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Abstract: In the frame of a comparison between Earth, Venus, and Mars, a vision on future geodesy missions to Mars is discussed with particular focus on furthering our understanding of the interior, rotation, and orientation of this terrestrial planet. We explain how radioscience instruments can be used to observe the rotation and orientation and therewith to study the deep interior of Mars and its global atmosphere dynamics. Transponders in X-band and Ka-band are proposed with radio links between a lander or a rover and an orbiter around Mars and/or directly to the Earth. The radio budget links are studied in the frame of possible mission constraints and simulations are performed, which show that important information on the interior of Mars can be obtained from the radioscience data. From the observation of Mars’ orientation in space and of tidal effects on a spacecraft orbiting around Mars we show that it is possible for instance to constrain the dimension and composition of the core, the percentage of light element within the core, and to determine the presence of a pressure-induced mineral-phase transition at the bottom of the mantle. [Copyright &y& Elsevier]

Martian rocky material available on Earth has been so far composed of meteorites and is limited in terms of mass and number. This restricted amount directly impairs the possibility to perform destructive analyses and experiments requiring large mass of sample, such as alteration and hydrothermal experiments. One of the main intents of the current Mars Sample Return (MSR) mission is to bring rock samples from Mars to Earth in the next 10 years. While we will have a geological context for the samples, the total mass that will be collected will also be limited. It is thus crucial to seek analogs of martian rocks, not suffering from this limitation while bearing specific martian properties required by the planned experiments. To overcome this problem in the frame of alteration and hydrothermal experiments, we have built a flexible powder analog system to mimic a typical non-altered shergottite from a chemical and mineralogical perspective. To do so, we have selected the six main mineral phases in weight percentage present in shergottites. For each phase we selected multiple pure terrestrial mineral powders chosen for their chemistry close to their shergottite counterparts. As these mineral phases come from only three different relatively easy access locations, the assemblage is virtually unlimited. From the Shergottite Analog System (SAS), the Shergottite Sample Powder (SSP)-1 analog has been created to focus on serpentinization and abiotic methane formation experiments under martian conditions. The SAS could also be used to create analogs of Oxia Planum, Gale Crater, or Jezero Crater, and to test possible detection interferences and to determine the sensitivity of multiple analytic techniques by varying the selected phases and their proportions. • Martian rock are limited in quantity, thus analogs are required for destructive analyses and experiments. • We have created a terrestrial mineral library to create various martian analogs. • Minerals are kept separated and can be mixed at will to fit the purpose of experiments. • This analog system is created mainly for alteration/hydrothermal experiments. [ABSTRACT FROM AUTHOR]

Abstract: Classified as a terrestrial planet, Venus, Mars, and Earth are similar in several aspects such as bulk composition and density. Their atmospheres on the other hand have significant differences. Venus has the densest atmosphere, composed of CO2 mainly, with atmospheric pressure at the planet''s surface 92 times that of the Earth, while Mars has the thinnest atmosphere, composed also essentially of CO2, with only several millibars of atmospheric surface pressure. In the past, both Mars and Venus could have possessed Earth-like climate permitting the presence of surface liquid water reservoirs. Impacts by asteroids and comets could have played a significant role in the evolution of the early atmospheres of the Earth, Mars, and Venus, not only by causing atmospheric erosion but also by delivering material and volatiles to the planets. Here we investigate the atmospheric loss and the delivery of volatiles for the three terrestrial planets using a parameterized model that takes into account the impact simulation results and the flux of impactors given in the literature. We show that the dimensions of the planets, the initial atmospheric surface pressures and the volatiles contents of the impactors are of high importance for the impact delivery and erosion, and that they might be responsible for the differences in the atmospheric evolution of Mars, Earth and Venus. [Copyright &y& Elsevier]

The Mars Express spacecraft is operating in Mars orbit since early 2004. The Mars Express Radio Science Experiment (MaRS) employs the spacecraft and ground station radio systems (i) to conduct radio occultations of the atmosphere and ionosphere to obtain vertical profiles of temperature, pressure, neutral number densities and electron density, (ii) to conduct bistatic radar experiments to obtain information on the dielectric and scattering properties of the surface, (iii) to investigate the structure and variation of the crust and lithosphere in selected target areas, (iv) to determine the mass, bulk and internal structure of the moon Phobos, and (v) to track the MEX radio signals during superior solar conjunction to study the morphology of coronal mass ejections (CMEs). Here we report observations, results and discoveries made in the Mars environment between 2004 and 2014 over almost an entire solar cycle. [ABSTRACT FROM AUTHOR]

The Mars Express mission was launched in June 2003 and was inserted into orbit around Mars in December 2003. Its main objective is to study the Mars' subsurface, surface, atmosphere and interaction with the solar wind. A secondary objective is to study the martian moons, in particular the largest one Phobos, thanks to a near polar and elliptical orbit which allows the spacecraft to perform close flybys about every five months. The Mars Express data not only consist of high-resolution 3D color images, but also astrometric images, spectra from 0.18 to 20 μm, radar echoes, Doppler signals from gravity experiments, and ion data. A new view of the moons has emerged from this data set, favoring now the idea that they are not captured asteroids, but rather the result of a re-accretion following a major impact on Mars. This unique set of data is available in the ESA Planetary Science Archive (PSA) and mirror imaged in the NASA Planetary Data System (PDS). This paper presents an overview of the Mars Express Phobos flybys, the specificities of their operations and the scientific achievements. [ABSTRACT FROM AUTHOR]

Abstract: Atmospheric angular momentum variations of a planet are associated with the global atmospheric mass redistribution and the wind variability. The exchange of angular momentum between the fluid layers and the solid planet is the main cause for the variations of the planetary rotation at seasonal time scales. In the present study, we investigate the angular momentum variations of the Earth, Mars and Venus, using geodetic observations, output of state-of-the-art global circulation models as well as assimilated data. We discuss the similarities and differences in angular momentum variations, planetary rotation and angular momentum exchange for the three terrestrial planets. We show that the atmospheric angular momentum variations for Mars and Earth are mainly annual and semi-annual whereas they are expected to be “diurnal” on Venus. The wind terms have the largest contributions to the LOD changes of the Earth and Venus whereas the matter term is dominant on Mars due to the CO2 sublimation/condensation. The corresponding LOD variations (ΔLOD) have similar amplitudes on Mars and Earth but are much larger on Venus, though more difficult to observe. [Copyright &y& Elsevier]

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 determination of the ephemeris of the Martian moons has benefited from observations of their plane-of-sky positions derived from images taken by cameras onboard spacecraft orbiting Mars. Images obtained by the Super Resolution Camera (SRC) onboard Mars Express (MEX) have been used to derive moon positions relative to Mars on the basis of a fit of a complete dynamical model of their motion around Mars. Since, these positions are computed from the relative position of the spacecraft when the images are taken, those positions need to be known as accurately as possible. An accurate MEX orbit is obtained by fitting two years of tracking data of the Mars Express Radio Science (MaRS) experiment onboard MEX. The average accuracy of the orbits has been estimated to be around 20–25m. From these orbits, we have re-derived the positions of Phobos and Deimos at the epoch of the SRC observations and compared them with the positions derived by using the MEX orbits provided by the ESOC navigation team. After fit of the orbital model of Phobos and Deimos, the gain in precision in the Phobos position is roughly 30m, corresponding to the estimated gain of accuracy of the MEX orbits. A new solution of the GM of the Martian moons has also been obtained from the accurate MEX orbits, which is consistent with previous solutions and, for Phobos, is more precise than the solution from the Mars Global Surveyor (MGS) and Mars Odyssey (ODY) tracking data. It will be further improved with data from MEX-Phobos closer encounters (at a distance less than 300km). This study also demonstrates the advantage of combining observations of the moon positions from a spacecraft and from the Earth to assess the real accuracy of the spacecraft orbit. In turn, the natural satellite ephemerides can be improved and participate to a better knowledge of the origin and evolution of the Martian moons. [Copyright &y& Elsevier]

Abstract: The BepiColombo Laser Altimeter (BELA) has been selected for flight on board the European Space Agency''s BepiColombo Mercury Planetary Orbiter (MPO). The experiment is intended to be Europe''s first planetary laser altimeter system. Although the proposed system has similarities to the Mercury Laser Altimeter (MLA) currently flying on board NASA''s MESSENGER mission to Mercury, the specific orbit and construction of the MPO force the use of novel concepts for BELA. Furthermore, the base-lined range-finding approach is novel. In this paper, we describe the BELA system and show preliminary results from some prototype testing. [Copyright &y& Elsevier]

Abstract: The Venus Express Radio Science Experiment (VeRa) uses radio signals at wavelengths of 3.6 and 13cm (“X”- and “S”-band, respectively) to investigate the Venus surface, neutral atmosphere, ionosphere, and gravity field, as well as the interplanetary medium. An ultrastable oscillator (USO) provides a high quality onboard reference frequency source; instrumentation on Earth is used to record amplitude, phase, propagation time, and polarization of the received signals. Simultaneous, coherent measurements at the two wavelengths allow separation of dispersive media effects from classical Doppler shift. VeRa science objectives include the following: [(1)] Determination of neutral atmospheric structure from the cloud deck (approximately 40km altitude) to 100km altitude from vertical profiles of neutral mass density, temperature, and pressure as a function of local time and season. Within the atmospheric structure, search for, and if detected, study of the vertical structure of localized buoyancy waves, and the presence and properties of planetary waves. [(2)] Study of the H2SO4 vapor absorbing layer in the atmosphere by variations in signal intensity and application of this information to tracing atmospheric motions. Scintillation effects caused by radio wave diffraction within the atmosphere can also provide information on small-scale atmospheric turbulence. [(3)] Investigation of ionospheric structure from approximately 80km to the ionopause (<600km), allowing study of the interaction between solar wind plasma and the Venus atmosphere. [(4)] Observation of forward-scattered surface echoes obliquely reflected from selected high-elevation targets with anomalous radar properties (such as Maxwell Montes). More generally, such bistatic radar measurements provide information on the roughness and density of the surface material on scales of centimeters to meters. [(5)] Detection of gravity anomalies, thereby providing insight into the properties of the Venus crust and lithosphere. [(6)] Measurement of the Doppler shift, propagation time, and frequency fluctuations along the interplanetary ray path, especially during periods of superior conjunction, thus enabling investigation of dynamical processes in the solar corona. [Copyright &y& Elsevier]

The scientific objectives of a geodetic experiment based on a network of landers, such as NEIGE (NEtlander Ionosphere and Geodesy Experiment) are to improve the current knowledge of Mars'' interior and atmosphere dynamics. Such a network science experiment allows monitoring the motions of the Martian rotation axis with a precision of a few centimeters (or milli-arc-seconds (mas)) over annual and sub-annual periods. Thereto, besides radio tracking of a Mars orbiter from the Earth, radio Doppler shifts between this orbiter and several landers at the planet''s surface will be performed. From the analysis of these radio Doppler data, it is possible to reconstruct the orbiter motion and Mars'' orientation in space. The errors on the orbit determination (position and velocity of the orbiter) have an impact on the geodetic parameters determination from the Doppler shifts and must be removed from the signal in order to achieve a high enough accuracy. In this paper, we perform numerical simulations of the two Doppler signals involved in such an experiment to estimate the impact of the spacecraft angular momentum desaturations on the determination of Mars'' orientation variations. The attitude control of the orbiter needs such desaturation maneuvers regularly repeated. They produce velocity variations that must be taken into account when determining the orbit. For our simulations, we use a priori models of the Martian rotation and introduce the spacecraft velocity variations induced by each desaturation event. By a least-squares adjustment of the simulated Doppler signals, we then estimate the orbiter velocity variations and the parameters of the Mars'' rotation model. We show that these velocity variations are ill resolved when the spacecraft is not tracked, therefore requiring a near-continuous tracking from the Earth to accurately determine the orbit. In such conditions we show that only 15– of lander–orbiter tracking per week allows recovering Mars'' orientation parameters with a precision of a few mas over a period of 1 Martian year. [Copyright &y& Elsevier]

LaRa is a radio-science payload of the ExoMars 2020 mission. The LaRa instrument consists of an X-band transponder accompanied by a set of three antennas and three RF cables, all mounted on the stationary ExoMars surface platform. This instrument is designed to measure with a couple of mHz of accuracy the Doppler shift induced by the variations in Mars rotation and orientation on a direct-to-Earth round-trip radio link. The main scientific objective of the LaRa experiment is to constrain the interior structure of Mars by precisely measuring the nutations of the planet's spin axis. LaRa's measurements will also be used to refine the rotation model of Mars and infer constraints on the dynamic of its atmosphere. This paper aims at characterising the impact of different parameters, related to the design of the LaRa instrument itself and to its operations, on the determination of the rotation and orientation parameters of Mars, and especially on the nutation parameters. Among other quantities, we analyze the effects of the measurements noise, the tracking pass length and occurrence, the mission duration, the radio signal elevation and azimuth in the lander sky, the blackout periods, and the onboard power availability. The work is a comparative study, where we examine different scenarios/cases with respect to a nominal one. From this study, general conclusions can be drawn on the nutation determination from direct-to-Earth Doppler data provided by a landed mission (like InSight). This study provides quantitative inputs that can be used for the programmatic and operation strategy of a radio-science experiment from a lander. In particular, we show that regular tracking from both East and West sides of the lander (i.e. at Earth-rises and Earth-sets) is mandatory to best fit the rotation parameters. Since power issues are frequent on solar-powered landers, we might have to wait for the spacecraft batteries to recharge before operating LaRa. This study shows that turning on LaRa up to one hour after sunrise (i.e. ≤ 15 ∘ of Sun elevation) is acceptable, while requiring higher elevation of the Sun to operate LaRa would significantly reduce its science return. One can finally mention that blackout periods of any kind would compromise the scientific achievement of the LaRa experiment if last too long (hundreds of days). • LaRa (Lander Radio-science) is a scientific payload of the ExoMars 2020 mission. • Sensitivity analysis of the LaRa experiment to Mars' nutation parameters. • Impact of different parameters related to LaRa design and operations. • Inputs for programmatic and operation strategy of lander radio-science experiments. [ABSTRACT FROM AUTHOR]

Two years after InSight's arrival at Mars, the ExoMars 2020 mission will land on the opposite side of the red planet. Similarly to InSight, which carries the RISE (Rotation and Interior Structure Experiment) radio-science experiment, the ExoMars mission will have on board the Lander Radio-science (LaRa) experiment. The X-band transponders on RISE and LaRa, allowing for direct radio-link between the landers and stations on Earth, are dedicated to the investigation of Mars' deep interior through the precise measurement of the planet's rotation and orientation. The benefit of having LaRa after RISE for the determination of the Mars orientation and rotation parameters is demonstrated and the resulting improved constraints on the interior structure of Mars and, in particular, on its core are quantified via numerical simulations. In particular, we show that the amplitudes of the semi-annual prograde ( p 2 ) and the ter-annual retrograde ( r 3 ) nutations will be determined with a precision of 6 and 4 milliarcseconds respectively by combining 700 days of RISE data with 700 days of LaRa data, about 35% more precise than what is expected from RISE alone. The impact of such an improvement on the determination of the core size of Mars is discussed and shown to be significant. • Mars rotation and Orientation Parameters (MOP) determination using Doppler data from landers. • Assessment of the benefit of having LaRa after RISE for the MOP determination. • Implications of the RISE and LaRa combination on our knowledge of the interior of Mars. • An independent validation of the RISE results provided by LaRa. [ABSTRACT FROM AUTHOR]