Quadrant 37:
— Images and text provided by Howard Eskildsen
Copernicus to Lansberg
Copernicus stands out as an eye-catching
crater on the upper right corner of the
quadrant. The 96 km diameter crater typifies
the structure of large craters on the moon.
A prominent group of peaks rises near the
center of the crater, surrounded by a flat inner
floor. The inner rim rises from the floor in
a series of steps or terraces to the roughly
circular outer crater rim. Outside the rim,
rough rubble extends in an ever thinning
ring that extends nearly a full crater diameter
beyond the outer ring. This material, known
as ejecta, was violently ejected during the
formation of the crater by an explosive
impact of an asteroid or comet. Intermittent
fingers of ejecta extend even farther than
the continuous apron surrounding the crater.
Additionally, small irregular craters appear
in the surrounding area that are secondary
craters from blocks of material ejected during
the crater formation.
Reinhold and Lansberg, 49 and 41 km diameters
respectively, show similar structural features to
Copernicus on a smaller scale, but appear softened
in appearance as if there has been some weathering
compared to Copernicus. They are older than
Copernicus and have endured eons of erosion caused by
strikes from small meteors, known as gardening. Both
also endured a massive moonquake by the formation of
Copernicus as well as scouring from material ejected
from it.
The lower left half of the quadrant consists of a mostly
smooth surface interrupted by scattered craters. Some of
those craters appear fresh and deep, while others appear
worn and shallow; indeed there is a nearly completely
buried crater between Lansberg and Hortensius with
only its outer rim rising above the plains. What could
have buried and nearly completely filled the crater?
The plains consist of a type of lava known as basalt
and are known as mare (singular) or maria (plural),
such as Mare Insularum on the image. It arose from
swarms of fractures in the lunar surface and, layer
by layer, laid down the smooth plains. Either before
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or during the emplacement of the basalt, the
flooded crater formed by meteor impact, and
then was filled inside and out by rising lava
until only the uppermost portion of its outer rim
remained. Tests run on the basalt recovered from
the moon’s lava plains by the Apollo missions
show that it was about as thin and runny as warm
motor oil or pancake syrup, and flowed freely
into flat layers.
Later, when that phase of volcanism had
ended, some last gasps of volcanic activity
left domes of lava that was much thicker
when it erupted. The rounded domes the lava
formed feature central pits or caldera. Several
of these are visible on this image including
the Hortensius Domes and Dome π near
Milichius.
In this image it is possible to see several
processes that have shaped the moon over the
eons. There are craters caused by impacts with
meteors, asteroids or comets. Erosion of the craters
shows up as wear from impacts of small meteors