The observation of gullies on Mars indicates the presence of liquid water near the surface in recent times, which is difficult to reconcile with the current cold climate. Gullies have been proposed ...to form through surface runoff from subsurface aquifers or through melting of near-surface ice under warmer conditions. But these gullies are observed to occur preferentially in cold mid-latitudes, where the presence of liquid water is less likely, and on isolated surfaces where groundwater seepage would not be expected, making both potential explanations unsatisfactory. Here I show that gullies can form by the melting of water-rich snow that has been transported from the poles to mid-latitudes during periods of high obliquity within the past 105 to 106 years (refs 5, 6). Melting within this snow can generate sufficient water to erode gullies in about 5,000 years. My proposed model for gully formation is consistent with the age and location of the gullies, and it explains the occurrence of liquid water in the cold mid-latitudes as well as on isolated surfaces. Remnants of the snowpacks are still present on mid-latitude, pole-facing slopes, and the recent or current occurrence of liquid water within them provides a potential abode for life.
Thermal inertia values at 100 m per pixel are determined using nighttime temperature data from the Thermal Emission Imaging System (THEMIS) on the Mars Odyssey spacecraft, producing the ...highest‐resolution thermal inertia data set to date. THEMIS thermal inertia values have an overall accuracy of ∼20%, a precision of 10–15%, and are consistent with both Thermal Emission Spectrometer orbital and Miniature Thermal Emission Spectrometer surface thermal inertia values. This data set enables the improved quantification of fine‐scale surface details observed in high‐resolution visible images. In the Tharsis region, surface textures and crater rims observed in visible images have no corresponding variation in the THEMIS thermal inertia images, indicating that the dust mantle is pervasive at THEMIS scales and is a minimum of a few centimeters and up to 1–2 m thick. The thermal inertia of bed form material indicates particle diameters expected for aeolian sediments, and these materials are likely currently saltating. Variations in the thermal inertia within interior layered deposits in Hebes Chasma can be distinguished, and the thermal inertia is too low to be consistent with bedrock or a lava flow. Thus a secondary emplacement of volcanic material or a volcanic ash deposit is a more likely method of formation. Higher‐resolution THEMIS thermal inertia enables the identification of exposed bedrock on the Martian surface. In Nili Patera and Ares Vallis, bedrock material corresponds to distinct compositional and morphologic surfaces, indicating that a specific unit is exposed and is likely currently being kept free of unconsolidated material by aeolian processes.
Mars Global Surveyor Thermal Emission Spectrometer (MGS‐TES) data are used to derive the modal mineralogy of spectrally distinct Martian low‐albedo regions and to identify spatial trends in ...mineralogic assemblages. Results from this work are consistent with the major results of previous spectroscopic studies: (1) Plagioclase and clinopyroxene are the dominant minerals of most southern highlands regions, (2) the northern plains exhibit the lowest pyroxene abundance within Martian low‐albedo regions, and (3) the highest concentrations of high‐silica phase(s) are found in the northern plains, Solis Planum and a few southern high‐latitude regions. Low‐albedo regions may be classified into four units on the basis of relative abundances of plagioclase, pyroxene, and high‐silica phase(s). Unit distributions between ±45° latitude exhibit moderate correlation with distinct provinces (e.g., Syrtis Major, Aonium Sinus) defined by large‐scale morphology, elevation, and to some extent, surface age, suggesting that the spectral and compositional differences between these units are more strongly controlled by original bedrock mineralogy than by surface‐atmosphere interactions and alteration. Syrtis Major exhibits a difference in mineralogy from the surrounding highlands suggesting a differing degree of fractional crystallization, assimilation, or source region composition. Areas with thick crust near the Tharsis Plateau exhibit lower abundances of olivine and greater plagioclase/pyroxene ratios than surrounding highland terrains, suggesting that magmas in this region may have undergone increased olivine fractionation. Regions where surface alteration is more likely to be the primary control on observed spectral signatures are the high‐latitude areas (>45°), where globally, surfaces dominated by high‐silica phase(s) are most commonly found.
Condensation and sublimation of ices at the surface of the planet is a key part of both the Martian H2O and CO2 cycles, either from a seasonal or diurnal aspect. While most of the ice is located ...within the polar caps, surface frost is known to be formed during nighttime down to equatorial latitudes. Here, we use data from the Emirates Mars Infrared Spectrometer onboard the Emirates Mars Mission to monitor the diurnal and seasonal evolution of the ices at the surface of Mars over almost one Martian year. The unique local time coverage provided by the instrument allows us to observe the apparition of equatorial CO2 frost in the second half of the Martian night around the equinoxes, to its sublimation at sunrise.
Plain Language Summary
The H2O and CO2 ices that form at the surface on Mars play an important role in the exchange between the atmosphere and the surface of the planet. While most of the ice is located within the two polar caps that grew and shrink seasonally, ice is also known to condensate as surface frost during the night and sublimate during the day. This nighttime surface frost deposition can be observed even at equatorial latitudes. In this paper we use data from the Emirates Mars Infrared Spectrometer onboard the Emirates Mars Mission to detect the H2O and CO2 ices at the surface of the planet at all local times over almost one Martian Year, which allows us to monitor both the seasonal and diurnal evolution of the distribution of ices at the surface of Mars. We observe that nighttime CO2 frost forms at equatorial latitudes in the second half of the night to disappear at sunrise around the Martian equinoxes.
Key Points
We monitor the seasonal growth and retreat of both polar caps over MY 36
We monitor the presence of CO2 ice on the surface of Mars over MY 36, through the season and through all times of day
CO2 ice appears at the surface at equatorial latitudes during the second half of the night around the equinoxes
Past studies of the thermophysical properties of the Martian surface layer have assumed temperature‐independent thermal inertia, which is a function of the material density, specific heat, and bulk ...conductivity. In this paper, we evaluate the temperature‐driven variations of these quantities for particulated and cemented material under Martian conditions of atmospheric pressure and temperature. Temperature‐driven density variations are negligible. The specific heat of a basaltic material is strongly influenced by the temperature (∼75% increase from 150 to 315 K), inducing significant variations of the thermal inertia. The thermal conductivity of uncemented Martian regolith is weakly controlled by the solid phase conductivity and strongly controlled by the gaseous phase conductivity. As a result, the conductivity of the solid phase (i.e., composition, temperature) is unimportant, whereas medium to large variations (30–50%) of the bulk conductivity are associated with temperature‐induced fluctuations of the pore‐filling gas conductivity. Overall, the thermal inertia of uncemented Martian soils is predicted to vary significantly (∼80%) throughout the range of the observed surface temperatures. In the case of cemented soils, the contribution of the gas conductivity is generally small, and the solid phase (i.e., grains and cement) conductivity (i.e., composition, temperature) becomes more important. Consequently, the magnitude of the thermal inertia change for cemented soils is variable, and smaller than that predicted for uncemented materials (10–50%). Large diurnal and seasonal temperature variations only occur within the top material, and most of the near‐surface regolith does not experience large thermal inertia variations. The shapes of modeled diurnal temperature curves are not significantly modified (e.g., the 0200 LT (Martian local time) apparent thermal inertia of uncemented regolith is up to ∼15% lower than the average daily inertia of the top material). Thermally derived grain sizes are usually based on conductivity measurements operated at room temperature or above, where the thermal inertia and specific heat are higher than on Mars, implying that grain size predictions for Mars are currently underestimated. However, in situ observations by the Mars Exploration Rovers and thermal conductivity modeling suggest that this underestimation is not significant.
Key Points
The thermal inertia of the Martian surface is strongly temperature dependent
The amplitude of this dependency depends on the grain size and cement
Thermally derived grain sizes from orbit are usually underestimated
The Thermal Emission Imaging System (THEMIS) on 2001 Mars Odyssey will investigate the surface mineralogy and physical properties of Mars using multi-spectral thermal-infrared images in nine ...wavelengths centered from 6.8 to 14.9 mm, and visible/near-infrared images in five bands centered from 0.42 to 0.86 mm. THEMIS will map the entire planet in both day and night multi-spectral infrared images at 100-m per pixel resolution, 60% of the planet in one-band visible images at 18-m per pixel, and several percent of the planet in 5-band visible color. Most geologic materials, including carbonates, silicates, sulfates, phosphates, and hydroxides have strong fundamental vibrational absorption bands in the thermal-infrared spectral region that provide diagnostic information on mineral composition. The ability to identify a wide range of minerals allows key aqueous minerals, such as carbonates and hydrothermal silica, to be placed into their proper geologic context. The specific objectives of this investigation are to: (I) determine the mineralogy and petrology of localized deposits associated with hydrothermal or sub-aqueous environments, and to identify future landing sites likely to represent these environments; (2) search for thermal anomalies associated with active sub-surface hydrothermal systems; (3) study small-scale geologic processes and landing site characteristics using morphologic and thermophysical properties; and (4) investigate polar cap processes at all seasons. THEMIS follows the Mars Global Surveyor Thermal Emission Spectrometer (TES) and Mars Orbiter Camera (MOC) experiments, providing substantially higher spatial resolution IR multi-spectral images to complement TES hyperspectral (143-band) global mapping, and regional visible imaging at scales intermediate between the Viking and MOC cameras. The THEMIS uses an uncooled microbolometer detector array for the IR focal plane. The optics consists of all-reflective, three-mirror anastigmat telescope with a 12-cm effective aperture and a speed of f/1.6. The IR and visible cameras share the optics and housing, but have independent power and data interfaces to the spacecraft. The IR focal plane has 320 cross-track pixels and 240 downtrack pixels covered by 10 --1-p.m-bandwidth strip filters in nine different wavelengths. The visible camera has a 1024 x 1024 pixel array with 5 filters. The instrument weighs 11.2 kg, is 29 cm by 37 cm by 55 cm in size, and consumes an orbital average power of 14 W.
Thermal infrared spectra of the martian surface indicate the presence of small concentrations (~2 to 5 weight %) of carbonates, specifically dominated by magnesite (MgCO3). The carbonates are widely ...distributed in the martian dust, and there is no indication of a concentrated source. The presence of small concentrations of carbonate minerals in the surface dust and in martian meteorites can sequester several bars of atmospheric carbon dioxide and may have been an important sink for a thicker carbon dioxide atmosphere in the martian past.
The Objective was to determine the diagnostic accuracy of thoracic ultrasound (TUS) for detecting (ILD) in rheumatoid arthritis (RA) with respiratory symptoms.
Individuals with RA visiting ...Rheumatological outpatient clinics in the Region of Southern Denmark were systematically screened for dyspnoea, cough, recurrent pneumonia, prior severe pneumonia or a chest X-ray indicating interstitial abnormalities. Eighty participants with a positive screening were consecutively included. Individuals were not eligible if they had a chest high-resolution CT (HRCT) <12 months or were already diagnosed with ILD. A blinded TUS expert evaluated TUS, and TUS was registered as positive for ILD if ≥10 B-lines or bilateral thickened and fragmented pleura were present. The primary outcomes were TUS's sensitivity, specificity, and positive predictive value (PPV) and negative predictive value (NPV). An ILD-specialised thoracic radiologist assessed HRCT, followed by a multi-disciplinary team discussion, which was the reference standard. The accepted window of HRCT was <30 days after TUS was performed.
77 participants received HRCT <30 days after TUS, and 23 (30%) were diagnosed with ILD. TUS had a sensitivity of 82.6% (95% CI: 61.2% to 95.0%) and a specificity of 51.9% (95% CI: 37.8% to 65.7%), corresponding to a PPV of 42.2% (95%CI 27.7% to 57.8%) and an NPV of 87.5% (95% CI 71.0% to 96.5%).
To our knowledge, this prospective study is the first to use respiratory symptoms in RA as inclusion criteria. Systematic screening for respiratory symptoms combined with TUS can reduce the diagnostic delay of ILD in RA.
Recent Mars‐orbiting spectrometers continue to detect surface materials containing hydrated silicates, particularly clays and amorphous phases (e.g., silica glasses), concentrated within the heavily ...cratered Noachian highlands crust. This paper provides a review, summary, and synthesis of observations from terrestrial impact structures with current Martian data. It is suggested that numerous and frequent impacts into the volatile‐rich silicate crust of Mars, through direct and indirect impact‐generated mechanisms, represent a plausible hypothesis that can explain the widespread distribution of hydrated silicates in the surface and subsurface of the heavily cratered Noachian highlands crust largely independent of climate. In addition to impact‐generated hydrothermal activity, devitrification, autometamorphism, and the voluminous production of impact “damaged” materials that are susceptible to alteration must be considered. When taken together, a drastically different early climate on Mars, in which water is stable at the surface for extended periods of time, cannot be ruled out; however, it is noted here that these additional impact mechanisms can operate and thereby extend the range of possible alteration settings to include climate conditions that may have been predominately colder and drier. Such a climate would not be dissimilar to the conditions of today, with the important exceptions of a higher geothermal gradient, and punctuated thermal disturbance to the cryosphere and hydrosphere from igneous activity and an exponentially higher impact flux.
Key Points
Frequent impacts into the volatile‐rich crust can produce hydrated silicates.Does not require drastic climate change.Additional impact‐induced alteration mechanisms explained.
Diurnal analyses of water ice cloud optical depths retrieved from thermal infrared spectra by the Emirates Mars Infrared Spectrometer showed changing cloud abundance throughout the Martian day. ...Observations began with the start of the Emirates Mars Mission science phase near the beginning of aphelion‐season in Mars Year 36 and included the prominent aphelion cloud belt (ACB) and orographic clouds in the vicinity of volcanoes. A midday minimum with higher morning and afternoon optical depths was typical for the ACB, though with considerable spatial variability in this diurnal pattern. Clouds near volcanoes reached a minimum before local noon and tended to increase in abundance throughout the afternoon. Comparisons against the Laboratoire de Météorologie Dynamique global circulation model showed analogous spatial patterns in the diurnal signal, which suggested thermal tides and topographic effects to be the predominant drivers of ACB variability, while more localized circulations affected volcano clouds.
Plain Language Summary
Observations from the Emirates Mars Infrared Spectrometer onboard the Emirates Mars Mission (EMM) spacecraft were used to measure the abundance of clouds in the Martian atmosphere and investigate how they changed throughout the day. Due to the unique nature of EMM's high orbit, the observations provided by EMIRS cover all times of day and provide more detailed information about how clouds change as compared to many previous missions. In these results we present information about this daytime cloud variability for different regions on Mars. A prominent region of clouds that is commonly observed near the equator during Mars' cold season—known as the aphelion cloud belt—was observed to reach a minimum near midday, with more clouds typically observed in both the morning and afternoon. Distinct differences were found in clouds observed near volcanoes, which tended to reach a minimum before local noon and increase throughout the afternoon. These results add detail to our understanding of cloud behavior and help us to validate computer models of the Martian atmosphere.
Key Points
Infrared spectra from the Emirates Mars Infrared Spectrometer were used to obtain water ice cloud optical depths throughout the day
The aphelion cloud belt had a midday minimum with higher optical depths in the morning and afternoon
Orographic clouds near volcanoes were observed to increase throughout the afternoon
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