 When we imagine astronauts someday setting up a base on the moon, we usually picture them having to assemble some kind of space-age structure to live in. But what if there were already a place to stay on site? Scientists have just discovered the moon's first cave, one they think could be part of a whole network. Living underground would act as a shield from all kinds of threats. So, as our science reporter Georgina Ranard explains, the caves could provide an ideal home for would-be lunar residents.