Researchers have uncovered the scorching history of the moon’s surface through its lava plains and volcanic remnants, but much of the secrets hidden underground remain a mystery. A study published on April 11 in the Journal of Planetary Science described peculiar surface features that support the existence of underground cave networks.
Each so-called “spider” structure is made up of multiple channels (the “legs” of the spider), seemingly formed as lunar soil flowed into a central depression about 10 meters wide (the “body” of the spider). Researchers studying high-resolution images captured by NASA’s Lunar Reconnaissance Orbiter (LRO) found the initial four almost imperceptible “spiders,” with their legs nearly reaching the limit of resolution. The primary author of the study, planetary scientist Mikhail A. Kreslavsky of the University of California, Santa Cruz, stated.
Once they understood what to look for, scientists discovered more “spiders” in the Mare Tranquillitatis region where volcanic activity had been frequent. James W. Head, a planetary geologist at Brown University and co-author of the research, believes the moon’s relatively lower gravity may have allowed for the formation of large gas bubbles in magma, leading to the formation of underground caves. If the tops of these caves collapsed due to seismic activity, surface materials flowing in could create the distinctive spider-like shapes.
In a previous study, the LRO detected a void extending from a large crater in Mare Tranquillitatis. Researchers speculate that there may be spacious caves beneath about 300 other known craters on the moon.
The study authors suspect many “spider” structures that once existed have now disappeared. “The lunar surface is continuously bombarded by micro meteorite impacts,” said planetary scientist and physicist Nicolle Zellner of Albion College in Michigan. “The top meter of material has been stirred up by these impacts.”
Noah Petro, a scientist at NASA’s Goddard Space Flight Center on the LRO project, pointed out that the proximity of “spider” structures to disturbed areas on the ground in other volcanic deposits and the possible appearance of “spiders” near craters could suggest that the voids might be larger than imagined and interconnected underground. “Perhaps these underground caves are more extensive than we previously thought,” he added.
Since these “spider” structures seen today likely formed in relatively recent geological periods, they serve as a warning for future explorers: beneath the fragile surface of the moon in certain areas, dangerous caves may still lurk. ◇