re: I have an offer/challenge to all geologists and geophysicists on HZ.
What about lava tubes on the Moon? We have pictures of partly collapsed tubes on the Moon.
I don't know if I count. I have been studying Geology for two decades now, and I have even taught Geology classes, but I am not a professional.
I would be willing to bet that Mars has caves, both lava and water formed.
I would also bet that Triton has caves around the Nitrogen Geysers.
IO probably has caves due to Volcanism. Venus probably does to.
