Simulation of Galileo probe descent through Jovian clouds

One of the instruments on-board the Galileo probe that entered Jupiter’s atmosphere was a Nephelometer. This instrument measures the light scattered from cloud particles, and, by comparing the results to model particles, the particle size, phase, and number density can be determined. Unfortunately, some of the results obtained from the Nephelometer can not be explained by any known particles. One hypothesis for this result is that the Nephelometer instrument, part of which extends outward from the probe body, modifies the flow in such a way to change the particle distribution in the measurement region. To investigate this hypothesis, a three-step simulation has been performed. First, the gas-phase flow around the orbiter is modeled using a Navier-Stokes solver. Second, particles are tracked through the numerically-determined flow using a particle-trajectory simulator. Third, The trajectories of thousands of particles are analyzed to determine the number density in the vicinity of the Nephelometer instrument. ‘The results of this study reveal that the number density in the vicinity of the Nephelometer measurement region is affected by the portion of the Nephelometer that extends into the flow. These results are currently being used to correct the data sent back from the Nephelometer probe. Simulations such as that performed here might be used in the future to aid in the design of similar planetary-probe instruments.