Helium isotopes in the earth's interior and in the atmosphere: A degassing model of the earth

A first-order degassing model was applied to describe the evolution of helium content and isotope composition in the earth and in the atmosphere. The main events described by the model are: (1) the earth-trapped primordial rare gases at the moment of its accretion; (2) later, the solid earth lost primordial and radiogenic rare gases, and (3) they were accumulated in the atmosphere; (4) in addition,³He was formed in the atmosphere due to cosmic irradiation, accretion from solar wind, etc.; (5)³He and⁴He dissipated into space at different loss rates.Study of this model confirms the concept that some of primordial helium is retained in the interior of the earth; terrestrial helium (³He/⁴He～ 2 × 10^?5) was most probably formed as a mixture of primordial (³He/⁴He= 3 × 10^?4) and radiogenic (³He/⁴He～ 3 × 10^?8) helium. For achondritic concentrations of heavy radioactive elements (U= 2.25 × 10^?8g/g) the calculated⁴He flux from the earth is equal to 5.7 × 10⁶ at cm^?2 sec^?1. The corresponding³He flux is about 114 at cm^?2 sec^?1. In discussing the aeronomic problem of helium it is necessary to take into account that the earth is the main source of the light helium isotope.     

Trapped solar wind He,Ne, and Ar and energetic He in Surveyor 3

The Apollo 12 mission brought back sections of the Surveyor 3 vehicle suitable for mass spectrometric studies of implanted solar wind and solar cosmic rays. Using this method, we have determined an average solar wind ⁴He flux of 6.1 × 10⁶ ions/cm² sec for the 31 months of exposure. We have also measured ⁴He/³He= 2700 ± 50;⁴He/²⁰Ne= 410 ± 30;²⁰Ne/²²Ne= 13.5 ± 0.2;²⁰Ne/³⁶Ar= 24.5 ± 2.5; and ³⁶Ar/³⁸Ar= 5.41 ± 0.20. These measurements provide solar wind values averaged over considerably longer periods of time than the Apollo Solar Wind Composition experiments and suggest that the short term SWC measurements during a period of high solar activity may not be a reliable measure of average solar wind composition.     

Influence of the solar wind plasma density on the auroral precipitation characteristics

Based on the DMSP F6 and F7 satellite observations, the characteristics of precipitating particles in different auroral precipitation regions of the dayside sector have been studied depending on the solar wind plasma density. Under quiet geomagnetic conditions (|AL| < 100 nT and B _z > 0), a considerable increase in the fluxes of precipitating ions is observed in the zones of structured auroral oval precipitation (AOP) and soft diffuse precipitation (SDP). A decrease in the mean energy of precipitating ions is observed simultaneously with the flux growth in these regions. The global pattern of variations in the fluxes of precipitating ions, which shows the regions of effective penetration of solar wind particles into the magnetosphere at a change in the solar wind density from 2 to 20 cm^?3, has been constructed. The maximal flux variation (ΔJ _i = 1.8 · 10⁷ cm^?2 s^?1, i.e., 3.5% of an increase in the solar wind particle flux) is observed in the SDP region on the dayside of the Earth. The dependence of precipitating ion fluxes in the low-latitude boundary layer (LLBL), dayside polar cusp, and mantle on the solar wind density at positive and negative values of the IMF B _z component has been studied. In the cusp region, an increase in the precipitating ion flux is approximately 17% of an increase in the solar wind density. The IMF southward turning does not result in an appreciable increase in the ion precipitation fluxes either in the cusp or in the mantle. This fact can indicate that the reconnection of the geomagnetic field with southward IMF is not the most effective mechanism for penetration of solar wind particles into these regions.     

Effect of active processes on alpha particle density in the solar wind

The properties of alpha particle fluxes, the density of which increase under the action of flares and development of coronal mass ejections (CMEs) and solar wind structural inhomogeneities, have been studied. The maximal alpha particle density in plasma fine structure volumes reaches 12 cm^?3. The amount of ?? particles is sometimes higher than that of protons. This is explained by the effect of the mechanism by which individual solar wind zones are nonuniformly enriched in helium nuclei when strong flares develop.     

Trapped solar and cosmogenic noble gas abundances in Apollo 15 and 16 deep drill samples

Abundances and isotopic compositions of all the stable noble gases have been measured in 19 different depths of the Apollo 15 deep drill core, 7 different depths of the Apollo 16 deep drill core, and in several surface fines and breccias. All samples analyzed from both drill cores contain large concentrations of solar wind implanted gases, which demonstrates that even the deepest layers of both cores have experienced a lunar surface history. For the Apollo 15 core samples, trapped⁴He concentrations are constant to within a factor of two; elemental ratios show even greater similarities with mean values of⁴He/²²Ne= 683±44,²²Ne/³⁶Ar= 0.439±0.057,³⁶Ar/⁸⁴Kr= 1.60±0.11·10³, and⁸⁴Kr/¹³²Xe= 5.92±0.74. Apollo 16 core samples show distinctly lower⁴He contents,⁴He/²²Ne(567±74), and²²Ne/³⁶Ar(0.229±0.024), but their heavy-element ratios are essentially identical to Apollo 15 core samples. Apollo 16 surface fines also show lower values of⁴He/²²Ne and²²Ne/³⁶Ar. This phenomenon is attributed to greater fractionation during gas loss because of the higher plagioclase contents of Apollo 16 fines. Of these four elemental ratios as measured in both cores, only the²²Ne/³⁶Ar for the Apollo 15 core shows an apparent depth dependance. No unambiguous evidence was seen in these core materials of appreciable variations in the composition of the solar wind. Calculated concentrations of cosmic ray-produced²¹Ne,⁸⁰Kr, and¹²⁶Xe for the Apollo 15 core showed nearly flat (within a factor of two) depth profiles, but with smaller random concentration variations over depths of a few cm. These data are not consistent with a short-term core accretion model from non-irradiated regolith. The Apollo 15 core data are consistent with a combined accretion plus static time of a few hundred million years, and also indicate variable pre-accretion irradiation of core material. The lack of large variations in solar wind gas contents across core layers is also consistent with appreciable pre-accretion irradiation. Depth profiles of cosmogenic gases in the Apollo 16 core show considerably larger concentrations of cosmogenic gases below ～65 cm depth than above. This pattern may be interpreted either as an accretionary process, or by a more recent deposition of regolith to the upper ～70 cm of the core. Cosmogenic gas concentrations of several Apollo 16 fines and breccias are consistent with ages of North Ray Crater and South Ray Crater of ～50·10⁶ and ～2·10⁶ yr, respectively.     

Primordial gases in graphite-diamond-kamacite inclusions from the Haveröureilite

Stepwise heating experiments on separated graphite-diamond-kamacite aggregates have revealed a pronounced difference in the release patterns of spallogenic³He and trapped gases. About half the³He is released at T ? 920°C, without being accompanied by significant amounts of primordial gases; the latter, together with the remaining³He, is given off only at T ? 1200°C. Acid treatment of an aliquant dissolved about 2/3 of the total Fe in the sample but did not cause a significant change in the gas concentrations. It is concluded that (a) there is no evidence for a loss of spallogenic³He from the graphite-diamond-kamacite aggregates, (b) one major constituent of the aggregates - graphite - is almost void of trapped gases, (c) kamacite is not a main carrier of the gases. This leaves diamond as the most probable site of the primordial gases.The elemental abundance pattern in the noble gases is essentially as reported previously. In particular, the excellent correlation between relative depletion factors, normalized to the cosmic abundance ratios, and the respective ionisation energies is confirmed. Other important features of the trapped gases are a²⁰Ne/²²Ne ratio of 12.3 ± 0.6, intermediate between solar wind and solar flare implanted Ne,³⁶Ar/³⁸Ar = 5.20 ± 0.06 and a measured⁴⁰Ar/³⁶Ar ratio (before blank correction) of 0.0076.Possible modes of trapping of the noble gases are discussed.     

The abundances of3H and 14C in the solar wind

Tritium is measured as a function of depth in a Surveyor 3 sample. The upper limit for solar-wind-implanted tritium gives a³H/¹H limit for the solar wind of 1 × 10^?11. The temperature release patterns of¹⁴C from lunar soils are measured. The¹⁴C release patterns from surface soils differ from a trench bottom soil and gives evidence for the presence of¹⁴C in the solar wind with a¹⁴C/¹H ratio of approximately 4 × 10^?11. The implications of these radio nuclide abundances in the solar wind are discussed.     

Fission-track retention age of the Bondoc mesosiderite

Whitlockites have been extracted from the Bondoc mesosiderite and found to contain ～(0.7–2.7) × 10⁶ cm^?2 of spontaneous-fission tracks. Thermal-neutron irradiation of these crystals along with terrestrial apatite age standards, and measurement of the track densities so induced, lead to the determination of a whitlockite track-retention age of 2.68 (±0.30) Gyr for Bondoc, which is essentially independent of the initial (Pu/U) ratio.This young age is in qualitative, and, within the experimental uncertainties, in quantitative, agreement with the slow cooling rates determined for many mesosiderites [1,2] and specifically for Bondoc [6] from Ni distributions in the metal phase.     

Manifestations of the ray structure of the coronal streamer belt in the form of sharp peaks of the solar wind plasma density in the Earth’s orbit

White corona images are analyzed based on the calibrated data of the LASCO-C2/SOHO instrument (processing level 1) and the solar wind (SW) parameters with hourly and minute resolutions on the Wind spacecraft. The quasistationary events, excluding coronal mass ejections and their manifestations in SW are studied. It has been indicated that the angular dimensions and relative variations in the density of the streamer belt segments remain almost unchanged over the entire distance from the Sun to the Earth’s orbit. In the Earth’s orbit, the ray structure of the belt streamer manifests itself as sharp (with steep fronts lasting several minutes and less) peaks (of several hours in duration) of the solar wind plasma density with maximal values N _max > 10 cm^?3.     

Formation chronology for C2 meteorites

The times at which phyllosilicate matrix and euhedral olivines became associated have been determined for five C2 meteorites. The ages, calculated from fission track densities on crystal surfaces, are based on an initial²⁴⁴Pu/²³⁸U ratio in the matrix material of 0.0154 at 4.6 b.y., and range from 4.22 b.y. for Nogoya to 4.42 b.y. for Murray. Unless the initial²⁴⁴Pu/²³⁸U ratio was less than 0.004, the meteorites cannot have existed in their present form for 4.6 × 10⁹ yr. The measured ages place limits on the time when pre-compaction effects such as micrometeorite craters and solar flare tracks were produced, and they may approximately date the formation of the olivine crystals themselves.     

Cosmogenic21Ne and22Ne depth profiles in chondrites

The production rate profiles of²¹Ne and²²Ne as a function of depth in meteoroids due to spallation by solar flare cosmic rays (SCR) and galactic cosmic rays (GCR) are calculated and their dependence on size and composition of meteoroids has been evaluated. The GCR production rate at a given depth increases with size for radii<25cm and then decreases whereas the²²Ne²¹Ne ratio (NeR) generally decreases with size and depth. The calculated GCR production rates and NeR are consistent with the measurements in several Chondrites. A plot of track production rate vs. NeR shows that some chondrites have NeR values smaller than those expected for their sizes. Thes obeervation suggestsat least a two-stage irradiation for such meteorites; the meteoroid exposure as a small body in the interplanetary space must have been preceded by exposure under deep shielding, possibly in its parent body.     

Dissipation of the rare gases contained in the primordial Earth's atmosphere

If the Earth was formed by accumulation of rocky bodies in the presence of the gases of the primordial solar nebula, the Earth at this formation stage was surrounded by a massive primordial atmosphere (of about 1 × 10²⁶ g) composed mainly of H₂ and He. We suppose that the H₂ and He escaped from the Earth, owing to the effects of strong solar wind and EUV radiation, in stages after the solar nebula itself dissipated into the outer space.The primordial atmosphere also contained the rare gases Ne, Ar, Kr and Xe whose amounts were much greater than those contained in the present Earth's atmosphere. Thus, we have studied in this paper the dissipation of these rare gases due to the drag effect of outflowing hydrogen molecules. By means of the two-component gas kinetic theory and under the assumption of spherically symmetric flow, we have found that the outflow velocity of each rare gas relative to that of hydrogen is expressed in terms of only two parameters — the rate of hydrogen mass flow across the spherical surface under consideration and the temperature at this surface. According to this result, the rare gases were dissipated below the levels of their contents in the present atmosphere, when the mass loss rate of hydrogen was much greater than 1 × 10¹⁷ g/yr throughout the stages where the atmospheric mass decreased from 1 × 10²⁶ g to 4 × 10¹⁹ g.     

Relation between the active region magnetic field and solar flares

A weak active region (NOAA 11158) appeared on the solar disk near the eastern limb. This region increased rapidly and, having reached the magnetic flux higher than 10²² Mx, produced an X-class flare. Only weak field variations at individual points were observed during the flare. An analysis of data with a resolution of 45 s did not indicate any characteristic features in the photospheric field dynamics during the flare. When the flux became higher than 3 × 10²² Mx, active region NOAA 10720 produced six X-class flares. The field remained quiet during these flares. An increase in the magnetic flux above ～10²² Mx is a necessary, but not sufficient, condition for the appearance of powerful flares. Simple active regions do not produce flares. A flare originates only when the field distribution in an active region is complex and lines of polarity inversion have a complex shape. Singular lines of the magnetic field can exist only above such active regions. The current sheets, in the magnetic field of which the solar flare energy is accumulated, originate in the vicinity of these lines.     

Global electromagnetic induction in the Moon and planets

A summary of experiments and analyses concerning electromagnetic induction in the Moon and other extraterrestrial bodies is presented. Magnetic step-transient measurements made on the lunar dark side show the eddy current response to be the dominant induction mode of the Moon. Analysis of the poloidal field decay of the eddy currents has yielded a range of monotonic conductivity profiles for the lunar interior: the conductivity rises from 3·10^?4 mho/m at a depth of 170 km to 10^?2 mho/m at 1000 km depth. The static magnetization field induction has been measured and the whole-Moon relative magnetic permeability has been calculated to be $\text{μ}\text{μ}{}_0\text{= 1.01 ± 0.06}$. The remanent magnetic fields, measured at Apollo landing sites, range from 3 to 327 γ. Simultaneous magnetometer and solar wind spectrometer measurements show that the 38-γ remanent field at the Apollo 12 site is compressed to 54 γ by a solar wind pressure increase of 7·10^?8 dyn/cm². The solar wind confines the induced lunar poloidal field; the field is compressed to the surface on the lunar subsolar side and extends out into a cylindrical cavity on the lunar antisolar side. This solar wind confinement is modeled in the laboratory by a magnetic dipole enclosed in a superconducting lead cylinder; results show that the induced poloidal field geometry is modified in a manner similar to that measured on the Moon. Induction concepts developed for the Moon are extended to estimate the electromagnetic response of other bodies in the solar system.     

EISCAT measurements of the solar wind

EISCAT observations of interplanetary scintillation have been used to measure the velocity of the solar wind at distances between 15 and 130R (solar radii) from the Sun. The results show that the solar wind consists of two distinct components, a fast stream with a velocity of 800 km s^–1 and a slow stream at 400 kms^–1. The fast stream appears to reach its final velocity much closer to the Sun than expected. The results presented here suggest that this is also true for the slow solar wind. Away from interaction regions the flow vector of the solar wind is purely radial to the Sun. Observations have been made of fast wind/slow wind interactions which show enhanced levels of scintillation in compression regions.     

Rare-gas dating,I. A demountable metal system with low blanks

The construction and method of operation of an all-metal system for KAr and U-He dating is described in detail. The system is capable of handling samples in batches of about 15 g total weight. Blanks are typically 6 × 10^?9 cm³ STP for⁴⁰Ar_atmos, <1.2 × 10^?9 cm³ STP for⁴He, and ～2 × 10^?9 STP for⁴⁰Ar_radiogenic. The last of these quantities is independent of the quantity of⁴⁰Ar_radiogenic processed in the preceding run because vapor transport of the sample out of the hottest region of the crucible is very substantial and release of the rare gases in the sample is therefore almost complete. The system is very stable manometrically; monitoring of spike peaks therefore permits detection of any gas loss which amounts to more than a few percent. The system is not very suitable for analysis of large samples.     

Descriptive study of solar activity sudden increase and Halloween storms of 2003

During the declining phase of the last three solar cycles, secondary peaks have been detected 2–3 years after the main peak of sunspot number. The main peak of cycle 23 was in 2001, but a sudden increase of the solar activity occurred during the period October 17 to November 10, 2003 (the so-called Halloween storms). A similar storm occurred 1 year later, during the period October 3 to November 13, 2004. These events are considered as secondary peaks during the declining phase of cycle 23. Secondary peaks during declining phase of the last 10 solar cycles were detected by Gonzalez and Tsurutani [1990. Planetary and Space Science 38, 181–187]. During Halloween storm period, the sunspot area increased up to 1.11×10^?9 hemisphere on October 19, and grow up to 5.69×10^?9 hemisphere on October 30, 2003. Then it decreased to 1.11×10^?9 hemisphere on November 4, 2003. Also, the radio flux of λ=10.7 cm increased from 120 sfu on October 19, to 298 sfu on October 26, 2003, then decreased to 168 sfu on November 4, 2003. Two eruptive solar proton flares were released on 26 and 28 October 2003, the latter being the most eruptive flare recorded since 1976 (values reaching X17/4B).The aim of this study is to follow the morphological and magnetic changes of the active region before, during, and after the production of high-energy flares. Furthermore, the causes of release of these eruptive storms have been discussed for the period, October–November 2003, during the declining phase of the solar cycle 23.     

Recurrence of flare energy releases in solar active regions (Cycle 23)

The following results have been achieved in this work. The distribution of the recurrence times of solar flare events is generally lognormal. The typical flare recurrence times at the cycle 23 minimum and maximum are different: the average times (100–200 min) are most typical of the maximum; at the same time, the minimum is simultaneously characterized by short (several tens of seconds) and long (from several hundreds to a thousand of minutes). The minimal flare recurrence time tends to decrease in an active region with increasing sunspot group area in this region. The average flare recurrence times in an active region have typical values of 120^m, 210^m, 300^m, 400^m, and 530^m, which is close to the typical periods of long-period sunspot oscillations. The total number of flares in an active region depends on the sunspot area in this region and the flare energy release rate.     

Global aspects of solar wind–ionosphere interactions

Recent observations have quantified the auroral wind O⁺ outflow in response to magnetospheric inputs to the ionosphere, notably Poynting energy flux and precipitating electron density. For moderate to high activity periods, ionospheric O⁺ is observed to become a significant or dominant component of plasma pressure in the inner plasma sheet and ring current regions. Using a global circulation model of magnetospheric fields and its imposed ionospheric boundary conditions, we evaluate the global ionospheric plasma response to local magnetospheric conditions imposed by the simulation and evaluate magnetospheric circulation of solar wind H⁺, polar wind H⁺, and auroral wind O⁺. We launch and track the motions of millions of test particles in the global fields, launched at randomly distributed positions and times. Each particle is launched with a flux weighting and perpendicular and parallel energies randomly selected from defined thermal ranges appropriate to the launch point. One sequence is driven by a two-hour period of southward interplanetary magnetic field for average solar wind intensity. A second is driven by a 2-h period of enhanced solar wind dynamic pressure for average interplanetary field. We find that the simulated ionospheric O⁺ becomes a significant plasma pressure component in the inner plasma sheet and outer ring current region, particularly when the solar wind is intense or its magnetic field is southward directed. We infer that the reported empirical scalings of auroral wind O⁺ outflows are consistent with a substantial pressure contribution to the inner plasma sheet and plasma source surrounding the ring current. This result violates the common assumption that the ionospheric load is entirely confined to the F layer, and shows that the ionosphere is often an important dynamic element throughout the magnetosphere during moderate to large solar wind disturbances.     

The probabilistic approach to estimating the origination of certain types of extreme solar events

The probability of origination of superpower flares (super-flares) on the Sun, the power of which is higher than that of the observed flares, is discussed. The probabilistic approach, which makes it possible to find the analytical expression for the distribution of the observed values of any solar activity parameter and to extrapolate the obtained function to the range of values that were not observed previously, is proposed. The estimated probabilities of implementation of the Wolf number (400) and the flare proton fluxes in the Earth’s orbit (from 60000 to 160000 s⁻¹ cm⁻²) are presented as an example. It has been obtained that these events occur ones per 10 000 and 100 years, respectively.