ARIA (Askaryan Regolith Imaging Array): An Instrument Concept for Novel Radio Frequency Characterization of Planetary Subsurfaces

Planetary bodies can be affected by a number of geologic processes, including impacts, volcanism, volatile deposition, mass wasting, and weathering. Local stratigraphic sequences record the effects of these processes like a time capsule, revealing how geologic processes have shaped the site through time. Many geologic processes leave their fingerprints within the stratigraphy on many meters to decameters scales. While most remote sensing techniques are sensitive only to surface materials at the shallowest (µm to m) depth scales, radio frequencies (RF) are well poised for geologic characterization of planetary bodies at these deeper scales, providing insight on regolith thickness, subsurface deposits, and geologic chronology.Ground penetrating radar (GPR) sounding is a non-invasive geophysical technique often employed to sense the subsurface that has been used on Earth, the Moon (the Chang’E 3 and 4 Yutu rovers’ Lunar Penetrating Radars, and the orbital Kaguya Lunar Radar Sounder), and Mars (the Mars Perseverance Rover’s RIMFAX, Mars Reconnaissance Orbiter’s SHARAD, and Mars Express’ MARSIS instruments), with Europa Clipper’s REASON instrument currently en route to Europa. Collecting GPR data, however, requires lateral translation of the antenna(s) to build up a 2D profile of the subsurface, adding risk and operational complexity. Additionally, a major challenge in interpreting traditional 2D GPR data is subsurface “clutter,” signals returned at the same time as subsurface targets of interest which disguise signals from the target.Here, we present a surface-deployed RF instrument concept under development, which we call ARIA (the Askaryan Regolith Imaging Array) (Fig.1). ARIA features a dual-polarization, bistatic antenna array that measures full Stokes parameters and applies interferometric techniques that have never before been used for planetary radar, providing an unprecedented opportunity for 3D subsurface imaging at a landing site — all while stationary. ARIA utilizes a unique combination of traditional and cutting-edge RF techniques, including: active GPR, bistatic radar methods that capitalize on cosmic rays as a natural RF source, and passive radiometry for temperature profiling.ARIA’s active radar system features a circularly-polarized transmit antenna that measures regolith properties, buried geologic units, and rocks embedded in the subsurface through the spectral, temporal, and polarimetric characteristics of radio signals received at 250–750 MHz using dual-polarized sinuous antennas, employed as a beamforming array to provide both lateral and depth resolution.ARIA’s passive bistatic radar observes radio emission from cosmic ray cascades within the regolith, which illuminate an extended radius surrounding the antenna array. These relativistic particle cascades create highly impulsive, 100% linearly-polarized radio emission via the Askaryan effect (Saltzberg et al. 2001), a well-known and studied electrodynamic process in high energy physics, which has not previously been exploited for planetary science.ARIA can also operate as a passive radiometer, measuring the RF spectra from 250 MHz out to 1500 MHz. Different frequencies are sensitive to temperatures at different depths, which can be exploited to constrain geothermal gradient (Siegler et al. 2023; Brown et al. 2023). ARIA would use its radiometric measurements in concert with independent constraints on dielectric properties from its other RF techniques to help pioneer a technique for measuring geothermal heat flux without the need to drill.With ARIA, we can address many outstanding questions in lunar and planetary science, such as:Are there subsurface deposits of ice in the cold polar regions of the Moon? What is the thickness of the regolith at a given landing site, and what is the nature of the regolith-megaregolith contact? Are there buried impact ejecta or melt deposits present in the subsurface, illuminating the chronology of impact processes that have occurred in that region? How thick are individual volcanic units, what are the stratigraphic relationships between them, and how do these units vary laterally? What is the geothermal heat flux at a given landing site? Figure 1: An implementation of ARIA depicted on the lunar surface.Cosmic ray RF sounding was recently recognized in a report (CLOC-SAT, 2022) commissioned by the Lunar Exploration and Analysis Group. We can use the cosmic ray spectrum and radio emission properties to cross-calibrate the active GPR results. Using ARIA’s beamforming methods, we are able to map cosmic ray events to their reflection points, and ultimately back to the shower vertex. From the cosmic ray methodology, we can directly measure dielectric parameters of the regolith and subsurface interfaces, a capability not possible with traditional GPR, which must assume a dielectric constant to infer a given target’s depth. This methodology has been demonstrated by the NASA-funded Antarctic Impulsive Transient Antenna (ANITA) stratospheric balloon payloads (Gorham et al. 2009), and was used to measure Antarctic ice properties (e.g., Prohira et al. 2018). ARIA would be the first extension of this cosmic ray methodology beyond Earth. While here we focus on deployment of the ARIA instrument on the lunar surface, simulations by Costello et al. (2025) show that cosmic ray-induced RF showers could be detectable from a sensor deployed in orbit. Tai Udovicic et al. (2025) suggest hundreds of events should be observable from the Moon’s permanently shadowed regions during a 2-year mission with the Cosmic Ray Lunar Sounder (CoRaLS) detector in an LRO-like orbit. Simulations also show that utilizing RF pulses generated by the Askaryan Effect yield capabilities for sensing subsurface layers thinner than that detectable by more traditional radar sounding or synthetic aperture radar methods. Additionally, ARIA can be integrated with other instrumentation (e.g., a seismometer suite) for comprehensive and complementary investigations (Bramson et al. 2023). Lastly, while the Moon is a logical location to employ an instrument like ARIA, the utility of this RF instrumentation could be realized for many applications across the Solar System (Prechelt et al. 2022). References:Bramson et al. (2023) 54th LPSC, Abstract #1797,https://www.hou.usra.edu/meetings/lpsc2023/pdf/1797.pdf.Brown et al. (2023) JGR-Planets, https://doi.org/10.1029/2022JE007609.Costello et al. (2025) GRL, https://doi.org/10.1029/2024GL113304.Gorham et al. (2009) Astroparticle Physics, https://doi.org/10.1016/j.astropartphys.2009.05.003.Greenhagen, Pieters, Glotch, and the CLOC-SAT Specific Action Team (2022). Continuous Lunar Orbital Capabilities Specific Action Team Report. Lunar Exploration Analysis Group.Prechelt et al. (2022) arXiv:astro-ph.EP, https://doi.org/10.48550/arXiv.2212.07689.Prohira et al. (2018) Phys. Rev. D, https://doi.org/10.1103/PhysRevD.98.042004.Saltzberg et al. (2001) Phys. Rev. Lett., https://doi.org/10.1103/PhysRevLett.86.2802.Siegler et al. (2023) Nature, https://doi.org/10.1038/s41586-023-06183-5.Tai Udovicic et al. (2025) 56th LPSC, Abstract #2860,https://www.hou.usra.edu/meetings/lpsc2025/pdf/2860.pdf.