Title: Multiple generations of grain aggregation in different environments preceded solar system body formation

Abstract

The solar system formed from interstellar dust and gas in a molecular cloud. Astronomical observations show that typical interstellar dust consists of amorphous (a-) silicate and organic carbon. Bona fide physical samples for laboratory studies would yield unprecedented insight about solar system formation, but they were largely destroyed. The most likely repositories of surviving presolar dust are the least altered extraterrestrial materials, interplanetary dust particles (IDPs) with probable cometary origins. Cometary IDPs contain abundant submicron a-silicate grains called GEMS (glass with embedded metal and sulfides), believed to be carbon-free. Some have detectable isotopically anomalous a-silicate components from other stars, proving they are preserved dust inherited from the interstellar medium. However, it is debated whether the majority of GEMS predate the solar system or formed in the solar nebula by condensation of high-temperature (>1,300 K) gas. Here, we map IDP compositions with single nanometer-scale resolution and find that GEMS contain organic carbon. Mapping reveals two generations of grain aggregation, the key process in growth from dust grains to planetesimals, mediated by carbon. GEMS grains, some with a-silicate subgrains mantled by organic carbon, comprise the earliest generation of aggregates. These aggregates (and other grains) are encapsulated in lower-density organic carbon matrix, indicatingmore » a second generation of aggregation. Since this organic carbon thermally decomposes above ~450 K, GEMS cannot have accreted in the hot solar nebula, and formed, instead, in the cold presolar molecular cloud and/or outer protoplanetary disk. We suggest that GEMS are consistent with surviving interstellar dust, condensed in situ, and cycled through multiple molecular clouds.« less

Authors:

Ishii, Hope A.  ^[1];

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Bradley, John P. ^[1]; Bechtel, Hans A. ^[2]; Brownlee, Donald E. ^[3]; Bustillo, Karen C. ^[4]; Ciston, James ^[4]; Cuzzi, Jeffrey N. ^[5]; Floss, Christine ^[6]; Joswiak, David J. ^[3]

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+ Show Author Affiliations

1. Univ. of Hawaii at Manoa, Honolulu, HI (United States). Hawaii Inst. of Geophysics and Planetology
2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
3. Univ. of Washington, Seattle, WA (United States). Dept. of Astronomy
4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Center for Electron Microscopy, Molecular Foundry
5. NASA Ames Research Center (ARC), Moffett Field, Mountain View, CA (United States)
6. Washington Univ., St. Louis, MO (United States). Lab. for Space Sciences

Publication Date:

2018-06-11

Research Org.:

Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division; National Aeronautics and Space Administration (NASA)

OSTI Identifier:

1506319

Grant/Contract Number:  

AC02-05CH11231; NNX14AH86G; NNX16AK41G; NNX14AI39G; NNX14AG25G

Resource Type:

Accepted Manuscript

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Volume: 115; Journal Issue: 26; Journal ID: ISSN 0027-8424

Publisher:

National Academy of Sciences, Washington, DC (United States)

Country of Publication:

United States

Language:

English

Subject:

79 ASTRONOMY AND ASTROPHYSICS; dust accretion; solar system origin; interstellar dust; cosmic dust