The transport and deposition of sand is the most prevalent agent of landscape modification on Mars today, with fluxes comparable to some sand dunes on Earth. Until now, the relationship between sand ...flux and dune field morphology has been poorly constrained. By tracking dune movement over ∼10 km-long dune fields in Herschel Crater and Nili Patera, representative of many dune fields on Mars, we find a downwind flux decrease that correlates with a sequence of changing morphology from barchans to barchanoids and seifs (longitudinal dunes) to isolated dome dunes and ending with sand sheets. We show empirical consistency with atmospheric Internal Boundary Layer (IBL) theory which can describe these broad flux and morphology changes in Martian dune fields. Deviations from IBL flux predictions are from wind streamline compressions up slopes, leading to a speedup effect. By establishing a dune field morphology type example and correlating it with measured and predicted flux changes, we provide an integrated morphology and flux model that can be applied to other areas of Mars and be used to infer paleo-environmental conditions from preserved sandstone.
•Mars dune fields exhibit a downwind evolution in morphology and sediment flux.•Internal boundary layer theory and slope speedup explain observed sediment flux.•These findings have implications for interpreting Martian stratigraphy.
Muscodor vitigenus is a recently described endophytic fungus of Paullinia paullinioides, a liana growing in the understorey of the rainforests of the Peruvian Amazon. This fungus produces naphthalene ...under certain cultural conditions. Naphthalene produced by M. vitigenus was identified by gas chromatography/mass spectrometry. Its chromatographic and mass spectral properties were identical to authentic naphthalene. Agar plugs supporting growth of the fungus and producing known amounts of naphthalene effectively repelled the adult stage of the wheat stem sawfly, Cephus cinctus, in Y-tube bioassay tests. Authentic naphthalene, at comparable concentrations to those in tests involving the fungus itself, mimicked the insect repellency of the fungus. Although other Muscodor spp. produce volatile antimicrobials, M. vitigenus is unique in its ability to produce naphthalene almost exclusively. This report also describes the potential practical implications of M. vitigenus.
Aeolian transport of sand is abundant on modern-day Mars, as revealed by remote sensing measurements of the motion of dunes, and of the meter-scale ripples that mantle them. We study a large-scale ...natural sand trap within the Meroe Patera dune field: a 1.8-km diameter crater which features a dune-free “shadow” in its lee. We compare the volume of sand trapped within this crater to the sand volume that would be expected to cover the area of the crater and its dune-free shadow behind it if the crater were not present. We find that the crater holds less sand than this “missing” volume would predict, implying that sand escapes from the crater over time. Modern day imagery shows an apparent lack of sand escaping from the Meroe crater, however, suggesting that changes in the wind regime at the site may have allowed sand to escape in the past. The persistence of an altered dune morphology all the way to the far downwind edge of the dune field suggests consistent wind conditions over the time of the crater-dune field interaction.
•A partially sand-filled crater in the active Meroe Patera dune field has a dune-free shadow stretching behind it downwind.•We compare its trapped volume of sand to a “missing” volume.•This missing volume is the volume we’d expect to see in the dune-free shadow if the crater were not present.•The crater holds much less sand than predicted by missing volume estimates.•This implies that the crater is probably an ineffective sand trap despite its appearance in modern images.
Both Earth and the Moon share a common history regarding the epoch of large basin formation, though only the lunar geologic record preserves any appreciable record of this Late Heavy Bombardment. The ...emergence of Earth's first life is approximately contemporaneous with the Late Heavy Bombardment; understanding the latter informs the environmental conditions of the former, which are likely necessary to constrain the mechanisms of abiogenesis. While the relative formation time of most of the Moon's large basins is known, the absolute timing is not. The timing of Crisium Basin's formation is one of many important events that must be constrained and would require identifying and dating impact melt formed in the Crisium event. To inform a future lunar sample dating mission, we thus characterized possible outcrops of impact melt. We determined that several mare lava‐embayed kipukas could contain impact melt, though the rim and central peaks of the partially lava‐flooded Yerkes Crater likely contain the most pure and intact Crisium impact melt. It is here where future robotic and/or human missions could confidently add a key missing piece to the puzzle of the combined issues of early Earth‐Moon bombardment and the emergence of life.
Plain Language Summary
How could life get started on Earth nearly four billion years ago if our planet was constantly being impacted by asteroids and comets? While we do not yet know, we are starting to piece together parts of the answer. Earth's largest impact basins are long gone because of our planet's active geology, life, and flowing water. But the Moon's big craters are well preserved. The formation of those large basins melted lots of rocks, which then cooled; by collecting those rocks on future missions and figuring out how old they are, we can determine the timing of when large basins formed on the Moon and, by extension, on Earth. Crisium basin is one of those large basins that we need to get the age for. Most of the rock that was melted from this impact and then cooled is buried by much younger lava flows, but we believe that some of it was brought up when the crater Yerkes formed on top of Crisium. The central mountain of Yerkes Crater is where we believe future robots and/or astronauts should go to collect once‐molten rock and figure out how old it and the basin are.
Key Points
Relatively pure impact melt from Crisium Basin is exposed in the central peaks of Yerkes Crater
Diluted Crisium impact melt may be exposed in some previously identified kipukas in Crisium
Radiogenic dating of impact melt exposed in Yerkes' central peak during a future mission would yield the age of the Crisium impact event
Pluto's Far Side Stern, S.A.; White, O.L.; McGovern, P.J. ...
Icarus (New York, N.Y. 1962),
03/2021, Letnik:
356
Journal Article
Recenzirano
Odprti dostop
The New Horizons spacecraft provided near-global observations of Pluto that far exceed the resolution of Earth-based datasets. However, most previous Pluto New Horizons analyses focused on the New ...Horizons encounter hemisphere (i.e., the anti-Charon hemisphere containing Sputnik Planitia). In this work, we summarize and interpret data on Pluto's “far side” (i.e., its non-encounter or alternatively, its sub-Charon hemisphere), providing the first integrated New Horizons overview of Pluto's far side terrains. We find strong evidence for widespread bladed (i.e., aligned CH4-mountain) deposits, evidence for an impact crater about as large as any on the “near side” hemisphere, evidence for complex lineations approximately antipodal to Sputnik Planitia that may be causally related, evidence that the far side maculae (i.e., equatorial dark regions) are smaller and more structured than Pluto's encounter hemisphere maculae, and more.
•Pluto's New Horizons non-encounter (i.e., ‘far side’) hemisphere is explored.•Maps are presented and interpreted.•Important geological and geophysical conclusions are reached regarding the far side.
The topography of rifts on icy bodies can be used to probe their internal properties. Uplifted and curved rift flanks occur when the elastic thickness (te) of the crust is low, indicative of high ...heat flow out of the body. Stereo topography of Pluto shows no evidence of rift-flank uplift associated with large extensional graben to the west of Sputnik Planitia. Modeling the amount of topographic deflection expected from varying elastic thicknesses yields a conservative lower bound on te of 8 km at the time of deformation; the maximum implied heat flux since graben formation is 66–85 mWm−2. This upper bound is consistent with the predicted paleo-heat fluxes from radioactive decay (~6 mWm−2), but likely only marginally consistent with nearby apparently viscously-relaxed impact craters. Additionally, we also analyze the shear stresses on these faults and find that Pluto's faults only need to support low stresses in the range of 100–300 kPa to explain their dimensions.
•Extensional graben on Pluto's surface show little to no signals of flexure.•This sets a lower limit of 8 km for the elastic layer of Pluto's icy crust.•An upper bound of 85 mWm−2 on the surface heat flux is also set.•This upper bound limits explanations for surface features via high heat flux processes.
1 Adult wheat stem sawflies Cephus cinctus, pests of cultivated cereals that also infests wild grasses, migrate into wheat fields where they oviposit in elongating, succulent stems. 2 Volatiles ...released by wheat plants at susceptible stages were analyzed to determine potential semiochemical compounds. Seven major compounds were identified and quantified. 3 A Y-tube bioassay was developed to evaluate upwind orientation of adult sawflies in response to an airstream that passed over elongated wheat plants. The bioassay was also conducted with synthetic volatile compounds. The compounds were tested using a range of concentrations spanning those identified in the airstream passing over wheat plants. 4 A significant number of adult females were attracted to wheat plants when given a choice of either purified air or the air passing over plants. 5 A significant number of female C. cinctus were attracted to (Z)-3-hexenyl acetate, β-ocimene, and (Z)-3-hexen-1-ol, but were repelled by 6-methyl-5-hepten-2-one. Females did not respond to (E)-2-hexenal, or (E)-2-hexenyl acetate. The behavioural responses were concentration dependent; the highest tested concentration of (Z)-3-hexenyl acetate was repellent to females of this species. 6 Adult males did not discriminate between air passing over wheat plants and air from a purified airstream. Males did not respond to any tested synthetic compound at any concentration. 7 The present study demonstrates for the first time that adult females of wheat stem sawfly display innate behaviours in response to synthetic volatiles. These results provide a basis for the potential development of resistant wheat varieties and for the development of semiochemically-based pest management.
Anesthesia and/or surgery accelerate Alzheimer's disease pathology and cause memory deficits in animal models, yet there is a lack of prospective data comparing cerebrospinal fluid (CSF) Alzheimer's ...disease-related biomarker and cognitive trajectories in older adults who underwent surgery versus those who have not. Thus, the objective here was to better understand whether anesthesia and/or surgery contribute to cognitive decline or an acceleration of Alzheimer's disease-related pathology in older adults.
The authors enrolled 140 patients 60 yr or older undergoing major nonneurologic surgery and 51 nonsurgical controls via strata-based matching on age, sex, and years of education. CSF amyloid β (Aβ) 42, tau, and p-tau-181p levels and cognitive function were measured before and after surgery, and at the same time intervals in controls.
The groups were well matched on 25 of 31 baseline characteristics. There was no effect of group or interaction of group by time for baseline to 24-hr or 6-week postoperative changes in CSF Aβ, tau, or p-tau levels, or tau/Aβ or p-tau/Aβ ratios (Bonferroni P > 0.05 for all) and no difference between groups in these CSF markers at 1 yr (P > 0.05 for all). Nonsurgical controls did not differ from surgical patients in baseline cognition (mean difference, 0.19 95% CI, -0.06 to 0.43; P = 0.132), yet had greater cognitive decline than the surgical patients 1 yr later (β, -0.31 95% CI, -0.45 to -0.17; P < 0.001) even when controlling for baseline differences between groups. However, there was no difference between nonsurgical and surgical groups in 1-yr postoperative cognitive change in models that used imputation or inverse probability weighting for cognitive data to account for loss to follow up.
During a 1-yr time period, as compared to matched nonsurgical controls, the study found no evidence that older patients who underwent anesthesia and noncardiac, nonneurologic surgery had accelerated CSF Alzheimer's disease-related biomarker (tau, p-tau, and Aβ) changes or greater cognitive decline.
Uranus and Neptune are the least-explored planets in our Solar System. This paper summarizes mysteries about these incredibly intriguing planets and their environments spurred by our limited ...observations from
Voyager 2
and Earth-based systems. Several of these observations are either inconsistent with our current understanding built from exploring other planetary systems, or indicate such unique characteristics of these Ice Giants that they leave us with more questions than answers. This paper specifically focuses on the value of all aspects of magnetospheric measurements, from the radiation belt structure to plasma dynamics to coupling to the solar wind, through a future mission to either of these planets. Such measurements have large interdisciplinary value, as demonstrated by the large number of mysteries discussed in this paper that cover other non-magnetospheric disciplines, including planetary interiors, atmospheres, rings, and moons.
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