NASA’s New Mission to Peek Inside a Giant Moonhole

When you look up at the Moon on a clear night you see a smooth, pock‑marked sphere, but hidden beneath those cratered hills are probably some truly cavernous spaces. One of those spaces might be staring back at us right now, a gaping opening known as the Marius Hill Pit (MHP).

The pit is no ordinary dent. From orbit it looks like a perfect circle, roughly 300 feet across and perhaps 150 feet deep—a skylight, scientists think, formed when the roof of an ancient lava tube collapsed.

If that’s the case, the hole could be a literal window into a massive underground tunnel that formed billions of years ago when the Moon was still volcanically active. Imagine walking into a natural tunnel that stretches for miles beneath the regolith—something that could reshape how we think about lunar geology.

NASA is taking that imagination seriously. The agency has green‑lit a mission called Geophysical Instruments for Marius Lunar pit Investigation, or GIMLI, to send a small rover down to the rim of the pit and start poking around with a toolbox of sensors.

The rover’s kit will read like a miniature science lab: ground‑penetrating radar to map what’s hidden below, seismic probes that can “listen” to the Moon’s internal vibrations, and a gravimeter to sense tiny variations in the lunar gravity field. On top of that, a suite of cameras will snap high‑resolution photos of the pit’s walls, giving us a close‑up look at the exposed layers of regolith and ancient lava flows.

“Confirming a substantial lava tube would give us an insight into how volcanism operated on the Moon,” says Gareth Morgan, a senior scientist at the Planetary Science Institute and deputy PI for GIMLI. In other words, we could finally piece together the story of how molten rock once carved its way across the Moon’s surface.

Beyond pure science, there’s a very practical reason to be excited. The Moon’s surface is a harsh place—no atmosphere to block solar wind, constant bombardment by cosmic rays, and temperatures that swing wildly from blistering heat to bone‑chilling cold. A cavern shielded by kilometers of rock would naturally protect future crews from radiation and provide a much more stable thermal environment. That’s why many researchers see lava tubes as the most promising real‑estate for the first permanent lunar bases.

Most of the rover’s hardware is being built by Honeybee Robotics, a company that’s been supplying clever machines for planetary exploration for years. The whole payload is funded through NASA’s Payloads and Research Investigations on the Surface of the Moon (PRISM) program and will hitch a ride to the Moon via a commercial launch provider under the agency’s Commercial Lunar Payload Services (CLPS) initiative.

When the rover finally touches down near MHP, it will start its quiet, methodical work—sending back data that could confirm whether the pit opens up into a sprawling cavern, and perhaps even map the interior geometry of the tube itself. If the results are positive, the next step might be to send a larger rover, or even a crewed mission, to explore the tunnel’s depths.

So, while most of us still think of the Moon as a barren, dusty ball, the reality may be that it hides vast underground highways—natural shelters that could become the foundation of humanity’s next giant leap.