NASA selected GIMLI to investigate whether the Marius Hills Pit opens into an underground lunar lava tube.Radar, seismic and gravity measurements could reveal a cave\u2019s dimensions and clarify the Moon\u2019s volcanic history.A cave could offer future astronauts natural protection, but its existence at this site remains unconfirmed.<\/p>\n
A hole in the Moon\u2019s volcanic terrain may lead to a much larger space hidden beneath the surface. NASA has selected an investigation<\/a> to find out whether that underground space exists, and how large it might be.<\/p>\n The Planetary Science Institute<\/a> will lead the project, called Geophysical Instruments for Marius Lunar pit Investigation, or GIMLI. Its target is the Marius Hills Pit, a possible entrance to a lava tube left by ancient volcanic activity.<\/p>\n The investigation will combine radar, seismic measurements, gravity readings and cameras. Together, those instruments could turn an intriguing opening seen from orbit into a clearer picture of the surrounding subsurface.<\/p>\n That picture matters for geology and future exploration. A substantial cave could provide natural shielding from radiation, micrometeoroids and extreme surface temperatures, although the selected project has not yet confirmed one.<\/p>\n The Marius Hills Pit (MHP) on the surface of the Moon. MHP will be studied by PSI-led GIMLI, through the NASA PRISM program, to investigate a possible lava tube beneath the surface. (CREDIT: NASA\/GSFC\/Arizona State University) Moving a cave search from orbit to the surface<\/p>\n NASA announced the selection on September 30 as part of its Payloads and Research Investigations on the Surface of the Moon program. Known as PRISM, the program selects scientific investigations for delivery through the Commercial Lunar Payload Services initiative, or CLPS.<\/p>\n GIMLI\u2019s instruments will be carried on a commercially provided lander and rover. Nathaniel \u201cThan\u201d Putzig, PSI\u2019s associate director and senior scientist, will lead the investigation.<\/p>\n Orbital observations have already provided evidence that underground caves and lava tubes<\/a> may exist on the Moon. However, identifying a pit does not automatically establish how far an opening extends beneath nearby ground.<\/p>\n Earlier research using Japan\u2019s SELENE, also called Kaguya, examined radar echoes near the Marius Hills opening. A 2017 study reported patterns that could indicate an intact lava tube, providing a reason to investigate more closely.<\/p>\n Another study, published in Nature Astronomy in 2024, found radar evidence of a cave conduit beneath the Mare Tranquillitatis pit. That finding concerns a different location and does not establish the geometry beneath Marius Hills.<\/p>\n GIMLI will address its target directly from the lunar surface. The central question is whether the visible pit connects to a larger underground void, rather than simply ending below its opening.<\/p>\n Artist\u2019s rendering depicting astronauts, habitats, rovers, power systems, and cargo operations supporting sustained human activities at the Moon Base near the lunar South Pole. (CREDIT: NASA) Three ways to investigate hidden ground<\/p>\n Ground-penetrating radar, seismic sensors and a gravimeter will give the team different ways to examine the subsurface. Cameras will add views of the terrain and the exposed pit walls.<\/p>\n Radar probes underground structures using reflected electromagnetic signals. Seismic measurements<\/a> investigate how vibrations travel through the ground, while gravity measurements can help constrain the distribution of material below the surface.<\/p>\n Combining these methods should provide a stronger interpretation than relying on a single measurement. The team intends to search for a void extending away from the pit and estimate its size if one exists.<\/p>\n For Putzig, the seismic component also revives an approach used during the Apollo era. Active-source surveys deliberately generate vibrations and measure their passage through the ground, rather than waiting only for naturally occurring events.<\/p>\n \u201cIt\u2019s long been a desire of mine to reintroduce intentional active-source seismic methods to planetary science, as it has essentially not been done since the Apollo astronauts<\/a> conducted the first seismic surveys on the Moon,\u201d Putzig said.<\/p>\n Honeybee Robotics, a Blue Origin company, will build the active-source seismic instrumentation, gravimeter and cameras. It will also provide project management and integrate the instruments onto the lander and rover.<\/p>\n The Norwegian Space Agency will provide the ground-penetrating radar. Honeybee Robotics and PSI will jointly lead surface operations, with collaborators from Boise State University, Johns Hopkins University, the Lunar and Planetary Institute and the University of Oslo.<\/p>\n The Passive Seismic Experiment was the first seismometer placed on the Moon\u2019s surface. It detected lunar “moonquakes” and provided information about the internal structure of the Moon. (CREDIT: NASA) A possible shelter, with important unanswered questions<\/p>\n The appeal of lunar caves begins with the hazards above them. Rock overhead could reduce exposure to radiation and micrometeoroids, while sheltered spaces may experience smaller temperature changes than exposed terrain.<\/p>\n A 2022 study in Geophysical Research Letters<\/a> examined lunar pit temperatures using orbital observations and thermal models. It found that permanently shaded parts of the Mare Tranquillitatis pit remained near 17 degrees Celsius.<\/p>\n Those results help explain the interest in underground environments. They are not measurements of conditions inside a confirmed Marius Hills cave, and GIMLI must first establish what space exists there.<\/p>\n NASA describes the investigation as groundwork for potential natural shelters supporting a sustained human presence. Detecting a void would provide information relevant to habitat planning, rather than demonstrate that astronauts could immediately occupy it.<\/p>\n The distinction is important because the project is a selected scientific investigation, not a completed cave survey<\/a>. Its instruments are intended to answer questions that orbital images alone cannot settle.<\/p>\n Pit walls preserve a volcanic record<\/p>\n Even without an underground cave, Marius Hills offers a useful view into lunar geology. Its pit walls expose layers of regolith and lava flows that usually remain hidden beneath the surface.<\/p>\n 250 m per pixel mapping using the mean of all Channels 6 and 8 brightness temperature measurements taken between 9 p.m. and 4 a.m. LST for (a) the Mare Tranquillitatis pit and (b) the Mare Ingenii pit. (CREDIT: Geophysical Research Letters 2022) <\/p>\n Studying those layers could help researchers understand how lava moved through the region. They may also reveal whether long intervals separated eruptions, adding detail to the area\u2019s volcanic history.<\/p>\n Subsurface measurements could help explain how the pit itself formed. A negative cave result would therefore still contribute evidence about the structure and history of the surrounding ground.<\/p>\n \u201cConfirming a substantial lava tube would give us an insight into how volcanism operated on the Moon<\/a>,\u201d said Gareth Morgan, PSI senior scientist and GIMLI\u2019s deputy principal investigator.<\/p>\n Morgan noted that lava tubes are common features of basaltic volcanism on Earth. Identifying comparable structures on the Moon would allow researchers to draw on terrestrial knowledge while investigating lunar volcanic processes.<\/p>\n Two other payloads will examine hazards and ice<\/p>\n GIMLI was one of three payload suites selected in the same PRISM announcement. The other investigations address environmental hazards and resources that could affect future lunar operations under NASA\u2019s Artemis and Moon Base programs.<\/p>\n The Lunar Environment Monitoring Station\u2013South Pole, or LEMS-SP, will monitor micrometeoroids and volatile materials in the Moon\u2019s thin outer layer of gases. A short-period seismometer will track seismic events, contributing information about hazards to surface equipment.<\/p>\n