Planetary surfaces

Abstract:

Methane (CH4) on Mars is of high scientific importance, particularly for its generation and destruction mechanisms. With an estimated photochemical lifetime of approximately 300 years, sporadic methane plumes observed on Mars by orbital, landed missions, and Earth-based telescopes suggest the presence of unknown destruction processes. Here, we present an experiment to examine CH4 destruction through heterogeneous electrochemistry (HEC) triggered by Martian dust activities. We performed a series of mid-strength electrostatic discharge (ESD) experiments in mixtures of CO2 and CH4 under conditions relevant to the Martian near-surface atmosphere. We characterized (1) the free radicals produced from the breakdown of CH4 and CO2; (2) the gaseous and solid products of CH4 and CO2 decomposition; and (3) the half-life of CH4 in this experiment. Based on a newly reported mission observation of electric discharge during a dust devil (DD) on Mars, we extrapolated the experimentally derived half-life to an approximate dust-devil-effective half-life of CH4 on Mars, with uncertainties spanning orders of magnitude. The result demonstrates that dust-driven HEC can cause CH4 destruction at rates hundreds to thousands of times faster than photochemistry. In future missions to Mars, if the knowledge gaps in the E-properties of dust activity are filled through regular measurements, this experimental finding may imply that Martian dust activity could be the primary factor reducing methane's lifetime, thereby contributing to understanding methane loss in the Martian atmosphere.

Abstract:

The modern world is increasingly computerised and, as more functionality is shifted to the edges of systems in bids to reduce latency or energy consumption, the Internet of Things (IoT) increasingly includes safety-critical systems. A typical such system is 'functionally dense,' with a time-shared processing element (PE) carrying out many tasks; we believe that they should instead be functionally sparse, with many small PEs dedicated to single tasks. We present case studies of this design approach and introduce FUNK, our effort to build the tools that will support the development of hard real-time, functionally safe systems that follow this approach.

Abstract:

Abstract We investigate the diurnal temperature variations of Europa’s surface using brightness temperatures taken by Galileo’s Photopolarimeter-Radiometer (PPR) instrument. Diurnal curves created from these data are compared to those predicted by a thermophysical model to determine what thermal inertias and Bond albedos can fit the data within a reduced chi-squared cutoff of $\chi _{\textrm {red}}^2\le 1.0$. This analysis is used to extensively quantify the uncertainty for the first time of the two thermophysical parameters derived from PPR. We map the albedo and thermal inertia for 33% and 24% of Europa’s surface area, respectively. We find a range of 0.375-0.75 for albedo and 20-110 J m−2 K−1 s−1/2 for thermal inertia. Our uncertainty analysis indicates well-constrained estimates for albedo, while upper limits for thermal inertia remain poorly constrained. When averaged across nine geological areas, albedo varies as expected: lower values are obtained for darker regions in visible wavelengths. Thermal inertia appears to vary independently from geological boundaries. The surface was also divided based on electron bombardment energy flux and non-ice composition fraction. Thermal inertia behaves opposite of what is expected: lower thermal inertias are located in regions of high-energy electron bombardment. This possibly indicates a mechanism competing with electron-induced sintering is present that is lowering the surface conductivity. No endogenic anomalies were detected that could not be explained by passive emission alone. Nevertheless, these results aid in preparing for future thermal measurements from Europa Clipper and Juice by improving the surface coverage of Europa’s passive thermal properties and providing uncertainties of their values.

Abstract:

Thermal measurements provide key constraints on the physical properties of icy satellite surfaces. On Europa, previous analyses of the Galileo Photopolarimeter-Radiometer (PPR) dataset revealed heterogeneities in thermal inertia, but the limited spatial resolution prevented a detailed thermophysical characterization. We derive high-resolution maps of the Europa surface albedo and thermal inertia and infer the microphysical properties of its icy regolith from a reanalysis of the Galileo PPR dataset by discussing the processes controlling its thermophysical evolution. We used the KRC thermal model (K refers to the conductivity ąppa, R to the density ̊ho, and C to the specific heat C) to analyze the PPR brightness temperatures and retrieve the albedo and thermal inertia. These values were then interpreted using conductivity models of porous ice to constrain the grain size and porosity. We derived a mean Bond albedo of 0.64 ± 0.06 and a mean thermal inertia of 56 ± 17 J m -2 $ K^-1 s^-1/2 (1σ). The thermal inertia shows significant spatial variations, with a low-inertia equatorial band (39 ± 7) and higher values at mid-latitudes on the leading hemisphere (56 ± 11). The trailing-hemisphere equator also exhibits higher thermal inertia (63 ± 17), likely related to compositional differences. Conductivity models indicate a porous icy regolith with grain sizes ranging from a few micrometers to a few centimeters and an average porosity of $0.61 ± 0.1 in the upper centimeters of the Europa surface. The thermal inertia distribution shows little correlation with geological units. Its agreement with modeled magnetospheric ion fluxes instead suggests that sputtering-driven sintering plays a fundamental role in shaping the thermophysical properties of Europa. The absence of a high-inertia equatorial band analogous to the PacMan anomaly on the icy moons of Saturn indicates inefficient electron-driven sintering, while temperature-gradient metamorphism might enhance grain growth at depth. The modeled surface temperatures range between ∼ 67 and 148 K at mid to low latitudes, with peak daytime values counteracting radiolytic amorphization while limiting volatile stability.

Abstract:

Abstract Unexpectedly following launch, the Lunar Trailblazer mission experienced software anomalies that led it to orient solar panels away from the sun and lose communication with Earth. This paper describes efforts to determine the spacecraft state and attempt recovery of the mission's science at the Moon. First, ground observatories at optical and radar wavelengths were engaged to maintain custody of the spacecraft and knowledge of its trajectory. Second, viability of recovery of the mission science objectives was established via testbed work to understand system behavior in fault conditions and determination of trajectories and maneuvers that would enable lunar orbit insertion. Third, optical photometry and radar doppler broadening were employed to determine Lunar Trailblazer's spin and orientation, using approaches similar to those in asteroid studies, to establish when solar panels might again receive sufficient power to boot the spacecraft and initialize its radio. Fourth, X‐band‐capable groundstations in addition to the NASA Deep Space Network were engaged to monitor for the spacecraft's radio carrier signal nearly continually, including crowd‐sourced monitoring and tip‐and‐cue style commanding. Lunar Trailblazer left the Earth‐Moon system and is in a 14‐year Earth return, heliocentric orbit. As it moved further away from Earth prospects for recovery became formidable; ultimately, the ability of the telecom system to return telemetry to Earth would have been insufficient to enable actions to recover the spacecraft, and the recovery attempt ended 6 July 2025. Lunar Trailblazer's mission recovery efforts illuminate capabilities in characterizing a 1–3.5 m 3 size non‐cooperative object in cis‐lunar space. Plain Language Summary Lunar Trailblazer is a NASA small satellite mission to study the Moon. Software errors after launch caused the spacecraft to orient solar panels away from the sun and the radio to reinitialize in a state that did not allow commanding or telemetry receipt; having depleted its batteries, it is now in a low power, “browned out” state. This paper describes the Lunar Trailblazer team recovery efforts to reestablish Earth‐spacecraft communication and return to the Moon to achieve the science objectives. The team used ground observatories at optical and radar wavelengths to keep track of the trajectory of the spacecraft, determine its orientation, and compute trajectories for Earth‐Moon system return. Along with power model and testbed data on power use during the boot/initialization sequence, this was used to determine when the spacecraft solar panels could next receive power sufficient to initialize the radio. Ultimately, while enough propellant is in the tanks that could have enabled a return to Earth through calendar year 2025, the inability to receive telemetry due to distance ended recovery attempts. The procedures employed to characterize Lunar Trailblazer's state can be used on other cis‐lunar spacecraft and near‐Earth asteroids. Key Points Over a 130‐day mission recovery attempt, Lunar Trailblazer was a non‐cooperative cis‐lunar object, characterized using Earth ground assets Radar and optical observatory data enabled reconstruction of spacecraft orientation (spin rate, spin pole) and precise long‐term trajectory An ad‐hoc global X‐band ground station network that included crowd‐sourced signal monitoring and tip‐and‐cue style commanding was created