Oxygen isotopic heterogeneity in the early Solar System inherited from the protosolar molecular cloud

Alexander N Krot; Kazuhide Nagashima; James R Lyons; Jeong-Eun Lee; Martin Bizzarro

doi:10.1126/sciadv.aay2724

Oxygen isotopic heterogeneity in the early Solar System inherited from the protosolar molecular cloud

Sci Adv. 2020 Oct 16;6(42):eaay2724. doi: 10.1126/sciadv.aay2724. Print 2020 Oct.

Authors

Alexander N Krot^{1

2}, Kazuhide Nagashima³, James R Lyons⁴, Jeong-Eun Lee⁵, Martin Bizzarro²

Affiliations

¹ Hawai'i Institute of Geophysics and Planetology, University of Hawai'i at Mānoa, Honolulu, HI, USA. sasha@higp.hawaii.edu.
² Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, Denmark.
³ Hawai'i Institute of Geophysics and Planetology, University of Hawai'i at Mānoa, Honolulu, HI, USA.
⁴ School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA.
⁵ Department of Astronomy and Space Science, School of Space Research, Kyung Hee University, Korea.

Abstract

The Sun is ¹⁶O-enriched (Δ¹⁷O = -28.4 ± 3.6‰) relative to the terrestrial planets, asteroids, and chondrules (-7‰ < Δ¹⁷O < 3‰). Ca,Al-rich inclusions (CAIs), the oldest Solar System solids, approach the Sun's Δ¹⁷O. Ultraviolet CO self-shielding resulting in formation of ¹⁶O-rich CO and ^17,18O-enriched water is the currently favored mechanism invoked to explain the observed range of Δ¹⁷O. However, the location of CO self-shielding (molecular cloud or protoplanetary disk) remains unknown. Here we show that CAIs with predominantly low (²⁶Al/²⁷Al)₀, <5 × 10^-6, exhibit a large inter-CAI range of Δ¹⁷O, from -40‰ to -5‰. In contrast, CAIs with the canonical (²⁶Al/²⁷Al)₀ of ~5 × 10^-5 from unmetamorphosed carbonaceous chondrites have a limited range of Δ¹⁷O, -24 ± 2‰. Because CAIs with low (²⁶Al/²⁷Al)₀ are thought to have predated the canonical CAIs and formed within first 10,000-20,000 years of the Solar System evolution, these observations suggest oxygen isotopic heterogeneity in the early solar system was inherited from the protosolar molecular cloud.

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