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Mare Tranquilitatis Fact Sheet: Zuh? May 22, 2008

Posted by Nick Azer in Mare Tranquillitatis, Selenology.

In a past bout of research on the Sea of Tranquility, I came across this fact sheet.

It starts off easy enough: “Mare Tranquillitatis sits within the Tranqillitatis basin.” Simple, and eponymous.

Then you happily trudge along to the next line and… “The mare material within the basin consists of basalt in the intermediate to young age group of the Upper Imbrian epoch.” Whoa!
What did they just say?

A point-by-point analysis:

Mare” is a basaltic lunar plain; basalt being a type of volcanic rock that gives the maria a bluish tint. “Upper Imbrian” refers to the Lunar geologic timescale, and a period of it that occured ~3500 million years ago; Upper Imbrian is the fourth period, with Pre-Nectarian, brief Nectarian, and Lower Imbrian periods preceding and the Eratosthenian and Copernican ages following.

Those are some crazy paragraphs even within the Wikipedia articles; I see a “Lunar geologic timsescale: Cliffs Notes edition” post in this blog’s future.

But, for now, the next section of this fact sheet:

“The surrounding mountains are thought to be of the Lower Imbrian epoch, but the actual basin is probably Pre-Nectarian.”

So the basin is older than the mountains around it. Interesting.

“The basin has irregular margins and lacks a defined multiple-ringed structure.”

…What? A search and dictionary/encyclopedia search turns up nothing definitive on the meaning of “irregular margins”; “multiple-ring structure”, though, comes up with this upon a search: “In the largest craters, the centre may rise and fall more than once leading to mulitple ring structure.” So they are saying Tranquilitatis does not have this multiple-ring structure, which by the mere mention of this fact suggests that is unusual (as it ‘lacks’ it).

“The irregualr (sic) topography in and near this basin results from the intersection of the Tranquillitatis, Nectaris, Crisium, Fecunditatis, and Serenitatis basins with two throughgoing rings of the Procellarum basin.”

So this basin is apparently kind of screwy due to a bunch of basins coming together, within the rings of Procellarum, also known as Oceanus Procellarum. Procellarum is the mother of lunar maria, covering 4 million square kilometers and (as we’ve seen here) encompassing, at least partially, smaller maria like Tranquilitatis.

The fact sheet goes on to talk about a “Palus Somn” , which is both a crazy-cool name and apparently a typo, as it is supposed to be “Palus Somni” (which translates to ‘Marsh of Sleep’ from Latin, which is an even more crazy-cool name for a place). A picture, below:

This Marsh of Sleep is 143 km (~88-90 miles or so) wide, with the whole mare Tranquilitatis being about the size of The Phillipines or New Zealand.

I’ll start wrapping my head around that geologic timetable, and I’ll get back to you all in the future with that in plain English…but, for now, you have a better understanding on some level of that rather blunt fact sheet :)



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