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Numrering	Referens	Omslagsbild	Hitta
1.	Becker, T. M., et al. (författare) The Far-UV Albedo of Europa From HST Observations 2018 Ingår i: Journal of Geophysical Research - Planets. - : AMER GEOPHYSICAL UNION. - 2169-9097 .- 2169-9100. ; 123:5, s. 1327-1342 Tidskriftsartikel (refereegranskat)abstract We present an analysis of Europa's far-UV spectral albedo using observations during the 1999-2015 time period made by the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. Disk-integrated observations show that the far-UV spectrum in the similar to 130 to 170-nm range is relatively flat or slightly blue (increasing albedo with decreasing wavelength) for the studied hemispheres: the leading, trailing, and anti-Jovian hemispheres. At Lyman- (121.6nm), the albedo of the trailing hemisphere continues the blue trend, but it reddens for the leading hemisphere. Also at this wavelength, the albedo of the leading hemisphere, which is higher than the trailing hemisphere at near-UV and visible wavelengths, is lower than the trailing hemisphere, exhibiting spectral inversion. We find no evidence of a sharp water-ice absorption edge at 165nm on any hemisphere of Europa, which is intriguing since such an absorption feature has been observed on the icy Saturnian satellites. Plain Language Summary We used observations spanning from 1999 to 2015 obtained by the Space Telescope Imaging Spectrograph on the Hubble Space Telescope to study the surface reflectance of Europa at far-ultraviolet (UV) wavelengths. We find that Europa has a low reflectance in the UV and that there is little variation in the surface brightness at most of the UV wavelengths. When observed at visible wavelengths, one of Europa's hemispheres is brighter than the other, but at the UV wavelength of 121.6nm, the hemisphere brightness is reversed. We also find that Europa looks different from the icy moons of Saturn at far-UV wavelengths.
2.	Bellucci, Jeremy, et al. (författare) The Pb isotopic evolution of the Martian mantle constrained by initial Pb in Martian meteorites 2015 Ingår i: Journal of Geophysical Research - Planets. - 2169-9097 .- 2169-9100. ; 120, s. 2224-2240 Tidskriftsartikel (refereegranskat)
3.	Benison, K. C., et al. (författare) Depositional and Diagenetic Sulfates of Hogwallow Flats and Yori Pass, Jezero Crater : Evaluating Preservation Potential of Environmental Indicators and Possible Biosignatures From Past Martian Surface Waters and Groundwaters 2024 Ingår i: Journal of Geophysical Research - Planets. - : John Wiley and Sons Inc. - 2169-9097 .- 2169-9100. ; 129:2 Tidskriftsartikel (refereegranskat)abstract The Mars 2020 Perseverance rover has examined and sampled sulfate-rich clastic rocks from the Hogwallow Flats member at Hawksbill Gap and the Yori Pass member at Cape Nukshak. Both strata are located on the Jezero crater western fan front, are lithologically and stratigraphically similar, and have been assigned to the Shenandoah formation. In situ analyses demonstrate that these are fine-grained sandstones composed of phyllosilicates, hematite, Ca-sulfates, Fe-Mg-sulfates, ferric sulfates, and possibly chloride salts. Sulfate minerals are found both as depositional grains and diagenetic features, including intergranular cement and vein- and vug-cements. Here, we describe the possibility of various sulfate phases to preserve potential biosignatures and the record of paleoenvironmental conditions in fluid and solid inclusions, based on findings from analog sulfate-rich rocks on Earth. The samples collected from these outcrops, Hazeltop and Bearwallow from Hogwallow Flats, and Kukaklek from Yori Pass, should be examined for such potential biosignatures and environmental indicators upon return to Earth.
4.	Bruschini, E., et al. (författare) Spectroscopic Characterization of Impactites and a Machine Learning Approach to Determine the Oxidation State of Iron in Glass‐Bearing Materials 2023 Ingår i: Journal of Geophysical Research - Planets. - : American Geophysical Union (AGU). - 2169-9097 .- 2169-9100. ; 128:3 Tidskriftsartikel (refereegranskat)
5.	Chinnery, H. E., et al. (författare) The Penetration of Solar Radiation Into Granular Carbon Dioxide and Water Ices of Varying Grain Sizes on Mars 2020 Ingår i: Journal of Geophysical Research - Planets. - : John Wiley & Sons. - 2169-9097 .- 2169-9100. ; 125:4 Tidskriftsartikel (refereegranskat)
6.	Chinnery, H. E., et al. (författare) The Penetration of Solar Radiation Into Water and Carbon Dioxide Snow, With Reference to Mars 2019 Ingår i: Journal of Geophysical Research - Planets. - : John Wiley & Sons. - 2169-9097 .- 2169-9100. ; 124:2, s. 337-348 Tidskriftsartikel (refereegranskat)
7.	Corpolongo, A., et al. (författare) SHERLOC Raman Mineral Class Detections of the Mars 2020 Crater Floor Campaign 2023 Ingår i: Journal of Geophysical Research - Planets. - : John Wiley and Sons Inc. - 2169-9097 .- 2169-9100. ; 128:3 Tidskriftsartikel (refereegranskat)abstract The goals of NASA's Mars 2020 mission include searching for evidence of ancient life on Mars, studying the geology of Jezero crater, understanding Mars' current and past climate, and preparing for human exploration of Mars. During the mission's first science campaign, the Perseverance rover's SHERLOC deep UV Raman and fluorescence instrument collected microscale, two-dimensional Raman and fluorescence images on 10 natural (unabraded) and abraded targets on two different Jezero crater floor units: Séítah and Máaz. We report SHERLOC Raman measurements collected during the Crater Floor Campaign and discuss their implications regarding the origin and history of Séítah and Máaz. The data support the conclusion that Séítah and Máaz are mineralogically distinct igneous units with complex aqueous alteration histories and suggest that the Jezero crater floor once hosted an environment capable of supporting microbial life and preserving evidence of that life, if it existed.
8.	Cui, J., et al. (författare) The electron thermal structure in the dayside Martian ionosphere implied by the MGS radio occultation data 2015 Ingår i: Journal of Geophysical Research - Planets. - 2169-9097 .- 2169-9100. ; 120:2, s. 278-286 Tidskriftsartikel (refereegranskat)abstract We propose a revised Chapman model for the ionosphere of Mars by allowing for vertical variation of electron temperature. An approximate energy balance between solar EUV heating and CO2 collisional cooling is applied in the dayside Martian ionosphere, analogous to the method recently proposed by Withers et al. (2014). The essence of the model is to separate the contributions of the neutral and electron thermal structures to the apparent width of the main ionospheric layer. Application of the model to the electron density profiles from the Mars Global Surveyor (MGS) radio occultation measurements reveals a clear trend of elevated electron temperature with increasing solar zenith angle (SZA). It also reveals that the characteristic length scale for the change of electron temperature with altitude decreases with increasing SZA. These observations may imply enhanced topside heat influx near the terminator, presumably an outcome of the solar wind interactions with the Martian upper atmosphere. Our analysis also reveals a tentative asymmetry in electron temperature between the northern and southern hemispheres, consistent with the scenario of elevated electron temperature within minimagnetospheres.
9.	de Pater, Imke, et al. (författare) An Energetic Eruption With Associated SO 1.707 Micron Emissions at Io's Kanehekili Fluctus and a Brightening Event at Loki Patera Observed by JWST 2023 Ingår i: Journal of Geophysical Research - Planets. - : American Geophysical Union (AGU). - 2169-9097 .- 2169-9100. ; 128:8 Tidskriftsartikel (refereegranskat)abstract We observed Io with the James Webb Space Telescope (JWST) while the satellite was in eclipse, and detected thermal emission from several volcanoes. The data were taken as part of our JWST-ERS program #1373 on 15 November 2022. Kanehekili Fluctus was exceptionally bright, and Loki Patera had most likely entered a new brightening phase. Spectra were taken with NIRSpec/IFU at a resolving power R ≈ 2,700 between 1.65 and 5.3 µm. The spectra were matched by a combination of blackbody curves that showed that the highest temperature, ∼1,200 K, for Kanehekili Fluctus originated from an area ∼0.25 km2 in size, and for Loki Patera this high temperature was confined to an area of ∼0.06 km2. Lower temperatures, down to 300 K, cover areas of ∼2,000 km2 for Kanehekili Fluctus, and ∼5,000 km2 for Loki Patera. We further detected the a1Δ ⇒ X3Σ− 1.707 µm rovibronic forbidden SO emission band complex over the southern hemisphere, which peaked at the location of Kanehekili Fluctus. This is the first time this emission has been seen above an active volcano, and suggests that the origin of such emissions is ejection of SO molecules directly from the vent in an excited state, after having been equilibrated at temperatures of ∼1,500 K below the surface, as was previously hypothesized.
10.	Farrell, W. M., et al. (författare) Ion trapping by dust grains : Simulation applications to the Enceladus plume 2017 Ingår i: Journal of Geophysical Research - Planets. - : AMER GEOPHYSICAL UNION. - 2169-9097 .- 2169-9100. ; 122:4, s. 729-743 Tidskriftsartikel (refereegranskat)abstract Using a particle-in-cell electrostatic simulation, we examine the conditions that allow low-energy ions, like those produced in the Enceladus plume, to be attracted and trapped within the sheaths of negatively charged dust grains. The conventional wisdom is that all new ions produced in the Enceladus plume are free to get picked up (i.e., accelerated by the local E field to then undergo vB acceleration). However, we suggest herein that the presence of submicron-charged dust in the plume impedes this pickup process since the local grain electric field greatly exceeds the corotation E fields. The simulations demonstrate that cold ions will tend to accelerate toward the negatively charged grains and become part of the ion plasma sheath. These trapped ions will move with the grains, exiting the plume region at the dust speed. We suggest that Cassini's Langmuir probe is measuring the entire ion population (free and trapped ions), while the Cassini magnetometer detects the magnetic perturbations associated with pickup currents from the smaller population of free ions, with this distinction possibly reconciling the ongoing debate in the literature on the ion density in the plume.
11.	Freissinet, C., et al. (författare) Organic molecules in the Sheepbed Mudstone, Gale Crater, Mars 2015 Ingår i: Journal of Geophysical Research - Planets. - 2169-9097 .- 2169-9100. ; 120:3, s. 495-514 Tidskriftsartikel (refereegranskat)abstract The Sample Analysis at Mars (SAM) instrument [Mahaffy et al., 2012] onboard the Mars Science Laboratory (MSL) Curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface regolith and rocks to help evaluate the past and present habitability potential of Mars at Gale Crater [Grotzinger et al., 2012]. Central to this task is the development of an inventory of any organic molecules present to elucidate processes associated with their origin, diagenesis, concentration and long-term preservation. This will guide the future search for biosignatures [Summons et al., 2011]. Here we report the definitive identification of chlorobenzene (150–300 parts per billion by weight (ppbw)) and C2 to C4 dichloroalkanes (up to 70 ppbw) with the SAM gas chromatograph mass spectrometer (GCMS), and detection of chlorobenzene in the direct evolved gas analysis (EGA) mode, in multiple portions of the fines from the Cumberland drill hole in the Sheepbed mudstone at Yellowknife Bay. When combined with GCMS and EGA data from multiple scooped and drilled samples, blank runs and supporting laboratory analog studies, the elevated levels of chlorobenzene and the dichloroalkanes cannot be solely explained by instrument background sources known to be present in SAM. We conclude that these chlorinated hydrocarbons are the reaction products of martian chlorine and organic carbon derived from martian sources (e.g. igneous, hydrothermal, atmospheric, or biological) or exogenous sources such as meteorites, comets or interplanetary dust particles.
12.	G. Trainer, Melissa, et al. (författare) Seasonal Variations in Atmospheric Composition as Measured in Gale Crater, Mars 2019 Ingår i: Journal of Geophysical Research - Planets. - : John Wiley & Sons. - 2169-9097 .- 2169-9100. ; 124:11, s. 3000-3024 Tidskriftsartikel (refereegranskat)abstract 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.
13.	Gebhardt, C., et al. (författare) Characterizing Dust‐Radiation Feedback and Refining the Horizontal Resolution of the MarsWRF Model down to 0.5 Degree 2021 Ingår i: Journal of Geophysical Research - Planets. - : John Wiley & Sons. - 2169-9097 .- 2169-9100. ; 126:3 Tidskriftsartikel (refereegranskat)abstract In this study, three simulations by the Mars Weather Research and Forecasting (MarsWRF) model are compared: two 10 Martian Year (MY) 2° × 2° simulations with (i) fully radiatively‐active dust and (ii) a prescribed dust scenario, and a (iii) 1 MY 0.5° × 0.5° simulation with prescribed dust as in (ii). From comparing (i) and (ii), we found that the impact of dust‐radiation feedback is individually different for any region. The most striking evidence are major dust lifting activities to the south of Chryse Planitia (S‐CP) seen in (i) but not in (ii). By contrast, dust lifting and deposition on the southern slopes and inside the Hellas Basin are similar in both simulations. The latter, in turn, points towards a similar near‐surface atmospheric circulation. In (iii), the total global amount of wind stress lifted dust is by a factor of ∼8 higher than in (ii), with S‐CP being a major lifting region as in (i). Nonetheless, the surface dust lifting by wind stress in (iii) may be also reduced regionally, as seen at the peak of Elysium Mons because of its unique topography. The zonal mean circulation in (i) is generally of a comparable strength to that in (ii), with exceptions in global dust storm years, when it is clearly stronger in (i), in line with a dustier atmosphere. The differences in the zonal mean circulation between (ii) and (iii) are mostly at lower altitudes, and may arise due to differences in the representation of the topography.
14.	Gebhardt, C., et al. (författare) Fully Interactive and Refined Resolution Simulations of the Martian Dust Cycle by the MarsWRF Model 2020 Ingår i: Journal of Geophysical Research - Planets. - : John Wiley & Sons. - 2169-9097 .- 2169-9100. ; 125:9 Tidskriftsartikel (refereegranskat)abstract The MarsWRF model is set up with fully interactive dust at 5° × 5° and 2° × 2 resolution. The latter allows for a better representation of topography and other surface properties. An infinite reservoir of surface dust is assumed for both resolutions. For 5° × 5°, surface dust lifting by wind stress takes place over broad areas, occurring in about 20% of the model’s grid cells. For 2° × 2°, it is more spatially restricted, occurring in less than 5% of the grid cells, and somewhat reminiscent of the corridors Acidalia‐Chryse, Utopia‐Isidis, and Arcadia‐West of Tharsis. The onset times of major dust storms ‐ large regional storms or global dust storm events (GDEs) ‐ do not exhibit much inter‐annual variability, typically occurring at around Ls 260°. However, their magnitude does show significant inter‐annual variability ‐ with only small regional storms in some years, large regional storms in others, and some years with GDEs ‐ owing to the interaction between major dust lifting regions at low latitudes. The latter is consistent with observed GDEs having several active dust lifting centers. The model’s dust distribution is found to better agree with observation‐based albedo and dust cover index maps for the 2° × 2° run. For the latter, there is also significant surface dust lifting by wind stress in the aphelion season that is largely confined to the Hellas basin. It has a recurring time pattern of 2‐7 sols, possibly resulting from the interaction between mid‐latitude baroclinic systems and local downslope flows.
15.	Gõmez-Elvira, Javier, et al. (författare) Curiosity's rover environmental monitoring station : Overview of the first 100 sols 2014 Ingår i: Journal of Geophysical Research - Planets. - 2169-9097 .- 2169-9100. ; 119:7, s. 1680-1688 Tidskriftsartikel (refereegranskat)abstract In the first 100 Martian solar days (sols) of the Mars Science Laboratory mission, the Rover Environmental Monitoring Station (REMS) measured the seasonally evolving diurnal cycles of ultraviolet radiation, atmospheric pressure, air temperature, ground temperature, relative humidity, and wind within Gale Crater on Mars. As an introduction to several REMS-based articles in this issue, we provide an overview of the design and performance of the REMS sensors and discuss our approach to mitigating some of the difficulties we encountered following landing, including the loss of one of the two wind sensors. We discuss the REMS data set in the context of other Mars Science Laboratory instruments and observations and describe how an enhanced observing strategy greatly increased the amount of REMS data returned in the first 100 sols, providing complete coverage of the diurnal cycle every 4 to 6 sols. Finally, we provide a brief overview of key science results from the first 100 sols. We found Gale to be very dry, never reaching saturation relative humidities, subject to larger diurnal surface pressure variations than seen by any previous lander on Mars, air temperatures consistent with model predictions and abundant short timescale variability, and surface temperatures responsive to changes in surface properties and suggestive of subsurface layering. Key Points Introduction to the REMS results on MSL mission Overiview of the sensor information Overview of operational constraints
16.	Guzewich, Scott D., et al. (författare) 3D Simulations of the Early Martian Hydrological Cycle Mediated by a H-2-CO2 Greenhouse 2021 Ingår i: Journal of Geophysical Research - Planets. - : American Geophysical Union (AGU). - 2169-9097 .- 2169-9100. ; 126:7 Tidskriftsartikel (refereegranskat)abstract For decades, the scientific community has been trying to reconcile abundant evidence for fluvial activity on Noachian and early Hesperian Mars with the faint young Sun and reasonable constraints on ancient atmospheric pressure and composition. Recently, the investigation of H-2-CO2 collision-induced absorption has opened up a new avenue to warm Noachian Mars. We use the ROCKE-3D global climate model to simulate plausible states of the ancient Martian climate with this absorptive warming and reasonable constraints on surface paleopressure. We find that 1.5-2 bar CO2-dominated atmospheres with >= 3% H-2 can produce global mean surface temperatures above freezing, while also providing sufficient warming to avoid surface atmospheric CO2 condensation at 0 degrees-45 degrees obliquity. Simulations conducted with both modern topography and a paleotopography, before Tharsis formed, highlight the importance of Tharsis as a cold trap for water on the planet. Additionally, we find that low obliquity (modern and 0 degrees) is more conducive to rainfall over valley network locations than high (45 degrees) obliquity.
17.	Guzewich, Scott D., et al. (författare) The Vertical Dust Profile over Gale Crater, Mars 2017 Ingår i: Journal of Geophysical Research - Planets. - : American Geophysical Union (AGU). - 2169-9097 .- 2169-9100. ; 122:12, s. 2779-2792 Tidskriftsartikel (refereegranskat)abstract We create a vertically coarse, but complete, vertical profile of dust mixing ratio from the surface to the upper atmosphere over Gale Crater, Mars, using the frequent joint atmospheric observations of the orbiting Mars Climate Sounder (MCS) and the Mars Science Laboratory (MSL) Curiosity rover. Using these data and an estimate of planetary boundary layer (PBL) depth from the MarsWRF general circulation model, we divide the vertical column into three regions. The first region is the Gale Crater PBL, the second is the MCS-sampled region, and the third is between these first two. We solve for a well-mixed dust mixing ratio within this third (middle) layer of atmosphere to complete the profile.We identify a unique seasonal cycle of dust within each atmospheric layer. Within the Gale PBL, dust mixing ratio maximizes near southern hemisphere summer solstice (Ls = 270°) and minimizes near winter solstice (Ls = 90-100°) with a smooth sinusoidal transition between them. However, the layer above Gale Crater and below the MCS-sampled region more closely follows the global opacity cycle and has a maximum in opacity near Ls = 240° and exhibits a local minimum (associated with the “solsticial pause” in dust storm activity) near Ls = 270°. With knowledge of the complete vertical dust profile, we can also assess the frequency of high-altitude dust layers over Gale. We determine that 36% of MCS profiles near Gale Crater contain an “absolute” high-altitude dust layer wherein the dust mixing ratio is the maximum in the entire vertical column.
18.	Haberle, R. M., et al. (författare) Preliminary interpretation of the REMS pressure data from the first 100 sols of the MSL mission 2014 Ingår i: Journal of Geophysical Research - Planets. - : John Wiley & Sons. - 2169-9097 .- 2169-9100. ; 119:3, s. 440-453 Tidskriftsartikel (refereegranskat)abstract We provide a preliminary interpretation of the Rover Environmental Monitoring Station (REMS) pressure data from the first 100 Martian solar days (sols) of the Mars Science Laboratory mission. The pressure sensor is performing well and has revealed the existence of phenomena undetected by previous missions that include possible gravity waves excited by evening downslope flows, relatively dust-free convective vortices analogous in structure to dust devils, and signatures indicative of the circulation induced by Gale Crater and its central mound. Other more familiar phenomena are also present including the thermal tides, generated by daily insolation variations, and the CO2 cycle, driven by the condensation and sublimation of CO2 in the polar regions. The amplitude of the thermal tides is several times larger than those seen by other landers primarily because Curiosity is located where eastward and westward tidal modes constructively interfere and also because the crater circulation amplifies the tides to some extent. During the first 100 sols tidal amplitudes generally decline, which we attribute to the waning influence of the Kelvin wave. Toward the end of the 100 sol period, tidal amplitudes abruptly increased in response to a nearby regional dust storm that did not expand to global scales. Tidal phases changed abruptly during the onset of this storm suggesting a change in the interaction between eastward and westward modes. When compared to Viking Lander 2 data, the REMS daily average pressures show no evidence yet for the 1-20 Pa increase expected from the possible loss of CO 2 from the south polar residual cap. Key Points REMS pressure sensor is operating nominally New phenomena have been discovered Familiar phenomena have been detected ©2014. American Geophysical Union. All Rights Reserved.
19.	Hamilton, Victoria E., et al. (författare) Observations and preliminary science results from the first 100 sols of MSL Rover Environmental Monitoring Station ground temperature sensor measurements at Gale Crater 2014 Ingår i: Journal of Geophysical Research - Planets. - : John Wiley & Sons. - 2169-9097 .- 2169-9100. ; 119:4, s. 745-770 Tidskriftsartikel (refereegranskat)abstract We describe preliminary results from the first 100 sols of ground temperature measurements along the Mars Science Laboratory's traverse from Bradbury Landing to Rocknest in Gale. The ground temperature data show long-term increases in mean temperature that are consistent with seasonal evolution. Deviations from expected temperature trends within the diurnal cycle are observed and may be attributed to rover and environmental effects. Fits to measured diurnal temperature amplitudes using a thermal model suggest that the observed surfaces have thermal inertias in the range of 265-375?J m-2 K-1 s-1/2, which are within the range of values determined from orbital measurements and are consistent with the inertias predicted from the observed particle sizes on the uppermost surface near the rover. Ground temperatures at Gale Crater appear to warm earlier and cool later than predicted by the model, suggesting that there are multiple unaccounted for physical conditions or processes in our models. Where the Mars Science Laboratory (MSL) descent engines removed a mobile layer of dust and fine sediments from over rockier material, the diurnal temperature profile is closer to that expected for a homogeneous surface, suggesting that the mobile materials on the uppermost surface may be partially responsible for the mismatch between observed temperatures and those predicted for materials having a single thermal inertia. Models of local stratigraphy also implicate thermophysical heterogeneity at the uppermost surface as a potential contributor to the observed diurnal temperature cycle. Key Points Diurnal ground temperatures vary with location Diurnal temperature curves are not well matched by a homogeneous thermal model GTS data are consistent with a varied stratigraphy and thermophysical properties.
20.	Harri, A.-M., et al. (författare) Mars Science Laboratory relative humidity observations : Initial results 2014 Ingår i: Journal of Geophysical Research - Planets. - 2169-9097 .- 2169-9100. ; 119:9, s. 2132-2147 Tidskriftsartikel (refereegranskat)abstract The Mars Science Laboratory (MSL) made a successful landing at Gale crater early August 2012. MSL has an environmental instrument package called the Rover Environmental Monitoring Station (REMS) as a part of its scientific payload. REMS comprises instrumentation for the observation of atmospheric pressure, temperature of the air, ground temperature, wind speed and direction, relative humidity (REMS-H), and UV measurements. We concentrate on describing the REMS-H measurement performance and initial observations during the first 100 MSL sols as well as constraining the REMS-H results by comparing them with earlier observations and modeling results. The REMS-H device is based on polymeric capacitive humidity sensors developed by Vaisala Inc., and it makes use of transducer electronics section placed in the vicinity of the three humidity sensor heads. The humidity device is mounted on the REMS boom providing ventilation with the ambient atmosphere through a filter protecting the device from airborne dust. The final relative humidity results appear to be convincing and are aligned with earlier indirect observations of the total atmospheric precipitable water content. The water mixing ratio in the atmospheric surface layer appears to vary between 30 and 75 ppm. When assuming uniform mixing, the precipitable water content of the atmosphere is ranging from a few to six precipitable micrometers.
21.	Harri, A.-M., et al. (författare) Pressure observations by the Curiosity rover : Initial results 2014 Ingår i: Journal of Geophysical Research - Planets. - : John Wiley & Sons. - 2169-9097 .- 2169-9100. ; 119:1, s. 82-92 Tidskriftsartikel (refereegranskat)abstract REMS-P, the pressure measurement subsystem of the Mars Science Laboratory (MSL) Rover Environmental Measurement Station (REMS), is performing accurate observations of the Martian atmospheric surface pressure. It has demonstrated high data quality and good temporal coverage, carrying out the first in situ pressure observations in the Martian equatorial regions. We describe the REMS-P initial results by MSL mission sol 100 including the instrument performance and data quality and illustrate some initial interpretations of the observed features. The observations show both expected and new phenomena at various spatial and temporal scales, e.g., the gradually increasing pressure due to the advancing Martian season signals from the diurnal tides as well as various local atmospheric phenomena and thermal vortices. Among the unexpected new phenomena discovered in the pressure data are a small regular pressure drop at every sol and pressure oscillations occurring in the early evening. We look forward to continued high-quality observations by REMS-P, extending the data set to reveal characteristics of seasonal variations and improved insights into regional and local phenomena. Key Points The performance and data quality of the REMS / MSL pressure observations. MSL pressure observations exhibit local phenomena of the Gale crater area. Small pressure oscillations possibly linked to gravity waves. ©2013. American Geophysical Union. All Rights Reserved.
22.	Hausrath, E. M., et al. (författare) An Examination of Soil Crusts on the Floor of Jezero Crater, Mars 2023 Ingår i: Journal of Geophysical Research: Planets. - : American Geophysical Union (AGU). - 2169-9097 .- 2169-9100. ; 128:10 Tidskriftsartikel (refereegranskat)abstract Martian soils are critically important for understanding the history of Mars, past potentially habitable environments, returned samples, and future human exploration. This paper examines soil crusts on the floor of Jezero crater encountered during initial phases of the Mars 2020 mission. Soil surface crusts have been observed on Mars at other locations, starting with the two Viking Lander missions. Rover observations show that soil crusts are also common across the floor of Jezero crater, revealed in 45 of 101 locations where rover wheels disturbed the soil surface, 2 out of 7 helicopter flights that crossed the wheel tracks, and 4 of 8 abrasion/drilling sites. Most soils measured by the SuperCam laser-induced breakdown spectroscopy (LIBS) instrument show high hydrogen content at the surface, and fine-grained soils also show a visible/near infrared (VISIR) 1.9 µm H2O absorption feature. The Planetary Instrument for X-ray Lithochemistry (PIXL) and SuperCam observations suggest the presence of salts at the surface of rocks and soils. The correlation of S and Cl contents with H contents in SuperCam LIBS measurements suggests that the salts present are likely hydrated. On the “Naltsos” target, magnesium and sulfur are correlated in PIXL measurements, and Mg is tightly correlated with H at the SuperCam points, suggesting hydrated Mg-sulfates. Mars Environmental Dynamics Analyzer (MEDA) observations indicate possible frost events and potential changes in the hydration of Mg-sulfate salts. Jezero crater soil crusts may therefore form by salts that are hydrated by changes in relative humidity and frost events, cementing the soil surface together.
23.	Honing, Dennis, et al. (författare) Early Habitability and Crustal Decarbonation of a Stagnant-Lid Venus 2021 Ingår i: Journal of Geophysical Research - Planets. - : American Geophysical Union (AGU). - 2169-9097 .- 2169-9100. ; 126:10 Tidskriftsartikel (refereegranskat)abstract Little is known about the early evolution of Venus and a potential habitable period during the first 1 billion years. In particular, it remains unclear whether or not plate tectonics and an active carbonate-silicate cycle were present. In the presence of liquid water but without plate tectonics, weathering would have been limited to freshly produced basaltic crust, with an early carbon cycle restricted to the crust and atmosphere. With the evaporation of surface water, weathering would cease. With ongoing volcanism, carbonate sediments would be buried and sink downwards. Thereby, carbonates would heat up until they become unstable and the crust would become depleted in carbonates. With CO2 supply to the atmosphere the surface temperature rises further, the depth below which decarbonation occurs decreases, causing the release of even more CO2. We assess the habitable period of an early stagnant-lid Venus by employing a coupled interior-atmosphere evolution model accounting for CO2 degassing, weathering, carbonate burial, and crustal decarbonation. We find that if initial surface conditions allow for liquid water, weathering can keep the planet habitable for up to 900 Myr, followed by evaporation of water and rapid crustal carbonate depletion. For the atmospheric CO2 of stagnant-lid exoplanets, we predict a bimodal distribution, depending on whether or not these planets experienced a runaway greenhouse in their history. Planets with high atmospheric CO2 could be associated with crustal carbonate depletion as a consequence of a runaway greenhouse, whereas planets with low atmospheric CO2 would indicate active silicate weathering and thereby a habitable climate.
24.	Kahanpää, Henrik, et al. (författare) Convective vortices and dust devils at the MSL landing site : annual variability 2016 Ingår i: Journal of Geophysical Research - Planets. - 2169-9097 .- 2169-9100. ; 121:8, s. 1514-1549 Tidskriftsartikel (refereegranskat)abstract Two hundred fifty-two transient drops in atmospheric pressure, likely caused by passing convective vortices, were detected by the Rover Environmental Monitoring Station instrument during the first Martian year of the Mars Science Laboratory (MSL) landed mission. These events resembled the vortex signatures detected by the previous Mars landers Pathfinder and Phoenix; however, the MSL observations contained fewer pressure drops greater than 1.5 Pa and none greater than 3.0 Pa. Apparently, these vortices were generally not lifting dust as only one probable dust devil has been observed visually by MSL. The obvious explanation for this is the smaller number of strong vortices with large central pressure drops since according to Arvidson et al. [2014] ample dust seems to be present on the surface. The annual variation in the number of detected convective vortices followed approximately the variation in Dust Devil Activity (DDA) predicted by the MarsWRF numerical climate model. This result does not prove, however, that the amount of dust lifted by dust devils would depend linearly on DDA, as is assumed in several numerical models of the Martian atmosphere, since dust devils are only the most intense fraction of all convective vortices on Mars, and the amount of dust that can be lifted by a dust devil depends on its central pressure drop. Sol-to-sol variations in the number of vortices were usually small. However, on 1 Martian solar day a sudden increase in vortex activity, related to a dust storm front, was detected.
25.	Kaufmann, Erika, et al. (författare) Hardness and Yield Strength of CO 2 Ice Under Martian Temperature Conditions 2020 Ingår i: Journal of Geophysical Research - Planets. - : John Wiley & Sons. - 2169-9097 .- 2169-9100. ; 125:3 Tidskriftsartikel (refereegranskat)
26.	Kim, Myung-Hee Y., et al. (författare) Comparison of Martian surface ionizing radiation measurements from MSL-RAD with Badhwar-O'Neill 2011/HZETRN model calculations 2014 Ingår i: Journal of Geophysical Research - Planets. - 2169-9097 .- 2169-9100. ; 119:6, s. 1311-1321 Tidskriftsartikel (refereegranskat)abstract Dose rate measurements from Mars Science Laboratory-radiation assessment detector (MSL-RAD) for 300 sols on Mars are compared to simulation results using the Badhwar-O'Neill 2011 galactic cosmic ray (GCR) environment model and the high-charge and energy transport (HZETRN) code. For the nuclear interactions of primary GCR through Mars atmosphere and Curiosity rover, the quantum multiple scattering theory of nuclear fragmentation is used. Daily atmospheric pressure is measured at Gale Crater by the MSL Rover Environmental Monitoring Station. Particles impinging on top of the Martian atmosphere reach RAD after traversing varying depths of atmosphere that depend on the slant angles, and the model accounts for shielding of the RAD “E” detector (used for dosimetry) by the rest of the instrument. Simulation of average dose rate is in good agreement with RAD measurements for the first 200 sols and reproduces the observed variation of surface dose rate with changing heliospheric conditions and atmospheric pressure. Model results agree less well between sols 200 and 300 due to subtleties in the changing heliospheric conditions. It also suggests that the average contributions of albedo particles (charge number Z < 3) from Martian regolith comprise about 10% and 42% of the average daily point dose and dose equivalent, respectively. Neutron contributions to tissue-averaged effective doses will be reduced compared to point dose equivalent estimates because a large portion of the neutron point dose is due to low-energy neutrons with energies.
27.	Litvak, M.L., et al. (författare) Local variations of bulk hydrogen and chlorine-equivalent neutron absorption content measured at the contact between the Sheepbed and Gillespie Lake units in Yellowknife Bay, Gale Crater, using the DAN instrument onboard Curiosity 2014 Ingår i: Journal of Geophysical Research - Planets. - 2169-9097 .- 2169-9100. ; 119:6, s. 1259-1275 Tidskriftsartikel (refereegranskat)abstract Data gathered with the Dynamic Albedo of Neutron (DAN) instrument onboard rover Curiosity were analyzed for variations in subsurface neutron flux and tested for possible correlation with local geological context. A special DAN observation campaign was executed, in which 18 adjacent DAN active measurements were acquired every 0.75–1.0 m to search for the variations of subsurface hydrogen content along a 15 m traverse across geologic contacts between the Sheepbed and Gillespie Lake members of the Yellowknife Bay formation. It was found that several subunits in Sheepbed and Gillespie Lake could be characterized with different depth distributions of water-equivalent hydrogen (WEH) and different chlorine-equivalent abundance responsible for the distribution of neutron absorption elements. The variations of the average WEH at the top 60 cm of the subsurface are estimated at up to 2–3%. Chlorine-equivalent neutron absorption abundances ranged within 0.8–1.5%. The largest difference in WEH and chlorine-equivalent neutron absorption distribution is found between Sheepbed and Gillespie Lake.
28.	Lue, Charles, et al. (författare) Chandrayaan-1 observations of backscattered solar wind protons from the lunar regolith : Dependence on the solar wind speed 2014 Ingår i: Journal of Geophysical Research - Planets. - 2169-9097 .- 2169-9100. ; 119:5, s. 968-975 Tidskriftsartikel (refereegranskat)abstract We study the backscattering of solar wind protons from the lunar regolith using the Solar Wind Monitor of the Sub-keV Atom Reflecting Analyzer on Chandrayaan-1. Our study focuses on the component of the backscattered particles that leaves the regolith with a positive charge. We find that the fraction of the incident solar wind protons that backscatter as protons, i.e., the proton-backscattering efficiency, has an exponential dependence on the solar wind speed that varies from similar to 0.01% to similar to 1% for solar wind speeds of 250km/s to 550km/s. We also study the speed distribution of the backscattered protons in the fast (similar to 550km/s) solar wind case and find both a peak speed at similar to 80% of the solar wind speed and a spread of similar to 85km/s. The observed flux variations and speed distribution of the backscattered protons can be explained by a speed-dependent charge state of the backscattered particles.
29.	Martell, J., et al. (författare) Combined Neutron and X-Ray Tomography-A Versatile and Non-Destructive Tool in Planetary Geosciences 2024 Ingår i: Journal of Geophysical Research - Planets. - : American Geophysical Union (AGU). - 2169-9097 .- 2169-9100. ; 129:2 Forskningsöversikt (refereegranskat)abstract With several upcoming sample return missions, such as the Mars Sample Return Campaign, non-destructive methods will be key to maximizing their scientific output. In this study, we demonstrate that the combination of neutron and X-ray tomography provides an important tool for the characterization of such valuable samples. These methods allow quantitative analyses of internal sample features and also provide a guide for further destructive analyses with little to no sample treatment, which maintains sample integrity, including minimizing the risk of potential contamination. Here, we present and review the results from four case studies of terrestrial impactites and meteorites along with their analytical setup. Using combined X-ray and neutron tomography, a Ni-Fe silicide spherule, that is, projectile material, was located within a Libyan Desert Glass sample and the distribution of hydrous phases was pinpointed in selected impactite samples from the Chicxulub IODP-ICDP Expedition 364 drill core and the Luizi impact structure, as well as in the Miller Range 03346 Martian meteorite. Neutron and X-ray tomography give complementary three-dimensional information about the distribution of different phases within a geologic sample. We demonstrate that these two methods can be successfully used to locate meteoritic material (i.e., from the impacting object) and hydrous components in terrestrial impactites and meteorites. This can help shed light on aqueous processes in the Solar System as well as the impact cratering process. Non-destructive methods like these will be important for up-coming sample return missions to characterize the returned samples and guide further destructive analyses. Combined neutron and X-ray imaging was used to locate projectile material and hydrous phases in meteorites and terrestrial impactites Locating and identifying projectile material can shed light on the impact cratering process Combined neutron/X-ray tomography can serve as a fundamental method for the characterization of material from (future) sample return missions
30.	Marzok, A., et al. (författare) Mapping the Brightness of Ganymede's Ultraviolet Aurora Using Hubble Space Telescope Observations 2022 Ingår i: Journal of Geophysical Research - Planets. - : American Geophysical Union (AGU). - 2169-9097 .- 2169-9100. ; 127:6 Tidskriftsartikel (refereegranskat)abstract We analyze Hubble Space Telescope observations of Ganymede made with the Space Telescope Imaging Spectrograph between 1998 and 2017 to generate a brightness map of Ganymede's oxygen emission at 1,356 angstrom. Our Mercator projected map demonstrates that the brightness along Ganymede's northern and southern auroral ovals strongly varies with longitude. To quantify this variation around Ganymede, we investigate the brightness averaged over 36 degrees-wide longitude corridors centered around the sub-Jovian (0 degrees W), leading (90 degrees W), anti-Jovian (180 degrees W), and trailing (270 degrees W) central longitudes. In the northern hemisphere, the brightness of the auroral oval is 3.7 +/- 0.4 times lower in the sub-Jovian and anti-Jovian corridors compared to the trailing and leading corridors. The southern oval is overall brighter than the northern oval, and only 2.5 +/- 0.2 times fainter on the sub- and anti-Jovian corridors compared to the trailing and leading corridors. This demonstrates that Ganymede's auroral ovals are strongly structured in auroral crescents on the leading side (plasma downstream side) and on the trailing side (plasma upstream side). We also find that the brightness is not symmetric with respect to the 270 degrees meridian, but shifted by similar to 20 degrees towards the Jovian-facing hemisphere. Our map will be useful for subsequent studies to understand the processes that generate the aurora in Ganymede's non-rotationally driven, sub-Alfvenic magnetosphere.
31.	Mogan, Shane R. Carberry R., et al. (författare) Callisto's Atmosphere : First Evidence for H-2 and Constraints on H2O 2022 Ingår i: Journal of Geophysical Research - Planets. - : American Geophysical Union (AGU). - 2169-9097 .- 2169-9100. ; 127:11 Tidskriftsartikel (refereegranskat)abstract We explore the parameter space for the contribution to Callisto's H corona observed by the Hubble Space Telescope from sublimated H2O and radiolytically produced H-2 using the Direct Simulation Monte Carlo method. The spatial morphology of this corona produced via photoelectron and magnetospheric electron-impact-induced dissociation is described by tracking the motion of and simulating collisions between the hot H atoms and thermal molecules including a near-surface O-2 component. Our results indicate that sublimated H2O produced from the surface ice, whether assumed to be intimately mixed with or distinctly segregated from the dark nonice or ice-poor regolith, cannot explain the observed structure of the H corona. On the other hand, a global H-2 component can reproduce the observation, and is also capable of producing the enhanced electron densities observed at high altitudes by Galileo's plasma-wave instrument, providing the first evidence of H-2 in Callisto's atmosphere. The range of H-2 surface densities explored, under a variety of conditions, that are consistent with these observations is similar to(0.4-1) x 10(8) cm(-3). The simulated H-2 escape rates and estimated lifetimes suggest that Callisto has a neutral H-2 torus. We also place a rough upper limit on the peak H2O number density (less than or similar to 10(8) cm(-3)), column density (less than or similar to 10(15) cm(-2)), and sublimation flux (less than or similar to 10(12) cm(-2) s(-1)), all of which are 1-2 orders of magnitude less than that assumed in previous models. Finally, we discuss the implications of these results, as well as how they compare to Europa and Ganymede.
32.	Navarro‐González, Rafael, et al. (författare) Abiotic Input of Fixed Nitrogen by Bolide Impacts to Gale Crater During the Hesperian : Insights From the Mars Science Laboratory 2019 Ingår i: Journal of Geophysical Research - Planets. - : John Wiley & Sons. - 2169-9097 .- 2169-9100. ; 124:1, s. 94-113 Tidskriftsartikel (refereegranskat)abstract Molecular hydrogen (H2) from volcanic emissions is suggested to warm the Martian surface when carbon dioxide (CO2) levels dropped from the Noachian (4100 to 3700 Myr) to the Hesperian (3700 to 3000 Myr). Its presence is expected to shift the conversion of molecular nitrogen (N2) into different forms of fixed nitrogen (N). Here we present experimental data and theoretical calculations that investigate the efficiency of nitrogen fixation by bolide impacts in CO2‐N2 atmospheres with or without H2. Surprisingly, nitric oxide (NO) was produced more efficiently in 20% H2 in spite of being a reducing agent and not likely to increase the rate of nitrogen oxidation. Nevertheless, its presence led to a faster cooling of the shock wave raising the freeze‐out temperature of NO resulting in an enhanced yield. We estimate that the nitrogen fixation rate by bolide impacts varied from 7 × 10−4 to 2 × 10−3 g N·Myr−1·cm−2 and could imply fluvial concentration to explain the nitrogen (1.4 ± 0.7 g N·Myr−1·cm−2) detected as nitrite (NO2−) and nitrate (NO3−) by Curiosity at Yellowknife Bay. One possible explanation is that the nitrogen detected in the lacustrine sediments at Gale was deposited entirely on the crater's surface and was subsequently dissolved and transported by superficial and ground waters to the lake during favorable wet climatic conditions. The nitrogen content sharply decreases in younger sediments of the Murray formation suggesting a decline of H2 in the atmosphere and the rise of oxidizing conditions causing a shortage in the supply to putative microbial life.
33.	Němec, F., et al. (författare) Characterizing Average Electron Densities in the Martian Dayside Upper Ionosphere 2019 Ingår i: Journal of Geophysical Research - Planets. - 2169-9097 .- 2169-9100. ; 124:1, s. 76-93 Tidskriftsartikel (refereegranskat)abstract We use more than 10years of the Martian topside ionospheric data measured by the Mars Advanced Radar for Subsurface and Ionosphere Sounding radar sounder on board the Mars Express spacecraft to derive an empirical model of electron densities from the peak altitude up to 325km. Altogether, 16,044 electron density profiles obtained at spacecraft altitudes lower than 425km and at solar zenith angles lower than 80 degrees are included in the analysis. Each of the measured electron density profiles is accurately characterized by the peak electron density, peak altitude, and three additional parameters describing the profile shape above the peak: (i) steepness at high altitudes, (ii) main layer thickness, and (iii) transition altitude. The dependence of these parameters on relevant controlling factors (solar zenith angle, solar irradiance, crustal magnetic field magnitude, and Sun-Mars distance) is evaluated, allowing for a formulation of a simple empirical model. Mars Atmosphere and Volatile EvolutioN Extreme Ultraviolet monitor data are used to show that the solar ionizing flux can be accurately approximated by the F10.7 index when taking into account the solar rotation. Electron densities predicted by the resulting empirical model are compared with electron densities locally evaluated based on the Mars Advanced Radar for Subsurface and Ionosphere Sounding measurements, with the Langmuir Probe and Waves electron density measurements on board the Mars Atmosphere and Volatile EvolutioN spacecraft, and with electron densities obtained by radio occultation measurements. Although the electron densities measured by the Langmuir Probe and Waves instrument are systematically somewhat lower than the model electron densities, consistent with former findings, the model performs reasonably well.
34.	Nemec, F., et al. (författare) Oblique Reflections of Mars Express MARSIS Radar Signals From Ionospheric Density Structures : Raytracing Analysis 2019 Ingår i: Journal of Geophysical Research - Planets. - : AMER GEOPHYSICAL UNION. - 2169-9097 .- 2169-9100. ; 124:5, s. 1177-1187 Tidskriftsartikel (refereegranskat)abstract Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) radar sounder on board the Mars Express spacecraft revealed oblique reflections coming systematically from apparently stable density structures in the Martian ionosphere. Although these were typically interpreted by assuming a straight line propagation of the sounding signal at the speed of light, the ionospheric plasma is clearly a dispersive medium. Consequently, the ray propagation paths may be significantly bent, and, moreover, the observed time delays need to be interpreted in terms of realistic group velocities of the signal propagation. We select a single particularly well-pronounced event with oblique reflections observable over a large range of signal frequencies, and we employ raytracing calculations to perform its detailed analysis. An isolated density structure responsible for the reflection of the sounding signal back to the spacecraft is assumed, and the relevant ionospheric signal propagation is properly evaluated. We show that initially oblique sounding signals get progressively more oblique during their propagation, imposing an upper threshold on the angular propagation distance between the spacecraft and the reflecting density structure, in line with the observations. Considering realistic propagation paths further allows us to explain the frequency dependence of the observed time delays and to accurately model the entire event. The obtained results are consistent with the spacecraft passing very close to a spatially limited density structure. We also show that the results obtained using realistic raytracing calculations are significantly different from the results obtained using additional simplifying assumptions.
35.	Persson, Moa, et al. (författare) The Venusian Atmospheric Oxygen Ion Escape : Extrapolation to the Early Solar System 2020 Ingår i: Journal of Geophysical Research - Planets. - : American Geophysical Union (AGU). - 2169-9097 .- 2169-9100. ; 125:3 Tidskriftsartikel (refereegranskat)abstract The present atmosphere of Venus contains almost no water, but recent measurements indicate that in its early history, Venus had an Earth-like ocean. Understanding how the Venusian atmosphere evolved is important not only for Venus itself but also for understanding the evolution of other planetary atmospheres. In this study, we quantify the escape rates of oxygen ions from the present Venus to infer the past of the Venusian atmosphere. We show that an extrapolation of the current escape rates back in time leads to the total escape of 0.02-0.6 m of a global equivalent layer of water. This implies that the loss of ions to space, inferred from the present state, cannot account for the loss of an historical Earth-like ocean. We find that the O+ escape rate increases with solar wind energy flux, where more energy available leads to a higher escape rate. Oppositely, the escape rate decreases slightly with increased extreme ultraviolet radiation (EUV) flux, though the small variation of EUV flux over the measured solar cycle may explain the weak dependency. These results indicate that there is not enough energy transferred from the solar wind to Venus' upper atmosphere that can lead to the escape of the atmosphere over the past 3.9 billion years. This means that the Venusian atmosphere did not have as much water in its atmosphere as previously assumed or the present-day escape rates do not represent the historical escape rates at Venus. Otherwise, some other mechanisms have acted to more effectively remove the water from the Venusian atmosphere. Plain Language Summary Today, Venus only has small amounts of water in its atmosphere. In its early history, Venus presumably contained an Earth-like ocean of several meters. The evolution of the atmosphere may have been caused by escape of atmospheric content to space. In this study, we investigate how much the escape of oxygen ions to space could have affected the atmospheric evolution for Venus from measurements of the present-day escape rates. Using measurements of oxygen ions in the vicinity of Venus, we show that the amount of energy available in the solar wind to be transferred to the upper atmosphere of Venus determines how much of the atmosphere escapes. From the evolution of the energy in the solar wind over the past 3.9 billion years, together with the relation between the solar wind energy and oxygen ion escape, we show that in total, about 0.02-0.6 m of water depth, if spread equally over the entire Venusian surface, was lost. This indicates that either Venus did not have as much water as previously assumed or the current escape rates are not representative of the historical escape rates. Otherwise, some other mechanisms must have acted to more effectively remove the water from Venus.
36.	Rafkin, Scot C.R., et al. (författare) Diurnal variations of energetic particle radiation at the surface of Mars as observed by the Mars Science Laboratory Radiation Assessment Detector 2014 Ingår i: Journal of Geophysical Research - Planets. - 2169-9097 .- 2169-9100. ; 119:6, s. 1345-1358 Tidskriftsartikel (refereegranskat)abstract The Radiation Assessment Detector onboard the Mars Science Laboratory rover Curiosity is detecting the energetic particle radiation at the surface of Mars. Data collected over the first 350 Martian days of the nominal surface mission show a pronounced diurnal cycle in both the total dose rate and the neutral particle count rate. The diurnal variations detected by the Radiation Assessment Detector were neither anticipated nor previously considered in the literature. These cyclic variations in dose rate and count rate are shown to be the result of changes in atmospheric column mass driven by the atmospheric thermal tide that is characterized through pressure measurements obtained by the Rover Environmental Monitoring Station, also onboard the rover. In addition to bulk changes in the radiation environment, changes in atmospheric shielding forced by the thermal tide are shown to disproportionately affect heavy ions compared to H and He nuclei.
37.	Ramstad, Robin, 1986-, et al. (författare) The Martian atmospheric ion escape rate dependence on solar wind and solar EUV conditions : 1. Seven years of Mars Express observations 2015 Ingår i: Journal of Geophysical Research - Planets. - 2169-9097 .- 2169-9100. ; 120:7, s. 1298-1309 Tidskriftsartikel (refereegranskat)abstract More than 7 years of ion flux measurements in the energy range 10 eV–15 keV have allowed the ASPERA-3/IMA (Analyzer of Space Plasmas and Energetic Ions/Ion Mass Analyzer) instrument on Mars Express to collect a large database of ion measurements in the Mars environment, over a wide range of upstream solar wind (density and velocity) and radiation (solar EUV intensity) conditions. We investigate the influence of these parameters on the Martian atmospheric ion escape rate by integrating IMA heavy ionflux measurements taken in the Martian tail at similar (binned) solar wind density (nsw), velocity (vsw), and solar EUV intensity (IEUV) conditions. For the same solar wind velocity and EUV intensity ranges (vsw and IEUV constrained), we find a statistically significant decrease of up to a factor of 3 in the atmospheric ion escape rate with increased average solar wind density (5.6 × 1024 s−1 to 1.9 × 1024 s−1 for 0.4 cm−3 and 1.4 cm−3, respectively). For low solar wind density (0.1–0.5 cm−3) and low EUV intensity, the escape rate increaseswith increasing solar wind velocity from 2.4 × 1024 s−1 to 5.6 × 1024 s−1. During high solar EUV intensities the escape fluxes are highly variable, leading to large uncertainties in the estimated escape rates; however, a statistically significant increase in the escape rate is found between low/high EUV for similar solar wind conditions. Empirical-analytical models for atmospheric escape are developed by fitting calculated escape rates to all sufficiently sampled upstream conditions.
38.	Rennó, Nilton O., et al. (författare) Possible physical and thermodynamical evidence for liquid water at the Phoenix landing site 2009 Ingår i: Journal of Geophysical Research - Planets. - 2169-9097 .- 2169-9100. ; 114:10 Tidskriftsartikel (refereegranskat)
39.	Roth, Lorenz, et al. (författare) Detection of a hydrogen corona at Callisto 2017 Ingår i: Journal of Geophysical Research - Planets. - : Blackwell Publishing. - 2169-9097 .- 2169-9100. ; 122:5, s. 1046-1055 Tidskriftsartikel (refereegranskat)abstract In December 2001, the Space Telescope Imaging Spectrograph of the Hubble Space Telescope obtained far-ultraviolet spectral images of Jupiter's moon Callisto. The leading and trailing hemispheres were observed in the spectral range 1190 Å to 1720 Å when the moon was at eastern and western elongations, respectively. We analyzed the hydrogen Lyman α (1216 Å) signal in the two observations and found that faint atmospheric emissions extending up to several moon radii away are present in addition to the solar flux reflected off the surface. We show that the detected atmospheric Lyman α emissions are consistent with an escaping hydrogen corona with a vertical column density in the range of (6–12) ×1011 cm−2. The derived hydrogen abundance is about 2 times higher when the moon is at eastern elongation, possibly related to increased water sublimation when the visibly darker leading hemisphere is illuminated by the Sun. The detected hemispheric difference is larger than the measurement uncertainties providing first evidence for variations in Callisto's neutral atmosphere.
40.	Siljeström, Sandra, et al. (författare) Evidence of Sulfate-Rich Fluid Alteration in Jezero Crater Floor, Mars 2024 Ingår i: Journal of Geophysical Research - Planets. - : John Wiley and Sons Inc. - 2169-9097 .- 2169-9100. ; 129:1 Tidskriftsartikel (refereegranskat)abstract Sulfur plays a major role in martian geochemistry and sulfate minerals are important repositories of water. However, their hydration states on Mars are poorly constrained. Therefore, understanding the hydration and distribution of sulfate minerals on Mars is important for understanding its geologic, hydrologic, and atmospheric evolution as well as its habitability potential. NASA's Perseverance rover is currently exploring the Noachian-age Jezero crater, which hosts a fan-delta system associated with a paleolake. The crater floor includes two igneous units (the Séítah and Máaz formations), both of which contain evidence of later alteration by fluids including sulfate minerals. Results from the rover instruments Scanning Habitable Environments with Raman and Luminescence for Organics and Chemistry and Planetary Instrument for X-ray Lithochemistry reveal the presence of a mix of crystalline and amorphous hydrated Mg-sulfate minerals (both MgSO4·[3–5]H2O and possible MgSO4·H2O), and anhydrous Ca-sulfate minerals. The sulfate phases within each outcrop may have formed from single or multiple episodes of water activity, although several depositional events seem likely for the different units in the crater floor. Textural and chemical evidence suggest that the sulfate minerals most likely precipitated from a low temperature sulfate-rich fluid of moderate pH. The identification of approximately four waters puts a lower constraint on the hydration state of sulfate minerals in the shallow subsurface, which has implications for the martian hydrological budget. These sulfate minerals are key samples for future Mars sample return.
41.	Simon, J. I., et al. (författare) Samples Collected From the Floor of Jezero Crater With the Mars 2020 Perseverance Rover 2023 Ingår i: Journal of Geophysical Research - Planets. - : John Wiley and Sons Inc. - 2169-9097 .- 2169-9100. ; 128:6 Tidskriftsartikel (refereegranskat)abstract The first samples collected by the Mars 2020 mission represent units exposed on the Jezero Crater floor, from the potentially oldest Séítah formation outcrops to the potentially youngest rocks of the heavily cratered Máaz formation. Surface investigations reveal landscape-to-microscopic textural, mineralogical, and geochemical evidence for igneous lithologies, some possibly emplaced as lava flows. The samples contain major rock-forming minerals such as pyroxene, olivine, and feldspar, accessory minerals including oxides and phosphates, and evidence for various degrees of aqueous activity in the form of water-soluble salt, carbonate, sulfate, iron oxide, and iron silicate minerals. Following sample return, the compositions and ages of these variably altered igneous rocks are expected to reveal the geophysical and geochemical nature of the planet's interior at the time of emplacement, characterize martian magmatism, and place timing constraints on geologic processes, both in Jezero Crater and more widely on Mars. Petrographic observations and geochemical analyses, coupled with geochronology of secondary minerals, can also reveal the timing of aqueous activity as well as constrain the chemical and physical conditions of the environments in which these minerals precipitated, and the nature and composition of organic compounds preserved in association with these phases. Returned samples from these units will help constrain the crater chronology of Mars and the global evolution of the planet's interior, for understanding the processes that formed Jezero Crater floor units, and for constraining the style and duration of aqueous activity in Jezero Crater, past habitability, and cycling of organic elements in Jezero Crater.
42.	Solomonidou, A., et al. (författare) The Spectral Nature of Titan's Major Geomorphological Units : Constraints on Surface Composition 2018 Ingår i: Journal of Geophysical Research - Planets. - : AMER GEOPHYSICAL UNION. - 2169-9097 .- 2169-9100. ; 123:2, s. 489-507 Tidskriftsartikel (refereegranskat)abstract We investigate Titan's low-latitude and midlatitude surface using spectro-imaging near-infrared data from Cassini/Visual and Infrared Mapping Spectrometer. We use a radiative transfer code to first evaluate atmospheric contributions and then extract the haze and the surface albedo values of major geomorphological units identified in Cassini Synthetic Aperture Radar data, which exhibit quite similar spectral response to the Visual and Infrared Mapping Spectrometer data. We have identified three main categories of albedo values and spectral shapes, indicating significant differences in the composition among the various areas. We compare with linear mixtures of three components (water ice, tholin-like, and a dark material) at different grain sizes. Due to the limited spectral information available, we use a simplified model, with which we find that each albedo category of regions of interest can be approximately fitted with simulations composed essentially by one of the three surface candidates. Our fits of the data are overall successful, except in some cases at 0.94, 2.03, and 2.79m, indicative of the limitations of our simplistic compositional model and the need for additional components to reproduce Titan's complex surface. Our results show a latitudinal dependence of Titan's surface composition, with water ice being the major constituent at latitudes beyond 30 degrees N and 30 degrees S, while Titan's equatorial region appears to be dominated partly by a tholin-like or by a very dark unknown material. The albedo differences and similarities among the various geomorphological units give insights on the geological processes affecting Titan's surface and, by implication, its interior. We discuss our results in terms of origin and evolution theories. Plain Language Summary Titan, Saturn's moon, has been investigated by the Cassini mission for almost 13 years, unveiling an exotic world with many features similar to Earth. One of the mysteries that still has not been resolved even after that many years of exploration is the nature of its surface composition. Titan is a very complex world with multivariable geology and a very thick and hazy atmosphere that shields the surface from remote sensing observations, prohibiting direct evaluation of its composition. In our study we analyze spectro-imaging data from the Cassini visual and infrared spectrometer. We first infer the atmospheric contribution and then extract true surface properties. We study major geomorphological regions on Titan, which include among other mountains, plains, craters, and dunes. We derive their surface albedo values and shapes that reveal the brightness of the surface and compare them with materials that we expect to find on Titan's surface, such as water ice, tholins (atmospheric products), and a very dark unknown component. The results from this analysis show that Titan presents a pattern in its surface composition distribution with its equator being dominated by organic materials from the atmosphere and a very dark unknown material, while higher latitudes contain more water ice.
43.	Sturkell, Erik, 1962, et al. (författare) The Proximal Ejecta Around the Marine-Target Lockne Impact Structure, Sweden 2023 Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS. - 2169-9097 .- 2169-9100. ; 128:7 Tidskriftsartikel (refereegranskat)abstract Very few impact craters on Earth have preserved proximal ejecta (ejecta blanket), which when present help us to better understand the cratering processes when asteroid hits Earth. The 458 Ma old Lockne impact structure consists of a 7.5-km wide nested crater in the crystalline basement surrounded by an approximately 3-km wide brim developed in the upper sedimentary target. The asteroid struck a marine environment with 500 m sea water, 50-m lithified limestone, and 30 m of Cambrian clay covering a peneplainized crystalline basement. The transient crater that developed in rock and water obtained a "soup-plate" shape and reached about 7 km from the impact crater center, the farthest on the down-range side. The brim of the soup-plate was partially stripped of Ordovician limestone and water before the emplacement of inner impact crater ejecta. Most of the ejecta rest upon the Cambrian clay (today shale). The asteroid struck obliquely from the east, which is reflected in the ejecta distribution. The proximal ejecta field is divided into two crescent-shaped areas to the northwest and southwest of the nested crater and covers 26 km(2). Resistivity profiles, mapping, and core drilling show that the thickness of the ejecta masses range between 30 and 50 m with a total volume of about 1 km(3). They were not re-worked by the resurge. They represent roughly 26 vol% of the calculated excavated volume of crystalline rocks. Thus, it can be concluded that the Lockne impact crater has a well-preserved ejecta blanket.
44.	Sun, Vivian Z., et al. (författare) Overview and Results From the Mars 2020 Perseverance Rover's First Science Campaign on the Jezero Crater Floor 2023 Ingår i: Journal of Geophysical Research: Planets. - : John Wiley and Sons Inc. - 2169-9097 .- 2169-9100. ; 128:6 Tidskriftsartikel (refereegranskat)abstract The Mars 2020 Perseverance rover landed in Jezero crater on 18 February 2021. After a 100-sol period of commissioning and the Ingenuity Helicopter technology demonstration, Perseverance began its first science campaign to explore the enigmatic Jezero crater floor, whose igneous or sedimentary origins have been much debated in the scientific community. This paper describes the campaign plan developed to explore the crater floor's Máaz and Séítah formations and summarizes the results of the campaign between sols 100–379. By the end of the campaign, Perseverance had traversed more than 5 km, created seven abrasion patches, and sealed nine samples and a witness tube. Analysis of remote and proximity science observations show that the Máaz and Séítah formations are igneous in origin and composed of five and two geologic members, respectively. The Séítah formation represents the olivine-rich cumulate formed from differentiation of a slowly cooling melt or magma body, and the Máaz formation likely represents a separate series of lava flows emplaced after Séítah. The Máaz and Séítah rocks also preserve evidence of multiple episodes of aqueous alteration in secondary minerals like carbonate, Fe/Mg phyllosilicates, sulfates, and perchlorate, and surficial coatings. Post-emplacement processes tilted the rocks near the Máaz-Séítah contact and substantial erosion modified the crater floor rocks to their present-day expressions. Results from this crater floor campaign, including those obtained upon return of the collected samples, will help to build the geologic history of events that occurred in Jezero crater and provide time constraints on the formation of the Jezero delta.
45.	Szabo, P.S., et al. (författare) Energetic neutral atom (ENA) emission characteristics at the moon and mercury from 3D regolith simulations of solar wind reflection 2023 Ingår i: Journal of Geophysical Research - Planets. - : American Geophysical Union (AGU). - 2169-9097 .- 2169-9100. ; 128:9 Tidskriftsartikel (refereegranskat)abstract The reflection of solar wind protons as energetic neutral atoms (ENAs) from the lunar surface has regularly been used to study the plasma-surface interaction at the Moon. However, there still exists a fundamental lack of knowledge of the scattering process. ENA emission from the surface is expected to similarly occur at Mercury and will be studied by BepiColombo. Understanding this solar wind backscattering will allow studies of both Mercury's plasma environment as well as properties of the hermean surface itself. Here, we expand on previous simulation studies of the solar-wind-regolith interaction with 3D grains in SDTrimSP-3D to compare the predicted scattering energies and angles to ENA measurements from the Moon by the Chandrayaan-1 and IBEX missions. The simulations reproduce a backward emission toward the Sun, which can be connected to the geometry of the regolith grain stacking. In contrast, the ENA energy distribution and its Maxwellian shape is mostly connected to the solar wind velocity. Our simulations also correctly describe a lunar ENA albedo between 10% and 20% and support its decrease with solar wind velocity. We further expand our studies to illustrate how BepiColombo will be able to observe ENAs at Mercury using hybrid simulations of Mercury's magnetosphere as an input for the complex surface precipitation patterns. We demonstrate that the variable ion precipitation will directly influence ENA emission from the surface. The orbits of BepiColombo's Mercury Planetary Orbiter and Mercury Magnetospheric Orbiter/Mio spacecraft are shown to be suitable to observe ENA emission patterns both on a local and a global scale.
46.	Szabo, P. S., et al. (författare) Experimental Insights Into Space Weathering of Phobos : Laboratory Investigation of Sputtering by Atomic and Molecular Planetary Ions 2020 Ingår i: Journal of Geophysical Research - Planets. - : AMER GEOPHYSICAL UNION. - 2169-9097 .- 2169-9100. ; 125:12 Tidskriftsartikel (refereegranskat)abstract Investigating the space weathering of the Martian moon Phobos represents an important step toward understanding the development from its origin to its present-day appearance. Depending on Phobos' orbital position, its surface is continuously sputtered by the solar wind and planetary ions that originate in the Martian atmosphere. Based on Mars Atmosphere and Volatile Evolution measurements, it has been proposed that sputtering by planetary O+ and O-2(+) ions dominates in the Martian tail region, where the planet mostly shadows Phobos from the solar wind. In these models, uncertainties for sputtering yield inputs still exist due to the lack of sufficient analog experiments. Therefore, sputtering measurements with O+, O-2(+), C+, and CO2+ ions between 1 and 5 keV were performed using augite samples as Phobos analogs. The experimental results for O+ irradiations show smaller mass changes than predicted by SDTrimSP simulations, which probably can be attributed to O implantation enabled by the Fe content of the target. Sputtering with O-2(+) and CO2+ in the low keV range shows no deviations in the sputtering yields attributable to molecular effects. Therefore, CO2+ ions will most likely be negligible for the sputtering of Phobos according to the current understanding of ion fluxes on the Martian moon. Ultimately, our experiments suggest that the sputtering contribution on Phobos by O ions is about 50% smaller than previously assumed. This does not change the qualitative outcome from previous modeling stating that planetary O ions are by far the dominant sputtering contribution on Phobos in the Martian tail region.
47.	Vaughan, A., et al. (författare) Regolith of the Crater Floor Units, Jezero Crater, Mars : Textures, Composition, and Implications for Provenance 2023 Ingår i: Journal of Geophysical Research - Planets. - : John Wiley and Sons Inc. - 2169-9097 .- 2169-9100. ; 128:3 Tidskriftsartikel (refereegranskat)abstract A multi-instrument study of the regolith of Jezero crater floor units by the Perseverance rover has identified three types of regolith: fine-grained, coarse-grained, and mixed-type. Mastcam-Z, Wide Angle Topographic Sensor for Operations and eNgineering, and SuperCam Remote Micro Imager were used to characterize the regolith texture, particle size, and roundedness where possible. Mastcam-Z multispectral and SuperCam laser-induced breakdown spectroscopy data were used to constrain the composition of the regolith types. Fine-grained regolith is found surrounding bedrock and boulders, comprising bedforms, and accumulating on top of rocks in erosional depressions. Spectral and chemical data show it is compositionally consistent with pyroxene and a ferric-oxide phase. Coarse-grained regolith consists of 1–2 mm well-sorted gray grains that are found concentrated around the base of boulders and bedrock, and armoring bedforms. Its chemistry and spectra indicate it is olivine-bearing, and its spatial distribution and roundedness indicate it has been transported, likely by saltation-induced creep. Coarse grains share similarities with the olivine grains observed in the Séítah formation bedrock, making that unit a possible source for these grains. Mixed-type regolith contains fine- and coarse-grained regolith components and larger rock fragments. The rock fragments are texturally and spectrally similar to bedrock within the Máaz and Séítah formations, indicating origins by erosion from those units, although they could also be a lag deposit from erosion of an overlying unit. The fine- and coarse-grained types are compared to their counterparts at other landing sites to inform global, regional, and local inputs to regolith formation within Jezero crater. The regolith characterization presented here informs the regolith sampling efforts underway by Perseverance. © 2023. The Authors.
48.	Way, Michael J., et al. (författare) Venusian Habitable Climate Scenarios : Modeling Venus Through Time and Applications to Slowly Rotating Venus-Like Exoplanets 2020 Ingår i: Journal of Geophysical Research - Planets. - 2169-9097 .- 2169-9100. ; 125:5 Tidskriftsartikel (refereegranskat)abstract One popular view of Venus' climate history describes a world that has spent much of its life with surface liquid water, plate tectonics, and a stable temperate climate. Part of the basis for this optimistic scenario is the high deuterium to hydrogen ratio from the Pioneer Venus mission that was interpreted to imply Venus had a shallow ocean's worth of water throughout much of its history. Another view is that Venus had a long‐lived (∼100 million years) primordial magma ocean with a CO2 and steam atmosphere. Venus' long‐lived steam atmosphere would sufficient time to dissociate most of the water vapor, allow significant hydrogen escape, and oxidize the magma ocean. A third scenario is that Venus had surface water and habitable conditions early in its history for a short period of time (<1 Gyr), but that a moist/runaway greenhouse took effect because of a gradually warming Sun, leaving the planet desiccated ever since. Using a general circulation model, we demonstrate the viability of the first scenario using the few observational constraints available. We further speculate that large igneous provinces and the global resurfacing hundreds of millions of years ago played key roles in ending the clement period in its history and presenting the Venus we see today. The results have implications for what astronomers term “the habitable zone,” and if Venus‐like exoplanets exist with clement conditions akin to modern Earth, we propose to place them in what we term the “optimistic Venus zone.”
49.	Wu, X. -S, et al. (författare) The Morphology of the Topside Martian Ionosphere : Implications on Bulk Ion Flow 2019 Ingår i: Journal of Geophysical Research - Planets. - 2169-9097 .- 2169-9100. ; 124:3, s. 734-751 Tidskriftsartikel (refereegranskat)abstract AbstractPrior to the Mars Atmosphere and Volatile Evolution mission, the only information on the composition of the Martian ionosphere came from the Viking Retarding Potential Analyzer data, revealing the presence of substantial ion outflow on the dayside of Mars. Extensive measurements made by the Mars Atmosphere and Volatile Evolution Neutral Gas and Ion Mass Spectrometer allow us to examine the morphology of the Martian ionosphere not only in unprecedented detail but also on both the dayside and the nightside of the planet. Above 300 km, various ionospheric species present a roughly constant density scale height around 100 km on the dayside and 180 km on the nightside. An evaluation of the ion force balance, appropriate for regions with near‐horizontal magnetic field lines, suggests the presence of supersonic ion outflow predominantly driven by the ambient magnetic pressure, with characteristic dayside and nightside flow velocities of 4 and 20 km/s, respectively, both referred to an altitude of 500 km. The corresponding total ion outflow rates are estimated to be 5 × 1025 s−1 on the dayside and 1 × 1025 s−1 on the nightside. The data also indicate a prominent variation with magnetic field orientation in that the ion distribution over regions with near‐vertical field lines tends to be more extended on the dayside but more concentrated on the nightside, as compared to regions with near‐horizontal field lines. These observations should have important implications on the pattern of ion dynamics in the vicinity of Mars.
50.	Xiao, Haifeng, et al. (författare) Spatio-Temporal Level Variations of the Martian Seasonal North Polar Cap From Co-Registration of MOLA Profiles 2022 Ingår i: Journal of Geophysical Research - Planets. - : John Wiley & Sons. - 2169-9097 .- 2169-9100. ; 127:10 Tidskriftsartikel (refereegranskat)abstract The seasonal deposition and sublimation of CO2 constitute a major element in Martian volatile cycles. We reprocess the Mars Orbiter Laser Altimeter (MOLA) data and apply co-registration procedures to obtain spatio-temporal variations in levels of the Seasonal North Polar Cap (SNPC). The maximum level over the Residual North Polar Cap (RNPC) is 1.3 m, approximately half of that at the south pole (2.5 m). However, the maximum level in the dune fields at Olympia Undae can be up to 3.8 m. Furthermore, off-season decreases up to 3 m during the northern winter at Olympia Undae are observed. These are likely due to metamorphism effects accentuated by the reduced snowfall at this period. Meanwhile, off-season increases of up to 2 m during the northern spring are noted, the cause of which remains to be explored. The volume of the SNPC peaks at the end of northern winter and is estimated to be approximately 9.6 × 1012 m3, which is 2% more than that of the Seasonal South Polar Cap. The bulk density of the SNPC can go through phased decreases in accordance with phased accumulation at northern high-latitudes. These findings can put important constraints on the Martian volatile cycling models.

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