Isotopically anomalous neon in meteoritic nanodiamonds: Formation during type II supernova explosions

We hypothesize the formation of neon associated with isotopically anomalous xenon (Xe-HL) in meteoritic nanodiamonds and designated as Ne-X through the mixing of the Ne-HL and Ne-S subcomponents. The Ne-HL subcomponent is neon from the helium (He/C) zone of a type II supernova or a mixture of neon from this zone and its hydrogen zone, while the Ne-S subcomponent is spallation neon formed during a supernova explosion in nuclear spallation reactions induced by high-energy protons. Based on this hypothesis and the presumed abundances of neon isotopes in the zones of a high-mass (25M _⊙) supernova after its explosion, we have calculated the abundances of neon components in nanodiamond separates and its grain-size fractions. Our calculations have shown the following. (1) The main source of Ne-HL is neon from the helium zone of the supernova; as a result, the ²⁰Ne/²²Ne and ²¹Ne/²²Ne ratios for Ne-X are 0.26 ± 0.03 and 0.19 ± 0.04, respectively. The isotopic composition of Ne-X is identical to that for Ne-A2 if Ne-HL is produced by the mixing of neon from the helium and hydrogen zones in proportion 1: 1.06. (2) In meteoritic nanodiamonds, the main neon abundance is determined by neon of the P3 component (Ne-P3). Ne-P3 is retained during thermal metamorphism, because it is sited in traps of the crystal lattice of diamond with a high energy of its activation. (3) The Ne-X/Ne-P3 ratio increases with nanodiamond grain size; as a result, there is no need to invoke an additional neon component (Ne-P6) to interpret the data on neon in meteoritic nanodiamonds.     

A Postulated Planetary Collision, the Terrestrial Planets, the Moon and Smaller Solar-System Bodies

In a scenario produced by the Capture Theory of planetary formation, a collision between erstwhile solar-system giant planets, of masses 798.75 and 598.37 M _⊕, is simulated using smoothed-particle hydrodynamics. Due to grain-surface chemistry that takes place in star-forming clouds, molecular species containing hydrogen, with a high D/H ratio taken as 0.01, form a layer around each planetary core. Temperatures generated by the collision initiate D–D reactions in these layers that, in their turn, trigger a reaction chain involving heavier elements. The nuclear explosion shatters and disperses both planets, leaving iron-plus-silicate stable residues identified as a proto-Venus and proto-Earth. A satellite of one of the colliding planets, captured or retained by the proto-Earth core, gave the Moon; two massive satellites released into heliocentric orbits became Mercury and Mars. For the Moon and Mars, abrasion of their surfaces exposed to collision debris results in hemispherical asymmetry. Mercury, having lost a large part of its mantle due to massive abrasion, reformed to give the present high-density body. Debris from the collision gave rise to asteroids and comets, much of the latter forming an inner reservoir stretching outwards from the inner Kuiper Belt that replenishes the Oort Cloud when it is depleted by a severe perturbation. Other features resulting from the outcome of the planetary collision are the relationship of Pluto and Triton to Neptune, the presence of dwarf planets and light-atom isotopic anomalies in meteorites.     

Fractionation of noble gases by thermal escape from accreting planetesimals

A model for the selective loss of noble gases by thermal escape of the gases from planetesimals as they grow to form the terrestrial planets has been developed. The initial elemental and isotopic abundance ratios are assumed to be solar. Competition between gravitational binding and escape determines the degree of fractionation that occurs. Two classes of planetesimals can be formed on a time scale consistent with modern models of accretion. One class is depleted in neon and, in some cases, partly in ³⁶Ar. The other class is neon rich. Subject to the validity of some assumptions regarding loss of planetary atmospheres following collisions between very large embryo planets and a strong radial dependence in the rate of accumulation of neon-rich planetesimals, the mechanism can account for all known properties of the noble gas volatiles on the terrestrial planets except one. This is the ³⁶Ar/³⁸Ar ratios for Earth and Mars which are predicted to be much lower than observed. This failure is probably fatal for the hypothesis.     

On the process of accretion in the formation of the planets and comets

The physically reasonable assumption that the seed bodies which initiated the accretion of the individual asteroids, planets, and comets (subsequently these objects are collectively called planetoids) formed by stochastic processes requires a radius distribution function which is unique except for two scaling parameters: the total number of planetoids and their most probable radius. The former depends on the ease of formation of the seed bodies while the second is uniquely determined by the average pre-encounter velocity, V, of the accretable material relative to an individual planetoid. This theoretical radius function can be fit to the initial asteroid radius distribution which Anders (1965) derived from the present-day distribution by allowing for fragmentation collisions among the asteroids since their formation. Normalizing the theoretical function to this empirical distribution reveals that there were about 10² precollision asteroids and that V = (2?4) × 10^?2 km/sec which was presumably the turbulent velocity in the Solar Nebula. Knowing V we can determine the scale height of the dust in the Solar Nebula and consequently its space density. The density of accretable material determines the rate of accretion of the planetoids. From this we find, for example, that the Earth formed in about 8 × 10⁶ yr and it attained a maximum temperature through accretion of about 3 × 10³°K. From the total mass of the terrestrial planets and the theoretical radius function we find that about 2 × 10³ planetoids formed in the vicinity of the terrestrial planets. Except for the asteroids the smaller planetoids have since been accreted by the terrestrial planets. About 15% of the present mass of the terrestrial planets was accumulated by the secondary accretion of these smaller primary planetoids. There are far fewer primary planetoids than craters on the Moon or Mars. The craters were likely produced by the collisional breakup of a few primary planetoids with masses between one-tenth and one lunar mass. This deduction comes from comparing the collision cross sections of the planetoids in this mass range to that of the terrestrial planets. This comparison shows that two to three collisions leading to the breakup of four to six objects likely occurred among these objects before their accretion by the terrestrial planets. The number of these fragments is quite adequate to explain the lunar and Martin craters. Furthermore the mass spectrum of such fragments is a power-law distribution which results in a power-law distribution of crater radii of just the type observed on the Moon and Mars. Applying the same analysis to the planetoids which formed in the vicinity of the giant planets reveals that it is unlikely that any fragmentation collisions took place among them before they were accreted by these planets due to the integrated collision cross section of the giant planets being about three orders of magnitude greater than that of the terrestrial planets. We can thus anticipate a marked scarcity of impact craters on the satellites of these outer planets. This prediction can be tested by future space probes. Our knowledge of the radius function of the comets is consistent with their being primary planetoids. The primary difference between the radius function of the planetoids which formed in the inner part of the solar system and that of the comets results from the fact that the seed bodies which grew into the comets formed far more easily than those which grew into the asteroids and the terrestrial planets. Thus in the outer part of the Solar Nebula the principal solid material (water and ammonia snow) accreted into a huge (～10¹²⁺) number of relatively small objects (comets) while in the inner part of the nebula the solid material (hard-to-stick refractory substances) accumulated into only a few (～10³) large objects (asteroids and terrestrial planets). Uranus and Neptune presumably formed by the secondary accretion of the comets.     

Extinct radioactive nucleus202Pb: Possible origin of isotopic anomalies of Hg in meteorites

The abundance of extinct radioactive nucleus²⁰²Pb trapped in chondrites is calculated from the anomalous isotopic ratio²⁰²Hg/¹⁹⁶Hg, assuming the isotopic anomalies are only due to the decay of²⁰²Pb. The magnitude of nonuniformity of the distribution of²⁰²Pb inferred from the excess isotopic abundance of²⁰²Hg is the same order of magnitude suggested by anomalous isotopic abundances of the other chemical elements found in meteoritic materials.     

Hydrogen collisions in planetary atmospheres, ionospheres, and magnetospheres

Hydrogen is the most abundant element in the universe. Molecular hydrogen is the dominant chemical species in the atmospheres of the giant planets. Because of their low masses, neutral and ionized hydrogen atoms are the dominant species in the high atmospheres of many planets. Finally, protons are the principal heavy component of the solar wind.Here we present a critical evaluation of the current state of understanding of the chemical reaction rates and collision cross sections for several important hydrogen collision processes in planetary atmospheres, ionospheres, and magnetospheres. Accurate ab initio quantum theory will play an important role. The collision processes are grouped as follows:

(a)

H⁺+H charge transfer,

(b)

H⁺+H₂(v) charge transfer and vibrational relaxation, and

(c)

H₂(v,J)+H₂ vibrational, rotational, and ortho-para relaxation.

In each case we provide explicit representations as tabulations or compact formulas. Particularly important conclusions are that H⁺+H₂(v) collisions are more likely to result in vibrational relaxation than charge transfer and H₂ ortho-para conversion is at least an order-of-magnitude faster than previously assumed.     

Presolar grains from novae: their isotopic ratios and radioactivities

Five SiC and two graphite presolar grains exhibit isotopic ratios characteristic of ONe nova nucleosynthesis: low ¹²C/¹³C (4–9), low ¹⁴N/¹⁵N (5–20), high ²⁶Al/²⁷Al, high ³⁰Si/²⁸Si (2×solar) with close-to-normal ²⁹Si/²⁸Si. The upper limit of ²⁰Ne/²²Ne (<0.01) of one graphite grain suggests that the ²²Ne excess is due to the decay of ²²Na. In order to achieve the isotopic ratios of the grains, however, synthesized material during nova explosion had to be mixed with isotopically close-to-solar material, which should consist of more than 95% of the mix.     

The relative abundance of the isotopes of Li,Be and B and the age of cosmic rays

Using a balloon borne double dE/dx x total energy telescope we have determined the isotopic composition of cosmic ray Li, Be and B nuclei in the energy range 100–250 MeV nuc.^–1. The measured mass resolution, for these nuclei is 0.3 AMU. The observed isotopic composition is in agreement with that predicted on the basis of interstellar fragmentation with the exception of a deficiency of Be¹⁰. If the low abundance of Be¹⁰ is attributed to the decay of this radioactive isotope we obtain a mean cosmic ray lifetime of (3.4 _–1.3 ^+3.4 )×10⁶ yr.A recent measurement which we have used in this paper gives this lifetime to be (1.5±0.3)×10⁶ yr (Yiou and Raisbeck, 1972).     

Orbital stability of systems of closely-spaced planets,II: configurations with coorbital planets

We numerically investigate the stability of systems of 1 \({{\rm M}_{\oplus}}\) planets orbiting a solar-mass star. The systems studied have either 2 or 42 planets per occupied semimajor axis, for a total of 6, 10, 126, or 210 planets, and the planets were started on coplanar, circular orbits with the semimajor axes of the innermost planets at 1 AU. For systems with two planets per occupied orbit, the longitudinal initial locations of planets on a given orbit were separated by either 60° (Trojan planets) or 180°. With 42 planets per semimajor axis, initial longitudes were uniformly spaced. The ratio of the semimajor axes of consecutive coorbital groups in each system was approximately uniform. The instability time for a system was taken to be the first time at which the orbits of two planets with different initial orbital distances crossed. Simulations spanned virtual times of up to 1 × 10⁸, 5 × 10⁵, and 2 × 10⁵ years for the 6- and 10-planet, 126-planet, and 210-planet systems, respectively. Our results show that, for a given class of system (e.g., five pairs of Trojan planets orbiting in the same direction), the relationship between orbit crossing times and planetary spacing is well fit by the functional form log(t _c /t ₀) = b β + c, where t _c is the crossing time, t ₀ = 1 year, β is the separation in initial orbital semimajor axis (in terms of the mutual Hill radii of the planets), and b and c are fitting constants. The same functional form was observed in the previous studies of single planets on nested orbits (Smith and Lissauer 2009). Pairs of Trojan planets are more stable than pairs initially separated by 180°. Systems with retrograde planets (i.e., some planets orbiting in the opposite sense from others) can be packed substantially more closely than can systems with all planets orbiting in the same sense. To have the same characteristic lifetime, systems with 2 or 42 planets per orbit typically need to have about 1.5 or 2 times the orbital separation as orbits occupied by single planets, respectively.     

The origin of the ‘FUN’ anomalies and the high temperature inclusions in the allende meteorite

The discovery of isotopic anomalies in white inclusions of the meteorite Allende has led to fundamental questions concerning the origin of these anomalies and of the white inclusions themselves. An analysis of the FUN anomalies in the inclusions C1 and EK1-4-1 demonstrates that these isotopic anomalies may be decomposed into individual nucleosynthetic components, which have been subjected to separate mass and component fractionations. There is no evidence that any freshlysynthesized material injected into the primitive solar nebula was of abnormal isotopic composition, or that the FUN anomalies were due to an injection of unusual material. Rather, they show the effects of form of interstellar grains whose size or chemistry served as a memory for the nucleosynthetic origins of their constituent atoms. Giant gaseous protoplanets, as described for the early solar nebula by Cameron (1978), are a potential site for achieving both mass and component fractionations, and for producing white inclusions in general.     

Toward consistency in the uses of ephemerides

The apparent coordinates in the printed material almanacs have inconsistencies concerning the reference frame. These inconsistencies produce secular errors of about 0 _. 001/century in the equatorial coordinates and periodic errors of about 0 _. 04 in the ecliptic coordinates. It is recommended that the calculation of apparent places of planets should be based on a consistent reference frame as well as on a consistent system of astronomical constants.     

Recently synthesizedr-process nuclei: Ultra-heavy cosmic rays and peculiar stars

Recently synthesized (t10⁹ yr)r-process material has actinide elemental and isotopic abundance characteristics which can be used to distinguish it from ancientr-process material. The time-dependence of relative actinide abundances provides detailed chronometric information. Also it is shown that, ifN=184 is a neutron magic number as predicted by nuclear thery, the resultingr-process production peak atA281 will in turn yield, due to symmetric fission, a broad abundance peak aroundA135–140. The present results can be used to help verify or refute some current hypotheses concerning the origin of UH cosmic rays and some of the abundance anomalies in peculiar stars.     

Dust blobs in the solar nebula — primary distended atmosphere

When planetary accretion proceeds in the gas disk-solar nebula, a protoplanet attracts surrounding gas to form a distended H₂-He atmosphere. The blanketing effect of the atmosphere, hampering the escape of accretional energy, enhances the surface temperature of planets. Furthermore, evaporation of ice or reduction of surface silicate and metallic oxide can supply a huge amount of water vapor into the atmosphere, which would raise the temperature and promote evaporation. Evaporated materials can be efficiently conveyed outward by vigorous convection, and condensed dust particles should keep the atmosphere opaque during accretion. The size of this opaque atmosphere dust blob is defined by the gravitational radius, which exceeds 3 × 10⁸ m when the planetary mass is the Earth's mass (5.97 × 10²⁴ kg). This is larger than the radii of present Jovian planets and so-called brown dwarfs. The expected lifetime of dust blobs is 10⁶–10⁷ yr, which is longer than that of the later gas accreting and cooling stages of Jovian planets. The number of dust blobs could exceed that of Jovian planets. If the gas disk is rather transparent, the possibility of observing such objects with a distended atmosphere may be higher than that of detecting Jovian planets. Contamination of the gas disk by the dust from primary atmospheres is negligible.Paper presented at the Conference on Planetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.     

Interstellar chemistry recorded by nitrogen isotopes in Solar System organic matter

The relationship between the organic and D/H ratios in small Solar System bodies (meteorites, interplanetary dust and comets) suggests that isotopic exchange reactions taking place at various temperatures are at the origin of the observed variations. These relationships are used to determine the exothermicity (ΔE) of ion-molecule reactions that fractionated the nitrogen isotopic ratio in the presolar molecular cloud; that is ΔE=43±10 K. Comparison with current models of interstellar chemistry suggests that such a value could be achieved by condensation of ¹⁵N-rich gas-phase precursors onto grain surfaces and their further isolation from the gas by incorporation into large macromolecular structures.     

Cometary collisions and the dark material on Iapetus

Iapetus (S8) is unique in our solar system in that the albedo of its leading hemisphere is only 0.05 while that of the trailing side is 0.5. Several existing hypotheses are examined and found inadequate. Photometric studies of the dark side are compared to comet nuclei and class D asteroids. It is hypothesized that in the last 10⁶–10⁸ yrs the leading side suffered a high-velocity collision with a cometary body of mass 10¹³–10¹⁵ kg and traveling at a speed of 20 km s^–1. About 5–16% of the excavated material was ejected into space, where the vaporized ices dissipated while the dark carbonaceous/silicate material was reaccreted on the leading side. The collision, although not sufficient to break Iapetus' tidal lock, resulted in a period of oscillation of about 5 yr. Until tidal friction reasserted a lock, the oscillation gave rise to the longitude effect, viz., the observed fact that the dark material covers more than 220 of longitude but only 110 of latitude.     

Isotopic lines of SiO in sunspots

As the isotopic shift for the vibration rotation band is generally much larger than the isotopic shift for the corresponding electronic transitions and thus facilitating separation of isotopic lines, the vibration rotation bands of SiO may find use in the determination of isotopic abundance ratio Si²⁸ Si²⁹ Si³⁰. To help identify the isotopic lines of SiO the wavenumbers for Si²⁹O¹⁶ and Si³⁰O¹⁶ have been calculated with an uncertainty of ±0.05 cm^–1.Taking note of the fact that SiO shows strong vibration rotation bands in the spectra of some cool stars the equivalent width calculations for P(40) and R(40) lines of the 1-0 and 2-1 vibration rotation bands of Si²⁹O¹⁶ and Si³⁰O¹⁶ have been made at the centre of the disc for the model ZSM-74 using two values of isotopic abundance ratio and three values of dissociation energy.The search for the isotopic lines of SiO near 7 to 8m is recommended in low noise centre to limb sunspot spectrum scans with a view to help improve the isotopic ratio Si²⁸ Si²⁹ Si³⁰ and oscillator strengths for the vibration-rotation transitions.     

Measurements of cosmic-ray Li,Be and B nuclei in the energy range 100 MeV/nuc to >22 BeV/nuc

We report on new measurements of the spectra of Li, Be and B nuclei in the primary cosmic radiation in the energy range 100 MeV/nuc to >22 BeV/nuc. The differential spectrum of these light nuclei is found to have a maximum at 400 MeV/nuc in 1966. The L/M ratio is found to be equal to 0.25±0.01, constant over the entire energy range of the measurement. Atmospheric and solar modulation effects on the L nuclei and the L/M ratio are discussed. It is concluded that this ratio is representative of conditions in interstellar space. Using the most recently available fragmentation parameters gives a material path length of 3.6 g/cm² of hydrogen for the particles producing the L nuclei. The absence of any variation of the L/M ratio with energy places severe constraints on models for the propagation of cosmic rays. Models in which the material path length is a strong function of energy — or that exhibit an exponential path-length distribution for a fixed energy are incompatible with these results. An examination of the abundance ratios of the individual L nuclei separately reveals major discrepancies with the predictions of interstellar diffusion theory based on presently accepted fragmentation parameters. The constancy of the measured Li/M and B/M ratios with energy is not in accord with the large energy dependence of these ratios expected from the energy dependence of the fragmentation cross-sections. The low Li/M ratio and high B/M ratio to be expected if these nuclei are created at a much lower energy than we observe are also not found. This presents difficulties for theories which suggest that the passage through matter has occurred at low energies subsequently followed by considerable acceleration.The Be/M ratio in cosmic rays is anomalous in that it is 40% larger than expected on the basis of the fragmentation cross-sections. Evidence presented here on the isotopic composition of Be nuclei suggests that this discrepancy is due to an enhanced abundance of Be⁹ or Be¹⁰ in cosmic rays. This discrepancy complicates the determination of a cosmic-ray age using the decay of Be¹⁰ into B.Nevertheless the Be/B ratio is observed to remain constant at 0.42±0.03 over the energy range from 100 MeV/nuc to over 10 BeV/nuc. Unless the fragmentation parameters into the various isotopes of Be and B are such that e.g. (Be/B)<0.05 as a result of this decay, then the age of cosmic rays is either >3×10⁸ years or <10⁶ years. The further observation that the mass to charge ratio of all Be nuclei of energy 1 BeV/nuc is =2.05±0.1 suggests that Be¹⁰ is present at these energies. This supports the idea of a short lifetime.     

Gas capture and rare gas retention by accreting planets in the solar nebula

In this paper, the physico-chemical effects of the nebula gas on the planets are reviewed from a standpoint of planetary formation in the solar nebula.The proto-Earth growing in the nebula was surrounded by a primordial atmosphere with a solar chemical composition and solar isotopic composition. When the mass of the proto-Earth was greater than 0.3 times the present Earth mass, the surface was molten because of the blanketing effect of the atmosphere. Therefore, the primordial rare gasses contained in the primordial atmosphere dissolved into the molten Earth material without fractionation and in particular the dissolved neon is expected to be conserved in the present Earth material. Hence, if dissolved neon with a solar isotopic ratio is discovered in the Earth material, it will indicate that the Earth was formed in the nebula and that the dissolved rare gases were one of the sources which degassed to form the present atmosphere.     

Explosive hydrogen burning in supernovae

Rapid proton capture is supposed to be responsible for the synthesis of a number of proton-rich nuclei. This process of hydrogen burning is considered here for mass elements, the atomic numbers of which range fromZ=10 toZ=20. The possible site for this process is assumed to be the outer envelope of the supernova at a proton number density (n _p )ranging fromn _p =10²² cm^–3 ton _p =10²⁸ cm^–3 at temperatures in the range ofT=2–3×10⁹ K.The capture path is determined by considering that a dynamical equilibrium between (p, ) and (,p) reactions exists between the reacting nuclei. In this situation, the abundances of elements become proportional to the lifetime of ⁺ decaying nuclei at the waiting points.It is suggested that these rapid proton-capture reactions are responsible for the production of a number of nuclei in the rangeA40 during supernova outbursts.