Molecules are emerging as new benchmark for metrology and fundamental physics research, driving the demand for spectroscopic techniques combining high sensitivity and resolution. Photoacoustic spectroscopy has proven to combine high sensitivity with appealing features like compactness, wavelength-independent and background-free detection. To date, photoacoustic sensing has mostly been focused on atmospheric applied trace-gas analysis, while accessing the low-pressure regime has been considered not compatible with efficient acoustic wave propagation. However, sensing gas samples at low pressure is the key to get access to high-resolution spectroscopy. Here, we demonstrate that sub-Doppler saturation spectroscopy can be performed on low-pressure trace gases in a cavity-enhanced photoacoustic sensor with mW-level mid-infrared radiation. Moreover, we show that the same setup can be operated at higher pressure, enabling trace-gas detection with 5parts-per-billion sensitivity at an integration time of 10s and with a laser power as low as 35µW. This allows to extend the unique advantages of the photoacoustic technique to metrology and fundamental physics, thus combining the high resolution typical of setups operating at shorter wavelengths with the high sensitivity enabled by the strong fundamental rovibrational transitions lying in the mid-infrared spectral range.
Analyses of the Martian surface suggest the existence of sedimentary lacustrine deposits that may have once harboured life. Lake Bagno dell’Acqua (Pantelleria, Italy) represents an optimal planetary field analogue for investigating the evolution and adaptation of life in Mars-like environments and for validating potential life-detection strategies. Accordingly, we characterised microbial communities and volatile organic compound profiles in actively growing organosedimentary structures within lake sediments and in biofilm covering hot springs at the lake margins. The microbial communities exhibited low taxonomic diversity and were dominated by a few extremophilic and extremotolerant taxa. Only a marginal difference in community composition was detected between sediment and biofilm samples; however, high variability was reported among the sampling sites and the replicates of each site. An exploratory volatile compound profiling revealed the presence of numerous terpenes, with small variability among sampling sites. The specialized assemblages detected in the Bagno dell’Acqua environment indicate that similar consortia could have adapted to analogous settings on ancient Mars. Patterns identified in these communities may serve as biosignatures, including redox imbalances generated by organisms driving oxidation-reduction processes. Moreover, pronounced fine-scale heterogeneity provides valuable insights into life-detection strategies in comparable extraterrestrial environments. The abundance of terpenes, ancient, widely distributed biomolecules across all domains of life, indicates that similar molecular adaptations may likewise have arisen in similar environments elsewhere. If preserved, these volatiles could represent promising biosignatures in clay-rich lacustrine sediments, such as those that were widespread on Noachian Mars and are abundant in the sediments of Lake Bagno dell’Acqua.
The Compton Spectrometer and Imager (COSI) is a Compton telescope designed to survey the 0.2–5 MeV sky, consisting of a compact array of cross-strip germanium detectors. It is planned to be launched in 2027 into an equatorial low-Earth (530 km) orbit with a prime mission duration of 2 yr. The observation of MeV gamma rays is dominated by background. Thus, background simulation and identification are crucial for predicting the sensitivities of instruments. In this work we perform Monte Carlo simulations of the background for the first 3 months in orbit, and we extrapolate the results to 2 yr in orbit in order to determine the buildup of the activation due to long-lived isotopes. The simulations account for the known background components and include time-dependent rate variations due to the geomagnetic cutoff and South Atlantic Anomaly (SAA) passages. In addition, they include detailed modeling of the delayed activation due to short- and long-lived isotopes. We determine the rates of events induced by the background that are reconstructed as Compton events in the simulated COSI data. We find that the extragalactic background photons dominate at low energies (<660 keV), while delayed activation from cosmic-ray primaries (proton/alpha) and albedo photons dominate at higher energies. As part of this work, a comparison at low latitude (∣ b ∣ ≤ 1°) between recent measurement of the SAA and the AP9/AE9 model has been made, showing an overestimation of the flux by a factor ∼9 by the model. The systematic uncertainties associated with these components are quantified.
This paper addresses the characterization of the subsonic flow in the 1.2 MW Inductively Coupled Plasma (ICP) wind tunnel at the von Karman Institute for Fluid Dynamics (VKI), targeting chamber pressures of 50 and 100 mbar, and input electric powers between 150 and 300 kW. Ultraviolet to near-infrared optical emission spectroscopy measurements of the free-jet flow are carried out with an updated experimental set-up, calibration procedure, and data processing, providing high-quality absolute spatially-resolved emission spectra. Emission measurements agree with thermochemical equilibrium predictions within a range of conditions, allowing to extract experimental maps of cold-wall heat flux and dynamic pressure against the inferred free-jet enthalpy. A detailed comparison with the characterization methodology traditionally employed is presented, highlighting the need for an improved modeling strategy. Using the measured free-jet temperature and dynamic pressure only, a forward procedure for the computation of the stagnation line flow is proposed. The latter agrees with intrusive heat flux measurements through a range of test conditions, and for values of the recombination coefficient of the reference copper probe commonly found in the literature. Results demonstrate that a consistent framework between numerical simulations and experimental data can be achieved, defining an improved method for the characterization of subsonic ICP jets.
VISTA (Volatile In-Situ Thermogravimeter Analyzer) is a QCM (Quartz Crystal Microbalance) based device designed to characterize the dust environment of the Didymos asteroid system by detecting the presence of dust particles with sizes smaller than 5-10 μ m and sub- μ m, as well as volatiles and light organics, within the framework of the European Space Agency (ESA) Hera Mission. Thanks to its customized subsystems design, VISTA is capable of monitoring deposition and desorption/sublimation processes in the space environment, as well as molecular contamination (in support to other instruments) originating from outgassing sources during different mission phases, and of performing Thermo-Gravimetric Analysis (TGA) on the collected materials. The VISTA Model development for Hera started in 2020 and continued through 2023, and included an Engineering Qualification Model 0 (EM0), an Engineering Qualification Model (EQM), a Flight Model (FM) and a Flight Spare (FS). The EM0 was electrically and mechanically representative of VISTA, while the EQM, FM and FS share the same mechanical structure and electrical connections. The prototype, as well as the Engineering, Flight and Spare Models, were delivered to the prime contractor, Tyvak International. VISTA Models are composed by three different subsystems: two quartz crystals mounted in a sandwich-like configuration; the Proximity Electronics; and the Thermal Control System, which includes two integrated and customized heaters and a Thermo-Electric Cooler to cool the sensor and facilitate dust and volatiles deposition. The VISTA EQM, FM and FS successfully passed the Qualification and Acceptance Test Campaigns. The main results obtained from simulations of particles and volatiles deposition in a vacuum chamber, heating cycles, and Thermo-Gravimetric Analyses are reported in this work.
