Rima Sirsalis
Posted: Tue Jun 21, 2022 10:24 pm
Sirsalis rhyme
Judging by what has been read on the internet recently, there is a lot of confusion and a lot of disagreement about the channels, or lunar grooves. Different websites say that Rima Sirsalis or Sirsalis Rille, shown in the attached image, is a lava tube or lava channel, but some admit some confusion as this volcanic feature formed in the highlands of the Moon rather than in the seas. The word rille (channel or groove) is used to describe a wide variety of valleys that are considerably longer than they are wide. Winding channels, like the Marius, are volcanic lava tubes. Linear ones such as Ariadaeus and concentric ones such as Hippalus are tectonic cracks normally associated with the stress regime related to the impact basins.
Linear channels are interpreted as depressions formed over vertical bundles of magma called dykes. Dikes are born in regions where the horizontal stress is extensional, making it easy for the dike to push up the surrounding rocks. Sirsalis Rille, is one of the largest channels, or linear grooves on the Moon, approximately 380 km long. According to bibliographic references, the channel has a maximum width of 3.7 km and an average depth of 230 meters. What supports the interpretation of this channel as a volcanic dyke, are the magnetic measurements made by the Apollo and Lunar Prospector spacecraft, which revealed a large linear anomaly over the dyke. Sirsalis Rille is among the 8 or 10 channels approximately radial to the hypothetical Gargantua impact basin which had its western third filled by Oceanus Procellarum. Somehow the dikes are related to the vast Gargantua depression, but exactly how this relationship occurs is still a mystery.
The Sirsalis Channel is fascinating because in addition to being large in length it has a strong gravitational field, but the channel seen in the image can also be considered striking as it falls into the De Vico A crater and then scales its wall continuing on the other side. Looking at it like this, it seems that he appeared in this region like lightning. But it actually emerged, thanks to forces coming from below, apparently a vertical sheet of magma that also likely traveled laterally and fed lava into Oceanus Procellarum. As the channel cannot float, it is lower inside the crater than in its rim. To the east the channel crosses the interior of a large unnamed crater where it undergoes a major detour. The reason for this deviation is completely mysterious, but one thing that is clear is a series of canals that appear to start at Sirsalis and head towards Darwin, where a large canal crosses the interior diagonally. Channels sometimes seem to have a life of their own doing what they want to do. At least that's how they appear to be when we fail to understand the forces that created them.
In April 2013, photographing the same location (https://www.astrobin.com/47300/?q=sirsa ... astroavani), my colleague Zeca saw the photo and made an interesting observation: It looks like the shadow of Sirsalis J is apparently abnormal!
He also launched some very interesting speculations and my curiosity was piqued.
I analyzed QuickMap and created a three-dimensional image of this crater. I searched the internet but didn't find specific information about it. I find it interesting to repeat your statements here:
"There is something unusual about Sirsalis J, this crater just below Sirsalis F. See that the direction of the shadow inside the crater is at a different angle to the other surrounding craters. Also, it appears to be on top of a hill and that might explain your wrong shadow".
Sirsalis J is an impact crater near the top of a mountain, it could have some inclination different from other craters that occur in plains, this would explain its shadow with different orientation. It could still be speculated that this mountain could be a volcano because of its apparent cone shape and for being in Rimae Sarsilis.
These are speculations, but they can generate interesting research.
I believe that the impact of an object this size on top of a hill would probably destroy the entire hill, but these are pure assumptions without any basis.
In fact, looking at the 3D QuickMap image, one has the strong impression that there is a super dome, something I don't know exists on the moon with such proportions. Anyway, as Zeca said, they are pure speculations, but they make the art of lunar photography such a delightful hobby.
