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In their Matter Arising Lalich et al.1 simulate MARSIS echoes at the base of the South Polar Layered Deposits (SPLD) assuming three different layering scenarios (Fig. 1 in ref.1): (a) dusty water ice overlaying bedrock; (b) one CO2 ice layer between dusty water ice and bedrock; and, (c) two basal CO2 ice layers interbedded with one layer of dusty water ice. A surficial layer of CO2 ice ranging from 0 m (no layer) to 2 m in thickness is also considered. The first layer in each simulation is a semi-infinite half space assigned the permittivity of free space, and the bedrock is a semi-infinite half space with pure basaltic rock permittivity. These authors argue that constructive interference generated by some layered configurations produce waveforms (Fig. 2 in ref.1) with local maxima corresponding to the bright basal reflections observed by MARSIS at Ultimi Scopuli 2,3. They conclude that this explanation is more plausible than liquid brines being the source of the bright reflections, as posited instead by Orosei et al.2 and Lauro et al.3. In an earlier paper, however, Orosei et al.4 explored the same model and mathematics covering the entire range of possible parameters for two and three basal CO2 ice layers. Through the quantitative analysis of 3.45 x 108 simulation results, these authors demonstrated that local maxima at one of the MARSIS operating frequencies are not matched by local maxima at the other operating frequencies: that is, a layer stack producing constructive interference at one frequency, does not produce the same effect at the other frequencies, which is inconsistent with MARSIS real data. Thus, constructive interference by basal layers is not a viable mechanism to explain the bright basal reflections at Ultimi Scopuli. Because most of the points in Lalich et al.1 are superseded by Orosei et al.’s4 work, we refer interested readers to that earlier paper for a full discussion of the models and results. Here, we focus on three critical aspects: electromagnetic model; dielectric values used in the simulations; and materials and geology.

The purpose of this project is to consolidate the Italian scientific competence about the geophysical features and composition of planetary surfaces and sub-surfaces in the solar system bodies and Earth itself, with particular interest in the exploration and characterization of the buried ice deposits, where bacterial primitive live could still exist.

The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) is an instrument for subsurface remote sensing of the Mars planet. Since its debut, many successful observations have been carried out. At this point of this fruitful mission, having acquired a good knowledge of the Mars environment, it is now necessary to improve the instrument science performances, mitigating some limitations of the on-board SW, that were required at the beginning of the mission, but which were proven to be excessive and above all limiting. The main purpose of this document is to define the requirements necessary to update the on-board SW, in order to add two new improved operative modes to the ones already in use. It is worth noting that, the existing operative modes will remain unchanged and can continue to be used after loading the updated SW. The first new operative mode (SSM) is related to the observation of Mars. It will be similar to the existing main dual channel sub surface mode (SS3). The processing for the first operative channel will remain unchanged, while calculations on the second channel will be modified to extract the most significant data from the full raw data set, discarding what is meaningless or providing poor scientific contribution. The new second operative mode (SSP), will be designed to optimize above all the observation of Phobos, which was not originally thought as a target for MARSIS, this means that a very complex on-board SW configuration is required, in order to force the radar to work properly even in this situation. Moreover, actual Phobos observation makes use of valuable SC resources for storing high quantity of useless data, that cannot be eliminated without modifications of MARSIS SW. The new operative mode will take care of removing these unnecessary data. It will also optimize adaptively the Receiver Gain during the flyby, thereby improving the dynamic range of the receiver of the recorded Science Data. At the same time data-rate on the SC OBDH bus will be strongly reduced, allowing the possibility for MARSIS, PFS and SPICAM to operate simultaneously.

Radars in orbit around Mars such as MARSIS on Mars Express and SHARAD on Mars Reconnaissance Orbiter provide evidence for the nature of the surface and some sub-surface layers. We have now extended our earlier work, which has indicated solar energetic particles are responsible for the attenuation of the reflected MARSIS and SHARAD radar signals from the surface of Mars, often resulting in radar blackouts. The MARSIS instrument also operates in a topside sounding mode, the Advanced Ionospheric Sounder AIS mode), which also receives surface reflections and we now investigate the impact of the solar energetic particles on the surface reflection during ionospheric sounding observations made by MARSIS. We present observations during two intervals in December 2014 and in September 2017. MARSIS AIS was making observations on the nightside as Mars Express moved towards periapsis and then towards the dayside. The nightside AIS observations clearly demonstrate a similar loss of the surface signal to that seen in the MARSIS sub-surface mode. In addition there is evidence of a reflection from the enhanced layer created by the electrons which is responsible for the attenuation in the signal. The critical frequency is of order 1 MHz, which is equivalent to a peak electron density of order 1010 m-3, at an altitude of about 100 km. These characteristics are similar to our previous modelling work of the impact of the solar energetic electrons.

The principal objective of the radar sounder MARSIS experiment is to look for ice and water in the Martian subsurface. One particular focus of investigations, since 2005, has been the search for basal liquid water in the south polar layered deposits (SPLD). Anomalously strong basal echoes detected from four distinct areas at the base of the deposits at Ultimi Scopuli have been interpreted to indicate the presence of bodies of liquid water in this location, beneath a 1.5 km thick cover of ice and dust. Other explanations for the bright basal reflections have been proposed, however, including the possibility of constructive interference in layered media. Here, we test this mechanism through simulations of MARSIS radar signals propagating in models of CO2-H2O ice se quences. We then compare the results to real MARSIS data acquired over Ultimi Scopuli, finding that no CO2-H2O ice model sequence reproduces the set of real data. The results of our work have implications in relation to the global CO2 inventory of Mars.

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.

In the context of space missions, where science is the most important goal, careful planning and detailed commanding are fundamental. The planning and commanding phases are activities whose complexity depends on the instrument characteristics, environmental constraints and scientific goals. The purpose of this work is to describe in detail these activities for the Jovian Infrared Auroral Mapper (JIRAM) on board the Juno spacecraft, a NASA mission to Jupiter. To maximize the scientific return, we fully employ the flexibility offered by the JIRAM operational modes to efficiently plan observations of various Jovian targets, in spite of the harsh Jovian radiation environment and the spinning state of the Juno spacecraft. Moreover, the JIRAM observations are limited by the challenging pointing and timing scheme of the mission, which impose constraints on both the observation planning and instrumental commanding.

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.

Rapporto presentato alla Riunione di Avanzamento n.3, relativo alle attività tecnico/scientifiche svolte nel periodo 16/11/2020-28/02/2021 nell'ambito del contratto ASI-INAF 2019-21-HH.0 riguardante i radar di Mars Express e di Mars Reconnaissance Orbiter Fase E2 Continuazione

The detection of liquid water by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) at the base of the south polar layered deposits in Ultimi Scopuli has reinvigorated the debate about the origin and stability of liquid water under present-day Martian conditions. To establish the extent of subglacial water in this region, we acquired new data, achieving extended radar coverage over the study area. Here, we present and discuss the results obtained by a new method of analysis of the complete MARSIS dataset, based on signal processing procedures usually applied to terrestrial polar ice sheets. Our results strengthen the claim of the detection of a liquid water body at Ultimi Scopuli and indicate the presence of other wet areas nearby. We suggest that the waters are hypersaline perchlorate brines, known to form at Martian polar regions and thought to survive for an extended period of time on a geological scale at below-eutectic temperatures. MARSIS provides enhanced coverage of the south polar region where there have been indications of a subglacial lake. These new data confirm the presence of a lake and suggest the existence of a complex hydrologic system including various smaller liquid bodies, probably composed of salty brines.

Rapporto presentato alla Riunione di Avanzamento n.2, relativo alle attività tecnico/scientifiche svolte nel periodo 01/02/2020-15/11/2020 nell'ambito del contratto ASI-INAF 2019-21-HH.0 riguardante i radar di Mars Express e di Mars Reconnaissance Orbiter Fase E2 Continuazione