by David North
More hole hunting tonight; I managed to sneak in some observing between clouds and rain, but the seeing was not too bad.
I decided to beat up on one area, since it looked interesting: the crater chain north of the western edge of Stadius (running rougly from Stadius G to T -- see Rukl page 32).
This formation is concentric to Copernicus, and I have more or less assumed in previous sessions that it is a string of secondary impacts. This idea is further supported by the strings of smaller craters seen running up toward this "catena," also presumably secondary impacts.
I'm far less sure after staring it down.
Tonight (with this 'chain' right on the meridian) I could clearly see that the craters were surrounded by a smooth ridge.
I suppose it's possible for them to have created "swellings" around themselves to build the ridge, but it just doesn't look likely.
Or maybe smaller, more fluid ejecta landed before the "cratering" fragments; possible, but a stretch..?
Further, as you travel north, there is a slash that cuts across the "line" of craters, and then they seem to end in a much more classic catena of the sort found in Rimae Hyginus.
There are vague indications of this "Hyginus structure" in Rukl (without any labels) but they are clearly drawn and marked in the Times Atlas -- the "crossing" line is Rima Stadius II, and the extension at the north is Rima Stadius I, exactly as observed: a Hyginus Class rille (made up of a string of small craters).
I refuse to think that this is "coincidentally" a rille that joins up to a string of secondary impact craters... but I don't know what it is. Perhaps the southern end of this structure (leading to Stadius) is actually a string of small volcanos?
Or the ridging is an uplift instead of the usual collapse, caused by a "shock ring" phenomenon from the Copernicus impact? (That wouldn't surprise me, since I also observed a ridge between Copernicus and the Stadius Line; it could also be a "shock" formation).
My uneducated guess tends to favor the shock hypothesis, but I'd be very glad to hear from anyone who knows something about this area...