Japan Geoscience Union Meeting 2016

Presentation information

International Session (Poster)

Symbol P (Space and Planetary Sciences) » P-CG Complex & General

[P-CG10] Small Solar System Bodies: General and Mars Satellite Sample Return Mission

Sun. May 22, 2016 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL6)

Convener:*Taishi Nakamoto(Tokyo Institute of Technology), Kiyoshi Kuramoto(Department of Cosmosciences, Graduate School of Sciences, Hokkaido University), Sei-ichiro WATANABE(Division of Earth and Planetary Sciences, Graduate School of Science, Nagoya University), MASATERU ISHIGURO(Department of Physics and Astronomy, Seoul National University), Masahiko Arakawa(Graduate School of Science, Kobe University), Masanao Abe(Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency), Tomoko Arai(Planetary Exploration Research Center, Chiba Institute of Technology), Sho Sasaki(Department of Earth and Space Sciences, School of Science, Osaka University)

5:15 PM - 6:30 PM

[PCG10-P16] 54Cr Isotopic Anomalies in Asteroids Caused by Injection and Diffusion in Solar Nebula

*Taishi Nakamoto1, Akira Takeishi1 (1.Tokyo Institute of Technology)

Keywords:Isotopic Anomaly, Solar Nebula, 54Cr, Meteorite Parent Body Formation, Injection

Temporal change of 54Cr isotopic ratio in meteorites:
Chromium has four stable isotopes: their mass numbers are 50, 52, 53, and 54. The ratio of 54Cr to the major isotope 52Cr in various meteorites including chondrites, differentiated meteorites, and iron meteorites shows variations (anomalies). Sugiura and Fujiya (2014) estimated formation ages of each meteorite parent body and found that ages of meteorite parent bodies and the degree of 54Cr isotopic anomalies in the meteorites are in a good correlation. They thought that this relation is caused by an increase of 54Cr-rich particles contained in meteorites. Based on this interpretation, they carried out numerical simulations, in which small 54Cr-rich dust particles are injected into the solar nebula at a certain time and diffuse in the nebula, and showed that the correlation can be reproduced by the small grain injection model.
Injection Model Revisited:
Although the Sugiura and Fujiya model is interesting and attractive, we think some points should be reconsidered. First, they assumed that small dust particles from a supernova arrive only at a narrow ring area on the disk at a certain distance from the central star. However, the injection to such a narrow ring seems unrealistic. Secondly, they supposed that the solar nebula is static. The solar nebula evolves in the time scale not much different from the time scale of parent body formation. Thus, we examine the concentration of 54Cr-rich dust particles in the solar nebula as a function of time with a uniform injection model. The solar nebula dynamical evolution is also taken into consideration.
We obtained results that the concentration of 54Cr-rich grains in the meteorite parent body formation region increases as the time. The surface density of the solar nebula decreases with radial distance, and we suppose that the material is injected uniformly, then after the injection, the concentration of 54Cr-rich small grains per unit disk area becomes an increasing function of the radial distance. Since the meteorite parent body formation region is rather close to the Sun, e.g., 2 - 4 AU, the concentration in that region is initially low. On the other hand, diffusive motion of small grains in the solar nebula is caused by turbulence, and the mass flux due to the diffusion is in proportion to the gradient of the concentration. So, the distribution of concentration approaches a flat one with time. Thus, the concentration in the meteorite parent body formation region increases with time.
According to our numerical simulations, the quantitative relation between the 54Cr anomalies and the parent body ages obtained by Sugiura and Fujiya (2014) can be reproduced when the turbulent diffusivity parameter a, which is a model parameter representing the strength of turbulence in the disk, is of the order of 10-3 - 10-2.