Research Abstract


Evidence for the late formation of hydrous asteroids from young meteoritic carbonates

2012年1月17日 Nature Communications 3 : 627 doi: 10.1038/ncomms1635


藤谷 渉1, 杉浦 直治1, 堀田 英之1, 市村 康治1 & 佐野 有司2

  1. 東京大学大学院理学系研究科 地球惑星科学専攻
  2. 東京大学 大気海洋研究所
The accretion of small bodies in the Solar System is a fundamental process that was followed by planet formation. Chronological information of meteorites can constrain when asteroids formed. Secondary carbonates show extremely old 53Mn-53Cr radiometric ages, indicating that some hydrous asteroids accreted rapidly. However, previous studies have failed to define accurate Mn/Cr ratios; hence, these old ages could be artefacts. Here we develop a new method for accurate Mn/Cr determination, and report a reliable age of 4,563.4+0.4/−0.5 million years ago for carbonates in carbonaceous chondrites. We find that these carbonates have identical ages, which are younger than those previously estimated. This result suggests the late onset of aqueous activities in the Solar System. The young carbonate age cannot be explained if the parent asteroid accreted within 3 million years after the birth of the Solar System. Thus, we conclude that hydrous asteroids accreted later than differentiated and metamorphosed asteroids.