The moon is a lumpy rock covered in countless craters, hills, ridges, cracks and rubble. Holes, not so much.
That’s why the rugged Marius Hills, by the moon’s equator on the near side, or the half facing Earth, has transfixed scientists.
Why on earth (or moon, rather) is there a massive hole in it?
Nasa recently selected a mission to send a rover to our lunar companion and finally see what lurks inside the Marius Hills pit.
Space officials picked a proposal by the Planetary Science Institute, a US-based non-profit, that says it could become shelter for an astronaut base.
So… what is this big old hole?
The Marius Hills pit is up to 150 feet deep and 300 feet across, or roughly as wide as a football pitch.
If the pit were on Earth, though, it wouldn’t be particularly interesting, says Gareth Morgan, a planetary geologist at the PSI.
‘Such pits are relatively common in volcanic terrains on Earth, think Iceland or Hawaii, and are formed by collapse into a subsurface void,’ he says.
‘In many cases on Earth, such pits are opening into lava tubes, a type of long, cylinder-like cave that can form during eruptions.’
Emphasis on ‘eruptions’, Morgan says. The ditch could be the result of the ancient volcanoes that once raged across the moon’s surface.
Around 300 lunar pits have been identified on the moon, according to a study in the International Journal of Mining Science and Technology.
Some of these are ‘skylights’, underground tubes carved out by lava that a meteor punched through the roof of.
The Marius Hills pit could be one of these, Morgan says. Unlike their Earth-equivalent, these tunnels could stretch for hundreds of miles and be as wide as New York’s Central Park due to the lack of gravity.
It’s also in the middle of a sinuous rille, bumpy lunar river valleys carved not by water but gooey magma billions of years ago.
If the PSI researchers can confirm the Marius Hills pit is a skylight, it could help scientists discover how our closest cosmic neighbour formed.
The go-to theory is that a planet the size of Mars, called Theia, slammed into a young Earth and sent into orbit rocks that squished into a moon.
Though some scientists suspect the moon was forged from the fires of an ocean of magma sloshing over Earth’s surface 4.46billion years ago.
PSI’s plans, called the Geophysical Instruments for Marius Lunar Pit Investigation, would send some serious gear on a Nasa payload flight.
It is being funded by the institute’s Payloads and Research Investigations on the Surface of the Moon programme.
The rover will have ground-penetrating radar to look beneath the surface, seismic sensors to map the underground, cameras and a gravimeter, which wiggles from tiny variations in gravity,
Honeybee Robotics, owned by Amazon’s rocket company, Blue Origin, is partnering with PSI to build the moon-walking tech.
If the opening isn’t a cave, the rover will hunt for alternative explanations locked beneath the moon’s pale, dead surface.
‘We will take images of the pit wall using our camera mast system by driving to a close – but safe! – distance to the pit edge,’ adds Morgan.
‘As geologists, we will use the layering to explore the local geologic history.’
Could a moon pit be a future astronaut base?
Morgan and Nasa are hoping for the pit to be a network of cosy tunnels – space officials want to have a permanent base on the moon by 2032.
Nasa plans to build £15billion worth of Tic Tac-shaped buildings powered by nuclear and solar energy.
The Marius Hills cave complex could be ready-made infrastructure for astronauts, a lunar version of the Tube.
‘Astronauts spending long durations on the moon will have to contend with high radiation levels, dangers from very fast travelling micrometeorites and extreme temperature swings,’ Morgan says.
The moon reaches 250°C in the sun and -250°C at night, as the natural satellite has no atmosphere to keep the heat in.
‘Cave systems would be thermally stable and would shield against radiation and micrometeorites and so would make an excellent place to build long-term bases,’ Morgan adds.
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A lunar outpost could also act as a trial run for humans one day calling Mars home, experts previously told Metro.
But for Morgan, people leaving boot prints on lunar dust could help us understand more about the place we’ve called home for 315,000 years.
‘The moon is sometimes considered the “eighth continent” – the reason being that the moon has recorded the full history of bombardment it has experienced since its formation, hence all the craters!’ he says.
‘The Earth has also been similarly affected by large impacts throughout its history, but due to the dynamic nature of our planet, it is constantly refreshing its surface and erasing large craters.
‘So in that sense, the moon gives us a way to look back into Earth’s deep geologic history.’
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