February 23, 2013

Railway Tracks

image from Kaguya Archives
This is a classic LPOD from Dec 30, 2008.

Can you imagine being in lunar orbit and seeing scenes like this passing by? A number of new stills from the Kaguya HDTV
are now available including this remarkable view looking north over the Hippalus Rilles. Campanus is the crater with a rille on
its floor at bottom right, and Hippalus is the large crater near the middle whose left side is missing and is embayed by lavas
from Mare Humorum. It is not completely clear why mare-facing crater walls disappear, but this oblique view shows that the
wall becomes progressively lower from its high right side until it disappears. This means that Hippalus formed on sloping ter-
rain and/or it was tilted inward as the basin's center subsided, and then was covered by lavas. The oblique view also suggests
that the floor of Campanus is at a higher level than the mare surface outside it to the right. This isn't certain, but if true means
that the mare and the lava inside the crater were not fed from the same reservoir.

Chuck Wood

2013 Update Using the LRO QuickMap altimetry data it is now possible to check the 2nd to last statement above about the height of lava inside Campanus compared to nearby Mare Nubium. The floor is slightly domed but actually about 1.3 km LOWER than the mare! Off the bottom right corner is another mare-floored crater, Mercator, whose floor is the same elevation as the mare. That sug- gests that Mercator may have been fed by the same source as the mare but Campanus' lavas had a source with a different hydrostatic pressure.

Related Links
Rükl plate 53

Yesterday's LPOD: Another Passing of the Apollo Era

Tomorrow's LPOD: Camouflage Moon

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