At the Moon’s south pole, there are craters that never receive direct sunlight. They are among the coldest places in the Solar System. For explorers, this permanent darkness may seem like a problem. For physicists seeking to build a timekeeping and navigation system on the Moon, it could be exactly the advantage they need.
In May 2026, researchers from NIST, JILA, NASA’s Jet Propulsion Laboratory and other institutions presented an unusual proposal: placing an ultrastable silicon optical cavity in a permanently shadowed lunar crater. Connected to a laser, it could provide an extremely stable frequency signal, useful for a kind of “lunar GPS”, for communications and for the Moon’s future time scale.
Why put a laser in a dark crater?
Optical clocks and highly stable lasers are sensitive to vibrations and temperature. On Earth, laboratories use elaborate isolation and cooling systems to reduce these disturbances.
The Moon offers two natural advantages: it has almost no atmosphere, meaning the environment is a very good vacuum, and permanently shadowed craters at the lunar poles are extremely cold.
NIST cites temperatures on the order of 50 kelvin in such regions. By radiating heat into space, the proposed system could cool a silicon cavity to around 16 K. At that temperature, changes in silicon’s dimensions can be dramatically reduced, helping the laser maintain an almost unchanged frequency.
What is an optical cavity?
Put simply, an optical cavity is a system with two reflective surfaces between which light can travel back and forth. The distance between them determines which light frequencies can resonate stably inside it.
If that distance changes even slightly because of temperature or vibrations, the reference frequency changes as well. That is why researchers seek to build a cavity that is as mechanically and thermally stable as possible.
In the NIST proposal, a commercial laser would be “locked” to one of the silicon cavity’s resonant frequencies, producing an extremely stable optical signal.
How a “lunar GPS” could emerge
GPS on Earth works because satellites transmit highly precise time signals, and the receiver calculates the time differences between them to determine its position.
There is no equivalent infrastructure on the Moon yet. For another example of how the Moon’s geometry directly changes observing conditions, see InfoBuz’s guide to the 2026 Draconids and a sky with almost no moonlight. Future vehicles, robots and astronauts will nevertheless need precise positioning, especially near the south pole, where long shadows and difficult terrain complicate navigation.
An ultrastable lunar laser, synchronized with atomic clocks aboard satellites, could provide one of the references needed for such a network. NIST refers to infrastructure for GPS-like navigation, precise distance measurements and optical Earth–Moon communications.
The Moon also needs its own time scale
The issue of lunar time is not merely administrative. Relativity means that clocks do not tick at exactly the same rate on the lunar surface as they do on Earth. NASA is working on the concept of Coordinated Lunar Time, a coordinated time scale for future activities in cislunar space.
NASA has explained that clocks on the lunar surface would appear to gain tens of microseconds per day relative to clocks on Earth if relativistic effects were not corrected. At the speed of light, an error of only a few tens of microseconds can mean kilometres of positioning error.
A stable optical system on the Moon could become an important component of a future local timekeeping network.
Could such a laser detect gravitational waves?
The authors go further still. If several ultrastable optical systems existed on the Moon, the distances between them could be measured with extraordinary precision. In principle, the passage of a gravitational wave alters distances between objects by a very small amount.
NIST mentions the possibility of using a lunar network for such fundamental-physics experiments as well. However, this is a long-term objective, not a capability already demonstrated on the Moon.
How close is the project to reality?
The distinction between a scientific proposal and an approved mission is important. The system is not installed on the Moon. The researchers have published the concept and argue that the underlying technology is mature enough to be demonstrated first in orbit.
One of the co-authors cited by NIST estimates that a silicon cavity could be tested in low Earth orbit within a few years and later on the lunar surface, but these time frames are the team’s estimates, not an official guaranteed schedule.
Why dark craters matter so much for future missions
Permanently shadowed regions are of interest for more than physics. Observations indicate the presence of water ice in some polar areas, and local resources could matter for a sustained human presence.
At the same time, the darkness and cold make landing and operations complicated. That is precisely why a highly precise positioning system would be valuable in these regions.
What is known for certain and what remains only a proposal
- Published: the concept of a silicon optical cavity for the lunar environment was presented in 2026.
- Demonstrated on Earth: optical cavities and optical clocks can achieve extraordinary stability.
- A real physical advantage: the vacuum and extremely low temperatures of permanently shadowed craters reduce disturbances.
- Proposal: using the system as part of a “lunar GPS,” a timekeeping network and fundamental-physics experiments.
- Not yet a reality: there is currently no such operational installation in a lunar crater.
