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

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 C-13/C-12 ratios of carbonates in meteorites record the abundances of carbon-bearing 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 C-13/C-12 ratios. The high abundance of C-13-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 C-13-rich CO2 ice. The estimated C-13/C-12 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).