Outflow Channels Research Articles

Low Intraocular Pressure Induces Fibrotic Changes in the Trabecular Meshwork and Schlemm's Canal of Sprague Dawley Rats.

Continuous artificial aqueous humor drainage in the eyes of patients with glaucoma undergoing trabeculectomy likely exerts abnormal shear stress. However, it remains unknown how changes in intraocular pressure (IOP) can affect aqueous humor outflow (AHO). Here, we induced and maintained low intraocular pressure (L-IOP) in healthy Sprague Dawley (SD) rats by puncturing their eyes using a tube (200-µm diameter) for 2 weeks. After the rats were euthanized, their eyes were removed, fixed, embedded, stained, and scanned to analyze the physiological and pathological changes in the trabecular meshwork (TM) and Schlemm's canal (SC). We measured SC parameters using ImageJ software and assessed the expression of various markers related to flow shear stress (KLF4), fibrosis (TGF-β1, TGF-β2, α-SMA, pSmad1/5, pSmad2/3, and fibronectin), cytoskeleton (integrin β1 and F-actin), diastolic function (nitric oxide synthase and endothelial nitric oxide synthase [eNOS]), apoptosis (cleaved caspase-3), and proliferation (Ki-67) using immunofluorescence or immunohistochemistry. L-IOP eyes showed a larger SC area, higher eNOS expression, and lower KLF4 and F-actin expression in the TM and SC (both P < 0.05) than control eyes. The aqueous humor of L-IOP eyes had a higher abundance of fibrotic proteins and apoptotic cells than that of control eyes, with significantly higher TGF-β1, α-SMA, fibronectin, and cleaved caspase-3 expression (all P < 0.05). In conclusion, a persistence of L-IOP for 2 weeks may contribute to fibrosis in the TM and SC and might be detrimental to conventional AHO in SD rat eyes. Clinicians should consider that aberrant shear force induced by aqueous humor fluctuation may damage AHO outflow channel when treating patients.

Density effects on the hydrodynamics and mixing at a large confluence with a compound channel tributary

Abstract Confluences are marked by converging streamlines, complex hydrodynamics features and mixing processes. Understanding such intricate flow patterns and their effects on the mixing at natural river junctions is difficult, particularly for large confluences with a compound channel tributary, due to the scarcity of field data. This research aims to assess the effects of density differences on hydrodynamics and mixing at the large river confluence between the Yangtze River and its tributary, the Poyang Lake, whose outflow channel has a large inner-side floodplain. Field data were collected during three surveys under various flow conditions to analyse how the alternate flow mechanism (compound channel vs single channel) of the Poyang Lake outflow channel influences the confluence mixing process. In high flow and relatively high flow conditions, the Poyang Lake outflow channel functioned as a compound channel and switched to a single channel in low flow. Acoustic Doppler current profiling (ADCP) was used in all three surveys to explore the features of hydrodynamics and the mixing process at the confluence, supplemented by water quality sampling to characterise the mixing patterns. Secondary flows observed during the field surveys were found to be affected by alterations in the flow mechanism (compound channel vs single channel) of the Poyang Lake outflow channel and the density effects, which were characterised using the densimetric Froude number Frd. Ultimately, the findings obtained in these field surveys confirm the role of density differences between the tributaries in significantly affecting hydrodynamics features and the mixing process at river confluences.

Potential for formation of methylated thioarsenates in geothermal environments

Geothermal waters typically have elevated arsenic (As) concentrations. Various As species have been identified, including methylated thioarsenates, which present a high environmental and health risk due to high mobility and toxicity. Upon discharge from hot springs, temperature and geogenic sulfide excess decrease, while redox potential increases. The combined effects of those parameters on activities of sulfate-reducing bacteria and methanogens and thereby on extent of As methylation versus thiolation is currently unknown. Here, we incubated sediments from alkaline hot springs and outflow channels at the Tengchong geothermal region in southwestern China, where inorganic and methylated thioarsenates had been detected, at temperatures between 20 to 90 °C with different initial aqueous As and sulfur species. Results from field samples and incubation experiments showed methylated thioarsenates, but no methylated oxyarsenates, implying quantitative thiolation even at low sulfide concentrations. Enrichment cultures derived from one sediment with quantitative formation of dimethyl-dithioarsenate (DMDTA) at 55 °C, showed a dominance of inorganic trithioarsenate at 35 °C and monomethylated thioarsenates at 55 °C when incubated with two other sediments. The rate-limiting step was microbially mediated As methylation from arsenite, which was not observed at 20 °C or >= 75 °C, in contrast to thiolation of already methylated arsenates. Addition of free sulfide and thiosulfate to incubation experiments promoted formation of inorganic or monomethylated high-thiolated arsenates, while sulfate promoted full methylation and formation of DMDTA, probably due to continuous low supply of microbially produced sulfide. Since DMDTA is more mobile and toxic than inorganic and monomethylated thioarsenates, understanding constraints to its formation is especially important for future risk assessment

Influence of axial distance between impeller and diffuser on the hydraulic performance and flow loss characteristics of bulb tubular pump

Abstract Bulb tubular pumps used in regional water transfer projects consume substantial power. Optimizing the geometric parameters of tubular pumps is crucial for enhancing efficiency and minimizing hydraulic losses. ANSYS CFX is used to investigate the axial distance between the impeller and the diffuser on the hydraulic performance and flow loss characteristics of the rear-bulb tubular pump, and the numerical simulation results are compared with the experimental data. Then, the entropy production theory is introduced to analyze flow losses. As the axial distance increases, the diffuser’s rectification effect on the flow at the impeller outlet deteriorates, leading to increased flow losses and decreased head and efficiency of the device. Flow losses in the bulb tubular pump are ranked from largest to smallest as follows: impeller, outflow channel, diffuser, inlet channel. The impeller exhibits the highest entropy production ratio, reaching 61.05% at an axial distance of 25 mm. By elucidating the energy loss distribution of each component under varying axial distances, this paper offers insights for the hydraulic optimization design of bulb tubular pumps.

Role and mechanism of autonomic nervous system regulation in primary glaucoma

The regulation of blood flow in the human eye, aqueous humor production, and the outflow channels of aqueous humor are all controlled by the autonomic nervous system (ANS), encompassing both sympathetic and parasympathetic nerves. Patients with primary glaucoma often exhibit autonomic nervous system dysfunctions, which may exacerbate visual impairment. The homeostasis of the autonomic nervous system is influenced by circadian rhythms, physical exercise, emotional states, medications, and other factors. Previous studies have indicated that activities such as aerobic exercise, yoga breathing, and meditation can promote the restoration of autonomic nervous system balance, thereby reducing intraocular pressure. However, further evidence is required to substantiate the efficacy of ANS activity regulation as an effective adjunct therapy for primary glaucoma. This review examines the role and mechanisms of autonomic nervous system regulation in the context of primary glaucoma.

Advantages of the hybrid revascularization technique in the treatment of extended occlusions of the superficial femoral artery and multilevel lesions of the lower extremity arteries

Introduction. Atherosclerotic lesions of the lower extremity arteries often have a multilevel character, the consequence of which is the disability of the population up to the development of post-ischemic necrosis. Conventional methods of surgical treatment of occlusion of the superficial femoral artery (SFA) and multilevel arterial lesions, however, are characterized by high traumatism causing an increase in mortality in this cohort of patients. Overcoming the above disadvantages required the development of alternative approaches, particularly hybrid revascularization. Objective. To analyze our own experience of the above-mentioned intervention in order to further evaluate its benefits. Material and methods. The study included 80 patients suffering from chronic limb-threatening ischemia (CLTI) with occlusion of the femoral-popliteal segment arteries &gt;20 cm long. The subjects were divided into two equal groups depending on the type of surgery performed – autovenous femoral-popliteal bypass with endovascular correction of outflow channels (hybrid bypass) or autologous femoral-tibial bypass (FTB). We analyzed the clinical and demographic characteristics of the patients, technical features of interventions, as well as their direct and long-term effects. The assessment of the shunt patency was carried out using Kaplan-Meyer tables. The differences in indicators between groups were determined using the logarithmic criterion. Results. Thirty-day mortality among patients in the hybrid bypass group was 2.5% versus 4.3% in the second group (p&gt;0.05). The frequency of graft failure is 5% versus 13%, respectively. A year after the operation, the primary shunt patency reached 77.7% (95% CI 61.7-93.7) in the first group. In the second group, this indicator was 57.1% (95% CI 42.9-71.3). One-year survival without amputation was 82.1% (95% CI 66.8-97.4) versus 69.6% (95% CI 56.1-83.1), respectively. The frequency of angiosomal revascularization in patients who underwent hybrid bypass surgery reached 90.0%. In the other group, the indicator was lower and amounted to 69.2% (p=0.006). Conclusions. The presented information proves the high efficiency of the investigated method of treatment.

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.

A global dataset of pitted cones on Mars

Pitted cones are positive-relief features that display prominent central craters, and are common features on the northern lowland plains of Mars. Pitted cones have been proposed to form from different mechanisms, including those producing volcanic cinder cones or sedimentary mud volcanoes. Here, we apply a deep learning model to globally map 65,620 pitted cones on Mars using Context Camera images from the Mars Reconnaissance Orbiter. Using model recall and a hand-mapped dataset, we conjecture there could be up to ∼81,900–162,000 individual pitted cones on Mars. A majority of pitted cones (>97%) occur in three of the northern plains' basins—Utopia, Isidis, and Acidalia Planitiae—and occur within geologic units from the late Hesperian and the early–middle Amazonian. The global dataset shows cone estimated diameter increases moving poleward, but pitted cones largely disappear north of ∼50 N, perhaps due to polar processes that erase or modify the cones. Approximately 94% of cones overlie a single geologic unit, the Vastitas Borealis Formation (VBF), interpreted as sediment from the highland terrains deposited via outflow channels. This global distribution supports sedimentary volcanism following deposition of sediments by the outflow channels. On Earth, rapidly-deposited sediments make an ideal setting for trapping water in the subsurface that is later erupted as mud flows, and this appears to be feasible on Mars.

Risk factors for exfoliation glaucoma - Current evidence and perspectives.

Exfoliation syndrome (XFS) and exfoliation glaucoma (XFG) represent a complex matrix of ocular age-related neurodegenerative changes. Numerous decades of research on this disease entity have highlighted the unique clinical features of ocular protein-complex aggregates, which lead to tissue dysfunction of the ocular outflow channels, leading to irreversible optic nerve damage and glaucoma. While genetic studies have reported several genes associated with XFS and XFG, numerous studies have shown their association with common systemic diseases such as ischemic heart disease, cerebrovascular accidents, and hypertension. Environmental factors are also reported to play a role in the disease pathogenesis by epigenetic control of gene expression and partly explain the difference in the prevalence rates of the disease process. Despite the identification of possible triggers for the disease onset or for the development of glaucoma, the exact mechanisms or the role of several reported risk factors in disease pathogenesis remain a mystery. This review comprehensively evaluated the several risk factors in XFS and XFG while discussing the interactive interplay between the risk factors that determine the disease onset or phenotype in XFS and XFG.

Sharp needle reconstructs peripheral outflow for patients with malfunctional arteriovenous fistula

Objective To investigate the feasibility and efficacy of combining ultrasound-guided sharp needle technique with percutaneous transluminal angioplasty (PTA) for treating outflow stenosis or dysfunction in arteriovenous fistula (AVF) among hemodialysis patients. Methods From October 2021 to March 2023, patients with occluded or malfunctional fistula veins not amenable to regularly angioplasty were retrospectively enrolled in the study. They underwent ultrasound-guided sharp needle intervention followed by PTA. Data on the location and length between the two veins, technical success, clinical outcomes, and complications were collected. Patency rates post-angioplasty were calculated through Kaplan-Meier analysis. Results A total of 23 patients were included. The mean length of the reconstructed extraluminal segment was 3.18 cm. The sharp needle opening was performed on the basilic vein (60.9%), brachial vein (26.1%), or upper arm cephalic vein (13%) to create outflow channels. Postoperatively, all cases presented with mild subcutaneous hematomas around the tunneling site and minor diffuse bleeding. The immediate patency rate for the internal fistulas was 100%, with 3-month, 6-month, and 12-month patency rates at 91.3%, 78.3%, and 43.5%, respectively. Conclusion Sharp needle technology merged with PTA presents an effective and secure minimally invasive method for reconstructing the outflow tract, offering a new solution for recanalizing high-pressure or occluded fistulas.

Carbon Nanoparticles Promoted the Absorption of Potassium Ions by Tobacco Roots via Regulation of K+ Flux and Ion Channel Gene Expression

Background: The regulatory effects of carbon nanomaterials (CNMs) on plant growth and their potential applications in agriculture have attracted a great deal of attention from researchers. CNMs have been shown to promote nutrient absorption and increase plant growth. However, the mechanisms by which CNMs affect plant growth and nutrient absorption are still unknown. Methods: The tobacco seedling biomass, potassium (K+) concentration, and accumulation in hydroponic were investigated to exposure of carbon nanoparticles (CNPs). To directly observe the effect of CNPs on K+ uptake by roots, we employed a noninvasive micro-test technique (NMT) to detect the net flux of K+ on the surface of tobacco roots. The K+-depletion experiment was carried out to explore the kinetic characteristics of K+ absorption, and qRT-PCR was used to monitor the expression levels of the K+ channel gene. Results: The results showed that tobacco seedling biomass significantly improved at 10 mg·L-1 CNP treatments, and K+ concentration and accumulation both in roots and shoots increased with 10 and 20 mg·L-1 CNPs. CNP treatments changed the flow rate of K+ from efflux to influx in tobacco roots; this was observed both in plants cultivated in a CNP-containing medium and after the addition of CNPs to previously untreated plants. A depletion test also showed that CNPs improved the K+ absorption capacity and low-K+ tolerance of tobacco seedlings. Conclusion: CNPs enhanced the K+ absorption capacity and low-K+ tolerance of tobacco seedlings. The promotion of K+ absorption by CNPs was closely related to the activation of K+ influx channel genes and inhibition of the K+ outflow channel gene. The K+ flux response and ion channel gene expression to CNPs in plants reveal the mechanism whereby CNPs promote plant nutrient absorption.

X-Rays from a Central “Exhaust Vent” of the Galactic Center Chimney

Using deep archival observations from the Chandra X-ray Observatory, we present an analysis of linear X-ray-emitting features located within the southern portion of the Galactic center chimney and oriented orthogonal to the Galactic plane, centered at coordinates l = 0.°08, b = −1.°42. The surface brightness and hardness ratio patterns are suggestive of a cylindrical morphology, which may have been produced by a plasma outflow channel extending from the Galactic center. Our fits of the feature’s spectra favor a complex two-component model consisting of thermal and recombining plasma components, possibly a sign of shock compression or heating of the interstellar medium by outflowing material. Assuming a recombining plasma scenario, we further estimate the cooling timescale of this plasma to be on the order of a few hundred to thousands of years, leading us to speculate that a sequence of accretion events onto the Galactic black hole may be a plausible quasi-continuous energy source to sustain the observed morphology.

Evaluating the effect of pulse energy on femtosecond laser trabeculotomy (FLT) outflow channels for glaucoma treatment in human cadaver eyes.

Femtosecond laser trabeculotomy (FLT) creates aqueous humor outflow channels through the trabecular meshwork (TM) and is an emerging noninvasive treatment for open-angle glaucoma. The purpose of this study is to investigate the effect of pulse energy on outflow channel creation during FLT. An FLT laser (ViaLase Inc.) was used to create outflow channels through the TM (500 μm wide by 200 μm high) in human cadaver eyes using pulse energies of 10, 15, and 20 μJ. Following treatment, tissues were fixed in 4% paraformaldehyde. The channels were imaged using optical coherence tomography (OCT) and assessed as full thickness, partial thickness, or not observable. Pulse energies of 15 and 20 μJ had a 100% success rate in creating full-thickness FLT channels as imaged by OCT. A pulse energy of 10 μJ resulted in no channels (n = 6), a partial-thickness channel (n = 2), and a full-thickness FLT channel (n = 2). There was a statistically significant difference in cutting widths between the 10 and 15 μJ groups (p < 0.0001), as well as between the 10 and 20 μJ groups (p < 0.0001). However, there was no statistically significant difference between the 15 and 20 μJ groups (p = 0.416). Fifteen microjoules is an adequate pulse energy to reliably create aqueous humor outflow channels during FLT in human cadaver eyes. OCT is a valuable tool when evaluating FLT.

Anatomical review of internal jugular vein cannulation.

The internal jugular veins (IJV) are the primary venous outflow channels of the head and neck. The IJV is of clinical interest since it is often used for central venous access. This literature aims at presenting an overview of the anatomical variations, morphometrics based on various imaging modalities, cadaveric and surgical findings, and the clinical anatomy of IJV cannulation. Additionally, the anatomical basis of complications, techniques to avoid complications, and cannulation in special instances are also included in the review. The review was performed by a detailed literature search and review of relevant articles. A total of 141 articles were included and organized into anatomical variations, morphometrics, and clinical anatomy of IJV cannulation. The IJV is next to important structures such as the arteries, nerve plexus, and pleura, which puts them at risk of injury during cannulation. Anatomical variations such as duplications, fenestrations, agenesis, tributaries, and valves, may lead to an increased failure rate and complications during the procedure, if unnoticed. The morphometrics of IJV, such as the cross-sectional area, diameter, and distance from the skin-to-cavo-atrial junction may assist in choosing the appropriate cannulation techniques and hence reduce the incidence of complications. Age, gender, and side-related differences explained variations in the IJV-common carotid artery relationship, cross-sectional area, and diameter. Accurate knowledge of anatomical variations in special considerations such as paediatrics and obesity may help prevent complications and facilitate successful cannulation.

Megaflood Erosion on Mars—How Lava‐Filled Craters Became Mesas (With Insights From Lava Physics, Stream Power, and Rock Mechanics)

AbstractRound mesas up to 500 m high occur in Martian outflow channels. Mesas in Ravi and Elaver Valles occur in deepest parts of the channels where the most intense megaflood erosion occurred. I theorize that Noachian basalts poured into craters which acted as lava traps, similar to Kilauean lava lakes. Subsequent flood basalts buried the infilled craters. Hesperian megafloods stripped away hundreds of meters of basalts, exhuming erosion‐resistant strata. Lava solidification theory is explored to assess the role of cooling in governing the structure and strength of the Martian basalts. The postulated lava lakes that formed the Ravi Vallis mesas would have needed millennia to cool. The larger Elaver Vallis mesa may have needed up to 20,000 years to solidify. Long cooling times led to coarse, doleritic mineral textures and reduced numbers of cooling joints, greatly increasing bulk rock strength and resistance to hydrodynamic erosion. Using rock mechanics theory, cores of exhumed lava‐filled craters would have bulk rock strengths at least 5 to 30 times greater than more highly fractured basalts. Discharge hydrographs for the Morella Crater breach flood that carved Elaver Vallis peak at ∼2.1 × 107 m3 s−1. Stream power per unit streambed area ranged up to &gt;150,000 W m−2 as the breach grew in size. The calculations provide an envelope of power sufficient to erode hundreds of meters of basalts, but not great enough to remove the large mesa. Thus the legacy of an ancient, lava‐filled crater is a high mesa on the floor of Elaver Vallis.

Deciphering Martian Flood Infiltration Processes at Hebrus Valles: Insights From Laboratory Experiments and Remote Sensing Observations

AbstractIn evaluating the unique geomorphology of Hebrus Valles on Mars, an outflow channel southeast of Utopia Planitia, we investigated the role of fluvial dynamics in forming subsurface conduits. Unlike typical Martian channels that terminate under younger sediment rocks, Hebrus Valles retains its downstream features, thus offering a window into surface and subsurface interactions between liquid water and regolith. Employing physical lab simulations, we utilized buried polygonal tunneling configurations in a sandy matrix to replicate the incision features observed at the channel's terminus. This study provides the first lab‐based evidence demonstrating the role of conduits in conveying large floods in the Hebrus Valles. Our results lend support to the interpretation that Hebrus Valles conveyed high‐volume floods by demonstrating that conduits are necessary to form the features observed on the surface of Hebrus Valles. The experiments also highlight the role of sinkholes as floodwater capture points, which suggests the formation of a regional interconnected network of subsurface channels and caverns. These findings affirm that fluvial dynamics in Hebrus Valles could have expanded subsurface discontinuities into functioning conduit systems, potentially directing floodwaters through an interconnected subterranean network.

3‐D geophysical modeling of a buried, simple impact crater: Holleford impact structure, Ontario, Canada

AbstractHolleford Crater is a deeply buried, 2.35 km diameter late Proterozoic‐early Cambrian (550 ± 50 Ma) simple impact crater located in southeastern Ontario, Canada. Exploration drilling in the 1950–60s indicated a &gt;450 m deep, simple impact structure with an infill stratigraphy of Cambro‐Ordovician clastic and carbonate sediments and a −2.2 mGal gravity anomaly. We conducted new ground‐based geophysical surveys (magnetics, gravity) and potential field modeling to better resolve the buried impact structure depth, subsurface geometry, and postimpact modification. Geophysical surveys reveal a well‐defined ~3 mGal Bouguer gravity low and &lt;20 nT residual magnetic anomaly over the crater basin. The lack of a well‐defined magnetic anomaly is due to the low magnetic contrast between Mesoproterozoic metasedimentary target rocks and Paleozoic infill sediments. The modeled basement surface shows a deeply buried (&gt;400 m), eroded simple impact structure with a rim‐to‐rim diameter (D) of 1.8–2 km, a residual rim height of about 30 m and a true depth (dt) &gt;400 m. The modeled diameter is smaller than the previous estimate (2.35 km) based on the surface outcrop pattern of Paleozoic strata, which overestimates the buried impact structure dimensions. The modeled basement surface identifies a rim breach and a possible fluvial outflow channel in the southeast impact structure rim. The channel is up to 150 m deep and 400 m in width and has morphology similar to outlet channels produced by fluvial rim dissection of terrestrial impact structures and “tadpole craters” on Mars.

Paleoenvironment implications of layered ejecta craters in the Chryse Planitia, Mars

The formation of martian layered ejecta craters (LECs), which have one or multiple distinctive fluidized layered ejecta deposits, is generally hypothesized to be directly related to subsurface volatiles. Using a high-resolution (5 m/pixel) context camera (CTX) mosaic as a base map, 525 LECs (including 157 newly identified) were catalogued in the Chryse Planitia and divided into three types according to the number of layered ejecta, i.e., single layer ejecta (SLE), double layer ejecta (DLE), and multiple layer ejecta (MLE). It is found that the minimum crater diameter (here called the onset diameter) decreases with increasing latitude, and could be as small as 1 km. The average ejecta mobility (EM) values usually increase from the low to the high latitude interval for each LEC type and gradually increase with the number of layered ejecta within each latitude interval. The lobateness values of the SLE craters have a decreasing trend with increasing latitude, however, such a trend is not obvious for the DLE and MLE craters. The absolute model ages (AMAs) of 135 LECs were determined from the crater size-frequency distribution (CSFD) method to constrain the timing of the fluvial activities of the circum-Chryse outflow channels and to investigate the local temporal-spatial evolution of the subsurface volatile-rich layer. The superposition relationship between the LECs and circum-Chryse channels suggests fluvial activity might have extended into the early Amazonian. Floods that carved the Ares, Tiu, and Simud Valles likely ended before ∼μ2.7 Ga, while those relating to theVedra, Manmee, and Maja Valles ceased between ∼μ2.2 Ga and ∼ μ1.9 Ga. The fluvial resurfacing activities in the Kasei Valles likely did not last past ∼μ2.8 Ga. The dating results and excavation depths of LECs (diam. < 6 km) suggest that the minimal roof depth of the volatile-rich layer has remained relatively stable at least around 560– 590 m since the early Amazonian, and regional differences indicate that it could be as shallow as ∼440 m at high latitudes and ∼540 m at low latitudes.

Revealing Elysium Planitia's Young Geologic History: Constraints on Lava Emplacement, Areas, and Volumes

AbstractElysium 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.

Effects of Solar Wind Density and Velocity Variations on the Martian Ionosphere and Plasma transport—A MHD Model Study

AbstractSolar wind dynamic pressure, consisting solar wind density nsw and velocity Vsw, is an important external driver that controls Martian plasma environment. In this study, a 3D magnetohydrodynamic model is applied to investigate the separate influences of solar wind density and velocity on the Martian ionosphere. The spatial distributions of ions in the dayside and near nightside ionosphere under different nsw and Vsw are analyzed, as well as the ion transport process. We find that for the same dynamic pressure condition, the ionosphere extends to higher altitudes under higher solar wind density, indicating that a solar wind velocity enhancement event is more efficient at compressing the Martian ionosphere. A higher Vsw will result in a stronger induced magnetic field, shielding the Martian ionosphere, preventing the penetration of solar wind particles. For the same dynamic pressure, increasing nsw (decreasing Vsw) leads to a higher horizontal ion velocity, facilitating day‐to‐night plasma transport. As a result, the ionosphere extends farther into the nightside. Also, the ion outflow flux is larger for high nsw, which may lead to a higher escape rate. Moreover, the strong crustal fields in the southern hemisphere also cause significant effect to the ionosphere, hindering horizontal ion transport. An additional outflow channel is also provided by the crustal field on the southern dayside, causing different responses of flow pattern between local and global scale while the solar wind condition is varied.