Lunar Laser Interferometer Antenna (LILA)

• Laser Interferometer Lunar Antenna (LILA) is a lunar-based facility designed to detect mid-frequency gravitational waves and advance lunar geophysics.
• It employs precision laser interferometry, quantum-enhanced metrology, and advanced seismic isolation to achieve noise levels orders of magnitude lower than Earth-based detectors.
• LILA’s phased mission targets early-warning detection, precise localization of gravitational wave sources, and comprehensive mapping of the Moon’s deep interior.

The Laser Interferometer Lunar Antenna (LILA) is a next-generation gravitational-wave and lunar geophysics facility designed for deployment on the Moon. By leveraging the Moon’s natural ultralow seismic noise environment and high-quality vacuum, LILA targets the mid-frequency gravitational wave band ($0.1 - 10$ Hz), a spectral region inaccessible to terrestrial and existing space-based detectors. The project also aims to advance planetary seismology, enabling detailed investigations of the lunar deep interior through interferometric and seismic measurements. LILA is planned as a collaborative, phased mission, integrating technological innovations in precision laser interferometry and quantum sensing, and structured to leverage commercial and governmental lunar payload infrastructure (Jani et al., 15 Aug 2025).

1. Mission Rationale and Scientific Objectives

LILA’s primary mission is to fill the observational gap in the mid-frequency gravitational-wave band. Presently, ground-based facilities such as LIGO, Virgo, and KAGRA are limited by seismic, Newtonian, and anthropogenic noise below approximately 10 Hz, while the planned space-based LISA mission is optimized for frequencies up to $0.1$ Hz. LILA targets the intermediate window ($0.1-10$ Hz) by operating in the Moon’s ultrastable seismic environment, where the seismic background is, by design, orders of magnitude lower than even the best terrestrial observatories.

Key scientific objectives include:

• Enabling early-warning, high-precision detections of compact binary mergers (e.g., black holes and neutron stars) with angular localization at the level of $\sim 1~$arcmin$^2$.
• Facilitating multi-messenger astrophysics by permitting mid-band GW detections contemporaneous and synergistic with terrestrial and space-based instruments.
• Measuring the normal modes of the Moon to an unprecedented degree, reconstructing its three-dimensional internal structure, and advancing geophysical models.
• Testing general relativity, probing alternative theories of gravity, and searching for signatures of dark matter (e.g., ultralight fields surrounding compact objects).

2. Technological Architecture and Innovations

LILA’s design incorporates several core technological advances:

• Precision laser interferometry implemented on the lunar surface, exploiting the natural vacuum and absence of atmospheric and anthropogenic perturbations.
• Optical readout schemes with nanometric precision, coupled with lunar-adapted low-noise seismometers and retroreflectors.
• Advanced seismic isolation, including suspended test masses, anti-spring arrays, and active compensation, especially in the long-term LILA-Horizon phase.
• Quantum-enhanced metrology, such as the proposed “GravComb” laser frequency comb sensor, which extends sensitivity further into the mid-frequency regime.

The baseline architecture envisions a network of lunar stations connected via long-arm interferometers (3–5 km for LILA-Pioneer; $\sim$40 km for LILA-Horizon), with a modular deployment strategy compatible with lunar surface transportation and assembly constraints (Jani et al., 15 Aug 2025).

3. Observational Capabilities and Sensitivity Regime

LILA is tailored to maximize sensitivity in the $0.1-10$ Hz band, a range unachievable for any current or planned terrestrial or space-based GW observatory. The principal factors enabling this sensitivity include:

• The absence of atmospheric pressure and wind noise, which on Earth require extreme vacuum engineering but are naturally provided on the Moon.
• Seismic quietude: lunar seismic background is lower by $\gtrsim 2-3$ orders of magnitude than at terrestrial observatories, as evidenced by Apollo seismometry and recent modeling.
• Reduced Newtonian noise, owing to the lack of fluid oceans, atmosphere, and environmental activity.

Although the sensitivity curve is not provided explicitly in the primary data, the fundamental relation governing strain sensitivity is $h(f) \propto (S_n(f))^{1/2}$, where $S_n(f)$ is the noise spectral density. On the Moon, the instrumental and environmental $S_n(f)$ can be significantly lower in the target band than Earth-bound systems.

Capabilities include:

• Detection and localization of GW sources previously unobservable in the mid-band, such as intermediate-mass black hole mergers and inspirals.
• Early warning and enhanced sky localization for binary coalescences observed by terrestrial detectors, directly enhancing multi-messenger follow-up.

4. Lunar Science and Geophysical Measurements

Beyond fundamental physics, LILA integrates comprehensive lunar science, utilizing its infrastructure for high-precision seismology:

• Measurement of the Moon’s normal modes, including those sensitive to the inner core, core–mantle boundaries, and mantle structure.
• The inference of three-dimensional density, compositional, and temperature gradients, illuminating the Moon’s differentiation, evolution, and present-day thermal state.
• Geodetic and rotational studies through integration with retroreflectors and laser ranging, offering superior reference frame fidelity.

These geophysical investigations simultaneously validate LILA’s GW measurement fidelity (by enabling accurate calibration of environmental effects) and advance comparative planetology.

5. Phased Development and Implementation Strategy

The LILA mission is structured around a phased deployment, aligning with the Commercial Lunar Payload Services (CLPS) and Artemis architectural timelines:

• LILA-Pioneer: The initial phase, deploying a 3–5 km interferometer with a primary focus on establishing mid-band GW sensitivity and verifying lunar normal mode detection. This stage leverages current robotic lander capabilities for site delivery and initial assembly.
• LILA-Horizon: The scalable, long-term vision with a 40 km triangular (three-station) array, expanded sensor sets (including quantum-enhanced readout), and enhanced seismic isolation. This phase anticipates astronaut assistance for large-scale assembly and occasional maintenance.

Deployment design emphasizes compatibility with robotic pre-positioning of components, modularity, and environmental hardening.

6. Collaboration and Institutional Structure

LILA is a broadly collaborative enterprise, uniting:

• U.S. governmental laboratories with space instrument development heritage.
• University research teams engaged in GW astrophysics, planetary geoscience, and precision metrology.
• Commercial space industries, particularly in the context of lunar transportation and payload delivery services.
• International scientists providing complementary expertise in instrument design, lunar science, and theoretical physics.

This institutional structure is essential for cross-disciplinary advances and for ensuring the scientific and technical breadth necessary for such a complex lunar facility (Jani et al., 15 Aug 2025).

7. Impact and Future Prospects

LILA’s anticipated impact includes:

• Establishing crucial observational continuity in the global GW detector network, enabling multi-band, multi-messenger astronomy and high-precision cosmological parameter estimation.
• Providing early-warning and precise localization for GW transients, critical for the next generation of electromagnetic and neutrino follow-up campaigns.
• Delivering the highest-fidelity measurements of a planetary deep interior to date, advancing comparative planetology and lunar exploration.

A plausible implication is that LILA’s comprehensive dataset will drive both fundamental physics (e.g., constraining alternative gravity theories and the Hubble parameter) and operational lunar exploration (e.g., improving reference frames for navigation).

This combination of breakthrough astrophysical, cosmological, and planetary science capabilities is uniquely enabled by the lunar environment and the collaborative, modular structure of the LILA mission (Jani et al., 15 Aug 2025).