Mars Express Spacecraft Research Articles

Magnetosonic waves in the Martian ionosphere driven by upstream proton cyclotron waves: Two-point observations by MAVEN and Mars Express

Recent observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) and Mars Express (MEX) spacecraft have suggested that pressure pulses originating from upstream proton cyclotron waves (PCWs) can “ring” the Martian magnetopause at the same frequency and drive magnetosonic waves in the upper ionosphere of Mars, thereby transporting energy from the solar wind into the ionosphere. However, the limitation of single-spacecraft measurements prevents simultaneous observations of the driver and response of this “ringing” process of the Martian magnetosphere. Here we utilize two-point measurements from MAVEN and MEX to characterize the ringing probability at which upstream PCWs drive compressional fluctuations in the ionospheric magnetic field. We develop an algorithm to identify PCW-driven magnetosonic waves in the upper ionosphere of Mars from the two-point magnetic field data. The derived ringing probability is higher on the dayside, outside strong crustal magnetic fields, and under high solar wind density conditions. We also show that the median power of dayside ionospheric magnetic field fluctuations is enhanced by a factor of ∼2 at corresponding frequencies in the presence of upstream PCWs compared to the median power in the absence of upstream PCWs. These results demonstrate the prevalence of energy deposits into the dayside Martian ionosphere from the solar wind mediated by the PCW-driven ringing of the magnetosphere. Future studies, possibly with new multi-point observations, should address the detailed processes of wave propagation and energy transport through the system and the long-term impact of this chain of processes on the planetary ion heating in the ionosphere and atmospheric loss from Mars.

Phobos photometric properties from Mars Express HRSC observations

Aims. This study aims to analyze Phobos’ photometric properties using Mars Express mission observations to support the Martian Moons exploration mission (MMX) devoted to the investigation of the Martian system and to the return of Phobos samples. Methods. We analyzed resolved images of Phobos acquired between 2004 and 2022 by the High Resolution Stereo Camera (HRSC) on board the Mars Express spacecraft at a resolution ranging from ~30 m px−1 to 330 m px−1. We used data acquired with the blue, green, red, and IR filters of HRSC and the panchromatic data of the Super Resolution Channel (SRC). The SRC data are unique because they cover small phase angles (0.2–10°), permitting the investigation of the Phobos opposition effect. We simulated illumination and geometric conditions for the different observations using the Marx Express and the camera spice kernels provided by the HRSC team. We performed photometric analysis using the Hapke model for both integrated and disk-resolved data. Results. The Phobos phase function is characterized by a strong opposition effect due to shadow hiding, with an amplitude and a half-width of the opposition surge of 2.28±0.03 and 0.0573±0.0001, respectively. Overall, the surface of Phobos is dark, with a geometric albedo of 6.8% in the green filter and backscattering. Its single-scattering albedo (SSA) value (7.2% in the green filter) is much higher than what has been found for primitive asteroids and cometary nuclei and is close to the values reported in the literature for Ceres. We also found a surface porosity of 87%, indicating the presence of a thick dust mantle or of fractal aggregates on the top surface. The SSA maps revealed high reflectance variability, with the blue unit area in the northeast Stickney rim being up to 65% brighter than average, while the Stickney floor is among the darkest regions, with reflectance 10 to 20% lower than average. Photometric modeling of the regions of interest selected in the red and blue units indicates that red unit terrains have a stronger opposition effect and a smaller SSA value than the blue ones, but they have similar porosity and backscattering properties. Conclusions. The HRSC data provide a unique investigation of the Phobos phase function and opposition surge, which is valuable information for the MMX observational planning. The Phobos opposition surge, surface porosity, phase integral, and spectral slope are very similar to the values observed for the comet 67P and for Jupiter family comets in general. Based on these similarities, we formulate a hypothesis that the Mars satellites might be the results of a binary or bilobated comet captured by Mars.

Evidence of Ice‐Rich Layered Deposits in the Medusae Fossae Formation of Mars

AbstractSubsurface reflectors in radar sounder data from the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument aboard the Mars Express spacecraft indicate significant dielectric contrasts between layers in the Martian Medusae Fossae Formation (MFF). Large density changes that create dielectric contrasts are less likely in deposits of volcanic ash, eolian sediments, and dust, and compaction models show that homogeneous fine‐grained material cannot readily account for the inferred density and dielectric constant where the deposits are more than a kilometer thick. The presence of subsurface reflectors is consistent with a multi‐layer structure of an ice‐poor cap above an ice‐rich unit analogous to the Martian Polar Layered Deposits. The volume of an ice‐rich component across the entire MFF below a 300–600 m dry cover corresponds to a global equivalent layer of water of ∼1.5 to ∼2.7 m or ∼30%–50% of the total estimated in the North Polar cap.

Geometric Calibration of the ESA Mars Express Orbiter High Resolution Stereo Camera

AbstractThe high‐resolution stereo camera mounted on the Mars Express (MEX) spacecraft of the European Space Agency is specifically designed for planetary photogrammetry and mapping missions. High‐precision geometric calibration is required to maintain the geometric quality of satellite imaging. This study aimed to develop a Martian geometric calibration model based on the detector look angle and offset matrix to compensate for systematic errors caused by the camera system parameters, Doppler shift measurements, and other parameters of the interior and exterior orientation during positioning. Moreover, the difficulty in identifying high‐precision geometric ground control points from extra‐terrestrial imagery was addressed by proposing an iterative Mars Orbiter Laser Altimeter extraction algorithm based on the similarity measure of terrain relief. Using this algorithm, constraint conditions were established, and a calibration model was introduced to achieve in‐orbit geometric calibration of the MEX satellite. The proposed method is effective in reducing the distortion of the camera in calibration images from 12 pixels to <1 pixel, both before and after calibration. Moreover, the plane accuracy of validation images improved from approximately 900 to 200 m, while elevation accuracy improved from 500 to 100 m, verifying the effectiveness of the proposed method.

Local Electron Density Depletions in the Martian Upper Ionosphere Obtained From MARSIS: Comparison With ASPERA‐3, and MAVEN, and the Connection With Crustal Magnetic Fields

AbstractSteep electron density depletions in the Martian ionosphere are important, especially because they could be regions of significant plasma escape. Local electron density profiles of the Martian ionosphere obtained from the radar sounder onboard the Mars Express spacecraft often show large fluctuations. In some cases, these fluctuations are observed as deep depletions in the electron density. Investigation over the past 12 years of Mars Advanced Radar for Subsurface and Ionospheric Sounding data have revealed over 200 cases of density depletions where the lowest density is less than one fifth of the density in the surrounding regions. These density dips occur both on the dayside and the nightside, with an abundance between solar zenith angles of 50–70° and 100–120°. They occur at all altitudes in the ionosphere. Many of the depletions occur in the southern hemisphere where the crustal magnetic field is stronger and there are more regions where the crustal magnetic field is mostly vertical. In more than half of the cases, the depletion in the local electron density corresponds to a decrease in the electron flux measured with the Analyzer of Space Plasmas and Energetic Atoms electron spectrometer. Several different mechanisms could be responsible for the formation of the depletions, including regions of localized electric fields or magnetic fields creating areas of increased field pressure, escape of the plasma along magnetic field lines depleting density locally, and the density decrease around the photoelectron boundary followed by an increase in the plasma density due to plasma clouds.

Data stream mining for predicting the thermal power consumption of the Mars Express spacecraft

The Mars Express (MEX) spacecraft, operated by the European Space Agency (ESA), has been orbiting Mars for the past 18 years. During this period, it has provided unprecedented scientific data about the red planet, but it has also aged, and its batteries have degraded. Thus, MEX needs careful and accurate power modeling to continue its significant contribution without breaking, twisting, deforming, or failure of any equipment. The power consumed by the autonomous thermal subsystem, that keeps all equipment within its operating temperature in a difficult environment, is the only unknown variable in the spacecraft’s power budget. In this pilot study, we address the task of predicting the thermal power consumption (TPC) of MEX on all of its 33 thermal power lines, learning predictive models from the stream of its telemetry data, which is a task of multi-target regression on data streams. To analyze such data streams and to model the MEX power consumption, we consider both local and global approaches, i.e., predicting each target by a separate model and predicting all targets at once by a single model, respectively. Our evaluation of the considered approaches investigates their performance in predicting the MEX power consumption, the influence of the time resolution of the measurements of TPC on this performance, and the success of the methods in detecting and adapting to change.

Simulation of Phobos gravity field estimation from Tianwen-1 flybys and implications for the modelling of Phobos’ internal structure

ABSTRACT Doppler radio tracking data from Tianwen-1, China’s first Mars mission, could contribute to a better estimate of the gravity field of Phobos. In this study, we show that a determination up to degree and order 3 is feasible by considering five additional flybys of Phobos by the Tianwen-1 spacecraft, in addition to the previous flybys already done by the Mars Express spacecraft, and probably degree and order 5 is within reach. Three cases of mass repartition are considered: (i) a homogeneous case, (ii) a core-dominated Phobos, and (iii) a mantle-dominated Phobos. The case of a mantle-dominated Phobos is the easiest to detect, followed by a homogeneous Phobos, and finally by a core-dominated Phobos. We also discuss implications about the modelling of the internal structure of Phobos.

Co-rotating Solar Wind Disturbances in Radio Sounding Data and Local Measurements

In this paper, we present the results of two series of experiments on radio sounding of near-solarplasma by the signals of the Mars Express and Venus Express spacecraft in 2006 and Mars Express in 2008.The radio sounding data are compared with measurements of the proton concentration near the Earth’s orbiton the Wind satellite. This analysis shows that the general nature of the temporal dynamics of disturbancesobserved in two series of measurements is qualitatively similar. The sequence of amplifications of fluctuationsin the frequency and density of protons indicates that the observed disturbances are associated with co-rotatingregions of interaction of solar wind flows of various velocities

A monitoring campaign (2013–2020) of ESA’s Mars Express to study interplanetary plasma scintillation

AbstractThe radio signal transmitted by the Mars Express (MEX) spacecraft was observed regularly between the years 2013–2020 at X-band (8.42 GHz) using the European Very Long Baseline Interferometry (EVN) network and University of Tasmania’s telescopes. We present a method to describe the solar wind parameters by quantifying the effects of plasma on our radio signal. In doing so, we identify all the uncompensated effects on the radio signal and see which coronal processes drive them. From a technical standpoint, quantifying the effect of the plasma on the radio signal helps phase referencing for precision spacecraft tracking. The phase fluctuation of the signal was determined for Mars’ orbit for solar elongation angles from 0 to 180 deg. The calculated phase residuals allow determination of the phase power spectrum. The total electron content of the solar plasma along the line of sight is calculated by removing effects from mechanical and ionospheric noises. The spectral index was determined as$-2.43 \pm 0.11$which is in agreement with Kolmogorov’s turbulence. The theoretical models are consistent with observations at lower solar elongations however at higher solar elongation ($>$160 deg) we see the observed values to be higher. This can be caused when the uplink and downlink signals are positively correlated as a result of passing through identical plasma sheets.

Machine-learning ready data on the thermal power consumption of the Mars Express Spacecraft

We present six datasets containing telemetry data of the Mars Express Spacecraft (MEX), a spacecraft orbiting Mars operated by the European Space Agency. The data consisting of context data and thermal power consumption measurements, capture the status of the spacecraft over three Martian years, sampled at six different time resolutions that range from 1 min to 60 min. From a data analysis point-of-view, these data are challenging even for the more sophisticated state-of-the-art artificial intelligence methods. In particular, given the heterogeneity, complexity, and magnitude of the data, they can be employed in a variety of scenarios and analyzed through the prism of different machine learning tasks, such as multi-target regression, learning from data streams, anomaly detection, clustering, etc. Analyzing MEX’s telemetry data is critical for aiding very important decisions regarding the spacecraft’s status and operation, extracting novel knowledge, and monitoring the spacecraft’s health, but the data can also be used to benchmark artificial intelligence methods designed for a variety of tasks.

The stability of a liquid-water body below the south polar cap of Mars

Radar data from the Mars Express spacecraft show bright subsurface reflections in the Planum Australe area that could be due to liquid water located at a depth of 1.5 km (Orosei et al., 2018). If this interpretation of the data is correct, the presence of such water would have important implications for the present-day thermal state of the region. In this article, we recalculate the depth of the liquid water and we analyze the influence of the regional thermal properties in the surface heat flow and the subsurface temperatures. We have obtained a new depth to the bright reflector between 1.3 and 1.5 km by using a temperature dependent relative permittivity for the water ice and taking into account the dust content in the area. We show that regional properties in the SPLD moderately influence the thermal state of the area where the liquid water is located. A better knowledge of the porosity profile in the studied area is necessary to constrain surface heat flow and subsurface temperatures accurately. Our findings are in agreement with previous work that shows anomalously high local heat flows would be required to sustain liquid water at this location.

Martian atmospheric water vapor abundances in MY26-30 from Mars Express PFS/LW observations

I report on retrievals of water vapor abundances in the Martian atmosphere using observations by Planetary Fourier Spectrometer Long Wavelength channel (PFS/LW) aboard the Mars Express (MEx) spacecraft. PFS/LW observations used in this work cover almost 4 Martian Years from Ls ~ 331° in MY26 (January 2004) to Ls ~ 209° in MY30 (December 2010). Vapor abundances were retrieved from nadir spectra collected over a range of latitudes, seasons and local hours. Most of the retrieved abundances correspond to daytime observations at local hours from 8 to 17 h. The spatial and temporal coverage of retrieved abundances varies significantly between years of observations, with the best coverage in MY27 and MY29. The average annual water vapor cycle observed by PFS/LW is qualitatively similar to the cycle observed by the Thermal Emission Spectrometer (TES) onboard Mars Global Surveyor (MGS), however the PFS/LW abundances are systematically lower. The likely reason for this difference is the difference in the respective water vapor absorption models. Comparison between PFS/LW abundances for time periods with low atmospheric dust opacity between different years of observations does not show significant interannual variability. PFS/LW abundances are significantly lower than the abundances retrieved from observations by Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on Mars Reconnaissance Orbiter (MRO) in MY29. The difference is likely due to the differences in retrieval models for different spectral regions used by CRISM and PFS/LW to retrieve water vapor abundances and due to different environmental parameters used in the retrievals. PFS/LW abundances are generally similar to abundances retrieved by the SPICAM IR instrument, except in the polar regions during summer. The difference likely arises because of non-uniform vertical distribution of water vapor in the summer polar atmospheres and different sensitivities of the two instruments to vertical distribution of vapor. The PFS/LW observed systematic longitudinal dependence of scaled vapor abundances in the northern tropics with two maxima at longitudes ~30–60°E and ~ 240–270°E. This longitudinal dependence resembles a standing wave forced in the local atmospheric flow by topography and surface thermo-physical properties. The longitudinal non-uniformity of water vapor possibly shows a seasonal dependence increasing around solstices and decreasing around equinoxes. During northern spring in the Northern Polar Region (NPR) PFS/LW observed an increase of vapor near the edge of the seasonal cap interpreted as a buildup of vapor by repeated cycles of water ice freezing and sublimation at the cap edge. Similar, but weaker and longitudinally non-uniform increase in vapor near the edge of the seasonal cap is observed in the Southern Polar Region (SPR) during spring. Tentative signs of water vapor diurnal variability were observed in the PFS/LW data over northern mid-latitudes during late spring and early summer, potentially reflecting vapor exchange between the regolith and the atmosphere.

Relationship Between the Ozone and Water Vapor Columns on Mars as Observed by SPICAM and Calculated by a Global Climate Model

AbstractOzone (O3) in the atmosphere of Mars is produced following the photolysis of CO2 and is readily destroyed by the hydrogen radicals (HOx) released by the photolysis and oxidation of water vapor. As a result, an anti‐correlation between ozone and water vapor is expected. We describe here the O3‐H2O relationship derived from 4 Martian years of simultaneous observations by the SPICAM spectrometer onboard the Mars Express spacecraft. A distinct anti‐correlation is found at high latitudes, where the O3 column varies roughly with the −0.6 power of the H2O column. The O3 and H2O columns are uncorrelated at low latitudes. To evaluate our quantitative understanding of the Martian photochemistry, the observed O3‐H2O relationship is then compared to that predicted by a global climate model with photochemistry. For identical model and observed abundances of H2O, the model underpredicts observed ozone by about a factor of 2 relative to SPICAM when using the currently recommended gas‐phase chemistry. Sensitivity studies employing low‐temperature CO2 absorption cross sections, or adjusted kinetics rates, do not solve this bias. Taking into account potential heterogeneous processes of HOx loss on clouds leads to a significant improvement, but only at high northern latitudes. More broadly, the modeled ozone deficits suggest that the HOx‐catalyzed photochemistry is too efficient in our simulations. This problem is consistent with the long‐standing underestimation of CO in Mars photochemical models, and may be related to similar difficulties in modeling O3 and HOx in the Earth's upper stratosphere and mesosphere.

Precise Orbit Determination of MEX Flyby Phobos Using Simulated Radiometric and Image Data.

A navigation camera or topography camera is a standard payload for deep space missions and the image data are normally used for auto-navigation. In this work, we study the potential contribution of image data in precise orbit determination for deep space spacecraft. The Mars Express (MEX) spacecraft has generated extensive Phobos image data during flybys of Phobos, but these data have not been used in precise orbit determination because of the difficulty in employing these image data. Therefore, we did an experiment using simulated image data as the first step for exploring how to use real image data in precise orbit determination of spacecraft. Our results demonstrate that image data can provide stronger constraints on orbit in the tangential and normal directions than Doppler data. When the image data were used in the MEX orbit determination during the MEX Phobos flyby, the orbit determination accuracies in the tangential and normal directions were significantly improved. This work will provide a reference for real image data processing during MEX Phobos flyby to improve MEX orbit accuracy as well as Phobos ephemeris accuracy.

Observation of Disturbed Plasma Structures in the Environment of the Sun and Near-Earth Space with Radio Sounding and Local Measurements

An experiment on radio sounding of the circumsolar plasma by signals from the Mars Express spacecraft in 2013 was carried out in the period from March 4 through May 31. The investigated characteristics were the frequency of signals in the centimeter and decimeter ranges and the differential frequency. A number of events were recorded in which the intensity of the frequency fluctuations of the signals probing the plasma was several times higher than the background values. As shown by the analysis of observations of solar activity, such as an increase in the flux of X-rays and SOHO LASCO coronagraph data, this is explained by the passage of disturbed plasma streams generated in the solar corona through the spacecraft radio communication path with the Earth. The comparison of the radio transmission data with the results of measurements of the parameters of the near-Earth plasma using the Wind spacecraft in adjacent periods of time. As a result of the analysis of the data on the proton concentration, it became clear that sharp increases in both the average values and fluctuations of this characteristic were also observed near the Earth. The time lag between the events observed in the circumsolar and near-Earth plasma shows that the cause of the disturbances is the increased activity of the same coronal region rotating with the Sun.

Observations of Sounder Accelerated Electrons by Mars Express

AbstractThe electron sensor of the Analyzer of Space Plasmas and Energetic Atoms experiment detects accelerated electrons during pulses of radio emissions from the powerful topside sounder: the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) on board the Mars Express spacecraft. Accelerated electrons are observed at energies up to 400 eV at the times when MARSIS transmits at a frequency between the local plasma frequency and its harmonics (up to 4 times the plasma frequency). When the electron density and magnetic field strength are low ( cm , 10 nT), the accelerated electrons are almost monoenergetic electron beams. An increase in density and magnetic field ( cm , 50 nT) leads to substantial broadening of the energy spectrum of the accelerated electrons. It is concluded that in the latter case, electrons are accelerated by the variable spacecraft potential resulting from the imbalance of the electron and ion currents to the MARSIS antenna during transmission.

A new method for determining the total electron content in Mars’ ionosphere based on Mars Express MARSIS data

We present a new method for determining the total electron content (TEC) in the Martian ionosphere based on the time delay of received radar pulses of the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on board the Mars Express spacecraft. Previous studies of the same dataset have produced differing results for the day-side ionosphere, so it is useful to have an alternative way to compute the TEC in this region. This method iterates a model ionosphere in order to simultaneously match the ionospheric delays of the signals received by the radar’s two channels by finding the model which minimizes the root mean square error (RMSE) between the measured and simulated delays. Topographical information is obtained from data from the Mars Orbiter Laser Altimeter (MOLA) instrument. The model parameters are held constant for a given orbit, and a very good agreement between the simulated and measured delays is obtained. The TEC can then be inverted from the ionospheric model. Matching the delays of both channels simultaneously applies an additional constraint to the model which has not been made in previous studies. The model is additionally validated by matching the simulated pulses with the raw range-compressed measurements for one orbit. Finally, typical model parameters are compared to those obtained by previous studies, which are also simulated. The method is applied to orbits during moderate solar activity, and results show very good agreement with previous studies.

Disturbed Flows in the Inner Solar Wind and Near Earth’s Orbit

Coronal mass ejections from active regions on the Sun can be observed as series of individual events separated in time in the inner solar wind and near-Earth plasma. To find such events we have analyzed experimental data of dual-frequency solar wind radio sounding by the Rosetta and Mars Express spacecraft. The cycles of experiments performed in 2010 and 2011 measured the frequency fluctuations of X- and S-band signals. The temporal variations in the level of frequency fluctuations measured in the inner solar wind have been compared with the time variations in average plasma parameters recorded near Earth’s orbit. Since radio-sounding cycles were sufficiently long, we have managed to record events where significant amplifications of frequency fluctuations in the inner solar wind and increases in the plasma concentration near Earth’s orbit are associated with flare processes in the same active region on the Sun. Here, the amplifications of frequency fluctuations on the east limb occur earlier than near Earth’s orbit, and those on the west limb occur later. The time shift for the west limb turns out to be less than for the east limb. The sign of the time shift and the ratios between its numerical values depend on active region displacement relative to the central meridian due to the rotation of the Sun.

Kinetic Monte Carlo Model for the Precipitation of High-Energy Protons and Hydrogen Atoms into the Atmosphere of Mars with Taking into Account the Measured Magnetic Field

Results of model computations of the interaction of the high-energy protons and hydrogen atoms (H/H+) precipitating into the Martian atmosphere are presented. These computations were performed using a modification of the kinetic Monte Carlo model developed earlier for the analysis of the data from the MEX/ASPERA-3 instrument onboard the Mars Express spacecraft and the MAVEN/SWIA instrument onboard the MAVEN spacecraft. In this modification of the model, an arbitrary (three-dimensional) structure of the magnetic field of Mars is taken into account for the first time. With local measurements of all three components of the magnetic field, not only the flux of protons penetrating into the atmosphere, but also the degradation of the H/H+ flux along the spacecraft orbit and the formation of upward fluxes of protons and hydrogen atoms scattered by the atmosphere, can now be described. A comparison of simulations and measurements of proton fluxes at low altitudes are used to infer the efficiency of charge exchange between the solar wind and the extended Martian hydrogen corona. It was found that the induced magnetic field plays a very important role in the formation of the proton flux back-scattered by the atmosphere and strongly controls its magnitude.

Oblique Reflections of Mars Express MARSIS Radar Signals From Ionospheric Density Structures: Raytracing Analysis

AbstractMars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) radar sounder on board the Mars Express spacecraft revealed oblique reflections coming systematically from apparently stable density structures in the Martian ionosphere. Although these were typically interpreted by assuming a straight line propagation of the sounding signal at the speed of light, the ionospheric plasma is clearly a dispersive medium. Consequently, the ray propagation paths may be significantly bent, and, moreover, the observed time delays need to be interpreted in terms of realistic group velocities of the signal propagation. We select a single particularly well‐pronounced event with oblique reflections observable over a large range of signal frequencies, and we employ raytracing calculations to perform its detailed analysis. An isolated density structure responsible for the reflection of the sounding signal back to the spacecraft is assumed, and the relevant ionospheric signal propagation is properly evaluated. We show that initially oblique sounding signals get progressively more oblique during their propagation, imposing an upper threshold on the angular propagation distance between the spacecraft and the reflecting density structure, in line with the observations. Considering realistic propagation paths further allows us to explain the frequency dependence of the observed time delays and to accurately model the entire event. The obtained results are consistent with the spacecraft passing very close to a spatially limited density structure. We also show that the results obtained using realistic raytracing calculations are significantly different from the results obtained using additional simplifying assumptions.