EVIDENCE FOR MAGNESIUM ISOTOPE HETEROGENEITY IN THE SOLAR PROTOPLANETARY DISK

Journal Article · Sun Jul 10 00:00:00 EDT 2011 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/735/2/L37· OSTI ID:21562555

Larsen, Kirsten K; Trinquier, Anne; Paton, Chad; Schiller, Martin; Wielandt, Daniel; Connelly, James N; Nordlund, Ake; Krot, Alexander N; Bizzarro, Martin ^[1]; Ivanova, Marina A ^[2]

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1. Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Copenhagen DK-1350 (Denmark)
2. Vernadsky Institute of Geochemistry and Analytical Chemistry, Moscow 119991 (Russian Federation)

With a half-life of 0.73 Myr, the {sup 26}Al-to-{sup 26}Mg decay system is the most widely used short-lived chronometer for understanding the formation and earliest evolution of the solar protoplanetary disk. However, the validity of {sup 26}Al-{sup 26}Mg ages of meteorites and their components relies on the critical assumption that the canonical {sup 26}Al/{sup 27}Al ratio of {approx}5 x 10{sup -5} recorded by the oldest dated solids, calcium-aluminium-rich inclusions (CAIs), represents the initial abundance of {sup 26}Al for the solar system as a whole. Here, we report high-precision Mg-isotope measurements of inner solar system solids, asteroids, and planets demonstrating the existence of widespread heterogeneity in the mass-independent {sup 26}Mg composition ({mu}{sup 26}Mg*) of bulk solar system reservoirs with solar or near-solar Al/Mg ratios. This variability may represent heterogeneity in the initial abundance of {sup 26}Al across the solar protoplanetary disk at the time of CAI formation and/or Mg-isotope heterogeneity. By comparing the U-Pb and {sup 26}Al-{sup 26}Mg ages of pristine solar system materials, we infer that the bulk of the {mu}{sup 26}Mg* variability reflects heterogeneity in the initial abundance of {sup 26}Al across the solar protoplanetary disk. We conclude that the canonical value of {approx}5 x 10{sup -5} represents the average initial abundance of {sup 26}Al only in the CAI-forming region, and that large-scale heterogeneity-perhaps up to 80% of the canonical value-may have existed throughout the inner solar system. If correct, our interpretation of the Mg-isotope composition of inner solar system objects precludes the use of the {sup 26}Al-{sup 26}Mg system as an accurate early solar system chronometer.

• OSTI ID: 21562555
• Journal Information: Astrophysical Journal Letters, Vol. 735, Issue 2; Other Information: DOI: 10.1088/2041-8205/735/2/L37; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ALUMINIUM 26
ALUMINIUM 27
ASTEROIDS
ELEMENT ABUNDANCE
MAGNESIUM 26
METEORITES
PROTOPLANETS
SOLAR SYSTEM
ABUNDANCE
ALKALINE EARTH ISOTOPES
ALUMINIUM ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-PLUS DECAY RADIOISOTOPES
EVEN-EVEN NUCLEI
ISOTOPES
LIGHT NUCLEI
MAGNESIUM ISOTOPES
NUCLEI
ODD-EVEN NUCLEI
ODD-ODD NUCLEI
RADIOISOTOPES
SECONDS LIVING RADIOISOTOPES
STABLE ISOTOPES
YEARS LIVING RADIOISOTOPES