Chondrule formation: Nebular gas confinement of impact splashes

陨石球粒的形成是陨石学中最古老的未解之谜之一。其中一种理论认为，它们是由于星子之间的碰撞而形成的，碰撞融化形成小液滴，这些小液滴固化成球粒。来自陨石的一些限制表明，这些物质在这些球粒形成后不久就重新聚集了。然而，如果碰撞发生在非常高的速度，碰撞飞溅的立即引力再吸积是困难的。 另一方面，低速碰撞只能产生碰撞熔化，如果星子已经几乎完全熔化的26铝衰变前的影响。我建议研究星云气体对撞击飞溅减速的影响，这会导致撞击飞溅保持受限并形成密集的“子弹”。这些“子弹”的密度可能保持在洛希密度之上，因此它们将被引力束缚并形成新的微行星。因此，即使在高速撞击下也可能发生再吸积。我们进行了两项试点研究。本提案旨在对这一设想方案进行全面研究和测试。

The formation of chondrules is one of the oldest unsolved mysteries in meteoritics. One of the theories states that they are formed as a result of collisions between planetesimals in which the impact melt forms small droplets which solidify to become chondrules. Some constraints from meteoritics suggest that the material reaccreted rather soon after these chondrules were formed. However, immediate gravitational re-accretion of impact splashes is hard if the collision happened at very high velocity. On the other hand, low velocity collisions can only produce impact melt if the planetesimals were already nearly fully molten by 26Al decay before impact. I propose to study the effect of the decelleration of the impact splash by the nebular gas, which can cause the impact splash to remain confined and form dense "bullets". The densities of these "bullets" likely remain above the Roche density, so that they will be gravitationally bound and form new planetesimals. Reaccretion can thus occur even for high-speed impacts. We have performed two pilot studies. This proposal is to perform the full study and test of this scenario.