HIGHLIGHTS

Our mapping area is 100x larger than previous studies of these regions.

91% of these ridge networks are confined to ancient Noachian terrain.

Most ridge networks are present on relatively flat areas.

Groundwater processes might be widespread across Noachian terrain.

Recent evidence of exposed H₂O ice on Mars suggests that this ice was deposited as dusty (<~1% dust) snow. This dusty snow is thought to have been deposited and subsequently buried over the last few million years. On Earth, freshly fallen snow metamorphoses with time into firn and, if deep enough, into glacier ice. While spectral measurements of martian ice have been made, no model of the spectral albedo of dusty martian firn or glacier ice exists at present. Accounting for dust and snow metamorphism is important because both factors reduce the albedo of snow and ice by large amounts. However, the dust content and physical properties of martian H₂O ice are poorly constrained. Here, we present a model of the spectral albedo of H₂O snow and ice on Mars, which is based on validated terrestrial models. We find that small amounts (<1%) of martian dust can lower the albedo of H₂O ice at visible wavelengths from ~1.0 to ~0.1. Additionally, our model indicates that dusty (>0.01% dust) firn and glacier ice have a lower albedo than pure dust, making them difficult to distinguish in visible or near-infrared images commonly used to detect H₂O ice on Mars. Observations of excess ice at the Phoenix landing site are matched by 350-μm snow grains with 0.015% dust, indicating that the snow has not yet metamorphosed into glacier ice. Our model results can be used to characterize orbital observations of martian H₂O ice and refine climate-model predictions of ice stability.

We expand on previous studies of the South Polar Layered Deposits' (SPLD) basal interface using data acquired by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) to obtain detailed maps of elevation, topography, and reflected radar power. Using these maps, we derive the thickness (ranging from 0 to 3.7 km) and volume of the SPLD (~1.60 x 10⁶ km³). While most basal interfaces reflect less power than the average SPLD surface, areas with basal echo power exceeding that of the surface are widespread throughout the SPLD, including at the location of potential subglacial water bodies in Ultimi Scopuli. The occurrence of these high basal echo power signatures appears to be largely frequency independent in MARSIS data. While the cause of the relatively high basal echo power values is uncertain, our observations suggest that this behavior is widespread, and not unique to Ultimi Scopuli.

KEY POINTS

CO₂ frost is detected at all latitudes, and near the equator it is largely restricted to low thermal inertia regions

Small amounts of H₂O frost can form at most latitudes during the night, but are difficult to detect with current instrumentation at Mars

47% of all gullies overlap with CO₂ frost detections but present-day activity appears to occur in loose, unconsolidated materials

Midlatitude slopes on Mars are mantled by deposits proposed to contain H₂O ice and dust, overlaid by a desiccated lag. However, direct evidence of their volatile content is lacking. Here we present novel evidence of light-toned materials within midlatitude gully alcoves eroded into these mantles. The appearance and Lambert albedo of these materials suggests that they are either dust or H₂O ice. We interpret them to be H₂O ice because it is unlikely for a short-term, localized dust deposit to form only within the mantle walls. The temperatures are generally too warm (>~240 K) for the ice to be a frost in equilibrium. Therefore, this ice is likely similar to the dusty ice documented within midlatitude scarps, but with more dust, and exposed in smaller patches by slumping. It has been proposed that CO₂ frosts remove the overlying lag, causing the exposed H₂O ice to sublimate, liberate dust within the ice for transport, and erode gullies in the mantle. But we observe gullies eroded in wall rock that continue into the mantle, implying that the same process erodes both substrates. H₂O ice melt can explain gullies eroded in the wall rock and the mantle. Numerical models show that relatively dense H₂O snow on Mars melts only when it contains small amounts of dust. The observed exposure of dusty ice provides a mechanism for it to melt under some conditions and form some gullies. Access to liquid water within this ice could provide potential abodes for any extant life.

Pulsed plasma thrusters (PPTs) typically utilize a solid propellant such as
Polytetrafluoroethylene (PTFE) to generate moderate specific impulse at the low-power scale. This work discusses the design and development of a multi-axis PPT module with a compact form factor of 0.9U and a maximum mass of ~1 kg, thereby minimizing system volume and mass to enable larger science payloads. The PPT has eight thrusters integrated into a single thruster module to allow for multi-axis control, a key feature not currently available in any COTS (commercial, off-the shelf) PPT. Copper-tungsten alloys and molybdenum, both of which have been shown to have relatively low electrode erosion rates, will be used for the PPT design’s electrodes. Analytical results have shown that the multi-axis PPT configuration enables fine pointing, which can allow for precise scientific measurements of targets in deep space, as well as the potential to enable formation flying missions. Additionally, the PPT can also be used for station keeping, deorbiting and reaction-wheel momentum dumping with a predicted minimum specific impulse of 1000s and a minimum impulse bit of 100 μN.