Previous studies have constrained the lithosphere at the north and south poles of Mars to be thick and cold, with elastic thicknesses of 330 to 450km [1], and >150km [2], respectively. The elastic thickness characterizes the stiffness of the lithosphere in response to loading and is directly linked to the thermal state of the lithosphere and the surface heat flow. Thus, elastic thickness estimates at the north and south poles provide crucial constraints on the present-day surface heat flow on Mars. Additional information on the present-day planetary thermal state comes from evidence of ongoing melting in the mantle, as indicated by the presence of both young lava flows in Tharsis and Elysium provinces and an active mantle plume beneath Elysium Planitia [3,4,5]. In this study we explore the thermal evolution of Mars using global 3D geodynamic models. These models improve upon our previous work [6] by including updated interior structure information from the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission [7,8] and by considering constraints on the present-day thermal state of the planet as noted above. Thermal evolution models using the most recent crustal thickness estimates [8,9], require that the crust contains more than half of the total amount of heat producing elements (HPEs) to explain localized recent volcanic activity on Mars [8]. We find that the crustal thickness variations control the surface heat flow and the elastic thickness pattern, as well as the location of melting zones in the present-day Martian mantle. The strongest constraint for the thermal history and present-day state of the interior is given by the elastic thickness at the north pole. While at the south pole, all models show values >150km, compatible with the latest estimate [2], only a few models present an elastic thickness >300km at the north pole, with values still lower than the recent estimate of [1]. A larger elastic thickness at the north pole could indicate: 1) a northern crust less enriched in HPEs, 2) a colder lithosphere due to a weaker blanketing effect caused by a thinner or higher-conductivity crust on the northern hemisphere, 3) ongoing viscoelastic relaxation, suggesting that the observed surface deflection beneath the north polar cap is not the final one [1], or a combination thereof. In contrast to the cold lithosphere inferred for the Martian polar regions, recent volcanic activity suggests a warmer interior beneath Tharsis and Elysium provinces [3,4]. This reveals an important spatial variability in the thermal state and thickness of the Martian lithosphere. Our work shows that only a narrow range of models can match elastic thickness estimates at the polar caps and explain Mars’ recent volcanic activity, thereby providing important insights into the structure and thermal evolution of the interior.References:[1] Broquet et al., 2020. [2] Broquet et al., 2021. [3] Voigt et al., 2023. [4] Hauber et al., 2011. [5] Broquet & Andrews-Hanna, 2023. [6] Plesa et al., 2018. [7] Stähler et al., 2021. [8] Knapmeyer-Endrun et al., 2021. [9] Wieczorek et al., 2023.

We use the crystallinity of hydrated silica, represented by the 1.4 mu m absorption position in orbiter spectroscopic data, as a proxy for the longevity of water-rock interaction in the Syrtis Major region. Geological maps and crater size-frequency distribution analyses are employed to contextualize mineral detections and estimate surface ages. Hydrated silica is detected within two distinct geological units: a younger "volcanic terrain" (vt) unit (similar to 2.4 Ga) and an older "highland terrain" (ht) unit (3.5-3.7 Ga). Hydrated silica in the vt unit typically has a band position <1.41 mu m, consistent with amorphous opal-A, suggesting these younger terrains have experienced limited interaction with water. In contrast, hydrated silica in the older highlands typically has a band position >1.41 mu m, indicating opal-CT, suggesting that these deposits have had more time to interact with water, while also producing accessory minerals such as kaolinite and Fe/Mg phyllosilicates.

Planetary analog mission simulations are essential for testing science operations strategies and technologies. They also teach us how to use terrestrial analogs to inform studies of extraterrestrial environments. Unoccupied aircraft systems (UASs) have great potential for planetary surface exploration as demonstrated by the Mars 2020 Ingenuity helicopter and the in-development Dragonfly mission to Saturn's moon Titan. Although applications of UAS technology for planetary exploration remain largely unexplored, simulated missions in planetary analog terrains can inform operational best practices. As part of the Rover-Aerial Vehicle Exploration Network project, we simulated a 12 sol UAS mission on Mars in the Holuhraun region of Iceland. The UAS had airborne imaging capability, as well as imaging, sampling, and geochemical analysis capabilities while landed. The mission evaluated the use of these instruments and developed operational strategies for using UASs to explore a planetary surface. Oblique airborne images were essential for mission planning and were used to scout large areas to identify both potential landing sites and targets for focused investigations. The airborne and landed data collected by the UAS allowed for detailed observations and interpretations not possible with analog orbital data sets, resulting in an improved scientific return for the simulated UAS mission compared to a premission analysis of only the analog orbital data. As a planetary exploration vehicle, a UAS is most advantageous for exploring large areas (many square kilometers) and is particularly useful when the terrain may be impassable to ground-based traverses (e.g., by rovers or humans).

The Rover–Aerial Vehicle Exploration Network project field-tested planetary mission operations within a Mars analog environment in Iceland using stand-alone rover and helicopter architectures. Mission planning, implementation, and results are reported for the rover mission and briefly summarized for the helicopter mission. The outcomes of both missions are subsequently compared. Field implementation occurred from 2022 July to August at the Holuhraun lava flow. The rover science operations team executed a 14 sol (Martian day) mission that achieved mission, science, and sampling goals, including the contextualization, acquisition, and planned caching of two eolian and two rock samples. The helicopter science operations team executed a plan of comparable length but emphasized different science goals given long-range flight capabilities and landing limitations. The resolution and targetability of the rover payload enabled more detailed analyses, whereas the helicopter was better able to map flow-scale morphologies. The rover’s exploration was limited by daily mobility duration limits and hazardous terrain, whereas the helicopter’s exploration was constrained by landing site hazards. Resource limitations resulted from lengthier rover drives and data-volume-intensive helicopter imaging surveys. Future missions using combined rover–helicopter architectures should account for each spacecraft’s resource needs and acknowledge system strengths in different geologic settings. Both missions served to establish operations strategies and mission outcomes to be applied to future combined rover and helicopter mission architectures, while the helicopter mission also evaluated strategies and outcomes for future stand-alone airborne missions. Findings in this work are relevant to future missions seeking to optimize strategies for planetary mission operations.

Elysium Planitia includes several outflow channels that were likely carved by aqueous erosion and subsequently infilled by younger lava flows, making Elysium Planitia the youngest volcanic terrain on Mars. Studying this region is critical for constraining the recent hydrological and thermal evolution of the planet. Here, we investigate the lava flow areas, thicknesses, and volumes in Elysium Planitia using Context (CTX) camera images in combination with SHAllow RADar (SHARAD) sounder data. Compiling 1,777 reflectors over an area of 9,126,790 km2 allows us to reconstruct the subsurface landscape evolution over time. Our findings show that Elysium Planitia is composed of material from about 40 episodes of effusive volcanic activity. We report volumes for individual eruptions of 4,000 +/- 1,600 km3 infilling Athabasca Valles, 12,200 +/- 2,500 km3 in Marte Vallis, and 16,000 +/- 4,000 km3 in Rahway Valles for the major flow units and volumes as small as 100 +/- 50 km3 in Cerberus Plains. The surface morphologies and inferred dielectric properties of lobe interfaces suggests that the regions consists of basaltic lava. The region also experienced multiple aqueous flooding events. Although, we found evidence of past lava-water interactions, present-day ground-ice (if present) is likely limited to local patches. Further, the pre-eruption landscape reveals that the aqueously carved Marte Vallis is more areal extensive, but shallower than previously suggested, with a likely paleo-flow direction from northwest to southeast. The channel is most likely sourced from a segment in the northwestern portion of Cerberus Fossae, and is now buried by multiple Late Amazonian lavas with the same lava flow direction. Elysium Planitia on Mars has a fascinating history of water and lava flows that shaped its landscape. It is the youngest volcanic terrain on the planet, and studying it helps us to better understand Mars' past as well as recent hydrological and volcanic history. We examined this region by using spacecraft images and radar data to constrain areas, thicknesses, and volumes. An area almost as large as Europe was investigated. The study revealed the products of more than 40 volcanic events, with one of the largest flows infilling Athabasca Valles with a volume of 4,000 km3. The surface appearance and material properties suggest that Elysium Planitia is composed of basalt, the most common type of lava on Earth. The area also experienced several large floods of water, and there is evidence that lava and water interacted in the past. However, while there could be ice in the ground today, it likely occurs in small patches. The study also provides new insights into the Marte Vallis outflow channel. It seems to be larger, but not as deep as previously thought, with water flowing from northwest to southeast and fed from a fissure in the northwest. Marte Vallis was later covered by several lava layers. We performed detailed surface and subsurface mapping of the entire Elysium Planitia region to constrain lava areas, thicknesses, and volumesElysium Planitia is composed of the products of about 40 effusive eruptions including large flood lava flows and lava shieldsResults indicate that there is no singular direction in dike propagation

Distinguishing between lava types and facies using remote sensing data is important for interpreting the emplacement history of lava flow‐fields on Earth and other planetary bodies. Lava facies typically include a mixture of lava types and record the collective emplacement history of material preserved at a particular location. We seek to determine if lava facies in the 2014–2015 Holuhraun lava flow‐field are discernible using radar roughness analysis. Furthermore, we also seek to distinguish between lava types using high resolution Light Detection and Ranging (LiDAR) data. We extracted circular polarization ratios (CPR) from the Uninhabited Aerial Vehicle Synthetic Aperture Radar and cross‐polarization (VH/VV) data from the Sentinel‐1 satellite to analyze the surface roughness of three previously mapped lava facies: rubbly, spiny, and undifferentiated rubbly–spiny. Using the Kruskal‐Wallis test, we reveal that all but one pair of the facies are statistically separable. However, the populations overlap by 88%–89% for CPR and 64%–67% for VH/VV. Therefore, owing to large sample populations ( n > 2 × 10 5 ), slight differences in radar data may be used to probabilistically infer the presence of a particular facies, but not directly map them. We also calculated the root‐mean‐square slope and Hurst exponents of five different lava types using LiDAR topography (5 cm/pixel). Our results show minute differences between most of the lava types, with the exception of the rubbly pāhoehoe, which is discernible at 1σ. In brief, the presence of “transitional” lava types (e.g., rubbly pāhoehoe) within fissure‐fed lava flow‐fields complicates remote sensing‐based mapping.

Low-frequency radar sounders have the potential to generate altimetric profiles, but the feasibility of utilizing planetary radar sounding data as an alternative to laser altimetry has not been assessed using existing data to date. Therefore, we have developed, implemented, and evaluated an algorithm to process SHAllow RADar sounder (SHARAD) data on Mars (Experiment Data Records as available on the planetary data system) first into altimetry profiles and ultimately into digital terrain models (DTMs). The minimally processed data are pulse compressed, corrected for ionospheric distortion, zero-Doppler filtered, and incoherently summed. We then apply pulse re-tracking techniques adapted from terrestrial ocean altimetry to identify the surface return. From the surface return we compute the time-of-flight and hence the range from the spacecraft to the surface of the planet. The altimetry groundtracks are then co-registrated with Mars Orbiter Laser Altimeter (MOLA) to remove any biases resulting from residual ionospheric effects or timing issues. The altimetric profiles are finally used to create DTMs based on SHARAD data. While the SHARAD altimetry data have coarser inherent resolution than laser altimeters or imaging radars, we demonstrate that radar sounding data is still a viable source for satellite-based altimetry measurements. This is particularly important for future planetary missions not carrying laser altimeters but radar sounders, such as the upcoming Europa Clipper mission.

Tyrrhena Terra hosts an intriguing variety of aqueously altered materials accompanied by unaltered mafic rocks. Our study region extends from the southern rim of the Isidis impact basin, including the Libya Montes region, southward to the Hellas Basin rim (Fig. 1). The NW part is dominated by lava flows from Syrtis Major that grade southwards into the TT highlands, dissected by fluvial channels and overprinted by abundant impact craters. These landforms together with lobate and fan-shaped deposits within impact craters are evidence for a variable history of erosion and deposition. Ancient phyllosilicate-rich materials have been exposed and uplifted from the subsurface, as they often occur in crater ejecta and central crater uplifts. Our previous studies used CRISM spectral data together with CTX, HiRISE, and HRSC images as well as their derived topography data to create geomorphological maps of the southern Isidis region and Tyrrhena Terra. These datasets were used to map and characterize the types and occurrences of phyllosilicates, chlorite, opal, zeolites, carbonates, olivines, and pyroxenes and to assess the relationships between selected aqueous outcrops and surface features. In this work, we build on these results by seeking correlations between aqueous mineral detections with our geomorphological map to assess 1) whether or not there are relationships between specific units and mineral occurrences, and 2) if there are trends across the study region in terms of mineral occurrence and abundance. The mineralogical map originates from a study that spans not only the inter-Isidis-Hellas region, but also extends northwards to Nili Fosse and westwards to Terra Sabea. The focus of that study was on the metamorphic- and hydrothermally-related alteration history using CRISM targeted and mapping data, including hundreds of calibrated MTRDR images. These mineral detections were available to us as a mapped shape file, enabling us to assess the minerals in context with the geomorphological map. We utilized ESRI’s ArcGIS system and conducted multiple statistical queries in terms of mineral occurrence/type versus map unit in order to reveal possible trends within and across the study region. Fe/Mg-phyllosilicates are the dominant aqueous mineral type within the study region and are more abundant in the central region compared to the proximity of either the Isidis or Hellas impact basin. Chlorites increase in abundance with distance from both impact basins, which could be an indication of hydrothermal processes from geothermal flux. The large Hellas impact event appears to have produced more varied temperatures and water chemistries, resulting in increased mineral variability near its rim.

Details about previous established links between emplacement conditions and lava types, data and methods, additional correlation results, and limitations.

MONTES, MARS. M. D. Lane, J. L. Bishop, D. Loizeau, D. Tirsch, L. L. Tornabene, L. Sacks, C. Viviano, J. R. C. Voigt Fibernetics LLC, Lititz, PA (lane@fibergyro.com), Carl Sagan Center, SETI Institute, Mountain View, CA, IAS, Université-Sud, Orsay, France, Institute of Planetary Research, German Aerospace Center (DLR), Berlin, Germany, Dept. of Earth Sciences, Institute for Earth and Space Exploration, University of Western Ontario, London, Canada, Johns Hopkins University Applied Physics Lab (JHUAPL), Laurel, MD, Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ.

Surface roughness is a commonly used parameter for the quantitative analysis and characterization of geological terrains on Earth, as well as on other planetary bodies, particularly where detailed optical data may not be available. Here, we statistically investigate if surface roughness can be used to distinguish between different lava facies in remote sensing data by examining the entire 2014–2015 Holuhraun lava flow-field in Iceland. Root-mean-square (RMS) height deviation, Hurst exponents, and breakpoints were calculated to quantify the surface roughness characteristics of eight facies using stereo-derived topographic datasets at three different pixel scales, ranging from 0.05 to 0.5 m/pixel. We show that most of the investigated lava facies (rubbly, spiny, undifferentiated rubbly–spiny, shelly, pāhoehoe, and flat-lying–knobby) are indistinguishable by surface roughness down to the 5 cm baseline, with the exception of topography-building facies like the vent-proximal edifice and the exceptionally blocky channel interior facies. Additionally, we considered baselines corresponding to radar S-band (10 cm), L-band (20 cm), and P-band (90 cm). Our findings imply that when transitional lava types are considered in addition to traditional end-members, topographic roughness data, including RMS height deviation and Hurst exponent values alone, cannot be used to uniquely identify lava facies at these baselines.

The 2014–2015 Holuhraun eruption extruded >1 km3 of lava in a barren region of the Icelandic highlands. Due to its large volume and the abundance of data for this eruption, Holuhraun is an ideal site to investigate fissure-fed eruption products for comparison with other large lava flow-fields on Earth and other planetary bodies. To characterize lava morphologies associated with this event, we used 0.01–0.5 m/pixel image data, acquired from aerial surveys and small Unoccupied Aircraft Systems (sUAS) to create a 1:800-scale facies map that was ground-truthed using field observations during the summers of 2015–2019. Each facies region exhibits similar attributes in the remote sensing data, including albedo, surface texture, and geomorphology. However, at our mapping scale of 1:800, the facies typically include mixtures of lava types. Results show that transitional lava types (e.g., rubbly pāhoehoe, slabby pāhoehoe, and spiny pāhoehoe) dominate the 2014–2015 Holuhraun lava flow-field (83.82 km2), rather than the traditional end-members of ʻaʻā and classical pāhoehoe. At 1:800-scale, we distinguish the following eight facies (with the percentage of total flow-field area shown in parentheses): rubbly (57.35%), spiny (25.96%), undifferentiated rubbly–spiny (9.59%), shelly (5.58%), pāhoehoe (1.24%), flat-lying–knobby (0.58%), vent-proximal edifice (0.19%), and channel interior (0.16%). Field observations show that initial coherent pāhoehoe surfaces were episodically disrupted to produce slabby and rubbly textures that resemble ʻaʻā in remote sensing data. Our observations also show that continued solidification of the lava beneath brecciated surfaces can cause the surfaces of disrupted lobes to stabilize, or restabilize and undergo inflation. These factors complicate the use of surface texture as a direct indicator of emplacement style, which can change over the course of an eruption. This complexity has important implications for reconstructing the emplacement history of flow-fields on Earth and other planetary bodies.

Determining the parameters that control fissure-fed lava morphologies is critical for reconstructing the complex emplacement histories of eruptions on Earth and other planetary bodies. We used a geomorphological map of the 2014–2015 Holuhraun lava flow field, in combination with new constraints on lava emplacement chronology and two independently derived time-averaged discharge rate (TADR) data sets, to analyze correlations between lava morphology and effusion rate. Results show that lava morphologies are dominantly controlled by effusion rate at the vent during the early phases of the eruption and by lava transport processes as the system evolves. Initially, TADR and its variance, which reflect pulsation in the lava supply rate from the vent, directly affect lava emplacement styles. However, as the eruption progresses, the lava transport system exerts a stronger control with channels and ponds that can either dampen variation in local effusion rate or create surges during sudden drainage events. The Holuhraun eruption predominantly produced rubbly lava in its earlier eruption phases and transitioned into the production of spiny lava toward the end of the eruption. However, a drop of TADR during the first phase of the eruption correlates with a decrease in rubbly lava formation and an increase in spiny lava production. This suggests that a change in effusion rate caused the observed transition in lava type. Our findings show that rubbly lava is formed under relatively high local effusion rates with pulsating supply conditions, whereas spiny lava is formed under lower local effusion rates and steadier supply.

Hypervelocity impacts on terrestrial bodies have the potential to rapidly heat and redistribute silicate target material to form impact melt flows. On the Moon, a subset of impact melt deposits exited the craters as laterally moving flows that moved away from the crater rim under the influence of gravity. These impact melt flows exhibit similarities to lava flows, but have the potential to be superheated by the impact cratering process. To estimate the initial temperature (T-0) and thickness (H-0) of these flows we combine new remote sensing analyses, experimentally-derived rheological relationships for three lunar analog materials, and numerical forward models of impact melt flow emplacement to identify combinations of parameters that yield flows matching the observed length of impact melt deposits on the Moon. We focus on the impact melt flows of four craters, which span a range of target materials and crater diameters (D): Giordano Bruno (D = 22.1 km), Necho (D = 36.9 km), Tycho (D = 85.3 km), and Copernicus (D = 96.1 km). We modeled three melt compositions-anorthosite, norite, and basalt-emplaced under cold ambient temperatures (T-amblent = -180 degrees C) on the Moon, to place a minimum bound on cooling-limited flow emplacement. Results show that observed flow lengths can be achieved by subliquidus melts emplaced within a laminar flow regime. For high-density (0% vesicularity) melts, best-fit inversions for T-0 and H-0 have mean values of 1253.3 +/- 149.8 degrees C and 21.6 +/- 8.7 m, respectively; for low-density (64% vesicularity) melts, mean T-0 and H-0 values are 1343.3 +/- 87.8 degrees C and 27.9 +/- 5.7 m-with uncertainties reported at 1 standard deviation. Model results also show that under cold ambient temperatures, impact melt flows with 0 to 64% vesicularity would be expected to have mean emplacement durations of 76, 78, 174, and 186 h for Giordano Bruno, Necho, Tycho, and Copernicus, respectively. Therefore, initial impact melt temperatures do not have to be in the super-liquidus range to form gravity-driven flow deposits matching observed lengths, and emplacement times are long enough for the majority of self-secondary fragments to land before the impact melt flows are fully emplaced. This suggests that some impact melt flow may be lava-like in their emplacement dynamics and that differences in crater populations on impact melt flows and adjacent ejecta may differ significantly, with impact melts providing a more robust estimate of the emplacement age of the young craters due to the presence of fewer secondaries. Impact melts could still have super-liquidus temperatures at the time of their initial formation, but turbulence would facilitate the rapid entrainment of external clasts, quickly lowering melt temperatures to generate flows that are similar to the products of effusive volcanic eruptions.