On migration of dust and ice grains on the surface of the rotating comet nucleus

Abstract

In the paper the migration of dust and ice grains over the surface of the comet nucleus is considered and analysed. This phenomenon is a consequence of interplay between the components of three forces tangential to the surface of comet nucleus and acting on the comet's grain. These forces are the gravity of the comet's nucleus, the frictional force coming from the comet's nucleus surface, and the centrifugal force resulting from the rotation of the comet nucleus. As a result, the grains move from the intermediate geographic latitudes towards the `equator of the comet', while the grains located closer to the poles of the comet's nucleus and in the comet's equatorial belt remain immovable. We have shown that the grains traveling to the equator of the comet can be thrown out into space. The analysis was performed for three different assumed shapes of comet nuclei, a sphere, a flattened rotational ellipsoid, and an elongated rotational ellipsoid. It was shown that due to dust migration over the surface of comet nucleus, regardless of its assumed shape, three types of areas can be distinguished: polar caps, midlatitude belts, and equatorial belts, whose sizes may vary significantly. The sizes however depend on the shape of the comet nucleus and on the friction of cometary particles. The time-scale of cometary particles migration was also estimated. The authors suggest that the migration of dust and small fragments of cometary matter studied here may speak in favour of clarification recently discovered redistribution of these particles on the surface of 67P/Churyumov-Gerasimenko comet and the redistribution of cometary particles across the nucleus. We also suggest that the analysed phenomenon may have a significant impact on comet activity.