August 3, 2006

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Snakey Map

map by J.B. Murray

Sinuous rilles are the Moon’s most interesting rilles because they are challenging to see, have complex shapes and are often near other volcanic features. And since the mid-1960s we have had good evidence that sinuous rilles are lava tube or channels. But how many are there, and where are they? John Murray gave answers to those questions 35 years ago, based upon his close inspection of Lunar Orbiter IV and V images. His map shows about 200 nearside rilles, the vast majority of which are on the western hemisphere of the Moon. There are strong concentrations of sinuous rilles near the Aristachus Uplift and the Marius Hills. Observers may be surprised that the map indicates rilles in familiar places (such as around Sinus Iridum) where they are not telescopically visible. That is because John included rilles that were very short, very thin, and in some cases perhaps non-existent! John did not publish a list of sinuous rilles and I am unaware of any that might exist. I recognized 27 sinuous examples in the rille list of the Lunar Section of the Italian Astronomical Union (UAI). Compilation of a modern sinuous rille catalog, based on Clementine and SMART-1 images, as well as Lunar Orbiter data, would be a very doable and valuable project for an individual or a group. And there is already the beginning of a sinuous rille image library - please contribute your images to it! Have you wondered why the rilles are mostly on the western hemisphere? There are two likely reasons. Lunar Orbiter IV images of the eastern 1/4 of the nearside were of low to miserable quality - there may be more sinuous rilles to discover there! And the eastern maria are compositionally different (and topographically higher) that the western ones. Are either of these possibly the cause of the paucity of sinuous rilles?

Chuck Wood

Technical Details:
The map comes from the chapter “Sinuous Rilles” by J.B. Murray in Geology and Physics of the Moon (edited by G. Fielder) Elsevier Publishing Co., Amsterdam, 1971, p 27-39.

Related Links:
Rükl plate: all!

Yesterday's LPOD: A New Concentric Crater!

Tomorrow's LPOD: Unexpected Fault


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