Comparison of terrestrial and Martian TEC at dawn and dusk during solstices

Abstract This paper used the similarities between the ionospheres on Mars and Earth, the most similar of the terrestrial planets, to examine the relative importance of photochemical and transport processes at dawn and dusk. The amount of plasma present in the ionosphere, as measured by the total electron content (TEC), was examined at different locations for both solstice seasons over a solar cycle. Using the rate of change of TEC as a function of solar zenith angle made it possible to compare the plasma production via photoionisation and loss via recombination in the main layer of each planetary ionosphere despite the extreme differences in the total quantity of plasma. This study finds that, at least to first order, the dawn and dusk TEC slopes at Mars are symmetric. This symmetry is interpreted as an indicator of photochemical equilibrium. Deviations from photochemical equilibrium in different geographic and aerographic regions were used to explore the underlying processes responsible for plasma transport. Seasonal and solar cycle variations were also examined at dusk. These variations found that differing interactions with solar forcing mechanisms resulted in a Martian ionosphere with regions that showed evidence of significant transport processes at solar maximum, while at Earth transport processes were most important at solar minimum. In general, the photochemical processes in both ionospheres behave similarly when no magnetic field is considered. The presence or absence of a magnetic field shape the production via photoionisation and loss via recombination processes in both ionospheres, especially when considering plasma transport. This study has notable implications for comparative aeronomy, as a good understanding of how the ionosphere of magnetised and un-magnetised bodies compares is important for characterising planetary environments and atmospheric evolution over long time scales

Galactic cosmic rays at 0.7 A.U. with Venus Express housekeeping data

We apply a previously developed procedure to characterize galactic cosmic rays (GCRs) at 0.7 A.U. with engineering data coming from the Venus Express mission. The engineering parameters are the Error Detection and Correction EDAC cumulative counters, used for detection and correction of memory errors induced by highly energetic particles. It has already been demonstrated that the slope of this counter measures GCR fluxes using data from Mars Express (1.5 A.U.) and Rosetta (up to 4 A.U.) data. Here, we reproduce these methods using Venus Express EDAC data in order to understand the behavior of GCRs closer to the Sun. We again witness the anti-correlation of EDAC slope with the solar activity and further investigate this procedure. The resulting time-lag between maximum sunspot number and minimum GCRs intensity at Venus is close to one day instead of the expected several months. This work represents one of the first characterization of galactic cosmic rays at small distances to the Sun over a long period of time and further cements the value of using EDAC counters as scientific information

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

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

The Impact of Energetic Particles on the Martian Ionosphere During a Full Solar Cycle of Radar Observations: Radar Blackouts

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

Jupiter Science Enabled by ESA’s Jupiter Icy Moons Explorer

ESA’s Jupiter Icy Moons Explorer (JUICE) will provide a detailed investigation of the Jovian system in the 2030s, combining a suite of state-of-the-art instruments with an orbital tour tailored to maximise observing opportunities. We review the Jupiter science enabled by the JUICE mission, building on the legacy of discoveries from the Galileo, Cassini, and Juno missions, alongside ground- and space-based observatories. We focus on remote sensing of the climate, meteorology, and chemistry of the atmosphere and auroras from the cloud-forming weather layer, through the upper troposphere, into the stratosphere and ionosphere. The Jupiter orbital tour provides a wealth of opportunities for atmospheric and auroral science: global perspectives with its near-equatorial and inclined phases, sampling all phase angles from dayside to nightside, and investigating phenomena evolving on timescales from minutes to months. The remote sensing payload spans far-UV spectroscopy (50-210 nm), visible imaging (340-1080 nm), visible/near-infrared spectroscopy (0.49-5.56 μm), and sub-millimetre sounding (near 530-625 GHz and 1067-1275 GHz). This is coupled to radio, stellar, and solar occultation opportunities to explore the atmosphere at high vertical resolution; and radio and plasma wave measurements of electric discharges in the Jovian atmosphere and auroras. Cross-disciplinary scientific investigations enable JUICE to explore coupling processes in giant planet atmospheres, to show how the atmosphere is connected to (i) the deep circulation and composition of the hydrogen-dominated interior; and (ii) to the currents and charged particle environments of the external magnetosphere. JUICE will provide a comprehensive characterisation of the atmosphere and auroras of this archetypal giant planet.</p