Evolution of organic matter with subcritical water during the formation of icy moons.

Recent models and observations suggest that organic matter (OM) is a major compound of the refractory cores of the icy moons of the solar system. This OM would have interacted with large amounts of water only during the accretion and differentiation of these bodies (before/during the formation of the refractory core). Inside larger water-rich exoplanets, these interactions could have happened at conditions above the critical point of water, leading to the efficient dissolution of the OM and to the formation of specific alteration minerals and volatiles (as was shown in our previous experiments). However, during the formation of the smaller icy moons of the solar system, water is not expected to have reached a supercritical state. The evolution of the OM in these conditions remains largely unknown. We propose to use in situ powder and single-crystal XRD, on anvil cell samples of OM and water, to establish a comprehensive picture of the fate of OM during the formation of icy moons.

近期的模型与观测结果表明，有机质（organic matter, OM）是太阳系冰质卫星难熔核的主要组成成分。此类有机质仅会在这些天体的吸积与分异过程中（即难熔核形成之前/形成期间）与大量水发生相互作用。在体积更大的富水系外行星内部，此类相互作用可能发生于水的临界点以上的环境中，进而促使有机质高效溶解，并形成特定的蚀变矿物与挥发分——这一结论已在我们此前的实验中得到验证。然而，在太阳系较小的冰质卫星形成过程中，水并未达到超临界状态。此类环境下有机质的演化过程目前仍未被充分了解。我们提议针对有机质与水的压砧样品开展原位粉末与单晶X射线衍射（XRD）研究，以全面阐明冰质卫星形成过程中有机质的演化归宿。