Off-disk penetration of ancient solar wind

Abstract

Solar wind implantation has been considered to be the noble gas source for gas-rich meteorites, lunar soils, and possibly for Venus' atmosphere. Here according to the idea of Wetherill (1981) ( Icarus 46, 70–80), capture of an ancient intense solar wind by primordial dust is estimated. After dissipation of the solar nebula, mutual collision of planetesimals should produce new dust grains in inter-planetary space. In this report, vertical distribution of the dust is newly taken into account. Even if the dust swarm is optically thick along its equatorial plane, the solar wind can penetrate through the less opaque off-disk region. As a result, an appreciable amount of solar wind species is trapped and the high abundances of solar-type noble gases in gas-rich meteorites and Venus (∼ 10 −9 [kg/kg] of 36Ar) can be explained. Among various parameters examined, results are most sensitive to the ratio of relative dust abundance to dust size and the power-law index of relative disk thickness. The off-disk trap is efficient when the disk is opaque and disk's relative thickness does not decrease with increasing heliocentric distance. Effects of dust size distribution on the results are also discussed.