A similar question came up on MPML about the grooves on Phobos. I thought this
answer by Alan Harris might be of interest.
--
Richard Kowalski
Full Moon Photography
IMCA #1081
Alan Harris wrote:
The "strings" or "grooves" have been seen since the time of the early
Mariners and Vikings, they're just seen a little (lot) better now. They
are not related to multiple impacts, in spite of some appearance of being
strings of craters. They have been studied extensively over the years, with
their nature not entirely resolved, but appear to be related in some way with
the tidal environment of Phobos. If it were a fluid, it would simply come
apart, since it is inside the classical Roche limit. However, even a "rubble
pile" can persist there, held together only by the "angle of repose" limit of
such material. When struck by an impact though, the vibration of the impact
may allow material to "slump", just as we sometimes see landslides triggered by
earthquakes. This kind of slumping may result in crack or "grooves" running
across the terrain. I co-authored a paper in Nature many years ago putting
this hypothesis forward (Soter, S., Harris, A. 1977, Are striations on PHOBOS
evidence for tidal stress? Nature 268, 421). This is not the last word on the
matter (in fact, it was sort of the
"first word"). There are a number of more recent publications on it.
Alan
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