  The observation of pits at the surface of comets offers the opportunity to
take a glimpse into the properties and the mechanisms that shape a nucleus
through cometary activity. If the origin of these pits is still a matter of
debate, multiple studies have recently suggested that known phase transitions
alone could not have carved these morphological features on the surface of
67P/C-G. We want to understand how the progressive modification of 67P's
surface due to cometary activity might have affected the characteristics of
pits. In particular, we aim to understand whether signatures of the formation
mechanism of these morphological features can still be identified. To quantify
the amount of erosion sustained at the surface of 67P since it arrived on its
currently observed orbit, we selected 380 facets of a medium-resolution shape
model of the nucleus, sampling 30 pits across the surface. We computed the
surface energy balance with a high temporal resolution, including shadowing and
self-heating. We then applied a thermal evolution model to assess the amount of
erosion sustained after ten orbital revolutions under current illumination
conditions. We find that the maximum erosion sustained after ten orbital
revolutions is on the order of 80 m, for facets located in the southern
hemisphere. We thus confirm that progressive erosion cannot form pits and
alcoves, as local erosion is much lower than their observed depth and diameter.
We find that plateaus tend to erode more than bottoms, especially for the
deepest depressions, and that some differential erosion can affect their
morphology. As a general rule, our results suggest that sharp morphological
features tend to be erased by progressive erosion. This study supports the
assumption that deep circular pits, such as Seth1, are the least processed
morphological features at the surface of 67P, or the best preserved since their
formation.
