Moon ‘spiders’ hint at vast caverns beneath the Moon
Newly discovered spider-like features suggest lunar explorers need to watch where they step
The “spider” of the moon (Outlined) was photographed by the Lunar Reconnaissance Orbiter Camera.
The lava plains and volcanic remains on the Moon’s surface suggest that the sphere was once a fiery sea, but what lies beneath remains largely a mystery. Planetary Science Journal, Researchers have described strange surface features that support the existence of an underground cavern known as the Cavern of the Earth.
The so-called spider web is made up of channels (the spider’s “legs”) that were likely formed when lunar soil flowed into a central depression (the spider’s “body”) about 10 meters wide. The researchers found the first four spiders, hiding almost inconspicuously, in photos taken with the powerful cameras on NASA’s Lunar Reconnaissance Orbiter (LRO). “The spider’s legs are close to the limit of resolution,” says Mikhail A. Kreslavsky, lead author of the study and a planetary scientist at the University of California, Santa Cruz.
Once they knew what to look for, the scientists found several more spiders, all in the Mare Tranquility, an area that previously experienced intense volcanic activity. The moon’s relatively low gravity likely caused large gas bubbles to form in the magma, creating underground cavities, says study co-author James W. Head, a planetary geoscientist at Brown University. If seismic activity caused the roofs of these cavities to collapse, the surface material that flowed inward would have created the spiders’ distinctive shape, the researchers say.
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In previous studies, LRO had detected open cavities beneath large holes in Mare Tranquility, leading researchers to speculate that spacious caverns may lie beneath some of the moon’s roughly 300 known holes.
The study authors speculate that there may have once been many more spiders, who have since disappeared. “There are still a lot of micrometeorites impacting the lunar surface,” says Nicole Zellner, a planetary scientist and physicist at Albion College in Michigan, who also studies the lunar surface. “The top meter of material on the surface is being stirred up by impacts.”
Noah Petro, LRO project scientist at NASA’s Goddard Space Flight Center, said the spider’s proximity to other signs of surface movement, called irregular seas, in the volcanic deposits, and the fact that it may have once appeared near the hole, may suggest that the cavity is larger than thought or connected underground. “The cavity may be much larger than we previously assumed,” he added.
Because the current spiders likely formed in the relatively recent geological past, they serve as a warning to future explorers that dangerous caverns may still lurk beneath the fragile surface in certain parts of the Moon.
