Lawrence Livermore National Laboratory



Lars Borg

Overview

The early evolution of the solar system is largely constrained by astrophysical and geophysical models in which future events are predicted by computer simulations. These calculations indicate that the solar system formed from a molecular cloud as a result of gravitational collapse caused by shock waves from a nearby supernova. This event produced our nascent sun surrounded by a short-lived, proto-planetary disk of gas and debris. This period of the solar system's history lasted a few tens of thousands of years and was followed by a period of planetary accretion and differentiation that took only a few tens of millions of years.

Our study identified cosmochemical evidence for this theory of solar system formation and evolution and refined the time scales of these events. Our work was based on the analysis of meteorites and samples collected from the moon by the Apollo space missions—specifically, isotopic analysis of the daughter products of now-extinct parent nuclides with well established (but short) half lives. One now extinct parent isotope investigated here, 126Sn, is only produced in supernovae, and was not found to be present in primitive meteorite samples when they formed within the (approximately) first 500 thousand years of solar system's history. This suggests that the collapse of the molecular cloud was not caused by a supernova. The time of planetary accretion and differentiation was constrained using three additional, now-extinct isotopic systems (53Mn-53Cr, 146Sm-142Nd and 182Hf-182W). These systems were applied to martian and lunar samples to evaluate when these bodies formed cores, mantles, and crusts. These investigations have had significant impact on our understanding of Solar System evolution, by confirming other theoretical models for its formation, and providing absolute age constrains for more refined astrophysical and geophysical modeling.

Impact on Mission

Our research leveraged Lawrence Livermore National Laboratory's core competencies in nuclear, chemical, and isotopic science and technology. Our results support the Laboratory's programmatic research in nuclear forensics, as many of the isotopic systems developed during this project are now used in this area of research. Scientists engaged in this study demonstrated the Laboratory's high quality and expertise by winning both the Clark Medal and the Nier Prize of the Geochemical and Meteoritical Society. Our work also enabled us to generate data used in related, NASA-funded research.

Publications, Presentations, Etc.

Borg, L., et al. 2017. "Age Relationship Between Slowly Cooled Lunar Crustal Troctolite Samples 76535 and Noritic Anorthosite Sample 60025." 48th Lunar and Planetary Science, The Woodlands, TX, March 2017. LLNL-ABS-716429.

——— . 2018. "Isotopic Systematics of Mafic and Felsic Lunar Cumulates." 49th Lunar and Planetary Science Conference, The Woodlands, TX, March, 2018. LLNL-ABS-744357.

——— . 2018. "Long Term Value of Apollo Samples: How Fundamental Understanding of Body takes Decades of Study." 2nd International Mars Sample Return Conference, Berlin, Germany, April 2018. LLNL-PRES-750265.

Eppich, G., et al. 2017. "Constraints on the Nature and Timing of Post-Formation Alteration of Chondrite Meteorites from 87Sr/86Sr and 143Nd/144Nd Systematics." 48th Lunar and Planetary Science, The Woodlands, March, 2017. LLNL-POST-725677.

Kruijer, T. and T. Kleine. 2017. "Isotopic Constraints on the Origin of the Moon." Interdisciplinary Workshop: Accretion and Early Differentiation of the Earth and Terrestrial Planets, Nice, France, June 2017. LLNL-CONF-731224.

Kruijer, T., et al. 2017. "Dating the Formation of Jupiter Using the Distinct Genetics and Formation Times of Meteorites." 80th Annual Meeting of the Meteoritical Society, Santa Fe, NM, July 2017. LLNL-CONF-734762.

——— . 2017. "Dating the Formation of Jupiter Using the Genetic Heritage and Isotopic Ages of Meteorites." Goldschmidt Conference, Paris, France, August 2017. LLNL-ABS-728425.

——— . 2018. "Chromium Isotope Systematics of Martian Meteorites: Implications for the Differentiation History of Mars." 49th Lunar and Planetary Science Conference, The Woodlands, TX, March, 2018. LLNL-CONF-744241.

——— . 2018. "Meteorite Dichotomy Implies that Jupiter Formed Early." Differentiation: Building the Internal Architecture of Planets Workshop, Pasadena, CA, May, 2018. LLNL-POST-752650.

Neumann, W., et al. 2018. "Multi-Stage Core Formation in Planetesimals Revealed by Numerical Modeling and Hf-W Chronometry of Iron Meteorites." 81st Annual Meeting of the Meteoritical Society, Moscow, Russia, July, 2018. LLNL-JRNL-739210.

Sio, C., et al. 2017. "Experimentally Determined Isotope Effect During Mg-Fe Interdiffusion in Olivine." American Geophysical Union Fall Meeting, New Orleans, LA, December 2017. LLNL-ABS-736661.

Sio, C. and L. Borg. 2018. "Sm-Nd Isotopic Systematics of Ferroan Anorthosite (FAN) 62237: Evidence of Co-Magmatism of FANs at 4.36 Ga." 49th Lunar and Planetary Science Conference, The Woodlands, TX, March, 2018. LLNL-ABS-744813.

Sio, C. and J. Moore. 2018. "Unlocking the Potential of Isotopes to Constrain Thermal Histories: Early Steps Toward a Versatile Tool for Diffusion Chronometry Using Chemical-Isotopic Profiles in Zoned Minerals." American Geophysical Union Fall Meeting, Washington, D.C., December 2018. LLNL-ABS-756174.