True (3D) chondrule size distributions: Basic data for the reconstruction of chondrule formation and asteroid accretion

火星和木星之间的小行星带主要由陨石小行星组成，主要由球粒组成，即毫米大小的结晶硅酸盐熔体珠。在怀尔德2号彗星中也发现了这种球粒的成分。这表明它们不仅是内太阳系行星天体的重要组成部分，而且可能对外太阳系天体的形成做出了重大贡献。它们是在原行星盘中第一个固体形成后约200万年，在未知的短暂加热事件中形成的。显然，球粒的形成是一个非常典型的，但仍然是一个谜，大量的物质瞬间转化为熔体droplet.High精度的平均球粒尺寸和球粒尺寸分布的过程中，天体物理学家需要的数据，以开发球粒的形成，球粒尺寸分选，和小行星吸积模型。然而，最近发表的文献调查显示，这些参数存在很大的知识差距。大多数可用的球粒数据是从二维（2D）切割面获得的，不能反映真实的3D球粒尺寸。不幸的是，目前还没有可靠的校正程序能够将2D数据转换为3D数据。因此，在发现球粒陨石200多年后，我们还没有这些重要参数的全面和一致的数据库，这些参数的测量是本研究建议的一个中心方面，计划建立所有主要球粒陨石群（H，L，LL，R，EH，EL，CV，CK，CR，CO，CM）的全面数据库。这些数据应使用多特蒙德技术大学现有的高分辨率X射线计算机断层摄影技术获得，计划与（瑞典）隆德大学的天体物理学家合作，利用新获得的数据改进一个关于在先前存在的微行星表面上通过球粒吸积形成小行星的模型。此外，这些数据将被用来搜索个人球粒大小和其他岩石学，化学和同位素参数，即球粒类型，氧同位素组成和厚度的增生尘埃地幔之间的相关性。

The asteroid belt between Mars and Jupiter is dominated by chondritic asteroids which mainly consist of chondrules, i.e. mm-sized beads of crystallized silicate melt. Components of such chondrules have also been found in comet Wild 2. This indicates that they were not only an important building block of planetary objects in the inner solar system, but also may have considerably contributed to the buildup of outer solar system bodies. They formed around 2±2 million years after the formation of the first solids in the protoplanetary disk in the course of unknown transient heating events. Obviously, chondrule formation was a very characteristic, nonetheless still enigmatic, process which transiently transformed vast amounts of material into melt droplets.High precision data on the mean chondrule size and chondrule size distributions are needed by astrophysicists in order to develop models on chondrule formation, chondrule size sorting, and asteroid accretion. However, a recently published literature survey reveals that large knowledge gaps concerning these parameters exist. Most available chondrule data were obtained from two-dimensional (2D) cut faces and do not reflect the true 3D chondrule sizes. Unfortunately, there is no reliable correction procedure at hand which is able to transform 2D into 3D data. Hence, more than 200 years after the discovery of chondrules we do not have a comprehensive and consistent database at hand for these important parameters.The measurement of these parameters is one central aspect of this research proposal and it is planned to establish a comprehensive data base for all major chondrite groups (H, L, LL, R, EH, EL, CV, CK, CR, CO, CM). These data shall be obtained by using high resolution X-ray computed tomography (µ-CT) techniques, available at the Technical University of Dortmund.In cooperation with astrophysicist from the University of Lund (Sweden) it is planned to use the newly obtained data to refine a model of asteroid formation by chondrule accretion on surfaces of preexisting planetesimals. Furthermore, these data shall be used to search for correlations between the individual chondrule size and other petrologic, chemical, and isotopic parameters, namely chondrule type, oxygen isotopic composition, and thickness of accretionary dust mantles.