Comet 81P/Wild 2: A record of the Solar System's wild youth

Ogliore, Ryan C.

doi:10.1016/j.chemer.2023.126046

Cited by 1 publication

(1 citation statement)

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“…The 67P/C-G nucleus is made of two lobes (one ∼4 km and the other ∼2.5 km) connected by a short neck, which was likely formed by low-energy, sub-catastrophic collisions of similarly sized bodies (Sierks et al 2015;Jutzi & Benz 2017;Schwartz et al 2018). The Wild 2 nucleus is a 4.5 km diameter lobe covered by depressions made by sublimation/ejection and impact processes, which is unlikely to be a rubble pile nor a collisional fragment of a larger body (Brownlee et al 2004;Ogliore 2023). The two comets appear to be primordial objects that have not been severally modified by internal heating via short-lived nuclei (mainly 26 Al) decay.…”

Section: Introductionmentioning

confidence: 99%

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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