Migration of D-type asteroids from the outer Solar System inferred from carbonate in meteorites

Abstract

Recent dynamical models of Solar System evolution and isotope studies of rock-forming elements in meteorites have suggested that volatile-rich asteroids formed in the outer Solar System beyond Jupiter's orbit, despite being currently located in the main asteroid belt 1-4 . The ambient temperature under which asteroids formed is a crucial diagnostic to pinpoint the original location of asteroids and is potentially determined by the abundance of volatiles they contain. In particular, abundances and 13 C/ 12 C ratios of carbonates in meteorites record the abundances of carbonbearing volatile species in their parent asteroids. However, the sources of carbon for these carbonates remain poorly understood 5-8 . Here we show that the Tagish Lake meteorite contains abundant carbonates with consistently high 13 C/ 12 C ratios. The high abundance of 13 C-rich carbonates in Tagish Lake excludes organic matter as their main carbon source 5,9 . Therefore, the Tagish Lake parent body, presumably a D-type asteroid 10 , must have accreted a large amount of 13 C-rich CO2 ice. The estimated 13 C/ 12 C and CO2/H2O ratios of ice in Tagish Lake are similar to those of cometary ice 11,12 . Thus, we infer that at least some D-type asteroids formed in the cold outer Solar System and were subsequently transported into the inner Solar System owing to an orbital instability of the giant planets 1,3 .We performed in situ C-isotope measurements on individual grains of carbonate minerals, calcite (CaCO3) and dolomite (CaMg(CO3)2), in Tagish Lake, an ungrouped carbonaceous chondrite (CC) with a petrologic type of 2, indicating that it underwent aqueous alteration 13,14 (Methods). For comparison, we also conducted C-and O-isotope measurements on calcite grains in two Mighei-type carbonaceous chondrites (CM chondrites) with a petrologic type of 2, Nogoya and LaPaz Icefield (LAP) 031166. Due to the small grain size of Tagish Lake carbonates, we were not able to measure O isotopic ratios ( Supplementary Fig. 1). The  13 C and  18 O values ( 13 C/ 12 C and 17,18 O/ 16 O ratios are also expressed as  13 CVPDB and  17,18 OVSMOW, respectively, which represent permil, 10 -3 expressed as ‰, deviations from the isotopic ratios of standard materials: VPDB, Vienna Pee Dee Belemnite; VSMOW, Vienna Standard Mean Ocean Water) of CM carbonates are highly variable, ranging from approximately 20 to 80‰ and from approximately 15 to 40‰, respectively, and do not correlate with each other (Fig. 1a and Supplementary Table 1).The O-isotope data of CM carbonates plot on a single trend line (Fig. 1b), reflecting a change in formation temperatures and/or in the O isotopic ratios of fluids from which they formed. Therefore, the lack of correlation between  13 C and  18 O indicates that the variable  13 C values of CM carbonates must reflect isotopic heterogeneity of carbon sources (Methods). In contrast to CM carbonates, Tagish Lake carbonates have 478, 218-220 (2011). 28. Dauphas, N. The isotopic nature of the Earth's accreting material through time. Nature 541, 5...

Constraints on the Distances and Timescales of Solid Migration in the Early Solar System from Meteorite Magnetism

“…Constrained MHD models of our nebula argue that the magnetic field it supported reached this intensity at a heliocentric distance of ∼9.8 AU, indicating that the WIS 91600 parent body formed in the far reaches of the solar system. As such, our results support previous claims (Bryson et al 2020;Fujiya et al 2019) that the parent asteroids of some meteorites formed in this region of the solar system.…”

“…As such, the paleointensities recovered from bulk meteorites and their components that recorded magnetic remanences within the lifetime of the solar nebula can be used as a proxy for the formation distances of their parent asteroids within the solar system. This approach has been applied to the ungrouped C2 chondrite Tagish Lake, a unique meteorite with mineralogical and chemical signatures (Brown et al 2000;Hiroi et al 2001;Zolensky et al 2002;Grady et al 2002;Fujiya et al 2019) that suggest its parent body formed at a larger heliocentric distance than those of most other meteorites (i.e., 4 AU, Desch et al 2018). Tagish Lake was extensively aqueously altered on its parent asteroid (Zolensky et al 2002).…”

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“…These two extreme cases for the captured model may be tested on the basis of the heliocentric gradients of volatile isotopes and abundances (e.g., CO 2 /H 2 O, D/H, 15 N/ 14 N and noble gases) and the isotopes of rock-forming elements of O, Cr, and Ti in the solar system (Figs. 2, 3, and 4) (Trinquier et al 2007;Trinquier et al 2009;Qin et al 2010;Warren 2011;Marty 2012;Fujiya et al 2019).…”

“…The CO 2 /H 2 O ratios of ice in CM chondrites are calculated from carbonate abundances and hydrogen contents. Modified afterFujiya et al (2019)…”