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The Mars2020 Perseverance Rover landed successfully on the Martian surface on the Jezero Crater floor (18.44°N, 77.45°E) at Martian solar longitude, $L_s$, $\sim$5 in February 2021. Since then it has produced highly valuable environmental measurements with a versatile scientific payload including the MEDA (Mars Environmental Dynamics Analyzer) suite of environmental sensors. One of the MEDA systems is the PS pressure sensor system which weighs 40 grams and has an estimated absolute accuracy of better than 3.5 Pa and a resolution of 0.13 Pa. We present initial results from the first 414 sols of Martian atmospheric surface pressure observations by the PS whose performance was found to meet its specifications. Observed sol-averaged atmospheric pressures follow an anticipated pattern of pressure variation in the course of the advancing season and are consistent with data from other landing missions. The observed diurnal pressure amplitude varies by $\sim$2-5 \% of the sol-averaged pressure, with absolute amplitude 10-35 Pa in an approximately direct relationship with airborne dust. During a regional dust storm, which began at $L_s~135^\circ$ the diurnal pressure amplitude roughly doubles. The diurnal pressure variations were found to be remarkably sensitive to the seasonal evolution of the atmosphere. In particular analysis of the diurnal pressure signature revealed diagnostic information likely related to the regional scale structure of the atmosphere. Comparison of Perseverance pressure observations to data from other landers reveals the global scale seasonal behaviour of Mars’ atmosphere.

Air temperature, ground temperature, pressure, and wind speed and direction data obtained from the APSS (Auxiliary Payload Sensor Suite) and HP3 radiometer (RAD) onboard the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander are compared to data from the Mars Regional Atmospheric Modeling System. A full diurnal cycle at four different seasons (Ls 0º, 90º, 180º and 270º) is investigated at the lander location at 4.5° N 135.6° E in Elysium Planitia on Mars (Figure shows comparison results for Ls 180º). This work extends the atmospheric observations perform by [1]. Model results are shown to be in good agreement with observations. The good agreement provides justification for utilizing the model results to investigate the broader meteorological environment of Elysium Planitia in a companion paper. The observed air temperature, pressure and winds are taken at ∼1m above ground, while MRAMS provides those values at the lowest atmospheric model level of ∼14 m. As expected, the MRAMS air temperature values at this height tend to be cooler than the observed in the morning and early afternoon, and then tend to be warmer in the late afternoon and through the night. Also, the difference in height should not have a large impact on wind direction, but modeled wind speeds at ∼14 m are faster than the observed at 1.5 m due to frictional effects. Small discrepancies in ground temperatures could be attribute to a different initialization of thermal inertia, dust and clouds in the model when compared with the data. The diurnal pressure amplitude at Elysium Planitia varies from 2.52% to 4.5% depending on the season. The total amplitude is then considerably smaller compared to Gale crater (up to ∼13%, [2]). [3] attributed the amplification at Gale due to a mesoscale hydrostatic adjustment process in regions of topographic slopes. We also use a Computational Fluid Dynamics (CFD) to study the mechanical disturb of the wind directions due to other instruments onboard the lander and it effect into the wind directions discrepancy between modeling and observations [4]. For low wind speeds (~3.4 m/s), there is an important mechanical contamination in the 330º-30º wind directions range for FM1 and in the 210-330º range for FM2 (Figure bottom left), mostly during nighttime. Figure 1. Observed and modeled diurnal air temperature, ground temperature, pressure, wind speed and wind direction signal at Ls 180. MRAMS are the black dots. InSight data taken within a few sols of the Ls 180 are shown in different colors, which each color representing data from a single sol. CFD results with the mechanical disturb (from the higher value -0- to the lower value -1.2-) of the wind directions due to other instruments onboard the lander for low wind speeds (~3.4 m/s) are shown in the bottom left.

Pressure, ground temperature, air temperature close to the surface and at 40 m height, and wind speed and direction data obtained from MEDA [Rodriguez-Manfredi et al. 2021] onboard Perseverance rover are compared to data from MRAMS [Rafkin and Michaels 2019]. A full diurnal cycle at twelve different times of a complete martian year (Ls 30º, 60º, 90º, 105º, 160º, 180º, 210º, 240º, 270º, 300º, 330º and 360º) are investigated at the rover location at 18.44°N; 77.45°E inside Jezero crater on Mars. Figure shows comparison results for Ls 90º. This work extends the predictions shown in [Pla-García et al. 2020, Newman et al. 2021]. A diurnal structure variation of the pressure throughout the year is shown both in modeling and observations. The diurnal pressure amplitude is generally well matched in the model but the phase of the diurnal tide is shifted about ~90 min. The general shape of the diurnal cycle of surface temperature are similar between the two datasets. MRAMS surface properties are interpolated from data sets obtained from TES thermal inertia (nighttime) and albedo, with insufficient resolution to capture the known variation of thermal inertia in Jezero crater and the misestimating the diurnal amplitude. The lowest MRAMS thermodynamic level is ∼14 m above the ground, so modeled air temperatures tend to be cooler than MEDA observations at ∼1.5 m above the surface in the morning and early afternoon, and then tend to be warmer in the late afternoon and through the night. This is a direct result of the steep afternoon superadiabatic lapse rate and a strong nocturnal inversion [Schofield et al. 1997]. There is a good match in wind directions between MRAMS and MEDA, but MRAMS wind speeds are generally higher than those observed with MEDA, especially between 23:00 and dawn. The difference in height should not have a large impact on wind direction but can contribute to the wind speed differences due to frictional effects with the surface. Those wind speed differences are indeed bigger during nighttime, where MRAMS winds between 01:00 and sunrise could be so strong because the downslope winds penetrate a little bit too far into the crater for that time of sol when compared with other modeling predictions [Newman et al. 2021]. It is also noticeable that the wind speeds are systematically extremely low after sunset both in MRAMS and MEDA, following the collapse of daytime convection [Banfield et al. 2020], but then at 20:00 the wind speeds start to increase again both in modeling and observations. Although there are some periods with differences, generally there is a good agreement between MRAMS results and MEDA observations, and this agreement provides justification for utilizing the model results to investigate the broader meteorological environment of the Jezero crater region in a companion paperFigure. Observed and modeled diurnal air temperature, ground temperature, pressure, wind speed and wind direction signal at Ls 90. MRAMS are the black dots. MEDA data taken within a few sols of the Ls 90 are shown in blue.

After one year of surface operations at Jezero, the MEDA meteorological sensors have captured the signals produced by the close approach of hundreds of vortices and dust devils over different seasons and terrains. Here we update findings on the vortex and Dust Devils published in Hueso et al. (JGR: Planets, 2023). That work analyzed MEDA data from spring to early autumn identifying vortices as pressure drops and later characterizing them from the ensemble of MEDA measurements. In this updated analysis we show that, in winter, declining surface temperatures and smaller vertical gradients result in a wane of vortex activity. This decreased activity affects more the frequency of intense vortices (Δp >1.5 Pa) without showing a stiff decay in the total number of vortices (Δp>0.5 Pa). In this contribution we concentrate on the specific aspects of the thermodynamics of the vortices from temperature measurements obtained by MEDA that characterize the vertical thermal gradient at the time of the vortex passage. In addition, when vortices approach the rover closely in a favorable geometry (coming from the front of the vortex) we measure the increased temperatures inside the vortex. We also explore the increased nighttime vortex activity found on some sols, when pressure drops equivalent to those created by daytime vortices appear in the early morning before sunrise, with clusters of nighttime activity in winter and early spring.

Since February 18, 2021, Perseverance has been exploring Jezero Crater (18ºN, 77ºE). The meteorology of this location is being investigated with the Mars Environmental Dynamics Analyzer (MEDA) [1], which among many other sensors has 5 Air Temperature Sensors (ATS) to measure near surface temperatures. These sensors are located at two altitudes: two are at 0.85 m, in the front of the rover, and three are at 1.45 m around the Remote Sensing Mast (RSM), distributed azimuthally so that at least one sensor is located upwind. Local air temperatures are measured with a frequency that can be as high as 2 Hz. In addition, the temperature of the surface and at an approximate altitude of about 40 m are measured with the Thermal Infrared Sensor (TIRS), which operates with a sampling frequency of 1 Hz. MEDA records atmospheric variables typically over 50% of a full sol. Here we present consolidated analysis of data up to sol 400, which covers a period from the start of northern Spring (Ls=5º) to early Autumn (beyond Ls=180º). This analysis takes into account different instrumental effects affecting ATS and TIRS which have been characterized over the course of the mission. Firstly, we will present the daily temperature cycle at Jezero, including mean values and its fluctuations plus their daily and seasonal evolution. Hence, we report phenomena at various altitudes, in different time scales, ranging from thermal tides to continuous rapid fluctuations, as well as the effects caused by the different environments as Perseverance explores Jezero. The convective and calmed regimes, at daytime and nighttime respectively, and the transitions between them are well differentiated in the MEDA data and can be well characterized. We will also discuss vertical thermal gradients (surface to 40 m altitude) along the mission and the evolution of nighttime inversions. Secondly, we quantify the influence of different forcings on temperatures: The thermal changes associated with clouds, dust load, variations of the solar flux and changes in the surface properties on the ground and near-surface temperatures. Specific effects associated with a regional dust storm over Jezero will be presented. Lastly, we will comment on the comparison of temperatures at Jezero with in situ data from other locations [2-3] and models [4-5]. [1] Rodriguez-Manfredi, J. A., et al. (2021). The Mars Environmental Dynamics Analyzer, MEDA. A suite of environmental sensors for the Mars 2020 mission. Space science reviews, 217(3), 1-86. [2] Davy, R., et al. (2010). Initial analysis of air temperature and related data from the Phoenix MET station and their use in estimating turbulent heat fluxes. Journal of Geophysical Research: Planets, 115(E3). [3] Mason, E. L., & Smith, M. D. (2021). Temperature fluctuations and boundary layer turbulence as seen by Mars Exploration Rovers Miniature Thermal Emission Spectrometer. Icarus, 360, 114350. [4] Newman et al. (2020). Multi-model Meteorological and Aeolian Predictions for Mars2020 and the Jezero Crater Region, Space Sci. Rev. 215, 148. [5] Pla-García et al., (2020). Meteorological Predictions for Mars 2020 Perseverance Rover Landing Site at Jezero, Space Sci. Rev., 215, 148.

This work aims to examine the atmospheric pres-sure, ground and air temperatures and relative humid-ity obtained by The Rover Environmental Monitoring Station REMS on its journey from the Mars Science Laboratory (MSL) landing site to its current position on the slopes of Mount Sharp. It seeks to extend the work done by Pla-García et al. [1] and Rafkin et al. [2], studying the evolution of the meteorology during the rover's traverse. The results help to better under-stand the martian meteorology inside Gale Crater, re-vealing changes in pressure and temperature driven by the change in altitude of the rover and meteorological cycles, and confirming the hypothesis of Rafkin et al. [2] about the existence of a pocket of cold air at the bottom of the crater. 2. Methods We report 3457 sols observations performed by REMS from Martian Year (MY) 31 to 36 for air tem-perature (Figure 1), daily maximum relative humidity (Figure 2), water vapor VMR (Figure 3) and daily mean atmospheric pressure vs elevation (Figure 4).In an effort to better understand the different me-teorological environments observed inside Gale crater, the Mars Regional Atmospheric Modeling System (MRAMS) was applied to the landing site re-gion using nested grids with a spacing of 330 meters on the innermost grid that is centered over the landing site. MRAMS is ideally suited for this investigation; the model is explicitly designed to simulate Mars’ at-mospheric circulations at the mesoscale and smaller with realistic, high-resolution surface properties. The model is run for 4 sols with 4 grids and then the 3 ad-ditional grids are added and run for at least 3 more sols. Initialization and boundary condition data are taken from a NASA Ames GCM simulation with col-umn dust opacity driven by zonally-averaged TES re-trievals. Vertical dust distribution is given by a Con-rath-v parameterization that varies with season and latitude. 3. Results Surface pressure drops when climbing Mt Sharp (Figure 4) since the atmosphere column above a unit area shortens as altitude increases [4].MRAMS results are shown to be in good agree-ment with observations (Figures 5 and 6) when con-sidering the uncertainties in the observational data set. The good agreement provides justification for utiliz-ing the model results to investigate the meteorological environment changes experienced by the rover during mission traverse.As expected, both REMS and MRAMS show nighttime air temperatures up to 10 K warmer for re-cent years (MY35-36) compared to postlanding years (MY31-32), when the rover was exposed to cold air masses at the crater floor (Figure 5), and lower pres-sure (Figure 6).During MY31-32 (first and second MSL years), the rover was in the crater floor, completely exposed to the strong N-W downslope (mostly dynamically driven) winds from Peace Vallis during Ls 225-315 [2]. The overturning circulation aloft due to upslope winds during daytime along Gale’s northern rim and Mt. Sharp creates an intense subsidence area in the crater floor area, suppressing the PBL [5]. During the MY33 (third MSL year), the rover climbed the slopes of crater Mt Sharp (Figure 6) and was less exposed to the high subsidence area and to the strong N-W downslope wind flow from Peace Vallis. This new en-vironment condition should favor the dust devil activ-ity. After MY34 (fourth MSL year), the rover could be much more exposed to "free" (and putative wet) atmosphere, that is, outside Gale crater floor air masses that could explain, among other features, the relative humidity and water vapor VMR increment during mission traverse (Figures 2 and 3). Figure 1: Interannual and seasonal evolution of daily maximum, average and minimum air temperature during the first 3457 sols of the Mars Science Laboratory mission. Color code is used to represent different Martian Years. Figure 2: Seasonal evolution of daily maximum relative humidity during the first 3457 sols of the Mars Science Laboratory mission. Color code is used to represent different Martian Years. Figure 3: Same as Fig. 3, but for daily water vapor VMR. Figure 4: Seasonal evolution of daily mean atmospheric pressure vs elevation changes during the first 3457 sols of the Mars Science Laboratory mission. Color code is used to represent different Martian Years in the pressure. Figure 5: MRAMS model predictions and REMS observations of diurnal air temperature at solstices and equinoxes of MSL years 0-1 (MY31-32) vs MSL years 4-5 (MY35-36). As expected, air temperature during nighttime is up to 10 K warmer at years 4-5 locations (600 m higher in elevation compared to landing site), far away from the cold air masses of the crater floor. Figure 6: Same as Fig. 7, but for daily mean atmospheric pressure. References: [1] Pla-Garcia et al. (2016), Icarus. [2] Rafkin et al. (2016) [3] Gómez-Elvira, J., et al. (2012), Space Science Reviews, 170(1-4), 583-640. [4] Pascal, Blaise (1648) Oeuvres completes. [5] Moores et al. (2015). Icarus, 249, 129-142.

Observations of the South Polar Residual Cap suggest a possible erosion of the cap, leading to an increase of the global mass of the atmosphere. We test this assumption by making the first comparison between Viking 1 and InSight surface pressure data, which were recorded 40 years apart. Such a comparison also allows us to determine changes in the dynamics of the seasonal ice caps between these two periods. To do so, we first had to recalibrate the InSight pressure data because of their unexpected sensitivity to the sensor temperature. Then, we had to design a procedure to compare distant pressure measurements. We propose two surface pressure interpolation methods at the local and global scale to do the comparison. The comparison of Viking and InSight seasonal surface pressure variations does not show changes larger than +-8 Pa in the CO2 cycle. Such conclusions are supported by an analysis of Mars Science Laboratory (MSL) pressure data. Further comparisons with images of the south seasonal cap taken by the Viking 2 orbiter and MARCI camera do not display significant changes in the dynamics of this cap over a 40 year period. Only a possible larger extension of the North Cap after the global storm of MY 34 is observed, but the physical mechanisms behind this anomaly are not well determined. Finally, the first comparison of MSL and InSight pressure data suggests a pressure deficit at Gale crater during southern summer, possibly resulting from a large presence of dust suspended within the crater.

This review provides an analysis of activities undertaken by the Mars 2020 Council of Atmospheres (CoA) in support of the entry, descent, and landing (EDL) of the Mars 2020 rover Perseverance in Jezero crater, Mars. The activities of the CoA were designed to evaluate the safety of early-stage landing site candidates and, later, to constrain the range of plausible conditions expected at Jezero crater during the early northern spring season of EDL, following the successful blueprint of similar councils for prior landed Mars missions. The multiyear effort of the CoA involved using a combination of numerical modeling of the local Martian atmosphere with limited-domain mesoscale models and atmospheric reanalysis using data assimilation techniques, along with atmospheric observations from multiple orbiting assets, to generate an atmospheric “forecast” for the day of landing. Here we present an overview of these activities, focusing in greater detail on those elements that depart from prior CoA activities as performed for Mars Phoenix, Mars Science Laboratory, and the InSight lander. Following the successful landing of Perseverance on 2021 February 18, reconstruction and reassessment activities were performed and are presented here, comparing prelanding predictions with actual, as-flown conditions.

The surface pressure measurements recorded by InSight seem to be the best in terms of precision and stability for comparison with Viking data and to rule on a possible secular climate change. However, the comparison of the measurements between the two consecutive mission years reveals an offset imposed by the sensor temperature. We propose here a correction of this effect by exploiting the MSL REMS data acquired at the same time. The corrected data then follow perfectly the pressure models based on the pressure recorded by MSL during MY 34 and 35 interpolated with the help of the LMD GCM. Further investigations studying the possible difference between Viking 1 and InSight seasonal variations will be presented during the conference. Introduction Remote observations of interannual variations in polar cap coverage suggest that the south polar residual cap (SPRC) might be eroding [1,2,3]. Such a change in the SPRC would raise the surface pressure every year. Previous comparisons of surface pressures recorded by Viking 1 with Phoenix data [4] or MSL REMS measurements [5] report a possible increase of pressure at the surface of Mars within 30 years. However, the conclusions were unsure due to the uncertainty of the data for Phoenix, and the sensitivity of the hydrostatic adjustment imposed by the climbing of MSL on the complex Gale crater topography. In 2018, the InSight lander brought an accurate pressure sensor at Elysium Planitia. The uncertainty due to the long-term instrumental drift and the accuracy of the sensor is negligible compared to the requirement of accuracy to detect this secular climate change [4]. We thus propose to detect any change of CO2 mass in the atmosphere or a change in the seasonality of the polar cap with an accurate comparison between the seasonal pressure variations recorded by Viking 1 and InSight. Thermal Sensitivity of the Pressure SensorA direct comparison between pressure measurements made during the first and second years of the InSight mission shows a strong difference, thus questioning the reliability of the measurements (Figure 1). Considering the large difference between the measured pressure over the two years, and the correlation of some pressure decreases with some drops of the sensor temperature, we believe that the measurements are affected by a possible thermal offset due to a gradient of temperature within the sensor. Figure 1. (a) Uncorrected diurnal-averaged surface pressure recorded by InSight during the first and second years of the mission. (b) Diurnal-averaged pressure sensor temperature. Red dashed lines indicate the correlation between drops in the pressure measurements and drops in the sensor temperature records. Recalibration of the Pressure dataWe propose here an empirical calibration to correct this sensor thermal effect. To remove any meteorological effects (thermal tides, baroclinic waves), the measured pressure P is averaged over 10-sols to give < P >10sols. As reported in [6] who used MSL data, it seems that the pressure recorded at the beginning of the mission (Ls < 70°, MY = 35) could be slightly lower than the pressure recorded at the end of the mission (Ls < 70°, MY = 36), possibly as a result of the MY34 global dust storm. To quantify this difference, we interpolated the MSL REMS data available on the PDS with careful altitude corrections. Neglecting the difference of scale height between MY35 and MY36, one may have: Where: with E the thermal-induced offset on pressure data described previously. Assuming that E can be written as a polynomial function of the sensor temperature, and introducing (2) and (1) yield to a minimization problem that needs to be constrained to avoid any non-physical solution. Figure 1 presents an unexpected increase of uncorrected pressure at Ls~63°, and then a drop, both certainly resulting from a rise of temperature at T = 270K, followed by a decrease of temperature at T = 275K. Based on this observation, we simply assumed that: E(T = 0°C) = 0. With this constraint, the optimization problem can be solved and a first temporary correction is: Applying this correction to InSight measurements following Eq. (2) leads to the results presented in Figure 2. Figure 2. (a) Uncorrected diurnal-averaged surface pressure recorded by InSight during the first and second years of the mission. (b) Diurnal averaged pressure after sensor temperature correction following Eq. (2). Comparison of the Corrected Pressure and MSL MeasurementsTo assess the quality of this correction, we interpolate the MSL Measurements from MY35 et MY34 (assuming that MY34 behaves like MY36 for Ls < 70°) to predict the surface pressure at the InSight landing site. MSL measurements are interpolated to the InSight landing site using the hydrostatic correction presented in [7]. Dynamical effects from MSL to InSight landing site are corrected using GCM runs with MY34 and MY35 as input dust scenarios. The comparison is presented in Figure 3 and reveals a good match between the model and the result obtained after correction. Figure 3. Surface pressure as predicted from the interpolation of MSL REMS measurements, after hydrostatic and dynamic correction (dashed curves) and observations from InSight after thermal correction (crosses). Observations are diurnally-averaged whereas predictions are 10-sols averaged. Comparison of InSight and Viking 1 Surface Pressure The comparison between Viking 1 and InSight data after hydrostatic, dynamical, and temperature-induced offset will be presented during the talk. Interpretations and conclusions on a possible secular climate change will be drawn. References [1] Malin et al., 2001, Science294(5549), 2146–2148 [2] Thomas et al., 2009, Icarus203, 352–375 [3] Blackburn et al., 2010, Space Sci.58, 780–791 [4] Haberle and Kahre, 2010, Mars Int. J. Mars Sci. Explor5., 68–75 [5] Haberle et al., 2014, J. Geophys. Res., Planets119,440–453 [6] de la Torre Juarez et al., 2019, AGU fall meeting abstracts, Vol. 2019, p. P51C-02 [7] Forget et al., 2007, Planets112(E11), 8

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(s) 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; Savijarvi 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.

Weather forecasting is the task of determining future states of the atmosphere for a given location and time. The techniques to carry out the prediction range from deterministic approaches using complex fluid dynamics models to data-driven approaches using artificial intelligence. While the former is mainly focused on the creation of General Circulation Models, the later are starting to replace them in many situations for Earth’s meteorology and astrophysics. Here, we develop an artificial neural network to perform Mars’ weather forecasting using environmental measurements from the Vikings and Mars Science Laboratory missions. The methodology followed in of this study is a data-driven approach; we make use of computer science expertise which has been long applied to Earth, but not on Mars yet. To do so, we create an artificial neuronal network that predicts the meteorological conditions of the following day using the previous day as input. We show that temperature and pressure are among the most important variables, and that ANN can perform with a 0.5 to 1% accuracy in forecasting diurnal changes in the selected variables. Keywords: ANN, Mars, Weather, Forecast, Curiosity

International audience; The Curiosity rover discovered fine-grained sedimentary rocks, which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. Carbon, hydrogen, oxygen, sulfur, nitrogen, and phosphorus were measured directly as key biogenic elements; by inference, phosphorus is assumed to have been available. The environment probably had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial-lacustrine environments in the post-Noachian history of Mars.

International audience; The Radiation Assessment Detector (RAD) on the Mars Science Laboratory's Curiosity rover began making detailed measurements of the cosmic ray and energetic particle radiation environment on the surface of Mars on 7 August 2012. We report and discuss measurements of the absorbed dose and dose equivalent from galactic cosmic rays and solar energetic particles on the martian surface for similar to 300 days of observations during the current solar maximum. These measurements provide insight into the radiation hazards associated with a human mission to the surface of Mars and provide an anchor point with which to model the subsurface radiation environment, with implications for microbial survival times of any possible extant or past life, as well as for the preservation of potential organic biosignatures of the ancient martian environment.

Mars' Atmosphere from Curiosity The Sample Analysis at Mars (SAM) instrument on the Curiosity rover that landed on Mars in August last year is designed to study the chemical and isotopic composition of the martian atmosphere. Mahaffy et al. (p. 263 ) present volume-mixing ratios of Mars' five major atmospheric constituents (CO 2 , Ar, N 2 , O 2 , and CO) and isotope measurements of 40 Ar/ 36 Ar and C and O in CO 2 , based on data from one of SAM's instruments, obtained between 31 August and 21 November 2012. Webster et al. (p. 260 ) used data from another of SAM's instruments obtained around the same period to determine isotope ratios of H, C, and O in atmospheric CO 2 and H 2 O. Agreement between the isotopic ratios measured by SAM with those of martian meteorites, measured in laboratories on Earth, confirms the origin of these meteorites and implies that the current atmospheric reservoirs of CO 2 and H 2 O were largely established after the period of early atmospheric loss some 4 billion years ago.