Exploring the evidence of Middle Amazonian aquifer sedimentary outburst residues in a Martian chaotic terrain.

The quest for past Martian life hinges on locating surface formations linked to ancient habitability. While Mars' surface is considered to have become cryogenic ~3.7 Ga, stable subsurface aquifers persisted long after this transition. Their extensive collapse triggered megafloods ~3.4 Ga, and the resulting outflow channel excavation generated voluminous sediment eroded from the highlands. These materials are considered to have extensively covered the northern lowlands. Here, we show evidence that a lacustrine sedimentary residue within Hydraotes Chaos formed due to regional aquifer upwelling and ponding into an interior basin. Unlike the northern lowland counterparts, its sedimentary makeup likely consists of aquifer-expelled materials, offering a potential window into the nature of Mars' subsurface habitability. Furthermore, the lake's residue's estimated age is ~1.1 Ga (~3.2 Ga post-peak aquifer drainage during the Late Hesperian), enhancing the prospects for organic matter preservation. This deposit's inferred fine-grained composition, coupled with the presence of coexisting mud volcanoes and diapirs, suggest that its source aquifer existed within abundant subsurface mudstones, water ice, and evaporites, forming part of the region's extremely ancient (~ 4 Ga) highland stratigraphy. Our numerical models suggest that magmatically induced phase segregation within these materials generated enormous water-filled chambers. The meltwater, originating from varying thermally affected mudstone depths, could have potentially harbored diverse biosignatures, which could have become concentrated within the lake's sedimentary residue. Thus, we propose that Hydraotes Chaos merits priority consideration in future missions aiming to detect Martian biosignatures.

Evidence of an oceanic impact and megatsunami sedimentation in Chryse Planitia, Mars.

In 1976, NASA's Viking 1 Lander (V1L) was the first spacecraft to operate successfully on the Martian surface. The V1L landed near the terminus of an enormous catastrophic flood channel, Maja Valles. However, instead of the expected megaflood record, its cameras imaged a boulder-strewn surface of elusive origin. We identified a 110-km-diameter impact crater (Pohl) ~ 900 km northeast of the landing site, stratigraphically positioned (a) above catastrophic flood-eroded surfaces formed ~ 3.4 Ga during a period of northern plains oceanic inundation and (b) below the younger of two previously hypothesized megatsunami deposits. These stratigraphic relationships suggest that a marine impact likely formed the crater. Our simulated impact-generated megatsunami run-ups closely match the mapped older megatsunami deposit's margins and predict fronts reaching the V1L site. The site's location along a highland-facing lobe aligned to erosional grooves supports a megatsunami origin. Our mapping also shows that Pohl's knobby rim regionally represents a broader history of megatsunami modification involving circum-oceanic glaciation and sedimentary extrusions extending beyond the recorded megatsunami emplacement in Chryse Planitia. Our findings allow that rocks and soil salts at the landing site are of marine origin, inviting the scientific reconsideration of information gathered from the first in-situ measurements on Mars.

Pre-operative prone radiographs can reliably determine spinal curve flexibility in adolescent idiopathic scoliosis (AIS).

PURPOSE: The purpose of this study was to evaluate the correlation between non-effort prone and bending radiographs in determining curve flexibility in adolescent idiopathic scoliosis (AIS). METHODS: A retrospective review of AIS patients who underwent pre-operative full spine radiographic imaging from 2006 to 2019 was performed. The Cobb angle (CA) of proximal thoracic (PT), main thoracic (MT) and thoracolumbar/lumbar (TL/L) curves were measured and correlated on standing, prone and bending radiographs. Standing, bending, and prone measurements were correlated using Spearman's analysis, and intra-rater reliability was evaluated using intraclass correlation analysis. RESULTS: A total of 381 patients (74% female) with a mean age of 15.1 ± 2.5 years were identified. A strong correlation existed between the prone and bending CA for the PT (rs = 0.797, p < 0.01) and MT (rs = 0.779, p < 0.01) curve and a moderate correlation existed between the prone and bending TL/L curve (rs = 0.641, p < 0.01). For a non-structural PT curve, a prone CA < 25° correctly identified a bending CA < 25° 96.7% of the time (p < 0.005). For a non-structural MT curve, a prone CA < 35° correctly identified a bending CA < 25° 90.2% of the time (p < 0.005). For a non-structural TL/L curve, a prone CA < 35° correctly identified a bending CA < 25° 95% of the time (p < 0.005). CONCLUSION: Prone radiographs demonstrated a moderate to strong correlation with bending radiographs and may be used as a proxy for determining spinal flexibility, especially when bending films are deemed unreliable. LEVEL OF EVIDENCE: III.

The Oldest Highlands of Mars May Be Massive Dust Fallout Deposits.

The oldest terrains of Mars are cratered landscapes, in which extensive valleys and basins are covered by ubiquitous fluvial plains. One current paradigm maintains that an impact-generated megaregolith underlies these sediments. This megaregolith was likely largely generated during the Early Noachian (~4.1 to ~3.94 Ga) when most Martian impact basins formed. We examined the geologic records of NW Hellas and NW Isidis, which include this epoch's most extensive circum-basin outcrops. Here, we show that these regions include widespread, wind-eroded landscapes, crater rims eroded down by several hundred meters, pitted plains, and inverted fluvial and crater landforms. These surfaces exhibit few fresh craters, indicating geologically recent wind erosion. The deep erosion, topographic inversions, and an absence of dunes on or near talus across these regions suggest that sediments finer than sand compose most of these highland materials. We propose that basin-impact-generated hurricane-force winds created sediment-laden atmospheric conditions, and that muddy rains rapidly settled suspended sediments to construct extensive Early Noachian highlands. The implied high abundance of fine-grained sediments before these impacts suggests large-scale glacial silt production and supports the previously proposed Noachian "icy highlands" hypothesis. We suggest that subglacial meltwater interactions with the sedimentary highlands could have promoted habitability, particularly in clay strata.

The Chaotic Terrains of Mercury Reveal a History of Planetary Volatile Retention and Loss in the Innermost Solar System.

Mercury's images obtained by the 1974 Mariner 10 flybys show extensive cratered landscapes degraded into vast knob fields, known as chaotic terrain (AKA hilly and lineated terrain). For nearly half a century, it was considered that these terrains formed due to catastrophic quakes and ejecta fallout produced by the antipodal Caloris basin impact. Here, we present the terrains' first geologic examination based on higher spatial resolution MESSENGER (MErcury Surface Space ENvironment GEochemistry and Ranging) imagery and laser altimeter topography. Our surface age determinations indicate that their development persisted until ~1.8 Ga, or ~2 Gyrs after the Caloris basin formed. Furthermore, we identified multiple chaotic terrains with no antipodal impact basins; hence a new geological explanation is needed. Our examination of the Caloris basin's antipodal chaotic terrain reveals multi-kilometer surface elevation losses and widespread landform retention, indicating an origin due to major, gradual collapse of a volatile-rich layer. Crater interior plains, possibly lavas, share the chaotic terrains' age, suggesting a development associated with a geothermal disturbance above intrusive magma bodies, which best explains their regionality and the enormity of the apparent volume losses involved in their development. Furthermore, evidence of localized, surficial collapse, might reflect a complementary, and perhaps longer lasting, devolatilization history by solar heating.

Gender Disparity between Donor Sites of the Trochlea Used for Autologous Osteoarticular Transfer: An MRI Analysis.

The purpose of this study was to assess potential gender differences in size of the lateral and medial trochlea of the male and female knee as well as the variation within gender of potential osteochondral autograft transfer (OAT) donor site area. Two hundred and twelve skeletally mature patients, 106 males and 106 females, who underwent a 3T magnetic resonance imaging of the knee for a variety of indications were utilized for analysis. Exclusion criteria included degenerative arthritis, trochlear dysplasia, and poor image quality. Medial and lateral femoral trochlear cartilage width was obtained using a linear radiologic measurement tool. Widths were measured from a reproducible anatomic location representing the maximal trochlear dimension in a region where donor plugs are commonly harvested. Trochlear width was also plotted as a function of patient height. Statistical analysis was performed using a two-sample t-test. The mean and standard deviation of the lateral trochlear cartilage width (mm) for males and females were 23.38 +/- 2.14 and 20.44 +/- 2.16, respectively (p < 0.00001). The mean and standard deviation of the medial trochlear cartilage width (mm) for males and females were 14.16 +/- 2.17 and 11.78 +/- 2.03, respectively (p < 0.00001). The overall range in trochlear width for both the lateral and medial sides was 22.22 and 19.73 mm for males and females, respectively. A graft measuring 10 mm could represent as little as 34% of the lateral trochlea in males versus as much as 65% in females. Our results indicate that donor OAT plug diameter relative to available trochlear cartilage width will vary significantly both between genders and individual patients. Trochlear width variability and its potential implications on donor site morbidity may be an important consideration when contemplating osteochondral plug harvest for OAT or other indications. The level of evidence is IV.

Martian outflow channels: How did their source aquifers form, and why did they drain so rapidly?

Catastrophic floods generated ~3.2 Ga by rapid groundwater evacuation scoured the Solar System's most voluminous channels, the southern circum-Chryse outflow channels. Based on Viking Orbiter data analysis, it was hypothesized that these outflows emanated from a global Hesperian cryosphere-confined aquifer that was infused by south polar meltwater infiltration into the planet's upper crust. In this model, the outflow channels formed along zones of superlithostatic pressure generated by pronounced elevation differences around the Highland-Lowland Dichotomy Boundary. However, the restricted geographic location of the channels indicates that these conditions were not uniform. Furthermore, some outflow channel sources are too high to have been fed by south polar basal melting. Using more recent mission data, we argue that during the Late Noachian fluvial and glacial sediments were deposited into a clastic wedge within a paleo-basin located in the southern circum-Chryse region, which at the time was completely submerged under a primordial northern plains ocean [corrected]. Subsequent Late Hesperian outflow channels were sourced from within these geologic materials and formed by gigantic groundwater outbursts driven by an elevated hydraulic head from the Valles Marineris region. Thus, our findings link the formation of the southern circum-Chryse outflow channels to ancient marine, glacial, and fluvial erosion and sedimentation.