From: "Tim" <tjp314@pacbell.net>

Date: November 29, 2007 9:06:52 AM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: Schiller

Duane:

Jay Melosh has published at least one book on impact cratering.  There

are others in the field as well, of course, but his name comes to mind.

After the SL-9 impact on Jupiter, a colleague of mine made a

correlation between statistics of comet breakups around Jupiter, and

the possibilities of some of those comets being swept up by the

satellites instead of Jupiter.  Sure enough, there are crater chains

on Ganymede and Callisto in abundances commensurate with their

different probabilities of sweeping up the most comets (I think

Ganymede has more than Callisto).  These are really cool, consisting

of dozens of distinct craters all in very long chains, with some

ellipticals as well.

-Tim.

--- In Astro_IIDC@yahoogroups.com, "Duane" <macastronomer@...> wrote:

I agree with that assessment. I'll throw out some inexperienced

"thought" physics and 

make a guess that when the impactor broke apart, the piece that

impacted first was on 

the side that was spinning forward and the other piece spun

backwards making it lag 

behind differentiating the first impact, which was on the left of

the image and the final 

impact which trailed immediately behind on the right. This

interaction would mess-up the 

formation of a central peak on the left and the one on the right

would be malformed by 

both the combination of kicked up debris from the previous impact

(which would linger 

due to low gravity and roll over the top of the subsequent

explosion, landing on the far 

side of the second impact and/or get blown clear) and also due to

the lack of material on 

its predecessor's side. (note, impacts that are slightly more

separated by distance or time 

would still meld together but have two central peaks)

I don't know if that's how this really takes place, but that's how

I'd picture it happening in 

my mind. Looking at the image and the mess of mountains on the right

crater, it sure 

seems like a messed up central peak to me.

I'm probably wrong about this too, but would the case of an oblong

impact, which you are 

correct that it requires an extremely low angle impact, the central

peak would be still 

centralized but possibly, slightly, elongated? If that were the

case, it wouldn't fit the 

results.

If anybody knew of a book that explained impact physics, I sure

would be interested in 

checking it out. The Moon is much more interesting when you can

mentally picture its 

dynamics.

--- In Astro_IIDC@yahoogroups.com, "Tim" <tjp314@> wrote:

Hi Duane:

The problem with the suggestion that it's two craters that overlap is

that there should be a rim between the two, where their ejecta sheets

interacted.  Likewise, if they formed at different times, the younger

crater's rim should extend across the line between them.  With an

oblique impact (and they really have to be very low angles - like less

than 5 degrees - in order to not form a circular crater), you really

can form an elliptical crater.  I think that those folks I know who

work on the physics of these things will say that the appearance of

two (or more) overlapping craters is due to the impactor breaking into

multiple pieces before impact, but not separating by enough distance

to form two separate craters.

-Tim.

--- In Astro_IIDC@yahoogroups.com, "Duane" <macastronomer@> wrote:

I can see how it's debatable, but with a nice shot like this, it

sure looks like two craters to 

me. I popped that out there with a couple circles showing what I

think clearly looks like 

two nice ovals:

http://homepage.mac.com/deal/schiller20060410_1628.jpg

--- In Astro_IIDC@yahoogroups.com, Alan Friedman <alan@> wrote:

Hi Duane -

I think the jury is still out on the formation of Schiller (but  

leaning towards an oblique impact):

http://www.lpod.org/index.php?s=schiller&paged=3

Looking straight down via Lunar Orbiter images (or in earth

based  

images taken at a low sun angle) that bizarre caldera topped

mountain  

is clearly seen as two separate features - a long hill with a

crater  

on the floor of Schiller just behind.

Thanks,

Alan

On Nov 27, 2007, at 2:32 AM, Duane wrote:

Hi Alan,

Nice shot. It makes me eager for ver. 4 but then again I

know this  

image is from you and

part of me knows you're taking it beyond my capability :)

I never looked at Schiller closely before, but it appears to be

two  

craters joined (and

flooded) together creating the potato shape, doesn't it? Maybe  

that's already known, but

then again self discovery is good too.

Thanks for sharing and keep'em coming.

Duane

.