Observing and Modeling Water Activity and Surface Changes over Dust Cover on Comet 67P/Chruryumov-Gerasimenko

Comet 67P/Churyumov-Gerasimenko (67P), the target of Rosetta mission, is a Jupiter-family member with a four-kilometersized, highly irregular-shaped nucleus. The obliquity of the nucleus with respect to its elliptical orbit gives rise to strong asymmetry of seasons on the comet. The northern hemi-nucleus is covered by a layer of dust deposits that appear overall desiccated over the surface. However, 67P exhibited prevalent activity of water outgassing and dust emission before the perihelion passage in 2015 while the north was illuminated. The dust cover had undergone significant erosion over the surface as a natural consequence of intensifying activity. The northern hemi-nucleus was not changeless even when its activity diminished through winter months around perihelion, as an appreciable amount of dust in the coma could not overcome the weak gravity of the nucleus and came to settle over the north, thereby forming a fresh dust cover. The picture of comet evolution is thus not only of constituent loss but also of material redistribution. The work in this dissertation presents and studies these phenomena, which shed light on the physical and compositional properties of the dust cover with implications on its origin and its fundamental role in sustaining the cyclic activity of 67P over orbits.