Phoenix Landing Research Articles

Organic Carbon and Ca‐Rich Carbonate Detections in Soils of the Northern Plains, Mars: Evaluation of Unreported Data From the Mars Phoenix Scout's Thermal Evolved Gas Analyzer (TEGA)

AbstractThe Thermal Evolved Gas Analyzer (TEGA) analysis of surface and icy subsurface Phoenix landing site soils consisted of low (300–700°C) and high (>700°C) temperature CO2 evolutions that were attributed to organic carbon (83–1,484 μgC/g) and Ca‐rich carbonate (1.1–2.6 wt.%). Total carbon abundances ranged from 1,143 to 4,905 µgC/g, which is the highest soil carbon concentration so far detected on Mars. Low temperature CO2 was attributed to oxidized organic C (e.g., oxalates, acetates), while hydrocarbon combustion was indicated in two soils by the detection of coevolved CO2 and O2 (perchlorate). Combustion reactions may have prevented the detection of hydrocarbon masses in the Phoenix landing site soils. Organic C was likely derived from meteoritic and igneous/hydrothermal sources, but microbiological sources cannot be excluded. CO2 evolved at high temperatures was consistent with Ca‐rich carbonate along with possible minor contributions from macromolecular organic carbon and mineral/glass vesicle CO2. Carbon detected in the Phoenix landing site soil and other landing site soils and sands (e.g., Gale/Jezero craters) would be consistent with global organic C and carbonate in soils and sand across Mars. However, oxidizing water thin films derived from the near‐surface ice in the Phoenix soils favor Ca‐carbonate over Fe‐carbonate, which is likely more stable in the ice‐free regions of Mars (e.g., Gale/Jezero craters). The global carbon budget on Mars inferred from these results emphasizes that Mars Sample Return should yield carbon bearing soil/rock that would allow the identification of the origin of carbon and any possible connections to ancient martian microbiology.

Dust Emissions on Mars From Phoenix Lidar Measurements in Relation to Local Meteorological Conditions

AbstractThe diurnal cycle of dust aerosols on Mars is studied by analyzing lidar observations at the Phoenix landing site under cloud‐ and fog‐free conditions and in the absence of elevated, long‐range transported dust layers. There is a pronounced diurnal cycle in the dust‐layer height with minimum heights of 4–6 km occurring between 11:00 and 17:00 local time. The ratio of the aerosol optical depth (AOD) within the lowermost 2 km to the total AOD reaches peak values at the same time. This can be explained by local dust emissions driven by the diurnal cycle of heating and cooling in the boundary layer. Analysis of wind and pressure measurements show that the gustiness of surface winds and the frequency of convective vortices undergo diurnal variations resembling those of AOD, indicating that these processes are the main drivers for local dust emissions.

Comparing Atmospheric Temperature Fluctuations Across Landed Missions

AbstractWe analyze and compare atmospheric temperature data from three landed missions: Mars Science Laboratory (MSL) Curiosity rover, Phoenix lander, and Pathfinder lander. Pathfinder and Phoenix were lander missions that operated for 84 and 151 sols, respectively. MSL Curiosity is a rover that operates on the surface of Mars. It has recorded air temperature for more than five Mars Years (MY). We denoise and detrend temperature data from each mission and use those results to calculate variance in air temperature as a diagnostic for atmospheric variability at the surface. The results show a consistent seasonal pattern in MSL air temperature variance with little interannual variability outside major dust storms. The global dust storm in MY 34 was accompanied by a decrease in temperature variance and a muted response in peak MY 35 variance the following year. Phoenix (68°N, 2 m measurement height) and Pathfinder (19.7°N, 1.1 m measurement height) air temperatures have larger variance than air temperature from environmental data records at the MSL location (5.4°S, 1.6 m measurement height) at its equatorial latitude. Pathfinder variances per sol are larger than those of Phoenix, possibly due to a combination of Pathfinder's lower albedo surface and lower latitude. This occurs despite the Pathfinder location's higher thermal inertia, which would act to decrease noontime variance relative to a lower thermal inertia surface. Comparison of MSL temperature variance to pressure drops related to convective vortex activity shows consistent seasonal patterns; however, pressure drops tend to increase with increasing rover elevation, while variance remains consistent.

Using AI to Fine Tune the Search for Life

Using AI to Fine Tune the Search for Life

Investigation of the Cytotoxicity of Mars-Relevant Minerals upon Abrasion.

Since the Viking Labeled Release experiments were carried out on Mars in the 1970s, it has been evident that the martian surface regolith has a strong oxidizing capacity that can convert organic compounds into CO2 and probably water. While H2O2 was suggested originally for being the oxidizing agent responsible for the outcome of the Viking experiments, recent analyses of the martian regolith by the Phoenix lander and by consecutive missions point toward radiation-mediated decomposition products of perchlorate salts as the primary oxidant. In a series of experiments, we have shown that abrasion and triboelectric charging of basalt by simulated saltation could be an additional way of activating regolith. We have also shown that abraded basalt with a chemical composition close to that of martian regolith is toxic to several bacterial species and thus may affect the habitability of the martian surface. In the present study, we investigated the effect of the quantitatively most important minerals (olivine, augite, and plagioclase) and iron oxides (hematite, magnetite, and maghemite) on the survival of bacterial cells to elucidate whether a specific mineral that constitutes basalt is responsible for our observations. We observed that suspensions of iron-containing minerals olivine and augite in phosphate-buffered saline (1 × PBS) significantly reduce the number of surviving cells of our model organism Pseudomonas putida after 24 h of incubation. In contrast, the iron-free mineral plagioclase showed no effect. We also observed that suspending abraded olivine and augite in 1 × PBS led to a dramatic increase in pH compared to the pH of 1 × PBS alone. The sudden increase in pH caused by the presence of these minerals may partly explain the observed cytotoxicity. The cytotoxic effect of augite could be relieved when a strong buffer (20 × PBS) was used. In contrast, olivine, despite the stronger buffer, maintained its cytotoxicity. Iron oxides per se have no negative effect on the survival of our test organism. Overall, our experiments confirm the cytotoxicity of basalt and show that no single constituent mineral of the basalt can account for its toxicity. We could show that abraded iron-containing minerals (olivine and augite) change the pH of water when brought into suspension and thereby could affect the habitability of martian regolith.

Small crater relaxation and ice abundance at high northern latitudes on Mars

The cold, northern high-latitudes around the Phoenix landing site feature a population of small and very shallow craters known as palimpsest craters or boulder halos that could give insight into the subsurface ice content of the region. Notably there is also a split in the population by the size of craters that feature blocky ejecta: the smallest crater sizes that are <200–350 m in diameter typically do not feature blocky ejecta, while craters larger than this size range do. This has been interpreted as there being a less consolidated layer of mainly ice that sits over a more consolidated layer containing more silicate material from which the larger craters are able to excavate the blocky ejecta. This work focuses on determining whether these 200 m - 1 km shallow craters could be indicative of topographic relaxation due to substantial ice in the subsurface, with goals to determine the subsurface structure and most importantly the amount of ice present through its abundance and depth extent. We use finite element modeling of axisymmetric simple craters, employing the most recent characterizations of solid-state creep for water ice, silicate-rich ice, and CO2 ice, to determine the timescales and magnitudes of relaxation accommodated by an icy single or multiple material layered subsurface to determine the environment's properties. Our models include a 35 m thick layer of pure ice (water, or water and CO2) over a mobile substrate of particulate rich water ice of variable thicknesses able to accommodate relaxation for larger crater sizes up to 1 km in diameter. Our findings demonstrate that relaxation is able to account for significant flattening of crater topography, though for smaller craters the relaxation is incomplete, leaving about half the depth. The accommodated relaxation of our modeled subsurface does imply associated increases in ice abundances of 4 to 10 times greater than is currently estimated for the region, dependent on the extent of the mobile layer.

Laboratory Studies of Brine Growth Kinetics Relevant to Deliquescence on Mars

Although previous studies have shown that the near-surface environmental conditions on Mars may permit salt deliquescence and therefore brine production, there is significant uncertainty in the kinetics of the process. Indeed, experimental studies have shown that deliquescence is either very rapid or too slow to be relevant to Mars. To resolve this uncertainty, we performed laboratory experiments to investigate the growth rate of Mars-relevant calcium perchlorate brines over a range of temperatures (184–273 K) and water vapor pressures (0.2–220 Pa). We show that the brine growth is faster at higher water vapor pressures and lower temperatures and for smaller particles. From our data, we determined a temperature-dependent net uptake coefficient for gas phase water molecules colliding with a perchlorate brine surface in the range of 3.8 × 10−4 at 185 K to 4.2 × 10−6 at 273 K. These values suggest that deliquescence on Mars is likely to be slow even when conditions thermodynamically permit a brine to form. We find that along the Curiosity rover traverse at Gale Crater, the near-surface conditions would only allow particles <1 μm to fully deliquesce over a typical sol. At the higher-latitude Phoenix landing site, deliquescence may be 30% faster due to the higher water vapor pressures, but still, only micron-scale salt grains or coatings would be expected to deliquesce during a typical sol. These results suggest that brines formed via deliquescence on the surface of Mars are likely only present on small scales that may not be readily detected using conductivity or imaging techniques.

Partially‐Saturated Brines Within Basal Ice or Sediments Can Explain the Bright Basal Reflections in the South Polar Layered Deposits

AbstractStrong radar reflections have been previously mapped at the base of the Martian South Polar Layered Deposits. Here, we analyze laboratory measurements of dry and briny samples to determine the cause of this radar return. We find that liquid vein networks consisting of brines at the grain boundaries of ice crystals can greatly enhance the electrical conductivity, thereby causing strong radar reflections. A brine concentration of 2.7–6.0 vol% in ice is sufficient to match the electrical properties of the basal reflection as observed by Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS). When brine is mixed with sediments, the brine‐ice mixture in the pores must be 2–5 times more concentrated in salt, increasing the brine concentration to 6.3–29 vol%. Our best fit of the median observed MARSIS value suggests a salt‐bulk sample concentration of ∼6 wt%. Thus, salt enhancement mechanisms on the order of a magnitude greater than the Phoenix landing site are needed. To form brine, the basal reflector must reach a temperature greater than the eutectic temperature of calcium perchlorate of 197.3 ± 0.2 K, which may be possible if more complex thermal modeling is assumed. Colder metastable brines are possible, but stability over millions of years remains unclear. Conversely, gray hematite with a concentration of 33.2–59.0 vol% possess electrical properties that could cause the observed radar returns, but require concentrations 2–3 times larger than anywhere currently detected. We also argue that brines mixed with high‐surface‐area sediments, or dry red hematite, jarosite, and ilmenite cannot create the observed radar returns at low temperatures.

Limited Stability of Multicomponent Brines on the Surface of Mars

The formation and stability of brines on the surface of present-day Mars remains an important question to resolve the astrobiological potential of the red planet. Although modeling and experimental work have constrained the processes controlling the stability of single-salt brines exhibiting low freezing temperatures, such as calcium perchlorate, the Martian regolith is far more complex because multiple salts coexist in various concentrations, leading to brines whose behavior remains untested. Here we modeled the stability of complex brines of compositions determined from the Phoenix lander’s Wet Chemistry Laboratory. We find that such brines would form in equilibrium with sodium and magnesium perchlorates, chlorides, and calcium chlorate, but never calcium perchlorate, which has been widely considered as the most likely to produce brines on Mars. Furthermore, we find that only chlorate-rich brines can potentially remain liquid, for small periods of time, at temperatures compatible with those measured by the Phoenix lander. Therefore, liquid brines remain overly unstable under present-day Martian conditions and are unlikely to contribute to surface geomorphological activity, such as recurring slope lineae. In these conditions, of cold and salty brines, the present-day Martian surface remains highly unhabitable.

A Record of Water-ice Clouds at the Phoenix Landing Site Derived from Modeling MET Temperature Data

Water-ice clouds were frequently detected throughout the 151-sol Phoenix mission by the Phoenix lidar, providing insight into the Martian water cycle. However, the lidar could not be used continuously, and as such, the cloud data were temporally constrained to when observations were acquired. Here we reconstruct a record of water-ice clouds at the Phoenix landing site by examining the radiative contribution made by the clouds to the surface energy balance. This is accomplished by modeling the data from the 2 m MET air temperature sensor on board the lander. Clouds radiating from 0 and 30 W m−2 of energy toward the surface are consistent with the MET record over the course of the mission. The additional longwave flux at the surface induced a warming of the surface and near-surface temperatures, usually between 1–3 K; however, the clouds showed a high degree of sol-to-sol variability. This radiative analysis indicates that clouds were present much earlier in the mission than previously known, and cloud emission reached a maximum near sol 90, consistent with analyses of the annular cloud at the Phoenix landing site. The modeled flux from clouds was compared to the water-ice optical depth retrieved from the Phoenix lidar, showing that optically thicker clouds emitted more radiation toward the surface.

Cryogenic origin of fractionation between perchlorate and chloride under modern martian climate

The high perchlorate (ClO4−) to chloride (Cl−) ratios observed at the Phoenix landing site, northern polar region of Mars, have been puzzling since detection. However, a lack of understanding of perchlorate-chloride-water systems under cryogenic conditions makes it difficult to assess ClO4−/Cl− ratios during deliquescence-related processes. Here we quantitatively evaluate ClO4−/Cl− fractionation in deliquescence-induced brines of magnesium- and calcium-perchlorate-chloride salt mixtures under subzero conditions, by measuring solubility data and constructing temperature-dependent thermodynamic models. We find that under specific relative humidity (RH) and temperature (T) conditions, deliquescence of perchlorate-chloride mixtures may form brines with fractionated ClO4−/Cl− signatures. Appropriate RH-T, water-limited conditions, and aeolian processes are required to produce and preserve the elevated ClO4−/Cl− signatures in soils. Under the present climate, the north polar region can support ClO4−/Cl− fractionation and potentially enrich perchlorate for longer periods on global Mars. This highlights the uniqueness of Mars’ arctic environment and its implications for modern habitability.

Electrolytic Fuel and Oxygen Harvesting from Ultra-Cold, Hypersaline Martian Regolithic Brines

The United States National Aeronautics and Space Administration’s (NASA) current mandate is to land humans on Mars by 2033. The active Maritain water cycle, discovered by NASA’s Phoenix lander and confirmed by other probes, includes a shallow water table, water/ice precipitation and soluble perchlorates in the Martian regolith (soil) which depress water’s freezing point to ca. -60 ⁰C. These conditions enable the concurrent production of hydrogen fuel and life-support oxygen on Mars through perchlorate brine electrolysis. As a solution for astronaut life-support and rocket re-fueling, we demonstrate an in-situ resource utilization (ISRU) approach to produce ultra-pure H2 and O2 from liquid-phase Martian regolithic brine at ca. -36 ⁰C and under Martian atmospheric conditions(1). We built a perchlorate brine electrolyzer utilizing a Pb2Ru2O7-δ pyrochlore O2-evolution electrocatalyst, a Pt/C H2-evolution electrocatalyst and commercial anion exchange membrane separator. Our electrolyzer demonstrated >25x the O2 production rate of the high-temperature, CO2 electrolyzing Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) from NASA’s Mars 2020 mission for the same input power under Martian terrestrial conditions while also avoiding the need to remove CO by-product. This work provides an additional route to help NASA fulfill its mandate to land humans on Mars by 2033. Furthermore, our perchlorate brine electrolyzers are more efficient than state-of-the-art alkaline water electrolyzers on Earth, providing a pathway to utilize sub-optimal input feeds to produce ultra-pure hydrogen and oxygen. References P. Gayen, S. Sankarasubramanian, V. K. Ramani, Fuel and oxygen harvesting from Martian regolithic brine. Proc. Natl. Acad. Sci. U. S. A. 117, 31685–31689 (2020). Figure 1

InSight Entry, Descent, and Landing Preflight Performance Predictions

On 26 November 2018, the Interior Exploration Using Seismic Investigations, Geodesy and Heat Transport (InSight) lander successfully touched down on the surface of Mars. Over its more than seven year development, NASA Langley Research Center’s Program to Optimize Simulated Trajectories II (POST2) was used to assess the mission’s entry, descent, and landing (EDL) vehicle system performance against related requirements across the full range of possible environmental and spacecraft conditions. Due to the high degree of entry body, lander platform, and EDL design heritage, much of the simulation code was derived from the 2007 Mars Phoenix Lander mission. The InSight POST2 six-degree-of-freedom simulation included models for Mars atmosphere, gravity, and digital elevation maps of the landing location. Additionally, vehicle-specific aerodynamic, parachute, engine, navigation sensor, flight software, and landing radar models were included. A set of dispersions for each model, as well as for additional simulation input parameters, was also included in order to provide a statistical, Monte Carlo prediction of the EDL system performance. An overview of the preflight performance assessments completed, including the various simulation campaigns used, will be provided. Ultimately, this work was critical in the assessment of readiness for the InSight launch. A brief description of the use of this simulation in support of flight operations is also discussed.

Nighttime convection in water-ice clouds at high northern latitudes on Mars

We investigate water-ice clouds and their influence on the temperature structure of the Martian atmosphere at high northern latitudes in early summer. New results are obtained through coordinated analysis of two types of data from Mars Global Surveyor: atmospheric profiles retrieved from radio occultation (RO) measurements and wide-angle images from the Mars Orbiter Camera (MOC). Some RO profiles contain a layer of neutral static stability, which indicates the presence of convective mixing at a local time (about 5 h) when it does not usually occur. These nocturnal mixed layers (NMLs) were observed frequently in early summer of Mars year 27 at latitudes of 53–72°N and longitudes of 210–330°E. The base of a typical NML is 3 km above the surface, about the same height as the nighttime cloud layer detected by the Phoenix LIDAR in early summer of Mars year 29 at 234°E, 68°N. The depth of the NMLs ranges from less than 1 km to more than 5 km. Comparisons with nearly simultaneous MOC images demonstrate that NMLs are closely associated with water-ice clouds. There is a dense cluster of NMLs within the annular cloud that appears every year in early summer between Alba Mons and the north polar residual ice cap. The lighting conditions at this location and season allowed MOC to observe the annular cloud on most orbits, at 118-min intervals. Its appearance varies dramatically with local time, becoming more symmetrical and better organized at night and dissipating to a crescent shape during the day. According to high-resolution numerical simulations (Spiga et al., 2017), including a large-eddy simulation at the Phoenix landing site, NMLs form when radiative cooling by water-ice aerosols causes convective instability; the mixed layer is forced from above by negative buoyancy. Our results strongly support this conclusion. In addition, MOC images from midsummer contain eastward-moving frontal clouds. Temperature profiles within these clouds show signs of near-surface advection of warm air, which reduces the static stability of the lower atmosphere and contributes, along with cloud radiation, to the formation of an NML.

Spectral Albedo of Dusty Martian H2O Snow and Ice

AbstractRecent evidence of exposed H2O ice on Mars suggests that this ice was deposited as dusty (&lt;∼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 (&lt;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 (&gt;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.

Identification of a new spectral signature at 3 [formula omitted]m over martian northern high latitudes: Implications for surface composition

Mars northern polar latitudes are known to harbor an enhanced 3 μm spectral signature when observed from orbit. This may indicate a greater amount of surface adsorbed or bound water, although it has not yet been possible to easily reconcile orbital observations with ground measurements by Phoenix. Here we re-analyzed OMEGA/Mars Express observations acquired during the Northern summer to further characterize this 3 μm absorption band increase. We identify the presence of a new specific spectral signature composed of an additional narrow absorption feature centered at 3.03 μm coupled with an absorption at λ≥3.8μm. This signature is homogeneously distributed over a high-albedo open ring surrounding the circumpolar low-albedo terrains between ∼68°N and 76°N and ∼0°E and 270°E. This location includes the Phoenix landing site. This feature shows no time variability and can be confidently attributed to a seasonally stable surface component. All together, the stability, spectral shape and absence of significant correlation with other signatures in the 1–2.5 μm range discard interpretations relying on water ice or easily exchangeable adsorbed water. Sulfates, notably anhydrite, provide interesting comparisons to several sections of the spectrum. Analogies with Earth samples also show that the spectral signature could result from a latitudinal modification of the hydration state and/or grains size of salts contaminants. While the exact full spectral shape cannot be easily reproduced, plausible explanations to this observation seem to involve geologically recent water alteration at high northern latitudes.

Decameter-scale rimmed depressions in Utopia Planitia: Insight into the glacial and periglacial history of Mars

Currently, Mars appears to be in a frozen state, with the clear majority of the planet's surface maintaining year-round sub-zero temperatures. The discovery of features consistent with landforms found in periglacial environments on Earth, suggests a recent climate history for Mars dominated by the presence of permafrost and/or freeze-thaw cycling. Landforms indicative of such periglacial activity include hummocky, polygonized, scalloped, and pitted terrains in the mid-to high-latitudes of both hemispheres. The detection of near-surface and surface ice by the Phoenix lander, excavation of ice by recent impacts, complemented by interpreted results from the SHAllow RADar (SHARAD) instrument, further unveil a landscape in the mid-latitudes enriched in subsurface ice. We report here on the landscape analysis of a region within Utopia Planitia, where we aim to assess the influence of periglacial processes in the formation of a new landform that we have dubbed ‘Decameter-scale Rimmed Depressions’ or DRDs for short. These features are small-scale depressions surrounded by a narrow rim, ranging from <1 ​m to no higher than a few metres in height. We categorized 3 different DRD morphologies: ellipse morphologies, labyrinth, and tear-drops. DRDs share many morphological similarities with so-called “brain terrain”, although unlike “brain terrain”, most of the DRDs we mapped occur on intra-crater plains and not in association with glacial flow features. The presences of isolated fully enclosed ellipse morphologies is also a notable difference. We discuss the possibility that “brain terrain” and DRDs are genetically different features, but given the similarity in morphology and geographic distribution, we find this unlikely. Thus, while we cannot rule out an origin of DRDs through periglacial sorting, we favour a process for DRD formation similar to that proposed “brain terrain”, whereby ground ice, likely in the form of buried glacial ice, underwent thermal contraction and differential degradation, resulting in the formation of the landform that we see today. DRDs thus represent a further morphological marker for the presence of ground ice in the northern plains of Mars.

Fuel and oxygen harvesting from Martian regolithic brine

NASA's current mandate is to land humans on Mars by 2033. Here, we demonstrate an approach to produce ultrapure H2 and O2 from liquid-phase Martian regolithic brine at ∼-36 °C. Utilizing a Pb2Ru2O7-δ pyrochlore O2-evolution electrocatalyst and a Pt/C H2-evolution electrocatalyst, we demonstrate a brine electrolyzer with >25× the O2 production rate of the Mars Oxygen In Situ Resource Utilization Experiment (MOXIE) from NASA's Mars 2020 mission for the same input power under Martian terrestrial conditions. Given the Phoenix lander's observation of an active water cycle on Mars and the extensive presence of perchlorate salts that depress water's freezing point to ∼-60 °C, our approach provides a unique pathway to life-support and fuel production for future human missions to Mars.

An estimate of convective vortex activity at the InSight landing site on Mars

A number density of convective vortices (a number of vortices per km2) at the InSight landing site on Mars is estimated as a metric of vortex activity, using a theoretical expression that relates this number density to the recorded number of nearby passages of vortices experienced by the InSight Mars lander. A very high estimate, i.e. 56 vortices per km2, of the average, over the whole period of observed vortex activity, number density of the vortices was obtained. Taking into account all the uncertainties involved in this quantity estimate, the latter can be reduced by a factor of about two, at most, but still remains at an unprecedented high level. For the sake of comparison, this methodology also applies to the Mars Science Laboratory and the Phoenix Lander vortices.

Automated Discontinuity Detection and Reconstruction in Subsurface Environment of Mars Using Deep Learning: A Case Study of SHARAD Observation

Machine learning (ML) algorithmic developments and improvements in Earth and planetary science are expected to bring enormous benefits for areas such as geospatial database construction, automated geological feature reconstruction, and surface dating. In this study, we aim to develop a deep learning (DL) approach to reconstruct the subsurface discontinuities in the subsurface environment of Mars employing the echoes of the Shallow Subsurface Radar (SHARAD), a sounding radar equipped on the Mars Reconnaissance Orbiter (MRO). Although SHARAD has produced highly valuable information about the Martian subsurface, the interpretation of the radar echo of SHARAD is a challenging task considering the vast stocks of datasets and the noisy signal. Therefore, we introduced a 3D subsurface mapping strategy consisting of radar echo pre-processors and a DL algorithm to automatically detect subsurface discontinuities. The developed components the of DL algorithm were synthesized into a subsurface mapping scheme and applied over a few target areas such as mid-latitude lobate debris aprons (LDAs), polar deposits and shallow icy bodies around the Phoenix landing site. The outcomes of the subsurface discontinuity detection scheme were rigorously validated by computing several quality metrics such as accuracy, recall, Jaccard index, etc. In the context of undergoing development and its output, we expect to automatically trace the shapes of Martian subsurface icy structures with further improvements in the DL algorithm.