Investigating the deep mantle neon signature is key to understand Earth's formation and that of its primitive atmosphere. The only potential evidence for the existence of the latter is the fact that the neon isotopic signature of the deep mantle approaches that of the solar wind, indicating the presence of a primitive reservoir. The literature suggests that one possible origin of such a reservoir is from the dissolution of a H2 and He-rich primordial atmosphere into a magma ocean [1]. Our study investigates how much neon can be incorporated into the magma ocean based on the basal pressure of such an atmosphere and the neon solubility in mafic to ultramafic melts (SiO2 as low as 34 wt% and MgO as high as 21 wt%) obtained from high temperature experiments. We also plan to establish the He solubility in ultramafic melts to ascertain the 3He/22Ne of the primitive mantle. From our neon solubility results, the theoretical neon content of the primitive mantle cannot be reached in a slow accretion scenario, since the nebula gas cannot be captured as the mass would be too low. Although fast accretion scenarios have been proposed in the literature [2], Hf-W isotopes yield a core formation age approaching 30 Myr [3], and most models indicate that the nebula dissipates before 10 Myr [4]. Considering the planetary embryo mass necessary to accumulate enough neon (> 0.8 times the mass of the Earth), the hypothesis of partial dissolution of the atmosphere into the magma ocean remains improbable, requiring alternative models for neon origin on Earth.

[1] Yokochi & Marty (2004), EPSL, 225(1–2); [2] Olson & Sharp (2019), Phys. Earth Planet. Inter., 294; [3] Kleine & Walker (2017), Ann. Rev. Earth Planet. Sci., 45. [4] Ercolano & Pascucci (2017), R. Soc. Open Sci., 4(4).