Kaguya finds lunar cave and tunnel

The viral claim is real in spirit, but the timing is off. Kaguya — Japan’s SELENE lunar orbiter — did spot a striking hole in the Moon’s Marius Hills region. But that happened in 2009, not this week. What’s new is that people are rediscovering the imagery, while later radar work from both JAXA and NASA made the “cave and tunnel” interpretation much stronger. ### What did Kaguya actually find? Kaguya imaged a nearly circular vertical hole in Marius Hills, a volcanic area on the Moon’s near side. The original 2009 paper described it as a possible lava-tube skylight — basically an opening in the roof of a subsurface tunnel left behind by ancient flowing lava. The team estimated the pit at about 65 meters across and roughly 80 to 88 meters deep from lighting geometry in the images. (agupubs.onlinelibrary.wiley.com) ### Why do people call it a cave? Because a skylight is not just a pit. It can be the doorway into a larger hollow space underground. That is the whole excitement here — not the hole itself, but what the hole implies. In lava-tube systems on Earth, the roof stays intact over long distances, and only a few sections collapse open. The Moon version is thought to work the same way. (agupubs.onlinelibrary.wiley.com) ### Why Marius Hills? Marius Hills is packed with volcanic features, especially sinuous rilles — long, winding channels carved by ancient lava. The pit sits right in one of those rilles, which makes the lava-tube explanation much more convincing than a normal impact crater story. NASA’s high-resolution LRO camera page puts it plainly: the location strongly suggests a collapse in the roof of a lava tube. ### Did later missions confirm a tunnel? (agupubs.onlinelibrary.wiley.com) They got much closer to that. In 2017, JAXA said radar sounding from Kaguya confirmed multiple intact lunar lava tubes under the volcanic region, with one floor extending several tens of kilometers westward from the east end of the detected tube. Then in July 2024, NASA said reanalysis of LRO Mini-RF radar data found evidence of a cave extending more than 200 feet from the base of a pit in Mare Tranquillitatis, with the full extent unknown and possibly much longer. (lroc.im-ldi.com) That is not the exact same pit as Marius Hills, but it strengthens the broader case that lunar pits can open into real caves. ### Why are the measurements different? Because different instruments and viewing angles give different estimates. The 2009 Kaguya paper gave the famous 65-meter width and 80-to-88-meter depth. Later LRO imaging revised the Marius Hills pit to about 58 by 49 meters and around 40 meters deep. That sounds like a contradiction, but it is really refinement — better images, better geometry, tighter numbers. (global.jaxa.jp) ### Why does any of this matter for astronauts? Radiation, micrometeorites, and temperature swings are the big three. A lava tube could act like a ready-made bunker. JAXA has said intact lava tubes are valuable both scientifically and for future exploration, and NASA has made the same point — these underground spaces could preserve pristine geology while also offering safer places for equipment or crews. Basically, the Moon may already have natural shelters waiting to be mapped. (agupubs.onlinelibrary.wiley.com) ### So what’s the bottom line? The viral post is recycling an old discovery, not revealing a brand-new one. But the underlying idea has only gotten stronger with time. Kaguya found the skylight. Later radar work backed the existence of subsurface lunar caves. So the exciting part is not “Japan just found a cave” — it’s that one of the Moon’s most promising natural shelters has been sitting in the data for years, and scientists now have better reasons to think it really does connect to a tunnel underground. (global.jaxa.jp) (agupubs.onlinelibrary.wiley.com)