ORIGIN OF THE SOLAR SYSTEM AND ITS ELEMENTS
O. K. MANUEL, J. T. LEE, D. E. RAGLAND, J. M. D. MACELROY*, BIN LI** AND W. K. BROWN***
Nuclear Chemistry, University of Missouri, Rolla, MO 65401 (USA)
Correspondence author’s e-mail address: firstname.lastname@example.org
(Journal of Radioanalytical and Nuclear Chemistry, in press)
Formation of the Solar System from heterogeneous debris of a supernova (SN) that exploded 5 billion years ago was recorded as a) inter-linked chemical and isotopic heterogeneities in meteorites, b) higher levels of extinct nuclides in grains that trapped larger isotopic anomalies, c) the physical properties of grains mentioned in part b, and d) patterns of isotopic anomalies in meteorites, in the solar-wind, and in solar flare particles. The Sun formed on the SN core, and planets formed in a rotationally-supported, equatorial disk of SN debris. Interiors of the Sun and the inner planets accreted first in a central, Fe-rich region surrounding the SN core. These were layered as condensate from other parts of the SN fell toward the condensing Sun. Elements in outer SN layers formed low-density, giant Jovian planets. Intra-solar diffusion enriches hydrogen and lighter isotopes of individual elements at the Sun’s surface.
*Chemical Engineering, Univ. College Dublin, Belfield, Dublin 4 (Ireland)
**Lunar & Planetary Lab, University of Arizona, Tucson, AZ 85721 (USA)
*** 5179 Eastshore Drive, Lake Almanor, CA 96137 (USA)
This paper was presented at the Conference on Presolar Grains in St. Louis, MO (USA) on October 31, 1996 and at the International Conference on Isotopes in the Solar System in Ahmedabad (India) on November 13, 1997. Parts were also presented as papers #25.03 and #27.02 at the 189th and 191st Meeting of the American Astronomical Society on January 13, 1997 (Toronto, Canada) and January 7, 1998 (Washington, D.C., USA). This is a summary of recent data that compelled us to consider local element synthesis and formation of the Solar System from heterogeneous supernova debris, rather than remote synthesis and collection of our elements from vast regions of space. A few earlier observations and conclusions that are consistent with local element synthesis are noted below.
REYNOLDS1 discovery of radiogenic 129Xe in isotopically anomalous meteoritic Xe would be expected, since extinct 129I and heterogeneities in the SN debris would diminish with time. SN debris is a natural site for a) heterogeneous accretion of cores of the inner planets2-4 and the Sun5,6 in a central Fe-rich region of the nebula and b) production of IAB iron meteorites and their inclusions by nebular, rather than igneous, processes7,8.
Over 40 years ago, BURBIDGE et al.9 noted that “...the back sides of the abundance peaks of the r-process isotopes might suggest that the conditions obtaining in a single supernova were responsible for their synthesis.” After considering astronomical implications, they concluded that “It does not appear unreasonable from this point of view, therefore, that a single supernova has been responsible for all of the material built by the r-process currently in the solar system” (BURBIDGE et al.9 , p. 639).
Four years later, FOWLER et al.10 suggested local element synthesis, induced by the bombardment of planetesimals with charged particles from the condensing Sun, to explain the abundances of deuterium, lithium, beryllium, and boron in the Solar System. In addition, they noted that several short-lived nuclides, like 129I, 107Pd and 26Al, might have been produced locally by this irradiation of planetesimals.
Inter-linkage of chemical and isotopic heterogeneities provided the first clue, over 20 years ago, that not only r-products but the entire Solar System came from a single supernova11,12. Elemental abundances of He and Ne in meteorites were shown to be linked with specific isotopes of heavy noble gases, as expected of stellar debris. Noble gases are ideally suited to preserve the primordial linkage of elemental and isotopic heterogeneities before condensation: The inertness of these elements protected them from the chemical reactions that most elements underwent as they mixed and reacted to form condensable compounds.
Exotic material from a multiplicity of stellar sources is currently the accepted13-16 explanation for isotopic anomalies seen in tiny grains of meteorites. In the following sections, we review observations which suggest that these grains are instead early condensate of a local supernova17 which exploded in the manner shown in Fig. 1. It has been suggested that such asymmetric supernovae explosions may produce bipolar nebulae18 and allow SN debris in the equatorial plane to retain heterogeneities of the parent star17.
We will show below how this explains inter-linked chemical heterogeneities, short-lived radioactivities, physical aspects of the matrix grains, and isotopic anomaly patterns in meteorites, in solar flare particles and in the solar-wind. In 1980, LAVRUKHINA19 also noted that formation of the Solar System from debris of one supernova might explain planetary scale variations in the isotopic compositions of some elements.
Decay products of extinct 41Ca, 26Al, 53Mn, 107Pd, 182Hf, 129I, 244Pu, or 146Sm might be used to date the supernova event shown in Fig. 1. Of these, 244Pu is best suited because a) decay products of 244Pu occur in U,Th-Pb dated samples, i.e., the 244Pu-136Xe and the U,Th-Pb chronometers can be linked, and b) 244Pu is an r-product that could not be made after the supernova by irradiation from the condensing Sun10. The volatile nature of the fission product, 136Xe, is the major disadvantage.
KURODA20 predicted the occurrence of 244Pu in nature, ROWE and KURODA21 discovered its decay products, and KURODA and MYERS22 used 244Pu to show that the supernova event shown in Fig. 1 occurred about 5 billion years ago. According to their calculations, the first carbonaceous chondrites started to retain fissiogenic 136Xe about 100 My later. Their results are shown in Fig. 2, where data from the Kapoeta achondrite are used to link the 244Pu-136Xe and the U,Th-Pb chronometers23.
Significant mixing may occur over planetary distances in 100 My, although this is short for galactic mixing10. Grains that formed in this time might incorporate products from different SN regions, before 244Pu-rich minerals start to retain gaseous 136Xe --- 100 My after the SN event. If mixing occurred, larger isotopic anomalies would be expected in grains that formed first and trapped even shorter-lived radioactivities, like 26Al.
However, early results suggested meteorites trapped rather uniform initial levels of extinct radioactivities ≈ 10-4 those of neighboring nuclides, in spite of a wide range in half-lives. FOWLER13 and WASSERBURG14 thus concluded that mixing 0.0001 parts exotic nucleogenetic material with 0.9999 parts normal solar system material could explain the decay products of extinct nuclides and isotopic anomalies found in meteorites.
Recent measurements have revealed levels of extinct radioactivities >>10-4 that of neighboring nuclei. For example, radiogenic 26Mg from the decay of 26Al corresponds to initial values of 26Al/27Al up to 0.06 in graphite from the Murchison meteorite24. Five SiC grains of that meteorite, labelled X grains25, formed when 0.10 < 26Al/27Al < 0.60. These trapped very large isotopic excesses of 12C, 15N, 28Si, 49Ti and 44Ca. The authors25 note that different zones of supernovae can “...account for almost all the isotopic compositions observed in grains X....” (AMARI et al.25, p. L46).
These results25 confirm that high levels of radioactive 26Al are associated with large isotopic anomalies, as expected of early condensate of supernova debris. They support neither the suggestion of a “canonical” value26 of 26Al/27Al ≈ 5 x 10-5 nor reports that short-lived radioactivities and isotopic anomalies in the solar system can be explained by the addition of 10-4 parts exotic nucleogenetic material. These X grains also have the physical properties expected for early condensate of supernova debris.
KURODA and MYERS27 recently reviewed data on extinct 26Al. They note that, like radioactivity trapped in fresh atmospheric fallout particles from nuclear weapons testing, the 26Al/27Al ratios25 in the X grains of SiC decrease with particle size. They calculate 26Al/27Al = 1.15 for the production ratio at the surface of an exploding supernova and conclude that X grains of SiC formed soon after a supernova. The 26Al-26Mg chronometer in Fig. 3 indicates that “X” grains formed within 1-3 My of the supernova. Early nucleation would form larger grains in local condensation, but this trend is unexpected if interstellar grains28 brought this exotic nucleogenetic material into the solar system from multiple stellar sources14-17.
More recently, AMARI et al.29 note that isotopic anomaly patterns of titanium change systematically with grain size in eight other SiC grains from Murchison, samples KJA-KJH. They note that this might be explained by “... assuming that SiC grains with different sizes come from AGB stars with different metallicities ...” (AMARI et al.29, p. 23). Even if grain size were preserved as a marker of the star-of-origin as interstellar grains traversed space, local condensation of heterogeneous supernova debris is a more simple, direct explanation for the observations.
The time scale shown in Fig. 3 indicates rapid condensation of solids following the supernova event. New measurements suggest an even earlier separation30,31 of supernova products and a single stellar source for short-lived nuclides79. Isotope ratios of r-products in Xe, Kr and Te in diamonds of the Allende meteorite suggest that chemical separation30,31 of these elements occurred within 104 seconds of the supernova event, even before the decay of precursor nuclei like 131I, 83Br, 125Sb, etc.
Inter-Linked Chemical and Isotopic Heterogeneities
Abundances of ordinary, planetary He and Ne in meteorites correlate with isotopically exotic components of Ar, Kr and Xe and extrapolate to isotopically normal Ar, Kr and Xe at the intercept32, where [He] ≈ [Ne] ≈ 0. This was the first clue that the solar system formed out of material with the inter-linked chemical and isotopic heterogeneities expected in supernova debris11,12. One example of these correlations is shown in Fig. 4.
The 136Xe/132Xe isotope ratios are shown in the top section of Fig. 4, and the elemental ratios of 4He/132Xe and 20Ne/132Xe are shown in the bottom. Similar correlations could be shown between elemental abundances of ordinary He and Ne with each exotic isotope ratio of Ar, Kr and Xe. This inter-linkage of ordinary He and Ne with exotic Ar, Kr and Xe is a common property of meteoritic noble gases32.
The correlations shown in Fig. 4, illustrate the difficulty in explaining isotopic anomalies by the addition of exotic nucleogenetic material13,14. If exotic Ar, Kr and Xe were alien nucleosynthesis products, for example, why do they accompany isotopically normal He and Ne? Why do the correlations extrapolate to isotopically normal Ar, Kr and Xe as elemental abundances of isotopically normal He and Ne approach zero?
These correlations led to the suggestion11,12 that the solar system condensed from heterogeneous SN debris: Normal He and Ne and exotic Ar, Kr and Xe came from outer layers that were rich in low-Z elements; normal Ar, Kr and Xe came from the interior where fusion reactions had depleted He, Ne and other low-Z elements. In the astrophysics community, it was suggested28 that interstellar grains may have carried normal He and Ne and exotic Ar, Kr and Xe into the solar system. Fig. 1 of this manuscript and Fig. 4 of CLAYTON28 offer alternative explanations for the observed association of normal He and Ne with exotic Ar, Kr and Xe.
Recently PEPIN et al.34 suggested that the exotic heavy noble gas component in Allende accounts for 8% of the 136Xe in the Sun. If so, the correlations of He and Ne with 136Xe (See Fig. 4) suggest that large amounts of He and Ne in the Sun are from this exotic noble gas component.
CLAYTON et al.35 provide additional evidence for large scale, inter-linked isotopic and elemental heterogeneities in the solar system. They found that fractional enrichments of an exotic oxygen component (monoisotopic 16O) can be used to group meteorites and planets into at least six categories. Objects of one category cannot be derived by fractionation or differentiation of material in another category. On the basis of exotic oxygen, material in the earth and its moon is like that in stony-iron meteorites, achondrites and enstatite chondrites, but isotopically distinct from material in carbonaceous and ordinary chondrites or urelites. Heterogeneous supernova debris (Fig. 1) offers a natural site for radial sorting of exotic oxygen, characteristic of the region where the material formed.
The occurrence of terrestrial-type Xe and its host minerals also provides a record of coupled chemical and isotopic heterogeneities related to radial distance from the sun. REYNOLDS1 found that the isotopic composition of terrestrial Xe is distinct from that in chondrites. Terrestrial-type Xe occurs in iron sulfide of diverse meteorites36, in atmospheres of Earth and Mars37, and in the Sun38, as expected if this were the dominant form of Xe in the inner Fe,S-rich region of the early solar nebula36.
The matrix composition of carrier grains of exotic xenon and other noble gases also demonstrates linkage of chemical and isotopic heterogeneities at the source. Diamonds trapped Xe enriched in r- and p-products; SiC trapped Xe enriched in s-products. This coupling of chemical and isotopic heterogeneities so thoroughly permeated the solar nebula that measurements of the isotopic compositions of xenon and other noble gases in acid residues have recently been used to determine the abundances of diamonds and SiC grains in seven different types of chondrites39.
LEE et al.40 cite other indications that chemical and isotopic heterogeneities were coupled throughout the early solar nebula40. A related discovery is the radial heterogeneity of 53Mn (t1/2 = 3.7 My), as evidenced by the correlation of excess 53Cr with heliocentric distance for material from the Earth-Moon, Mars, ordinary chondrites and eucrites41.
Formation of the solar system from supernova debris (See Fig. 1) predicts both inter-linked chemical and isotopic heterogeneities in the early solar nebula11-12,19,32,35-37,39,40 and a dependence of composition on radial distance from the Sun2-4,11-12,19,32,35,36,40,41.
Isotopic Anomaly Patterns
BEGEMANN42 offers compelling evidence that isotopic anomalies are unmixed products of the same nuclear processes that made our elements. Allende’s inclusion EK1-4-1 has excess (+) r- and p-products in Ba, Nd and Sm; Murchison’s SiC has deficits (-) of these same isotopes. These mirrorimage isotopic anomaly patterns are shown in Fig. 5. Smaller anomalies in Allende’s EK1-4-1 are multiplied by a factor of ≈102 to depict the mirror-image anomaly pattern. Although “quantitatively, the (anti)-match of the anomalies pattern is not perfect for all elements”, he concludes that it “---appears too good to be entirely serendipitous---” (BEGEMANN42, p. 524). This pattern is expected in poorly mixed products of the reactions that made our elements, but it is unlikely that exotic material, added to an otherwise homogeneous presolar nebula, would mimic the nucleosynthesis products required from one r-process and one s-process, so that the sum yields the isotopic composition of normal, solar-system material.
The sun accounts for 99% of the mass of the solar system. Isotopic compositions of solar elements provide additional evidence for large reservoirs of isotopically diverse material at the birth of the solar system. In general, planetary-type noble gases are enriched in the heavy isotopes relative to gases in the solar wind. KAISER38 showed, for example, that isotopic ratios of solar-type Xe can be reproduced by a mass fractionation enrichment of 4.1% per atomic mass unit in lighter mass isotopes of terrestrial Xe. KURODA and MANUEL43 noted a correlated fractionation effect in neon. However, early efforts to understand other solar isotopic ratios were frustrated by apparently large fractionation effects in the isotopes of solar Xe, Ne and He, accompanied by little or no fractionation effects across the isotopes of solar Ar and Kr.
Following the discovery of nucleogenetic isotopic anomalies in many elements, and linkage of primordial He and Ne with isotopically anomalous Ar, Kr and Xe in diverse meteorites32, MANUEL and HWAUNG44 suggested that noble gases in the Sun are a mixture of the nucleogenetic components seen in planetary material. They noted a systematic mass fractionation pattern across isotopes of all five noble gases in the solar wind, assuming that terrestrial Xe is dominant in the bulk sun38, that He, Ne and Ar there have the isotopic compositions of noble gases that accompany anomalous Xe in meteorites33, and that solar Kr is a mix of these two components.
Their results, shown in Fig. 6, suggest that intrasolar diffusion enriches lighter isotopes of He, Ne, Ar, Kr and Xe at the solar surface by about 200%, 30%, 9%, 6% and 4% per amu, respectively44. Light isotopes are less enriched in solar flares45, as expected if energetic events disrupt diffusive fractionation in the Sun46. Recent observations47,48 show 1H/4He in solar flares to be ≈10 times less than that in the solar photosphere.
If plasma diffusion49 produced the fractionation pattern shown in Fig. 6, the Sun’s interior may be Fe-rich44 like the inner planets. When this was first suggested44, diffusional fractionation was considered relatively unimportant in the Sun and solar-type stars50-52. However, we will show in the next section that these views are changing. It has been noted that heterogeneous accretion of the Sun and the four inner planets, beginning with core formation in a central Fe-rich region of the nebula53, may have assisted diffusive fractionation in stratification of the Sun.
Recently, PEPIN et al.34 also attempted to resolve the isotopic composition of solar Xe in terms of different isotopic components observed in planetary material. They concluded that the exotic Xe shown in Fig. 4 accounts for about 8% of the 136Xe in the solar wind.
We agree that the primordial noble gas component with normal He and Ne and exotic Ar, Kr and Xe may constitute a significant part of the Sun’s noble gases34,44. However, since “... the composition of condensed bits of interstellar matter would favor easily condensed elements over the noble gases” (ARNETT54, p. 2) , this conclusion is incompatible with prevailing opinion that interstellar grains28 brought the exotic Ar, Kr and Xe into the solar system from a multiplicity of stellar sources13-16.
Intrasolar Diffusion: Does it Operate in the Sun?
Several recent articles55-57 stress the importance of diffusional fractionation in the Sun. More than a decade ago, MACELROY and MANUEL58 attempted to evaluate the contribution of intrasolar diffusion to isotopic anomalies in the solar wind. We will briefly review their conclusions, some of the more recent work on diffusion in the Sun, and provide a few comments on issues that must be addressed for a quantitative understanding of intrasolar diffusion.
Possible fractionation effects for primordial 4He/H mixtures are shown in Fig. 7 as a function of the effective depth, d, of the perfectly mixed outer layers of the sun. The value of d shown there is linearly proportional to the total mass within this mixed zone58.
For the current solar surface ratio59,60 of 4He/H = 0.04, it is found that values of d required to satisfy a primordial 4He/H ratio of 0.09-0.15, the currently accepted range for cosmic abundances, are ~ 43 - 65. This value of d corresponds to a temperature of about 106 K for the transition region between the diffusion limited zone and the perfectly mixed zone.
One typical example of the possible influence of intrasolar diffusion on an isotopic ratio of xenon, 124Xe/130Xe, is shown in Fig. 8. From the results shown there, it is concluded that the enrichment of light isotopes of xenon is accurately predicted for intrasolar diffusion conditions very similar to those suggested by Fig. 7: A diffusion limited/perfectly mixed transition region corresponding to a temperature of approximately 106 K in the standard solar model and a Xe ionization state of +15. This result, coupled with additional observations from numerical data reported earlier58, provides independent support for the existence of significant diffusional fractionation occurring in the sun.
Further support for the influence of intrasolar diffusion and its relative importance in modelling the solar interior is seen in the very recent detailed numerical analyses conducted by a number of independent research groups.
(1) DAR and SHAVIV55 have demonstrated that reliable prediction of the observed flux of solar neutrinos requires consideration of the effects of diffusion within the sun. When the standard solar model is modified to include diffusion, they find that in one of the models investigated the observed solar neutrino flux is only 50% higher than the predicted value. By comparison, the observed neutrino flux is 100%-150% higher than the predicted value when intrasolar diffusion is assumed to be insignificant.
(2) GUENTHER et al.56 have shown that observed solar oscillations can be predicted with reasonable accuracy only when intrasolar diffusion is incorporated into the standard solar model.
(3) BAHCALL et al.57 show that sound speeds for solar models that include diffusion agree with helioseismological measurements for almost the entire sun. They also note that helioseismological measurements effectively rule out solar models that do not include diffusion, or which assume that the interior of the sun is significantly mixed.
We have already noted that another observation, namely noble gas isotope ratios in the solar wind, also requires consideration of intrasolar diffusion. We are encouraged that these disparate fields of research may be gradually approaching a common consensus. There are a few remaining issues that need to be addressed.
An accurate hydrodynamic analysis of the interfacial region between the radiative zone and the convection zone within the sun is one major problem on the computational side which has yet to be properly addressed.
This could help to eliminate a number of the apparent inconsistencies in the predictions in all these areas of research. One particular inconsistency concerns the locations of the diffusion limited transition region and the base of the convection zone. These need not necessarily occur at the same point within the sun.
The mixing length theories employed in modelling of intrasolar diffusion are known to inadequately describe convection in the outer layers of the sun61. Advanced computational fluid mechanics has, in fact, shown that mixing within the convection zone is not as complete as implied in the classical mixing length approach. Detailed hydrodynamic modelling of the solar interior, coupled with consideration of elemental and isotopic diffusion, will probably be required to provide the agreement sought between theory and observations.
On the experimental side, there is a need for measurements on the isotopic compositions of refractory elements in the solar wind62 and for an understanding of the origin of the Fractionation part of FUN anomalies63 in meteorites. We suspect that both may be the result of stellar diffusion. However, two fractionation processes, one acting on elements in the Sun and the other on elements present at the birth of the solar system, can be confusing. There were, for example, early indications of mass fractionation in the isotopes of Ne and Xe in the solar wind43, but not for the intermediate elements, Ar and Kr. Recognition of a common fractionation effect44 across the isotopes of solar Ar and Kr awaited discovery33 of a primordial, exotic noble gas component in which Ar and Kr are enriched in the heavier isotopes.
Recently, the isotopic compositions of Mg have been reported in the solar wind64 and in solar flare particles65. These results are from direct measurements of particles coming from the Sun, and error limits are much larger than those on elements that have accumulated in lunar soil over geologic time periods. In spite of large uncertainties, systematic trends in the data suggest possible interference from MgH+ which increases with particle energy46. Natural isotopic abundances cause this interference to be greatest at m/q = 25. The 24Mg/26Mg ratio is less effected. Shifts in the best values for 3He/4He, 20Ne/22Ne, 26Mg/24Mg and 36Ar/38Ar in solar flares and in the solar wind match46 the pattern expected if solar flares are disrupting diffusional processes that enrich lighter nuclei at the solar surface. However, for magnesium isotope ratios these shifts are within experimental uncertainties reported on the measurements.
Finally, it should be noted that an experiment already completed may provide important information on isotopic anomalies in the solar system and the role of intrasolar diffusion in producing anomalous isotope ratios in the solar wind. Isotopic analyses of elements in Jupiter with the mass spectrometer on the Galileo probe may shed new insight on this matter. To date, only the isotope ratios of H, He and C have been reported66 but we expect to have information on isotope ratios of Ne, Ar, Kr and Xe in Jupiter within the current calendar year.
From Supernovae to Planetary Systems
Until recently, formation of a planetary system from supernova debris was considered highly unlikely. However, recent astronomical observations on supernova remnants may be changing this view.
The Crab nebula, the remnant of a 1054 AD supernova, has long served as a model for explosions of supernovae, especially Type II SNs. Progress in this area of study is limited by the infrequency of such events. However, about 10 years ago, on February 23, 1987, Ian Shelton discovered a supernova explosion in the Large Megellanic Cloud. This is now known as Supernova 1987A or SN 1987A. GOLDSMITH67 tells how this discovery has changed our understanding of supernovae. For example, the parent star was not a red giant star, as expected, but clearly blue. It was the first stellar explosion observed in the Local Group of galaxies since 1885, and the first one bright enough to be seen with the naked eye since Kepler’s supernova of 1604. The suspected pulsar in SN 1987A is rotating much more rapidly than expected of a newborn neutron star, suggesting the possibility of rapid rotation in the parent star.
CHEVALIER68,69 reviewed observations on SN 1987A, five and ten years after the explosion. In the first68, he noted that the light emitting region is a ring, rather than a shell. In the second, he reports three rings of light. The smaller ring is in the central plane of the supernova, with larger rings of light above and below that. He also notes little or no radiation from any central compact object associated with either SN 1987A or SN 1993J. In both cases, radiation from the central compact object is estimated to be < 0.01 of radiation from the Crab Nebula pulsar.
Another recent astronomical observation on supernova remnants has been even more surprising. The first planetary system discovered70 and confirmed71 beyond our solar system was that orbiting the collapsed core of a supernova, the millisecond pulsar, PSR 1257+12.
There had been earlier reports that planets might be orbiting other pulsars. These were not confirmed, but they stimulated thinking about possible mechanisms for producing a planetary system from supernova debris. LIN et al.72 suggest that such a planetary system could be produced from a rotationally-supported disk of material that may fall back after a supernova explosion. The planetary system that WOLSZCZAN71 confirmed around PSR1257+12 consists of three, Earth like planets within 0.5 AU of the central pulsar. In the Appendix, we show that such a planetary system could be produced around PSR1257+12 from a rotationally-supported, disk of material (0.068 Msun mass) that falls back after the SN explosion.
The computed mass distributions, with and without shear, are shown in Fig. 9, together with the positions and relative masses of the planets WOLSZCZAN71 reports orbiting PSR1257+12.
From these results, we conclude that the formation of a planetary system from supernova debris is clearly possible. In earlier sections of this paper, we have summarized observations which suggest that the solar system was in fact produced in this manner.
The record of inter-linked chemical and isotopic heterogeneities and short-lived radioactivities that has been preserved in meteorites and in the planetary system is not explained by the addition of small amounts of exotic material. These are products of the supernova event, outlined in Fig. 1, that gave birth to the solar system 5,000 My ago.
This paper is dedicated to the memory of Dr. Dwarka Das Sabu.
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Fig. 1. The solar system formed directly from heterogeneous debris of a spinning supernova17 that exploded axially to produce a bipolar nebula18.
Fig. 2. Carbonaceous chondrites start to retain gaseous fission products of 244Pu about 100 My after the SN event22,23.
Fig. 3. Radioactive 26Al and large isotopic anomalies were trapped in graphite24 and in X grains of silicon carbide25 from the Murchison meteorite within a few My of the SN event27.
Fig. 4. Isotopic ratios of Xe correlate with elemental abundances of He and Ne in mineral separates of the Allende meteorite33. “Normal” Xe is at the intercept where [He] = [Ne] = 0.
Fig. 5. Mirror image (+ & -) isotopic anomalies that BEGEMANN42 noted in elements with 7 stable isotopes like Ba, Nd or Sm.
Fig. 6. Isotopic ratios of solar-wind-implanted gases44 show a smooth, mass-dependent fractionation pattern, as expected if intrasolar diffusion enriches lighter elements and lighter isotopes of individual elements at the solar surface. Mass fractionation is shown relative to 20Ne.
Fig. 7. Predicted primordial values of the 4He/H ratio are shown as a function of the effective mixing depth, d, for outer layers of the Sun. The lines marked a, b, and c correspond to predictions for current solar surface 4He/H values of 0.06, 0.04 and 0.02, respectively.
Fig. 8. Predicted solar wind values of the 124Xe/130Xe ratio (relative to the primordial value) are shown as a function of ionization state in the transition region between the diffusion-limited zone and the perfectly-mixed zone within the Sun. The curves from left to right correspond to 4He/H surface number ratios of 0.05, 0.03 and 0.01 for a primordial solar ratio of 4He/H = 0.15.
Fig. 9. Computed mass distributions, with and without shear, for fallback material72 rotating in the nebular disk, with Wolszczan’s three planets71 superimposed.
Fig. 10. A differential cylinder of radius, r1, thickness dr1, and height, h, inscribed in a sphere of radius RFB, and rotating with an angular velocity w.
Fig. 11. The mass distribution in the planetary disk, with and without shear, are quite similar.