Scientists want to put a super laser on the moon

Scientists want to build a laser inside one of the Moon’s coldest craters that could help lunar landers and rovers navigate with precision.

Ultrastable lasers are essential for timing and navigation systems that require extreme precision. They work by bouncing a beam between two mirrors inside a cavity. The beam reflects between the mirrors at a very precise speed, in part because the chamber stays almost exactly the same size instead of expanding or contracting. To keep this beam length stable, mirrors are typically held in a vacuum at extremely low temperatures, isolated from external vibrations.

On the Moon, there are hundreds of craters around the poles that never receive direct sunlight because the Moon does not tilt much as it rotates. This makes these permanently shadowed regions exceptionally cold, with some craters predicted to be around -253°C (20 kelvins) in lunar winter.

Jun Ye of JILA in Boulder, Colorado, and his colleagues proposed that these frigid conditions — along with the Moon’s natural lack of vibrations and virtually nonexistent atmosphere — could make these craters the ideal location for an ultrastable laser, with potential stability far greater than that of any laser on Earth.

“The whole environment is stable, that’s the key,” says Ye. “Even when you spend summers and winters on the moon, the temperature still varies between 20 and 50 kelvins. It’s an incredibly stable environment.”

Ye and his team’s laser device would be similar to devices they have already built in JILA’s labs, called optical cavities, which consist of a silicon chamber with two mirrors.

The best optical cavity lasers on Earth cannot remain coherent, meaning the laser’s light waves remain in sync for a few seconds. However, researchers believe a Moon-based laser could remain coherent for at least a minute.

This would allow it to serve as a reference laser for many different lunar activities, such as maintaining a time zone on the Moon or coordinating satellites that fly in formation and use lasers to measure their distance from each other. It could even be used as a reference laser for activities on Earth, since it takes just over a second for a beam from the Moon to reach Earth, Ye says.

Although it will be difficult to implement, the idea behind it makes sense and could help in future moon landings, says Simeon Barber of the UK’s Open University. “We have seen several polar lunar landers recently experience suboptimal landing events due to lighting conditions, which hamper the use of vision-based landing systems,” says Barber. “Using a stable laser to support positioning, navigation and timing could increase the reliability of successful high-latitude landings.”