Moon’s thick crust could amplify elusive gravitational-wave signals
Gravitational waves are tiny ripples in the fabric of spacetime that are produced when massive objects in the cosmos accelerate or collide. By detecting these waves, astrophysicists can study various ...
Gravitational waves are tiny ripples in the fabric of spacetime that are produced when massive objects in the cosmos accelerate or collide. By detecting these waves, astrophysicists can study various cosmic events, including black hole mergers, neutron star collisions and the early evolution of the universe.
There are several gravitational-wave observatories in different geographic regions worldwide. While these detectors are highly sensitive to the tiny changes associated with ripples in spacetime, they cannot yet detect waves across all frequency ranges.
Researchers at the Chinese Academy of Sciences and Peking University recently revisited the possibility of using the moon to amplify gravitational waves with frequencies between 0.01 and 1 hertz (Hz), a range that remains largely inaccessible to current gravitational-wave detectors.
Their paper, published in Physical Review Letters, suggests that the moon's rugged surface could strengthen detectable gravitational-wave signals.
"About three years ago, a scientist from the Chinese Academy of Sciences contacted me to ask whether I could provide some details on the deployment of a lunar seismometer, since professor Menyao Wang from Beijing Normal University hoped to learn about the basic lunar environment for designing a LIGO-like system on the moon," Jinhai Zhang, co-author of the paper, told Phys.org.
"Since then, I gradually became part of an amazing collaboration among astronomers, engineers and planetary scientists. As the principal investigator of the lunar seismometer aboard the Chang'e-7 mission, I provided detailed information that I had learned about the moon; meanwhile, I learned a lot about what is going on at the frontiers of physics and astronomy."
Using the moon as a natural gravitational-wave detector
When gravitational waves pass through the moon, they cause it to minimally stretch and squeeze, which can produce tiny seismic vibrations. The researchers explored the possibility of detecting these seismic responses, essentially using the moon as a giant Weber bar. A Weber bar is a gravitational-wave detector invented by Joseph Weber that resonates when gravitational waves pass through it.
"During our early discussions, I realized that all existing analyses of the seismic response to gravitational waves are based on ideal lunar models, without considering the effects of topographic variations and the strong lateral heterogeneity of the moon," explained Zhang.
"Fortunately, the related technical challenges have been fully considered in the geophysics field, especially by my team, including how to construct a strongly heterogeneous global model and how to avoid numerical artifacts caused by using coarse grids or high frequencies."
To reliably assess the feasibility of using the moon as a Weber bar, the researchers first needed to develop a more realistic model of the moon's interior structure. Zhang created a new lunar model in close collaboration with Xian Chen, an astrophysics professor at Peking University, as well as other young Chinese physicists Lei Zhang and Han Yan.
"China's Chang'e-7 mission plans to deploy the first broadband lunar seismometer close to the south pole in fall 2026, almost 50 years after the shutdown of pioneering seismic observations during 1969–1977," said Zhang. "This would provide an actual background noise level for the moon, facilitating lunar gravitational-wave detection. Therefore, it is time to carefully consider the actual effect of the real moon."
Lunar models developed in the past treat the moon as a perfectly smooth and evenly structured sphere. The reality, however, is that the moon is rugged and significantly messier, with many craters, small mountains and an unevenly shaped crust.
The researchers created the most realistic lunar model to date and used it to predict its response to gravitational waves. This model allowed them to determine how specific locations on the moon would respond more strongly to gravitational waves, which in turn helped them identify an optimal landing site for the Chang'e-7 lunar seismometer.
"Based on the ideal lunar model, previous works suggest that the dominant resonance frequency of the moon should be around the decihertz range, but we do not know the actual effect due to lateral variations in topography and crustal thickness," explained Lei Zhang, first author of the paper.
"Thus, we built the first high-resolution numerical model by considering the real lunar model that had been constructed by geophysicists to simulate the vibration of the moon resonantly induced by a wide range of frequencies, from 0 to 0.2 Hz. Specifically, our model includes the moon's rugged surface topography and, most importantly, the strong variations in crustal thickness across the lunar surface."
A way to advance future lunar observatories
The analyses carried out by the researchers suggest that gravitational-wave signals will be amplified by as much as 10% in regions where the moon's rocky outermost layer (i.e., crust) is thicker. In addition, they suggest that, at these sites, signals with frequencies of around 0.1 Hz could be amplified by more than a factor of 10, which means they could be detected by carefully designed future instruments.
"We also verified our numerical results using semi-analytical models, which essentially involve a harmonic decomposition of the lunar structure and the corresponding vibration," said Chen. "The agreement is satisfactory, which also hints that mixing of different harmonic modes may be responsible for the amplification of gravitational-wave signals in thick lunar crustal regions."
The recent work by Jinhai Zhang, Yan, Chen and Lei Zhang could guide future efforts aimed at developing and deploying gravitational-wave detectors on the moon. If these detectors are positioned at specific sites on the moon where the crust is thicker, they could help pick up and monitor gravitational-wave signals that were inaccessible so far, potentially offering new insight into various cosmological events.
"We found that the moon may ring louder in response to gravitational waves than people previously thought," said Chen. "In the past, the missing ingredient was the variation in lunar crust thickness. We think our work is important for deciding deployment sites for future lunar seismometers. And such better-informed decisions would greatly enhance the science payback of lunar seismology projects."
The team at the Chinese Academy of Sciences and Peking University is planning new studies aimed at further exploring the ideas presented in its paper. Specifically, the researchers will use theory to predict the signals that could soon be detected by the Chang'e-7 seismometer so they can compare their predictions with real observations.
"China's Chang'e-7 will be launched this year and will deploy a seismometer near the south pole of the moon," added Lei Zhang and Chen.
"We plan to simulate the Chang'e-7 seismometer's output and compare this theoretical prediction with real data. Even though Chang'e-7's seismometer lacks the sensitivity to detect gravitational waves, it will provide valuable data that will significantly improve our lunar model and help us better plan the next Chang'e missions and seismometers."
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Publication details
Lei Zhang et al, Thick Lunar Crust Amplifies Deci-Hertz Gravitational-Wave Signals, Physical Review Letters (2026). DOI: 10.1103/d9jf-gxk5.
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Citation: Moon's thick crust could amplify elusive gravitational-wave signals (2026, July 28) retrieved 28 July 2026 from https://phys.org/news/2026-07-moon-thick-crust-amplify-elusive.html
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