Tuesday, October 27, 2015

Cracks perpendicular to and crossing the rotation plane of 67P

Although cracks are ubiquitous on 67P's  varied terrain, the largest and most interesting are on the neck. This post summarises the properties of these cracks and how they relate to stretch of the neck.

Cracks on 67P C-G's "neck region" being in this case mainly Anuket, but also Hapi and other areas, have been documented by the Rosetta mission teams (citation required). Many explanations have been postulated relating to these cracks. Within the Contact Binary paradigm, a possibility has been of general wobbling of the head or from an impact related to Contact Binary.

These features have been observed by A.Cooper and M.Parigi and noted as further circumstantial evidence for a stretch event in the recent geological past. It also connects with other circumstantial evidence which may indicate ongoing stretch that should be measurable by Rosetta.

These are the main features evident in images of the (neck) cracks.

1) Up to several metres in width.
2) Up to 500 metres in length [citation required]
3) Notionally perpendicular to the rotation plane.
4) Most visible in Anuket and most straddling the rotation plane at Anuket.
5) Also have been observed in Hapi.
6) Ephemeral - large cracks visible in one image are non evident in other images of the same area.
7) Ridges perpendicular to the rotation plane are also evident in the same general region of Anuket
8) Large directional outbursts have been witnessed by Rosetta in the same general region of Anuket.

Anuket is the region which has the rotation plane going through it at the point on the neck furthest from the rotational axis. Through Equinox, Anuket has far more insolation time than does Bastet, at the other side of the neck, and therefore more high resolution images are available of Anuket than Bastet. Thus it may be premature to come to too many conclusions, as there are some very obvious cracks, but too few images of the same crack to work out their evolution. It is unclear at this stage whether the cracks are related to other linear features such as ridges that are also perpendicular to the rotation plane. With all paradigms, whether Contact Binary, Erosion, Stretch or even others , a considerable evolution of the surface of the neck regions is expected. How the evolution takes place with regards to before and after images of the regions, will favour one paradigm over another.

The following post argues that the nature of the cracks is another signature for stretch having occured:
Neck crack blog post

This post argues how the surface morphology of the neck and the nature of the torque and outgassing may be leading to measureable ongoing stretch:
 Case for continuing stretch