The Early Solar System

Comptes Rendus Geoscience, 2007

The origin of short-lived (T $ 1 Myr) radionuclides (SRs) in the early solar system is a matter of debate. Some short-lived radionuclides had abundances in the solar protoplanetary disk in excess compared to the expected galactic background (7 Be, 10 Be, 26 Al, 36 Cl, 41 Ca and possibly 53 Mn and 60 Fe). These SRs thus either originated from a supernova contamination, or were produced by in situ irradiation of solar system dust or gas, or by Galactic Cosmic Ray (GCR) trapping in the molecular cloud core progenitor of our solar system (for 10 Be only). GCR trapping in the molecular cloud core seems to fail to reproduce the initial abundance of 10 Be, because trapping timescales exceed by one order of magnitude the observed core lifetimes. On the other hand, irradiation models can synthesize large quantities of 10 Be and other SRs (7 Be, 36 Cl, 26 Al, 41 Ca and 53 Mn). In addition, X-ray observations of young, solar-like stars provide direct evidence for protoplanetary disk irradiation in a different energy window. The initial abundance of 60 Fe is poorly known, and its presence in the early solar system might be accounted for galactic abundance rather than by a nearby supernova. To cite this article: M.

Meteorites and the Early Solar System II

During recent years, a growing body of evidence, both astrophysical observations of young stellar objects and cosmochemical observations made on meteorites, has strengthened the case that a fraction of the dust and gas of the solar accretion disk has been irradiated by cosmic rays emitted by the young forming active Sun. We review this meteoritic evidence, specifically the most convincing data obtained on Ca-Al-rich inclusions (CAIs) of primitive chondrite meteorites. Boron-isotopic variations in CAIs can be explained by decay products of short-lived 10 Be (T 1/2 = 1.5 m.y.) while a combination of extinct 7 Be (T 1/2 = 53 d) and of spallogenic Li may explain 7 Li/ 6 Li variations. We then discuss irradiation models that attempt to account for the origin of short-lived radionuclides and evaluate the predictions of these models in light of experimental data. Several anomalies, such as 21 Ne and 36 Ar excesses, suggest an exposure of CAIs and of chondrules (or their precusors) to cosmic rays emitted by the young Sun. The possible effects of early solar irradiation processes on the mineralogy, chemistry, and lightelement isotopic compositions (e.g., O, H, N) of early solar system solids are also considered and evaluated.

Proceedings of the International Astronomical Union, 2008

Galactic cosmic rays (GCR) provide information on the solar neighborhood during the sun's motion in the galaxy. There is now considerable evidence for GCR acceleration by shock waves of supernova in active star-forming regions (OB associations) in the galactic spiral arms. During times of passage into star-forming regions increases in the GCR-flux are expected. Recent data from the Spitzer Space Telescope (SST) are shedding light on the structure of the Milky Way and of its star-forming-regions in spiral arms. Records of flux variations may be found in solar system detectors, and iron meteorites with GCR-exposure times of several hundred million years have long been considered to be potential detectors (Voshage, 1962). Variable concentration ratios of GCR-produced stable and radioactive nuclides, with varying half-lives and therefore integration times, were reported by Lavielleet al. (1999), indicating a recent 38% GCR-flux increase. Potential flux recorders consisting of differ...

2011

Meteorites, which are remnants of solar system formation, provide a direct glimpse into the dynamics and evolution of a young stellar object (YSO), namely our Sun. Much of our knowledge about the astrophysical context of the birth of the Sun, the chronology of planetary growth from micrometer-sized dust to terrestrial planets, and the activity of the young Sun comes from the study of extinct radionuclides such as 26 Al (t 1/2 = 0.717 Myr). Here we review how the signatures of extinct radionuclides (short-lived isotopes that were present when the solar system formed and that have now decayed below detection level) in planetary materials influence the current paradigm of solar system formation. Particular attention is given to tying meteorite measurements to remote astronomical observations of YSOs and modeling efforts. Some extinct radionuclides were inherited from the long-term chemical evolution of the Galaxy, others were injected into the solar system by a nearby supernova, and some were produced by particle irradiation from the T-Tauri Sun. The chronology inferred from extinct radionuclides reveals that dust agglomeration to form centimeter-sized particles in the inner part of the disk was very rapid (<50 kyr), planetesimal formation started early and spanned several million years, planetary embryos (possibly like Mars) were formed in a few million years, and terrestrial planets (like Earth) completed their growths several tens of million years after the birth of the Sun.

Science (New York, N.Y.), 2014

Among the short-lived radioactive nuclei inferred to be present in the early solar system via meteoritic analyses, there are several heavier than iron whose stellar origin has been poorly understood. In particular, the abundances inferred for (182)Hf (half-life = 8.9 million years) and (129)I (half-life = 15.7 million years) are in disagreement with each other if both nuclei are produced by the rapid neutron-capture process. Here, we demonstrate that contrary to previous assumption, the slow neutron-capture process in asymptotic giant branch stars produces (182)Hf. This has allowed us to date the last rapid and slow neutron-capture events that contaminated the solar system material at ~100 million years and ~30 million years, respectively, before the formation of the Sun.

Little is known about the stellar environment and the genealogy of our solar system. Short-lived radionuclides (SLRs, mean lifetime τ shorter than 100 Myr) that were present in the solar protoplanetary disk 4.56 Gyr ago could potentially provide insight into that key aspect of our history, were their origin understood. Aims. Previous models failed to provide a reasonable explanation of the abundance of two key SLRs, 26 Al (τ 26 = 1.1 Myr) and 60 Fe (τ 60 = 3.7 Myr), at the birth of the solar system by requiring unlikely astrophysical conditions. Our aim is to propose a coherent and generic solution based on the most recent understanding of star-forming mechanisms.

Astrophysical Journal, 2008

Based on early solar system abundances of short-lived radionuclides (SRs), such as 26 Al (T 1/2 = 0.74 Myr) and 60 Fe (T 1/2 = 1.5 Myr), it is often asserted that the Sun was born in a large stellar cluster, where a massive star contaminated the protoplanetary disk with freshly nucleosynthesized isotopes from its supernova (SN) explosion. To account for the inferred initial solar system abundances of short-lived radionuclides, this supernova had to be close (∼ 0.3 pc) to the young ( 1 Myr) protoplanetary disk.

Protostars and Planets VI, 2014

We review some of the major findings in cosmochemistry since the Protostars and Planets V meeting: (1) the results of the sample-return space missions Genesis, Stardust, and Hayabusa, which yielded the oxygen and nitrogen isotopic composition of the Sun, evidence for significant radial transport of solids in the protoplanetary disk and the chondrite-comet connection, and the connection between ordinary chondrites and S-type asteroids, respectively; (2) the D/H ratio of chondritic water as a test of the Nice and Grand Tack dynamical models and implications for the origin of the Earth's volatiles; (3) the origin, initial abundances, and distribution of the short-lived radionuclides 10 Be, 26 Al, 36 Cl, 41 Ca, 53 Mn, 60 Fe in the early Solar System; (4) the absolute (U-Pb) and relative (short-lived radionuclide) chronology of early Solar System processes; (5) the astrophysical setting of the Solar System formation; (6) the formation of chondrules under highly nonsolar conditions; and (7) the origin of enstatite chondrites.

Chondrites and the …, 2005

Evidence for the presence of about a dozen short-lived now-extinct radionuclides in the early solar system has been found in meteorites. The half-lives of these nuclides range from 100,000 years to more than a hundred million years. Three plausible modes of origin for these nuclides have been proposed. Some of them, particularly those with half-life more than several million years, could be products of continuous galactic nucleosynthesis, while others could be freshly synthesized stellar products injected into the protosolar molecular cloud or products of energetic particle interactions taking place in a presolar or early solar environment. The inferred abundances of these short-lived nuclides have been used to delineate time scales of processes taking place during the formation and early evolution of the solar system. In particular, inferences have been made about the time interval between the last addition of stellar nucleosynthesis products to the protosolar cloud and the formation of solar system objects, the time scale for the collapse of the protosolar cloud, the time interval between formation of various early solar system objects such as the Ca-Al-rich inclusions, chondrules and differentiated meteorites and also about the energetic particle environment in the early solar system. These inferences have strongly molded our current understanding of the origin and early evolution of the solar system. However, some of these inferences depend critically on our knowledge regarding the origin of short-lived radionuclides in the early solar system. It appears that different sets of nuclides may have different origins and some of them may have contributions from more than one source. In this chapter, we summarize the present status in this field and some of the robust conclu-486 Goswami et al.