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 […]

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