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Title: A nonmagnetic differentiated early planetary body

Paleomagnetic studies of meteorites have shown that the solar nebula was likely magnetized and that many early planetary bodies generated dynamo magnetic fields in their advecting metallic cores. The surface fields on these bodies were recorded by a diversity of chondrites and achondrites, ranging in intensity from several μT to several hundred μT. In fact, an achondrite parent body without evidence for paleomagnetic fields has yet to be confidently identified, hinting that early solar system field generation and the dynamo process in particular may have been common. Here we present paleomagnetic measurements of the ungrouped achondrite NWA 7325 indicating that it last cooled in a near-zero field (<~1.7μT), estimated to have occurred at 4563.09 ± 0.26 million years ago (Ma) from Al–Mg chronometry. Because NWA 7325 is highly depleted in siderophile elements, its parent body nevertheless underwent large-scale metal-silicate differentiation and likely formed a metallic core. This makes NWA 7325 the first recognized example of an essentially unmagnetized igneous rock from a differentiated early solar system body. These results indicate that all magnetic fields, including those from any core dynamo on the NWA 7325 parent body, the solar nebula, young Sun, and solar wind, were <1.7 μT at the locationmore » of NWA 7325 at 4563 Ma. Finally, this supports a recent conclusion that the solar nebula had dissipated by ~4 million years after solar system formation. NWA 7325 also serves as an experimental control that gives greater confidence in the positive identification of remanent magnetization in other achondrites.« less
ORCiD logo [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [1] ;  [2] ;  [1] ;  [5] ;  [1] ;  [6] ;  [7] ;  [7]
  1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Dept. of Earth, Atmospheric, and Planetary Sciences
  2. Arizona State Univ., Tempe, AZ (United States). School of Earth and Space Exploration
  3. Aix-Marseille Univ., and CNRS/IN2P3, Aix-en-Provence (France)
  4. Univ. of California, Berkeley, CA (United States). Dept. of Earth and Planetary Science; Berkeley Geochronology Center, Berkeley, CA (United States)
  5. Harvard Medical School, Boston, MA (United States). Dept. of Neurobiology
  6. Univ. of Washington, Seattle, WA (United States). Dept. of Earth and Space Sciences
  7. Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source II (NSLS-II)
Publication Date:
Report Number(s):
Journal ID: ISSN 0012-821X
Grant/Contract Number:
SC0012704; NNA14AB01A; ANR-14-CE33-0012; 29835; AC02-98CH10886
Accepted Manuscript
Journal Name:
Earth and Planetary Science Letters
Additional Journal Information:
Journal Volume: 468; Journal Issue: C; Journal ID: ISSN 0012-821X
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Aeronautic and Space Administration (NASA)
Country of Publication:
United States
36 MATERIALS SCIENCE; planetesimals; paleomagnetism; meteorites; dynamo; differentiation
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1396590