Posted on 29/10/2014 by emily
CometWatch – 26 October
This four-image NAVCAM mosaic comprises images taken on 26 October from a distance of 9.8 km from the centre of comet 67P/C-G – about 7.8 km from the surface. The corresponding image scale is about 66 cm/pixel, so each 1024 x 1024 pixel frame is about 676 metres across.
Changes in perspective and shadows due to rotation and translation of the comet and spacecraft with respect to each other seem to be limited across this particular set of four images, which is why we’ve decided to present a mosaic this time. The mosaic covers roughly 1200 x 1350 metres. But as usual, we urge you to be cautious in over-interpreting the mosaic: the individual images, presented at the end of this post, provide the ‘ground truth’.
This scene focuses on the same part of the comet as seen in the 18 October image set, but you will notice some interesting new features, as well as some previously visited areas in a new light. (See CometWatch 8 October and the OSIRIS image of 6 August for additional context.)
Visible towards the upper left is a region of brighter material that was previously cast in shadow in the 18 October image, and that appears to lie at the base of a cliff. Some additional bright material is seen at the top of the cliff. This material may be freshly revealed and yet to be covered in dust, perhaps as the result of a recent ‘landslide’. It remains to be seen what its composition is, but no doubt the science teams will be looking out for its signature in the remote sensing data.
Remember though, that this material isn’t in fact bright white on the comet; comets are blacker than coal, and the NAVCAM images are grey-scaled according to their brightness with additional contrast adjustments to bring out the full range of features (see NAVCAM’s shades of grey for a full recap of the way in which intensities are displayed in NAVCAM images).
Also not seen previously in this much detail are the two boulders just below the centre of the mosaic, one of which takes on a heart-shaped appearance from this angle. Zooming in reveals hints of a layered structure and both objects seems to be appearing from beneath the dusty layer, just like some of the smaller ‘boulders’ around them.
Finally, over on the right hand side of the mosaic, the region cast in dramatic shadow on 18 October can now be seen in much more detail. And don’t forget the boulder Cheops and friends above the centre of the mosaic too!