Hybrid dust-tracking method for modeling Io's Tvashtar volcanic plume

Abstract

A novel computational technique was used to simulate eruptions from Io's Tvashtar Catena region to better understand the origin of the visible structure of the gas/particulate plumes observed by the New Horizons spacecraft in its 2007 flyby of the Jovian system. The direct simulation Monte Carlo (DSMC) method was used to produce number density, temperature, and velocity fields for SO2 gas erupting from rectangular vents of aspect ratio 1:1, 3:1, 10:1, and 15:1. Simulations of eruptions of visible particles entrained in the gas were subsequently conducted in a separate MATLAB simulation by injecting particles at the vent and propagating them through the plume by interpolating the gas velocity fields. The temperature and number density fields were used to implement a particle growth model in which the grains grow/shrink via condensation/sublimation. With these simulations, we investigated the plume's lack of a prominent spout, how particulate structures in the vent are transformed as they move through the plume and how this could produce filamentary structure, and the origin of the traveling canopy wave observed in some of the images. Simulations showed that the presence of an observable spout in a given plume image can depend on several factors including vent aspect ratio, observer vantage point, particulate size, and eruption frequency. Several possible explanations for the lack of an observable spout in the Tvashtar images were explored, and the most plausible is that the particles are pulsed from the vent infrequently rather than being emitted in a continuous spray. The transformation of particulate structures in the vent as they travel through the plume depends primarily on vent aspect ratio and the structure's region of origin in the vent. Simulations showed that the continuous emission of particles from concentrated regions in the vent can produce filamentary structures similar to those seen in Tvashtar images, but the appearance of such structures is highly dependent on the observer's vantage point. The traveling canopy wave was replicated in simulations, to varying degrees, with two different mass flux functions: a traveling wave in the vent and the pulsing of particles out of thin cracks parallel to the vent's long axis. With a pulsing frequency of 10–15 min, the latter mass flux function was able to replicate, in a broad sense, much of the plume's interesting structure including the filaments, the traveling canopy wave, and the lack of an observable spout.