We have developed a new global map of shallow ground ice distribution, SWIM23, based on Mars Global Surveyor Thermal Emission Spectrometer data and made systematic comparisons between this new map and two similar, previously developed data products. We have explored the origin of differences between the three ice maps by detailing technical and procedural differences in their development, by making global pixel-by-pixel comparisons, and by carrying out a series of one-dimensional thermal simulations to explore fundamental physical limitations of thermal ice-detection techniques. These efforts and the production of a composite thermal ice-consistency map supported integration of multiple geophysical data products relevant to ice detection in the upper meter of the Martian regolith into the larger Mars Subsurface Water Ice Mapping project. Our work also highlights fundamental physical limitations to thermal ice detection as a technique, particularly the rapid fall-off in ice detection sensitivity at depths >30 cm, which produces maximum uncertainty in the presence and depth of ice within regions preferred for potential human landing sites. A future Mars orbiter mission designed to detect ice and support crewed landing site selection in the midlatitude region should give payload priority to an instrument capable of probing the 1–5 m depth range (i.e., a high-frequency radar), over a next-generation thermal spectrometer, which is unlikely to offer clarity on ice table depths or lateral continuity of the ice table in the locations of highest interest.

An alpine glacier below Sunlight Peak in northwest Wyoming was first photographically documented in 1893, near the end of the Little Ice Age and during the time of industrialization. Since then, evolving technologies have been applied to observe this glacier and nearby discontinuous permafrost for studies spanning Earth, environmental, and planetary sciences. Surveys in the 21st century indicate negative mass balance coinciding with rising average air temperature. This paper reviews the geological and geophysical data on record for the Sunlight Glacier system, presents new results from a 2023 fieldwork campaign combined with remote sensing analysis and comments on likely scenarios of future evolution for this individual body of ice within a broader alpine cryosphere feeding the watersheds of western North America.

Future lunar exploration requires advanced multi-frequency radar sounders capable of mapping geological structures and detecting volatiles. This paper presents the design of a compact, fully-digital radar sounder and the implementation of its demonstrator on the Xilinx ZCU111 Radio Frequency System-on-Chip (RFSoC) platform. Exploiting the device's Direct RF capabilities, we propose a parallelized, multiplier-free digital waveform generation architecture capable of synthesizing coherent Linear Frequency Modulated (LFM) chirps at HF (15, 60 MHz) and VHF (150 MHz) bands without requiring analog up-conversion. The design leverages a parallel Numerically Controlled Oscillator (NCO) approach to bridge the gap between the FPGA clock frequency and the mega sample-per-second RF sampling rates required for wideband operation. Experimental validation via hardware loopback confirms the high quality of the digitally generated LFM waveforms. Furthermore, the pulse compressed output shows the vertical resolution predicted by theory. Finally, the resource utilization table highlights that no DSP slices are used for signal generation, thus preserving significant logic resources for future on-board radar signal processing.

Subsurface water ice deposits on Mars are an important resource for potential future human exploration. They are also an indicator of the planet’s past climate. However, the distribution of subsurface water ice in Mars’s midlatitudes is uncertain because spacecraft imagery cannot directly observe subsurface ice in most cases. Various spacecraft remote sensing instruments are sensitive to subsurface water ice, including thermal imaging spectrometers, radar sounders, and neutron spectrometers. Geomorphic analyses of images can also implicate subsurface ice. Building upon the data products from the Mars Subsurface Water Ice Mapping project, we provide a probabilistic framework to jointly interpret existing data and estimate the likelihood of subsurface water ice in the Martian midlatitudes between 60 ^∘ S and 60 ^∘ N with uncertainty. Broadly, we find that near-surface ice is likely present poleward of ∼45 ^∘ in both the northern and southern hemispheres. However, closer to the equator, existing remote sensing data cannot uniquely constrain the presence of subsurface water ice. Our probabilistic results provide a framework for quantifying the abundance of ice on Mars, and our uncertainty estimates allow future analysis and exploration to target regions of high uncertainty.

The Mars Reconnaissance Orbiter (MRO) is uniquely qualified to meet objectives required by human missions to Mars. Landing site characterization capabilities include imaging for boulders and other terrain difficult for landing and/or driving, understanding soil properties for future construction, and locating resources such as subsurface ice deposits and caves. During the entry, descent, and landing phase, the Ultra High Frequency (UHF) radio can provide real-time data return, while several instruments can provide weather and atmospheric density information. The high-resolution imager can capture photos of a vehicle mid-descent and after touchdown. These capabilities could prove vital for determining the root cause after an anomaly. Once human presence on Mars is established, the UHF radio can provide positioning information, relay data from equipment placed outside of direct communication with the landing site, and serve as a backup voice communication system during extravehicular activities. Other MRO capabilities include creating stereo maps for extravehicular route planning, dust storm prediction and monitoring, atmospheric density measurements for aerobraking, improvement of spacecraft ephemerides to assist with precisely targeted landings, and finding lost hardware in orbit and on the ground. MRO remains healthy and retains sufficient fuel to operate until 2038.

Anomalously bright radar reflections from the base of Mars' south polar cap raise the tantalizing possibility of present‐day liquid water. Orosei et al. (2018, https://doi.org/10.1126/science.aar7268 ) first reported bright subsurface echoes from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) prompting studies of whether the high reflectivity, stems from liquid water or dry scattering interfaces. A key challenge has been the prior inability of the higher‐frequency Shallow Radar (SHARAD) to detect this basal zone, hindering potential diagnostic cross‐frequency comparisons. Due to a novel spacecraft maneuver, SHARAD has now obtained a basal return associated with the putative body of water. Modeling of the radar response is not consistent with the liquid water explanation, instead suggesting a localized, low roughness region of dry rock/dust beneath the ice could explain the SHARAD response. Reconciling the divergent responses of SHARAD and MARSIS remains essential to determine the nature of this anomalous south polar region.

Throughout its mission, the Mars Reconnaissance Orbiter (MRO) has often rolled about its along-track axis by up to 28° to partially compensate for the suboptimal location of the Shallow Radar (SHARAD) antenna along an edge of the spacecraft that is opposite the imaging payload deck, thereby enhancing the signal-to-noise ratio (S/N) of echoes returned from the surface. After recent modeling work predicted that a much larger roll would improve the S/N by ~10 dB relative to nadir-pointed observing, MRO began a limited series of 120° roll maneuvers to test the effects on radar sounding. Three such SHARAD very-large-roll (VLR) observations were acquired between 2023 May and 2024 September, and they show dramatic improvements in signal clarity and depth of penetration, with S/N increasing by 9, 11, and 14 dB over that of nearly coincident observations at 0° roll angle. In low dielectric terrains, the first and second VLR observations enabled basal detections at depths previously unachievable, reaching depths of 800 m in Medusae Fossae materials and 1500 m through the ice of Ultimi Scopuli, respectively. The second VLR observation also obtained enhanced reflections throughout the ice stack. In the higher dielectric terrain of Amazonis Planitia, the third VLR observation improved continuity of a dipping subsurface interface, but it revealed neither an extension of the interface to greater depths nor any deeper interfaces. The MRO mission intends to obtain more SHARAD VLR observations of polar terrains and of midlatitude glacial and ground ices, sediments, and volcanics.

The Shallow Radar (SHARAD) instrument aboard Mars Reconnaissance Orbiter (MRO) has been conducting sounding operations of Mars' near surface for more than 16 years. Results of the SHARAD investigation have been well documented in the literature, with relatively high coverage density in the polar regions leading to some of the earliest scientific discoveries there. Data collection and ensuing surprises of SHARAD's primary and first extended science phases were the impetus for choosing the north polar region for producing a first 3D radar image. This early attempt was successful, producing the first 3D radar image of Mars' north polar layered deposits in Planum Boreum, and shortly thereafter a companion 3D radar image of the south polar layered deposits in Planum Australe. Subsequent work refined the 3D methodology used to produce these images, leading to a significantly higher quality 3D image of the former as well as the first 3D radar image of the debris-covered glaciers in the east-central portion of Deuteronilus Mensae (DM) in the mid-latitudes. Prior experience in terrestrial seismic data processing and analysis methods forms the basis of the 3D methodology used with Martian radar data, and has been indispensable in ongoing efforts to improve this methodology to further clarify the 3D images of the targets. The purposes of this article are to review 1) the SHARAD 3D work history and results, 2) the methodology developed and challenges encountered thus far in producing the SHARAD 3D images, 3) the broader impact on the processing and analysis of SHARAD data, and 4) current efforts and plans for producing follow-on SHARAD 3D images. Similarities and differences between orbital radar and seismic sounding and data processing are sprinkled throughout the article as reminders that the outcomes in this case are very much the product of cross-disciplinary knowledge and experience.

We present an analysis of radar blackouts observed by MARSIS on Mars Express and SHARAD on Mars Reconnaissance Orbiter for the interval 2006 – 2017. The period of interest encompasses the extended solar minimum between solar cycles 23 and 24 as well as the solar maximum of cycle 24. Blackouts have been identified by eye through scanning daily plots of the surface reflection for both radars. A blackout occurs when, for no apparent instrumental reason, the surface reflection normally expected is either not observed (total) or when the surface reflection is seen for only part of the orbit or the surface reflection is both weaker and spread over a significant time delay (partial). Such blackouts are caused by enhanced ionisation at altitudes below the main ionospheric electron density peak resulting in increased absorption of the radar signal. There are more occurrences observed by MARSIS than SHARAD, which is expected due to the lower absorption at the higher operating frequency of SHARAD. We also observe more blackouts during solar maximum than solar minimum. Indeed, there are no total blackouts during the extended solar minimum, although both radars do have partial blackouts. There is no apparent relationship between blackout occurrence and crustal magnetic fields. Following previous work, which has indicated that solar energetic particles, specifically electrons are responsible for the enhanced ionisation in the atmosphere, we also present the analysis of the MAVEN SEP electrons between 20 keV and 2 MeV during events when all three spacecraft were operational. We find that the SEP electron flux-energy relationship is much enhanced during the total blackouts, in particular where both radars are impacted, while for partial blackouts the flux-energy spectrum is closer to those from orbits where no blackout occurs. We also find that for certain events, the average spectrum which result in a blackout is particularly enhanced at the higher energy end of the spectrum, above 50 keV. The average spectra from each condition is presented. We conclude that there is a higher probability of a radar blackout during solar maximum, that crustal magnetic fields play no apparent role in the their observational occurrence, that the higher energy (< 50 keV) electrons are responsible, and that for events where both radars observe a radar blackout the SEP electron fluxes are at their highest.

We present a three-dimensional radargram of a 13° x 11° region of Deuteronilus Mensae, produced from 457 Mars Reconnaissance Orbiter Shallow Radar (SHARAD) observations. We assess the viability of the 3D imaging algorithms developed to work with SHARAD observations in mid-latitude regions of interest. The quality of subsurface imaging in topographically complex regions is highly improved due to the proper positioning and mitigation of off-nadir reflections in the resulting image. The initial analysis of debris-covered glaciers using 3D radargrams has yielded results that are consistent with previous 2D-based mapping efforts. However, the use of 3D radargrams has enabled the analysis of 3× more area resulting in more accurate estimates of total ice volume, indicating over 9% more ice than previously estimated. Such discrepancies have important implications for Mars climate history studies and in situ resource utilization. The success of this imaging study paves the way for future 3D radargrams in the martian mid-latitudes and stands to increase our confidence in the distribution of many subsurface features of interest.

In operation for >16 years to date, the Mars Reconnaissance Orbiter (MRO) Shallow Radar (SHARAD) sounder has acquired data at its nominal 300-450 m along-track and 3-km cross-track resolution covering >55% of the Martian surface, with nearly 100% overlap in coverage at that scale in the polar regions and in a number of smaller mid-latitude areas. While SHARAD data have opened a new window into understanding the interior structures and properties of Martian ices, volcanics, and sedimentary deposits up to a few kilometers in depth, they have also led to new revelations about the deeper interior and the behavior of the planet's ionosphere. Here we summarize the data collected by SHARAD over this time period, the methods used in the analysis of that data, and the resulting scientific findings. The polar data are especially rich, revealing complex structures that comprise up to several dozen reflecting interfaces that extend to depths of 3 km, which inform the evolution of Martian climate in the late Amazonian period. SHARAD observations of mid-latitude lobate debris aprons and other glacier-like landforms detect strong basal reflections and low dielectric loss, confirming that they are icerich debris-covered glaciers. In other mid-latitude terrains, SHARAD data demonstrate the presence of widespread ground ices, likely at lower concentrations. SHARAD signals also probe non-icy materials, mapping out stacked lava flows, probing low-density materials thought to be ash-fall deposits, and occasionally penetrating sedimentary deposits, all of which reveal the structures and interior properties diagnostic of emplacement processes. SHARAD signals are impacted by their passage through the Martian ionosphere, revealing variations in time and space of the total electron content linked with the remanent magnetic field. Advanced techniques developed over the course of the mission, which include subband and super-resolution processing, coherent and incoherent summing, and three-dimensional (3D) radar imaging, are enabling new discoveries and extending the utility of the data. For 3D imaging, a cross-track spacing at the nominal 3-km resolution is more than sufficient to achieve good results, but finer spacing of 0.5 km or less significantly improves the spatially interpolated radar images. Recent electromagnetic modeling and a flight test show that SHARAD's signal-to-noise ratio can be greatly improved with a large (similar to 120 degrees) roll of the spacecraft to reduce interference with the spacecraft body. Both MRO and SHARAD are in remarkably fine working order, and the teams look forward to many more years in which to pursue improvements in coverage density, temporal variability in the ionosphere, and data quality that promise exciting new discoveries at Mars.

Launched on August 12, 2005, the Mars Reconnaissance Orbiter (MRO) entered Mars orbit on March 10, 2006. Following a period of aerobraking, MRO completed its entry into its primary science orbit in September 2006, initiating a program of systematic observations of Mars that still continues. Five providers, including the Italian Space Agency, provided 6 instruments for flight, observing the surface, atmosphere, and subsurface of Mars with greater spatial resolution and systematic coverage than ever before. Two investigations utilized the spacecraft accelerometers and tracking of the orbiter via the Deep Space Network to study upper atmosphere densities and the gravity field of the planet. The data acquired by MRO have revealed a dynamic planet whose change from an ancient wetter climate to the drier climate of today was a complex transition and not a simple “drying out”. Furthermore, that climate continues to change even today. The diversity of the early habitable environments, the ice ages recorded in the polar cap layering and subsurface ice deposits, the repeating patterns of dust storms, and the revelation of new features at the limit of resolution are all part of the scientific return from MRO during nearly a decade of Mars years. The story of that mission, of the evolution of its capabilities, and its contributions to our current understanding of Mars are the subject of nearly two dozen papers in the Icarus special issue, MRO: Sixteen Years Observing a Changing Mars. Three papers describe in more detail the evolution of instrument operations and data products over the mission; several papers describe new analysis techniques for the radar, including construction of 3-dimensional views, and for the atmospheric sounder, enabling better retrievals in a dusty lower atmosphere. Other papers report on recent research including, but not limited to, dune movement, the roles of water and carbon dioxide ice in surface change, and attempts to understand the formation and fading of the enigmatic recurring slope lineae. This paper describes general aspects of the MRO spacecraft, payload, and mission as context for the special issue papers; it also summarizes scientific results and mission support events on a mission phase by mission phase basis to give a time history of discovery and effort.

Layered deposits are found on the plateaus surrounding the western portion of Valles Marineris, mantling the chasmata rims. These rim deposits exhibit intricate layering and are described as light-toned layered deposits (LLDs) in previous studies. Light-toned layered deposits are thought to be composed of pyroclastic ash that was emplaced during volcanic eruptions and later chemically altered. Using Shallow Radar (SHARAD) observations to map radar reflections from what appears to be the base of these deposits, we discovered two additional types of rim deposits that are contiguous with the well-known LLDs; weakly layered deposits (WLDs) that exhibit less obvious stratification and completely unstratified deposits designated as nonlayered deposits (NDs). Complementing the SHARAD data with imagery from Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) and with narrow-angle imagery from the Mars Global Surveyor Mars Observer Camera (MOC-NA), we mapped the full extent of all rim deposits and present the finished map within this study. We hypothesize that all three deposits originate from pyroclastic ashfall but experienced different degrees of modification due to the variable presence of liquid water. This hypothesis requires a source of volcanic depositional material and past aqueous environments in regions with LLDs and WLDs. We discuss the potential for several large Tharsis volcanoes and a hypothesized degraded volcano within Noctis Labyrinthus as sources of the ash, and we examine the evidence for past aqueous environments.

Surface roughness properties provide context for geologic terrains, and are commonly partnered with field-based mapping on Earth and satellite-based photogeologic mapping in planetary sciences. In this study, we combine morphology-based facies mapping and perform quantitative roughness analysis and characterization of facies for the Athabasca Valles lava flow-field on Mars to identify flow features, provide insight into eruption conditions, and link roughness patterns throughout the flow to emplacement conditions. The root-mean-square (RMS) height and effective slope were acquired at 15 m wavelength for 14 unique lava facies using statistically derived components from the Shallow Radar (SHARAD) surface echo strength. Quantitative RMS height surface roughness of Athabasca lava features range from 1.09 m to 1.76 m. We show that the RMS height response is generally consistent with facies transitions, confirming the linkage between surficial morphologies and lava flow roughness, including the ability to constrain the relative spatial and temporal evolution of emplacement processes. Roughness patterns and facies localities suggest that the emplacement of Athabasca lava experienced a dynamic progression of local discharge surges and substrate influence on morphology. Given a more complete view of the surface statistical properties, our analyses of nadir-looking radar tracks prove to be a useful tool to distinguish between transitional lava facies.

This communication deals with a newly developed electromagnetic model of the Mars Reconnaissance Orbiter Shallow Radar (SHARAD) HF antenna and its interaction with the spacecraft. The model has been developed considering the effect of spacecraft materials and components and the orientation of appendages such as the solar arrays and high-gain antenna. The model appears very useful in designing new operational scenarios of the SHARAD sub-surface sounder, confirming the ability to increase up to 10 dB the signal-to-noise ratio in radar sounding performances by altering the geometry of the observations. We show results from a first test wherein the spacecraft roll angle was set to 120°while obtaining an observation over a ground track previously observed at 0°roll angle, and the expected performance improvement was achieved.

Both sets of Martian polar layered deposits (PLDs) display semi-rhythmic reflector stratigraphy in radargrams. The southern PLDs (SPLD), among other peculiarities, also contain widespread, distinctive deposits with few to no reflections that commonly occur at or near the top of the stratigraphic column. Here, we study the low reflectivity zones (LRZs) to determine whether they exhibit radar properties indicative of non-water ice. We find that the previously reported CO2-ice LRZ exhibits a distinct radar signature compared to all other LRZs. We also found behavior that suggests that the other LRZs may contribute to increased radar signal attenuation, which does not support a CO2 ice composition. We observe many instances of LRZs comprising the entire SPLD column and find that the radar attenuation varies across different LRZs, suggesting unique properties within each of these deposits. Variable radar attenuation of LRZs may be connected to differences in bulk compositions, radar-sensitive roughness characteristics, and/or distributions of stratigraphic materials. From orbital data, we know that both of the Martian polar caps contain widespread layers of dusty water ice. However, radar data, in particular, reveal that the southern cap also contains large sections of layer-free material. Previous studies have established that one of these occurrences of layer-free material is composed of carbon dioxide ice. We looked at the remaining occurrences of layer-free zones in the southern cap and found that they do not show the same radar signatures as those used to deduce the composition of the carbon dioxide unit. These other layer-free units are often associated with decreased signal strength compared to regions where layers are present. We also see variations in the signal strength across these layer-free units, suggesting subtle differences in their composition, material distribution, or surface roughness of the polar cap. The large carbon-dioxide ice deposits of Australe Mensa exhibit radar characteristics distinct from other low reflectivity zones The outlying low reflectivity zones show evidence of increased radar attenuation relative to layered regions Variation in attenuation characteristics across low reflectivity zones suggests unique properties across units

Since November 2006, the Shallow Radar (SHARAD) aboard the U.S. National Aeronautics and Space Administration's (NASA's) Mars Reconnaissance Orbiter (MRO) has been conducting subsurface sounding operations from orbit around Mars. This extended campaign has provided tens of thousands of radar profiles of Mars shallow subsurface, with coverage density in some regions having become sufficient for performing three-dimensional (3D) imaging. Adapting methods and tools used to produce, analyze, and interpret terrestrial seismograms, we have produced and studied fully imaged 3D radargrams in Mars' polar and mid-latitudes regions. In this report, we provide some background on the SHARAD instrument, summarize the methods and tools used in creating 3D radargrams from SHARAD data, and present example views from the latest 3D radargram in the north polar region known as Planum Boreum (PB).

Honeybee’s RedWater system is being developed as an in situ resource utilization (ISRU) approach to mining glacial ice on Mars. Our investigation addresses the environmental and geological considerations vital for system success (e.g., site latitude, ice purity, nature of impurities, and constraints on overburden). We will present an assessment of several site locales suitable for the implementation of the RedWater system using existing orbital spacecraft data. A combination of radar sounding, imagery, and other data at landing-site scales will enable constraints to be placed on the thickness, properties, and distribution of ice resources and overburden.

Honeybee Robotics has designed, built, and tested a technology readiness level (TRL) 4/5 system known as RedWater, intended to drill into the surface of Mars and melt/extract water from locations identified by the Shallow Radar (SHARAD). RedWater combines proven terrestrial technologies to extract water from the subsurface Martian ice. Rodriguez Wells, or Rodwells, are a type of water well employed in Antarctica to maintain large pools of liquid water within an ice sheet and pumping water to the surface while heating and recirculating a portion to facilitate continuous well growth. RedWater also repurposes coiled tube drilling technology, which uses a thin-walled metal or composite tube to drive a bottom hole assembly into a borehole; the coiled tube itself is wound onto a drum and deployed by an injector system which transmits the required drilling forces through the tube as it is driven down. The combination of these two technologies with Honeybee’s existing rotary percussive drilling and pneumatic transport technologies make for an efficient means of producing large quantities of liquid water on Mars. Honeybee is currently working on evolving this technology to TRL 6 and will be conducting end-to-end TVAC testing in 2022.