Future space explorers could go back to being cave dwellers with the discovery of an apparently huge cavernous space beneath the moon’s surface tens of kilometres long.

In a paper published in Geophysical Research Letters, Japanese and US researchers offer evidence of what could be a marvellous place for a moon base — an intact lava tube that could shield humans from cosmic radiation, extreme temperatures and space debris, reports nationalpost.com.

‘Dreams of putting people into lava tubes on the Moon have been ongoing for decades,’ the journal’s editors write, ‘and this work is an important step in turning that dream into reality.’

 In 2009, Japanese scientists discovered a huge, deep vertical hole, a ‘skylight,’ in the Marius Hills region, on the moon’s nearside. More of these black pits were found by NASA’s GRAIL (Gravity Recovery and Interior Laboratory) orbiters. What wasn’t clear was how far the openings extended, or not.

In the new papers, scientists with Japan’s space agency, using radar data gathered by Japan’s Selene orbiter, say they detected a ‘mass deficit signature’ far larger than expected, ‘which implies the existence of a large void space beneath the visible surface extending 60 km’ to the west of the Marius Hills hole.

Space researchers have speculated about the existence of lava-tube caves on the moon since first days of the US Apollo missions. For years, NASA has been using lunar reconnaissance orbiters to try and learn more about the pits.

‘Even a few pictures from ground level would answer a lot of the outstanding questions about the nature of the voids that the pits collapsed into,’ said Robert Wagner, a lunar researcher who teaches at Arizona State University, in a 2014 NASA interview, reports the Quartz.

The timing might be right for moon exploration. While Elon Musk wants to use his company SpaceX to get astronauts to Mars, US president Donald Trump has signaled that he’s more interested in getting more people to the moon—contributing to the larger debate about which would be better to further explore first.