Posted on 20/10/2014 by emily
CometWatch – 18 October
This four-image NAVCAM montage comprises images taken on 18 October from a distance of 9.8 km from the centre of comet 67P/C-G – about 7.8 km from the surface. The four 1024 x 1024 pixel images making up the montage are provided at the end of this post.
At a distance of 7.8 km from the surface, the image scale is about 66.5 cm/pixel, so each 1024 x 1024 pixel frame is about 680 m across (although if we assume the furthest point away is an additional ~1 km further from the centre, the image scale is about 92 cm/pixel).
The combined effect of the comet rotating between the first and last images taken in the sequence and the spacecraft moving in the same time is particularly apparent if you try to match features in the lower left and lower right images, which are the first and last images in the 20-minute sequence, respectively.
In this orientation, the larger lobe of the comet is to the left, the smaller lobe to the right. The image highlights the features of the comet’s neck, including the active region (you might like to compare with the previous, more distant, view of 26 September). A fracture-like feature seen in the 19 September image is also visible in this montage, about 1/3 down from the top of the lower right frame. In the same frame, we also have a much closer look at a group of boulders, some of which appear to be more like protrusions, perhaps exposed by the removal of surrounding material.
Elsewhere, and particularly in the upper frames, you may notice a number of bright streaks. Some of these will likely be dust grains ejected from the comet, captured in the six-second exposure time of the images.