Surface evolution processes in the Ash region on comet 67P

Abstract:

Introduction

The study of morphological changes on the nucleus of comet 67P/Churyumov-Gerasimenko allows to better understand and constrain its evolution. Changes have already been identified on several regions of 67P (Groussin et al., (2015); El-Maarry et al., (2017); Pajola et al. (2017)). We have continued the investigations of changes on 67P, and in this work we present new morphological changes that we discovered in the Ash region.

Method

We used the high spatial resolution images of the Narrow Angle Camera (NAC) onboard Rosetta, to perform a morphometrical analysis of the Ash region before and after perihelion, in order to detect and measure surface modifications. After performing a detailed cartography of the Ash region, we made a before/after perihelion comparison in two ways: (1) a morphological approach and (2) a geometrical approach.

Results

For the morphological approach, before perihelion, we observed several terraces with a high boulder density and the presence of landslides and land collapse. After perihelion, we observed that one of the landslides has been modified and we observed new boulders in the same area (Fig. 1). For the geometrical approach, using gravitational height and slopes, we were able to characterize the terraces geometry and to quantify the landslide changes. The terraces geometry reveals an alternation of steep slopes (> 50°) and flat areas (< 10°), with boulders accumulating on the latter. We did not observe any changes in the terraces during the mission. On the contrary, one landslide grew up by 1.95 m in width and 9 m in length. The result of these modifications is the apparition of ten’s of meter boulders at the downstream of the landslide (Fig.1). This mass movement may be driven by the sublimation of volatiles in the subsurface. Overall, our results, together with the presence of former terraces and landslides, suggest that the surface evolution processes observed in the Ash region are likely common and key in eroding and shaping the whole nucleus at each perihelion passage.

References

Groussin, H. Sierks, C. Barbieri, P. Lamy et al., Astron. Astrophys.583, A36 (2015)

M.R. El-Maarry, O. Groussin, N. Thomas, M. Pajola, et al., Science (80-) 355, 1392 (2017)

Pajola, M., Höfner, S., Vincent, J. et al., Nat Astron 1, 0092 (2017).