[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.

[Hungry4info]

While I can see how that would apply to Phobos (though reorientation events would be required to explain the observed sets of grooves), I'm not sure it could be stretched to cover Lutetia. Lutetia, as far as we know, hasn't orbited a planet, and getting a situation to work where the asteroid would spend enough time in the vicinity of one to experience reorientation events would be difficult.

Furthermore, for ring impacts to create lines, the moon's orbit must be coplanar with the ring plane, otherwise an entire hemisphere gets blanketed when puncturing through the ring(s). In the case of Phobos, coplanarity with a ring would be best explained if Phobos formed from the ring. IIRC, Mars and Phobos are not believed to have the same composition, so having Phobos form from the ring is implausible. Another idea is that a hypothetical third moon could come in and get disrupted at the altitude where Phobos passed though on its current tidal inspiral toward Mars. This requires the hypothetical third moon to be coplanar with Phobos' orbit. If this is satisfied, we need a mechanism for reorientating Phobos. Interaction with a fourth moon that was since ejected?