Valeri Dikarev

Impact-generated dust clouds around planetary satellites: spherically symmetric case

Abstract An analytic model of an impact-generated, steady-state, spherically symmetric dust cloud around an atmosphereless planetary satellite (or planet—Mercury, Pluto) is constructed. The projectiles are assumed to be interplanetary micrometeoroids. The model provides the expected mass, density, and velocity distributions of dust in the vicinities of parent bodies. Applications are made to Jupiters moon Ganymede and six outer satellites of Saturn. In the former case, the model is shown to be consistent with the measurements of the dust detector system onboard the Galileo spacecraft. In the latter case, estimates are given and recommendations are made for the planned experiment with the Cassini cosmic dust analyzer (CDA) during targeted flybys of the spacecraft with the moons. The best CDA pointing to maximize the number of detections is in the ram direction. With this pointing, measurements are possible within a few to about 20 min from the closest approach, with maximum minute impact rates ranging from about 1 for Phoebe and Hyperion to thousands for Enceladus. Detections of the ejecta clouds will still be likely if CDAs angular offset from the ram direction does not exceed 45°. The same model can be applied to dust measurements by other space missions, like New Horizons to Pluto or BepiColombo to Mercury.

The Dust Halo of Saturn's Largest Icy Moon, Rhea

Saturns moon Rhea had been considered massive enough to retain a thin, externally generated atmosphere capable of locally affecting Saturns magnetosphere. The Cassini spacecrafts in situ observations reveal that energetic electrons are depleted in the moons vicinity. The absence of a substantial exosphere implies that Rheas magnetospheric interaction region, rather than being exclusively induced by sputtered gas and its products, likely contains solid material that can absorb magnetospheric particles. Combined observations from several instruments suggest that this material is in the form of grains and boulders up to several decimetres in size and orbits Rhea as an equatorial debris disk. Within this disk may reside denser, discrete rings or arcs of material.

Towards a new model of the interplanetary meteoroid environment FUTURE

Improved models of the interplanetary meteoroid environment enjoy the interest of both spacecraft engineers and dust researchers. The engineers need it for risk assessments for their spacecraft instruments. Modelling dynamical and collisional evolution of interplanetary dust should lead to a match with observations, and an empirical model can be a good mediator between physical models and sparse observational data. Our current effort is directed towards the construction of a new model of the interplanetary meteoroid environment based on a number of observational data sets including in-situ dust flux measurements onboard spacecraft, radar meteor surveys and thermal emission of zodiacal dust. In contrast to earlier models, we use long-term particle dynamics to define populations for the new model. Based on these populations, we have constructed a prototype model which reasonably fits in-situ impact counts by Galileo and Ulysses dust experiments.

4.3.5 Interplanetary dust

Dust is finely dispersed solid material in interplanetary space. It derives from a number of sources: larger meteoroids, comets, asteroids, the planets, their satellites, and rings, and there is interstellar dust sweeping through the Solar System. These dust particles are also often called micrometeoroids, and range in size from assemblages of a few molecules to tenth millimetersized grains, above which size they are called meteoroids. Dust particles strongly interact with their environment. Impacts of dust particles onto other solid objects cause cratering or even fragmentation and generation of secondary ejecta particles. Interplanetary dust particles are charged by the photo effect from solar UV flux and by interaction with the solar wind. Because of their small sizes forces additional to solar and planetary gravity affect their trajectories. Radiation pressure and the interactions with ubiquitous magnetic fields disperse dust particles in space away from their sources. Dust particles absorb and scatter solar radiation and emit thermal radiation giving rise to Zodiacal light at visible wavelengths and thermal emission at infrared wavelengths. Astronomical observations of both emissions provide information on the average properties of a very large number of particles and their spatial distribution. Figure 1 shows a comparison of various methods to characterize dust in interplanetary space.