High Radiation Pressure on Interstellar Dust Computed by Light-scattering Simulation on Fluffy Agglomerates of Magnesium-silicate Grains with Metallic-iron Inclusions

Abstract

Recent space missions have provided information on the physical and chemical properties of interstellar grains such as the ratio β of radiation pressure to gravity acting on the grains in addition to the composition, structure, and size distribution of the grains. Numerical simulation on the trajectories of interstellar grains captured by Stardust and returned to Earth constrained the β ratio for the Stardust samples of interstellar origin. However, recent accurate calculations of radiation pressure cross-sections for model dust grains have given conflicting stories in the β ratio of interstellar grains. The β ratio for model dust grains of so-called "astronomical silicate" in the femto-kilogram range lies below unity, in conflict with β ∼ 1 for the Stardust interstellar grains. Here, I tackle this conundrum by re-evaluating the β ratio of interstellar grains on the assumption that the grains are aggregated particles grown by coagulation and composed of amorphous MgSiO 3 with the inclusion of metallic iron. My model is entirely consistent with the depletion and the correlation of major rock-forming elements in the Local Interstellar Cloud surrounding the Sun and the mineralogical identification of interstellar grains in the Stardust and Cassini missions. I find that my model dust particles fulfill the constraints on the β ratio derived from not only the Stardust mission but also the Ulysses and Cassini missions. My results suggest that iron is not incorporated into silicates but exists as metal, contrary to the majority of interstellar dust models available to date.

Modelling DESTINY+ interplanetary and interstellar dust measurements en route to the active asteroid (3200) Phaethon

“…The Stardust particles also showed that interstellar dust with mass 3 · 10 −15 kg might be porous and has higher β and charge-to-mass ratios . Interstellar dust with mass exceeding 5 · 10 −16 kg might be porous aggregates of submicron-sized silicate grains Kimura, 2017). Silicate grains do not stick to each other in the interstellar medium, but organic matter would assist them in sticking, if their surfaces are covered by organic matter.…”

Dust cleansing of star-forming gas

“…1 of Ferrara et al (1991), indicating that a higher value up to q = 2.5 could be appropriate for minor graphite grains. Similarly, if the grains have a composite fluffy character, as suggested by Kimura (2017) on the basis of captured Local Interstellar Cloud grains, an increase of q by up to a factor of two may be adequate for the more massive particles. The speed of light is c and Newton's constant of gravity is G. The dust grain is retarded by a drag force, described by the last term of the right-hand side of Eq.…”

Dust cleansing of star-forming gas: II. Did late accretion flows change the chemical composition of the solar atmosphere?

“…For the relevant dust and stellar light discussed here a mean q pr ≡ q of about 1.5 may be adopted, see, however, Fig 1 of Ferrara et al (1991), indicating that a higher value up to q = 2.5 could be appropriate for minor graphite grains. Similarly, if the grains have a composite fluffy character, as suggested by Kimura (2017) on the basis of captured Local Interstellar Cloud grains, an increase of q by up to a factor of two may be adequate for the more massive particles. The speed of light is c and Newton's constant of gravity is G. The dust grain is retarded by a drag force, described by the last term of the right-hand side of Equation ( 1).…”