Abstract
We use rapidly cooled achondrites to test the assumption of 26Al homogeneity in the solar nebula, by checking if there is a single value of tSS, the absolute “Pb-Pb” age of the Solar System's t=0, that makes concordant their ages from the Al-Mg and Pb-Pb systems. We find that values tSS=4568.42±0.24 Myr do make these ages concordant, and therefore the hypothesis of homogeneous 26Al is not falsified. This age, defined to be when the solar nebula had (26Al/27Al)=5.23×10−5, is significantly older than the ≈4567.3 Myr inferred from direct measurements of Pb-Pb ages in CAIs. Discrepancies between the Al-Mg and Pb-Pb chronometers in chondrules and CAIs have previously been interpreted as arising from heterogeneities in 26Al, under the presumption that the Al-Mg and Pb-Pb systems in CAIs closed simultaneously. We examine this assumption and show that resetting is to be expected in CAIs. In particular, we quantitatively demonstrate that it is plausible that Pb-Pb ages of CAIs were reset at late times, without resetting the earlier Al-Mg ages, if they were transiently heated in the same manner as chondrules. We critically examine Pb-Pb isochrons, refining data and suggesting best practices for their calculation and reporting. We advocate reporting chronometry as times of formation after t=0 rather than absolute ages, as only the former is useful for astrophysical models of the solar nebula. We advocate averaging of multiple samples, rather than anchoring to individual meteorites, to improve precision.
| Original language | English |
|---|---|
| Article number | 115607 |
| Journal | Icarus |
| Volume | 402 |
| DOIs | |
| State | Published - 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 Zachary Torrano for useful discussions. We thank Francois Tissot and two other anonymous reviewers, whose suggestions greatly improved the quality of our work. The work herein benefitted 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 in Table 1 and the calculations by which we derived our results are included as an Excel spreadsheet 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 Zachary Torrano for useful discussions. We thank Francois Tissot and two other anonymous reviewers, whose suggestions greatly improved the quality of our work. The work herein benefitted 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 in Table 1 and the calculations by which we derived our results are included as an Excel spreadsheet as Research Data.
| Funders | Funder number |
|---|---|
| Francois Tissot | |
| National Aeronautics and Space Administration | |
| Science Mission Directorate | 2020-1829, NNX15AD53G |
Keywords
- Achondrites
- Chondrites
- Meteorites
- Planet formation
- Solar system formation