Forming Chondrules in Impact Splashes. I. Radiative Cooling Model
Cornelis Petrus Dullemond, Sebastian Markus Stammler, and Anders Johansen
The Astrophysical Journal Volume 794 Number 1
Published 25 September 2014
The formation of chondrules is one of the oldest unsolved mysteries in meteoritics and planet formation. Recently an old idea has been revived: the idea that chondrules form as a result of collisions between planetesimals in which the ejected molten material forms small droplets that solidify to become chondrules. Pre-melting of the planetesimals by radioactive decay of 26Al would help produce sprays of melt even at relatively low impact velocity. In this paper we study the radiative cooling of a ballistically expanding spherical cloud of chondrule droplets ejected from the impact site. We present results from numerical radiative transfer models as well as analytic approximate solutions. We find that the temperature after the start of the expansion of the cloud remains constant for a time t cool and then drops with time t approximately as T sime T 0[(3/5)t/t cool + 2/5]–5/3 for t > t cool. The time at which this temperature drop starts t cool depends via an analytical formula on the mass of the cloud, the expansion velocity, and the size of the chondrule. During the early isothermal expansion phase the density is still so high that we expect the vapor of volatile elements to saturate so that no large volatile losses are expected.