Silicon nanowires (SiNWs) are known to exhibit a large piezoresistance (PZR) effect, making them suitable for various sensing applications. Here, we report the results of a PZR investigation on randomly distributed and interconnected vertical silicon nanowire arrays as a pressure sensor. The samples were produced from p-type (100) Si wafers using a silver catalyzed top-down etching process. The piezoresistance response of these SiNW arrays was analyzed by measuring their I-V characteristics under applied uniaxial as well as isostatic pressure. The interconnected SiNWs exhibit increased mechanical stability in comparison with separated or periodic nanowires. The repeatability of the fabrication process and statistical distribution of measurements were also tested on several samples from different batches. A sensing resolution down to roughly 1$\mathrm{m}$ pressure was observed with uniaxial force application, and more than two orders of magnitude resistance variation were determined for isostatic pressure below atmospheric pressure.

Silicon nanowires (SiNWs) are known to exhibit large piezoresistance (PZR) effect, making it suitable for various sensing applications. Here, we report the results of a PZR investigation on randomly distributed and interconnected vertical silicon nanowire arrays as a pressure sensor. The samples were produced from p-type (100) Si wafers using a silver catalysed top-down etching process. The piezoresistance response of these SiNW arrays was analysed by measuring their I-V characteristics under applied uniaxial as well as isostatic pressure. The interconnected SiNWs exhibit increased mechanical stability in comparison with separated or periodic nanowires. The repeatability of the fabrication process and statistical distribution of measurements were also tested on several samples from different batches. A sensing resolution down to roughly \SI{1}{\milli\bar} pressure was observed with uniaxial force application, and more than two orders of magnitude resistance variation was determined for isostatic pressure below atmospheric pressure.

The use of astronomical radio sources has been demonstrated for sounding and echo detection using quiescent solar emissions in VHF (300 MHz). Here, we present the first demonstration of using Jovian HF radio bursts (25 MHz) to detect a reflection off the hills of Dante’s View in Death Valley, California.Solar emissions are governed by blackbody radiation, which at HF is not resolvable from the galactic background noise. In contrast, Jovian bursts are governed by the interaction of Jupiter’s magnetosphere and Io’s magnetic field, which produces a significantly stronger and detectable HF emission on Earth, Mars, and Europa. While this mechanism is not continuous, it is highly predictable, as the orbital parameters of Jupiter System III central meridian longitude and Io’s orbital phase dictate the probability of a burst occurring.As part of the Passive Autonomy, Navigation, Topography, and Habitability Exploration Radar (PANTHER), our system setup uses an HF dipole antenna and software-defined radio (Ettus X310 TwinRX) to receive radio signals at a 25 MHz center frequency with a 20 MHz bandwidth. The expectation of the experiment was to observe the reflection of a Jovian burst from Badwater Basin, which behaves like a flat specular reflector. However, during the field demonstration, the timing of the bursts—combined with Jupiter’s elevation angle and viewing geometry from Dante’s View—did not produce a basin reflection. Instead, this experiment required a more complex geometric analysis and signal processing to determine a reflection point on the hillside of Dante’s View. We emphasize that demonstrations using Jovian bursts thus require additional geometric and timing constraints that were not required for prior passive sounding experiments using continuous quiescent solar emissions. In addition to predicting the burst windows, this technique requires selecting an antenna location that provides favorable reflection geometry.Our results provide the first demonstration of a Jovian radio burst as an HF source for passive radar echo detection, which is the first step towards a low-resource passive HF system that uses Jovian bursts for future planetary sounding missions. Building on this first demonstration, PANTHER aims to utilize the benefits of the HF signal and its lower attenuation coefficient to sound geologic targets in Iceland including glaciers, lava flow fields, and subsurface ice deposits.

Recent work has shown the potential for passive sounding to increase the science return for radar investigations of the icy satellites of Jupiter in a noisy sub-Jovian environment. For example, Schroeder et al. analyzed the active radar link budget during Jovian burst activity (which can exceed the background noise environment by several orders of magnitude) and showed that strong Jovian Decametric radio bursts could severely degrade the detectability of surface and subsurface radar returns [1,2]. Gerekos et al. simulated radargrams for the icy moons of Jupiter and found that active radar sounding was unable to reveal surface features for key target areas in the presence of noise at the expected Jovian burst flux densities, whereas passive radar processing was still able to recover the surface reflections using both modeled and observed Jovian noise signals [3]. Peters et al. further demonstrated the potential for passive synthetic aperture radar (SAR) imaging using radio-astronomical sources to recover surface topography [4]. The Radar for Icy Moon Exploration (RIME) or Radar for Europa Assessment and Sounding: Ocean to Near- surface (REASON) could be potential candidates for the addition of a passive sounding mode that complements active radar techniques in the presence of strong Jovian Decametric radio bursts [1,2]; however, this proposed technique had never been experimentally demonstrated. Astronomical radio sources have been tested on Earth as sources for sounding and echo detection using the passive radar approach, by using the quiescent solar emissions in VHF (300 MHz) [5] as well as Jovian radio bursts in the HF band (25MHz) [6]. These sources are one of the strongest in the sky in their respective bands. The Sun’s flux increases with frequency following blackbody radiation curve and approaches the magnitude of the diffused galactic background around 300MHz [5]. The Jovian bursts however are mainly due to the interaction of Jupiter’s magnetosphere and Io‘s magnetic field, which creates a strong radio burst centered around 25MHz [7]. While this mechanism indicates that Jovian bursts are not continuous like solar emissions, they are predictable based on 26 years of observations. Recent work has shown that there exists a clear combination pattern of Io’s phase and Jupiter’s system III central meridian longitude (CML) facing observer, which offers a way to forecast opportunity windows of highest burst probability and activity [8].The Passive Autonomy, Navigation, Topography, and Habitability Exploration Radar (PANTHER) project utilizes both sources by capturing their emissions using the Ettus X310 + TwinRX software defined radio (SDR). The wide instantaneous bandwidth and usable range of receiver center frequencies allows us to rapidly test both passive sounding configurations. In the spring of 2025, the PANTHER team went to the hills of Dante’s view to experimentally demonstrate the predictability of Jovian bursts using the hardware mentioned prior to it being integrated and operated off AC powered power station. The results showed a significant increase across the received power spectrum (15-35MHz) during the predicted Jovian burst activity window, and the autocorrelation of the received signals showed a strong echo peak in the range profile. This result served as the first experimental demonstration of using the Jovian radio burst as a predictable illumination source in HF band [6] The PANTHER team has now scheduled its first extensive field-testing campaign during the summer 2026 in the Icelandic volcanic and glacier environment, which will focus on the radar sounding of buried ice [9], glacier structures [10], in addition to water lava contacts at the Holuhraun lava flow [11]. At these field sites, passive sounding using radio-astronomical sources will be tested, as well as validated with a commercial GPR, to identify the technique’s limits and potential for future applications. Passive sounding is a promising approach for geological monitoring on Earth and in future planetary exploration missions.Acknowledgments: The PANTHER project was funded by the National Aeronautics and Space Administration (NASA) through PSTAR grant No. 80NSSC24K1261. A portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.[1] D. M. Schroeder et al., Planetary and Space Science, 2016[2] A. Romero-Wolf et al., Icarus, 2015 [3] C. Gerekos et al., IEEE Transactions on Geoscience and Remote Sensing, 2020[4] S. T. Peters et al., IEEE Transactions on Geoscience and Remote Sensing, 2021[5] S. T. Peters et al., IEEE Transactions on Geoscience and Remote Sensing, 2018[6] T. H. Kristinsson et al., EGU General Assembly 2026[7] P. Zarka et al., Journal of Geophysical Research (Space Physics), 2004[8] M. S. Marques et al., AA, 2017 [9] E. S. Shoemaker Thackston et al., Journal of Geophysical Research: Planets, 2024[10] H. Björnsson H, Annals of Glaciology. 2020 [11] C. M. Dundas et al., Journal of Volcanology and Geothermal Research, 202