Moon Zoo team member Katie sent me an e-mail with a link to an article about a newly discovered lunar feature!! The feature is a natural bridge likely formed by a dual collapse into a lava tube. The one Katie linked to is one of 2 found in the impact melt around King Crater on the lunar farside. This and a smaller neighbouring bridge (also in impact melt material) are the only examples of natural bridges that have been found on the Moon and she asked if we could look out for some more.
These are similar to the lava tube skylights we are already looking for and might be quite tricky to spot. Look out for 2 or more “holes” and some evidence of sunlight shining through from one hole to another showing that it really is a larger cavity spanned by a “bridge.”
You might come across bridges in impact melts (like the King Crater bridge) or in rilles (valleys carved out by lava flows or created by the collapse of lava tubes) running over the mare basalts. Rilles may have some uncollapsed roofed over sections. These are the natural “bridges” we should look out for.
The area around King crater seems a good place to start. Have a look at these LROC strips showing the King Crater bridge under different illumination:
Other locations rich in impact melt would also be good hunting grounds. In large impacts the impact itself and the damage caused by shock waves raises the temperature of the surrounding area and significant amounts of lunar rock melt or vaporize together with the original impactor. Some of this impact melt rock is ejected, but most remains in or around the crater. Impact melt can be seen as flows or ponds.
More information about about impact melt can be found here:
BYRGIUS A CRATER IMPACT MELTS – AN LROC PERSPECTIVE. There is more about Byrgius A here.
IMPACT MELT MOVEMENT IN LUNAR CRATERS.
IMPACT MELT FLOWS ON GIORDANO BRUNO.
These features are interesting to lunar scientists because they are essentially covered caves and ideal places to build future Moon bases as the bridge roof will offer protection from solar wind and cosmic ray radiation. There’s a paper on how bridges may form here: A Search for Intact Lava Tubes on the Moon: Possible Lunar Base Habitats.
This is the King Crater Bridge from LROC image number M113168034R with what I think is the second bridge. Can you find a better candidate for the second one? The small blue rectangle in the inset shows the locations.
Thanks to Katie for additional info and links.
Jules is a volunteer moderator for the Moon Zoo Forum.