Bill F
super member
Reged: 05/30/05
Posts: 158
Loc: scotland
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Hello,
Since there is no moon to look at, I've been looking at past LPODs and other photos. It is often said that crater chains are radial to major impacts. I noticed, however, that a surprising number of chains have a bend in them. I can't think of a mechanism for this. Any ideas?
Bill
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Orion Optics (UK) SPX 250 F4.8
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kraterkid
Post Laureate
Reged: 03/07/05
Posts: 3881
Loc: Poway, California
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Hey Bill,
Splay patterns? Overlapping chains from adjacent craters or more distant basins? The human tendency to seek patterns where sometimes it's more like connect the dot? Wierd trajectories? 
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Rich 
[image]http://www.cloudynights.com/stars/CNS0606.jpg" border="0[/image]
My CN Gallery
[image]http://cleardarksky.com/c/JBObCAcs0.gif" border="0[/image]
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droid
rocketman
Reged: 08/29/04
Posts: 3114
Loc: ohio
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chance ???????????????
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andy
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Bill F
super member
Reged: 05/30/05
Posts: 158
Loc: scotland
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I don't think any of the above ideas will work. There are just too many crater chains with a neat bend in them to be any variation on chance or connect the dots.
Bill
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Orion Optics (UK) SPX 250 F4.8
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kraterkid
Post Laureate
Reged: 03/07/05
Posts: 3881
Loc: Poway, California
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Hi Bill,
What about the possibilty that some of these bent crater chains are not impact related, but rather, are endogenic (volcanic) features arrayed along straight rilles that intersect? Collapse calderas such as Hyginus and the other small collapse features along the famous "clock" hand Rille?
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Rich
[image]http://www.cloudynights.com/stars/CNS0606.jpg" border="0[/image]
My CN Gallery
[image]http://cleardarksky.com/c/JBObCAcs0.gif" border="0[/image]
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Bill F
super member
Reged: 05/30/05
Posts: 158
Loc: scotland
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Hello Rich,
Won't work. The ones I am thinking of are defitely craters. I'll have another look to give some examples.
Bill
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Orion Optics (UK) SPX 250 F4.8
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photonovore
Moonatic
Reged: 12/24/04
Posts: 2471
Loc: tacoma wa
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The most comprehensive paper written on lunar secondary impacts that i know of is "Laboratory Simulation of the Herringbone Pattern Associated with Lunar Secondary Crater Chains" written by Oberbeck, V. R.; Morrison, R. H. in 1974. It can be read here. (Large pdf, be patient)
The authors posit that "dogleg" secondary impact chains are the result of the initial simultaneous group of secondary impactors ricocheting and then re-impacting at a divergent angle to the original line of impact and thus becoming tertiary impactors. (see page actual 449-454).
Another mechanism which can diverge crater chain impacts from absolute straight lines is break-up of one or more of the original secondary impactors after launch from the parent crater. This is addressed on pages 445-446 in the above paper.
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Mardi
AR-5 ldx75 refractor, 80mm f/11 refractor, 6" eq3 RFT, ETX-70.
Whitepeak Lunar Observatory Website
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Bill F
super member
Reged: 05/30/05
Posts: 158
Loc: scotland
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Thanks Mardi, I'll read that. On first thought, I find it difficult to see how a set of ricocheting objects would produce a neat bend and further straight section. Similarly, I would have thought a break up would have produced a random scatter. I'll read the article.
Bill
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Orion Optics (UK) SPX 250 F4.8
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Bill F
super member
Reged: 05/30/05
Posts: 158
Loc: scotland
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Mardi,
I've studied the paper you suggested, (the "large pdf" and mention of pages 449-454 had me worried). My reading of it is that the repetition of the bent crater chain further down range was an argument for ricochets, but not an argument for the initial bent chain. Similarly, the break up of an initial projectile would generate the linear craters, but not the neat bend and further straight stretch.
Bill
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Orion Optics (UK) SPX 250 F4.8
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photonovore
Moonatic
Reged: 12/24/04
Posts: 2471
Loc: tacoma wa
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Bill, i'm sorry but that is not what i read. The authors specifically referred to a dogleg" in craterchains, identified two examples in the secondary field of Copernicus, and went on from there. A doglegged crater chain is not two crater chains, it is one chain--with a dogleg! 
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Mardi
AR-5 ldx75 refractor, 80mm f/11 refractor, 6" eq3 RFT, ETX-70.
Whitepeak Lunar Observatory Website
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Bill F
super member
Reged: 05/30/05
Posts: 158
Loc: scotland
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Mardi,
Agreed on the two dogleg crater chains, it's the interpretation of these two that I read differently. I read it that the presence of the second dogleg chain (an almost carbon copy of the first) directly down range of the first chain is a reasonable proof that the second chain was produced by ricochets from the uprange chain, not a reason for the initial dogleg. The problem with trying to determine which were the initial debris impacts and which were the ricochets in a normal, straight chain, would be that the ricochets would look like just another chain. A copy of the first dogleg chain, but downrange, would be far more indicative of ricochets.
Bill
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Orion Optics (UK) SPX 250 F4.8
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photonovore
Moonatic
Reged: 12/24/04
Posts: 2471
Loc: tacoma wa
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Bill, i guess i may not be understanding what sort of feature you are referring to. Perhaps it would help if you gave an example?
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Mardi
AR-5 ldx75 refractor, 80mm f/11 refractor, 6" eq3 RFT, ETX-70.
Whitepeak Lunar Observatory Website
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Bill F
super member
Reged: 05/30/05
Posts: 158
Loc: scotland
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Mardi,
Catena Brigitte (there's a photo on wikimoon, LPOD, Special features list, catenae. Sorry, I haven't cracked how to do links yet!)is an example. The bend on that is fairly gentle and not through a big angle. I'll look for some better examples.
Bill
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Orion Optics (UK) SPX 250 F4.8
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photonovore
Moonatic
Reged: 12/24/04
Posts: 2471
Loc: tacoma wa
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Catena Brigitte, ok. Here's the NASA image of the area (a portion of AS17-M-0597):
Catena Brigitte is indicated with arrows along it's length.
This chain appears at least partially endogenic (volcanic) in origin, specifically the oblong collapse features which make up a substantial portion of its lower extent. Looking around this area (in Mare Serenitatis i believe?) other features of a type generally considered to be endogenic abound; ex. a sinuous rille runs along the lower edge of the image which appears to connect the lower end of the catena to other collapse features in the center right of the image. Now if this feature type was in the highlands far from any volcanic activity areas (like the maria represent) then the endogenic origin would be a weaker claim, but located as it is, the endogenic nature of this chain would be considered very probable. So, this particular feature probably wouldn't be considered an ideal example of a curved or doglegged _impact_ related crater chain at least.
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Mardi
AR-5 ldx75 refractor, 80mm f/11 refractor, 6" eq3 RFT, ETX-70.
Whitepeak Lunar Observatory Website
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Bill F
super member
Reged: 05/30/05
Posts: 158
Loc: scotland
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My poor choice of an example. Looking at it again I can see exactly what you mean.
Having noticed a number of the more probably impact formed chains in the past, now I need to quote a few examples I can't find them! I'll keep looking, just out of interest.
Thanks
Bill
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Orion Optics (UK) SPX 250 F4.8
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Mert
scholastic sledgehammer
Reged: 08/31/05
Posts: 978
Loc: Spain, Pamplona
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Bill, I just read this thread and I was quit surprised
with this finding.
To me it seems a bit weird how the chain bends and keeps
bending further down the chain.
To me it looks like some debris was rotating and when
touching down just some part broke off ( having also
rotation ) and was launched with some angular
offset due to the rotation. 
Just my 2 micro-euro-cents.
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Mert
42º49"N 1º38"W
3" Unitron refractor
6" F12 SW Maksutov,CS2-S
EQ6 + EQMOD 
Webcam with 1.25" nosepiece
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Bill F
super member
Reged: 05/30/05
Posts: 158
Loc: scotland
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Mert,
I can see how rotation on impact might possibly change the direction of a single ricochet (like spin balling in cricket), but I would have thought it more likely that it would cause breakup and random scatter, rather than the neat bend and further straight line of similar size craters that I am thinking of. I just wish I could find the examples I am thinking of!
Bill
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Orion Optics (UK) SPX 250 F4.8
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Mert
scholastic sledgehammer
Reged: 08/31/05
Posts: 978
Loc: Spain, Pamplona
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Bill, my second thought on this rotation is this:
if the object impacts, the first hit, it still has
a very high velocity, every subsequent impact or
touch down will have less velocity and hence the
rotational offset will influence more and more.
Also the hardness of the ground where the impact
takes place will influence a lot.
Maybe also the consistency of the object will provoke
a partial break up, where the second big part still
has this rotational component.
On second touch down, again an offset and a speed
loss, more offset every subsequent touch down ( is that
ricocheting? )
Then on most objects likely random scatter will occur,
but maybe the consistancy of the object together
with the consistency of the ground where impact takes
place might effect.
Likely I just haven't got a clue but it's nice to
think on this!
Regards,
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Mert
42º49"N 1º38"W
3" Unitron refractor
6" F12 SW Maksutov,CS2-S
EQ6 + EQMOD
Webcam with 1.25" nosepiece
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Bill F
super member
Reged: 05/30/05
Posts: 158
Loc: scotland
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I've just read the LPOD for April 18th. The link to the paper by Greeley has some excellent photos of bent crater chains. Collapsed lava tubes in Washington, not the moon. The same area as those two very interesting articles on your website, Mardi? this would agree with your suggestion of a volcanic cause for the bent chains on the moon.
Scottish volcanoes died millions of years ago, so we don't have such interesting examples here. Mind you, at least our scenery doesn't try to shake itself to bits or blow itself up at regular intervals!
Bill
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Orion Optics (UK) SPX 250 F4.8
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photonovore
Moonatic
Reged: 12/24/04
Posts: 2471
Loc: tacoma wa
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Hi Bill,
took a look at that paper by Greeley--he mentions one of the tubes i visited and wrote about--"Lava Tube" in Oregon just s. of Bend, Oregon. I didn't see any mention of the tubes in Washington may have missed it but they are certainly similar in formative mechanisms to all the other lava tube examples on Earth. (seemed most of his references were related to the Siskiyou lava tubes in California).
Yes, interesting recent geology we have around here, pacific "ring of fire", big subductive fault just offshore (pacific plate doing its thing with the continental plate)--latter will probably end up being the death of many who live here when the next big movement on this fault occurs--don't feel too jealous--but nice place to visit and all that! No one knews when, but most think Mt Rainer will go off about like St. Helens eventually...don't wanna be around for that....nice to be able to examine the aftermath though--St Helens is a pretty fascinating area geologically--but Oregon is even better.
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Mardi
AR-5 ldx75 refractor, 80mm f/11 refractor, 6" eq3 RFT, ETX-70.
Whitepeak Lunar Observatory Website
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Bill F
super member
Reged: 05/30/05
Posts: 158
Loc: scotland
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Mardi,
Sorry, the collapsed tube craters are, indeed, in California. I didn't notice the name change.
Over here a magnitude 5 earthquake will have media headlines something like ,
"Major earthquake in Scotland. 5 chimney pots fall down!!!"
Bill
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Orion Optics (UK) SPX 250 F4.8
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