LILA Lunar Interferometer: Fundamental Noises and Gravitational-Wave Sensitivity ✛
Context
Ground-based gravitational-wave detectors such as LIGO and Virgo are limited by seismic noise below ~10 Hz and cannot operate in the millihertz to decihertz range. Space-based antennas like LISA cover millihertz frequencies but leave a gap at decihertz. The lunar surface offers a uniquely quiet seismic environment: background vibrations are orders of magnitude lower than on Earth, and the vacuum eliminates acoustic disturbances. LILA fills the niche between ground-based and space-based detectors, using the Moon as a resonant amplifier at its own modes.
Methods
The authors analyze fundamental noise sources for a suspension-free interferometer on the Moon: thermal noise in the optics (via the fluctuation-dissipation theorem), laser shot noise, and light scattering by dust. The response to gravitational waves is computed in two regimes: inertial (the Moon as a set of free masses) and mechanical (resonant excitation of normal modes). Numerical models of lunar modes and quality factors Q are taken from the literature, with exponential suppression above 0.05 Hz due to scattering in the regolith.
Results
For LILA Pioneer (5 km baseline, 90° angle), the characteristic sensitivity reaches ~$10^{-21}$ at frequencies around 1 mHz, comparable to LISA but with extension into the decihertz range. LILA Horizon (40 km, triangular) improves sensitivity by roughly an order of magnitude. Thermal noise from the optics dominates below ~0.1 Hz, while shot noise dominates above. Resonant amplification of lunar modes boosts the response by up to $10^4$ times at low frequencies. The sensitivity allows detection of intermediate-mass black hole mergers, white dwarf binaries, and possibly the primordial gravitational-wave background.
Implications
LILA fills the gap between LISA and ground-based detectors, opening the decihertz range where signals from intermediate-mass black hole mergers and the early inspiral stages of stellar-mass black holes are expected. Using the Moon as a resonant amplifier is a fundamentally different approach compared to fully suspended ground-based interferometers or free-flying space-based ones. This is the first detailed sensitivity estimate for a suspension-free lunar interferometer that accounts for the Moon's actual modes.
Future development
The next step will be detailed modeling of thermal noise for specific optical components and the development of laser frequency stabilization systems. Electro-optic modulators may be used instead of piezoelectric ones to reduce mechanical losses. Experimental measurement of the lunar seismic background at the landing site is also required. In the long term, LILA Horizon could be expanded into a network of detectors to probe the stochastic background.
Impact
Gravitational-wave astrophysics, lunar geophysics (selenophysics), space technology.
Next steps
Perform numerical modeling of thermal noise for the final optical layout and develop a prototype of a stabilized laser for lunar conditions.
Key open problems
The actual level of the lunar seismic background in the millihertz range remains an open question: there are no direct measurements, and LILA's sensitivity could be limited by unknown local noises. Also unresolved is the precise modeling of the quality factor Q of lunar modes due to uncertainties in the Moon's internal structure.
The knowledge machine's view
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
This paper presents noise and sensitivity estimates for the LILA laser interferometer on the Moon. We consider fundamental noises (thermal, shot, and scattering) and the response to gravitational waves in both inertial and resonant modes. We show that LILA Pioneer (5 km) achieves a sensitivity of ~10^-21 around 1 mHz, while Horizon (40 km) improves it by an order of magnitude, filling the gap between LISA and ground-based detectors.
Where its strength is
The strong point is the detailed account of real lunar modes and their resonant enhancement, which offers a fundamentally new approach to detection in the decihertz band.
Where it could go next
- It might be interesting to compare LILA's sensitivity with proposals for lunar detectors searching for primordial black holes and dark matter; our archive contains related papers that consider exactly such sources in this band.based on: Lunar detector to hear ancient black holes · Laser Interferometers as Detectors of Axion Dark Matter arXiv:2605.11283v1 arXiv:2606.16099
- The resonant enhancement of lunar modes echoes the idea of using Earth and the Moon as a gravitational-wave resonator (Cosmic Tuning Fork); perhaps one should compare the expected responses and noise budgets of the two approaches.based on: Cosmic Tuning Fork: Earth and Moon Resonate with Gravitational Waves arXiv:2605.04110v1
- For LILA Horizon with a 40 km arm length and triangular configuration, one could consider adapting the signal analysis methods developed for LISA, especially in terms of source separation and parameter estimation.based on: Music of the Spheres: How LISA Will Hear Dark Matter's Duet arXiv:2607.08248
Worth trying
- Test LILA's sensitivity to a specific source, the merger of intermediate-mass black holes, using waveforms from the LISA and dark matter paper.
- Check how much the Moon's resonant modes can amplify signals from extremely light black holes, as proposed in the quick review on ancient black holes.
- Compare LILA's expected response with that of Earth as a resonator from the Cosmic Tuning Fork paper to identify optimal frequency windows.
Why this may matter
LILA paves the way to filling a gap in the gravitational-wave spectrum, potentially granting access to new astrophysical and cosmological sources, including primordial black holes and phase transitions in the early Universe.
Nearby works in our archive
- Lunar detector to hear ancient black holessimilarity 0.64
- Laser Interferometers as Detectors of Axion Dark Mattersimilarity 0.55
- New Sensors Open Low Frequencies for Gravitational Wavessimilarity 0.55
- A Laser from the Moon's Eternal Shadowsimilarity 0.55
- The Moon — a Giant Gravitational Bellsimilarity 0.54
- The Moon as a Gravitational Wave Detectorsimilarity 0.53
- Music of the Spheres: How LISA Will Hear Dark Matter's Duetsimilarity 0.53
- Cosmic Tuning Fork: Earth and Moon Resonate with Gravitational Wavessimilarity 0.53
The closest work in the archive sits at 0.64 by meaning — the usual level for our corpus.
Lunar dust, kicked up by micrometeorites, creates scattered light, but its contribution to noise is 5 orders of magnitude below the laser shot noise.
The idea of using the Moon as a gravitational-wave detector echoes Arthur C. Clarke's story "A Fall of Moondust," where the lunar environment is used for scientific purposes, albeit in a different context.
Key numbers
- LILA Pioneer baseline: 5 km
- LILA Horizon baseline: 40 km
- optics temperature: 300 K
- characteristic sensitivity: ~10-21 at 1 mHz
- lunar mode amplification: up to 104 times