The Solar System calcium isotopic composition inferred from Ryugu samples

CO CV CM CI Ryugu A Ryugu C 0.0 0.5 1.0 1.5 44/40CaSRM915a (age corrected) The Hayabusa2 spacecraft has returned samples from the Cb-type asteroid (162173) Ryugu to Earth. Previous petrological and chemical analyses support a close link between Ryugu and CI chondrites that are presumed to be chemically the most primitive meteorites with a solar-like composition. However, Ryugu samples are highly enriched in Ca compared to typical CI chondrites. To identify the cause of this discrepancy, here we report stable Ca isotopic data (expressed as delta 44/40CaSRM915a) for returned Ryugu samples collected from two sites. We found that samples from both sites have similar delta 44/40CaSRM915a (0.58 +/- 0.03 parts per thousand and 0.55 +/- 0.08 parts per thousand, 2 s.d.) that fall within the range defined by CIs. This isotopic similarity suggests that the Ca budget of CIs and Ryugu samples is dominated by carbonates, and the variably higher Ca contents in Ryugu samples are due to the abundant carbonates. Precipitation of carbonates on Ryugu likely coincided with a major episode of aqueous activity dated to have occurred similar to 5 Myr after Solar System formation. Based on the pristine Ryugu samples, the average delta 44/40CaSRM915a of the Solar System is defined to be 0.57 +/- 0.04 parts per thousand (2 s.d.).

CO、CV、CM、CI、龙宫A、龙宫C 0.0、0.5、1.0、1.5 44/40CaSRM915a（年龄校正） 隼鸟2号宇宙飞船已将Cb型小行星（162173）龙宫的样本带回地球。先前的岩石学和化学分析支持龙宫与CI球粒陨石之间存在密切联系，CI球粒陨石被认为是化学成分上最原始的陨石，具有类似太阳的成分。然而，与典型的CI球粒陨石相比，龙宫样本中的钙含量极高。为了确定这种差异的原因，在此我们报告了从两个地点采集的龙宫返回样本的稳定钙同位素数据（以δ44/40CaSRM915a表示）。我们发现来自两个地点的样本具有相似的δ44/40CaSRM915a（分别为0.58±0.03‰和0.55±0.08‰，2倍标准差），该值处于CI所定义的范围内。这种同位素相似性表明，CI和龙宫样本的钙收支主要由碳酸盐控制，龙宫样本中钙含量较高是由于碳酸盐丰富。龙宫上碳酸盐的沉淀可能与一次重大的水活动事件同时发生，该事件发生在太阳系形成后约500万年。基于原始的龙宫样本，太阳系的平均δ44/40CaSRM915a被确定为0.57±0.04‰（2倍标准差）