A larger (396k) GIF version of this image is
here. (Page created 4/6/96)
Peirce crater, like Picard, is an Eratosthenian crater formed after the surrounding basaltic surface of Mare Crisium had solidified. It is at 18.3deg North, 53.5deg East and is approximately 50 miles north of Picard. It's diameter is 11.5 miles (18.5km). Like Picard, the smaller Peirce has a series of terraces on its inner wall that have been attributed by selenologists to collapse of the crater floor rathern than to the slumping of the walls themselves that more commonly occurs in much larger craters.
Within Peirce are two other fairly sizable craters. This is a rather unusual circumstance because Peirce is a relatively recent crater that was formed after the lunar maria and therefore after the solar system epoch called the Late Heavy Bombardment, the last period of time when meteor and asteroid impacts on planetary bodies were so frequent that large impactors would often fall within pre-existing craters. Impacts capable of creating craters the size of those within Peirce were relatively rare after the Late Heavy Bombardment, yet two such impacts occurred within Peirce - two "direct hits." Whether or not these secondary craters are evidence of deliberate war-like acts is, of course, still a matter of fanciful speculation. But we have seen no better evidence yet anywhere else that there have been destructive forces at work on the moon other than micrometeorite erosion. (Disclaimer: this whole "war in Crisium" thing is Jon Floyd's idea, not mine. It is my firm belief that the moon has always been a nice peaceful sort of place, kind of like Club Med but with a less agreeable climate).
The NASA support data for this photograph and information on the digital image preparation are here. The two secondary craters within Peirce can be seen in this image. The larger of them is almost 1/5 the size of Peirce itself.
A larger (396k) GIF version of this image is
here.
Other interesting features of Peirce are the two "ramps," one to the north (right in this image) and the other to the south, both leading down from the rim of Peirce to the floor of the crater. These ramps do not fan out onto the crater floor as one would expect rock slides to do. Also, if these structures were the result of rock slides, some evidence of collapse depressions at the crater rim should be present. Instead, at the top of the northern ramp there is a curious domed structure with small ridges radiating out around its perimeter outside of the crater. The southern ramp has several large bright patches on its surface.
yOn the floor of Perice are some other features which seem out of the ordinary. Perhaps the most curious is the bright patch to the northwest (above and to the right) of the larger of the two inner craters. The boundaries on three sides of this bright diamond-shaped area appear to be perfect lyly straight , as delineated in red in the clip from peirce.gif below. The central "peak" that defines the irregular southern boundary of this region is not at all unusual-looking, and it is hard to interpret its relationship to the diamond-shaped patch in which it lies. We have speculated that the "diamond" might be the outlines of a building that has collapsed inward, and that the "peak" is a remnant of the structure that is still standing.
Floor of Peirce
Click here for a stand-alone gif of the image below.
There are several other interesting features in close proximity to this "diamond". A series of furrows (outlined in blue) run parallel to its north (right) side the north-eastern (lower-right). To the east (below) the "diamond" is a linear trench running from a circular mound (both in green) down over the rim of the secondary crater. This trench, perhaps, could be a fault line created by the impact that caused the inner crater, or it might be an indication this small inner crater served some function and that its origins were of a somewhat less bellicose nature than we have speculated. To the right of the "diamond" is the bottom of the northern ramp, which, judging from the shadow it casts, has has a very angular, blocky shape (outlined in yellow).
Additional pages on the crater Peirce will be here sometime around May 1, 1996.
