Solar energetic events can have considerable effects on planetary ionospheres. However, the erratic nature of these solar energetic events make observations difficult. Here we show a mutual radio occultation observation, which serendipitously occurred just 10 minutes after a large solar flare impacted Mars. This resulted in the largest lower ionospheric layer ever recorded, where it was 278% its typical size. We used in-situ soft x-ray irradiance measurements to show a threefold increase in flux. This infers a different relation of soft X-ray to this layer's density than previously thought, with variations depending on the amount of spectrum 'hardening' leading to the increase of ionisation from secondaries.

The Jupiter Icy Moons Explorer (JUICE) is a European Space Agency mission to explore Jupiter and its three icy Galilean moons: Europa, Ganymede, and Callisto. Numerous JUICE investigations concern the magnetised space environments containing low-density populations of charged particles that surround each of these bodies. In the case of both Jupiter and Ganymede, the magnetic field generated internally produces a surrounding volume of space known as a magnetosphere. All these regions are natural laboratories where we can test and further our understanding of how such systems work, and improved knowledge of the environments around the moons of interest is important for probing sub-surface oceans that may be habitable. Here we review the magnetosphere and plasma science that will be enabled by JUICE from arrival at Jupiter in July 2031. We focus on the specific topics where the mission will push forward the boundaries of our understanding through a combination of the spacecraft trajectory through the system and the measurements that will be made by its suite of scientific instruments. Advances during the initial orbits around Jupiter will include construction of a comprehensive picture of the poorly understood region of Jupiter’s magnetosphere where rigid plasma rotation with the planet breaks down, and new perspectives on how Jupiter’s magnetosphere interacts with both Europa and Callisto. The later orbits around Ganymede will dramatically improve knowledge of this moon’s smaller magnetosphere embedded within the larger magnetosphere of Jupiter. We conclude by outlining the high-level operational strategy that will support this broad science return.

Despite the growing importance of planetary Space Weather forecasting and radiation protection for science and robotic exploration and the need for accurate Space Weather monitoring and predictions, only a limited number of spacecraft have dedicated instrumentation for this purpose. However, every spacecraft (planetary or astronomical) has hundreds of housekeeping sensors distributed across the spacecraft, some of which can be useful to detect radiation hazards produced by solar particle events. In particular, energetic particles that impact detectors and subsystems on a spacecraft can be identified by certain housekeeping sensors, such as the Error Detection and Correction (EDAC) memory counters, and their effects can be assessed. These counters typically have a sudden large increase in a short time in their error counts that generally match the arrival of energetic particles to the spacecraft. We investigate these engineering datasets for scientific purposes and perform a feasibility study of solar energetic particle event detections using EDAC counters from seven European Space Agency Solar System missions: Venus Express, Mars Express, ExoMars-Trace Gas Orbiter, Rosetta, BepiColombo, Solar Orbiter, and Gaia. Six cases studies, in which the same event was observed by different missions at different locations in the inner Solar System are analyzed. The results of this study show how engineering sensors, for example, EDAC counters, can be used to infer information about the solar particle environment at each spacecraft location. Therefore, we demonstrate the potential of the various EDAC to provide a network of solar particle detections at locations where no scientific observations of this kind are available.

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.

Context. 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. Aims. 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. Methods. We advanced a novel approach to spacecraft data processing using the techniques of Doppler and phase-referenced very long baseline interferometry spacecraft tracking. Results. We achieved, on average, mHz precision (30 μm/s at a 10 s 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.