In the Moon's permanently shadowed craters near its south pole—among the darkest and coldest places in the solar system—physicist Jun Ye and his colleagues have identified the ideal location for a technology that could revolutionize space navigation and timekeeping: an ultrastable laser locked to a silicon cavity that could operate at temperatures colder than any human-built laboratory on Earth.
The idea emerged from conversations about what instruments NASA's Artemis mission could carry to the lunar surface. What makes this concept compelling is not the ambition, but the physics: the Moon's environment offers natural advantages that Earth cannot match. Unlike terrestrial laboratories, the lunar surface experiences far fewer vibrations, exists in a natural high vacuum, and—crucially—the permanently shadowed craters operate at around 50 kelvins (50 degrees above absolute zero), drastically reducing thermal jitter in the mirrors that keep laser light bouncing at precisely the same frequency.
An optical silicon cavity, a block of silicon with mirrors at each end, would form the system's heart. The distance between those mirrors determines which frequencies of light can resonate within it; for a highly stable cavity, that distance cannot vary. Silicon has a remarkable property: at the crater's expected operating temperature of 16 kelvins, the material neither expands nor contracts when exposed to tiny temperature changes—meaning light would always traverse exactly the same distance between mirrors. The cavities would be cooled even further simply by radiating heat directly into the frigid vacuum of space, without needing cryogenic equipment.
Once deployed, a commercially available laser would be positioned nearby and locked to the cavity's resonant frequency, ensuring it emits light of a single, unchanging color. That stable laser signal could serve as a lunar GPS, guiding spacecraft—especially those landing in dimly lit polar regions—safely to the surface. It could also become the backbone of the Moon's first optical atomic clock, a timekeeping system that would rival the most precise optical atomic clocks built on Earth.
The applications extend beyond navigation. Multiple copies of these lunar lasers could precisely measure distances between objects across vast spaces. They could form the infrastructure for Earth-Moon optical communication and satellite-based space distance measurements. Some researchers envision them detecting exotic physics phenomena, such as ripples in spacetime predicted by Einstein's theories.
The team, led by Ye of both the National Institute of Standards and Technology (NIST) and JILA at the University of Colorado Boulder, included researchers from NASA's Jet Propulsion Laboratory, Germany's Physikalisch-Technische Bundesanstalt, and Lunetronic Inc. in San Francisco. Their proposal, published in Proceedings of the National Academy of Sciences, arrives at a moment when NASA has already designated regions near the lunar south pole's permanently shadowed craters as Artemis landing sites—meaning the infrastructure for this technology could be installed during humanity's next chapter of lunar exploration.
What began as what Ye called "another crazy idea" in conversation with colleagues has proven surprisingly sound. The Moon's harshest environment, it turns out, may be exactly what precise timekeeping and deep-space navigation have needed all along.