240-5 Using Iron Meteorites to Constrain the Chemical and Physical Structures of the Protoplanetary Disk

Session: From Atoms to Asteroids and Habitable Planets: Coordinated Analysis of Planetary Samples and Their Terrestrial Analogues

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Abstract:

Magmatic iron meteorites are from the metallic cores of the earliest formed asteroids in the solar system. Nucleosynthetic isotopic anomalies show that they may have formed in two distinct compositional reservoirs: the carbonaceous-type (CC) in the outer Solar System and the noncarbonaceous-type (NC) in the inner Solar System. The accretion of magmatic iron-meteorite parent bodies occurred within the first million years of Solar System history, predating the formation of chondrite parent bodies. Hence, these iron meteorites can provide the earliest information about the elemental distribution, physical structure, and temporal evolution of the protoplanetary disk.

Eleven magmatic iron-meteorite groups and one grouplet have been identified. Each of these groups/grouplet represents an asteroid. Interelement trends show that the magmatic groups fractionally crystallized from the metallic cores of their respective parent bodies. The bulk compositions and crystallization processes of these asteroidal cores can therefore be reconstructed using fractional crystallization modeling. We compiled compositional data and performed fractional crystallization modeling to reconstruct the bulk concentrations of (up to) 19 elements for all groups/grouplet.

The elemental concentrations were then used to reconstruct the distribution pattern of calcium-aluminum-rich inclusions (CAIs), which are the first solid to form close to the Sun. The inner disk had very low CAI abundances; the outer disk had higher and variable CAI abundances. The distribution pattern indicates that CAIs were transported to the outer solar system and then trapped in the outer Solar System within the first million years. This pattern has important implications for the physical structure of the disk.

Two recent studies (Grewal et al., 2024, 2025) used the elemental concentrations in our studies to reconstruct the water contents and moderately-volatile-element (MVE) abundance in the precursor materials of iron-meteorite parent bodies. The results challenge the traditional notion that the inner disk had relatively low water and MVE contents.

Our future study will focus on ungrouped irons that do not belong to any current established groups. Ungrouped irons, with a much larger quantity, represent a wider sampling of the disk. We will use the elemental compositions of ungrouped irons to extract additional constraints on the chemical and physical structures of the protoplanetary disk.

References: Grewal D. S. et al. (2025) Science Advances 11(6), eadq7848. Grewal D. S. (2024) Nature Astronomy 8(3), 290-297.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8340

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