[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.

[algorimancer]

I like the ring-intersection theory for creating the grooves. I would interpret them as being the result of the decay of one or more non-equatorial ring systems, which I could easily envision having formed as the result of grazing impacts on Lutetia. This is similar to the ring system decay speculated to have formed the equatorial bulge around Iapetus, except for a non-equatorial ring. We might anticipate that these would be common on asteroids large enough to support a ring system following grazing impact (enough gravity to keep the fragments in orbit). With this in mind, watch for grooves around Vesta and Ceres. We'd probably see them on the Moon if not for the instability of lunar orbit.

[bk_2]

I like the ring-intersection theory for creating the grooves.

Your idea of rings around Lutetia (and others) in decaying orbits is new to me. What mechanism would cause the decay?

My theory is that the grooved body was in orbit around a much larger one, and that the rings were associated with the large mass. The grooved body had an elliptical orbit co-planar with the circular rings, and ploughed through them edge on as it swooped in for each close approach. For a tidally locked satellite this would also account for the lack of grooves on the trailing face, as we see so clearly on Phobos.