User placidstorm posted some Ina-like formations in the Dark Halo Craters thread in December 2011.
I think these look more like “notched cavities” than INA-like formations – see end of posting for references to these features.
These cavities appear to be associated with lava which covers a lava tube or rille, part of which later collapses leaving depressions. I don’t know if that’s what has happened here but this whole region is full of interesting features.
The LPOD Lunar Photo of the Day for 10 August 2007 mentions this area:
A feature, previously unknown to me, is the degraded linear rille segment that extends westward from between Arago Beta and Manners. A similar short but more subtle rille is nearly perpendicular to the Sosigenes Rilles between Beta and Sosigenes A. These two rilles must relate to structures that are now covered by the Tranquillitatis lavas – perhaps whatever is under Lamont. Linear collapse troughs just north of Sosigenes A is evidence for a buried lava tube, another feature from the past of this mare area.
An overview of the features that placidstorm found. This area is in Mare Tranquillitatis north of Sosigenes A crater at approximate coordinates, latitude = 8.1 longitude = 19.0.
Left image: M177508146LE Right image: M177508146RE
Closeup of one of the “bays”.
The image below gives some context to this feature – the area inside the orange oval is the approximate site of the images above. It shows that there is a rille running underneath the feature and this could help explain how the “notched cavities” were formed. The “feature” crossing the rille is a secondary crater chain.
The Lunar Networks article referenced below the image is well worth a read but does contain a mistake where it refers to “linear rille system in the northeast Mare Tranquillitatis” it should say “southwest”.
Full two kilometer width segment of LROC NAC frame M146858595LE as shown on Lunar Networks 16 Sep 2011
[NASA/GSFC/Arizona State University]
The Moon Zoo forum has elected this curious portion of the Moon’s surface as the 2010 Moon Zoo Image of the Year. Named Ina, this puzzling lunar feature may be the result of fairly recent volcanic activity (millions rather than billions of years old) with two distinct types of terrain: rough jagged rubble-like brighter areas and smoother, darker mounds. No-one knows for certain what caused these two different types of terrain but one view is that it is the result of a “recent” gaseous outburst which has removed part of the top layer of regolith.
The Moon is full of odd and peculiar features and it is fitting that Ina has been elected the favourite so far. The Moon Zoo forum and this blog have become places to discuss just such odd features. So congratulations to the Moon Zoo community on an amazing first year – and may we find many more ‘Ina’s in the future.
If you want to learn more about Ina, you can read an excellent NASA article explaining more about it.