Sustained wet-dry cycling on early Mars.

The presence of perennially wet surface environments on early Mars is well documented1,2, but little is known about short-term episodicity in the early hydroclimate3. Post-depositional processes driven by such short-term fluctuations may produce distinct structures, yet these are rarely preserved in the sedimentary record4. Incomplete geological constraints have led global models of the early Mars water cycle and climate to produce diverging results5,6. Here we report observations by the Curiosity rover at Gale Crater indicating that high-frequency wet-dry cycling occurred in early Martian surface environments. We observe exhumed centimetric polygonal ridges with sulfate enrichments, joined at Y-junctions, that record cracks formed in fresh mud owing to repeated wet-dry cycles of regular intensity. Instead of sporadic hydrological activity induced by impacts or volcanoes5, our findings point to a sustained, cyclic, possibly seasonal, climate on early Mars. Furthermore, as wet-dry cycling can promote prebiotic polymerization7,8, the Gale evaporitic basin may have been particularly conducive to these processes. The observed polygonal patterns are physically and temporally associated with the transition from smectite clays to sulfate-bearing strata, a globally distributed mineral transition1. This indicates that the Noachian-Hesperian transition (3.8-3.6 billion years ago) may have sustained an Earth-like climate regime and surface environments favourable to prebiotic evolution.

In situ recording of Mars soundscape.

Before the Perseverance rover landing, the acoustic environment of Mars was unknown. Models predicted that: (1) atmospheric turbulence changes at centimetre scales or smaller at the point where molecular viscosity converts kinetic energy into heat1, (2) the speed of sound varies at the surface with frequency2,3 and (3) high-frequency waves are strongly attenuated with distance in CO2 (refs. 2-4). However, theoretical models were uncertain because of a lack of experimental data at low pressure and the difficulty to characterize turbulence or attenuation in a closed environment. Here, using Perseverance microphone recordings, we present the first characterization of the acoustic environment on Mars and pressure fluctuations in the audible range and beyond, from 20 Hz to 50 kHz. We find that atmospheric sounds extend measurements of pressure variations down to 1,000 times smaller scales than ever observed before, showing a dissipative regime extending over five orders of magnitude in energy. Using point sources of sound (Ingenuity rotorcraft, laser-induced sparks), we highlight two distinct values for the speed of sound that are about 10 m s-1 apart below and above 240 Hz, a unique characteristic of low-pressure CO2-dominated atmosphere. We also provide the acoustic attenuation with distance above 2 kHz, allowing us to explain the large contribution of the CO2 vibrational relaxation in the audible range. These results establish a ground truth for the modelling of acoustic processes, which is critical for studies in atmospheres such as those of Mars and Venus.

Mars Extant Life: What's Next? Conference Report.

On November 5-8, 2019, the "Mars Extant Life: What's Next?" conference was convened in Carlsbad, New Mexico. The conference gathered a community of actively publishing experts in disciplines related to habitability and astrobiology. Primary conclusions are as follows: A significant subset of conference attendees concluded that there is a realistic possibility that Mars hosts indigenous microbial life. A powerful theme that permeated the conference is that the key to the search for martian extant life lies in identifying and exploring refugia ("oases"), where conditions are either permanently or episodically significantly more hospitable than average. Based on our existing knowledge of Mars, conference participants highlighted four potential martian refugium (not listed in priority order): Caves, Deep Subsurface, Ices, and Salts. The conference group did not attempt to reach a consensus prioritization of these candidate environments, but instead felt that a defensible prioritization would require a future competitive process. Within the context of these candidate environments, we identified a variety of geological search strategies that could narrow the search space. Additionally, we summarized a number of measurement techniques that could be used to detect evidence of extant life (if present). Again, it was not within the scope of the conference to prioritize these measurement techniques-that is best left for the competitive process. We specifically note that the number and sensitivity of detection methods that could be implemented if samples were returned to Earth greatly exceed the methodologies that could be used at Mars. Finally, important lessons to guide extant life search processes can be derived both from experiments carried out in terrestrial laboratories and analog field sites and from theoretical modeling.

Sporotrichosis caused by Sporothrix brasiliensis in Argentina: Case report, molecular identification and in vitro susceptibility pattern to antifungal drugs.

Sporotrichosis is considered a neglected disease of humans and animals in many regions of the world and is the most frequent implantation mycosis in Latin America. OBJECTIVES: To illustrate the zoonotic importance of the disease, describing a case involving a veterinarian and an infant that acquired the disease from a domestic cat and to describe, genotype and characterize these new isolates. METHODS: Direct examination of tissue samples from the two patients and feline lesions revealed the presence of Sporothrix yeast-like organisms. Fungal cultures and molecular identification of the strains were performed. Since antifungal susceptibility data of animal-borne isolates are scarce, the in vitro susceptibility testing by a microdilution reference method was determined against azoles, amphotericin B and terbinafine. RESULTS: Fungal culture and sequence analysis of the ITS region of rDNA and calmodulin and ß-tubulin genes confirmed the diagnosis and the causative agent as Sporothrix brasiliensis. In all cases, terbinafine was the most active drug, followed by posaconazole, itraconazole and voriconazole; the least active drugs were amphotericine B and fluconazole. Lack of clinical response in the veterinarian and in the infant to itraconazole and potassium iodide, respectively was observed. CONCLUSIONS: This study contributed to the molecular epidemiology of Sporothrix species in Argentina and the characterization of the in vitro susceptibility pattern of S. brasiliensis isolates recovered from a cat and two humans involved in this case of zoonotic sporotrichosis. Bearing in mind the "One Health" concept, the experience described in the present study highlights the need for future strategies for sporotrichosis treatment, control and prevention.

El ojo seco está relacionado con un aumento intrasujeto de la variabilidad de osmolaridad lagrimal confirmado por tecnología de aprendizaje de máquinas / Dry eye is matched by increased intrasubject variability in tear osmolarity as confirmed by machine learning approach

Objetivo: La medición de la osmolaridad lagrimal en pacientes con ojo seco ha sido cuestionada debido a su alta variabilidad. El entendimiento del origen de dicha variabilidad ayudaría a la interpretación clínica de los valores obtenidos. Esta investigación evalúa la medición de la variabilidad lagrimal en la práctica clínica. Material y métodos: Veinte pacientes con ojo seco y 20 controles fueron evaluados. Fueron realizadas 3 mediciones consecutivas de osmolaridad a intervalos de 5min. La variabilidad fue definida como la diferencia entre las mediciones más extremas obtenidas en cada ojo. Se utilizaron técnicas de aprendizaje de máquinas para evaluar la capacidad discriminadora de la osmolaridad lagrimal. Resultados: La osmolaridad promedio en el grupo control y ojo seco fueron 295,1 ± 7,3 mOsm/L y 300,6 ± 11,2 mOsm/L, respectivamente (p = 0,004). La variabilidad de la osmolaridad lagrimal fue 7,5 ± 3,6 mOsm/L en el grupo control y 16,7 ± 11,9 mOsm/L en los pacientes con ojo seco (p < 0,001). Basado en la osmolaridad, un clasificador logístico obtuvo un 85% de precisión. Conclusiones: La osmolaridad promedio y la variabilidad fueron significativamente más altas en pacientes con ojo seco. Por otra parte, las técnicas de aprendizaje de máquina demostraron buena precisión para clasificar a los pacientes. Por tanto, la alta variabilidad parece ser característica propia de la enfermedad de ojo seco

Objective: Because of high variability, tear film osmolarity measures have been questioned in dry eye assessment. Understanding the origin of such variability would aid data interpretation. This study aims to evaluate osmolarity variability in a clinical setting. Material and methods: Twenty dry eyes and 20 control patients were evaluated. Three consecutive osmolarity measurements per eye at 5min intervals were obtained. Variability was represented by the difference between both extreme readings per eye. Machine learning techniques were used to quantify discrimination capacity of tear osmolarity for dry eye. Results: Mean osmolarities in the control and dry eye groups were 295.1 ± 7.3 mOsm/L and 300.6 ± 11.2 mOsm/L, respectively (P=.004). Osmolarity variabilities were 7.5 ± 3.6 mOsm/L and 16.7 ± 11.9 mOsm/L, for the control and dry eye groups, respectively (P < .001). Based on osmolarity, a logistic classifier showed an 85% classification accuracy. Conclusions: In the clinical setting, both mean osmolarity and osmolarity variability in the dry eye group were significantly higher than in the control group. Machine learning techniques showed good classification accuracy. It is concluded that higher variability of tear osmolarity is a dry eye feature

Dry eye is matched by increased intrasubject variability in tear osmolarity as confirmed by machine learning approach. / El ojo seco está relacionado con un aumento intrasujeto de la variabilidad de osmolaridad lagrimal confirmado por tecnología de aprendizaje de máquinas.

OBJECTIVE: Because of high variability, tear film osmolarity measures have been questioned in dry eye assessment. Understanding the origin of such variability would aid data interpretation. This study aims to evaluate osmolarity variability in a clinical setting. MATERIAL AND METHODS: Twenty dry eyes and 20 control patients were evaluated. Three consecutive osmolarity measurements per eye at 5min intervals were obtained. Variability was represented by the difference between both extreme readings per eye. Machine learning techniques were used to quantify discrimination capacity of tear osmolarity for dry eye. RESULTS: Mean osmolarities in the control and dry eye groups were 295.1±7.3mOsm/L and 300.6±11.2mOsm/L, respectively (P=.004). Osmolarity variabilities were 7.5±3.6mOsm/L and 16.7±11.9mOsm/L, for the control and dry eye groups, respectively (P<.001). Based on osmolarity, a logistic classifier showed an 85% classification accuracy. CONCLUSIONS: In the clinical setting, both mean osmolarity and osmolarity variability in the dry eye group were significantly higher than in the control group. Machine learning techniques showed good classification accuracy. It is concluded that higher variability of tear osmolarity is a dry eye feature.

Soil diversity and hydration as observed by ChemCam at Gale crater, Mars.

The ChemCam instrument, which provides insight into martian soil chemistry at the submillimeter scale, identified two principal soil types along the Curiosity rover traverse: a fine-grained mafic type and a locally derived, coarse-grained felsic type. The mafic soil component is representative of widespread martian soils and is similar in composition to the martian dust. It possesses a ubiquitous hydrogen signature in ChemCam spectra, corresponding to the hydration of the amorphous phases found in the soil by the CheMin instrument. This hydration likely accounts for an important fraction of the global hydration of the surface seen by previous orbital measurements. ChemCam analyses did not reveal any significant exchange of water vapor between the regolith and the atmosphere. These observations provide constraints on the nature of the amorphous phases and their hydration.