Implications for the Ice Phase of 67P/Churyumov-Gerasimenko from ROSINA/DFMS
Wednesday, 16 December 2015
Poster Hall (Moscone South)
The arrival of the Rosetta mission at the Jupiter family comet 67P/Churyumov-Gerasimenko (67P) opened a new chapter in cometary research. The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument has been, and continues giving us chemical information of the coma of 67P in unprecedented detail. One of ROSINA’s first findings was a strongly heterogeneous coma observed in the major and various minor volatile species depending on the location of the spacecraft with respect to the comet. In this work, we argue that the time variation of volatile species observed by ROSINA, which correlates with 67P’s rotational phase, has implications for the ice structure of the nucleus. The data indicate that the near-surface layers of the nucleus of 67P are composed of a mixture of crystalline water ice, clathrate hydrates, and pure volatile ices. We argue that the coma profiles of all volatile species observed in the September-October 2014 time period would be difficult to explain by gas release from a porous amorphous ice phase. However, at this point, we cannot conclude on the ice structure in the deep layers of the nucleus. Analysis of data obtained after the equinox and near perihelion will provide further clues about the ice structure, hence the origin of 67P.