Statistical chronometry of Meteorites: II. Initial abundances and homogeneity of short-lived radionuclides

Steven J. Desch, Daniel R. Dunlap, Curtis D. Williams, Prajkta Mane, Emilie T. Dunham

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9 Scopus citations

Abstract

Astrophysical models of planet formation require accurate radiometric dating of meteoritic components by short-lived (Al–Mg, Mn–Cr, Hf–W) and long-lived (Pb–Pb) chronometers, to develop a timeline of such events in the solar nebula as formation of Ca-rich, Al-rich Inclusions (CAIs), chondrules, planetesimals, etc. CAIs formed mostly around a time (“t=0”) when the short-lived radionuclide 26Al (t1/2=0.72 Myr) was present and presumably homogeneously distributed at a known level we define as (26Al/27Al)SS≡5.23×10−5. The time of formation after t=0 of another object can be found by determining its initial (26Al/27Al)0 ratio and comparing it to (26Al/27Al)SS. Dating of meteoritic objects using the Mn–Cr or Hf–W systems is hindered because the abundances (53Mn/55Mn)SS and (182Hf/180Hf)SS at t=0 are not known precisely. To constrain these quantities, we compile literature Al–Mg, Mn–Cr, Hf–W and Pb–Pb data for 14 achondrites and use novel statistical techniques to minimize the discrepancies between their times of formation across these systems. We find that for (53Mn/55Mn)SS=(8.09±0.65)×10−6, (182Hf/180Hf)SS=(10.42±0.25)×10−5, tSS=4568.36±0.20Myr, and a 53Mn half-life of 3.80±0.23 Myr, these four free parameters make concordant 37 out of 38 formation times recorded by the different systems in 14 achondrites. These parameters also make concordant the ages derived for chondrules from CB/CH achondrites, formed simultaneously in an impact, and are apparently concordant with the I–Xe chronometer as well. Our findings provide very strong support for homogeneity of 26Al, 53Mn, and 182Hf in the solar nebula, and our approach offers a framework for more precise chronometry.

Original languageEnglish
Article number115611
JournalIcarus
Volume402
DOIs
StatePublished - Sep 15 2023

Funding

The authors would like to acknowledge the efforts of cosmochemists from multiple laboratories around the world whose work makes possible the data cited in Table 1 and throughout this paper. Statistical chronometry necessarily distills very difficult and painstaking analytical work into mere numbers to be crunched, but the efforts to obtain those numbers are appreciated. We thank Zack Torrano for useful discussions. We thank Francois Tissot and two anonymous reviewers whose suggestions greatly improved the quality of our work. The work herein benefited from collaborations and/or information exchange within NASA's Nexus for Exoplanetary System Science research coordination network sponsored by NASA's Space Mission Directorate (grant NNX15AD53G, PI Steve Desch). Emilie Dunham gratefully acknolwedges support from a 51 Pegasi b Fellowship, grant #2020-1829. The data and scripts used to create Table 1 and Fig. 3 are included as Research Data. The authors would like to acknowledge the efforts of cosmochemists from multiple laboratories around the world whose work makes possible the data cited in Table 1 and throughout this paper. Statistical chronometry necessarily distills very difficult and painstaking analytical work into mere numbers to be crunched, but the efforts to obtain those numbers are appreciated. We thank Zack Torrano for useful discussions. We thank Francois Tissot and two anonymous reviewers whose suggestions greatly improved the quality of our work. The work herein benefited from collaborations and/or information exchange within NASA’s Nexus for Exoplanetary System Science research coordination network sponsored by NASA’s Space Mission Directorate (grant NNX15AD53G , PI Steve Desch). Emilie Dunham gratefully acknolwedges support from a 51 Pegasi b Fellowship , grant #2020-1829 . The data and scripts used to create Table 1 and Fig. 3 are included as Research Data.

FundersFunder number
Francois Tissot
National Aeronautics and Space Administration
Science Mission Directorate2020-1829, NNX15AD53G

    Keywords

    • Achondrites
    • Chondrites
    • Meteorites
    • Planet formation
    • Solar system formation

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