NASA selects a mission to probe a lunar pit for a hidden lava tube
On 1 October 2026, the Planetary Science Institute announced that NASA had selected its proposal, GIMLI, to investigate whether a large cave extends beyond the opening of the Marius Hills Pit, funded through NASA's PRISM program with instruments flying on a lander and rover supplied through the CLPS initiative. The suite pairs ground-penetrating radar provided by the Norwegian Space Agency with an active-source seismic system, a gravimeter and cameras built by Honeybee Robotics, a Blue Origin company; the team says it would be the first intentional active-source seismic survey on the Moon since the Apollo astronauts. PSI says even a null result would still address how the pit formed, and that the pit walls expose layers of regolith and lava flows usually hidden underground.
The record ends here. Everything below this line is invented.
What if a lunar survey heard a source it did not cause, inside the cave it came to find?
Part one
The Gravity Deficit
The first shot record came down at two in the morning: one thump from the rover's hammer, an hour of listening, the plot scrolling up like a slow tide.
Halfway down the coda, an arrival that was not theirs.
It came in behind their own echo, small and clean, with the sharp edge a geophone writes for a strike. Their source sat on the rim. This arrival was too early for any path from it and too late for a moonquake. It repeated: every twenty-six minutes, something inside the pit struck, and the ground answered.
A moonquake was the easy answer; thermal quakes keep the sun's clock. Then she checked the clock. Sunrise comes every twenty-nine and a half Earth days; her source drifted against it four minutes a day, like a clock nobody had corrected.
Perla had one reason to want the pit quiet: Diego, her brother, had signed on with the landing team in March, and their mother had started saying "when Diego lands".
She ran the travel times twice. The second source sat eleven hundred metres along the passage, under eighty metres of basalt. Inside the cave.
Every thump on the Moon rings for nearly an hour, because dry rock swallows almost none of it. That was how a strike buried in the dark stayed loud in a record made for a source two hundred metres away.
At 6:40 the operations loop lit up for the landing review. Her phone buzzed once. "green?"
What’s real
- NASA selected GIMLI to probe the Marius Hills Pit.
- Radar, seismic equipment, a gravimeter and cameras will fly on a lander.
- Active-source seismic would return for the first time since Apollo.
- Even a null result would say how the pit formed.
What’s invented
- Perla, her brother Diego, and the Hemlock landing program.
- The Wren-2 lander and the thumper that outlived it.
- A void 1.1 kilometres along the passage, 80 metres down.
Part two: The Cycle in the Dark
Part two isn’t on sale yet. Check back soon.