The methods used by Rosetta scientists to determine that Comet 67P/Churyumov–Gerasimenko’s shape arises from two separately forming comets.
Left: high-resolution OSIRIS images were used to visually identify over 100 terraces (green) or strata – parallel layers of material (red dashed lines) – in exposed cliff walls and pits all over the comet surface (top: Hathor and surrounding regions on comet’s small lobe; bottom: Seth region on comet’s large lobe).
Middle: a 3D shape model was used to determine the directions in which the terraces/strata are sloping and to visualise how they extend into the subsurface. The strata ‘planes’ are shown superimposed on the shape model (left panel) and alone (right panel) and show the planes coherently oriented all around the comet, in two separate bounding envelopes (scale bar indicates angular deviation between plane and local gravity vector).
Right: local gravity vectors visualised on the comet shape model perpendicular to the terrace/strata planes further realise the independent nature of the two lobes.
A selection of high-resolution OSIRIS images used to identify patterns in Comet 67P/Churyumov–Gerasimenko’s extensive layering.
Top left: main terraces (green) and exposed layers (red dashed lines) seen in the Seth region on the comet’s large lobe. The terraces become more inclined towards the comet neck region. The close-up shows terraces in two locations (thin white and yellow arrows) together with examples of parallel lineaments (large white arrows) that define a continuous stratification.
Bottom left: outline of exposed layers (red dashed lines) primarily in the Imhotep and Ash region on the comet’s large lobe. The terraces in Ash change their dip direction from that in Seth to very slightly dip towards Imhotep. Some layers are also indicated on the comet’s small lobe in the background. The close-up shows the details of the parallel layers in a section along the Imhotep-Ash boundary.
Top right: main layers (red dashed lines) and cross-cutting fractures (blue dashed lines) in the Hathor cliff face on the comet’s small lobe. No abrupt change in the orientation of the layers is seen between Hathor and Ma’at. The close-up shows stratification in an alcove at the Hathor-Anuket boundary, providing a view of the Anuket inner structure, which appears to extend under Ma’at. Terraces on Anuket (white arrows) are seen in different orientations to neighbouring regions. Taken together, this reinforces the idea that Hathor represents the inner comet structure that has been exposed, with Anuket as the remnant.
Bottom right: layers (white dashed lines) at the boundary of Anubis and Seth on the comet’s large lobe. This continuous scarp suggests the thickness of the Seth region is about 150 m. The three arrow heads point to a terrace margin in Anubis and the single white arrow points to a terrace in the adjacent Atum region.
- This striking view of Comet 67P/Churyumov–Gerasimenko reveals portions of both comet lobes, with dramatic shadows on the 'neck' region between them. It was taken by Rosetta’s navigation camera (NavCam) on 30 June 2016, from a distance of 25.8 km, and measures about 2.3 km across.
Since reaching the comet on 6 August 2014, Rosetta has extensively mapped its surface. The comet nucleus has a curious shape consisting of two lobes that are often referred to as the 'head' and the 'body'.
Depicted in the lower right part of the image is the region Hathor, a very intriguing portion of the comet head, named after the ancient Egyptian deity of love, music and beauty. In this region, the head declines steeply towards the neck and body of the comet.
This view shows a good fraction of the 900-m high cliff that forms Hathor, with marked linear features crossing the region from left to right. Perpendicular to these, additional streaks and even small terraces can be seen.
Beyond the cliff of Hathor, on the right, are hints of the Ma'at region, named after the ancient Egyptian goddess of truth and balance.
In the upper right corner, smoother patches of the large comet lobe, or body, are visible, covered in dust and boulders. The large lobe casts its shadow on the comet's neck, which separates the two lobes and is hidden from view in this image.
- Copyright ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; M. Massironi et al