PLANETESIMAL COLLISIONS AS A CHONDRULE FORMING EVENT

1Shigeru Wakita, 1,2Yuji Matsumoto, 1Shoichi Oshino, 3Yasuhiro Hasegawa
The Astrophysical Journal 834, 125 Link to Article [http://dx.doi.org/10.3847/1538-4357/834/2/125]
1Center for Computational Astrophysics, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan
2Planetary Exploration Research Center, Narashino, Chiba 275-0016, Japan
3Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA

Chondritic meteorites contain unique spherical materials named chondrules: sub-mm sized silicate grains once melted in a high temperature condition in the solar nebula. We numerically explore one of the chondrule forming processes—planetesimal collisions. Previous studies have found that impact jetting via protoplanet–planetesimal collisions can make chondrules with 1% of the impactors’ mass, when the impact velocity exceeds 2.5 km s−1. Based on the mineralogical data of chondrules, undifferentiated planetesimals would be more suitable for chondrule-forming collisions than potentially differentiated protoplanets. We examine planetesimal–planetesimal collisions using a shock physics code and find two things: one is that planetesimal–planetesimal collisions produce nearly the same amount of chondrules as protoplanet–planetesimal collisions (~1%). The other is that the amount of produced chondrules becomes larger as the impact velocity increases when two planetesimals collide with each other. We also find that progenitors of chondrules can originate from deeper regions of large targets (planetesimals or protoplanets) than small impactors (planetesimals). The composition of targets is therefore important, to fully account for the mineralogical data of currently sampled chondrules.

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