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A cometary building block in a primitive asteroidal meteorite

Matters Arising to this article was published on 05 July 2019


Meteorites originating from primitive C-type asteroids are composed of materials from the Sun’s protoplanetary disk, including up to a few per cent organic carbon. In contrast, some interplanetary dust particles and micrometeorites have much higher carbon contents, up to >90%, and are thought to originate from icy outer Solar System bodies and comets. Here we report an approximately 100-µm-diameter very carbon-rich clast, with highly primitive characteristics, in the matrix of a CR2 chondrite, LaPaz Icefield 02342. The clast may represent a cometary building block, largely unsampled in meteorite collections, that was captured by a C-type asteroid during the early stages of planet formation. The existence of this cometary microxenolith supports the idea of a radially inward transport of materials from the outer protoplanetary disk into the CR chondrite reservoir during the formation of planetesimals. Moreover, the H-isotopic composition of the clast is suggestive of a temporal evolution of organic isotopic compositions in the comet-forming region of the disk.

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Fig. 1: CRC in section of LAP 02342 meteorite.
Fig. 2: O-rich presolar grains in LAP 02342.
Fig. 3: 16O-poor material in the CRC.
Fig. 4: OM in CRC.
Fig. 5: FIB sections from LAP 02342.
Fig. 6: STEM data for CRC FIB section.
Fig. 7: STEM data for 16O-poor CRC FIB section.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


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J.M.T.-R. and C.E.M.-C. acknowledge funding support from Spanish grants AYA 2011-26522 and AYA 2015-67175-P. C.E.M.-C. and S.T. participated in this study in the frame of a PhD in Physics at the Autonomous University of Barcelona. L.R.N., C.M.O’D.A., R.M.S. and B.T.D. acknowledge funding support from NASA grants NNX10AI63G and NNH16AC42I. This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. We thank H. Yabuta and J. Duprat for helpful comments that improved this paper.

Author information




J.M.T.-R. and C.E.M.-C. identified the C-rich clast and brought it to the attention of the other authors. J.M.T.-R., L.R.N. and R.M.S. designed the study. All authors participated in data acquisition and analysis. L.R.N. and J.M.T.-R. wrote the paper with substantial input from other authors.

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Correspondence to Larry R. Nittler.

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The authors declare no competing interests.

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Journal peer review information: Nature Astronomy thanks Jean Duprat, Hikaru Yabuta and the other anonymous reviewers for their contribution to the peer review of this work.

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Supplementary Figures 1–7, Supplementary Tables 1–7

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Nittler, L.R., Stroud, R.M., Trigo-Rodríguez, J.M. et al. A cometary building block in a primitive asteroidal meteorite. Nat Astron 3, 659–666 (2019).

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