the Bushveld Complex (BC) was formed by the impact of large extraterrestrial objects. Field and petrographie studies concentrated on two geological environments in which current impact cratering theories predict the formation and preservation of such shock-metamorphic effects as shatter cones, unusual fragmental or melt breccias, and shock lamellae in quartz. These are: (1) pre-BC quartzite xenoliths in the Rooiberg Group, a thick sequence of acid lavas (rhyolites and rhyodacites) and related rocks, proposed by earlier workers as a possible crater-filling impact melt; and (2) the locally observable contact between the Rooiberg Group and the underlying pre-BC basement (Pretoria Group), a contact possibly corresponding to the original crater floor in established impact structures. More than 320 samples of pre-BC quartzite were collected and examined petrographically for shock-metamorphic effects. No megascopic shock-metamorphic effects (shatter cones or unusual breccias) were observed in any outcrop. In thin section, no petrographic shock effects (e.g., shock lamellae hi quartz and kink bands in biotite) were observed in any sample. The quartzites from both the basement (80 samples) and the Rooiberg xenoliths (245 samples) are virtually undeformed. Cataclastic textures are rare, and individual quartz grains show only normal metamorphic deformation lamellae (Böhm lamellae) and single or multiple sets of fluid inclusions arranged along irregular planes which appear to be healed fractures. Although some of these parallel sets superficially resemble so-called “decorated” shock lamellae, universal stage measurements of their orientation demonstrate that they are totally different. The absence of both megascopic and microscopic shock-metamorphic effects in a large suite of carefully selected samples strongly indicates that impact models for the BC are not correct and that the BC is not an impact structure. This conclusion also agrees with: (1)the complex stratigraphy now recognized in the lower Rooiberg Group, which is not consistent with an impact melt origin, (2) the absence in the Rooiberg Group of any of the distinctive melt-rich fragmentai breccias which dominate the crater-filling deposits in established large impact structures, and (3) the undeformed character of the basement rocks below the Rooiberg Group and the apparently concordant contact between them.

Kalman filtering of Earth orientation changes

The orientation of the earth in space changes unpredictably in a rapid and irregular manner, in addition to the uniform rotation of the earth. Observations of extra-terrestrial objects from the surface of the earth are affected by these variations, and knowledge of these changes is required for a variety of geodetic and astrometric purposes as well as being of interest in its own right. The orientation of the earth (specified by a three dimensional rotation vector) is measured by a variety of techniques; combination of these data sets is complicated by irregular changes in the spacing and accuracy of the various time series, and also by the existence of lower dimensional measurements of different linear combinations of the rotation vector components. A Kalman filter has been developed at JPL to smooth and predict earth orientation changes for application to spacecraft navigation by the NASA Deep Space Network. The filter, which provides estimates of the earth orientation changes (and of the excitation of these changes) based on whatever measurements are available, has been used for a number of research applications, both in the reduction of geodetic and astrometric data, and in research into the geophysical causes of earth orientation changes. The JPL Kalman filter uses stochastic models to account statistically for otherwise unpredictable changes in earth orientation; these models make it possible to provide reasonable estimates of the error in the smoothed time series, and to automatically vary the amount of smoothing according to the accuracy and density of the data. The derivation of the stochastic models used by the filter, the implementation of the models into the filter, a statistical description of what the filter does, and the results of filtering specific data sets will be discussed.

Thick-target bombardments with high energy charged particles: Experimental improvements and spatial distribution of low-energy secondary neutrons

A thick target with dimensions of 100×100×200 cm and a mass of about 16 000 kg was constructed for the simulation of effects of the galactic cosmic radiation (GCR) with matter. After irradiations of this target with 2.1-GeV protons and 800-MeV/nucleon alpha particles, the spatial distribution of low-energy secondary neutrons was determined by neutron-capture reaction products. Due to the large dimensions of the bombarded target and the water-free material used, conditions close to those expected in anhydrous planetary surfaces were successfully simulated, with the exception of the 2π incidence of the GCR. Secondary low-energy neutron fluxes developed broad maxima at depths of 100 to 200 g/cm 2 for the proton irradiation and at depths of 70 to 150 g/cm 2 for the alpha-particle irradiation, however, demonstrates the role that these particles, which only comprise ∼10% of the GCR particle flux, play on the development of the subsurface low-energy neutron fluxes in extraterrestrial objects. Comparisons with similar results from other thick target experiments demonstrate the advantages of the thick target arrangement used.

Predicting the production rates of cosmogenic nuclides in extraterrestrial matter

The production rates of nuclides made by the galactic and solar cosmic rays are important in the interpretations of measurements made with lunar samples, meteorites, and cosmic spherules. Production rates of cosmogenic nuclides have been predicted by a variety of methods that are reviewed in this paper, ranging from systematic studies of one or a group of meteorites to purely theoretical calculations. Production rates vary with the chemical composition and the preatmospheric depth of the sample and with the size and shape of the object. While the production systematics for cosmogenic nuclides are fairly well known, our ability to predict their production rates can be improved, with a corresponding increase in the scientific return. Additional detailed studies of cosmogenic nuclides in extraterrestrial objects are needed, especially for fairly small and very large objects. Nuclides made in simulation experiments and cross sections for many major nuclear reactions should be measured. Such studies are especially needed for the long-lived radionuclides that have only recently become readily measurable by accelerator mass spectrometry.

Do Asteroid Impacts Trigger Geomagnetic Reversals?

It's been about 700 000 years since the last time the Earth's magnetic field reversed its polarity. Considering that the average over the last 30 million years has been about four geomagnetic reversals per million years, we're a bit overdue. But if Berkeley physicists Richard Muller and Donald Morris are right, the onset of the next reversal will be more than just an inconvenience to navigators. In the November issue of Geophysical Research Letters, they make an intriguing, if rather speculative, case for the thesis that many, perhaps all, polarity reversals of the dynamo churning in our planet's liquid‐iron outer core are caused by the impact of large extraterrestrial objects falling to Earth.

Limitations to the statistical analysis of episodic and periodic models of geologic time series

Nonrandom distributions of ages of mass extinctions, magnetic reversals, and other geologic phenomena have been used to support the hypothesis that catastrophic events driven by the periodic motions of planets, stars, or our galaxy play a major role in the history of Earth and its life. Such conclusions have been based on statistical comparison of observed ages to a single reference model, the Poisson distribution. However, probability grids based on multiple reference models show that a wide range of distributions, including some that are periodic and some that are intrinsically random (episodic), can fit the observations. Viable models include some with a fairly large variability in age interval (∼30%). There is no statistical motivation for favoring periodic motions of extraterrestrial objects over the organized, dissipative processes that operate on Earth as an explanation for mass extinctions.

Antonio Marussi 1908”1984

Antonio Marussi, one of the most prominent geodesists of this century, died in Trieste, Italy, on April 24, 1984, at the age of 75. Blessed with good health and a robust physical constitution for most of his life, he was struck down by amyotrophic lateral sclerosis (Lou Gehrig's disease) which he had contracted in 1982.Marussi is best known among geodesists as the father of modern three‐dimensional geodesy. Following an initial presentation at the 1948 Oslo General Assembly of the IUGG, he published in 1949 in the Bulletin Géodésique an article entitled “Fondements de géométrie differentielle absolue du champ potential terrestre,” acknowledged now as one of the seminal works of the geodetic literature. In this and subsequent papers, Marussi developed in a general, rigorous, mathematical setting a unified approach to the solution of both geometric and physical problems in geodesy, obliterating the artificial distinction between horizontal and vertical which had been built up by geodesists over many years because of observational difficulties. He thus introduced many geodesists to the 20th century by demonstrating the value and, indeed, the necessity of advanced mathematical techniques like the tensor calculus and by anticipating useful data to be obtained by observations on close extraterrestrial objects like satellites.

The effects of atmospheric turbulence on telescopic observations

Telescopic observations to terrestrial and extraterrestrial objects are affected by atmospheric turbulence. The structure of atmospheric turbulence is reviewed in tems of the refractive index structure parameter. The mean and fluctuating refraction effects of the turbulent atmosphere on the propagation of electromagnetic waves are addressed. The known formulae for the variance and the spectrum of the angle-of-arrival fluctuations are presented and experimental results are summarised. The angular resolution is compared with the pointing precision of a telescope for visual observations through a turbulent atmosphere. The ultimate precision of direction measurements is shown to be a function of instrumental design parameters, the strength of atmospheric turbulence, and the length of the averaging period.

Reference Coordinate System Requirements for Geodesy and Ocean Dynamics

AbstractThe requirements for systems of reference in geodesy and ocean dynamics should be framed against the background of the distinct possibility of achieving in the foreseeable future measurements with a resolution of 1 part in 108. The current techniques promising this precision, with one exception, are based on observations to extraterrestrial sources/responders. The principal geodetic goals calling for such precision are, broadly stated, the determination of:1. Positions of stations in global tracking networks.2. Crustal motion.3. Polar motion.4. The radial component of instantaneous sea surface position from satellite altimetry for the estimation of phenomena related to ocean circulation.5. Earth model improvement.These goals cannot be achieved without the definition of adequate models for relating measurements from observing stations on Earth to extraterrestrial objects, possibly in an iterative manner in the first instance.While the specific choice of a system of geodetic reference is not critical for determinations of position in three dimensions, the maintenance of the continuity of geodetic concepts at the highest level of resolution in terms of four-dimensional considerations narrows the possible alternatives available.Criteria desirable in such a system of reference for observations of the highest precision made from the surface of a non-rigid Earth undergoing secular crustal motion are the following:1. These observations should be capable of direct relation to the system of reference in four dimensions.2. The crustal motion vector at a point should be defined in terms of the variations of the coordinatesof that pointwith time.3. Near-Earth orbital positions should have unambiguous relationships to the origin of ocean geoid determinations in four dimensions.4. Coordinates on the adopted system of reference should have relevance over an epoch of practical significance (e.g., one year).5. The scale for the space as obtained from the observations should not be influenced by factors other than the velocity of light and the adopted definition for the second.An important corollary is that only one point should be treated as “fixed” at the surface of the nonrigid Earth. Positional variations which have a periodic character, effective over an epoch of observation or less, are best treated as effects to be removed from observations by appropriate modeling. Reported secular changes in mean sea level require that the geoid be defined in relation to mean sea level in four dimensions for any determination of sea surface topography, thereby completing a unified system of reference which, would meet all the requirements of high-precision geodesy and ocean dynamics.

Art and Science Project: 'Waiting-for-Light-Planes'

In 1969 I became interested in the motion and the distances of extraterrestrial celestial objects and the geological time scale of our Earth and I made a series of drawings for an art project that would cause a viewer at a given site on the Earth to become aware of them. A drawing from the series is shown in Fig. 1. I was able to execute this project at the Center for Advanced Visual Studies at the Massachusetts Institute of Technology (M.I.T.) for a travelling exhibition entitled 'Multiple Interaction Team'. The project, which I called 'Star-Pits-Waiting-forLight-Planes', met the following criteria established for the exhibition: that it have significance for viewers at each location where executed; that it involve viewers in an active way and that it apply some aspects of the natural sciences or of modern technology. I wrote the following description of the project for the exhibition catalogue: 'The Star-Pits juxtapose two immense time-space structures, the celestial and the geological. I dig pits into the Earth to a layer at a depth equivalent in time to the age in light years of the light coming from two light sources: the globular star cluster in Hercules, some 22,000 light years from us; and the Great Spiral Galaxy in Andromeda, approximately 2,000,000 light years from us. These two sources come directly overhead at particular times of day or night. They are also located near somewhat square pits in the night sky, the central square in Hercules and the great rectangle of Pegasus. The pits are entered by long ramps or grooves in the Earth. Down these grooves the Sun enters the pits marking the boundaries of night at sunset and dawn. The walls of the pits are carefully cut to reveal the layering of the Earth. The floor of the pit is mirror-water and placed upon it is a large water prism. The water in the open water prism blows breaking spectra upon the fresh earth walls. In the day and Sun these pits are pits of light with

Domaine et objet de la sémiotique [Scope and aims of semiotics

In the context of the semiotic field, the author first defines the functional area of message exchange and the structural area of subjacent sign systems, each of which implies the other. He then goes on to set out the criteria which enable one to make a classification of signs in a synchronic perspective from an extrinsic viewpoint — i.e. from the point of view of communications functions — as well as from an intrinsic standpoint — from the point of view of their structure. (The possibility of a diachronic form of classification if not entered into.) First the criteria which would probably be useful in an extrinsic synchronic sign classification system are set out in the framework of a simple communication model consisting of a transmitter and a receiver linked by various channels transmitting a coded message within a given context. With reference to the codifier, i.e. the transmitter, the author distinguishes between transmitters consisting of inorganic objects (natural or manufactured) and of terrestrial (men and animals) or extraterrestrial organic objects, as well as between these and transmitters consisting in part or in entirety of an organism. When speaking of the transmitter-receiver unit, he distinguishes animal communication from human communication, which can be intra-, inter- or pluri-personal. Dealing next with the channels, he distinguishes between matter-channels and energy-channels. With regard to the overall features of the pattern, he differentiates between human and animal communication with or without the use of an instrument as medium bringing into play signs produced either by the subject himself or by means of an instrument. Finally, he remarks that superior organised beings, including man, enjoy the ability to use several semiotic systems simultaneously. An intrinsic synchronic system of sign classification brings one back to the problem of the sign and the relationship between content and expression. This is the concern of semantics, a field of study which poses two fundamental questions concerning the reference of a «token» and the meaning of a «type» (to use Peirce's terminology) and the distinction to be made between relationships of references and of designation. Proceeding from these notions, the author sets out a sign classification system or, to be more precise, a system for classifying the superior aspects of signs which are used to refer to them and which differentiates signals, symptoms, syndromes, icons, indexes, symbols and names.

Consequences of a Universal Cosmic-ray Theory for γ-ray Astronomy

THE problem of the origin of cosmic rays is well known; but in spite of considerable advances in knowledge concerning energetic extra-terrestrial objects in recent years, no satisfactory solution has appeared. It is not clear, even, whether the important sources are within the Galaxy or outside it1,2.

Possible Magnetic Interaction of Asteroids with the Solar Wind

Investigation of extraterrestrial objects is habitually accompanied by the observation of extraterrestrial magnetic fields, which often have significant effects on the solar wind in the vicinity of the objects. Should we be surprised to find this experience repeated at an asteroid?A recent study considered the conditions that would have to be satisfied by the surface magnetic field of a small planetary body at asteroidal distances so that the field would be an obstacle capable of stopping the solar wind or deflecting it sufficiently to generate a detectable magnetic interaction (Greenstadt, 1971).

An 8–14 Micron Infrared Astronomical Photometer

A system for measurement of 8-14 µ infrared emission from extra-terrestrial objects is described. The photometric system utilizes a mercury-doped germanium detector cooled to liquid hydrogen temperature to achieve increased sensitivity in this spectral region. A method is presented for minimizing the problem of atmospheric and component emission. The system has been used to measure the radiation from the star α Orionis, from the unilluminated moon, and from several planets.

Oxygen isotope studies on the origin of tektites

O^(18)/O^(16) ratios of thirteen tektites from Czechoslovakia, Libya, Texas, Indochina, Philippine Islands, Australia, Java, and Peru have been determined by the fluorine-extraction technique. All but one of these lie in relatively restricted range of O^(18)/O^(16) ratio, with δ = 9.6 to 10.4 per mil relative to the ocean-water standard. Tektites are therefore 0.5 to 1.5 per mil heavier than average granitic igneous rocks or about the same as average igneous quartz. The sample from Macusan, Peru (δ = 12.0), is anomalous and is probably not a true tektite. Six analyzed shales are isotopically heavier than tektites and show a much wider range in values (δ = 14.2, 14.8, 15.3, 15.5, 17.6, 18.2). Several detrital sedimentary rocks previously analyzed by Silverman and the present authors have δ values of 10.2 to 15.5; analyzed metasedimentary rocks have δ values of 12.1 to 15.7 per mil. Therefore, tektites are not sedimentary or metasedimentary material fused by lightning or by impact of an astronomical body with the earth. Chemically, tektites are unlike terrestrial igneous rocks, and their oxygen isotopic composition is unlike that of sedimentary or metasedimentary rocks. They therefore may be extraterrestrial objects.

Extraterrestrial Effects of Cosmic Rays

So far only interactions of cosmic rays with terrestrial matter have been investigated. If cosmic rays are present in interstellar and intergalactic space, they produce physical changes on extraterrestrial objects also. The question therefore arises if such changes are observable. The following considerations make it probable that this question is to be answered in the affirmative.