[X] My Assistant

[Phil Stooke]

The best set of grooves on any object since Phobos. This has to put an end to the 'grooves caused by Mars ejecta' argument. fantastic object and a wonderful data set. And this is just the highest priority data, all the rest still to come.

Phil

[bk_2]

The best set of grooves on any object since Phobos. This has to put an end to the 'grooves caused by Mars ejecta' argument. fantastic object and a wonderful data set. And this is just the highest priority data, all the rest still to come.

Phil

The similarities with Phobos are striking, the photos clearly show two families of roughly parallel grooves, in two different planes. But the grooves seem to have been obliterated over most of the surface by later big impacts.

Once again I have to say they look like the tracks of intersection with rings, edge on. What else could carve a long smooth trench on the surface of a large object in space? Where Lutetia might have encountered rings is not going to be easy to answer, the chaos of the early Solar System is way beyond our scrutiny. The grooves do seem to be very old features, pockmarked with small craters, as well as restricted to areas clear of debris from the big ones.

[tasp]

Ring materials will preferentially strike the highest elevated spot(s) along their ground track, assuming circular orbits. As we consider primary objects that are successively smaller in size, the irregularity of the object, on average, will increase. For altitudes that are sufficient high, even a quite irregular object will manifest a gravitational field as emanating from a point source, as the altitude decreases, however, the irregularity of the object and the resulting gravitational field will cause increased dissipative losses in the ring plane materials as the orbiting particles 'feel' the irregularities and experience velocity changes, and even out of plane effects. The ring 'particles' will grind amongst each other more, and the angular momentum transfer process will increase in efficiency in dissipating the ring structure.

For scenarios that might require considerable time for successive realignments of the spin axis, the rapid dissipation of the ring materials (either from the high or low side) would seem to present a difficulty in having sufficient duration while the materials are available.

Another complication, for orbiting materials to collapse to the LaPlacian plane, my understanding is the oblateness of the primary is the key factor in facilitating the process. For grossly non-spherical objects, I am not sure how oblateness might be characterized. Perhaps there might be some guidelines on how close the measurements of a triaxial ellipsoid have to be to each other for the LaPlacian process to commence.