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jlhredshift
2010-Jul-12, 04:06 PM
Way back in 2006 Grant Hutchinson and I had a conversation about the striations on Phobos.

Why is Phobos striated? (http://www.bautforum.com/showthread.php/50164-Why-is-Phobos-striated/page2)

Grants theory was that the striations were caused by Phobos flying through a debris spray, I thought that they might have been caused by compaction, but I was not convinced of either mechanism. In any case it is a geologic structure. Now, Fraser has posted the story on Rosetta images of the asteroid Lutetia.

http://www.bautforum.com/showthread.php/105830-Rosetta-Meets-Asteroid-Lutetia?p=1760418#post1760418

The full size NASA image (http://www.nasa.gov/images/content/468195main_4_closest_approach_full.jpg)shows striations on Lutetia's bottom (of the image) section. Though these striations are muted by regolith they are still easily discernible.

It is conjectured that Mars captured Phobos and if that is true then both Phobos and Lutetia spent time in a similar deep space environment and the striations may have a similar cause for the geologic structures that are seen on both bodies.

grant hutchison
2010-Jul-12, 06:47 PM
Grants theory was that the striations were caused by Phobos flying through a debris spray ...Well, not really my theory: someone else's theory which I tried to explain. :)
I gave the relevant links here (http://www.bautforum.com/showthread.php/50164-Why-is-Phobos-striated?p=877766#post877766).

Grant Hutchison

jlhredshift
2010-Jul-12, 07:04 PM
Well, not really my theory: someone else's theory which I tried to explain. :)
I gave the relevant links here (http://www.bautforum.com/showthread.php/50164-Why-is-Phobos-striated?p=877766#post877766).

Grant Hutchison

The "grooves" on Lutetia also seem to be associated with a large impact crater, but obviously not from debris from Mars, not that that means anything. If asteroids are as much a rubble pile as has been suggested, they could be impact faults in non consolidated materials, maybe.

jlhredshift
2010-Jul-12, 07:39 PM
Malin MOC image 50103 (http://www.msss.com/mars_images/moc/9_11_98_phobos_rel/index.html) of Phobos.

JohnD
2010-Jul-14, 10:01 AM
Lutetia is about 200 times bigger than Phobos (Mass 2.57 10^18 kg, v. Phobos 1.072 10^16 kg), but that difference means that the gravity on either body is virtually zero. An impact would produce debris that went away from the object with almost no decelleration due to gravitational attraction. So the striations cannot be due to secondary impacts. In either case, crater chains are the most probable cause, from 'Strings of Pearls' as in the Shoemaker-Levy Jupiter impact.

The Universe Today page quotes an observer as saying that the pics show an extremely ancient object. Indeed, an SoP requires a deep gravity well to produce from a single body, so the original events must have occured after Jupiter (or an outer planet) was formed) and before the system was cleared of multiple objects. A long, long time ago.

John

Sticks
2010-Jul-14, 12:42 PM
Moved to Astronomy

jlhredshift
2010-Jul-14, 10:39 PM
I came across this:

Puzzling asteroid 21 Lutetia: our knowledge prior to the Rosetta fly-by (http://arxiv.org/PS_cache/arxiv/pdf/1003/1003.1845v1.pdf)

2010