Morphology, Morphometry and Distribution of Isolated Landforms in Southern Chryse Planitia, Mars

The margin of Chryse Planitia, Mars, contains >10⁵ kilometer‐scale mesas, buttes, and plateaus (“mounds”), many of which are found in and around Oxia Planum, the ExoMars 2022 Rover landing site. Despite this, their origins and evolution are unknown. We have analyzed the morphologies and morphometries of 14,386 individual mounds to: (1) classify them based on their geomorphology; (2) constrain when they formed based on their stratigraphic and spatial relationships; and (3) develop hypotheses for their geological history. The mounds are classified as compound mounds, mesas, clustered mounds, and hills. Mound heights show that their elevations above the plains tend to a maximum height of 500 m. We interpret this as the thickness of a previously continuous layer that extended several hundred kilometers from the southern highlands into Chryse Planitia. Stratigraphy constrains the deposition of this layer to the Early‐Middle Noachian, correlatable to the phyllosilicate‐bearing strata of Mawrth Vallis, with similar layering also observable in some mounds, suggesting a genetic relationship. The mounds sometimes occur in circular arrangements, interpreted as an association with buried impact structures. We propose that the mounds formed through differential erosion after the premound layer was indurated by mineralization from groundwater in areas superposing underlying crustal weaknesses, for example, at buried crater margins. The subsequent differential erosion of this layer preferentially removed areas unaffected by this induration in the Late Noachian‐Early Hesperian leaving the mound population seen at present. These features present accessible three‐dimensional exposures of ancient layered rocks, and so are exciting targets for future study

Acid-evoked Ca2+ signalling in rat sensory neurones: effects of anoxia and aglycaemia

Ischaemia excites sensory neurones (generating pain) and promotes calcitonin gene-related peptide release from nerve endings. Acidosis is thought to play a key role in mediating excitation via the activation of proton-sensitive cation channels. In this study, we investigated the effects of acidosis upon Ca2+ signalling in sensory neurones from rat dorsal root ganglia. Both hypercapnic (pHo 6.8) and metabolic–hypercapnic (pHo 6.2) acidosis caused a biphasic increase in cytosolic calcium concentration ([Ca2+]i). This comprised a brief Ca2+ transient (half-time approximately 30 s) caused by Ca2+ influx followed by a sustained rise in [Ca2+]i due to Ca2+ release from caffeine and cyclopiazonic acid-sensitive internal stores. Acid-evoked Ca2+ influx was unaffected by voltage-gated Ca2+-channel inhibition with nickel and acid sensing ion channel (ASIC) inhibition with amiloride but was blocked by inhibition of transient receptor potential vanilloid receptors (TRPV1) with (E)-3-(4-t-butylphenyl)-N-(2,3-dihydrobenzo[b][1,4] dioxin-6-yl)acrylamide (AMG 9810; 1 μM) and N-(4-tertiarybutylphenyl)-4-(3-cholorphyridin-2-yl) tetrahydropryazine-1(2H)-carbox-amide (BCTC; 1 μM). Combining acidosis with anoxia and aglycaemia increased the amplitude of both phases of Ca2+ elevation and prolonged the Ca2+ transient. The Ca2+ transient evoked by combined acidosis, aglycaemia and anoxia was also substantially blocked by AMG 9810 and BCTC and, to a lesser extent, by amiloride. In summary, the principle mechanisms mediating increase in [Ca2+]i in response to acidosis are a brief Ca2+ influx through TRPV1 followed by sustained Ca2+ release from internal stores. These effects are potentiated by anoxia and aglycaemia, conditions also prevalent in ischaemia. The effects of anoxia and aglycaemia are suggested to be largely due to the inhibition of Ca2+-clearance mechanisms and possible increase in the role of ASICs