Chondrules from high-velocity collisions: thermal histories and the agglomeration problem. (arXiv:2009.10093v3 [astro-ph.EP] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Choksi_N/0/1/0/all/0/1">Nick Choksi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chiang_E/0/1/0/all/0/1">Eugene Chiang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Connolly_H/0/1/0/all/0/1">Harold C. Connolly Jr.</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gainsforth_Z/0/1/0/all/0/1">Zack Gainsforth</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Westphal_A/0/1/0/all/0/1">Andrew J. Westphal</a>
We assess whether chondrules, once-molten mm-sized spheres filling the oldest
meteorites, could have formed from super-km/s collisions between planetesimals
in the solar nebula. High-velocity collisions release hot and dense clouds of
silicate vapor which entrain and heat chondrule precursors. We show how
chondrule thermal histories may be reproduced in sufficiently massive vapor
clouds. What remains a mystery is how chondrules so dispersed into the nebula
agglomerated en masse into meteorite parent bodies, either by assembling into
new planetesimals or accreting onto existing ones. The same orbital
eccentricities and inclinations that enable energetic collisions also cause
planetesimals to shatter chondrules upon accreting them. While we cannot
explain why planetesimal interiors are filled with round and intact chondrules,
we do expect that planetesimal surfaces may be littered with their broken
remains. The micron-sized igneous particles recovered from comet 81P/Wild-2 may
thus have originated from in-situ collisions in the proto-Kuiper belt,
obviating the need to transport thermally-processed solids across large nebular
distances. Asteroid sample returns from Hayabusa2 and OSIRIS-REx may similarly
contain micro-chondrule fragments.
We assess whether chondrules, once-molten mm-sized spheres filling the oldest
meteorites, could have formed from super-km/s collisions between planetesimals
in the solar nebula. High-velocity collisions release hot and dense clouds of
silicate vapor which entrain and heat chondrule precursors. We show how
chondrule thermal histories may be reproduced in sufficiently massive vapor
clouds. What remains a mystery is how chondrules so dispersed into the nebula
agglomerated en masse into meteorite parent bodies, either by assembling into
new planetesimals or accreting onto existing ones. The same orbital
eccentricities and inclinations that enable energetic collisions also cause
planetesimals to shatter chondrules upon accreting them. While we cannot
explain why planetesimal interiors are filled with round and intact chondrules,
we do expect that planetesimal surfaces may be littered with their broken
remains. The micron-sized igneous particles recovered from comet 81P/Wild-2 may
thus have originated from in-situ collisions in the proto-Kuiper belt,
obviating the need to transport thermally-processed solids across large nebular
distances. Asteroid sample returns from Hayabusa2 and OSIRIS-REx may similarly
contain micro-chondrule fragments.
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