Acidalia Planitia Research Articles

Habitat site selection on Mars: Suitability analysis and mapping

Growing interest in extraterrestrial colonization has increasingly centered on Mars, bolstered by extensive environmental data from Mars exploration missions. However, the planet's harsh conditions—including extreme temperatures, dust storms, varied terrain, high radiation, and scarce water resources—pose significant challenges to selecting suitable sites for human habitation. This study evaluated potential habitats on Mars by considering factors such as temperature, wind, radiation, terrain, dust, and water ice. Through the development of comprehensive suitability maps, we identified potential areas for future human construction, primarily concentrated in south Arcadia Planitia, south Utopia Planitia, and the junction of Acidalia Planitia and Arabia Terra. The analysis revealed that, except for Hellas Planitia, most of Mars' southern hemisphere is largely unsuitable for long-term human habitation. This work establishes a continually expandable novel framework and offers a new perspective for interdisciplinary approaches in studying human habitation environments in the context of future Martian exploration. Moreover, it can be adjusted based on different future technological scenarios.

A Global Database of Pitted Cones on Mars for Research on Martian Volcanism

This study presents a global database of pitted cones on Mars. This database was created using an active deep-learning approach based on a global mosaic of Mars Context Camera (CTX) images, followed by extensive manual verification. The global database contains 250,547 pitted cones along with their central coordinates and diameters. 94.2% of the pitted cones have diameters ranging from 100 m to 1 km. Most of them are in the northern lowlands, while some are scattered in the southern highlands. Systematic evaluation of the extracted pitted cones is performed in Isidis Planitia, Acidalia Planitia, and Cerberus Palus on Mars. The results reveal that the precision ranges from 79.2% to 85.6%, and the recall rate ranges from 62.4% to 87.7%, indicating a varying among regions but satisfactory performance. Manual digitizing evaluation indicates that over 94.1% of manual labels by different annotators have a differentiation rate of 10%, showing promising precision and consistency. This global database can facilitate further research on the origin and evolution of pitted cones on Mars.

Clay mineralogy in west Chryse Planitia, Mars: Comparison with present and future landing sites

On Mars, the well-known crustal dichotomy marks the boundary between the old southern highlands and the younger northern lowlands. Among these lowlands, Chryse Planitia resembles a quasi-circular basin surrounded by several highlands, and blends into Acidalia Planitia, another flat lowland located farther north. The transition area between these highlands and the Chryse basin is often designated as “circum-Chryse Planitia”, and is the terminus for many outflow channels. Infrared datasets display several sites therein with extensive clay-bearing outcrops, further testifying for aqueous activity on early Mars – notably around Mawrth Vallis, Oxia Planum and Xanthe Terra. In this study, we investigate clay-bearing outcrops identified along the western margins of circum-Chryse basin, often overlooked in the Martian literature. We also compare them with outcrops found in other regions along the crustal dichotomy and relevant in the Martian literature, such as Oxia Planum, Mawrth Vallis and Nili Fossae. Investigating such deposits is crucial for astrobiological perspectives, as they are appealing targets to search for organic compounds possibly stored throughout the rocks and soils. Fe,Mg-rich clays generally result from the interaction of liquid water with rocks under low temperatures, moderate pH levels and neutral to reducing conditions, factors favorable for life. Here, the clay minerals detected in west Chryse Planitia are consistent with either ferrosaponites or vermiculites associated with hydrobiotite, as recently inferred in Oxia Planum and north Xanthe Terra. Diverse alteration pathways might be involved based on either of these clay species. The clay-bearing rocks crop out in isolated hills in Lunae Planum, and along inverted channels and small craters in Tempe Terra. Further geologic investigations in circum-Chryse Planitia should certainly provide new clues on their origin and weathering conditions, while supporting the upcoming ExoMars rover mission and other future explorations.

Analyzing vertical dust distribution and associated meteorological characteristics over Acidalia Planitia during a regional and global dust event

This study analyzed the vertical distribution of dust and associated atmospheric structural changes over Acidalia Planitia during one regional dust event (RDE) (MY 32, Ls = 220°) and one global dust event (GDE) (MY 28, Ls = 260°), using Mars Climate Sounder observations and Mars Weather Research and Forecasting (MarsWRF) model simulations. Multilinear Regression Coefficient (MLRC) analysis suggests that dustiness at 25–35 km and ~ 40–50 km altitudes contributed significantly to the column integrated opacity during the RDE and GDE, respectively. Both dust events reduced water ice opacity at ~40 km altitude. The atmosphere subsequently warmed ~10 K during the RDE and ~ 30 K during the GDE because of dust radiative heating. An inversion layer formed below ~20 km altitude during RDE due to the combined effect of reduced surface temperature and the downwelling radiation from suspended dust. However, the GDE's much larger opacity at higher altitudes helped form a similar inversion layer at 40 km. This atmospheric warming with the inversion layer below could be associated with heating/cooling layers centered around 35–50 and 20–35 km heights, influencing the variability of water ice within them. The MarsWRF simulations showed downwelling over Acidalia Planitia at ~35–50 km altitude, which supports the presence of the heating layer due to the suspended atmospheric dust during the GDE. However, findings from the heating rate analysis indicated a dominance of dust radiative heating compared to adiabatic heating due to compression on the atmospheric warming during the dust storm occurrences. The simulated boundary layer height and surface radiation flux suggest weaker vertical mixing from the surface and a surface energy budget dominated by downward radiation from the suspended dust, which helped form heating/cooling layers and drove variability in water ice clouds. The Empirical Orthogonal Function analysis (carried out using MCS observations) suggests that the seasonal cycle of the southern hemispheric dust storms, northern hemispheric active storm track, and the cap-edge storms possibly influenced the seasonality observed in the heating/cooling layer clouds.

Deliquescence probability maps of Mars and key limiting factors using GCM model calculations

There may be a chance of small-scale ephemeral liquid water formation on present day Mars, even though the current climate does not support the existence of larger bodies of water. Through a process called deliquescence, hygroscopic salts can enter solution by absorbing water vapor directly from the atmosphere. Due to the absence of in-situ deliquescence experiments so far, the most reliable way to forecast deliquescence is through atmospherical modeling, however, the locations and times when salty liquid water could emerge are not yet well known. In this paper we present our results of likely brine formation on Mars, their proposed locations and seasons, as well as the possible limiting factors. For our calculations we used the data of Laboratoire de M\'et\'eorologie Dynamique Mars General Circulation Model version 5. The results show that from L$_s$ 35$^\circ$ - L$_s$ 160$^\circ$, between 9 PM and 11 PM there is a good chance for calcium perchlorate deliquescence above 30$^\circ$ N, while in this zone the ideal regions are concentrated mostly to Acidalia Planitia and Utopia Planitia between 1 AM and 3 AM. We found that in the Southern Hemisphere, between L$_s$ 195$^\circ$ and L$_s$ 320$^\circ$, there is a noticeable, but weaker band in the vicinity of 60$^\circ$ S, and both Argyre Planitia and Hellas Planitia show some chance for brine formation. According to our statistics the key limiting factor of deliquescence could be relative humidity in most cases. Our results suggest that during summer -- early fall seasons, there could be deliquescence in both hemispheres in specific areas from the late evening until the early morning hours. There are only few studies detailing the geological and temporal distribution of brine formation through deliquescence, thus this work could be used as a good guide for future landing site analysis or in choosing a specific location for further research.

Evidence of mud volcanism due to the rapid compaction of martian tsunami deposits in southeastern Acidalia Planitia, Mars

Thumbprint terrain was first recognized in Viking Orbiter data and described as sets of alternating continuous parallel ridges and depressions up to several tens of kilometres in length, with high and low albedo respectively. We performed a geomorphological analysis of these features using both Context Camera and High Resolution Imaging Science Experiment images, as well as topographic profiles based on Mars Orbiter Laser Altimeter data, with the aim to provide an origin for thumbprint terrain and constrain the geological evolution of southeastern Acidalia Planitia. The identification of runup lobate deposits, coupled with the putative presence of a Late Hesperian ocean in the northern lowlands, led to speculations that evidence of tsunamis may be present in the geologic record of the area. There are several hypotheses that have been proposed previously to explain the origin of thumbprint terrain and include ice-related, volcanic-related, liquefaction and mud-volcanism driven processes. However, a tsunami-related origin provides a strong geological framework for the energy required for the associated lobes to flow uphill and leaving peripheral termination ridges as a result of viscosity. Numerical simulations indicate that - prior to their emplacement - the lobes sustained high velocities, thereby lending further support to the tsunami hypothesis and their origin from the Lomonosov crater impact. Wave interference patterns, formed during the propagation of the tsunamis over and around prominent topography, likely explain the thumbprint terrain spatial arrangement. The thumbprint terrain sedimentary cones are, herein, considered mud volcanoes related to a tsunami that occurred in southeastern Acidalia Planitia.

Impact cratering rate consistency test from ages of layered ejecta on Mars

Ages of geological units of planetary bodies are determined from impact crater counts on their surface. These ages are model-dependent, and several models largely used in the community assume a constant production function and a constant cratering rate over the last 3 Ga. We have mapped the population of small impact craters (>200 m in diameter) formed over a population of large impact craters (>5 km in diameter) with layered ejecta on Acidalia Planitia, Mars. We have deduced the age of each large impact crater under the assumption of a constant impact rate and constant production function. The impact rate inferred from this set of ages is, however, not constant and show a significant increasing during the last ~1 Ga compared to chronology models commonly used. We interpret this inconsistency as an evidence for temporal variations in the size-frequency distribution (SFD) of impactors in the main belt, consistent with recent studies argued for a late increasing of the large impactor flux on Earth and the Moon.

The Onset and Growth of the 2018 Martian Global Dust Storm

AbstractWe analyze the onset and initial expansion of the 2018 Martian Global Dust Storm (GDS 2018) using ground‐based images in the visual range. This is the first case of a confirmed GDS initiating in the Northern Hemisphere. A dusty area extending about 1.4×105 km2 and centered at latitude +31.7°±1.8° and west longitude 18°±5°W in Acidalia Planitia was captured on 30 and 31 May 2018 (Ls = 184.9°). From 1 to 8 June, daily image series showed the storm expanding southward along the Acidalia corridor with velocities of 5 m/s and simultaneously progressing eastward and westward with horizontal velocities ranging from 5 to 40 m/s. By 8 June the dust reached latitude ‐55° and later penetrated in the South polar region, whereas in the North the dust progression stopped at latitude approximately +46°. We compare the onset and expansion stage of this GDS with the previous confirmed storms.

Grid Mapping the Northern Plains of Mars: A New Overview of Recent Water‐ and Ice‐Related Landforms in Acidalia Planitia

AbstractWe used a grid‐mapping technique to analyze the distribution of 13 water‐ and ice‐related landforms in Acidalia Planitia as part of a joint effort to study the three main basins in the northern lowlands of Mars, that is, Acidalia, Utopia, and Arcadia Planitiae. The landforms were mapped at full Context Camera resolution along a 300‐km‐wide strip from 20°N to 84°N. We identified four landform assemblages: (1) Geologically recent polar cap (massive ice), which superposes the latitude‐dependent mantle (LDM) (LA1); (2) ice‐related landforms, such as LDM, textured terrain, small‐scale polygons, scalloped terrain, large‐scale viscous flow features, and gullies, which have an overlapping distribution (LA2); (3) surface features possibly related to water and subsurface sediment mobilization (LA3; kilometer‐scale polygons, large pitted mounds, small pitted mounds, thumbprint terrain); and (4) irregularly shaped pits with raised rims on equator‐facing slopes. Pits are likely the result of an energetic release of volatiles (H2O, CO2, and CH4), rather than impact‐, volcanism‐, or wind‐related processes. LDM occurs ubiquitously from 44°N to 78°N in Acidalia Planitia. Various observations suggest an origin of air fall deposition of LDM, which contains less ice in the uppermost tens of meters in Acidalia Planitia than in Arcadia and Utopia Planitiae. However, LDM may be thicker and more extended in the past in Acidalia Planitia. The transition between LDM‐free terrain and LDM is situated further north than in Utopia and Arcadia Planitiae, suggesting different past and/or present climatic conditions among the main basins in the northern lowlands.

The distribution of putative periglacial landforms on the martian northern plains

In this investigation, HiRISE images were surveyed across three regions of the Northern Plains of Mars; Acidalia, Arcadia and Utopia Planitiae. A sample of HiRISE images within each of these areas was examined. The aim of the investigation was to determine the distribution of three varieties of landform; clastic patterned ground, lobate hill-slope features and scalloped depressions. These features are of importance, as they are morphologically similar to terrestrial periglacial features.Examples of these landforms were found across the study areas. Scalloped depressions are common at mid latitudes in each of the three regions. Sorted patterned ground was not as widespread. Some examples of sorted patterned ground were found in all three study areas, but the main concentration occurs in the north-western region of Acidalia Planitia. Lobate hill-slope features were the least common of the three landform types. Despite occurring infrequently, several possible examples of lobate features were found to occur in proximity to other putative periglacial features.It was found that lobate hill-slope features and clastic patterns occurred further south than expected, beyond the southern extent of many previous studies. These features, and by extension the processes that form them, could thus occur more widely than previously thought.It also appears that although putative periglacial features are often found in crater interiors they are not limited to these environments. Extensive areas of patterned ground were found on the inter-crater plains. Lobate features and sorted stripes were often found on crater walls, which would support the hypothesis that they are analogous to hill-slope features on Earth. Scalloped depressions were most often found in crater interiors, or on crater ejecta, although examples on the inter-crater plains were not uncommon.

High-Resolution Topographic Analyses of Mounds in Southern Acidalia Planitia, Mars: Implications for Possible Mud Volcanism in Submarine and Subaerial Environments

A northern ocean of Mars is still debated and, if it existed, it may have accompanied valley networks and/or outflow channels, which may have led to the emplacement of a large amount of water to the northern lowlands during the Noachian and/or Hesperian times. However, it is unclear how and under what conditions (submarine or subaerial) geologic features such as mounds and giant polygons formed in the northern lowlands. The densely-distributed mounds in Chryse and Acidalia Planitia, >1000 km-wide basins of the northern plains, were suggested to be ancient mud volcanoes formed in an aqueous setting, which is controversial (i.e., mud vs. igneous and submarine vs. subaerial). However, these mounds have not been quantitatively well characterized, particularly with respect to their detailed topography. Here we generated forty digital elevation models (DEMs) with resolution of up to 1 m/pixel from High Resolution Imaging Science Experiment (HiRISE) stereo image pairs, and we accurately measured the morphometric parameters of ~1300 mounds within the southern part of the Acidalia basin. Their heights and diameters resulted in good accordance with those of mud and igneous volcanoes in submarine/subaerial settings on Earth. Maximum depths of their source reservoirs vary from ~30 to ~450 m for a subaqueous setting and from ~110 to ~860 m for a subaerial setting, both of which are consistent with fluid expulsion from the ~100–4500 m-thick flood deposits (Vastitas Borealis Formation, VBF). On the basis of the morphometric values, we estimated rheological properties of materials forming the mounds and found them consistent with a mud flow origin, which does not rule out an igneous origin. The conditions of possible submarine mud or igneous volcanoes may have harbored less hazardous environments for past life on Mars than those on an ocean-free surface.

Topography of the Deuteronilus contact on Mars: Evidence for an ancient water/mud ocean and long-wavelength topographic readjustments

In this paper, we present the results of our detailed study of morphology, topography, and age of the Deuteronilus contact that outlines Vastitas Borealis Formation (VBF) in the northern plains and the Isidis Planitia unit. The Deuteronilus contact represents a sharp and distinct geological boundary that can be traced continuously for many hundreds to thousands of kilometers. In the northern plains, segments of the Deuteronilus contact occur at two distinct topographic levels. In the northern plains, the long-wavelength topography of the Deuteronilus contact occur at two distinct topographic levels. In the Tempe, Chryse, Acidalia, and Cydonia-Deuteronilus regions (the total length is ∼14,000 km), the contact is at the mean elevation of about −3.92 km (the decile range is 180 m, from −4.01 km to −3.83 km). In the Pyramus-Astapus, Utopia, and Western Elysium regions (the total length is ∼7700 km), the mean elevation of the contact is about −3.58 km (the decile range is 270 m, from −3.73 km to −3.46 km). These levels to large extent (but not completely) correspond to the model geoids that may have been characterized the shape of Mars at the time of the VBF emplacement. Largest deviations of the actual topographic position of the contact from the model geoids occur in the Tantalus and Phlegra regions where the deviations are due to the post-VBF changes of the regional topography. The fact that the model geoids satisfactory describe the shape of the largest portion of the contact provides additional evidence for both the emplacement of the VBF edges near an equipotential surface and for relative stability of the shape of Mars during a long time interval of about 3.6 Ga. Within the northern plains in the Tempe Terra, Acidalia Planitia, Cydonia-Deuteronilus, Pyramus-Astapus, and the southern Utopia regions, the absolute model ages of the VBF surface near the Deuteronilus contact are tightly clustered around the age of ∼3.6 Ga, which we interpret as the age of the VBF emplacement. The surface of the VBF-like Isidis Planitia unit is distinctly younger, ∼3.50 ± 0.01 Ga, which suggests that this unit formed independently. Neither volcanic nor glacial modes of emplacement are consistent with the topographic configuration and the shape of the Deuteronilus contact within both the northern plains and in Isidis Planitia. The broad flooding and formation of extensive water/mud reservoirs remains to be the most plausible mode of formation of the VBF in the northern plains and the VBF-like unit on the floor of the Isidis basin.

Basaltic glass formed from hydrovolcanism and impact processes: Characterization and clues for detection of mode of origin from VNIR through MWIR reflectance and emission spectroscopy

The CheMin X-ray diffraction instrument on-board the Curiosity rover in Gale crater has measured a consistent X-ray amorphous component in drill core samples examined to-date, clearly demonstrating that X-ray amorphous materials are a significant fraction of the martian surface layer. Glasses are potential components of this amorphous material and in this study, basaltic tephras from several hydro- and glaciovolcanic centers, as well as impact melts from India's Lonar Crater, were examined using thin section petrography, visible and near-infrared reflectance and mid-wave infrared emission spectroscopy as well as measuring major and minor element chemistry of representative samples using X-ray fluorescence (XRF) spectroscopy. The objectives of this study have been to look for distinguishing characteristics between volcanic and impact glasses and to determine features that indicate whether the glasses are fresh or altered using methods available on current and planned Mars rovers. Spectral features in the visible and near-infrared (VNIR) that can be used as indicators of alteration include the development of hydration features at 1.9 and ∼3µm and a feature attributed to ferric oxide development at 0.48µm. In the mid-wave infrared, it was observed that glass-rich tephra field samples did not display a broad, disordered glass feature near 9–10µm (as is observed in pristine basaltic glasses) but rather a doublet with centers near 9.5 and 11µm attributed in earlier work to incipient devitrification into SiO4 chain and sheet structures respectively. A tentative observation was made that the Si–O bending feature, observed in all the sample spectra near 22µm was broader in the hydro- and glaciovolcanic glass samples than in the impact glass samples. Hydro- and glaciovolcanic glass-rich tephra samples were used as library spectra in linear deconvolution analyses of Mars Global Surveyor Thermal Emission Spectrometer (MGS TES) surface spectral types. These incipiently devitrified glass spectra were selected for all of the surface types and formed close to 40% of the N. Acidalia Planitia spectral type.

Observations and modeling of northern mid-latitude recurring slope lineae (RSL) suggest recharge by a present-day martian briny aquifer

Recurring slope lineae (RSL) are narrow (0.5–5m) dark features on Mars that incrementally lengthen down steep slopes, fade in colder seasons, and recur annually. These features have been identified from the northern to southern mid-latitudes. Here, we describe how observations of northern mid-latitude RSL in northern Chryse Planitia and southwestern Acidalia Planitia (CAP) suggest that brines start flowing before northern spring equinox and continue for more than half a Mars-year (490±40 sols, spanning solar longitude 337°±11°–224°±20°). All CAP RSL are found on the steep slopes of craters and their source zones are at or below the elevation of the surrounding plains. Spacecraft-derived surface temperature observations cannot resolve individual RSL, so thermal modeling was used to determine that CAP RSL have a freezing temperature of 238–252K, freeze and melt diurnally, and flow only occurs within the top ∼8cm of the regolith. Furthermore, we calculate that a typical CAP RSL has a water budget of 1.5–5.6m3/m of headwall. Therefore, such a large water budget makes annual recharge via atmospheric or subsurface diffusion sources unlikely. Alternatively, we hypothesize that the most plausible RSL source is a briny aquifer with a freezing temperature less than or equal to the mean annual CAP surface temperature (220–225K). The annual cycle is as follows: in late autumn, the shallowest part of the brine feeding the source zone freezes, forming an ice dam. As spring approaches, temperatures rise and the dam is breached. Brine is discharged and the RSL initially lengthens rapidly (>1.86m/sol), the lengthening rate then slows considerably, to ∼0.25m/sol. Eventually, the losses equal the discharge rate and the RSL reaches its equilibrium phase. As brine flows in the RSL some of the water is lost to the atmosphere, therefore the freezing temperature of the brine within the RSL is higher (238–252K) as the brine transitions to a super-eutectic salt concentration. In the late autumn, falling temperatures restore the ice dam and the H2O in the RSL slowly sublimates away. Overall, CAP RSL possess a significantly different seasonality and much longer duration than typical southern mid-latitude RSL, suggesting that RSL at different latitude bands have different source types. Lastly, CAP RSL are the best evidence that shallow groundwater may still exist on Mars.

Mars Orbiter Camera climatology of textured dust storms

We report the climatology of “textured dust storms”, those dust storms that have visible structure on their cloud tops that are indicative of active dust lifting, as observed in Mars Daily Global Maps produced from Mars Orbiter Camera wide-angle images. Textured dust storms predominantly occur in the equinox seasons while both solstice periods experience a planet-wide “pause” in textured dust storm activity. These pauses correspond to concurrent decreases in global atmospheric dust opacity. Textured dust storms most frequently occur in Acidalia Planitia, Chryse Planitia, Arcadia Planitia, and Hellas basin. To examine the nature of the link between textured dust storms and atmospheric dust opacity, we compare the textured dust storm climatology with a record of atmospheric dust opacity and find a peak global correlation coefficient of approximately 0.5 with a lag of 20–40° in solar longitude in the opacity compared to the solar climatology. This implies that textured dust storms observed at 1400 local time by MOC are responsible for a large fraction of atmospheric dust opacity and that other mechanisms (e.g., dust devil lifting or storm-scale lifting not observed in this study) may supply a comparable amount of dust.

Evidence for large reservoirs of water/mud in Utopia and Acidalia Planitiae on Mars

Utopia and Acidalia Planitiae show a set of similar morphologic features indicative of the presence of large reservoirs of water/mud in these regional topographic lows. The most important of these features are: (1) impact crater ejecta morphology that progressively changes from ballistic/rampart at the basins periphery to strongly degraded pancake-like in the central portions of the basins, and (2) etched flows (interpreted as mudflows) that are concentrated in those regions of the central portions of both basins where the pancake-like ejecta prevail. The Vastitas Borealis Formation (VBF) in Utopia and Acidalia Planitiae represents the uppermost stratigraphic limit of possible reservoirs in both basins and has practically the same age in these regions; ∼3.57 (±0.02) Ga in Utopia Planitia and ∼3.61 (+0.05/−0.08) Ga in Acidalia Planitia. The southern contact of the VBF closely follows specific contour lines in Utopia Planitia (∼−3.6km±54m, over a distance of ∼1500km) and Acidalia Planitia (∼−3.9km±70m, over the distance of ∼6000km). The presence of the large water/mud reservoirs and the age and topographic configuration of the VBF in Utopia and Acidalia Planitiae are consistent with the existence of an extensive single body of water (an ocean) in the northern plains of Mars.

Mud volcanoes of trinidad as astrobiological analogs for martian environments.

Eleven onshore mud volcanoes in the southern region of Trinidad have been studied as analog habitats for possible microbial life on Mars. The profiles of the 11 mud volcanoes are presented in terms of their physical, chemical, mineralogical, and soil properties. The mud volcanoes sampled all emitted methane gas consistently at 3% volume. The average pH for the mud volcanic soil was 7.98. The average Cation Exchange Capacity (CEC) was found to be 2.16 kg/mol, and the average Percentage Water Content was 34.5%. Samples from three of the volcanoes, (i) Digity; (ii) Piparo and (iii) Devil’s Woodyard were used to culture bacterial colonies under anaerobic conditions indicating possible presence of methanogenic microorganisms. The Trinidad mud volcanoes can serve as analogs for the Martian environment due to similar geological features found extensively on Mars in Acidalia Planitia and the Arabia Terra region.

Phyllosilicate and hydrated silica detections in the knobby terrains of Acidalia Planitia, northern plains, Mars

Here we report detections of Fe/Mg phyllosilicates and hydrated silica in discrete stratigraphic units within the knobby terrains of Acidalia Planitia made using data acquired by Compact Reconnaissance Imaging Spectrometer for Mars. Fe/Mg phyllosilicates are detected in knobs that were eroded during southward retreat of the dichotomy boundary. A second later unit, now eroded to steep-sided platforms embaying the knobs, contains hydrated silica, which may have formed via localized vapor weathering, thin-film leaching, or transient water that resulted in surface alteration. These are then overlain by smooth plains with small cones, hypothesized to be mud volcanoes which previous studies have shown to have no hydrated minerals. In spite of Acidalia's location within the putative northern ocean, collectively, the data record a history of aqueous processes much like that in the southern highlands with progressively less intensive aqueous chemical alteration from the Noachian to Amazonian.

Local Dynamics of Baroclinic Waves in the Martian Atmosphere

Abstract The paper investigates the processes that drive the spatiotemporal evolution of baroclinic transient waves in the Martian atmosphere by a simulation experiment with the Geophysical Fluid Dynamics Laboratory (GFDL) Mars general circulation model (GCM). The main diagnostic tool of the study is the (local) eddy kinetic energy equation. Results are shown for a prewinter season of the Northern Hemisphere, in which a deep baroclinic wave of zonal wavenumber 2 circles the planet at an eastward phase speed of about 70° Sol−1 (Sol is a Martian day). The regular structure of the wave gives the impression that the classical models of baroclinic instability, which describe the underlying process by a temporally unstable global wave (e.g., Eady model and Charney model), may have a direct relevance for the description of the Martian baroclinic waves. The results of the diagnostic calculations show, however, that while the Martian waves remain zonally global features at all times, there are large spatiotemporal changes in their amplitude. The most intense episodes of baroclinic energy conversion, which take place in the two great plain regions (Acidalia Planitia and Utopia Planitia), are strongly localized in both space and time. In addition, similar to the situation for terrestrial baroclinic waves, geopotential flux convergence plays an important role in the dynamics of the downstream-propagating unstable waves.

Distribution of polygon characteristic scale in Martian patterned ground terrain in the northern hemisphere using the Fourier transform

Permafrost patterned ground forms on the surface of nearly all landscapes between 50°N and 70°N on Mars. This landform appears in satellite imagery as an interconnected network of polygonal shapes. Previous studies used geomorphologic observations to characterize patterned ground terrains on Mars. These classification systems prove useful but suffer from somewhat subjective methods. We find objective analysis of the polygons comprising patterned ground terrains on the surface of Mars feasible using High Resolution Imaging Science Experiment imagery acquired from orbit. We perform a two‐dimensional Fourier transform on 124 images of patterned surfaces to characterize the spatial scale pertinent to scenes and analyze the distribution of these properties on the surface of Mars between 50°N and 70°N. We find two distinct sets of polygons: large polygons which form below 60°N and small polygons primarily above 60°N with exception for sites within Acidalia Planitia. Our findings show similar trends to those found in previous studies but also fundamental differences in the populations of polygons above and below 60°N. The polygons within 60°N–70°N share roughly the same polygonal scale, implying that seasonal temperature change is not the only factor forcing polygon development as previous models found. In some cases, our method indicates the presence of multiple scales of polygons, although it cannot quantify the larger scale. This method in conjunction with observational analysis improves our ability to characterize surfaces and examine patterned ground terrains on Mars.