NASA selected the GIMLI payload—Geophysical Investigation for Mapping Lunar Interior—for deployment at the approximately 65-meter-wide Marius Hills Pit. Announced on 30 September 2026, GIMLI will combine radar, seismic measurements, gravity readings, and cameras to determine whether the pit opens into an underground lava tube; the existence of a usable void remains unconfirmed.[2][3][5][8]
A sufficiently large, intact tube could provide passive protection against ionizing radiation, micrometeoroid impacts, abrasive lunar dust, and surface temperatures ranging from approximately −173°C to 127°C—a swing exceeding 250°C.[3][5] Earlier NASA technical analysis estimated that more than 16 meters of basaltic roof could provide adequate radiation and impact protection, while tube interiors may remain near −20°C, substantially reducing habitat thermal-control and shielding requirements.[6][9] However, access, structural stability, sealing, contamination control, communications, power distribution, and emergency egress remain unresolved engineering risks.
The Ark team should track GIMLI’s deployment schedule, raw subsurface maps, void dimensions, roof-thickness estimates, seismic stability data, and evidence of internal hazards. In parallel, integrate lava-tube siting into the Ark master plan: define minimum geometry and shielding thresholds, develop robotic reconnaissance and anchoring systems, model pressure-vessel and fire-safety strategies for cavernous environments, and preserve a surface fallback capable of protecting the archive if the Marius Hills site is inaccessible or structurally unsuitable.[2][5][6]