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Planetary ionospheres undergo many changes at dawn and dusk due to both photochemical and transport processes. The relative importance of these different processes vary depending on a variety of factors, including the amount of solar radiation, the composition of the thermosphere, and the characteristics of any local magnetic fields. This study uses the similarities between the ionospheres on Mars and Earth to examine the behaviour of the ionosphere at dawn and dusk. It has notable implications for comparative aeronomy, as a solid understanding of ionospheric processes on planets with and without magnetic fields is important for characterising the environments of solar and exoplanets, as well as atmospheric evolution over long time scales. The amount of plasma present in the ionosphere was measuring using the total electron content (TEC), and grouped so that both solstices and different phases of the solar cycle could be examined. To allow comparisons between the ionospheres of Mars and Earth, which differ greatly in density, the rate of change of TEC as a function of solar zenith angle was used to compare the plasma production and losses in the main layer of each planetary ionosphere. Examination of the dawn and dusk TEC slopes shows that, to first order, the Martian slopes are symmetric while those at Earth are not. This symmetry is interpreted as an indicator of photochemical equilibrium, and different reasons for deviations from symmetry were explored. The presence or absence of a magnetic field played a large role in shaping plasma transport, with photochemical processes in both ionospheres behaving similarly in the absence of a magnetic field. At Mars, it was found that transport processes were most important at solar maximum, while at Earth transport processes were most important at solar minimum.

International audience; We present the first long-term characterization of ionization layers in the lower ionosphere of Mars (below ∼90 km), a region inaccessible to orbital in-situ observations, based on an analysis of radar echo blackouts observed on Mars Express and the Mars Reconnaissance Orbiter from 2006 to 2017. A blackout occurs when the expected surface reflection is partly or totally attenuated for portions of an observation. Enhanced ionization at altitudes of 60-90 km, below the main ionospheric electron density peak, leads to increased absorption of the radar signal, resulting in the blackouts. We find that (a) MARSIS, operating at frequencies between 1.8 and 5 MHz, suffered more blackouts than SHARAD, which has a higher carrier frequency (20 MHz), (b) there is a clear correlation of blackout occurrence with solar cycle, (c) there is no apparent relationship between blackout occurrence and crustal magnetic fields, and (d) blackouts occur during both nightside and dayside observations, although the peak occurrence is deep on the nightside. Analysis of Mars Atmosphere and Volatile EvolutioN Solar Energetic Particle electron counts between 20 and 200 keV demonstrates that these electrons are likely responsible for attenuating the radar signals. We investigate the minimum SEP electron fluxes required to ionize the lower atmosphere and produce measurable attenuation. When both radars experience a blackout, the SEP electron fluxes are at their highest. Based on several case studies, we find that the average SEP spectrum responsible for a blackout is particularly enhanced at its higher energy end, that is, above 70 keV.

[Aims] To interpret adaptive-optics observations of (216) Kleopatra, we need to describe an evolution of multiple moons orbiting an extremely irregular body and include their mutual interactions. Such orbits are generally non-Keplerian and orbital elements are not constants. [Methods] Consequently, we used a modified N-body integrator, which was significantly extended to include the multipole expansion of the gravitational field up to the order ℓ = 10. Its convergence was verified against the 'brute-force' algorithm. We computed the coefficients Cℓ m, Sℓ m for Kleopatra's shape, assuming a constant bulk density. For Solar System applications, it was also necessary to implement a variable distance and geometry of observations. Our χ2 metric then accounts for the absolute astrometry, the relative astrometry (second moon with respect to the first), angular velocities, and silhouettes, constraining the pole orientation. This allowed us to derive the orbital elements of Kleopatra's two moons. [Results] Using both archival astrometric data and new VLT/SPHERE observations (ESO LP 199.C-0074), we were able to identify the true periods of the moons, P1 = (1.822359 ± 0.004156) d, P2 = (2.745820 ± 0.004820) d. They orbit very close to the 3:2 mean-motion resonance, but their osculating eccentricities are too small compared to other perturbations (multipole, mutual), meaning that regular librations of the critical argument are not present. The resulting mass of Kleopatra, m1 = (1.49 ± 0.16) × 10-12 M· or 2.97 × 1018 kg, is significantly lower than previously thought. An implication explained in the accompanying paper is that (216) Kleopatra is a critically rotating body., Broz, M. et al., This work has been supported by the Czech Science Foundation through grant 21-11058S (M. Brož, D. Vokrouhlický), 20-08218S (J. Hanuš, J. Ďurech), and by the Charles University Research program No. UNCE/SCI/023. This material is partially based upon work supported by the National Science Foundation under Grant No. 1743015. P.V., A.D., M.F. and B.C. were supported by CNRS/INSU/PNP. M.M. was supported by the National Aeronautics and Space Administration under grant No. 80NSSC18K0849 issued through the Planetary Astronomy Program. The work of TSR was carried out through grant APOSTD/2019/046 by Generalitat Valenciana (Spain). This work was supported by the MINECO (Spanish Ministry of Economy) through grant RTI2018-095076-B-C21 (MINECO/FEDER, UE). The research leading to these results has received funding from the ARC grant for Concerted Research Actions, financed by the Wallonia-Brussels Federation. TRAPPIST is a project funded by the Belgian Fonds (National) de la Recherche Scientifique (F.R.S.-FNRS) under grant FRFC 2.5.594.09.F. TRAPPIST-North is a project funded by the University of Liège, and performed in collaboration with Cadi Ayyad University of Marrakesh. E. Jehin is a FNRS Senior Research Associate.

International audience; We study the influence of the solar extreme ultraviolet (EUV) flux intensity on the precipitating ion fluxes as seen by the Solar Wind Ion Analyzer, an energy and angular ion spectrometer aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We defined three periods with significantly different EUV flux intensity (1.6 and 3.2 times the lowest EUV intensity) and compare the precipitating ion flux measured by MAVEN/Solar Wind Ion Analyzer during each period. At low energy [30–650] eV, we find that the median (average) precipitating ion flux during the medium and low EUV periods are, respectively, 1.7 (2.1) and 3 (3.5) times more intense than the flux during the high EUV period. At high energy [650–25,000] eV, a similar trend in the intensity of the precipitating ion flux is observed but with an increase by 50% (46%) and 70% (79%), respectively. A larger EUV flux does therefore not seem to favor heavy ion precipitation into Mars's atmosphere, contrary to modeling prediction and overall expectations.

Mars Express has been exploring Mars since late 2003 giving us fascinating views of the red planet as well as unique science insights. The long-life of Mars Express is an asset in order to understand the long-term evolution of the atmosphere of Mars, and in particular, of the ionosphere and upper atmosphere. Currently, we have about 16 years of ionospheric observations at Mars, which cover near two cycles of solar activity. This is the first time that such a long time series observations can be investigated in other planet rather than Earth. In particular, this work focuses on Mars’ ionospheric behaviour during two consecutive solar minima (23/24 and 24/25) using the same dataset. We use the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on board Mars Express to investigate the total electron content behaviour of the whole atmosphere in relation to key parameters, such as the solar flux, solar illumination, dust storms and Sun-Mars distance. The topside variability of the ionosphere is also investigated through variations in the neutral scale height, and results are supported by ionospheric modelling. The main goal of this study is to investigate whether the ionosphere during the recent solar minimum 24/25 was similar (and to which degree) to the ionosphere at solar minimum 23/24, which was characterised by a pronounced reduction of both the topside and bottomside regions.

The exploration of Callisto is part of the extensive interest in the icy moons characterization. Indeed, Callisto is the Galilean moon with the best-preserved records of the Jovian system formation. Led by the National Space Science Center (NSSC), Chinese Academy of Science (CAS), the planned Gan De mission aims to send an orbiter around Callisto in order to characterize its surface and interior. Potential orbit configurations are currently under study for the Gan De mission proposal.As part of a global characterization of Callisto, its gravity field can be inferred using radio tracking data from an orbiter. Mission characteristics such as orbit type, Earth beta angle and solar elongation will have a direct influence on the recoverability of its gravity field parameters. In this study, we will analyse this influence from closed-loop simulations using the planetary extension of the Bernese GNSS Softwareai.A number of reference orbits with different orbital characteristics will be selected for the Gan De mission and, using an extended force model, will be propagated from different starting dates and different initial Earth beta angles. Realistic Doppler tracking data (2-way X-band Doppler range rate) will be simulated as measurements from ground stations, with a dedicated noise model. These observations will then be used to reconstruct the orbit along with dynamical parameters. The focus of this presentation will be on the quality of the retrieved gravity field parameters and tidal Love number k2.

We study the interaction of three solar wind structures, two stream interaction regions and one interplanetary coronal mass ejection, with Mars' plasma environment during 20-27 November 2007. This period corresponds to the solar minimum between the solar cycles 23 and 24 which was characterized by very low values of the solar wind density and dynamic pressure and low IMF magnitude. During that time the Mars-Express orbit was in the terminator plane, while the Earth, Sun, and Mars were almost aligned, so we use the ACE and STEREO probes as solar wind monitors in order to identify and characterize the structures that later hit Mars. We find that the passage of these structures caused strong variations of in the bow shock location (between 2.2 and 3.0~R$_M$), compression of the magnetospheric cavity (up to 45~\%) and an increased transterminator flow below 2~R$_M$ (by a factor of $\leq$8). This study shows that during times of low solar activity, modest space weather phenomena may cause large variations of plasma flow at Mars., Comment: Published in Journal of Geophysical Research

The Mars' ionospheric behavior during two consecutive solar minima (23/24 and 24/25) is investigated with the same dataset. In particular, we use the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on board Mars Express to investigate the total electron content behavior of the whole atmosphere in relation to the solar irradiance (EUV and X-ray fluxes), the solar zenith angle and the heliocentric distance. The topside variability of the electron density profiles is also investigated through variations in the peak density and neutral scale height. Moreover, the equations of the NeMars empirical model of the Martian ionosphere for low solar activity are tested for both minima. We have found that the topside ionosphere of Mars behaved similarly at both solar minima. However, when considering the bottomside, a pronounced reduction in ionization in particular cases is suggested. In addition, larger TEC values are found during the solar minimum 24/25 in the nightside sector that may indicate possible larger plasma transport than during the minimum 23/24. Finally, this study confirms that the ionospheric empirical NeMars model equations derived by Sanchez-Cano et al. (2016) for the low solar activity period during the solar minimum 23/24 are also valid and accurate for the solar minimum 24/25. The long duration of Mars Express is a critical factor for determining the long-term Martian ionospheric variability, which in turn, is essential for understanding the global evolution of the planet's atmosphere.

This is an open access article under the CC BY-NC-ND license., This work uses a subset of “quiet” MaRS ionospheric dayside observations (MaRSquiet, 2004–2017) and a 1-D photochemical model (IonA-2) to investigate the potential formation processes of the excess electron densities merged with the base of the main ionosphere (Mm). 42% of the investigated MaRS observations contain identified Mm, which occur in a large variety of shapes ranging from smoothly decreasing electron densities to peak structures below the base of M1. The Mm appear over the full range of accessible solar zenith angles (50° - 90°) and are found between approximately 70 and 110 km altitude. Their base is found on average deeper in the atmosphere than the base of the averaged undisturbed MaRS electron density profiles. This indicates a dependence of the Mm formation on energy sources that penetrate deep into the atmosphere. This is supported by a strong positive correlation with increasing solar activity when solar flares, coronal mass ejections, and enhanced short solar X-ray and Ly-α intensities are more common. No relationship is found between the Mm occurrence rate and the magnitude/inclination of the weak crustal crustal magnetic field in MaRSquiet. Investigations with the IonA-2 photochemical model for undisturbed and flare conditions show that the ionization of the local neutral atmosphere by solar X-ray radiation, The Mars Express Radio Science Experiment (MaRS) is funded by the German Space Agency (DLR) under the Grant 50QM1802. Support for Mars Express Radio Science at Stanford University is provided by NASA through a JPL Contract. Support for the Multimission Radio Science Support Team is provided by NASA/JPL. Portions of this research were performed at the Jet Propulsion Laboratory, California Institute of Technology under contract with NASA. We thank everyone involved in the Mars Express project at ESTEC, ESOC, ESAC, JPL, and the ESTRACK and DSN ground stations for their continuous support. K. P. and M. P. acknowledge funding for this project by the Deutsche Forschungsgemeinschaft (DFG) under Grant PA 525/11-1, PA525/11-2 and PA 525/14-1. F.G.G. is funded by the Spanish Ministerio de Ciencia, Innovacion y Universidades, the Agencia Estatal de Investigacion and EC FEDER funds under project RTI2018-100920-J-I00, and acknowledges financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofisica de Andalucia (SEV-2017-0709). Solar Irradiance Platform historical irradiances are provided courtesy of W. Kent Tobiska and Space Environment Technologies. These historical irradiances have been developed with partial funding from the NASA UARS, TIMED, and SOHO missions. We acknowledge support for work conducted on the development of the Mars Climate Database from the European Space Agency (under ESTEC Contract 11369/95/NL/JG(SC)) and from CNES. CNRS (LMD group), the IAA and the UK Particle Physics and Astronomy Research Council (AOPP, Oxford Group) also provided support during the development of the Martian General Circulation Models.

High angular resolution disc-resolved images of (7) Iris collected by VLT/SPHERE instrument are allowed for the detailed shape modelling of this large asteroid revealing its surface features. If (7) Iris did not suffer any events catastrophic enough to disrupt the body (which is very likely) by studying its topography, we might get insights into the early Solar system’s collisional history. When it comes to internal structure and composition, thoroughly assessing the volume and density uncertainties is necessary. In this work, we propose a method of uncertainty calculation of asteroid shape models based on light curve and adaptive optics (AO) images. We apply this method on four models of (7) Iris produced from independent Shaping Asteroids using Genetic Evolution and All-Data Asteroid Modelling inversion techniques and multiresolution photoclinometry by deformation. Obtained diameter uncertainties stem from both the observations from which the models were scaled and the models themselves. We show that despite the availability of high-resolution AO images, the volume and density of (7) Iris have substantial error bars that were underestimated in the previous studies., This work has been supported by the Czech Science Foundation through grant 20-08218S (JH, MB) and by the Charles University Research program No. UNCE/SCI/023. This work has been partially supported by Horizon 2020 grant no. 871149 ‘EPN-2024-RI’.

Planetary Space Weather is the discipline that studies the state of the Sun and how it interacts with the interplanetary and planetary environments. It is driven by the Sun’s activity, particularly through large eruptions of plasma (known as coronal mass ejections, CMEs), solar wind stream interaction regions (SIR) formed by the interaction of high-speed solar wind streams with the preceding slower solar wind, and bursts of solar energetic particles (SEPs) that form radiation storms. This is an emerging topic, whose real-time forecast is very challenging because among other factors, it needs a continuous coverage of its variability within the whole heliosphere as well as of the Sun’s activity to improve forecasting. The long cruise of BepiColombo constitutes an exceptional opportunity for studying the Space Weather evolution within half-astronomical unit (AU), as well as in certain parts of its journey, can be used as an upstream solar wind monitor for Venus, Mars and even the outer planets. This work will present preliminary results of the Space Weather conditions encountered by BepiColombo since its launch until mid-2020, which includes data from the solar minimum of activity and few slow solar wind structures. Data come from three of its instruments that are operational for most of the cruise phase, i.e., the BepiColombo Radiation Monitor (BERM), the Mercury Planetary Orbiter Magnetometer (MPO-MAG), and the Solar Intensity X-ray and particle Spectrometer (SIXS). Modelling support for the data observations will be also presented with the so-called solar wind ENLIL simulations.

Jupiter's upper atmosphere is ∼700 K hotter than predicted based on solar extreme ultraviolet heating alone. The reason for this still remains a mystery and is known as the “energy crisis.” It is thought that the interaction between Jupiter and its dynamic magnetosphere plays a vital role in heating its atmosphere to the observed temperatures. Here, we present a new model of Jupiter's magnetosphere‐ionosphere‐thermosphere‐coupled system where we couple a three‐dimensional atmospheric general circulation model to an axisymmetric magnetosphere model. We find that the model temperatures are on average ∼60 K, with a maximum of ∼200 K, hotter than the model's two‐dimensional predecessor making our high‐latitude temperatures comparable to the lower limit of observations. Stronger meridional winds now transport more heat from the auroral region to the equator increasing the equatorial temperatures. However, despite this increase, the modeled equatorial temperatures are still hundreds of kelvins colder than observed. We use this model as an intermediate step toward a three‐dimensional atmospheric model coupled to a realistic magnetosphere model with zonal and radial variation.

International audience; On 19 October 2014, Mars experienced a close encounter with Comet C/2013 A1 Siding Spring. Using data from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) on board Mars Express (MEX), we assess the interaction of the Martian ionosphere with the comet's coma and possibly magnetic tail during the orbit of their closest approach. The topside ionospheric electron density profile is evaluated from the altitude of the peak density of the ionosphere up to the Mars Express altitude. We find complex and rapid variability in the ionospheric profile along the MEX orbit, not seen even after the impact of a large coronal mass ejection. Before closest approach, large electron density reductions predominate, which could be caused either by comet water‐damping, or comet magnetic field interactions. After closest approach, a substantial electron density rise predominates. Moreover, several extra topside layers are visible along the whole orbit at different altitudes, which could be related to different processes as we discuss.

(10) Hygiea is the fourth largest main belt asteroid and the only known asteroid whose surface composition appears similar to that of the dwarf planet (1) Ceres1,2, suggesting a similar origin for these two objects. Hygiea suffered a giant impact more than 2 Gyr ago3 that is at the origin of one of the largest asteroid families. However, Hygeia has never been observed with sufficiently high resolution to resolve the details of its surface or to constrain its size and shape. Here, we report high-angular-resolution imaging observations of Hygiea with the VLT/SPHERE instrument (~20 mas at 600 nm) that reveal a basin-free nearly spherical shape with a volume-equivalent radius of 217 ± 7 km, implying a density of 1,944 ± 250 kg m− 3 to 1σ. In addition, we have determined a new rotation period for Hygiea of ~13.8 h, which is half the currently accepted value. Numerical simulations of the family-forming event show that Hygiea’s spherical shape and family can be explained by a collision with a large projectile (diameter ~75–150 km). By comparing Hygiea’s sphericity with that of other Solar System objects, it appears that Hygiea is nearly as spherical as Ceres, opening up the possibility for this object to be reclassified as a dwarf planet. © 2019, The Author(s), under exclusive licence to Springer Nature Limited., P.V., A.D. and B.C. were supported by CNRS/INSU/PNP. M.Broz was supported by grant 18-04514J of the Czech Science Foundation. J.H. and J.D. were supported by grant 18-09470S of the Czech Science Foundation and by the Charles University Research Programme no. UNCE/SCI/023. This project has received funding from the European Union's Horizon 2020 research and innovation programmes under grant agreement nos 730890 and 687378. This material reflects only the authors' views, and the European Commission is not liable for any use that may be made of the information contained herein. TRAPPIST-North is a project funded by the University of Liege, in collaboration with Cadi Ayyad University of Marrakech (Morocco). TRAPPIST-South is a project funded by the Belgian Fonds (National) de la Recherche Scientifique (F.R.S.-FNRS) under grant FRFC 2.5.594.09.F. E.J. and M.G. are F.R.S.-FNRS Senior Research Associates.

Context. CM-like asteroids (Ch and Cgh classes) are a major population within the broader C-complex, encompassing about 10% of the mass of the main asteroid belt. Their internal structure has been predicted to be homogeneous, based on their compositional similarity as inferred from spectroscopy and numerical modeling of their early thermal evolution. Aims: Here we aim to test this hypothesis by deriving the density of the CM-like asteroid (41) Daphne from detailed modeling of its shape and the orbit of its small satellite. Methods: We observed Daphne and its satellite within our imaging survey with the Very Large Telescope extreme adaptive-optics SPHERE/ZIMPOL camera and complemented this data set with earlier Keck/NIRC2 and VLT/NACO observations. We analyzed the dynamics of the satellite with our Genoid meta-heuristic algorithm. Combining our high-angular resolution images with optical lightcurves and stellar occultations, we determine the spin period, orientation, and 3D shape, using our ADAM shape modeling algorithm. Results: The satellite orbits Daphne on an equatorial, quasi- circular, prograde orbit, like the satellites of many other large main- belt asteroids. The shape model of Daphne reveals several large flat areas that could be large impact craters. The mass determined from this orbit combined with the volume computed from the shape model implies a density for Daphne of 1.77 ± 0.26 g cm-3 (3 σ). This densityis consistent with a primordial CM-like homogeneous internal structure with some level of macroporosity (≈ 17%). Conclusions: Based on our analysis of the density of Daphne and 75 other Ch/Cgh-type asteroids gathered from the literature, we conclude that the primordial internal structure of the CM parent bodies was homogeneous. Based on observations made with (1) ESO Telescopes at the La Silla Paranal Observatory under programs http://281.C-5011 (PI Dumas), http://099.D-0098 (SPHERE GTO), and h ttp://199.C-0074(A) (PI Vernazza); and (2) the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.The reduced and deconvolved AO images and the 3D shape model are publicly available at h ttp://observations.lam.fr/astero/ and at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz- bin/qcat?J/A+A/623/A132

The ionization of the lower Martian atmosphere and the presence of charged species are fundamental in the understanding of atmospheric electricity phenomena, such as electric discharges, large scale electric currents and Schumann resonances. The present photochemical model of the lower ionosphere of Mars (0–70 km) is developed to compute the concentration of the most abundant charged species (cluster-ions, electrons and charged aerosols) and electric conductivity, at the landing site and epoch of the ExoMars 2016 mission. The main sources of ionization are galactic cosmic rays (during daytime as well as nighttime) and photoionization of aerosols due to solar UV radiation during daytime. Ion and electron attachment to aerosols is another major source of aerosol charging. The steady state concentration of charged species is computed by solving their respective balance equations (also known as continuity equations), which include the source and sink terms of their photochemical reactions. Since the amount of suspended dust can vary considerably and it has an important effect on atmospheric properties, several dust scenarios, in addition to the day-night variations, are considered to characterize the variability of the concentration of charged species. It has been found that, during daytime, aerosols tend to become positively charged due to electron photoemission, and during nighttime, tend to charge negatively due to electron attachment. The most dominant day-night variability in ion and electron concentration occurs when the amount of suspended dust is the largest. The electric conductivity has been found to vary in the 10−13–10−7 S/m range, depending on the altitude, dust scenario and local time.

Cold Atom Interferometry (CAI) is a promising new technology for gravity missions, enabling measurements with a potential error level that is several orders of magnitude lower compared to classical electro-static accelerometers. Whereas the latter typically suffer from high noise at low frequencies, with biases and scale factor instabilities, cold atom interferometers give an absolute measurement and are highly accurate over the entire frequency range. Especially for planetary missions, drift-free cold atom interferometry can be highly beneficial, because it does not need any on-board calibration. In this work we present the improvement of using a CAI instrument, with respect to classic Doppler-tracking technique, to retrieve the gravity field of Venus and Mars. In order to estimate the performances with many parameters (orbit altitude, mission duration, sensitivity) a scalar scale factor is proposed to fit a simulated CAI instrument on Earth orbit to other celestial bodies. The spherical harmonic degree strength of the gravitational field retrieval is estimated and the results presented here agree with Fast Error Propagation Tools.

Aims: Several scientific landers and rovers have reached the Martian surface since the 1970s. Communication between the asset (i.e., lander or rover) and Mars orbiters or Earth antennas uses radio signals in UHF to X-band frequencies passing through the Mars’ ionosphere. It is consequently necessary to take into account electron density variation in the Mars’ ionosphere to correct the refraction of the signal transmitted. Methods: We developed a new empirical model of the Mars’ ionosphere called MoMo. It is based on the large database of Total Electron Content (TEC) derived from the subsurface mode of the Mars Express MARSIS radar. The model provides vertical TEC as a function of solar zenith angle, solar activity, solar longitude and location. For validation, the model is compared with Mars Express radio occultation data as well as with the numerical model IPIM (IRAP Plasmasphere-Ionosphere Model). Results: We discussed the output of the model in terms of climatology behaviour of the Mars’ ionosphere. The output of MoMo is then uses to quantify the impact of the Martian ionosphere for radio-science experiments. From our results, the effect is of the order of 10−3 mm s−1 in Doppler observables especially around sunrise and sunset. Consequently, this new model could be used to support the data analysis of any radio-science experiment and especially for present InSight RISE and futur ExoMars LARA instruments aiming at better understand the deep-interior of Mars.

The paper provides the current understanding of the dust particle dynamics near the surface and in the circummatrian space of the Martian moons based on existing models developed for airless and non-magnetized bodies. In particular we discuss the response of the regolith of the Martian moons to exposure to radiation, the dynamics of charged dust on their surfaces, their plasma environments, the models and indirect observations of their putative dust tori. It is concluded that there is a good theoretical understanding of the behavior of the dynamics of dust particles near the moons Phobos and Deimos. Current models predict dust rings near orbits of the Martian moons based on detailed estimates for the sources and sinks of the dust particles as well as their lifetimes. However, there is no compelling observational evidence for the predicted dust torus around Phobos or Deimos orbits, and there are no observations yet of dust dynamics near their surfaces. Naturally, in order to detect the motion of dust near the surfaces of these moons, and their dust tori we need measurements using a complementary set of sensitive instruments, including impart dust detectors, electric field sensors, and optical cameras in future missions to Mars and its moons.

The electron density distributions of the lower ionospheres of Mars and Venus are mainly dependent on the solar X-ray and EUV flux and the solar zenith angle. The influence of an increasing solar flux is clearly seen in the increase of the observed peak electron density and total electron content (TEC) of the main ionospheric layers. The model “Ionization in Atmospheres” (IonA) was developed to compare ionospheric radio sounding observations, which were performed with the radio science experiments MaRS on Mars Express and VeRa on Venus Express, with simulated electron density profiles of the Mars and Venus ionospheres. This was done for actual observation conditions (solar flux, solar zenith angle, planetary coordinates) from the bases of the ionospheres to ∼160 km altitude. IonA uses models of the neutral atmospheres at ionospheric altitudes (Mars Climate Database (MCD) v4.3 for Mars; VenusGRAM/VIRA for Venus) and solar flux information in the 0.5–95 nm wavelength range (X-ray to EUV) from the SOLAR2000 data base. The comparison between the observed electron density profiles and the IonA profiles for Mars, simulated for a selected MCD scenario (background atmosphere), shows that the general behavior of the Mars ionosphere is reproduced by all scenarios. The MCD “low solar flux/clear atmosphere” and “low solar flux/MY24” scenarios agree best (on average) with the MaRS set of observations, although the actual Mars atmosphere seemed to be still slightly colder at ionospheric altitudes. For Venus, the VenusGRAM model, based on VIRA, is too limited to be used for the IonA simulation of electron density profiles. The behavior of the V2 peak electron density and TEC as a function of solar zenith angle are in general reproduced, but the peak densities and the TEC are either over- or underestimated for low or high solar EUV fluxes, respectively. The simulated V2 peak altitudes are systematically underestimated by 5 km on average for solar zenith angles less than 45° and the peak altitudes rise for zenith angles larger than 60°. The latter is the opposite of the observed behavior. The explanation is that VIRA and VenusGRAM are valid only for high solar activity, although there is also very poor agreement with VeRa observations from the recent solar cycle, in which the solar activity increases to high values. The disagreement between the observation and simulation of the Venus electron density profiles proves, that the true encountered Venus atmosphere at ionospheric altitudes was denser but locally cooler than predicted by VIRA.

The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) onboard the European Space Agency's Mars Express (MEX) spacecraft routinely detects evidence of localized plasma density structures in the Martian dayside ionosphere. Such structures, likely taking the form of spatially extended elevations in the plasma density at a given altitude, give rise to oblique reflections in the Active Ionospheric Sounder data. These structures are likely related to the highly varied Martian crustal magnetic field. In this study we use the polar orbit of MEX to investigate the repeatability of the ionospheric structures producing these anomalous reflections, examining data taken in sequences of multiple orbits which pass over the same regions of the Martian surface under similar solar illuminations, within intervals lasting tens of days. Presenting three such examples, or case studies, we show for the first time that these oblique reflections are often incredibly stable, indicating that the underlying ionospheric structures are reliably reformed in the same locations and with qualitatively similar parameters. The visibility, or lack thereof, of a given oblique reflection on a single orbit can generally be attributed to variations in the crustal field within the ionosphere along the spacecraft trajectory. We show that, within these examples, oblique reflections are generally detected whenever the spacecraft passes over regions of intense near-radial crustal magnetic fields (i.e., with a “cusp-like” configuration). The apparent stability of these structures is an important feature that must be accounted for in models of their origin.

Several models of the martian ionosphere have been developed in the last years. In this paper, a new empirical model for the dayside electron density of the martian ionosphere (primary and secondary layer), called NeMars, is described. The model is mainly based on MARSIS AIS data (Active Ionospheric Sounding from the Mars Advanced Radar and Ionospheric Sounding experiment aboard Mars Express mission) and to a lesser extent on radio occultation data from the Mars Global Surveyor mission. The model is able to reproduce to a reasonable degree the main characteristics of the electron density profiles obtained with the two techniques by considering solar zenith angle, solar flux F-10.7 as a proxy of the solar activity, and heliocentric distance. The model partially assumes the Chapman theory, the scale height for the main layer of the model varies with the solar zenith angle and the altitude, and the Chapman-like photochemical processes dominate diffusion up to about 200 km altitude. In addition, we assess the level of importance that parameters like heliocentric distance, solar longitude, solar activity or solar zenith angle have on the formation of the ionosphere. Eventually, we compare the Total Electron Content (TEC) derived from NeMars model with the values obtained from the MARSIS radar operating in subsurface mode.

In the recent years, the presence of dications in the atmospheres of Mars, Venus, Earth and Titan has been modeled and assessed. These studies also suggested that these ions could participate to the escape of the planetary atmospheres because a large fraction of them is unstable and highly energetic. When they dissociate, their internal energy is transformed into kinetic energy which may be larger than the escape energy. The goal of this study is to assess the impact of the doubly-charged ions in the escape of CO2-dominated planetary atmospheres and to compare it to the escape of thermal photo-ions. We solve a Boltzmann transport equation at daytime taking into account the dissociative states of CO 2 + + for a simplified single constituent atmosphere of a case-study planet. We compute the escape of fast ions using a Beer–Lambert approach. We study three test-cases. On a Mars-analog planet in today’s conditions, we retrieve the measured electron escape flux. When comparing the two mechanisms (i.e. excluding solar wind effects, sputtering, etc.), the escape due to the fast ions issuing from the dissociation of dications may account for up to 6% of the total and the escape of thermal ions for the remaining. We show that these two mechanisms cannot explain the escape of the atmosphere since the magnetic field vanished and even contribute only marginally to this loss. We show that with these two mechanisms, the atmosphere of a Mars analog planet would empty in another giga years and a half. At Venus orbit, the contribution of the dications in the escape rate is negligible. When simulating the hot Jupiter HD 209458 b, the two processes cannot explain the measured escape flux of C+. This study shows that the dications may constitute a source of the escape of planetary atmospheres which had not been taken into account until now. This source, although marginal, is not negligible. The influence of the photoionization is of course large, but cannot explain alone the loss of Mars’ atmosphere nor the atmospheric escape of HD 209458 b.

Solar cycle variations in solar radiation create notable changes in the Martian ionosphere, which have been analysed with Mars Express plasma datasets in this paper. In general, lower densities and temperatures of the ionosphere are found during the low solar activity phase, while higher densities and temperatures are found during the high solar activity phase. In this paper, we assess the degree of influence of the long term solar flux variations in the ionosphere of Mars.

The closest ever fly-by of the Martian moon Phobos, performed by the European Space Agency's Mars Express spacecraft, gives a unique opportunity to sharpen and test the Planetary Radio Interferometry and Doppler Experiments (PRIDE) technique in the interest of studying planet - satellite systems. The aim of this work is to demonstrate a technique of providing high precision positional and Doppler measurements of planetary spacecraft using the Mars Express spacecraft. The technique will be used in the framework of Planetary Radio Interferometry and Doppler Experiments in various planetary missions, in particular in fly-by mode. We advanced a novel approach to spacecraft data processing using the techniques of Doppler and phase-referenced very long baseline interferometry spacecraft tracking. We achieved, on average, mHz precision (30 {\mu}m/s at a 10 seconds integration time) for radial three-way Doppler estimates and sub-nanoradian precision for lateral position measurements, which in a linear measure (at a distance of 1.4 AU) corresponds to ~50 m., Comment: 9 pages, 14 figures. Astronomy and Astrophysics, accepted on 2016/05/31

Venus is Earth's near twin in mass and radius, and our nearest planetary neighbour, yet conditions there are very different in many respects. Its atmosphere, mostly composed of carbon dioxide, has a surface temperature and pressure far higher than those of Earth. Only traces of water are found, although it is likely that there was much more present in the past, possibly forming Earth-like oceans. Here we discuss how the first year of observations by Venus Express brings into focus the evolutionary paths by which the climates of two similar planets diverged from common beginnings to such extremes. These include a CO2-driven greenhouse effect, erosion of the atmosphere by solar particles and radiation, surface-atmosphere interactions, and atmospheric circulation regimes defined by differing planetary rotation rates.

International audience; The origin of Phobos and Deimos is still an open question. Currently, none of the three proposed scenarios for their origin (intact capture of two distinct outer solar system small bodies, co-accretion with Mars, and accretion within an impact-generated disk) are. able to reconcile their orbital and physical properties. Here. we investigate the expected mineralogical composition and size of the grains from which the moons once accreted assuming they formed within an impact-generated accretion disk. A comparison of our results with the present-day spectral properties of the moons allows us to conclude that their building blocks cannot originate from a magma phase, thus preventing their formation in the innermost part of the disk. Instead, gas-to-solid condensation of the building blocks in the outer part of an extended gaseous disk is found as a possible formation mechanism as it does allow reproducing both the spectral and physical properties of the moons. Such a scenario may finally reconcile their orbital and physical properties, alleviating the need to invoke an unlikely capture scenario to explain their physical properties.

Since 2005 the Mars Advanced Radar and Ionospheric Sounding experiment (MARSIS) aboard Mars Express has acquired a unique dataset on the ionosphere of Mars made up of ionospheric soundings taken by the instrument working in its active ionospheric sounding (AIS) mode. These soundings play a role similar to those of modern Terrestrial digisondes in the analysis of our planet ionosphere and have allowed us to dramatically improve our knowledge about the Martian ionosphere. This paper describes this kind of data, which are available from the public Planetary Science Archive, and introduces the MAISDAT tool developed by the European Space Agency to analyze and derive the vertical profile of electron density. Comparisons with radio occultation profiles obtained from Mars Express Radio Science instrument are performed to validate the procedure used in this study.

We report the first detection of two emission lines of the atomic oxygen doubly-charged ion at 495.8911 and 500.6843 nm in the terrestrial upper atmosphere. They correspond to the transitions 1D2-3P1 and 1D2-3P2 of the O++ ion, respectively. The measurements were performed on 30 October 2003 during the "Halloween" storms, with the Ultraviolet and Visual Echelle Spectrograph (UVES) mounted on the Very Large Telescope (VLT) in Chile. The intensities of these emissions are ~70 mRayleigh, and ~260 mRayleigh, respectively. These emissions constitute a new diagnostic of the state of the ionosphere.

The paper presents the concept, the objectives, the approach used, and the expected performances and accuracies of a radioscience experiment based on a radio link between the Earth and the surface of Mars. This experiment involves radioscience equipment installed on a lander at the surface of Mars. The experiment with the generic name lander radioscience (LaRa) consists of an X-band transponder that has been designed to obtain, over at least one Martian year, two-way Doppler measurements from the radio link between the ExoMars lander and the Earth (ExoMars is an ESA mission to Mars due to launch in 2013). These Doppler measurements will be used to obtain Mars’ orientation in space and rotation (precession and nutations, and length-of-day variations). More specifically, the relative position of the lander on the surface of Mars with respect to the Earth ground stations allows reconstructing Mars’ time varying orientation and rotation in space. Precession will be determined with an accuracy better by a factor of 4 (better than the 0.1% level) with respect to the present-day accuracy after only a few months at the Martian surface. This precession determination will, in turn, improve the determination of the moment of inertia of the whole planet (mantle plus core) and the radius of the core: for a specific interior composition or even for a range of possible compositions, the core radius is expected to be determined with a precision decreasing to a few tens of kilometers. A fairly precise measurement of variations in the orientation of Mars’ spin axis will enable, in addition to the determination of the moment of inertia of the core, an even better determination of the size of the core via the core resonance in the nutation amplitudes. When the core is liquid, the free core nutation (FCN) resonance induces a change in the nutation amplitudes, with respect to their values for a solid planet, at the percent level in the large semi-annual prograde nutation amplitude and even more (a few percent, a few tens of percent or more, depending on the FCN period) for the retrograde ter-annual nutation amplitude. The resonance amplification depends on the size, moment of inertia, and flattening of the core. For a large core, the amplification can be very large, ensuring the detection of the FCN, and determination of the core moment of inertia. The measurement of variations in Mars’ rotation also determines variations of the angular momentum due to seasonal mass transfer between the atmosphere and ice caps. Observations even for a short period of 180 days at the surface of Mars will decrease the uncertainty by a factor of two with respect to the present knowledge of these quantities (at the 10% level). The ultimate objectives of the proposed experiment are to obtain information on Mars’ interior and on the sublimation/condensation of CO2 in Mars’ atmosphere. Improved knowledge of the interior will help us to better understand the formation and evolution of Mars. Improved knowledge of the CO2 sublimation/condensation cycle will enable better understanding of the circulation and dynamics of Mars’ atmosphere.

This article reviews our understanding of the ionospheres in the solar system. It provides some basic information on the sources and sinks of the ionospheric plasma, its dynamics, the energetics and the coupling to the neutral atmosphere. Ionospheres in the solar system are reviewed and comparative ionospheric topics are discussed.

Temperature variations of Titan's upper atmosphere due to the plasma interaction of the satellite with Saturn's magnetosphere and Titan's high altitude monomer haze particles can imply an offset of up to ±30K from currently estimated model profiles. We incorporated these temperature uncertainties as an offset into the recently published Vervack et al. (2004) (Icarus, Vol. 170, 91-112) engineering model and derive extreme case (i.e. minimum and maximum profiles) temperature, pressure, and density profiles. We simulated the Huygens probe hypersonic entry trajectory and obtain, as expected, deviations of the probe trajectory for the extreme atmosphere models compared to the simulation based on the nominal one. These deviations are very similar to the ones obtained with the standard Yelle et al. (1997) (ESA SP-1177) profiles. We could confirm that the difference in aerodynamic drag is of an order of magnitude that can be measured by the probe science accelerometer. They represent an important means for the reconstruction of Titan's upper atmospheric properties. Furthermore, we simulated a Cassini low Titan flyby trajectory. No major trajectory deviations were found. The atmospheric torques due to aerodynamic drag, however, are twice as high for our high temperature profile as the ones obtained with the Yelle maximum profile and more than 5 times higher than the worst case estimations from the Cassini project. We propose to use the Cassini atmospheric torque measurements during its low flybys to derive the atmospheric drag and to reconstruct Titan's upper atmosphere density, pressure, and temperature. The results could then be compared to the reconstructed profiles obtained from Huygens probe measurements. This would help to validate the probe measurements and decrease the error bars.

International audience; We present a new method that uses high-resolution spectroscopy in the visible wavelength domain to measure planetary winds. A rotating atmosphere illuminated by the Sun induces a Doppler shift in the back-scattered solar light. Its analysis with a cross-dispersed echelle spectrometer allows the direct determination of both the wind speed and direction. We describe in this paper the image and data processing algorithms used in the method and implemented in a data reduction and analysis package. Since the velocity of planetary winds leads to Doppler shifts smaller than the width of the solar lines, accurate Doppler measurements are performed by running the algorithm proposed by [CITE], which is an optimum technique using the full available spectral information. We apply the method to Io as a test case, a small slowly-rotating body with no atmosphere, to measure its solid rotation. The observations span wavelengths from 414 to 621 nm and were carried out with the Ultraviolet and Visual Echelle Spectrograph (UVES) on the 8.2 m Kueyen unit at the Very Large Telescope (VLT ESO). The results we obtain for Io validate the principle of the method by optimally measuring the well-known surface rotational velocity of this moon, with an uncertainty smaller than 2 m s-1. However, the analysis of the set of observations shows that systematic errors are large and one needs to consider the retrieved velocity as a lower limit.

International audience; The Mars Express Radio Science (MaRS) experiment on board Mars Express has been providing radio-occultation data since early 2004. The analysis method currently used to retrieve neutral atmosphere and ionosphere profiles is based on the resolution of a complex inverse problem. The solution to such a problem is obtained under strong assumptions on the atmosphere and the ionosphere and with some limitations. Here we developed a novel method for radio-occultation data analysis based on a direct approach which overcomes some of the difficulties related to the standard inversion. This new method is based on a numerical model of the atmosphere and the ionosphere of Mars computing the propagation of the radio waves from the spacecraft to the receiver on Earth. The main interest of such an approach lies in the intrinsic and coherent coupling between the neutral part and the ionized part of the planetary environment, which gives physical constrains on the retrieved profiles. We have applied this new method to radio occultation experiments performed by MaRS, and we present the results obtained in two different occultation configurations. We discuss the differences which emerge from the standard analysis and the gain that such a method can give to the analysis of planetary environments.

Incoherent scatter radar data from 63 experiments during the period 1984–1997 have been used to update earlier published climatologies of ion drifts and neutral thermospheric winds at Millstone Hill. Data are binned according to season, solar activity, geomagnetic activity, and local solar time. The derived ion drift patterns are similar to those previously published, but we now find that the main effect of the increased magnetic activity is an enhancement of the usual nighttime west-ward ion drift. A tidal decomposition of the winds from geomagnetically quiet conditions is carried out for each season/solar activity level to extract diurnal means, diurnal amplitudes and phases, and semidiurnal components. These winds are compared with previous results at Millstone Hill and the HWM-93 model. Using our expanded wind database, statistically significant semidiurnal components are now found in both summer and winter, at both solar maximum and solar minimum. Our bin-averaged results confirm earlier published findings that at all seasons the diurnal mean winds are more strongly equatorward and the diurnal amplitudes are stronger at solar cycle minimum than at solar cycle maximum. Diurnal amplitudes derived in the present work are larger than those found previously because we now use a smaller value for the O+, O collision frequency. Differences in the diurnal mean and diurnal amplitude between recent solar minimum data (1993–1997) and data from the previous solar minimum (1984–1986) are attributed to a difference in the EUV flux as inferred from Millstone Hill electron density data which one would not expect from the F10.7 index. This affects the ion drag and apparently also the relative importance of the EUV and high latitude heat sources.

Solar cycle variations in solar radiation create density changes in any planetary ionosphere, which are well established in the Earth's case. At Mars, however, the ionospheric response to such changes is not well understood. We show the solar cycle impact on the topside ionosphere of Mars, using data from the Mars Advance Radar for Subsurface and Ionospheric Sounding (MARSIS) on board Mars Express. Topside ionospheric variability during the solar cycle is analyzed through neutral scale height behavior. For moderate and high solar activity phases, the topside electron density profile is reproduced with an altitude-variable scale height. However, for the period of extremely low solar activity in 2008 and 2009, the topside was smaller in density than in the other phases of the solar cycle, and there is evidence that it could be reproduced with either a constant scale height or a height-variable scale height with lower electron density. Moreover, the ionosphere during this time did not show any apparent dependence on the EUV flux. This singular behavior during low solar activity may respond to the presence of an induced magnetic field which can penetrate to lower ionospheric altitudes than in other phases of the solar cycle due to the reduced thermal pressure. Numerical simulations of possible scenarios for two different solar cycle phases indicate that this hypothesis is consistent with the observations.

International audience; To study the transport of the ionospheric plasma on Mars, we have included a 3D multifluid dynamical core in a Martian General Circulation Model (GCM). Vertical transport modifies the ion density above ~160 km on the dayside, especially the ions produced at high altitudes like O+, N+ and C+. Near the exobase, the dayside to nightside flow velocity reaches few hundreds of m/s, due to a large horizontal pressure gradient. Comparison with MEX/ASPERA-3 measurements between 290 - 500 km, suggests this flow could account for at least 20% of the flow produced by the solar wind. This flow is not sufficient to populate substantially the nightside ionosphere at high altitudes, in agreement with recent observations, because of a strong nightside downward flow produced by vertical pressure gradient. The O2+ and NO+ ion densities on the nightside at low altitudes (~130 km) are modified by this downward flow, compared to simulated densities without ion dynamics, while other ions are lost by chemical reactions. Variability at different time scales (diurnal, seasonal and solar cycle) are studied. We simulate diurnal and seasonal variations of the ionospheric composition due to the variability of the neutral atmosphere and solar flux at the top of the atmosphere. The ionospheric dynamics are not strongly affected by seasons and solar cycles and the retroaction of the ionosphere on the neutral atmosphere temperature and velocity is negligible compared to other physical processes below the exobase.

In this paper, we present a unique data set of more than one year's worth of regular observations of comet C/2013 A1(Siding Spring) with TRAPPIST in Chile, along with low-resolution spectra obtained with the ESO/VLT FORS 2 instrument. The comet made a close approach to Mars on October 19, 2014 and was then observed by many space and ground-based telescopes. We followed the evolution of the OH, NH, CN, $\mathrm{C_3}$, and $\mathrm{C_2}$ production rates as well as the $Af\rho$ parameter as a proxy for the dust production. We detected an outburst two weeks after perihelion, with gas and dust production rates being multiplied by a factor five within a few days. By modelling the shape of the CN and $\mathrm{C_2}$ radial profiles, we determined that the outburst happened around on November 10 around 15:30 UT ($\pm$ 5h) and measured a gas ejection velocity of $1.1\pm0.2$ km/s. We used a thermal evolution model to reproduce the activity pattern and outburst. Our results are consistent with the progressive formation of a dust mantle explaining the shallow dependence of gas production rates, which may be partially blown off during the outburst. We studied the evolution of gas composition, using various ratios such as CN/OH, $\mathrm{C_2}$/OH, or $\mathrm{C_3}$/OH, which showed little or no variation with heliocentric distance including at the time of the outburst. This indicates a relative level of homogeneity of the nucleus composition., Comment: Submitted to Astronomy and Astrophysics

[1] The vertical structure of the nightside ionosphere of Mars and its dependence on solar zenith angle are currently poorly determined, as is the importance of two key sources of nightside plasma, electron precipitation and transport of dayside plasma. We examined 37 electron density profiles of the ionosphere of Mars at solar zenith angles of 101°–123° obtained by the Mars Express Radio Science Experiment (MaRS) between 18 August and 1 October 2005. In general, solar activity was low during this period, although several solar energetic particle events did occur. The results show that (1) trends in peak electron density and altitude with solar zenith angle are consistent with transport of dayside plasma as an important plasma source up to 115°, but not higher; (2) peak altitudes of around 150 km observed at larger (>115°) solar zenith angles are consistent with simulated plasma production by electron precipitation; and (3) peak altitudes observed during solar energetic particle events are at 90 km, consistent with accepted models. Solar energetic particle events can be the main source of nightside plasma. These results challenge current models of the nightside ionosphere, including their implications for plasma sources. The total electron content is correlated with peak electron density, requiring explanation. Due to the geographical distribution of this data set (latitudes poleward of 38°N), we do not explore the influence of crustal field strength and direction on the nightside ionosphere.

The most significant aspect of the general circulation of the atmosphere of Venus is its retrograde super-rotation. A complete characterization of this dynamical phenomenon is crucial for understanding its driving mechanisms. Here we report on ground-based Doppler velocimetry measurements of the zonal winds, based on high resolution spectra from the UV–Visual Echelle Spectrograph (UVES) instrument at ESO’s Very Large Telescope. Under the assumption of predominantly zonal flow, this method allows the simultaneous direct measurement of the zonal velocity across a range of latitudes and local times in the day side. The technique, based on long slit spectroscopy combined with the high spatial resolution provided by the VLT, has provided the first ground-based characterization of the latitudinal profile of zonal wind in the atmosphere of Venus, the first zonal wind field map in the visible, as well as new constraints on wind variations with local time. We measured mean zonal wind amplitudes between 106 ± 21 and 127 ± 14 m/s at latitudes between 18°N and 34°S, with the zonal wind being approximately uniform in 2.6°-wide latitude bands (0.3 arcsec at disk center). The zonal wind profile retrieved is consistent with previous spacecraft measurements based on cloud tracking, but with non-negligible variability in local time (longitude) and in latitude. Near 50° the presence of moderate jets is apparent in both hemispheres, with the southern jet being stronger by ∼10 m/s. Small scale wind variations with local time are also present at low and mid-latitudes.

[1] One of the objectives of spectrometers onboard space missions is to retrieve atmospheric parameters (notably density, composition and temperature). To fulfill this objective, comparisons between observations and model results are necessary. Knowledge of these model uncertainties is therefore necessary, although usually not considered, to estimate the accuracy in planetary upper atmosphere remote sensing of these parameters. In Part I of this study, “Computing uncertainties in ionosphere-airglow models: I. Electron flux and species production uncertainties for Mars” (Gronoff et al., 2012), we presented the uncertainties in the production of excited states and ionized species from photon and electron impacts, computed with a Monte-Carlo approach, and we applied this technique to the Martian upper atmosphere. In the present paper, we present the results of propagation of these production errors to the main UV emissions and the study of other sources of uncertainties. As an example, we studied several aspects of the model uncertainties in the thermosphere of Mars, and especially the O( 1 S) green line (557.7 nm, with its equivalent, the trans-auroral line at 297.2 nm), the Cameron bands CO(a 3 P), and CO2 (B 2 Su ) doublet emissions. We first show that the excited species at the origin of these emissions are mainly produced by electron and photon impact. We demonstrate that it is possible to reduce the computation time by decoupling the different sources of uncertainties; moreover, we show that emission uncertainties can be large (>30%) because of the strong sensitivity to the production uncertainties. Our study demonstrates that uncertainty calculations are a crucial step prior to performing remote sensing in the atmosphere of Mars and the other planets and can be used as a guide to subsequent adjustments of cross sections based on aeronomical observations. Finally, we compare the simulations with observations from the SPICAM spectrometer on the Mars Express spacecraft. The production of excited species at the origin of the green line, the CO Cameron bands and the CO2 (B) doublet is found to be on the dayside, consistent with photon and electron impact on CO2 as the main source of excitation of the three emissions, in contrast to the findings of Huestis et al. (2010) for the O( 1 S) case. Moreover, we re-examine the cross section for the production of the Cameron bands by electron impact on CO2.

International audience; We simulate space weathering of Phobos' surface due to both sputtering by solar wind ions (H+ and He2+) and planetary protons, and surface material vaporization by micrometeoroids impact. Assuming an Iron-rich composition of Phobos' regolith, we find that densities of neutral species (Fe, O, Al, Ca, Mg, Na) in the martian environment are in the range (10-4 -- 10-1 cm-3), and observe an ejecta disk with a radius of 6 martian radii in the equatorial plane and a thickness of 3 martian radii in the perpendicular plane. In order to determine the observability of such species from space based instruments, we also estimate their solar scattering emission line intensities. We conclude that Magnesium would be the only potential candidate suitable for spectral detection.

[1] Venus Express is well and healthy and has now been providing exciting new data from Venus, our nearby twin planet, for over 2 years. Many of the new results are presented and discussed in the subsequent papers in this special section. The overall scientific objective of Venus Express is to carry out a detailed study of the atmosphere of Venus, including the interaction of the upper atmosphere with the solar wind and the interaction of the lowest part of the atmosphere with the surface of the planet. In addition, the plasma environment and magnetic fields as well as some aspects of the surface of the planet are addressed. For the first time, investigations make systematic use of the transparent infrared spectral windows in order to probe the atmosphere in four dimensions: three spatial dimensions plus time. The spacecraft design is taken from Mars Express with some modifications necessary owing to the specific environment around Venus. The payload is composed of three spectrometers, a camera, a magnetometer, an instrument for detecting energetic particles, and a radio science package. The orbit is polar and highly elliptic, with a pericenter altitude of about 200 km over the northern polar region and an apocenter altitude of 66,000 km. Presently, the coverage of the southern hemisphere is very good, but important gaps still do exist. The coverage of the northern hemisphere is much less dense. Venus Express is a part of the European Space Agency's program for the exploration of the inner solar system, which includes missions to study the Sun, Mercury, Venus, the Moon, Mars, and comets and asteroids.

This article reviews our understanding of the ionospheres in the solar system. It provides some basic information on the sources and sinks of the ionospheric plasma, its dynamics, the energetics and the coupling to the neutral atmosphere. Ionospheres in the solar system are reviewed and comparative ionospheric topics are discussed.

EGU2007-A-06650; For more than three years SPICAM UV spectrometer onboard ESA mission Mars Express has been successfully monitoring the upper atmosphere of Mars in the range 118-320 nm. We will present the preliminary results concerning the numerical modelling of Mars' dayglow through the computation of UV emission lines such as CO Cameron bands and N2 Vegard-aplan bands. The theory underlying this modelling uses Boltzmann's statistical kinetic and fluid approaches to yield electron/ion density and temperature profiles as a function of altitude as well as observable variables like the volume emission rates. The outputs of the model can be directly compared to the processed SPICAM data. A few characteristic orbits are then chosen for analysis in order to compare with the numerical modelling.

International audience; Context.Previous studies have shown that doubly-charged positive ions, including molecular ions, can have detectable densities in the ionospheres of Mars, Titan, and the Earth. Aims.In the present paper, we continue our approach by modelling the Venusian ionosphere. The neutral atmosphere of Venus has a similar composition to the ones encountered in the other terrestrial planets, with carbon dioxide (as on Mars), nitrogen (as on Earth and Titan), and atomic oxygen (as on Earth). Methods. We computed the doubly-charged positive ion production through photoionisation (primary production) and electron impact ionisation (secondary production). We computed the densities under the photochemical equilibrium assumption. Results. We predict a ${\rm CO_2}^$ layer centred around $140~{\rm km}$ altitude with a density reaching 30 dications per ${\rm cm}^{3}$ in active solar conditions and a ${\rm N_2}^$ layer centred around a $140{-}150~{\rm km}$ altitude with density reaching $0.3~{\rm cm}^$. We find good agreement between the modelled ${\rm O}^$ densities and Pioneer Venus Orbiter measurements. Finally, we investigate the problem of possible detection of these ions by the European spacecraft Venus Express. Conclusions. Although molecular doubly-charged positive ion densities are low, these ions cannot be considered as negligible compared to other minor ion species. Their detection should be possible in the future through remote sensing or in-situ methods including ion mass spectrometry and UV spectroscopy.

EGU05-A-08277; International audience; In the next weeks and years, the Cassini-Huygens mission will bring some new discoveries on the upper atmosphere of Titan. In this context, it is important to well caracterize the ion production and decay processes for a good understanding of the ionosphere chemistry. In Titan's ionosphere, the dissociative and non-dissociative photoionisation of N2 by solar vacuum ultra-violet are the principal processes responsible for the production of N+, N+2 and N++ 2 primary ions during the day. We will first discuss how these processes can lead to species with internal excitation (electronic and/or vibrational) and also with translational energy [1-3]. The subsequent reactions of these primary ions have been measured in laboratory experiments [1,4] and compared to the literature values [5-7] used in ionospheric models. We will show how the rate constants and the branching ratios to secondary products can be strongly affected by the primary ion internal and translational energy. Consequences on the ionospheric models are discussed.

Coordinated ground-based observations of Titan were performed around or during the Huygens atmospheric probe mission at Titan on 14 January 2005, connecting the momentary in situ observations by the probe with the synoptic coverage provided by continuing ground-based programs. These observations consisted of three different categories: (1) radio telescope tracking of the Huygens signal at 2040 MHz, (2) observations of the atmosphere and surface of Titan, and (3) attempts to observe radiation emitted during the Huygens Probe entry into Titan's atmosphere. The Probe radio signal was successfully acquired by a network of terrestrial telescopes, recovering a vertical profile of wind speed in Titan's atmosphere from 140 km altitude down to the surface. Ground-based observations brought new information on atmosphere and surface properties of the largest Saturnian moon. No positive detection of phenomena associated with the Probe entry was reported. This paper reviews all these measurements and highlights the achieved results. The ground-based observations, both radio and optical, are of fundamental importance for the interpretation of results from the Huygens mission.

Aurorae have been observed on most planets in the Solar System. Mars seemed to be one of the exceptions — until Mars Express got there. Its SPICAM ultraviolet spectrometer has detected a martian aurora, different in important ways from any reported for other planets. The martian aurora is localized to one spot, clearly associated with the crustal magnetic field discovered and mapped by the Mars Global Surveyor. This field is a remnant of an ancient intrinsic magnetic field now extinct. In the high-latitude regions of Earth, aurorae are the often-spectacular visual manifestation of the interaction between electrically charged particles (electrons, protons or ions) with the neutral upper atmosphere, as they precipitate along magnetic field lines. More generally, auroral emissions in planetary atmospheres “are those that result from the impact of particles other than photoelectrons” (ref. 1). Auroral activity has been found on all four giant planets possessing a magnetic field (Jupiter2, Saturn3, Uranus4 and Neptune5), as well as on Venus, which has no magnetic field6. On the nightside of Venus, atomic O emissions at 130.4 nm and 135.6 nm appear in bright patches of varying sizes and intensities6, which are believed to be produced by electrons with energy

A 1-D fluid/kinetic code is used to model WIND Imaging Interferometer measurements of the atomic oxygen (3P-1D) red and (-1D-1S) green thermospheric dayglows at 630.0nm and 557.7nm. This modelling is performed for different latitude and solar zenith angle conditions, in order to reproduce the measurements all along the satellite orbit. Results are successfully compared to the interferometer's observations, reproducing the measured volume emission rates, together with the maximum emission altitude. A good agreement is found regardless of the position considered along the satellite orbit, meaning that the solar flux and the solar zenith angle influences were successfully taken into account. Together with this model study, a four-year red and green oxygen lines set of WINDII data is analysed with regards to those geophysical parameters. Correlations between volume emission rates and solar flux are evaluated and it is found that the MgII index is better suited to this kind of study than the f10.7 decimetric index.