represents the northward facing part of the neck of 67P) is clearly seen here in this
orientation.
With the help of the regional classification, we can look at the different surface
morphologies, the relationships between them, and the individual processes that
might have produced them.
2.10.2 Textural Differences
The 9P/Tempel 1 observations already suggested that we should have expected
textural differences on the surface of 67P and often in close proximity. However,
the extent of the textural differences was probably underestimated. It is of course
straightforward to argue that differences in insolation will produce textural and/or
structural differences even on a body that is physically and chemically homogeneous. However, the regional classification of 67P shows that adjacent surfaces, that
should have experienced identical energy input (i.e. almost identical longitude and
latitude with similar orientation), often have markedly different surface textures and
characteristics.
This is evident in the example shown in Fig. 2.52 left. Here, points on the
boundary between Khonsu (to the left) and Atum (centre) are shown with arrows.
Atum is a narrow strip that sits between the very rocky, active, eroded, and rough
Khonsu region to the left and the smooth surface of Anubis to the top right. The
surface of Atum also appears “rocky” but is relatively smooth. It is important to be
careful in the use of terms such as rocky. The low density of the nucleus cannot be
reconciled with rock-like densities of, for example, silicate material. However, the
surface cannot be solid or porous ice alone, even with a high degree of structural
strength, because the albedo is low and significant erosion (sublimation) of this area
was not observed during the Rosetta mission. To avoid this issue, it has usually been
preferred to refer to the surface as appearing “consolidated” which is a more neutral
word with respect to composition.
Although there is change in elevation between the three areas (the surface of the
section of Khonsu shown in Fig. 2.52 left is topographically lower), the surfaces
have roughly the same orientation and are close to the same latitude. Yet their
surface textures could not be more different. Similarly, in Fig. 2.52 right, we see
the surface of Apis which forms an almost planar “face” in the northern hemisphere
next to the large Ash region. Despite the whole surface being almost identically
illuminated over both the comet’s rotation and its orbital motion, the surface has
distinctly different areas as characterized by the surface texture. A key question is
therefore whether this is a consequence of origin and formation or whether local
effects in the past have strongly influenced surface evolution.
Homogeneity is an attractive concept allowing us to make simplifying assumptions about cometary formation and evolution. However, it remains to be explained
how these many surface textures can all be produced from one initial physical and
chemical composition. Consequently, the development of surface evolution models
118
2 The Nucleus
orientation.
With the help of the regional classification, we can look at the different surface
morphologies, the relationships between them, and the individual processes that
might have produced them.
2.10.2 Textural Differences
The 9P/Tempel 1 observations already suggested that we should have expected
textural differences on the surface of 67P and often in close proximity. However,
the extent of the textural differences was probably underestimated. It is of course
straightforward to argue that differences in insolation will produce textural and/or
structural differences even on a body that is physically and chemically homogeneous. However, the regional classification of 67P shows that adjacent surfaces, that
should have experienced identical energy input (i.e. almost identical longitude and
latitude with similar orientation), often have markedly different surface textures and
characteristics.
This is evident in the example shown in Fig. 2.52 left. Here, points on the
boundary between Khonsu (to the left) and Atum (centre) are shown with arrows.
Atum is a narrow strip that sits between the very rocky, active, eroded, and rough
Khonsu region to the left and the smooth surface of Anubis to the top right. The
surface of Atum also appears “rocky” but is relatively smooth. It is important to be
careful in the use of terms such as rocky. The low density of the nucleus cannot be
reconciled with rock-like densities of, for example, silicate material. However, the
surface cannot be solid or porous ice alone, even with a high degree of structural
strength, because the albedo is low and significant erosion (sublimation) of this area
was not observed during the Rosetta mission. To avoid this issue, it has usually been
preferred to refer to the surface as appearing “consolidated” which is a more neutral
word with respect to composition.
Although there is change in elevation between the three areas (the surface of the
section of Khonsu shown in Fig. 2.52 left is topographically lower), the surfaces
have roughly the same orientation and are close to the same latitude. Yet their
surface textures could not be more different. Similarly, in Fig. 2.52 right, we see
the surface of Apis which forms an almost planar “face” in the northern hemisphere
next to the large Ash region. Despite the whole surface being almost identically
illuminated over both the comet’s rotation and its orbital motion, the surface has
distinctly different areas as characterized by the surface texture. A key question is
therefore whether this is a consequence of origin and formation or whether local
effects in the past have strongly influenced surface evolution.
Homogeneity is an attractive concept allowing us to make simplifying assumptions about cometary formation and evolution. However, it remains to be explained
how these many surface textures can all be produced from one initial physical and
chemical composition. Consequently, the development of surface evolution models
118
2 The Nucleus