Oxygen isotope study of the Asuka-881020 CH chondrite II: Porphyritic chondrules

Nakashima, Daisuke; Noguchi, Takaaki; Ushikubo, Takayuki; Kimura, Makoto; Kita, Noriko

doi:10.1016/j.gca.2024.04.011

Cited by 3 publications

(2 citation statements)

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“…Instead, we favor that comet nuclei could have formed by gentle gravitational collapse of pebble swarms concentrated by streaming instability at >3.6 Ma after CAIs before gas dispersal. (Connolly & Huss 2010;Kita et al 2010;Krot et al 2010;Schrader et al 2013Schrader et al , 2014Schrader et al , 2015Tenner et al 2015;Siron et al 2021Siron et al , 2022Schrader & Davidson 2022;Nakashima et al 2024). The forbidden triangle of CR chondrules is taken from Brownlee & Joswiak (2017) and Schrader & Davidson (2022).…”

Section: Discussionmentioning

confidence: 99%

“…Wild 2 data sources: Nakamura et al (2008), Nakashima et al (2012), Ogliore et al (2012, 2015), Joswiak et al (2014), Defouilloy et al (2017), Brownlee & Joswiak (2017), and Zhang et al (2024). Chondrules from CR, O, and CH/CB chondrites are plotted for comparison(Connolly & Huss 2010;Kita et al 2010;Krot et al 2010;Schrader et al 2013Schrader et al , 2014Schrader et al , 2015Tenner et al 2015;Siron et al 2021Siron et al , 2022Schrader & Davidson 2022;Nakashima et al 2024). The forbidden triangle of CR chondrules is taken fromBrownlee & Joswiak (2017) andSchrader & Davidson (2022).…”

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confidence: 99%

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Late Pebble Accretion of Comet 81P/Wild 2 Nucleus: Evidence from a Plagioclase-bearing Chondrule Fragment, Pyxie

Zhang,

Zolensky,

Fukuda

et al. 2024

ApJ

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Comet 81P/Wild 2 is a ∼4.5 km-sized primordial object that almost has not been modified by internal heating by 26Al decay. Its nucleus could have been formed by hierarchical agglomeration or gravitational collapse of pebble swarms concentrated by streaming instability. To shed light on the cometesimal formation mechanism from laboratory sample analysis, we reexamined the 26Al–26Mg isotope systematics of the plagioclase-bearing fragment, Pyxie (from Wild 2 track 81), with significantly improved analytical precision. The revised upper limit of the initial (26Al/27Al)0 of Pyxie is ≤1.5 × 10−6, 2 times smaller than those estimated from other Wild 2 fragments. Assuming homogenous distribution of 26Al in the early solar system, the minimum crystallization age of Pyxie is estimated to be >3.6 Ma after calcium–aluminum-rich inclusions. Additional petrologic examination demonstrated that it is a chondrule fragment formed in disk environments enriched in moderately volatile elements comparable to the Si-rich rim of CR chondrules before accreting by comet Wild 2. The late accretion of the Wild 2 nucleus with most silicates likely from a common source are not favored by the hierarchical agglomeration model that considers early and continuous accretion. Instead, the results are more in line with comet formation by gentle gravitational collapse of pebbles when the 26Al abundance is extremely low (26Al/27Al ≤ 1.5 × 10−6) before gas dispersal.

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