It is tempting to interpret these structures as indicating impact and compression of
porous ice-bearing material that has subsequently sintered or re-frozen to produce
more dense and stronger near-surface layers. The compaction also increases the
thermal conductivity. Hence, the sublimed mass from a compacted crater is lower
than for the surroundings and production of pedestal structures can arise. However,
the evidence supporting this concept is solely morphological.
The third crater in Fig. 2.56 (centre) is a small circular feature in Ma’at just 35 m
in diameter and appears to be covered by dust deposits. The observed depth/diameter
ratio has been used to place an upper limit on the depth of the dust deposit blanketing
the crater and will be discussed later. Some transient craters resulting from airfall
were also seen at 67P (Fig. 2.82).
Fig. 2.55 Density and temperature changes seen in smooth particle hydrodynamics (SPH) simulations of impacts into two targets of different density. The temperature rise in the base of the crater
is only locally greater than 10 K (Courtesy of Martin Jutzi)
Fig. 2.56 Three examples of possible impact structures on 67P. Left: Large structure in the Ash
region. Arrow A points to what appears to be a degraded rim with vertical fractures. Arrow B points
at talus possible resulting from collapse of the internal rim (Image number:
W20160903T005801763ID10F12) Centre: Small but circular structure in Ma’at probably covered
with dust deposits. (Image number: N20160902T232834745ID10F22). Right: An irregular circular
feature in Imhotep resembling a pedestal crater. Arrow C points at the rim. Layers are also evident
(D and E) (Image number: N20151212T205138158ID10F22)
124
2 The Nucleus
porous ice-bearing material that has subsequently sintered or re-frozen to produce
more dense and stronger near-surface layers. The compaction also increases the
thermal conductivity. Hence, the sublimed mass from a compacted crater is lower
than for the surroundings and production of pedestal structures can arise. However,
the evidence supporting this concept is solely morphological.
The third crater in Fig. 2.56 (centre) is a small circular feature in Ma’at just 35 m
in diameter and appears to be covered by dust deposits. The observed depth/diameter
ratio has been used to place an upper limit on the depth of the dust deposit blanketing
the crater and will be discussed later. Some transient craters resulting from airfall
were also seen at 67P (Fig. 2.82).
Fig. 2.55 Density and temperature changes seen in smooth particle hydrodynamics (SPH) simulations of impacts into two targets of different density. The temperature rise in the base of the crater
is only locally greater than 10 K (Courtesy of Martin Jutzi)
Fig. 2.56 Three examples of possible impact structures on 67P. Left: Large structure in the Ash
region. Arrow A points to what appears to be a degraded rim with vertical fractures. Arrow B points
at talus possible resulting from collapse of the internal rim (Image number:
W20160903T005801763ID10F12) Centre: Small but circular structure in Ma’at probably covered
with dust deposits. (Image number: N20160902T232834745ID10F22). Right: An irregular circular
feature in Imhotep resembling a pedestal crater. Arrow C points at the rim. Layers are also evident
(D and E) (Image number: N20151212T205138158ID10F22)
124
2 The Nucleus