Archive | April 2012

Notched Cavities or INA-like?

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:

Quote from: lpod

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]

More information about INA features will be found here: TLP Project – INA-like Features and here: INA Images
“Notched Cavities” are discussed here: TLP Project – Notched Cavities in Lava


Strange Whites

Forum member Ewan, otherwise known as Dynamo Duck, found some strange looking craters on the South-East edge of Mare Crisium at Latitude: 12.275° Longitude: 62.1034°. They appear to have unusually high albedo floors and possibly some ejecta of the same high albedo material.

Searching around the area I found some more of these “strange whites.”

Here are two.
And closer…

And then they were everywhere.

At the moment they remain a puzzle. They look like bench/concentric craters but why are the floors so “white”? What is this high albedo material and why are there so many of these craters in this region of Mare Crisium?

While we work out the answers here are some NACs for you to peruse showing the “strange whites” under different illumination.