NASA has greenlit an innovative mission to investigate whether a massive lunar pit opens up into an extensive subterranean cave system capable of housing future astronauts. Officially designated as the Geophysical Instruments for Marius Lunar pit Investigation (GIMLI), this project will examine the Marius Hills Pit—a prominent cavity situated within a highly volcanic lunar landscape—to determine if it connects to a cavernous underground lava tube.

Spearheaded by the Planetary Science Institute, GIMLI emerges as one of three fresh science initiatives backed by NASA’s PRISM program to lay the groundwork for a permanent lunar installation.

Located in the Oceanus Procellarum terrain on the western side of the full moon from the perspective of Earth's Northern Hemisphere, the Marius Hills Pit first appeared in imagery captured by Japan’s Kaguya spacecraft before undergoing closer scrutiny by NASA’s Lunar Reconnaissance Orbiter. Measurements show the depression spans approximately 213 by 295 feet (65 by 90 meters) with a depth of roughly 111 feet (34 meters).

Researchers hypothesize that the feature acts as a skylight, created when the roof of an ancient lava tube collapses. These tunnels form when molten lava develops a hardened crust on top while liquid rock continues to drain below, leaving a hollow conduit. To verify whether a cave extends past the opening, GIMLI will deploy advanced gravity measurements, seismic sensors, and ground-penetrating radar.

Natural Shelter For Astronauts

Subterranean lunar environments could eventually serve as prime real estate for future human outposts. Surface explorers must contend with severe temperature swings, micrometeorite strikes, and intense cosmic radiation. Sunlit zones experience scorching highs of 260 degrees Fahrenheit (127 degrees Celsius) alongside frigid lows plunging to minus 280 degrees Fahrenheit (minus 173 degrees Celsius) during the lunar night.

Conversely, data from the Lunar Reconnaissance Orbiter indicates that permanently shadowed regions within certain pits maintain a comfortable ambient temperature near 63 degrees Fahrenheit (17 degrees Celsius). Consequently, underground chambers might present safer, more thermally stable conditions for personnel, though researchers must first confirm their safety and accessibility.

GIMLI is paired with two other selected projects aimed at supporting a sustainable human footprint on the Moon. While the Lunar Environment Monitoring Station–South Pole (LEMS-SP) will monitor seismic activity and micrometeoroid hazards, the Depth Imager with Spectral and Color Optics (DISCO) focuses on analyzing surface conditions and lunar ice.

Collectively, these studies supply vital data for evaluating resources, mitigating risks, and spotting prospective shelters. Nicky Fox, associate administrator for NASA’s Science Mission Directorate, emphasized that these PRISM initiatives directly aid in reducing mission hazards for astronauts. While the upcoming lunar base is slated for the south pole, the Marius Hills Pit rests much closer to the equator in Oceanus Procellarum.

Exploring The Moon’s Volcanic Past

Than Putzig, PSI Associate Director and Senior Scientist, will direct the GIMLI mission, with instrument manufacturing led by Honeybee Robotics, a subsidiary of Blue Origin. Meanwhile, the ground-penetrating radar system is being supplied by the Norwegian Space Agency.

Even if the probe finds no cavern system, researchers anticipate that the gathered data will clarify the genesis of the Marius Hills Pit and illuminate lunar volcanic evolution. Gareth Morgan, PSI Senior Scientist and GIMLI’s Deputy Principal Investigator, noted that confirming a major lava tube sheds direct light on past lunar volcanism. Furthermore, the exposed geological layers inside the pit could expose ancient flow sequences, offering clues about the eruptions that formed the lunar landscape eons ago.