Mars Odyssey Research Articles

Long‐Term Variability of Mars' Exosphere Density Based on Precise Orbital Analysis of Mars Reconnaissance Orbiter and Mars Odyssey

AbstractThe variability of Mars exosphere over monthly to solar‐cycle scales at 251 and 412 km altitude is quantified by analysis of 41‐Ls mean densities derived from precise orbit determination of the Mars Reconnaissance Orbiter (MRO) and Mars Odyssey (MO) satellites, respectively. The data encompass 2006–2020 (MRO) and 2002–2020 (MO). At both altitudes, most of the variance is captured by cos(Ls–ϕ), where ϕ ≈ 258°. This term represents the effects of solar heating changes due to the eccentricity of Mars orbit around the Sun, and climatological changes in heating due to lower‐atmosphere dust loading, which does not play a significant role. The remaining variability is connected with the “irregular” variability of solar flux over monthly time scales. For MO, the presence of Helium disrupts a clean correlation with these sources.

Range resolution enhancement of SHAllow RADar (SHARAD) data via bandwidth extrapolation technique: Enabling new features detection and improving geophysical investigation

The SHAllow RADar (SHARAD) is a subsurface sounding radar provided by the Italian Space Agency (ASI) as a facility instrument for NASA's Mars Reconnaissance Orbiter (MRO) mission, the second longest-lived mission to orbit Mars after Mars Odyssey. Developed by an Italian-US Team, SHARAD was designed to investigate to depth of up to one kilometer in the Martian subsurface and to map dielectric discontinuities associated with compositional and/or structural changes. The radar mapping began in November 2006 and, after 16 years of operations, SHARAD has mapped most of the planet's surface (∼55%), contributing a data volume for the entire MRO mission that exceeds that of all the past Mars missions combined.Designed to complement the lower-frequency, relatively narrower bandwidth capability of the MARSIS sounding radar, SHARAD emits an 85μs, frequency-modulated (10 MHz) chirp at a central frequency of 20 MHz to increase the signal-to-noise ratio (SNR) and achieve a finer resolution compared to MARSIS. On the ground, echoes recorded by the radar are range compressed using conventional pulse compression techniques yielding a nominal range resolution of 15 m (vacuum, 5–8 m in typical Martian materials). Additionally, synthetic aperture processing is performed in along-track to increase the resolution up to 300–500 m.Throughout the entire mission duration, SHARAD provided a diverse and extensive range of imaging data. It was able to observe the internal structures of Planum Boreum and Planum Australe, two icy deposits that contain the North and South Polar Layered Deposits (NPLD-SPLD), thought to contain valuable information about the planet's past climate. The radar unveiled the massive deposits of buried CO2 ice below the southern residual ice cap (SRIC), which confirmed the influence of the planet obliquity and insolation in the accumulation of dry ice. Furthermore, it revealed the intricate lava flows structures in the Tharsis Volcanic region, suggesting that the planet experienced deposition by multiple volcanic episodes.However, radar resolution often poses a limitation for subsurface investigations in many regions. Only recently, processing techniques have focused on enhancing SHARAD radargrams vertical resolution by implementing the Bandwidth Extrapolation (BWE) technique. This approach has demonstrated an improvement of the vertical resolution while preserving the time-of-arrival (TOA) and amplitude of the detected echoes. The resulting super-resolved data products exhibit better separation between radar returns, thus improving the overall understanding of the investigated terrains. The obtained results demonstrate the value of implementing the BWE techniques in the data processing pipeline whenever radar sounders are involved.

Unfolding the Neutron Flux Spectrum on the Surface of Mars Using the MSL‐RAD and Odyssey‐HEND Data

AbstractUnderstanding the long‐term radiation environment at the surface of Mars allows us to estimate the exposure for future robotic and crewed missions. Typically, the radiation environment includes charged particles (i.e., protons and heavier ions) and neutral particles (i.e., gamma rays and secondary neutrons). Previous studies used in‐situ measurements, models, or both to determine the characteristics of the radiation at Mars. For example, the Mars Science Laboratory instrument, the Radiation Assessment Detector (RAD), has provided invaluable in‐situ data since landing in 2012. However, the RAD instrument is only sensitive to neutrons with energies > ∼6 MeV and therefore misses what is expected to be a substantial flux of lower‐energy neutrons. To address this gap, we have developed an approach to derive the surface neutron spectrum using the MSL RAD data augmented by orbital data from the High Energy Neutron Detector (HEND) onboard Mars Odyssey (neutron energy < ∼10 MeV). Using a power law fit, we determine neutron flux spectra that reproduce the measurements recorded by both RAD and HEND. Our approach involves a series of Monte Carlo simulations to develop a set of atmospheric transmission functions that enables us to convert the on‐orbit HEND data to their corresponding surface neutron flux spectra. The combined RAD—HEND data present a unique opportunity to obtain a complete picture of the surface neutron environment.

Bounding the unknowns of martian crustal heat flow from a synthesis of regional geochemistry and InSight mission data

The thermal evolution of terrestrial planets is primarily modulated by the distribution of heat-producing elements (HPE) within the crust and mantle. Chemical data from Martian meteorites suggest that Mars differentiated early, which led to an early partitioning of incompatible heat-producing elements in the crust. Previous estimates of Martian crustal heat flow that used the bulk regolith abundances of HPEs from the Gamma-Ray Spectrometer (GRS) suite on Mars Odyssey spacecraft have further corroborated this view of Mars, albeit with poorly known crustal column representativeness. Here we couple the GRS-derived chemical maps of Mars with estimates of crustal thickness and density from the InSight lander to revise the estimated Martian crustal heat flow. The mean crustal heat flow values range from 3.0 to 13.9 mW m−2 for the endmember gravity-derived crustal thickness models anchored by constraints from InSight. We also estimate the crustal heat flow from other factors such as the distribution of HPEs with depth and the Uranium content of the crust. Our results suggest that the mean crustal heat flow varies substantially across models, with the highest mean values being associated with higher densities and an increased enrichment of HPEs with depth. Further work is needed to constrain the crustal thickness of Mars, as the largest uncertainties in the estimate of crustal heat flow stem from uncertainty in the crustal thickness estimates, not geochemical variability. The results from this work corroborate previous estimates of a strong fractionation of heat-producing elements into the Martian crust.

Autonomous Decision-Making for Aerobraking via Parallel Randomized Deep Reinforcement Learning

Aerobraking is a process used to slow down and insert a spacecraft into a low orbit around a planet. It is composed of many orbital passages into the complex atmosphere of the planet, which is used for braking. The aerobraking atmospheric passages are challenging because of the high variability of the atmospheric environment. For this reason, autonomous aerobraking planning is essential for safety and mission performance. This paper develops a parallel domain randomized deep reinforcement learning architecture for autonomous decision-making in a stochastic environment, such as aerobraking atmospheric passages. In this context, the architecture is used for planning aerobraking maneuvers to avoid the occurrence of thermal violations during the atmospheric aerobraking passages and target a final low-altitude orbit. The parallel domain randomized deep reinforcement learning architecture is designed to account for large variability of the physical model, as well as uncertain conditions. Also, the parallel approach speeds up the training process for simulation-based applications, and the domain randomization improves resultant policy generalization. To use this architecture, a Markov-Decision process framework is developed for a general aerobraking-type mission. A three-dimensional running reward function, expressed in spacecraft state and action, is designed. This framework is applied to the 2001 Mars Odyssey aerobraking campaign, which is also used to verify the performance of the parallel domain randomized deep reinforcement learning architecture. With respect to the 2001 Mars Odyssey mission flight data and a Numerical Predictor Corrector (NPC)-based state-of-the-art heuristic for autonomous aerobraking, the proposed architecture outperforms the state-of-the-art heuristic algorithm with an average increase of 87.2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> in the cumulative reward and a decrease of 97.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> in the number of thermal violations. Specifically, the proposed architecture is able to predict and avoid thermal violations while requiring fewer computational resources. Furthermore, it yields a decrease of 98.7 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> in the number of thermal violations with respect to the Mars Odyssey mission flight data and requires 13.9 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> fewer orbits, with a comparable aerobraking duration and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta$</tex-math></inline-formula> V budget. Results also show that the proposed architecture can also learn a generalized policy in the presence of strong uncertainties, such as aggressive atmospheric density perturbations, different atmospheric density models, and a different simulator maximum step size and error accuracy. To this end, a generalization analysis is performed using out-of-distribution generalization environments. Results of the generalization analysis show that the architecture can perform safe aerobraking campaigns with only a maximum increase of 2 in the number of thermal violations for cases in which the simulator accurately described the physical model.

Localization of cosmic gamma-ray bursts in interplanetary space with MGNS/BepiColombo and HEND/Mars Odyssey experiments

This paper describes the methods and results for the localization by triangulation of cosmic gamma-ray bursts (GRBs) independently observed by two space experiments: the Mercury Gamma-ray and Neutron Spectrometer (MGNS) and the High Energy Neutron Detector (HEND). MGNS is onboard the MPO/BepiColombo mission and on a stage of cruise to Mercury whereas HEND is onboard Mars Odyssey mission and in orbit around Mars. An analysis is performed of the accuracy of localization of the GRBs jointly observed by the two instruments at interplanetary distances by comparing their light curves. Notable achievements and scientific opportunities are described also in light of the recent inclusion of MGNS within the program of interplanetary network for gamma-ray burst localization (IPN). • A localization procedure by triangulation of cosmic gamma-ray bursts (GRBs) independently observed by two space experiments MGNS and HEND procedure was created. • Describes the methods and results for the localization procedure. • An analysis is performed of the accuracy of localization of the GRBs. A comparison was performed with the localization done by other experiments. • The first results of the MGNS experiment as part of program of interplanetary network (IPN) are described.

Simplified Automatic Atmospheric Correction for THEMIS Infrared Data

AbstractThermal infrared spectral data from the Thermal Emission Imaging System (THEMIS) on Mars Odyssey can provide diagnostic information to characterize Martian surface compositions. Accurately isolating the atmospheric contribution from the thermal radiance of THEMIS data is essential for surface mineralogy analysis. In this work, we present improved semi‐automatic and fully automated tools to simplify the traditional atmospheric correction method for THEMIS data. Both methods use the Thermal Emission Spectrometer surface emissivity data but in different ways. These two methods are applied to several locations that have been well documented in previous studies, to assess their capability of determining surface spectral features. The fully automatic method demonstrates its simplicity, viability, and robustness by which more consistent results have been generated for the same area across multiple THEMIS images and for areas with large topographic gradients. The tools developed in this work will broaden the utilization of THEMIS infrared spectral data to the wider planetary science community.

Numerical modeling of mapping of Martian epithermal neutron emission: Applications to FREND investigation onboard ESA’s Trace Gas Orbiter

Neutron telescope FREND is operating onboard ESA TGO mission from May 2018 till present. The instrument measures epithermal neutron flux from the Martian surface. Measured variations of the neutron flux may be used to determine hydrogen abundance in the soil usually interpreted as a water/water ice. The unique design of the instrument provides measurements of the neutron flux with a spatial resolution that is much higher than the resolution of previous neutron spectrometers operating on orbit around Mars on board the NASA Mars Odyssey spacecraft. It is known that the spatial resolution of a neutron spectrometer in an orbit around Mars is determined not only by the parameters of the detectors, presence or absence of additional modules to improve the resolution, the orbital altitude of the spacecraft, but also by the fact that Mars has an atmosphere that scatters some of the neutrons that emerge from the Martian surface. One of the ways to increase the spatial resolution of orbital neutron detectors is the passive collimation method using neutron-absorbing substances. In this paper we consider the results of numerical modeling of parameters of the collimated instrument in order to determine its spatial resolution, taking into account the presence of the Martian atmosphere. The contribution of neutrons passing through the collimator walls to the total counting rate and how they affect the estimation of the hydrogen/water concentration in the soil are also considered. Therefore, a method was developed to take into account the imperfect absorbing properties of the collimator and to clear the measured signal from the contribution of neutrons that passed through the collimator wall. Comparison of the spatial resolution of non-collimated and collimated instruments is discussed. Moreover, the results obtained with the conventional method of data processing are compared with the results of developed method, which takes into account the contribution of non-collimated neutrons. The advantage of the results obtained by the developed method is shown.

The History of Water in Martian Magmas From Thorium Maps.

Water inventories in Martian magmas are poorly constrained. Meteorite‐based estimates range widely, from 102 to >104 ppm H2O, and are likely variably influenced by degassing. Orbital measurements of H primarily reflect water cycled and stored in the regolith. Like water, Th behaves incompatibly during mantle melting, but unlike water Th is not prone to degassing and is relatively immobile during aqueous alteration at low temperature. We employ Th as a proxy for original, mantle‐derived H2O in Martian magmas. We use regional maps of Th from Mars Odyssey to assess variations in magmatic water across major volcanic provinces and through time. We infer that Hesperian and Amazonian magmas had ∼100–3,000 ppm H2O, in the lower range of previous estimates. The implied cumulative outgassing since the Hesperian, equivalent to a global H2O layer ∼1–40 m deep, agrees with Mars’ present‐day surface and near‐surface water inventory and estimates of sequestration and loss rates.

Detection and Classification of Potential Caves on the Flank of Elysium Mons, Mars

Martian caves have revived interest in the field of subsurface exploration because they are the potential destinations for future human habitats and astrobiological research. There are many pits on Mars, but some of them look like collapsed cave roofs. These special pits are formed by the collapse of surface materials into the subsurface void spaces. The signature of life is probable in a subsurface cave on Mars as the subsurface environment can protect life from the harsh and dangerous radiation environment of the surface. In a cave, there may be an abundance of minerals, fluids, and other key resources. Therefore, locating the access point of the subsurface cave is essential and crucial for formulating plans for robotic/human explorations of the Red Planet, Mars. We have used remote sensing data from Mars Reconnaissance Orbiter (MRO; NASA), Mars Global Surveyor (MGS; NASA), and Mars Odyssey (NASA) for identifying, mapping, and classifying selected special pit candidates on the flank of Elysium Mons, Mars. A total of 32 special pit candidates has been identified and classified based upon morphology and geological context. Out of these, 26 are newly discovered ones. The thermal behavior of 23 special pit candidates confirms that the special pits are radiating heat energy at nighttime, similar to potential caves. Also, cave entrances have been detected in nine candidates using data from the HiRISE camera onboard MRO. These sites could be important destinations for future robotic/human exploration and the search for life on Mars.

The Origins of Long‐Term Variability in Martian Upper Atmospheric Densities

AbstractWe quantify and interpret the long‐term variability of dayside Martian upper thermosphere and lower exosphere densities within 180–275 km altitudes. Atmospheric CO2, N2, O, and Ar densities are from NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) observations during the time period of 2015–2020 near solar minimum. These neutral measurements, together with contemporaneous solar irradiance measurements at Mars, enable disentanglement of the orbital effect (due to the annual Sun‐Mars distance change with solar longitude) and the solar extreme ultraviolet (EUV) effect in atmospheric density variations. The relative importance of these two effects, which is obtained using a statistical method of Dominance Analysis, reveals the competition between the indirect effect of solar infrared (via the upward coupling from the middle atmosphere) and the direct effect of solar EUV (due to local heating). Our results show that, unlike the orbital effect which is relatively constant at low altitudes and then decreases with increasing altitude, the solar EUV effect nearly monotonically increases. These two effects are comparable at high altitudes (about 240/270/205 km for CO2/N2/O). This analysis is extended to include long‐term exospheric mass density estimates near 400 km from Mars Global Surveyor and Mars Odyssey data, with a focus on representative solar cycle phases of solar minimum and maximum. It is found that near 400 km, the orbital effect is always a key driver regardless of the solar cycle phase, while the solar EUV effect plays a minor role during solar minimum and is greatly enhanced and slightly exceeds the orbital effect during solar maximum.

Insight Into Formation Processes of Layered Ejecta Craters on Mars From Thermophysical Observations

AbstractUnderstanding the morphological characteristics of craters that are indicative of their formation environment can provide insight into surface geology. Layered ejecta (LE) craters, found on Mars and some other planetary bodies, have been hypothesized to have formed as a result of either interaction with subsurface volatiles (volatile fluidization model) and/or with the atmosphere (atmospheric entrainment model). Formation of LE craters by either model should result in different grain size distributions throughout the ejecta deposit. Using thermal inertia to infer surface properties, we investigated LE craters and their ejecta deposits in an effort to distinguish between possible LE formation processes on Mars. We used thermophysical properties of crater ejecta to determine grain size distribution, to model horizontal mixtures and vertical layering, and to identify materials present within the ejecta. We assessed the thermal properties of 50 uniformly sampled LE craters using Mars Odyssey Thermal Emission Imaging System (THEMIS) and Mars Global Surveyor Thermal Emission Spectrometer (TES) data. Our THEMIS analysis identifies 12 craters with grain size distributions consistent with the volatile fluidization model, 3 craters that have characteristics potentially associated with either model, and 22 craters that do not exhibit characteristics matching either model. Our TES analysis identifies 11 craters with characteristics consistent with the volatile fluidization model and 8 craters that are consistent with the atmospheric entrainment model. While some observations of grain size distributions provide evidence for either or both models, there is not overwhelming support for either model, potentially due to uncertainties of derived thermal inertia data.

Investigating Sources of Spectral Olivine Enrichments in Martian Bedrock Plains Using Diurnal Emissivity Changes in THEMIS Multispectral Images

AbstractWe investigate spectral olivine detections in the Noachian cratered highlands that are spatially associated with flat bedrock exposures. Strong olivine detections were previously attributed to relatively high (∼10%–15%) modal abundances of olivine in the bedrock, and then later hypothesized to instead originate from a patchy cover of olivine‐rich sediment formed from erosional lag deposits and mineral‐specific comminution/transport. We test these hypotheses by developing a new technique to partially separate the spectral signals of bedrock and unconsolidated surficial sediment. It uses the differing thermophysical properties of sand and indurated materials, which change the relative contributions of these materials to the emitted spectrum over the diurnal cycle. We use multispectral Mars Odyssey Thermal Emission Imaging System (THEMIS) observations collected in the mid‐afternoon and early evening to apply this technique to eight Terra Sabaea bedrock plains and the Nili Fossae olivine‐carbonate plain. Significant changes in spectral shape arising from compositional differences between bedrock and sediment cover are observed in four bedrock plains. Where these differences are observed, the spectral changes are consistent decreased olivine abundance in the sediment fraction, rather than increased as previously hypothesized. Our results indicate that bedrock materials in the Terra Sabaea region are olivine‐rich in composition, likely indicating a pyroclastic origin for these materials.

Thermophysical and Compositional Analyses of Dunes at Hargraves Crater, Mars

Abstract We analyze thermal emission spectra using the 2001 Mars Odyssey Thermal Emission Imaging System and the Mars Global Surveyor Thermal Emission Spectrometer to characterize grain size and mineralogical composition of dunes at Hargraves crater, Mars. Thermal inertia and bulk composition of the dunes were compared to inferred provenances from the thermal infrared response of surface constituent materials. We use a Markov Chain Monte Carlo technique to estimate the bulk amount of mineralogy contributed by each inferred provenance to the dune field composition. An average thermal inertia value of 238 ± 17 Jm−2 K−1 s−0.5 was found for the dunes, corresponding to a surface composed of an average effective grain size of ∼391 ± 172 μm. This effective particle size suggests the presence of mostly medium sand-sized materials mixed with fine and coarse grain sands. The dunes are likely composed of a weakly indurated surface mixed with unconsolidated materials. Compositional analysis specifies that the dunes are composed of a mixture of feldspar, olivine, pyroxene, and relatively low bulk-silica content. Dune materials were likely derived from physical weathering, especially aeolian erosion, predominantly from the crater ejecta unit at the crater, mixed with a small amount from the crater floor and crater rim and wall lithologies—indicating that the dune materials were likely sourced locally.

The unusual widespread solar energetic particle event on 2013 August 19

Context. Late on 2013 August 19, STEREO-A, STEREO-B, MESSENGER, Mars Odyssey, and the L1 spacecraft, spanning a longitudinal range of 222° in the ecliptic plane, observed an energetic particle flux increase. The widespread solar energetic particle (SEP) event was associated with a coronal mass ejection (CME) that came from a region located near the far-side central meridian from Earth’s perspective. The CME erupted in two stages, and was accompanied by a late M-class flare observed as a post-eruptive arcade, persisting low-frequency (interplanetary) type II and groups of shock-accelerated type III radio bursts, all of them making this SEP event unusual. Aims. There are two main objectives of this study, disentangling the reasons for the different intensity-time profiles observed by the spacecraft, especially at MESSENGER and STEREO-A locations, longitudinally separated by only 15°, and unravelling the single solar source related with the widespread SEP event. Methods. The analysis of in situ data, such as particle fluxes, anisotropies and timing, and plasma and magnetic field data, is compared with the remote-sensing observations. A spheroid model is applied for the CME-driven shock reconstruction and the ENLIL model is used to characterize the heliospheric conditions, including the evolution of the magnetic connectivity to the shock. Results. The solar source associated with the widespread SEP event is the shock driven by the CME, as the flare observed as a post-eruptive arcade is too late to explain the estimated particle onset. The different intensity-time profiles observed by STEREO-A, located at 0.97 au, and MESSENGER, at 0.33 au, can be interpreted as enhanced particle scattering beyond Mercury’s orbit. The longitudinal extent of the shock does not explain by itself the wide spread of particles in the heliosphere. The particle increase observed at L1 may be attributed to cross-field diffusion transport, and this is also the case for STEREO-B, at least until the spacecraft is eventually magnetically connected to the shock when it reaches ∼0.6 au.

Thermophysical Properties and Surface Heterogeneity of Landing Sites on Mars From Overlapping Thermal Emission Imaging System (THEMIS) Observations

AbstractOrbitally derived thermal inertia (TI) values of surfaces allow for remote interpretation of rock and sediment physical characteristics. The evolving local times of the Mars Odyssey Thermal Emission Imaging System (THEMIS) mission have enabled surface temperature data collection over multiple seasons and local times over ∼9 Mars years (MY). We utilize this higher temporal resolution data set to separate TI values of individual materials within THEMIS pixels (100 m sampling). In this study, we focus on geologic units within Gusev, Gale, and Jezero crater landing sites to determine their respective TI and ground‐truth our methods. We use the KRC model to predict temperatures for a range of homogeneous and two‐component thermophysical mixing scenarios (laterally and vertically heterogeneous), and compare those to THEMIS brightness temperatures. The Gusev and Gale crater results are consistent with rover‐based evaluations, indurated or clast‐covered sands. The best‐fit scenarios along the Jezero crater volcanic floor unit show low to moderate TI values representative of coarse sediment, volcaniclastic, or pyroclastic rocks. The light toned unit and western fan deposits both indicate sands and a moderate TI component; we interpret this as heavy fracturing within the rock. Difficulties in modeling some THEMIS temperatures are attributed to daily weather effects, local atmospheric dust variability, and real surface changes over time (e.g., dust deposition and removal); we also observe that some temperature observations lead to non‐unique modeled physical solutions. Nevertheless, these methods can still rule out a significant range of material properties and provide meaningful geologic information about Mars’ surface.

Observations of neutron radiation environment during Odyssey cruise to Mars

In April 2001, Mars Odyssey spacecraft with the High Energy Neutron Detector (HEND) onboard was launched to Mars. HEND/Odyssey was switched on measurement mode for most of transit to Mars to monitor variations of spacecraft background and solar activity. Although HEND/Odyssey was originally designed to measure Martian neutron albedo and to search for Martian subsurface water/water ice, its measurements during cruise phase to Mars are applicable to evaluate spacecraft ambient radiation background. The biological impact of the neutron component of this radiation background should be understood, as it must be taken into account in planning future human missions to Mars. We have modeled the spacecraft neutron spectral density and compared it with HEND measurements to estimate neutron dose equivalent rates during Odyssey cruise phase, which occurred during the maximum period of solar cycle 23. We find that the Odyssey ambient neutron environment during May – September 2001 yields 10.6 ± 2.0 μSv per day in the energy range from 0 to 15 MeV, and about 29 μSv per day when extrapolated to the 0–1000 MeV energy range during solar quiet time (intervals without Solar Particle Events, SPEs). We have also extrapolated HEND/Odyssey measurements to different periods of solar cycle and find that during solar minimum (maximum of GCR flux), the neutron dose equivalent rate during cruise to Mars could be as high as 52 μSv per day with the same shielding. These values are in good agreement with results reported for a similar measurement made with an instrument aboard the Mars Science Laboratory during its cruise to Mars in 2011–2012.

Martian Hydrated Minerals: A Significant Water Sink

AbstractQuantifying the water in all Martian water reservoirs is important for understanding the history of water on Mars, including Mars’ past climate and potential for habitability. Hydrated minerals are widespread on Mars and may comprise a significant portion of the water inventory. We calculated the possible volumes of water stored within and required to form hydrated minerals on Mars by estimating the weight percent (wt.%) water of ice‐free, near‐surface materials, the wt.% water required to form subsurface hydrated minerals, and the densities and thicknesses of rock units with hydrated minerals. We estimated the near‐surface wt.% water using Mars Odyssey Neutron Spectrometer and OMEGA 3 µm hydration feature surveys. We calculated the wt.% water required to form subsurface hydrated minerals by estimating: (1) percent occurrences of subsurface hydrated minerals using mineralogical crater surveys, (2) abundance per detection of hydrated minerals using published spectral unmixing results of hydrated mineral detections, and (3) the wt.% water required to form hydrated minerals using estimated masses and hydration states of hydrated minerals. We estimated the densities of rock units with hydrated minerals using prior crustal density estimates and measurements of sedimentary rock density in Gale Crater. We estimated the thicknesses of rock units with hydrated minerals using mineralogical crater surveys. Our best estimate for the volume of water stored within or required to form hydrated minerals on Mars is 130–260 m global equivalent layer (GEL) and our plausible range extends from 70–860 m GEL. Compared to other Martian reservoirs, hydrated minerals are a significant water sink.

Geologic and Thermal Characterization of Oxia Planum Using Mars Odyssey THEMIS Data

AbstractOxia Planum will be the landing site for the European Space Agency ExoMars 2022 “Rosalind Franklin” mission to conduct astrobiological and geological experiments investigating the region's past. Previous orbital short‐wave infrared (SWIR, 1.0–2.6 μm) spectroscopic studies reported widespread phyllosilicate detections in the region suggesting possible alteration of its original lithology by past aqueous activity. We used thermal infrared data (TIR, 6.8–14.8 μm) from the Thermal Emission Imaging System to assess regional bulk composition and thermophysical properties. We coupled these assessments with SWIR spectral analyses from the Compact Reconnaissance Imaging Spectrometer for Mars and with high‐resolution visible images to characterize the physical properties of the region. We cataloged four geologic units with varying spectral, thermophysical, and textural properties. The previously mapped phyllosilicate bearing materials are associated with our oldest mapped unit. This unit exhibits light/dark‐toned interbedding and TIR spectral characteristics consistent with phyllosilicate dominated and/or intermediate volcanic lithologies; evidence for mafic materials is lacking. Superposing that unit is a thin patchy dark‐toned unit that contains mafic signatures. Isolated locations within the region are superposed by a mechanically competent, rough unit that lacks mafic signatures and is interpreted as lava or well‐cemented fluvial deposits. The uppermost mapped unit is an eroded fan of possible deltaic or alluvial origin, with an inferred surface composition of unconsolidated sediment. Finally, based on stratigraphic and cross‐cutting relationships with ejecta from Kilkhampton crater nearby, we suggest that all units formed during or before the Early Hesperian period.

Trance-it to the Future

Trance-it to the Future