Irradiation- and Diffusion-Driven Hydrogen Isotope Fractionation in the Accretion Disk – FrIHIDDA

About 4.55 billions years ago, the Solar System formed from the protosolar nebula, a disk made of gas and dust, mainly composed of hydrogen and helium. A large fraction of this hydrogen accreted to form the Protosun and gazeous giant planets such as Jupiter. Another significant fraction of this gas has been oxidized into water and interacted with dust. The finest proxy to identify origins, mechanisms of formation and interactions of such cosmochemical reservoirs is the ratio deuterium/protium (D/H). This proxy also provides invaluable information on the astrophysical conditions under which the Solar System formed. In this framework, the signature of the water from Earth, Mars and major groups of meteorites is puzzeling. It is enriched in deuterium by at least ten times relative to the Sun and giant planets. As the interstellar medium is the only major reservoir highly enriched in deuterium, it has been proposed that Earth’s water could have an extrasolar origin. However, the carrier of interstellar water injected into the inner part of the disk is unknown so far.
Meanwhile, the fact that the protosun and giant planets have a D/H lighter than rocky planetary bodies orbiting between them suggests that some processes strongly fractionnated hydrogen between gas and condensed matter. Such processes have not been identified yet. However, recent theoretical and experimental advances points out unanticipated physico-chemical processes able to fractionate isotopes. The main ones are diffusion-driven and irradiation-driven fractionations. This ANR proposal is dedicated to the experimental characterization of these processes applied to the D/H systematics. We propose to study the behavior of H-bearing solids (silicates and organic matter) subjected to diffusion and irradiation processes. This work will allow us to identify new major fractionation processes that took place in the inner part of the solar system and affected the dust. Our results will then be used to disentangle the contribution of isotopic fractionation produced in situ in the inner disk from the possible contribution of extrasolar sources.