not... always?
the big thing in the case of the the lunar 'cave' is that it was something formed by a lava tube, which are honestly really neat (and have been something talked about for the moon for... years)
here's a picture from LRO from '09 showing a glimpse into a tube
like, here's a pair of other lunar lava tube photos, the first being a roughly 50km long which transitions from collapsed to non-collapsed and the second photo being an oblique image of an entrance into one at Marius Hills
Oh yeah, looks to be data from LRO that indicates an empty lava tube under the Sea of Tranquility.
It was something that's been discussed off-and-on since 2009 when it was first discovered by camera imagery, as seen below with the image of the opening into it.
I will not share the entirety of the folder, but I will share this from one of the documents I have discussing expendable logistics vehicles servicing Space Station Freedom.
I admit one significant thing that has made me [gestures hand over it all re:the press coverage of it] has also been stuff a bit like this re:the mention of the president not calling them for their birthday which is a '... wait, what' type bit
Or how Playtex, which was known as a bra manufacturer, were the ones that made the Apollo spacesuits. Like, here's a photo of the kind of cut patterns for instance on the suits.
I love how my package gets to my network distribution center (Cincy) and then zips off to Texas.
I predict it will wind up in like the Dakotas or something before it gets back here. :V
