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Astronauts returning from long-duration spaceflights experience visual-vestibular conflicts that causes motion sickness, perceptions that the environment is moving when it is not, and problems with walking and other functional tasks. To evaluate whether astronauts will have similar decrements after they land on Mars following exposure to weightlessness, participants were held by a device that offloads their weight, first entirely (0 G), and then partially (0.38 G) or not at all (1 G). Tandem (heel-to-toe) walk on a medium-density foam surface was used to assess the subject's walking performance. Two visual conditions in virtual reality were investigated: normal vision and a visual-vestibular conflict generated by disorienting optokinetic stimulation (DOS). Tandem walking performance with DOS was better in 0.38 G compared to 1 G. Tandem walking performance in DOS in 1 G was not significantly different from tandem walking performance after spaceflight or bed rest. The increased tandem walking performance in 0.38 G compared to 1 G was presumably due to an increased cone of stability, allowing a larger amplitude of body sway without resulting in a fall. Tandem walking on a compliant foam surface with a visual-vestibular conflict is a potential analog for simulating postflight dynamic balance deficits in astronauts. [ABSTRACT FROM AUTHOR]

Astronauts returning from long-duration spaceflights experience visual-vestibular conflicts that causes motion sickness, perceptions that the environment is moving when it is not, and problems with walking and other functional tasks. To evaluate whether astronauts will have similar decrements after they land on Mars following exposure to weightlessness, participants were held by a device that offloads their weight, first entirely (0 G), and then partially (0.38 G) or not at all (1 G). Tandem (heel-to-toe) walk on a medium-density foam surface was used to assess the subject’s walking performance. Two visual conditions in virtual reality were investigated: normal vision and a visual-vestibular conflict generated by disorienting optokinetic stimulation (DOS). Tandem walking performance with DOS was better in 0.38 G compared to 1 G. Tandem walking performance in DOS in 1 G was not significantly different from tandem walking performance after spaceflight or bed rest. The increased tandem walking performance in 0.38 G compared to 1 G was presumably due to an increased cone of stability, allowing a larger amplitude of body sway without resulting in a fall. Tandem walking on a compliant foam surface with a visual-vestibular conflict is a potential analog for simulating postflight dynamic balance deficits in astronauts.

With the increase of planetary exploration missions and thereby the resultant increase of extraterrestrial rovers deployed, their mobility performance meets new challenges. Wheel-soil interaction plays an important role in the movement of these rovers. Our research addresses the study of this interactions in the first moments of the trajectory. The investigations reported so far, focus on long-distance motion (approx. 20-30 cm). However, the authors believe that the firsts interactions are crucial for the future performance of the motion. Here, by means of a device that allows multiple and precise repetitions of a wheel rolling experiment at controlled gravities, we characterize the movement of a wheel on sandy soil, in the gravity of Mars. Our study reveals that gravity influences the performance of the wheel, under these conditions. The experiments show that, as the gravity decreases, the rolling efficiency also decreases. [ABSTRACT FROM AUTHOR]

Abstract The model of Wilson and Head (1989, 2005, 2015) interprets the grooves of Phobos as the product of sliding, rolling, and bouncing ejecta boulders from the Stickney Crater impact. To test the model of Wilson and Head (1989, 2005, 2015) we apply a dynamical physics simulation to a three-dimensional shape model of Phobos and systematically assess six specific objections to the rolling boulder model. Our simulation calculates the motions of Stickney Crater ejecta boulders under the influence of Mars gravitation, the post-Stickney-impact desynchronized rotation of Phobos and altered orbit of Phobos, a spherically symmetrical gravity field of Phobos, and a collision system that simulates the effects of surface friction. We also take the orbital history of Phobos into account and test the rolling boulder model at three semimajor axes greater than the present day (10,000 km, 12,000 km, and 14,000 km). At a Phobos semimajor axis of 12,000 km, we find that boulder motions are generally consistent with observed grooves – specifically 1) Test boulders travel in linear/parallel patterns that are consistent with observed grooves, including grooves that are not radially aligned with Stickney Crater; 2) test boulders drift into suborbital flights over the trailing hemisphere of Phobos and do not travel on the surface of Phobos in this region; 3) grooves inside Stickney Crater are produced by Stickney ejecta boulders that return to Stickney Crater; 4) boulders that travel around Phobos >180° from Stickney Crater crosscut the motions of other boulders that travel >180° from Stickney; 5) at boulder ejection velocities ≲6 m/s, test boulders moving in contact with Phobos typically follow the contours of local terrain. We also find that 6) a spike of Stickney secondary impacts likely destroyed missing groove-producing boulders and removed grooves with widths ≲80 m; 7) with respect to the motion of test boulders, the two possible pre-Stickney-impact tidal-lock orientations of Phobos produce the same boulder motion effects; and 8) where our 12,000 km semimajor axis testing model is consistent with observed grooves, this supports a ∼150 Ma prediction for the age of Phobos grooves and Stickney Crater. Highlights • We test the model that Phobos grooves were produced by Stickney ejecta boulders. • We describe the 'rolling boulder' model and six objections to the model. • We apply a quantitative simulation to assess the viability of five objections. • We assess the sixth objection based on previously published research. • We conclude that the 'rolling boulder' model is quantifiably plausible. [ABSTRACT FROM AUTHOR]

Enigmatic small-scale (<1 m) depositional and erosional features found in basaltic sands partly covering bedrock exposures, imaged at several locations in the equatorial Meridiani Planum region by the Mars Exploration Rover Opportunity , may be evidence of previously unrecognized, geologically young (or even contemporary) Martian surface processes. Leveed fissures appear to have formed by venting from beneath; possible explanations include aeolian blowholes near crater margins, volcanic fumarole activity, or gas/vapour escape resulting from the decomposition of small pockets of ground ice, methane clathrates or hydrated sulphate minerals. Some leveed fissures cross-cut and are therefore younger than aeolian ripples thought to have last been active c. 50,000 years ago. Erosional gutters are sharply defined and fresh-looking, internally terraced, sometimes are deeper near one end, and in one case seem to give way to small depositional fans downslope; they have the appearance of having been formed by liquid flow rather than by wind erosion. There is evidence elsewhere that contemporary ground-ice thaw and consequent transient surface run-off may occur occasionally under present conditions at low, near-equatorial latitudes on Mars; short-lived (even for just a few minutes) meltwater emission and flow at the surface could form gutters before evaporating. Further possibilities are the decomposition of buried pockets of methane clathrates (which theoretical considerations suggest might be present and stable even in equatorial regions) giving rise to both methane gas venting and transient surface water, or the release of liquid brines by decomposition of hydrated magnesium sulphate minerals or deliquescence of perchlorates. Dry granular flow mechanisms proposed as explanations for Recurring Slope Lineae seem inadequate to explain the morphologies of leveed fissures and gutters. [ABSTRACT FROM AUTHOR]

Dust and sand motion are a common sight on Mars. Understanding the interaction of atmosphere and Martian soil is fundamental to describe the planet’s weather, climate and surface morphology. We set up a wind tunnel to study the lift of a mixture between very fine sand and dust in a Mars simulant soil. The experiments were carried out under Martian gravity in a parabolic flight. The reduced gravity was provided by a centrifuge under external microgravity. The onset of saltation was measured for a fluid threshold shear velocity of 0.82 ± 0.04 m/s. This is considerably lower than found under Earth gravity. In addition to a reduction in weight, this low threshold can be attributed to gravity dependent cohesive forces within the sand bed, which drop by 2/3 under Martian gravity. The new threshold for saltation leads to a simulation of the annual dust cycle with a Mars GCM that is in agreement with observations. [ABSTRACT FROM AUTHOR]

Lower body positive pressure (LBPP) is an effective way of simulating hypogravity. This study measured the submaximal VO2, VCO2 and heart rate when walking on an LBPP treadmill at 1G and simulated Martian gravity (0.38G). Twelve healthy subjects with a mean age ± SD of 22.75 ± 5.38 yrs took part in this study with full consent. The LBPP box used was designed and built by the Microgravity Center. The subjects walked for 8 min at a control of 1G and then for another 8 min in simulated 0.38G 2 wks later. VO2 was 1.00 ± 0.61 L·min-1 at 1G and 0.68 ± 0.33 L·min-1 in the simulated 0.38G (P<0.05). Average caloric expenditure was significantly reduced at simulated Martian gravity (4.79 ± 2.80 kcal·min-1) when compared to the control (3.37 ± 1.49 Kcal·min-1) (P<0.05). The subjects' HR was reduced from 118.49 ± 15.07 beats·min-1 at 1G to 106.20 ± 11.17 beats·min-1 at simulated 0.38G (P<0.05). The average respiratory exchange ratio was significantly increased from 0.83 ± 0.13 to 1.14 ± 0.19 in simulated 0.38G (P<0.05), with no significant difference seen in VCO2. Energy consumption was significantly decreased when walking in LBPP simulated hypogravity. Further research into LBPP physiology can be used to calibrate EVA suits and advise on exercise regimes for future astronauts. [ABSTRACT FROM AUTHOR]

The European Space Agency has recently announced to progress from low Earth orbit missions on the International Space Station to other mission scenarios such as exploration of the Moon or Mars. Therefore, the Moon is considered to be the next likely target for European human space explorations. Compared to microgravity (μg), only very little is known about the physiological effects of exposure to partial gravity (μg < partial gravity

Increasing efforts to move into space have driven the need for new facilities that are capable of simulating weightlessness and other space gravity conditions on Earth. Simulation of weightlessness/microgravity (approximately 10-6 g) is conducted in different earthbound and flightbased facilities, often with poor availability. Other conditions such as lunar or Martian gravity with their partial Earth gravity/hypogravity cannot be performed at a large scale for scientific research on Earth. For multiple Earth gravity/hypergravity, simulation centrifuges are available, but they do not allow the possibility of abrupt acceleration changes. To support this wide range of conditions, a new technique is being developed to combine all of these requirements into a single drop tower facility. Currently under construction, the Einstein-Elevator of the Hannover Institute of Technology at the Leibniz Universität Hannover is an earthbound tool created for simulating micro-, hypo-, and hypergravity research with a high repetition rate. The facility will be capable of performing 100 experiments per day (8-h work shift), each creating 4 s of microgravity. For the first time, statistics can be applied in experiments under space gravity conditions at favorable costs and short mission times. The Einstein-Elevator offers room for large experiments with a diameter up to 1.7 m and a height up to 2 m as well as weights up to 1,000 kg. To perform larger experiments under different gravitational conditions, it was necessary to develop an innovative drive and guide concept. The Einstein- Elevator will be available for general research under different gravity conditions from 2018 onward. [ABSTRACT FROM AUTHOR]

The Martian gravity field has been improved significantly in terms of resolution, with the spatial resolution rising to 100 km and accuracy increasing up to the 110 degree and order, assisted by data collected in Mars exploration missions like MGS, MRO, and Odyssey. However, as the tracking data used for the Martian gravity field solution are from polar orbit at a low height (∼400 km), improvements in the low degree coefficients are possible with high orbiters and various inclinations. In our research, we simulate a future Chinese Mars mission, making use of its orbit, to investigate potential contributions to the Martian gravity field solution. As the Chinese Mars mission will include a lander, we investigate the same beam interferometry tracking mode for a more precise and accurate Martian gravity field solution. Our results show that this tracking mode will substantially improve the gravity field model accuracy in comparison with those models using only polar orbit data. Model accuracy is assessed by power spectrum analysis and precise orbit determination. All the simulation work are accomplished with our independent developed software. Our research will be a reference for the first Chinese Mars exploration mission. [ABSTRACT FROM AUTHOR]

Humans can inhabit other planets in future by advancement in science and technology, starting by closest ones and moving to farther planets. There are some projects underway currently for human settlement on Mars such as Mars-one project or new proposals by NASA. In this paper, possibility of creating and using underground structures in Mars for sheltering humans against harsh environment and dangerous rays goes under investigation. Primary locations such as Arsia Mons for early settlement on Mars was investigated providing its appropriate conditions. Numerical analysis for tunneling to create underground space was conducted considering different spatial orientation of main discontinuities such as fault and joints in Martian gravity. It was inferred that tunneling in near surface Martian rocks is not susceptible to major failures and instabilities. Frozen water in Mars climate, and low gravity result in lower amounts of required cohesion value to keep tunneling structure stable in different scenarios of discontinuities in Martian rocks. It was concluded that underground structures are among the best options for residing humans on Mars and sheltering them against harsh climate by providing insulation and creating enough thickness of burden rock mass against dangerous cosmic and solar rays. [ABSTRACT FROM AUTHOR]

This paper examines how humans adapt to novel physical situations with unknown gravitational acceleration in immersive virtual environments. We designed four virtual reality experiments with different tasks for participants to complete: strike a ball to hit a target, trigger a ball to hit a target, predict the landing location of a projectile, and estimate the flight duration of a projectile. The first two experiments compared human behavior in the virtual environment with real-world performance reported in the literature. The last two experiments aimed to test the human ability to adapt to novel gravity fields by measuring their performance in trajectory prediction and time estimation tasks. The experiment results show that: 1) based on brief observation of a projectile's initial trajectory, humans are accurate at predicting the landing location even under novel gravity fields, and 2) humans' time estimation in a familiar earth environment fluctuates around the ground truth flight duration, although the time estimation in unknown gravity fields indicates a bias toward earth's gravity. [ABSTRACT FROM PUBLISHER]

This paper is concerned with the study of expedition activity in Antarctica as a part of the search for useful analogies and solutions which can be taken into account in planning manned missions to the Moon and Mars. The following is considered: natural analogies, human factors, station facilities, means of transportation, scientific programs, safety issues, and historical and political analogies. A rationalization is given for the idea of creating a testing ground in Antarctica (stations Vostok, Novolazarevskaya, Jetty Oasis) for ground-based simulation of functioning of a lunar and Martian base. [ABSTRACT FROM AUTHOR]

With the expectation of human landing on Mars in the near future, it is critical to understand how the Martian particles deposit in the human terminal alveoli to prevent the astronauts from health damage by the Martian toxic particles. Therefore, this study has numerically investigated the micro-particle behaviours in an alveolar model under Martian gravity using an Euler-Lagrangian method considering several physical and physiological factors. The important findings are as following: 1) Martian particle deposition is sensitive to the alveolar direction and respiratory depth significantly, but not sensitive to the wall motion pattern; 2) both the particle size and density affect the deposition starting time and duration; 3) compared with the earth gravity, the total deposition efficiency decreases and the total deposition time is much extended under the Martian gravity. It concludes that the particle deposition under Martian gravity environment are obviously different from the one under the earth gravity environment. [Display omitted] • Martian particle size/density affect the starting and the ending deposition time. • Martian particle deposition is sensitive to alveolar direction and breathing depth. • The deposition efficiency decreases under the Martian than the earth gravity. • The deposition time is extended under the Martian than the earth gravity. [ABSTRACT FROM AUTHOR]

A discussion is presented about the constraints used in constructing a model for the internal structure of Mars. The most important fact is that the Martian chemical model proposed by Wänke and Dreibus (WD) has stood the test of time. This means that the chondritic ratio Fe/Si = 1.71 can be used as a constraint in constructing an interior structure model of the planet. Consideration is given to the constructing of the reference surface of Mars. It is concluded that the effectively hydrostatic-equilibrium model of Mars is well suited for this purpose. The areoid heights and gravity anomalies in the model of Mars are calculated. The results are shown in the figures (maps) and comments made. The results are compared with the similar data for the Earth. Mars deviates much more strongly from the hydrostatic equilibrium than the Earth. It is suggested that the average thickness of the Martian elastic lithosphere should exceed that of the Earth's continental lithosphere. [ABSTRACT FROM AUTHOR]

The Valles Marineris canyon system in Mars shows large landslides across its walls, which can be 40 km wide and up to 60 km long, with fall scarps height as high as 7 km. These landslides were produced through a large mass movement at high speed by gravity across the trough floor. Although the triggering factors are unclear, several mechanisms have been proposed as, among others, large amounts of subsurface water, quake produced through normal faulting close to the canyon walls, and meteoritic impacts. In this work we examine the limit equilibrium slope stability of three landslides (placed respectively at Ius, Candor, and Melas Chasmata), which can be considered representative, with the aims of constraining their formation conditions. Our results suggest that external factors (as high pore fluid pressure, seismic loading or rock mass disturbance) do not seem necessary for the failure of slopes if they are composed of unconsolidated materials, while high pore water pressure or ground acceleration are needed to trigger slides in slopes composed of strong basaltic-like materials. Moreover, the presence of sub-surface ice would contribute to slope stability. As a whole, our findings point to ground shaking due to meteorite impacts as the main triggering force for most landslides in the Valles Marineris. [ABSTRACT FROM AUTHOR]

Purpose: Weightlessness has a well-known effect on the autonomic control of the cardiovascular system. With future missions to Mars in mind, it is important to know what the effect of partial gravity is on the human body. We aim to study the autonomic response of the cardiovascular system to partial gravity levels, as present on the Moon and on Mars, during parabolic flight. Methods: ECG and blood pressure were continuously recorded during parabolic flight. A temporal analysis of blood pressure and heart rate to changing gravity was conducted to study the dynamic response. In addition, cardiovascular autonomic control was quantified by means of heart rate (HR) and blood pressure (BP) variability measures. Results: Zero and lunar gravity presented a biphasic cardiovascular response, while a triphasic response was noted during martian gravity. Heart rate and blood pressure are positively correlated with gravity, while the general variability of HR and BP, as well as vagal indices showed negative correlations with increasing gravity. However, the increase in vagal modulation during weightlessness is not in proportion when compared to the increase during partial gravity. Conclusions: Correlations were found between the gravity level and modulations in the autonomic nervous system during parabolic flight. Nevertheless, with future Mars missions in mind, more studies are needed to use these findings to develop appropriate countermeasures. [ABSTRACT FROM AUTHOR]

We introduce an instrument for a wide spectrum of experiments on gravities other than our planet's. It is based on a large Atwood machine where one of the loads is a bucket equipped with a single board computer and different sensors. The computer is able to detect the falling (or rising) and then the stabilization of the effective gravity and to trigger actuators depending on the experiment. Gravities within the range 0.4 g-1.2 g are easily achieved with acceleration noise of the order of 0.01 g. Under Martian gravity, we are able to perform experiments of approximately 1.5 s duration. The system includes features such as WiFi and a web interface with tools for the setup, monitoring, and data analysis of the experiment. We briefly show a case study in testing the performance of a model Mars rover wheel in low gravities. [ABSTRACT FROM AUTHOR]

The article presents a study aimed at formulating a solution procedure, exploring the robustness of the solution procedure and assessing various entry mission scenarios in Mars using the new methodology. It discusses the challenges of landing on Mars due to the aerodynamic combination of atmospheric density and gravity, the bank angle modulation and dynamics of entry module. It demonstrates the problem of parachute deployment and the derivation of bank control law using Pontryagin's principle.

Abstract: The rock walls of the Valles Marineris valleys (VM) in the equatorial area of Mars exhibit several gravitational failures which resulted in a series of large landslides up to several hundred cubic kilometers in volume. Questions arise as to forces at play and rock strength in the stability of the walls of VM. In this work we address the stability analysis of the walls of VM by considering the strength of the materials of the walls and the causes of landslides. Using finite element calculations and the limit analysis upper bound method, we explore the range of cohesion and friction angle values associated with realistic failure geometries, and compare predictions with the more classical Culmannʼs translational failure model. Our analysis is based both on synthetic, simplified slope profiles, and on the real shape of the walls of VM taken from the MOLA topographic data. Validation of the calibrated cohesion and friction angle values is performed by comparing the computed unstable cross sectional areas with the observed pre- and post-failure profiles, the estimated failure surface geometry and ridge crest retreat. This offers a link between rock mass properties, slope geometry and volume of the observed failure, represented in dimensionless charts. The role of groundwater flow and seismic action on the decrease of slope stability is also estimated. Pseudo-static seismic analyses provide another set of dimensionless charts and show that low seismicity events induced by meteoroid impacts, consistent with the size of craters, could be a cause for some of the observed landslides, if poor rock properties for VM are assumed. Analyses suggest that rock mass properties are more similar to their earth equivalents with respect to what has been previously supposed. [Copyright &y& Elsevier]

Since the continuation of an external gravity field inside topographic masses by a harmonic function results in topographic bias, geoid computation by means of global gravity models (GGMs) in terms of external-type series of spherical harmonics, at locations where the GGMs are evaluated inside the topographic masses, will be biased. Consequently, if the reference ellipsoid is defined based on the geoid, it will also be biased. In this paper, the effects of topographic bias on the geoid and reference ellipsoid of Venus, Mars, and the Moon are studied. Moreover, a thorough error analysis in the geoid and reference ellipsoid computation is presented, and it is shown that the estimated standard deviation (STD) of the geoid potential value, the geoidal heights, and the semimajor and semiminor axes of the reference ellipsoid are independent of the topographic bias. According to the results, the effects of topographic bias on the geoid potential value and the semimajor and semiminor axes of the reference ellipsoid in comparison with their estimated STDs are insignificant for Venus, Mars, and the Moon. Moreover, the effect of topographic bias on the geoidal heights of Venus as compared with the estimated STD of its geoidal heights is insignificant. However, the effects of topographic bias on the geoidal heights of Mars and the Moon can be significant, especially in high mountains such as the Tharsis volcanic region on Mars. [ABSTRACT FROM AUTHOR]

The gravity of Mars and the observation of a thick Phobos regolith suggest that nearly all Phobos ejecta returns to Phobos and re-impacts on Phobos. Primary ejecta from Mars typically impacts Phobos at velocities of ~2–3km/s and due to the low escape velocity from Phobos of ~4–10m/s, ~95–99% of the secondary ejecta from Phobos is inserted into temporary orbits around Mars. Most Phobos ejecta fragments remain trapped in orbits around Mars for several days to several hundred years until they re-impact with Phobos and produce new generations of ejecta. Mars-orbiting Phobos ejecta fragments typically re-impact on opposite hemispheres of Phobos from their previous impact sites, and when combined with the typical conical dispersion pattern of impact ejecta, this suggests that just two or three generations of re-impacts on Phobos are sufficient to uniformly disperse Mars ejecta fragments globally across the geographic surface of Phobos. Due to the energy conversion inefficiencies of impact processes, subsequent re-impacts produce subsequent generations of ejecta with lower launch velocities, and a higher proportion of Phobos ejecta remains on Phobos. Once no new ejecta fragments are launched from Phobos at velocities that are greater than the local escape velocity from Phobos, no new Mars-orbiting ejecta are produced. While in orbit around Mars, particles of ejecta are perturbed by martian gravity and solar photon forces that combine to produce an increase in the orbital eccentricities, which preferentially alters the orbits of the smallest fragments. Dust fragments ≲300µm are typically de-orbited to the atmosphere of Mars or to solar orbits within several years, whereas fragments ≳300mm tend to remain in orbit until they re-impact with Phobos. The rapid removal of dust fragments ≲300µm places a severe limit on their opportunities for a re-impact with Phobos and suggests a deficiency of dust grains ≲300µm in the regolith of Phobos. For the present-day altitude of Phobos, we calculate that the flux from solar system projectiles that impacts Phobos is ~200× greater than the flux from primary Mars ejecta. Based on lunar regolith observations, the bulk concentration of solar system projectiles in the regolith of Phobos is likely to be ~3%, which, when adjusted for solar system flux in the vicinity of Mars, suggests a bulk concentration of Mars ejecta fragments in the regolith of Phobos of ~250ppm. Phobos has orbited at least 4000km farther from Mars during all but the most recent ~500Myr, and throughout the majority of the early geological history of Phobos, ejecta plumes from Mars would have expanded to a much larger volumes and would have diffused to substantially lower volumetric densities at the point of intersection with Phobos. This suggests that our prediction of ~250ppm for the bulk concentration of Mars ejecta in the present day may only be found preferentially closer to the younger upper regolith of Phobos, and at depth, Mars ejecta fragments are likely to be found in bulk concentrations that are 10–60× less than at the surface of Phobos. We also calculate that ejecta fragments from the regolith of Phobos (Phobos meteorites) may be found on Mars in abundances comparable to lunar meteorites on Earth. [ABSTRACT FROM AUTHOR]

For future space exploration missions, it is important to determine the best method of simulating on Earth cardiovascular and biomechanical conditions for lunar and Martian gravities. For this purpose, we compared exercise performed within a lower body negative pressure (LBNP) and a lower body positive pressure (LBPP) chamber. Twelve subjects underwent a protocol of resting and walking (0.25 Froude) within supine LBNP and upright LBPP simulation. Each protocol was performed in simulated 1/6 G and 3/8 G. We assessed heart rate (HR), mean arterial blood pressure, oxygen consumption (Vo2), normalized stride length, normalized vertical peak ground reaction force, duty factor, cadence, perceived exertion (Borg), and comfort of the subject. A mixed linear model was employed to determine effects of the simulation on the respective parameters. Furthermore, parameters were compared with predicted values for lunar and Martian gravities to determine the method that showed the best agreement. During walking, all cardiovascular and biomechanical parameters were unaffected by the simulation used for lunar and Martian gravities. During rest, HR and Vo2 were lower in supine LBNP compared with upright LBPP. HR, Vo2, and normalized vertical peak ground reaction force obtained with supine LBNP and upright LBPP showed good agreement with predicted values. Since supine LBNP and upright LBPP are lacking significant differences, we conclude that both simulations are suited to simulate the cardiovascular and biomechanical conditions during activity in lunar and Martian gravities. Operational characteristics and the intended application should be considered when choosing either supine LBNP or upright LBPP to simulate partial gravities on Earth. [ABSTRACT FROM AUTHOR]

Abstract: Investigations of the mechanical properties of planetary analog materials are of great importance to improve future mission success and to enhance our understanding of the history and evolution of planetary surfaces and subsurfaces. Determining the stratigraphy of the subsurface using drills and penetrometers implies knowing the mechanical properties of the regolith. Therefore, we investigated the mechanical properties of Martian regolith analogs (JSC Mars-1 and an unaltered basaltic soil from Mojave desert). Penetration force is dependent on the bearing capacity factor (N q ) and the angle of internal friction which is found to be function of the level of compaction and increases with relative density. The bearing capacity factor (N q ) showed an exponential trend with the angle of internal friction. For Mojave soil, (N q ) increased from 64 to 338 with φ increasing from 32 to 41.3° while (N q ) increased from 161 to 3347 with φ increasing from 39.4 to 54.7° for JSC Mars-1. Based on estimation of the bearing capacity factor and the angle of internal friction, we predicted the force of penetration under the Martian gravity using a 1.2cm diameter penetrometer. Under a bulk density of 1240 and 1500kgm−3 in JSC Mars-1 and Mojave soil, 460 and 200N is the estimated force to reach a depth of about 20cm deep. Based on this investigation, distinguishing between different regolith layers on the subsurface of Mars is possible and observable using penetration force. [Copyright &y& Elsevier]

Abstract: Although the mechanisms of neural adaptation to weightlessness and re-adaptation to Earth-gravity have received a lot of attention since the first human space flight, there is as yet little knowledge about how spatial orientation is affected by partial gravity, such as lunar gravity of 0.16g or Martian gravity of 0.38g. Up to now twelve astronauts have spent a cumulated time of approximately 80h on the lunar surface, but no psychophysical experiments were conducted to investigate their perception of verticality. We investigated how the subjective vertical (SV) was affected by reduced gravity levels during the first European Parabolic Flight Campaign of Partial Gravity. In normal and hypergravity, subjects accurately aligned their SV with the gravitational vertical. However, when gravity was below a certain threshold, subjects aligned their SV with their body longitudinal axis. The value of the threshold varied considerably between subjects, ranging from 0.03 to 0.57g. Despite the small number of subjects, there was a significant positive correlation of the threshold with subject age, which calls for further investigation. [Copyright &y& Elsevier]

Vertical wavenumber spectra of Martian gravity waves were obtained for the altitude range 3-32 km from temperature profiles acquired by the Mars Global Surveyor (MGS) radio occultation experiments. The spectra, which cover vertical wavelengths from 2.5 to 15 km, generally show a decline of the spectral density with wavenumber similar to those obtained in the terrestrial stratosphere and mesosphere. The power-law spectral index is typically around -3 except near the low-wavenumber end, and the spectra frequently lie along the theoretical spectrum for saturated gravity waves developed for Earth's atmosphere. The results suggest that gravity wave saturation occurs in the atmosphere of Mars as well as that of Earth. [ABSTRACT FROM AUTHOR]

Abstract: We present a model that resolves the gravity field of Mars down to km-scales: Mars Gravity Model 2011 (MGM2011). MGM2011 uses Newtonian forward-modelling and the MOLA (Mars Orbiter Laser Altimeter) topography model to estimate the short-scale gravity field (scales of ∼3 to ∼125km). Combined with a reference gravity field and the satellite-tracking model MRO110B2, MGM2011 provides surface gravity accelerations and vertical deflections over the entire Martian surface at 3arc-min resolution. MGM2011 is beneficial for gravity field simulation, inversion and statistics, as well as engineering-driven applications such as topographic mapping and inertial navigation. [Copyright &y& Elsevier]

Abstract: Temperature measurements from the Mars Climate Sounder on NASA’s Mars Reconnaissance Orbiter are examined for gravity wave signals using the Stockwell transform, a technique previously applied to terrestrial temperature profiles. An analysis is presented for internal-gravity waves throughout the martian atmosphere for the period July 2007–May 2009, representing a full martian year of data, divided by season. Momentum fluxes observed in the altitude range 200–20Pa are measured as ∼10−5–10−3 Pa, significantly higher than at equivalent altitudes on Earth, and are primarily peaked around the tropics. Observed orographic effects are minimal; the primary observed effects are seasonal. Waves are shown to vary significantly in wavelength with latitude, but are generally approximately zonally symmetric. Horizontal wavelengths are consistently much shorter in the northern hemisphere than the southern. [Copyright &y& Elsevier]

Abstract: An improvement to the Martian gravity field may be achieved by means of future orbiting spacecraft with small eccentricity and low altitude exemplified through a newly proposed mission design that may be tested in upcoming reconnaissance of Mars. Here, the near equatorial orbital character (with an inclination approximating 10°, eccentricity as 0.01 and semi-major axis as 4000km) is considered, and its contribution to Martian gravity field solution is analyzed by comparing it with a hypothetical polar circular orbiter. The solution models are evaluated in terms of the following viewpoints: power spectra of gravity field coefficients, correlations of low degree zonal coefficients, precise orbit determination, and error distribution of both Mars free air gravity anomaly and areoid. At the same time, the contributions of the near equatorial orbiters in low degree zonal coefficients time variations are also considered. The present results show that the near equatorial orbiter allows us to improve the accuracy of the Martian gravity field solution, decrease correlation of low degree zonal coefficients, retrieve much better time variable information of low degree zonal coefficients, improve precise orbit determination, and provide more accurate Mars free air gravity anomaly and areoid around the equatorial region. [Copyright &y& Elsevier]

Abstract: This paper reports the results of a general study carried out on the Periodic Multi-SunSynchronous Orbits (PMSSOs), which the classical Periodic SunSynchronous Orbits (PSSOs) represent a specific solution of. Such orbits allow to obtain cycles of observation of the same region in which the solar illumination regularly varies according to the value of the orbit elements and comes back to the initial condition after a time interval which is multiple of the revisit time. Therefore this kind of orbits meets all the remote sensing applications that need observations of the same area at different local times (for example the reconstruction of the day-nighttime trend of the surface temperature of the planet) and it is particularly suitable to the study of several terrestrial and martian phenomena (diurnal cycle of the hazes and clouds, dynamics of the thermal tides, density variations, meteorology phenomena, etc.). The design of PMSSO is based on the variation of the Right Ascension of the Ascending Node due to the Earth oblateness (referred as basic solution). However, with respect to the basic solution, the analysis of the perturbative effects has demonstrated the need, especially in the case of Mars, to take into account all the superior harmonics of the gravitational field. To this end a corrective factor, to add to the basic equations, has been proposed, allowing a significant saving of propellant (of the order of 2km/s per year). Besides, single and multi-plane satellite constellations have been taken into account in order to improve the repetition of observation and the ground spatial resolution. [Copyright &y& Elsevier]

Abstract: The lack of distinct magnetic signatures observed by Mars Global Surveyor (MGS) over the impact craters and impact-related Quasi-Circular-Depressions (QCDs) with diameters greater than 200km located on South Province, south of 30S and from almost the west of Hellas to Argyre basins, implies a weakly magnetized crust. Using MOLA topography and the recent JPL gravity model of Mars we determine the structure of the crust beneath the craters and impact-related QCDs, and show that the impacts that have created these features were capable of strongly disturbing the crust directly beneath. On the basis of theoretical magnetic anomaly modeling and shock demagnetization models, we demonstrate that the impacts are capable of demagnetizing the entire crust beneath and creating distinct magnetic anomalies at the satellite altitude of 400km in case the crust was appreciably magnetized prior to the impacts. We derive the magnetic anomalies of these features using the radial component of the high-altitude nighttime MGS data. An upper limit of<2×104 A for the bulk magnetization of the crust beneath South Province is estimated, which is about 30times less than that underlying Terra Cimmeria and Terra Sirenum. Similar weak bulk magnetization is obtained for part of the crust surrounding Hellas, Isidis, and Argyre basins. [Copyright &y& Elsevier]

Dawn's ion propulsion system (IPS) is the most advanced propulsion system ever built for a deep-space mission. Aside from the Mars gravity assist it provides all of the post-launch Δ V required for the mission including the heliocentric transfer to Vesta, orbit capture at Vesta, transfer to various Vesta science orbits, escape from Vesta, the heliocentric transfer to Ceres, orbit capture at Ceres, and transfer to the different Ceres science orbits. The ion propulsion system provides a total Δ V of nearly 11 km/s, comparable to the ΔV provided by the 3-stage launch vehicle, and a total impulse of 1.2×10 N s. [ABSTRACT FROM AUTHOR]

Laboratory experiments were conducted to determine the effect of descent-engine plumes on the scouring of surface (microbial) contaminants from a spacecraft. A simulated touchdown of a half-scale lander engine and deck configuration was conducted at Mars atmospheric pressure in the NASA Ames Planetary Aeolian Laboratory. Low-density particles were used for the soil simulant to emulate the lower Martian gravity. The underside of the model had small witness plates with controlled microbial surface populations and particle impact detectors. For both steady-state engine thrust (Viking) and pulsed engine thrust (Phoenix), the exhaust plumes from the engines violently excavated the soil and produced particle-laden eddies beneath the lander that sandblasted the lander underside. The result was nearly complete erosion of microbial contaminants from the spacecraft model with their subsequent deposition in the surrounding area. It is concluded that different planetary protection cleanliness levels for different parts of a spacecraft do not necessarily prevent soil contamination because these cleaning strategies evolved without consideration of the effects of the descent engine plumes. [ABSTRACT FROM PUBLISHER]

Abstract: The convective instability in a rapidly rotating, self-graviting sphere sets up in the form of equatorially symmetric, non-axisymmetric columnar vortices aligned with the rotation axis, carrying heat away in the cylindrical radial direction. In this study, we present numerical simulations of thermal convection and dynamo action driven by internal heating (intended to model a planetary core subject to uniform secular cooling) in a rotating sphere where, from the classical columnar convection regime, we find a spontaneous transition towards an unexpected and previously unobserved flow regime in which an equatorially antisymmetric, axisymmetric (EAA) mode strongly influences the flow. This EAA mode carries heat away along the rotation axis and is the nonlinear manifestation of the first linearly unstable axisymmetric mode. When the amplitude of the EAA mode reaches high enough values, we obtain hemispherical dynamos with one single hemisphere bearing more than 75% of the total magnetic energy at the surface of the rotating sphere. We perform the linear analysis of the involved convective modes and the nonlinear study of this hydrodynamic transition, with and without dynamo action, to obtain scaling laws for the regime boundaries. As secular cooling in a full sphere (i.e. without inner core) is a configuration which has probably been widespread in the early solar system in planetary cores, including the core of Mars, we discuss the possible implications of our results for the past martian dynamo. [Copyright &y& Elsevier]

Frozen orbits are always important foci of orbit design because of their valuable characteristics that their eccentricity and argument of pericentre remain constant on average. This study investigates quasi-circular frozen orbits and examines their basic nature analytically using two different methods. First, an analytical method based on Lagrangian formulations is applied to obtain constraint conditions for Martian frozen orbits. Second, Lie transforms are employed to locate these orbits accurately, and draw the contours of the Hamiltonian to show evolutions of the equilibria. Both methods are verified by numerical integrations in an 80 × 80 Mars gravity field. The simulations demonstrate that these two analytical methods can provide accurate enough results. By comparison, the two methods are found well consistent with each other, and both discover four families of Martian frozen orbits: three families with small eccentricities and one family near the critical inclination. The results also show some valuable conclusions: for the majority of Martian frozen orbits, argument of pericentre is kept at 270° because J has the same sign as J; while for a minority of ones with low altitude and low inclination, argument of pericentre can be kept at 90° because of the effect of the higher degree odd zonals; for the critical inclination cases, argument of pericentre can also be kept at 90°. It is worthwhile to note that there exist some special frozen orbits with extremely small eccentricity, which could provide much convenience for reconnaissance. Finally, the stability of Martian frozen orbits is estimated based on the trace of the monodromy matrix. The analytical investigations can provide good initial conditions for numerical correction methods in the more complex models. [ABSTRACT FROM AUTHOR]

The exploration of planet moons and minor bodies (Avduevskii et al., 1996) is a basic task for comprehending the nature of the processes occurring in our Solar System. Knowing the current state of the moons, we can better describe their past and look into the future. This knowledge is important, first of all, for understanding the origin of the Solar System. Interest in the Martian moon Phobos has been displayed during recent decades. The interest is caused by some questions to which there have been no answers up until now (Sagdeev et al., 1988; 1989). For example, there is a question regarding the origin of the moon: whether it is an asteroid captured by Mars' gravitational field or it is an accumulated body in the Martian orbit. In connection with this, it is interesting to conduct studies aimed at answering this question. If Phobos appears to be an asteroid, then investigations regarding the chemical and isotopic compositions of the moon as the primary matter of the Solar System as well as its evolution are of great interest. As of today, we know that Phobos orbits 9400 km from the center of Mars, with the speed of its revolution being so great that it makes one revolution every one-third of a Martian day (7 h 39 min), outrunning the daily spin of Mars. The strong tidal friction occurring due to the Phobos' position close to Mars reduces the energy of its motion. The moon is slowly approaching the planet's surface and will make impact with it eventually (this should happen over the course of 100 million years) if by that time Mars' gravitational field does not tear it to pieces (this should happen over the course of 50 million years). Phobos is an elongated body with dimensions of 27 × 22× 18.6 km. The measurements of the spectral characteristics performed during the Phobos-2 mission (Ksanformality, Moroz, 1995) have indicated that the reflection spectra of Phobos and Deimos differ substantially from those obtained in observations of Mars, as well as from the spectra of carbonaceous chondrites and other asteroid analogs. The latest scientific results demonstrate that the Martian moons most likely belong to class-D asteroids, although the analogy is not perfect. The results of measuring the reflection characteristics display no bound water on the surface of the Martian moons. However, there are estimations, according to which the thermodynamic conditions on these moons are such that water may stay at a certain depth. Clarifying the issue regarding the presence of water (or hydrated molecules) on Phobos is very important not only from the scientific standpoint, but also from the practical one. Phobos is subject to a strong tidal effect by Mars; therefore, it always keeps the same side turned towards Mars. In connection with this, one of the most interesting characteristics of Phobos is libration. Phobos is a very amazing object among the known synchronously orbiting moons of the planets of the Solar System because it has a large amplitude of libration. The libration effect is always present in a several-body system. [ABSTRACT FROM AUTHOR]

Abstract: Dawn launched in September 2007 on a mission to orbit main belt asteroids (4) Vesta in 2011–2012 and (1) Ceres in 2015. The mission is enabled by an ion propulsion system, which will be operated for the majority of the interplanetary cruise. Following 10.5 months of thrusting that concluded in October 2008, the spacecraft began a period of optimal coast that ended in June 2009. A Mars gravity assist in February 2009 provided an effective Δv of 2.6km/s. The mission flexibility afforded by the use of ion propulsion provided relatively simple targeting at Mars. Additional engineering activities were conducted during the coast period after Mars, including loading new software into the spacecraft''s central computer. This paper describe the progress of the mission, including the approach to Mars, the encounter itself, special activities conducted prior to the resumption of ion thrusting, and the continuation toward Vesta. [Copyright &y& Elsevier]

The article presents a study which examines the characteristics of the five kinds of orbits around Mars. In order to analyze the orbits, researchers used analytical formulations and numerical simulation methods. The five orbits include sun-synchronous orbits, orbits at the critical inclination, frozen orbits, repeating ground track orbits and areostationary orbits. Researchers found that the restrictive definition of the orbits cannot be drawn in the 80 x 80 Mars gravity field.

Abstract: With human exploration of the Moon and Mars on the horizon, research considerations for space suit redesign have surfaced. Review of Apollo mission videos revealed repeated instance of falling during extravehicular activities. A better understanding of how suit weight influences the sagittal dynamic stability of the gait pattern may provide insight for new suit design such that space missions may have more productive extravehicular activities and smaller risk of falls that may cause injuries and damage equipment. Participants walked for 4min in simulated Martian gravity with additional loads of 0%, 15%, 30% and 45% of their body weight. Floquet and Lyapunov analysis techniques were used to quantify the dynamic stability of the sagittal plane gait pattern. Additionally, sagittal plane joint kinematics were evaluated to determine if any modification occurred. Results indicated that weight (i.e., added load) had little effect on the sagittal dynamic stability or joint kinematics while in simulated Martian gravity. Potentially, suit weight may not be a priority for space suit redesign. [Copyright &y& Elsevier]

This paper aims at reducing the sensitivity of the minimum-fuel powered descent trajectory on Mars in the presence of uncertainties and perturbations, using the desensitized optimal control methodology. The lander is modeled as a point mass in a uniform gravitational field, and the engine throttle is considered the control variable, which is bounded between two nonzero settings. Unlike the conventional practice of designing separately the nominal trajectory and a feedback tracking controller, desensitized optimal control strategy incorporates the two designs in synergy, delivering a superior performance. Sensitivities of the final position and velocity with respect to perturbed states at all times are derived and augmented onto the minimum-fuel performance index through penalty factors. The linear quadratic regulator technique is used to design the feedback control gains. To reduce the likelihood of the closed-loop throttle exceeding the prescribed bounds, a multiplicative factor is applied to the feedback gains. This reshapes the nominal trajectory from the well-known maximum-minimum-maximum structure in that the nominal throttle is encouraged to stay away from the prescribed bounds, leaving room for the feedback control. Monte Carlo simulations show that the occurrence of out-of-bound closed-loop throttles is significantly reduced, leading to improved landing precision. [ABSTRACT FROM AUTHOR]

With human exploration of the moon and Mars on the horizon, research considerations for space suit redesign have surfaced. The portable life support system (PLSS) used in conjunction with the space suit during the Apollo missions may have influenced the dynamic balance of the gait pattern. This investigation explored potential issues with the PLSS design that may arise during the Mars exploration. A better understanding of how the location of the PLSS load influences the dynamic stability of the gait pattern may provide insight, such that space missions may have more productive missions with a smaller risk of injury and damaging equipment while falling. We explored the influence the PLSS load position had on the dynamic stability of the walking pattern. While walking, participants wore a device built to simulate possible PLSS load configurations. Floquet and Lyapunov analysis techniques were used to quantify the dynamic stability of the gait pattern. The dynamic stability of the gait pattern was influenced by the position of load. PLSS loads that are placed high and forward on the torso resulted in less dynamically stable walking patterns than loads placed evenly and low on the torso. Furthermore, the kinematic results demonstrated that all joints of the lower extremity may be important for adjusting to different load placements and maintaining dynamic stability. Space scientists and engineers may want to consider PLSS designs that distribute loads evenly and low, and space suit designs that will not limit the sagittal plane range of motion at the lower extremity joints. [ABSTRACT FROM AUTHOR]

Abstract: Building on previous studies of volcanoes around the Hellas basin with new studies of imaging (High-Resolution Stereo Camera (HRSC), Thermal Emission Imaging System (THEMIS), Mars Orbiter Camera (MOC), High-Resolution Imaging Science Experiment (HiRISE), Context Imager (CTX)), multispectral (HRSC, Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (OMEGA)), topographic (Mars Orbiter Laser Altimeter (MOLA)) and gravity data, we define a new Martian volcanic province as the Circum-Hellas Volcanic Province (CHVP). With an area of >2.1millionkm2, it contains the six oldest central vent volcanoes on Mars, which formed after the Hellas impact basin, between 4.0 and 3.6Ga. These volcanoes mark a transition from the flood volcanism that formed Malea Planum ∼3.8Ga, to localized edifice-building eruptions. The CHVP volcanoes have two general morphologies: (1) shield-like edifices (Tyrrhena, Hadriaca, and Amphitrites Paterae), and (2) caldera-like depressions surrounded by ridged plains (Peneus, Malea, and Pityusa Paterae). Positive gravity anomalies are found at Tyrrhena, Hadriaca, and Amphitrites, perhaps indicative of dense magma bodies below the surface. The lack of positive-relief edifices and weak gravity anomalies at Peneus, Malea, and Pityusa suggest a fundamental difference in their formation, styles of eruption, and/or compositions. The northernmost volcanoes, the ∼3.7–3.9Ga Tyrrhena and Hadriaca Paterae, have low slopes, well-channeled flanks, and smooth caldera floors (at tens of meters/pixel scale), indicative of volcanoes formed from poorly consolidated pyroclastic deposits that have been modified by fluvial and aeolian erosion and deposition. The ∼3.6Ga Amphitrites Patera also has a well-channeled flank, but it and the ∼3.8Ga Peneus Patera are dominated by scalloped and pitted terrain, pedestal and ejecta flow craters, and a general ‘softened’ appearance. This morphology is indicative not only of surface materials subjected to periglacial processes involving water ice, but also of a surface composed of easily eroded materials such as ash and dust. The southernmost volcanoes, the ∼3.8Ga Malea and Pityusa Paterae, have no channeled flanks, no scalloped and pitted terrain, and lack the ‘softened’ appearance of their surfaces, but they do contain pedestal and ejecta flow craters and large, smooth, bright plateaus in their central depressions. This morphology is indicative of a surface with not only a high water ice content, but also a more consolidated material that is less susceptible to degradation (relative to the other four volcanoes). We suggest that Malea and Pityusa (and possibly Peneus) Paterae are Martian equivalents to Earth''s giant calderas (e.g., Yellowstone, Long Valley) that erupted large volumes of volcanic materials, and that Malea and Pityusa are probably composed of either lava flows or ignimbrites. HRSC and OMEGA spectral data indicate that dark gray to slightly red materials (often represented as blue or black pixels in HRSC color images), found in the patera floors and topographic lows throughout the CHVP, have a basaltic composition. A key issue is whether this dark material represents concentrations of underlying basaltic material eroded by various processes and exposed by aeolian winnowing, or if the material was transported from elsewhere on Mars by regional winds. Understanding the provenance of these dark materials may be the key to understanding the volcanic diversity of the Circum-Hellas Volcanic Province. [Copyright &y& Elsevier]

Abstract: The martian atmosphere seasonally exchanges CO2 with the surface by repeating condensation and sublimation, causing seasonal growth and decay of the polar CO2 snowcaps. These processes leave two kinds of geodetic signatures, i.e. seasonal changes of the martian gravity field and of surface elevation of the snow-covered regions. Here we study gradual increase of the volume density of the martian snow due to compaction, by combining these two data sets during 1999–2001 covering three martian winters. We found that light fresh snow of slowly becomes denser reaching or more immediately before it thaws. The maximum snow density varies slightly from year to year, and between hemispheres. In the second southern winter, the density became as high as . This might have been caused by a dust storm activity, e.g. increased mixing of silicate particles and/or enhancement of sintering. [Copyright &y& Elsevier]

Abstract  In this paper, we preliminarily explore the possibility of designing a dedicated satellite-based mission to measure the general relativistic gravitomagnetic Lense–Thirring effect in the gravitational field of Mars. The focus is on the systematic uncertainty induced by the multipolar expansion of the areopotential and on possible strategies to reduce it. It turns out that the major sources of bias are the Mars’equatorial radius R and the even zonal harmonics J ℓ, ℓ = 2, 4, 6, . . . of the areopotential. An optimal solution, in principle, consists of using two probes at high-altitudes (a ≈ 9,500–9,600 km) and different inclinations (one probe should fly in a nearly polar orbit), and suitably combining their nodes in order to entirely cancel out the bias due to δ R. The remaining uncancelled mismodelled terms due to δ J ℓ, ℓ = 2, 4, 6, . . . would induce a bias ≲ 1%, according to the present-day MGS95J gravity model, over a wide range of admissible values of the inclinations. The Lense–Thirring out-of-plane shifts of the two probes would amount to about 10 cm year−1. [ABSTRACT FROM AUTHOR]

The article proposes a method for the simulation of gravity in locations other than Earth. The generation of Earth-bound microgravity is described, noting that the microgravity is capable of simulating the gravity on the Moon or Mars or the microgravity involved in experiments on passive or reactive catalytic multiphase flows. An example of applying the method to trickle beds in which flowing gas and liquid are subject to artificial microgravity resulting from the activity of a superconducting magnet is presented.

Abstract: We present results of several years of research and data processing aimed at modelling the Mars gravity field and its longest wavelength time variations. The new solution includes tracking data from Mars Global Surveyor (MGS) from 1998 to 2006 (end of mission) and from Mars Odyssey from 2002 to the spring of 2008; this is the longest analyzed data set from these two orbiter missions as compared to previous works. The new model has been obtained by a team working in Europe, independently from the works of groups at NASA Jet Propulsion Laboratory (JPL) and Goddard Space Flight Center (GSFC), also with totally independent software. Observations consist in two and three-way Doppler measurements (also one way for MGS), and range tracking data collected by the Deep Space Network and have been processed in 4 day arcs, taking into account all disturbing forces of gravitational and non-gravitational origins; for each arc the state vector, drag and solar pressure model multiplying factors, and angular momentum dump parameters are adjusted. The static field (MGGM08A) is represented in spherical harmonics up to degree and order 95 and is very close to previously published models (in terms of spectral components and also over specific features); correlations with the global Mars topography are established and apparent depths of compensation by degree are derived. Lumped zonal harmonics of degree two and three are solved for every 10 days, exhibiting variations in line with previous results (including authors’ ones); the work also shows the difficulty of finding clean signatures (annual and semi-annual) for the zonal coefficient of second degree. The k 2 Love number is also derived from the ensemble of data, as well as from subsets of them; values between 0.110 and 0.130 are found, which are consistent with the existence of a Martian fluid core of significant radius. [Copyright &y& Elsevier]

Abstract: The numerical modeling of Mars’ forced nutation of the real Mars’ model with a radially heterogeneous, compressible, self-gravitating liquid core and elastic mantle is performed. Effects of three-axiality of Mars’ figure are taken into account to compute values for the periods of free core nutation (FCN) and the amplitudes of forced nutations. The effects of the liquid core for different models are of the order of few percents for the prograde semi-annual component and of the order of 10–15% for the semi-annual retrograde component. The absolute values of these effects are of the order of 5–20ms of arc (mas) and 1–3 mas, respectively. Taking into account, that the modern accuracy of VLBI measurements for the case of the Earth is of the order of 0.02 mas, we see, that important results about Mars’ internal structure may be obtained even if the accuracy of Mars’ nutational measurements 1–2 order of magnitude less than accuracy for the Earth. The effects of the shear stress relaxation during long time intervals are studied: the corrections to the nutational amplitudes for prograde semi-annual component are between 8.93 and 9.8, for retrograde semi-annual component are between −4.81 and −8.2ms of arc, and the period of free core nutation is varied in the limits between 257.2 and 295.8 Earth''s solar days. The differences exceed significantly the errors of Mars’ nutational components measurements, and, consequently, these measurements can give new important information about Martian mantle rheology. The possibilities of inferring properties of the interior structure of Mars based on the measurements of its rotation are discussed. [Copyright &y& Elsevier]