FROM AN ESTATE agent’s perspective, the lunar surface has little to recommend it. Its none-too-metaphorical lack of atmosphere means it is bombarded by meteorites, cosmic radiation is unrelentingly harsh and temperatures range from lows of -246°C to highs of 121°C. Subsurface lunar caves, on the other hand, with stable temperatures and cover from projectiles, would be much more enticing habitats. The only question is, do any exist?

In a paper published in Nature Astronomy, Lorenzo Bruzzone and Leonardo Carrer, at the University of Trento, and their colleagues, offer a definitively affirmative answer. They provide evidence of a cave about 80 metres long and 45 metres wide at the bottom of a 135-metre-deep pit in the Sea of Tranquility. The neighbourhood is a historic one: plains which surround the pit are the site of humanity’s first lunar landing. Though the site’s selenological (the lunar equivalent of geological) origins are unclear, it may be the remains of a subsurface tube forged by a river of lava. When the tube’s ceiling caved in—perhaps after a meteor impact—a giant pit (with its associated caves) was all that survived.