Today’s CometWatch entry presents an image taken on 25 June from a distance of 168 km from the comet centre. The image scale is 14.3 m/pixel and the image measures 14.6 km across. The image has been processed to highlight the details of the comet’s activity.
NAVCAM image of Comet 67P/C-G taken on 25 June 2015, 168 km from the comet centre. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0
In this orientation the unmistakable outline of the Hatmehit depression on the comet’s small lobe can be seen towards the ‘top’ of the scene. In the foreground, the ‘Nut’ depression is visible while Serqet is cast in dappled shadow.
Much of the large lobe is obscured by shadow, but a glimpse of Seth can just be seen on the bottom left with Babi in the distance.
On the right hand side a sharp transition between Seth and Anubis is seen, with a small patch of Atum just catching the sunlight at bottom right. The section in the background comprises areas previously in shadow and as such the boundaries are less well defined.
The original 1024 x 1024 pixel image is provided below.
Discussion: 2 comments
Once again we see in a routine image the region of origin of an evolved jet on the nucleus surface.
In this case a large bright patch, several hundred metres in diameter, in the top half of the smaller lobe. It is clearly evident in the non exposure modified image. In the enhanced image it appears to be the origin of the wide jet issuing vertically upwards at the 12 o’ clock position. Once again extremely high intensity of brightness at the origin. Such an area would appear to be an excellent candidate for a more detailed investigation of jets and their origin. Have any such specific measurements been made, Emily, preferably at a closer distance and with higher resolution than is possible from 168 km.
The original image is already stretched in a way such that the brightest pixel is mapped to white, and the darkest pixel is mapped to black.
So the bright region on the smaller lobe is extremal or near extremal only in the context of this particular image.
In terms of absolute albedo compare the grey values of other parts of the comet with the grey value of the brightest pixels. The values don’t vary very much on this scale, since otherwise the standard image processing pipe would map most of the surface to near black.
The small ice-rich bright surface patches possibly related to the base of the jets appear to be smaller than a pixel on this scale, if present.
See also the recent blog post about the origin of the jets:
https://blogs.esa.int/rosetta/2015/07/01/comet-sinkholes-generate-jets/