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The Mars Regional Atmospheric Modeling System (MRAMS) and a nested simulation of the Mars Weather Research and Forecasting model (MarsWRF) are used to predict the local meteorological conditions at the Mars 2020 Perseverance rover landing site inside Jezero crater (Mars). These predictions are complemented with the COmplutense and MIchigan MArs Radiative Transfer model (COMIMART) and with the local Single Column Model (SCM) to further refine predictions of radiative forcing and the water cycle respectively. The primary objective is to facilitate interpretation of the meteorological measurements to be obtained by the Mars Environmental Dynamics Analyzer (MEDA) aboard the rover, but also to provide predictions of the meteorological phenomena and seasonal changes that might impact operations, from both a risk perspective and from the perspective of being better prepared to make certain measurements. A full diurnal cycle at four different seasons (L 0 , 90 , 180 , and 270 ) is investigated. Air and ground temperatures, pressure, wind speed and direction, surface radiative fluxes and moisture data are modeled. The good agreement between observations and modeling in prior works [Pla-Garcia et al. in Icarus 280:103–113, 2016; Newman et al. in Icarus 291:203–231, 2017; Vicente-Retortillo et al. in Sci. Rep. 8(1):1–8, 2018; Savijärvi et al. in Icarus, 2020] provides confidence in utilizing these models results to predict the meteorological environment at Mars 2020 Perseverance rover landing site inside Jezero crater. The data returned by MEDA will determine the extent to which this confidence was justified., With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)

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.

C. E. Newman, H. Kahanpaa, M. I. Richardson, G. M. Martinez, A. Vicente‐Retortillo, M. T. Lemmon

The search for organic biosignatures on Mars will depend on finding material protected from the destructive ambient radiation. Solar ultraviolet can induce photochemical degradation of organic compounds, but certain clays have been shown to preserve organic material. We examine how the SHERLOC instrument on the upcoming Mars 2020 mission will use deep-ultraviolet (UV) (248.6 nm) Raman and fluorescence spectroscopy to detect a plausible biosignature of adenosine 5′-monophosphate (AMP) adsorbed onto Ca-montmorillonite clay. We found that the spectral signature of AMP is not altered by adsorption in the clay matrix but does change with prolonged exposure to the UV laser over dosages equivalent to 0.2–6 sols of ambient martian UV. For pure AMP, UV exposure leads to breaking of the aromatic adenine unit, but in the presence of clay the degradation is limited to minor alteration with new Raman peaks and increased fluorescence consistent with formation of 2-hydroxyadenosine, while 1 wt % Mg perchlorate increases the rate of degradation. Our results confirm that clays are effective preservers of organic material and should be considered high-value targets, but that pristine biosignatures may be altered within 1 sol of martian UV exposure, with implications for Mars 2020 science operations and sample caching. This work was funded by a NASA Postdoctoral Program Fellowship awarded to Joseph Razzell Hollis, administered by the Universities Space Research Association on behalf of NASA, and Teresa Fornaro was supported by the Geophysical Laboratory of the Carnegie Institution of Washington and the Italian Space Agency (ASI) grant agreement ExoMars number 2017-48-H.0. William Rapin was funded by an MSL-Curiosity Participating Scientist grant to Bethany Ehlmann. (c) 2019California Institute of Technology; government sponsorship acknowledged. Peerreview

Highlights Presents solar array dust factor evolution for 6 landed missions. Evaluates statistics of solar array output decline, typically 0.2%/Sol but ranging 0.05–2%/Sol. Determines statistics of cleaning events. Compares evolution with meteorological predictions at the different landing sites. The degradation in electrical output of solar arrays on Mars landers and rovers is reviewed. A loss of 0.2% per Sol is typical, although observed rates of decrease in ‘dust factor’ vary between 0.05% and 2% per Sol. 0.2%/Sol has been observed throughout the first 800 Sols of the ongoing InSight mission, as well as the shorter Mars Pathfinder and Phoenix missions. This rate was also evident for much of the Spirit and Opportunity missions, but the degradation there was episodically reversed by cleaning events due to dust devils and gusts. The enduring success of those rover missions may have given an impression of the long-term viability of solar power on the Martian surface that is not globally-applicable: the occurrence of cleaning events with an operationally-useful frequency seems contingent upon local meteorological circumstances. The conditions for significant cleaning events have apparently not been realized at the InSight landing site, where, notably, dust devils have not been detected in imaging. Optical obscuration by dust deposition and removal has also been observed by ultraviolet sensors on Curiosity, with a similar (but slightly higher) degradation rate. The observations are compared with global circulation model (GCM) results: these predict a geographically somewhat uniform dust deposition rate, while there is some indication that the locations where cleaning events were more frequent may be associated with weaker background winds and a deeper planetary boundary layer. The conventional Dust Devil Activity metric in GCMs does not effectively predict the different dust histories. We thank the InSight science and engineering teams for useful discussions. RL and CEN acknowledge the support of the NASA InSight Participating Scientist Program via Grants 80NSSC18K1626 and 80NSSC18K1630, respectively. AVR is supported by AEI Project No. MDM-2017-0737 Unidad de Excelencia “María de Maeztu”- Centro de Astrobiología (INTA-CSIC)". AS, FF, EM, TP acknowledge the support of CNES, ESA and of ANR (MAGIS, ANR-19-CE31-0008-08). This is InSight Contribution Number 193. We thank Matt Golombek and Veronique Ansan for useful comments. Peerreview

The Sample Analysis at Mars (SAM) instrument onboard the Mars Science Laboratory Curiosity rover measures the chemical composition of major atmospheric species (CO2, N2, 40Ar, O2, and CO) through a dedicated atmospheric inlet. We report here measurements of volume mixing ratios in Gale Crater using the SAM quadrupole mass spectrometer, obtained over a period of nearly 5 years (3 Mars years) from landing. The observation period spans the northern summer of MY 31 and solar longitude (LS) of 175° through spring of MY 34, LS = 12°. This work expands upon prior reports of the mixing ratios measured by SAM QMS in the first 105 sols of the mission. The SAM QMS atmospheric measurements were taken periodically, with a cumulative coverage of four or five experiments per season on Mars. Major observations include the seasonal cycle of CO2, N2, and Ar, which lags approximately 20¿40° of LS behind the pressure cycle driven by CO2 condensation and sublimation from the winter poles. This seasonal cycle indicates that transport occurs on faster timescales than mixing. The mixing ratio of O2 shows significant seasonal and interannual variability, suggesting an unknown atmospheric or surface process at work. The O2 measurements are compared to several parameters, including dust optical depth and trace CH4 measurements by Curiosity. We derive annual mean volume mixing ratios for the atmosphere in Gale Crater: CO2 = 0.951 (±0.003), N2 = 0.0259 (±0.0006), 40Ar = 0.0194 (±0.0004), O2 = 1.61 (±0.09) x 10-3, and CO = 5.8 (±0.8) x 10-4. ©2019. The Authors., All MSL data used in this manuscript (REMS and SAM) are freely available on NASA's Planetary Data System (PDS) Geosciences Node, from within 6 months after receipt on Earth (http://pds‐geosciences.wustl.edu/missions/msl/). The mixing ratios developed and presented in this paper are available at a publicly available archive (dataverse.org: doi.org/10.7910/DVN/CVUOWW) as cited within the manuscript. The successful operation of the Curiosity rover and the SAM instrument on Mars is due to the hard work and dedication of hundreds of scientists, engineers, and managers over more than a decade. Essential contributions to the successful operation of SAM on Mars and the acquisition of SAM data were provided by the SAM development, operations, and test bed teams. The authors gratefully thank the SAM and MSL teams that have contributed in numerous ways to obtain the data that enabled this scientific work. We also thank NASA for the support of the development of SAM, SAM data analysis, and the continued support of the Mars Science Laboratory mission. The contribution of F. Lefèvre was supported by the Programme National de Planétologie (PNP). R. Navarro‐Gonzalez acknowledges support from the Universidad Nacional Autónoma de México (PAPIIT IN111619). LPI is operated by USRA under a cooperative agreement with the Science Mission Directorate of the National Aeronautics and Space Administration. We thank members of the SAM and larger MSL team for insightful discussions and support. In particular, we thank R. Becker and R. O. Pepin for careful review of data analysis and interpretation. We thank M. D. Smith for discussion of CRISM CO measurements. We thank A. Brunner, M. Johnson, and M. Lefavor for their development of customized data analysis tools used here and in other SAM publications.

We calculate the seasonal and interannual variation in dust aerosol particle size above Gale Crater during the first 1413 sols of the Mars Science Laboratory (MSL) mission. Measurements of UV radiation made by the Rover Environmental Monitoring Station (REMS) 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° – 140°) to ~2 µm during the high opacity season (Ls = 180° – 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.

We analyze the complete set of in-situ meteorological data obtained from the Viking landers in the 1970s to today’s Curiosity rover to review our understanding of the modern near-surface climate of Mars, with focus on the dust, CO2 and H2O cycles and their impact on the radiative and thermodynamic conditions near the surface. In particular, we provide values of the highest confidence possible for atmospheric opacity, atmospheric pressure, near-surface air temperature, ground temperature, near-surface wind speed and direction, and near-surface air relative humidity and water vapor content. Then, we study the diurnal, seasonal and interannual variability of these quantities over a span of more than twenty Martian years. Finally, we propose measurements to improve our understanding of the Martian dust and H2O cycles, and discuss the potential for liquid water formation under Mars’ present day conditions and its implications for future Mars missions. Understanding the modern Martian climate is important to determine if Mars could have the conditions to support life and to prepare for future human exploration.

The REMS instrument on board the Curiosity rover has been collecting meteorological data from Gale crater on Mars since August 2012. A dust storm that developed north of Gale crater in sol 852 of the Mars Science Laboratory (MSL) mission spread above the location of the Curiosity rover during sols 853–855 (December 30, 2014 to January 1, 2015, areocentric solar longitude Ls 263°, MY32). The storm was observed by the MARCI imaging instrument on the Mars Reconnaissance Orbiter and its effects in the local meteorology were recorded in situ by the REMS instrument on MSL. Here we present a detailed report of the effects of the storm at Gale crater. Using MARCI images, we measured the size and altitude of the dust storm, which reached a size of 482,000 km2, attained an altitude of 19 km above the ground, and dispersed through the Gale crater and its surrounding area the next sol. The dispersion of the dust from the storm was roughly in agreement with the expected values of the winds on Ls 263° from climatological values in the Mars Climate Database (MCD). REMS data show that the storm produced the following effects when the dust arrived at Gale: (1) An increase in the daily amplitude of the atmospheric pressure variation (~15 ± 3 Pa) mainly through a reduction of the daily minimum pressure (~12 Pa) in the late afternoon hours. (2) A decrease of the UV signal (~30%). (3) An unexpected increase in the temperature of the air close to the surface (~14 ± 4 K) in the early afternoon (LT~14–15). (4) A cooling of the surface near noon (~6 ± 4.5 K). The warming of local air was contrary to previous observations of effects of dust storms on the Martian surface. This could be due to the vertical distribution of dust when the storm arrived at Gale crater, which was less vertically extended than in the previous sol. However, the data does not allow for a quantitative evaluation of this hypothesis. Although the storm could be observed from orbit only over one single sol above Gale crater its effects over the local meteorology lasted longer and dissipated in a time-scale of 3 sols.

In situ measurements by the Curiosity rover provide a unique opportunity for studying the effects of dust on assets placed at the surface of Mars. Here we use in situ measurements of solar UV radiation to quantify the seasonal and interannual variability of dust accumulation on the sensor on the rover deck. We show that the amount of dust accumulated on the sensor follows a seasonal cycle, with net dust removal during the perihelion season until Ls ~ 300°, and net dust deposition until the end of the aphelion season (Ls ~ 300°–180°). We use independent in situ measurements of atmospheric opacity and pressure perturbations in combination with numerical modeling, showing that daytime convective vortices and nighttime winds are likely responsible for the seasonal dust cleaning, with the role of nighttime wind being more important in Martian Year (MY) 32 than in MY 33 and that of daytime convective vortices being more important in MY 33 than in MY 32. The fact that the UV sensor is cleaner in MY 33 than in MY 32 indicates that natural cleaning events make solar energy an excellent candidate to power extended (multiannual) Mars missions at similar latitudes as the Curiosity rover.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited., We analyze 10 years of Mars Express total electron content (TEC) data from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument. We describe the spatial, seasonal, and solar cycle behavior of the Martian TEC. Due to orbit evolution, data come mainly from the evening, dusk terminator and postdusk nightside. The annual TEC profile shows a peak at Ls = 25–75° which is not related to the solar irradiance variation but instead coincides with an increase in the thermospheric density, possibly linked with variations in the surface pressure produced by atmospheric cycles such as the CO or water cycles. With the help of numerical modeling, we explore the contribution of the ion species to the TEC and the coupling between the thermosphere and ionosphere. These are the first observations which show that the TEC is a useful parameter, routinely measured by Mars Express, of the dynamics of the lower-upper atmospheric coupling and can be used as tracer for the behavior of the thermosphere.©2018. The Authors., B. S. -C. and M. L. acknowledge support through STFC grant ST/N000749/1. ESA-ESTEC Faculty and Europlanet funding are also gratefully acknowledged. MEX MARSIS RDR and EDR data can be downloaded from the ESA-PSA archive, TIMED-SEE data at the University of Colorado's website (http://lasp.colorado.edu/lisird/index.html), REMS data at the NASA Planetary Data System (http://atmos.nmsu.edu/PDS/data/mslrem_1001/DATA/), the MCD model at the Mars Climate Database web interface (http://www-mars.lmd.jussieu.fr/mars/access.html), and the IPIM model at the IRAP CDPP web interface (http://transplanet.irap.omp.eu/).

Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location.We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover.The background levels of methane have a mean value 0.41 ± 0.16 parts per billion by volume (ppbv) (95% confidence interval) and exhibit a strong, repeatable seasonal variation (0.24 to 0.65 ppbv).This variation is greater than that predicted from either ultraviolet degradation of impact-delivered organics on the surface or from the annual surface pressure cycle.The large seasonal variation in the background and occurrences of higher temporary spikes (∼7 ppbv) are consistent with small localized sources of methane released from martian surface or subsurface reservoirs., The authors thank the reviewers for constructive comments that greatly improved the manuscript. The research described here was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA). Funding: Funding from NASA’s Planetary Science Division is acknowledged by authors C.R.W., P.R.M., S.K.A., G.J.F., C.M., C.P.M., M.H.W., M.G.T., A.S., D.A., C.H.H., R.V.G., A.P., J.L.E., D.P.G., J.C.P., D.K., L.E.C., J.P.-G., S.C.R.R., M.D.S., D.M.H., M.L., J.C., R.W.Z., and A.R.V. R.N.-G. acknowledges funding from the National Autonomous University of Mexico and Consejo Nacional de Ciencia y Tecnología. J.E.M. and C.L.S. acknowledge funding from the Canadian Space Agency MSL participating scientist program. S.P.Sc. acknowledges funding from the UK Space Agency. A.-M.H. acknowledges funding from the Finnish Academy under grant 310509. J.P.-G. acknowledges funding from the Spanish Ministry of Economy and Competitiveness under contract ESP2016-79612-C3-1-R. Author contributions: C.R.W. and P.R.M. performed TLS-SAM instrument design, build, and testing (IDBT); surface operations (SO); test-bed activities (TBA); data analysis (DA); data correlations (DC); and science interpretation (SI). G.J.F. and C.M. performed IDBT, SO, TBA, and DA. S.K.A., J.E.M., C.P.M., C.L.S., A.S., D.A., B.S., P.J.C., C.F., P.-Y.M., R.V.G., C.H.H., A.P., J.L.E., D.P.G., S.P.Sa., and R.W.Z. performed SI. J.C. and A.R.V. performed SO. J.C.P., D.K., and L.E.C. performed IDBT. G.M., J.M.-T., J.G.-E., M.-P.Z., M.G.T., S.P.Sc., R.N.-G., A.V.-R., H.K., D.V.-M., M.D.S., A.-M.H., M.G., D.M.H., and M.L. performed DC. J.P.-G. and S.C.R.R. performed DC and SI. Competing interests: No potential conflicts of interest exist for any of the listed authors. Data and materials availability: The data described in this paper are publicly available from NASA’s Planetary Data System (PDS) under an arrangement with the Mars Science Laboratory (MSL) project at http://pds-geosciences.wustl.edu/missions/msl/sam. htm, under the run numbers given in table S2.

International audience; We 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.

Mars Science Laboratory Curiosity rover observations of the 2018/Mars year 34 global/planet-encircling dust storm represent the first in situ measurements of a global dust storm with dedicated meteorological sensors since the Viking Landers. The Mars Science Laboratory team planned and executed a science campaign lasting approximately 100 Martian sols to study the storm involving an enhanced cadence of environmental monitoring using the rover's meteorological sensors, cameras, and spectrometers. Mast Camera 880-nm optical depth reached 8.5, and Rover Environmental Monitoring Station measurements indicated a 97% reduction in incident total ultraviolet solar radiation at the surface, 30K reduction in diurnal range of air temperature, and an increase in the semidiurnal pressure tide amplitude to 40 Pa. No active dust-lifting sites were detected within Gale Crater, and global and local atmospheric dynamics were drastically altered during the storm. This work presents an overview of the mission's storm observations and initial results., This work was funded by a MSL Participating Scientist grant to S. Guzewich. A portion of the research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. MSL data are freely available on the Planetary Data System within 6 months after receipt on Earth. Data used to make the figures are included in the supporting information. Mastcam and Navcam images are freely available at https://mars.nasa.gov/msl/ multimedia/raw/. We thank two anonymous reviewers for their helpful comments, which have improved this manuscript