Determination of dust aerosol particle size at Gale Crater using REMS UVS and Mastcam measurements

We calculate the seasonal and interannual variation in dust aerosol particle size above Gale Crater during the first 1413 Martian solar days (sols = 24.6 h) of the Mars Science Laboratory mission. Measurements of UV radiation made by the Rover Environmental Monitoring Station in combination with atmospheric opacities retrieved from the Mastcam instrument are used for the calculations. Our results indicate that the dust effective radius varies significantly with season, ranging from ~0.6 μm during the low opacity season (Ls = 60°â 140°) to ~2 μm during the high opacity season (Ls = 180°â 360°). Our results suggest that Gale Crater is affected by dust events of high aerosol content originated at various distances from it. Our results improve the accuracy of estimations of ultraviolet radiation fluxes at the Martian surface. Moreover, our results have important implications because the lifetime of suspended dust and its ability to nucleate clouds are affected by particle size.Plain Language SummaryThe Martian atmosphere transports large amounts of dust, which interacts strongly with solar and infrared radiation. The large spatial and temporal variability in atmospheric dust load creates complex feedbacks connecting dust lifting with the evolving atmospheric circulations. The size of suspended aerosols affects the surface and atmospheric heating rates, influencing the Martian climate. In this work, we have calculated the dust aerosol particle size above Gale Crater during the first 1413 sols of the Mars Science Laboratory (MSL) mission using measurements of UV radiation made for the first time from the surface of Mars. Our results indicate that the dust effective radius varies significantly with season, ranging from ~0.6 μm during the clear season to ~2 μm during the dusty season. Our results suggest that Gale Crater is affected by dust events of high aerosol content originated at various distances from it. Our results are important because the lifetime of suspended dust and its ability to nucleate clouds are affected by the particle size.Key PointsWe have developed a novel methodology to retrieve dust aerosol particle size at Gale Crater using Mars Science Laboratory dataThe retrieved dust effective radii range from 0.6 μm during the clear aphelion season to 2 μm during the dusty perihelion seasonOur results improve the estimation of ultraviolet radiation fluxes at the Martian surfacePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137189/1/grl55782-sup-0001-2017GL072589-SI.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137189/2/grl55782_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137189/3/grl55782.pd

The Surface Energy Budget at Gale Crater During the First 2500 Sols of the Mars Science Laboratory Mission

We use in situ environmental measurements by the Mars Science Laboratory (MSL) mission to obtain the surface energy budget (SEB) across Curiosity's traverse during the first 2500 sols of the mission. This includes values of the downwelling shortwave solar radiation, the upwelling solar radiation reflected by the surface, the downwelling longwave radiation from the atmosphere, the upwelling longwave radiation emitted by the surface, the sensible heat flux associated with turbulent motions, and the latent heat flux associated with water phase changes. We then analyze their temporal variation on different timescales and relate this to the mechanisms causing these variations. Through its Rover Environmental Monitoring Station, MSL allows for a more accurate determination of the SEB than its predecessors on Mars. Moreover, the unprecedented duration, cadence, and frequency of MSL environmental observations allow for analyses of the SEB from diurnal to interannual timescales. The results presented in this article can be used to evaluate the consistency with predictions from atmospheric numerical models, to validate aerosol radiative properties under a range of dust conditions, to understand the energy available for solar-powered missions, and to enable comparisons with measurements of the SEB by the Perseverance rover at Jezero crater.Peer reviewe

Focal Distribution of Hepatitis C Virus RNA in Infected Livers

Background: Hepatitis C virus (HCV) is a plus-strand RNA virus that replicates by amplification of genomic RNA from minus strands leading to accumulation of almost one thousand copies per cell under in vitro cell culture conditions. In contrast, HCV RNA copy numbers in livers of infected patients appear to be much lower, estimated at a few copies per cell. Methodology/Principal Findings: To gain insights into mechanisms that control HCV replication in vivo, we analyzed HCV RNA levels as well as expression of interferon beta (IFNb) and several interferon stimulated genes (ISGs) from whole liver sections and micro-dissected subpopulations of hepatocytes in biopsy samples from 21 HCV-infected patients. The results showed that intrahepatic HCV RNA levels range form less than one copy per hepatocyte to a maximum of about eight. A correlation existed between viral RNA levels and IFNb expression, but not between viral RNA and ISG levels. Also, IFNb expression did not correlate with ISGs levels. Replication of HCV RNA occurred in focal areas in the liver in the presence of a general induction of ISGs. Conclusion/Significance: The low average levels of HCV RNA in biopsy samples can be explained by focal distribution of infected hepatocytes. HCV replication directly induces IFNb, which then activates ISGs. The apparent lack of a correlation between levels of IFNb and ISG expression indicates that control of the innate immune response during HCV infection

Daytime variation in hepatitis C virus replication kinetics following liver transplant

Background: There is a growing interest in the role of circadian regulated pathways in disease pathogenesis. Methods: In a cohort of hepatitis C virus (HCV) infected patients undergoing liver transplantation, we observed differences in early viral infection kinetics of the allograft that associated with the time of liver transplant. Results: A higher frequency of subjects transplanted in the morning showed a rebound in viral RNA levels (n=4/6) during the first week post-surgery. In contrast, no viral rebound was observed in seven subjects transplanted in the afternoon. None of the other parameters previously reported to influence viral replication in the post-transplant setting, such as donor age, cold-ischemia time and length of surgery associated with viral rebound. Conclusions: These observation highlights a role for circadian processes to regulate HCV infection of the liver and warrants further investigation

The diverse meteorology of Jezero crater over the first 250 sols of Perseverance on Mars

ASA’s Perseverance rover’s Mars Environmental Dynamics Analyzer is collecting data at Jezero crater, characterizing the physical processes in the lowest layer of the Martian atmosphere. Here we present measurements from the instrument’s first 250 sols of operation, revealing a spatially and temporally variable meteorology at Jezero. We find that temperature measurements at four heights capture the response of the atmospheric surface layer to multiple phenomena. We observe the transition from a stable night-time thermal inversion to a daytime, highly turbulent convective regime, with large vertical thermal gradients. Measurement of multiple daily optical depths suggests aerosol concentrations are higher in the morning than in the afternoon. Measured wind patterns are driven mainly by local topography, with a small contribution from regional winds. Daily and seasonal variability of relative humidity shows a complex hydrologic cycle. These observations suggest that changes in some local surface properties, such as surface albedo and thermal inertia, play an influential role. On a larger scale, surface pressure measurements show typical signatures of gravity waves and baroclinic eddies in a part of the seasonal cycle previously characterized as low wave activity. These observations, both combined and simultaneous, unveil the diversity of processes driving change on today’s Martian surface at Jezero crater

In Situ UV Measurements by MSL/REMS: Dust Deposition and Angular Response Corrections

Measurements by the REMS/UV sensor onboard the MSL Curiosity rover constitute the first in situ dataset of UV radiation flux at the surface of Mars. Due to its position on the Curiosity deck, the UV sensor has been directly exposed to dust deposition. Inaccuracies in the original angular response calibration functions have led to discrepancies between measured and physically-expected UV fluxes when the solar zenith angle (θ) relative to the rover frame is between 20 and 55 . Here we present a methodology to correct UV fluxes when θ 30 , relative differences are greater than 100%. Measurements acquired when 20 < θ< 55 represent ∼45% of the whole dataset with θ< 90 . UV fluxes generated in this study are available in the NASA Planetary Data System (https://atmos.nmsu.edu/PDS/data/mslrem_1001/DATA_UV_CORRECTED/), and are important to study the effect of UV radiation on the variability of atmospheric constituents, to recreate accurate UV doses for biological laboratory experiments, to perform combined analyses of satellite and ground-based measurements, and to allow comparisons of the UV radiation environment at different locations with the upcoming ExoMars 2020 and Mars 2020 missions.With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737

Likely frost events at Gale crater: Analysis from MSL/REMS measurements

International audienceWe provide indirect evidence for the formation of frost at the surface of Gale crater by analyzing the highest confidence data from simultaneous measurements of relative humidity and ground temperature during the first 1000 sols of the Mars Science Laboratory (MSL) mission. We find that except for sol 44, frost events could have occurred only between sols 400 and 710, corresponding to the most humid and coldest time of the year (from early fall to late winter). In particular, measurements at Dingo Gap during sols 529-535, at an unnamed place during sols 554-560, at Kimberley during sols 609-617 and at an unnamed place during sols 673-676 showed the largest likelihood of the occurrence of frost events. At these four locations, the terrain is composed of fine-grained and loosely packed material with thermal inertia values of ∼200 SI units, much lower than the 365 ± 50 SI units value found at the landing ellipse. This is important because terrains with exceptionally low thermal inertia favor the formation of frost by lowering minimum daily ground temperatures. An order-of-magnitude calculation to determine the thickness of the frost layer at these four locations results in values of tenths of μm, while the precipitable water content is a few pr-μm. Therefore, surface frost events can have important implications for the local water cycle at Gale crater. In addition, frost is the most likely type of water that can be temporarily found in bulk amounts on the surface of Mars at low latitudes and therefore can cause weathering, influencing the geology of Gale crater