Posted on 15/05/2015 by emily
CometWatch closeup: Hathor, from Seth
Today’s CometWatch post delves back in time to October last year, when Rosetta was orbiting the comet at a distance of just 10 km.
This single frame NAVCAM image was captured on 23 October, when the distance to the centre of the comet was 9.76 km. The average image scale is therefore about 83 cm/pixel and the image measures 850 m across (note that because of the viewing geometry, foreground regions are up to 2 km closer to the viewer, and therefore have an approximate scale of 67 cm/pixel). For reference, an image in a similar orientation was captured on 26 November.
The scene highlights the hauntingly beautiful backlit cliffs of Hathor, the summit just catching the sunlight at top left. The image has been lightly processed to better bring out the details of this region, and also reveals the diffuse glow of the comet’s activity. Indeed, subtly brighter patches can be traced against the darker background, in particular at the right of the frame at the transition from the foreground terrain to Hathor in the background.
If you were standing at the base of Hathor in the Hapi region – out of view in this image – these near-vertical cliffs would tower some 900m above you. As can be seen here, Hathor is characterised by sets of linear features that extend for much of the height of the cliff. In places, lineaments and terraces also cut across roughly perpendicular to them. As described by Thomas et al in an OSIRIS science paper earlier this year, Hathor may be an eroded surface and as such is showing us the internal structure of the comet’s head.
In the foreground, contrasting terrains within the Seth region on the comet’s large lobe are observed. While the left-hand portion exhibits a smooth surface, the right-hand portion shows outcrops of more rugged terrain and numerous boulders. The exposed surfaces also display linear structures in various orientations.
The portion of Seth seen here is at an intersection of several regions: at the far right of the frame lies the boundary between Seth and Anubis, while just out of view beyond the bottom of the frame are Ash and Atum.
Today's image is one of many that will be included in the NAVCAM data release scheduled for the end of this month. This will see the release of the entire collection of images taken from the 10 km orbit last year, along with images taken around the events of comet landing. You can browse all NAVCAM images released so far in the Archive Image Browser.
The original 1024 x 1024 pixel image is provided below: