Origin of the Earth's ocean basins

The Earth's original ocean basins are proposed to be mare-type basins produced 4 billion y.a. by the flux of asteroid-sized objects responsible for the lunar mare basins. Scaling upward from the observed number of lunar basins for the greater capture cross-section and impact velocity of the Earth indicates that at least 50% of an original global crust would have been converted to basin topography. These basins were flooded by basaltic liquids in times short compared to the isostatic adjustment time for the basin. The modern crustal dichotomy (60% oceanic, 40% continental crust) was established early in the history of the Earth, making possible the later onset of plate tectonic processes. These later processes have subsequently reworked, in several cycles, principally the oceanic parts of the Earth's crust, changing the configuration of the continents in the process. Ocean basins (and oceans themselves) may be rare occurences on planets in other star systems.     

Biological modulation of the Earth's atmosphere

We review the evidence that the Earth's atmosphere is regulated by life on the surface so that the probability of growth of the entire biosphere is maximized. Acidity, gas composition including oxygen level, and ambient temperature are enormously important determinants for the distribution of life. We recognize that the earth's atmosphere deviates greatly from that of the other terrestrial planets in particular with respect to acidity, composition, redox potential and temperature history as predicted from solar luminosity. These deviations from predicted steady state conditions have apparently persisted over millions of years. We explore the concept that these anomalies are evidence for a complex planet-wide homeostasis that is the product of natural selection. Possible homeostatic mechanisms that may be further investigated by both theoretical and experimental methods are suggested.     

The magnetic field in the Earth's tail

Detailed magnetic fields in the Earth's tail are calculated from a proposed model containing Beard's tail surface and a current sheet inferred from satellite observations. The component inside and perpendicular to the neutral sheet permits us to construct the drift pattern in the magnetic equatorial plane for charged particles. The computed results are in reasonable agreement with the experimental results, although some deviations are noted.     

Thermal response properties of the Earth's ionospheric plasma

The thermal response of the Earth's ionospheric plasma is calculated for various suddenly applied electron and ion heat sources. The time-dependent coupled electron and ion energy equations are solved by a semi-automatic computational scheme that employs Newton's method for coupled vector systems of non-linear parabolic (second order) partial differential equations in one spatial dimension. First, the electron and composite ion energy equations along a geomagnetic field line are solved with respect to a variety of ionospheric heat sources that include: thermal conduction in the daytime ionosphere; heating by electric fields acting perpendicular to the geomagnetic field line; and heating within a stable auroral red are (SAR-arc). The energy equations are then extended to resolve differential temperature profiles, first for two separate ion species (H⁺, O⁺) and then for four separate ion species (H⁺, He⁺, N⁺, O⁺) in addition to the electron temperature. The electron and individual ion temperatures are calculated for conditions within a night-time SAR-arc excited by heat flowing from the magnetosphere into the ionosphere, and also for typical midlatitude daytime ionospheric conditions. It is shown that in the lower ionosphere all ion species have the same temperature; however, in the topside ionosphere above about 400 km, ion species can display differential temperatures depending upon the balance between thermal conduction, heating by collision with electrons, cooling by collisions with the neutrals, and energy transfer by inter-ion collisions. Both the time evolution and steady-state distribution of such ion temperature differentials are discussed.The results show that below 300km both the electrons and ions respond rapidly (<30s) to variations in direct thermal forcing. Above 600 km the electrons and ions display quite different times to reach steady state, depending on the electron density: when the electron density is low the electrons reach steady state temperatures in 30 s, but typically require 700 s when the density is high; the ions, on the other hand, reach steady state in 700 s when the density is high, and 1500–2500 s when the density is low. Between 300 and 600 km, a variety of thermal structures can exist, depending upon the electron density and the type of thermal forcing; however steady state is generally reached in 200–1000 s.     

Dynamics of the chemical evolution of Earth's primitive atmosphere

The course of evolution of Earth's primitive reducing atmosphere is shown to possibly have been determined to a large extent by the effect of thunder shock waves, which is comparable to the effect of solar uv radiation. The major chemical reactions occurring during a thunderstorm in the troposphere were pyrolysis of hydrocarbons, their oxidation by water vapor and their reaction with molecular nitrogen. These reactions were studied by the single-pulse shock tube technique and their rates as well as their product distributions were determined.The greenhouse effect of water vapor and acetylene enhanced oxidation by water vapor and prevented the accumulation of large graphite and polymer deposits on the Earth's surface. This is in accordance with their absence on the contemporary Earth. Changes in the frequency and power of thunderstorms, within reasonable limits, affected the rate of evolution but caused only small changes in the concentration profiles of HCN and aldehydes, which are essential for further chemical evolution in the oceans. The surface temperature and relative hydrogen concentration are shown to be of prime importance in determining the course and outcome of atmospheric evolution.     

Orientation and shape of the Earth's bow shock in three dimensions

Nearly 2500 shock crossings from HEOS-1, HEOS-2 and 5 IMP spacecraft, covering most of the northern and part of the southern bow shock surface for X values X > ? 20 R_E, have been used to carry out a detailed study of the three-dimensional shape and location of the bow shock. The influence of the different solar wind conditions has been reduced by normalising the observed crossings to an average solar wind dynamical pressure (N₀ = 9.4 cm^?3, V₀ = 450 kms^?1). It has been shown that the shock surface is symmetric with respect to the ecliptic plane and intersects the coordinate axes at 11.9 R_E (X), + 27.0 and ? 22.9 R_E (Y), + 23.9 and ? 24.5 R_E (Z) for the average dynamical pressure (N₀ = 9.4 cm^?3, V₀ = 450kms^?1, with $\text{M}{}_{\mathrm{A}}\text{= 9.3}$, $\text{M}{}_{\mathrm{MS}}\text{= 6.1)}$. The observed aberration of the shock surface is 8.9° ± 1°, i.e. 5.1° larger than the aberration predicted from the Earth's motion. This asymmetry around the solar wind apparent direction is described by equation (6) for different Mach numbers M_A and confirms the predictions of Walters [J. geophys. Res. 71, 1319 (1964)] and Michel [J. geophys. Res. 70, 1 (1965)].The magnetosheath thickness is 3.3 R_E along the X-axis, 11.4 R_E (+ Y), 8.7 R_E (? Y), 9.9 R_E (+Z) and 10.9 R_E along the negative Z axis.     

PAET,an entry probe experiment in the Earth's atmosphere

On June 20, 1971, an instrumented probe designated PAET entered the atmosphere near Bermuda at a velocity of 6.6 km/sec carrying experiments designed for use at planets other than the Earth. Instruments to measure in situ the structure and composition of the atmosphere included accelerometers, pressure and temperature sensors, a mass spectrometer, and a radiometer (to sense characteristic emission from the probe shock layer at high speeds).The experiments were largely successful. The thermal structure of the atmosphere, including two major reversals in gradient, was shown to be well defined to an altitude of 80 km by comparison with more conventional meteorological soundings. The atmospheric mean molecular weight was defined within a percent by the structure experiment. The radiometers defined the bulk composition accurately and the trace quantity of CO₂ to one significant figure. The mass spectrometer functioned properly, but failed to give the correct composition because of problems in its sampling system. Oxygen was depleted, apparently by chemical reactions before reaching the spectrometer, and the inlet leak conductance was reduced from its preflight value by an order of magnitude. There is reason to believe that contamination by large molecules from the heat shield was responsible. This experiment should stimulate intensive laboratory work on sampling systems, so that similar problems do not arise in measurements of atmospheric composition at the planets.Results of auxiliary experiments to measure atmospheric water vapor, vehicle dynamics and heating, and communications blackout are also given.     

Interpretation of magnetic field perturbations in the earth's magnetopause boundary layers

Studies of the boundary layers in the vicinity of the Earth's dayside magnetopause are important in determining the nature of the processes which couple the magnetosphere to the flowing solar wind, thereby driving magnetospheric convection. In this paper we examine theoretically the magnetic field and plasma properties expected in the boundary regions for various models involving either diffusion or reconnection at the boundary. For diffusion models the transport of magnetosheath momentum across the magnetopause will result in field shears on either side of the boundary, the field rotations being in opposite senses on either side relative to the undisturbed fields. The directions of these rotations depend upon location at the magnetopause relative to the momentum transfer region and to the noon meridian. In reconnection models the effect of the tension of the open boundary layer field lines must be taken into account in addition to the magnetosheath flow, but on the super-Alfvénic flanks of the magnetosphere the latter still dominates, so that qualitatively similar effects will occur in the two models. More detailed, quantitative or statistical studies are then required to distinguish the two models in this regime. In the sub-Alfvénic dayside region, however, open field tension effects will dominate in reconnection models such that boundary layer field and plasma properties will then be determined mainly by the magnetosheath magnetic field configuration. In particular the East-West flow in the magnetospheric boundary layer will be controlled largely by the East-West field in the magnetosheath, leading to flow reversals across the magnetopause in some quadrants of the magnetopause. This behaviour is directly related to the Svalgaard-Mansurov effect and is a signature unique to reconnection models. The boundary layer fields are also expected to tilt towards the field on the opposite side of the boundary in these models on the dayside. “Toward” tilting can also occur in this regime in diffusion models, but “away” tilting, a signature unique to dayside diffusion, should also occur equally frequently. Finally, we briefly discuss previously published high-resolution ISEE 1 and 2 data from the boundary regions in the light of our results. We find that “toward” tilting generally occurs in boundary region crossings previously identified as being reconnection-associated and we present some examples in which the above unique reconnection signature has been observed. During impulsive FTE-like events, however, the field may tilt in either direction, possibly as a result of field line twists, thus complicating our simple picture in this case. We also show that the “reverse draping” observations presented by Hones et al. (1982) approximately satisfy the open magnetopause stress balance conditions.     

Boltzmann-Fokker-Planck model for the electron distribution function in the Earth's ionosphere

Using Boltzmann-Fokker-Planck methods and the diffusion approximation, we derive coupled non-linear equations for the first two angular moments of the electron distribution function in the Earth's ionosphere. The theory includes a phenomenological treatment of photionization of the neutral species by an externally produced photon flux; electron-ion recombination; electronneutral particle attachment; elastic, excitation, deexcitation, and ionizing electron-neutral particle collisions; and elastic electron-electron and electron-ion collisions. At high and low energies, we obtain approximate analytic solutions for the steady-state electron distribution function. Under certain conditions we also obtain the standard continuous slowing-down formulae for the steady-state electron distribution function in the diffusion approximation.     

Electric and magnetic drift of non-adiabatic ions in the Earth's geomagnetic tail current sheet

It has been shown recently that non-adiabatic particles in the Earth's magnetotail drift across the tail roughly as predicted for adiabatic particles with 90° pitch angles. In this paper we show that this result implies the existence of an approximate invariant of the motion. Adding the effect of convection associated electric fields, we can then obtain the approximate bounce averaged motion of non-adiabatic particles in the magnetotail. Thus the particle motion and energization due to combined magnetic and electric drifts in the magnetotail are easily predicted.     

Interaction of interplanetary MHD shock waves with the magnetopause

The interaction between a shock-wave and the magnetopause is formulated on the basis of one-dimensional magnetohydrodynamics. The magnetopause is assumed to be a tangential discontinuity, and the magnetic field is limited to the case of perpendicularity. Both the forward and reverse shocks' impact on the magnetopause are considered and analyzed separately. The forward shock-magnetopause interaction results in a transmitted shock, a tangential discontinuity, and a simple rarefaction wave. The reverse shock-magnetopause interaction creates a transmitted shock, a tangential discontinuity, and a reflected wave. The propagation of an SSC signal which is related to an interplanetary shock-induced geomagnetic storm's onset-time on Earth is discussed in general terms. It was found in earlier work (Shen and Dryer, 1972) that the propagation velocity of an inter-planetary shock is decreased by about 1015% following its impact with the earth's bow shock; the present study shows that its velocity is then suddenly increased by a factor of two to three after impact with the magnetopause. The fast propagating shock-wave inside the magnetosphere degenerates into a hydromagnetic wave as it advances into an increasing intensity of the distorted dipole geomagnetic field.     

Influence of the Earth's rotation and of possible perturbations,on the exobase and exospheric hydrogen densities

In this study, we try to refine the relation existing between the exobase temperature and density distributions of atomic hydrogen around the Earth (assuming that the zero net ballistic flux condition is satisfied all over the critical level). We find essentially that neither local heating in high latitude regions, nor the addition of proton fluxes around the Earth, induce large perturbations in the equatorial density distribution (less than 10 per cent). On the other hand, certain local heating can give large perturbations in the global density distribution (more than 50 per cent).The effect of the Earth's rotation is also studied. We find that at the exobase the density distribution of atomic hydrogen lags about one hour behind the temperature distribution. At higher altitudes this time lag increases, reaching 5–6 hr at 20 Earth radii.We show also that, due to a density inversion which takes place at 2 Earth radii, if the minimum of density at the exobase is on the dayside, above 2 Earth radii, a maximum of density is then on the dayside when going higher, due to the rotational effect, that density maximum shifts towards the evening, reaching early parts of the night at 20 Earth radii.     

A non-linear study of the possible effects of electron-ion collisions on the diffusion of a cylindrical column of ionisation in the Earth's ionosphere

The possible effects of electron—ion collisions on the diffusion of a cylindrical plasma irregularity orientated at right angles to the geomagnetic field lines, at altitude 300 km, are discussed. The results obtained indicate that the diffusion may proceed at a rate rather greater than for a case for which the effects of collisions of electrons with ions are assumed to be negligible. Furthermore, it is suggested that if the plasma density is great enough, the production of a 'fin' of ionisation along the magnetic field direction may be inhibited by the action of electron—ion collisions.     

Response of Earth's atmosphere to increases in solar flux and implications for loss of water from Venus

A one-dimensional radiative-convective model is used to compute temperature and water vapor profiles as functions of solar flux for an Earth-like atmosphere. The troposphere is assumed to be fully saturated, with a moist adiabatic lapse rate, and changes in cloudiness are neglected. Predicted surface temperatures increase monotonically from ?1 to 111°C as the solar flux increased from 0.81 to 1.45 times its present value. Surface temperatures corresponding to high solar fluxes may be underestimated, however, owing to neglect of H₂O continuum absorption outside of the 8- to 12-μm window region. These results imply that the surface temperature of a primitive water-rich Venus should have been at least 80–100°C and may have been much higher. The existence of liquid water at the surface depends on poorly known aspects of H₂O continuum absorption and on uncertainties concerning relative humidity and cloudiness. In any case, water vapor should have been a major atmospheric constituent at all altitudes, leading to the rapid hydrodynamic escape of hydrogen. The oxygen left behind by this process was presumably consumed by reactions with reduced minerals in the crust. Both the loss of oxygen and the presently observed enrichment of the deuterium-to-hydrogen ratio are most easily explained if oceans of liquid water were initially present.     

Tomography of the Earth’s core using supernova neutrinos

We investigate the possibility to use the neutrinos coming from a future galactic supernova explosion to perform neutrino oscillation tomography of the Earth’s core. We propose to use existing or planned detectors, resulting in an additional payoff. Provided that all of the discussed uncertainties can be reduced as expected, we find that the average matter densities of the Earth’s inner and outer cores could be measured with a precision competitive with geophysics. However, since seismic waves are more sensitive to matter density jumps than average matter densities, neutrino physics would give partly complementary information.     

Long-period pulsations of the Earth's magnetic field with periods more than 20 minutes before proton flares on the sun

Long-period (more than 20 min) quasi-periodic pulsations (QPP) occurring in the Earth's magnetic field (EMF) before the proton flare are studied by the method of spectral correlation analysis of geomagnetic field H-component. The corresponding data have been obtained at six stations located from 12°41'E up to 180° 52'E and from 52°04'N up to 68°52'N.QPP space-time distribution is shown to be correlated with that of the Earth's ionosphere current systems. The results obtained indicate that QPP of the EMF are influenced by QPP of the solar X-ray and ultraviolet radiation modulated by oscillation processes in the active solar region.     

On the azimuthal brightness variations of Saturn's rings

We present a simple, semiquantitative explanation that accounts both for the presence of the azimuthal brightness variations in Saturn's ring A and for their absence in ring B. Our explanation avoids any ad hoc reliance on albedo variations and/or synchronous rotation of ring particles. Instead, it requires only some degree of self-gravitation between nearby orbiting bodies. A bias in the particle distribution and corresponding photometric effects are thereby produced—the latter corresponding very closely to the variations observed in ring A. Their absence in ring B is primarily a consequence of the higher optical thickness and decreasing importance of self-gravitation in that ring.     

Kelvin-Helmholtz instability of the magnetopause boundary: Comparison with observed fluctuations

We present a numerical investigation of the Kelvin-Helmholtz instability problem, in MHD approximation, for transitions involving continuous variations of both magnetic field and plasma parameters. The variations have been chosen in such a way as to reproduce general features of possible magnetopause transitions. The study, which leads to prediction of a wavelength of maximum instability, has been confronted with recent observational results of surface fluctuations of the magnetopause.     

On solar wind interaction with the earth's magnetosphere

Hydrodynamic and electrodynamic problems of solar wind interaction with the Earth's magnetosphere on the day-side are investigated.The initial fact, well established, is that the density of the magnetic field energy in the solar wind is rather small. Magnetic field intensity and orientation are shown to determine the character of the solar wind flow around the magnetosphere. For mean parameters of the wind, if the tangential component of the magnetic field is more or equal 5γ, the flow in the magneto-sheath will be laminar. For other cases the flow is of a turbulent type.For turbulent flow, typical plasma parameters are estimated: mean free path, internal scale of inhomogeneities and dissipated energy. The results obtained are compared with experimental data.For the case of laminar flow, special attention is paid to the situation when magnetic fields of the solar wind and Earth are antiparallel. It is suggested, on the basis of solid arguments, that the southward interplanetary field diffuses from the magnetosheath into the Earth's magnetosphere. These ideas are used for the estimation of the distance to the magnetopause subsolar point. A detailed comparison with results of observation is made. The coincidence is satisfactory. Theoretical investigation has been made to a great extent for thin magnetopause with thickness δ ～ R_He-gyroradius of an electron.It is shown that during magnetospheric substorms relaxation oscillations with the period τ = 100–300 sec must appear. A theorem is proved about the appearance of a westward electrical field during the substorm development, when the magnetosphere's day-side boundary moves Earthward and about the recovery phase, when the magnetopause motion is away from the Earth, when there is an eastward electrical field.In the Appendix, plasma wave exitation in the magnetopause is considered and conductivity magnitudes are calculated, including the reduction due to the scattering by plasma turbulence.     

On inhomogeneous scattering models of Titan's atmosphere

The spectrum of Titan from 4800 to 11 000 Å has many CH₄ absorption bands which cover a range of intensities of several orders of magnitude. Yet even the strongest of these bands in Titan's spectrum has considerable residual central intensity. Some investigators have concluded that these strong CH₄ bands must be highly saturated, but recent laboratory measurements of the bands made at room temperature show that curve-of-growth saturation is very small. At the presumed low pressures and temperatures in Titan's atmosphere, we show that saturation is very dependent on the band model parameters. However, in either a simple reflecting layer model or in a homogeneous scattering model saturation cannot be the principal cause of the filling in of these strong CH₄ bands if our best estimates of the band model parameters are correct. We find that an inhomogeneous scattering model atmosphere with fine “Axel dust” above most ot the CH₄ gas is needed to fill in the band centers. The calculated spectrum of one particular model of this class is compared to observations of Titan. Our essential conclusion is that Titan does have most of its scattering particles above most of the CH₄ gas which has an abundance of at least 2 km-am. This large abundance of CH₄ is necessary to produce the 6420-Å feature recently discovered in Titan's spectrum.