Small Body Grooves, Theories for the formation of grooves on Lutetia and Phobos Options

[AndyG]

They'd be "straight" - well, great circles/great circle arcs - at the "impact equator" measured halfway between the impact point and the anti-impact point.

Hmmm...If your idea were right, there could be all sorts of interference patterns developing from a shook-up rubble pile following an impact. (I'm reminded of the wonderful phrase that the Moon "rang like a bell for hours" after Apollo hardware impacts).

Definitely a job for computer modelling, this.

Andy

[bk_2]

The Cassini image of the crater Penelope on Saturn's moon Tethys, from the recent flyby of three moons, Enceladus, Tethys and Dione, shows grooves crossing the lighted rim and within the walls. The crater is ~90Km across, the grooves look wider than those on Phobos, but they have the same characteristic family grouping, in at least one place. And there are a few curved grooves, the best long groove on the crater floor is one of them. The ring-whacker hypothesis predicts that the locus of each of these is in a plane.

[Guest_cassioli_*]

This cool picture from our moon could possibly suggest an alternate explanation for Lutetia and Phobos trails:


Compare it with trails in this picture:


Rolling stones both and our moon, Mars moons and Lutetia?

Could a low-mass object like a moon or an asteroid cause such a "light" impact that material coming from crater, rather than being thrown away, just starts rolling around the body?

But, again, I don't know where rocks would be right now...

[algorimancer]

...
Rolling stones both and our moon, Mars moons and Lutetia?
...

I like this idea, with caveats. I wouldn't rule it out in all cases, but the neat parallel rows makes me think it unlikely.

Phobos is just really weird. Those grooves appear to slice through the moon, even through deep craters, and they intersect at arbitrary angles. There's no way I can envision those grooves as fractures, and the only way I could realistically see them forming is for Phobos to have had a few transits of a very thin ring about Mars. A ring around Phobos itself couldn't have created these grooves. And I find it hard to believe that a ring around Mars would be that thin.

It's almost like there are clouds of oriented strings of particles which occasionally intersect asteroids. Here's a way-out notion... perhaps nickel-iron asteroids with residual magnetic fields are able to maintain clouds of particles aligned along the magnetic field lines, perhaps with the assistance of electrostatic levitation (which has been observed on the Moon). I could envision a near-pass or impact from such a system onto an asteroid yielding something like what we see on Phobos. Modeling such a system is beyond me, but if they're in the asteroid belt they should be detectable by remote sensing or transits. There would presumably be an optimal combination of mass and magnetic field strength to create such a system. Alternately, perhaps such a system can be temporarily generated by the combination of induced magnetism and debris due to an impact, such that the resulting grooves are the result of the decay of the magnetic field dropping the suspended debris onto the surface.

[edit](These last couple of posts should probably be in the Small Body Grooves section)

[Guest_cassioli_*]

what happened to last posts?!?

[centsworth_II]

what happened to last posts?!?

Are these the ones? Moved to the "Small Body Grooves" thread.

[Guest_cassioli_*]

Are these the ones? Moved to the "Small Body Grooves" thread.

without any warning?
this forum is magic!

[bk_2]

The grooves left by the rolling boulders on the moon are superficially similar to the grooves on Phobos, but they are recognizably different. For starters, there are no boulders at the ends of the grooves on Phobos, nor are there families of parallel grooves among the boulder tracks on the moon.

Algorimancer, you see the grooves as I do, the result of "a few transits of a very thin ring about Mars". But then you say you think such a thin ring improbable. Why? Saturn' rings are 10m thick across most of the extent. There are irregularities, collections of bigger boulders and wiggles on the edges caused by resonance with shepherd moons, shown so clearly at the recent equinox. If the putative (and now absent) rings of Mars were like that, you would expect the variety in the grooves we see on Phobos, from crater chains to smooth trenches.

[Hungry4info]

You cannot argue that a thin ring will produce a thin line of craters without requiring the moon's orbit to be coplanar with the ring. Otherwise, when the moon impacts the ring, it does not just transit it, it's blanketed by the ring. An entire hemisphere gets hit.

Another problem is that unless the body is in a high eccentric orbit, the ring particles...


wait....

I've already mentioned all this.

I'm done with this thread.

[Fran Ontanaya]

For starters, there are no boulders at the ends of the grooves on Phobos,

Hi.

How close should Phobos have orbited in order for Mars gravity to make one loose rock do suborbital jumps? Maybe it eventually broke apart, or reached escape velocity.

[ElkGroveDan]

The Admin team has concluded that we've whipped this horse long enough and it doesn't appear to be going anywhere. This discussion is now closed.

If and when a published paper or other reputable study provides something new on these features, then a new topic can be started.