Atmospheric entry heating and helium retentivity of interplanetary dust particles

Abstract

We have modeled atmospheric entry heating of interplanetary dust to characterize the population of particles carrying extraterrestrial He to the seafloor. We find that ∼0.5% of the mass and ∼4% of the surface area of the infalling dust transits the atmosphere at temperatures lower than that required for He release (∼600°C). Size-dependent heating causes the particles which retain He to be far smaller than those in the parental interplanetary dust population. The particle-size distribution of He-bearing dust is such that most of the mass is delivered by particles of ∼20 μm diameter, while most of the surface area (relevant for surface-correlated constituents, e.g., implanted solar wind He) is carried by particles of ∼7 μm diameter. Knowledge of these size distributions allows us to evaluate the possibility of sedimentary redistribution of extraterrestrial dust in the atmosphere and ocean. The size distributions also have important consequences for interpretation of He abundances in seafloor sediment samples that integrate over fairly small areas and times. Sediment samples generally will not record a representative distribution of interplanetary dust but will have a strong tendency to undersample rare large particles. We predict a high degree of variability in replicate He analyses of a single sediment sample, with a mass-correlated He component yielding greater variability than a surface-correlated component. Comparison with sediment measurements confirms such variability and demonstrates excellent agreement with the statistical distribution expected for a surface correlated component, consistent with suggestions that seafloor extraterrestrial He is surface-correlated implanted solar wind or solar flare He. A second important statistical effect is that sediment measurements systematically underestimate the true extraterrestrial He flux, typically by 50%.