Spacecraft-to-spacecraft radio occultations experiments are being conducted at Mars between the Mars Express (MEX) and Trace Gas Orbiter (TGO) spacecraft, the first ever periodic inter-spacecraft occultations at a planet other than Earth. Here we present results from the first 83 such occultations, conducted between 2\textsuperscript{nd} Nov 2020 and 5\textsuperscript{th} of July 2023. Of these, 44 observations have to-date resulted in the extraction of vertical electron density profiles. These observations are the successful results of a major feasibility study conducted by the European Space Agency to use pre-existing relay communication equipment for radio science purposes. Mutual radio occultations have numerous advantages over traditional spacecraft-to-ground station occultations. In this work, we demonstrate how raw data are transformed into electron density values and validated with models and other instruments.

Mantle convection models based on geophysical constraints have provided us with a basic understanding of the forces driving and resisting plate motions on Earth. However, existing studies computing the balance of underlying forces are contradicting, and the impact of plate boundary geometry on surface deformation remains unknown. We address these issues by developing global instantaneous 3-D mantle convection models with a heterogeneous density and viscosity distribution and weak plate boundaries prescribed using different geometries. We find that the plate boundary geometry of the Global Earthquake Model (GEM, Pagani et al., 2018), featuring open plate boundaries with discrete lithospheric-depth weak zones in the oceans and distributed crustal faults within continents, achieves the best fit to the observed GPS data with a directional correlation of 95.1% and a global point-wise velocity residual of 1.87 cm/year. A good fit also requires plate boundaries being 3 to 4 orders of magnitude weaker than the surrounding lithosphere and low asthenospheric viscosities between 5e17 and 5e18 Pa s. Models without asthenospheric and lower mantle heterogeneities retain on average 30% and 70% of the plate speeds, respectively. Our results show that Earth’s plate boundaries are not uniform and better described by more discrete plate boundaries within the oceans and distributed faults within continents. Furthermore, they emphasize the impact of plate boundary geometry on the direction and speed of plate motions and reaffirm the importance of slab pull in the uppermost mantle as a major plate driving force.

Media propagation delay and delay-rate induced by the water vapor within the Earth’s troposphere represent one of the main error sources for radiometric measurements in deep space. In preparation for the BepiColombo and JUICE missions, the European Space Agency has installed the prototype of a tropospheric delay calibration system (TDCS) at the DSA-3 ground station located in Malargüe, Argentina. An initial characterization of the TDCS performance was realized using the orbit determination of the Gaia spacecraft as a testbed. This work will further characterize the system by analyzing the BepiColombo tracking passes, which were recorded between March 2021 and February 2022 during the first two superior solar conjunction experiments. The performance exceeds the expectations based on the previous analysis, with an average 51% reduction of the Doppler noise when using the TDCS measurements in place of standard calibrations based on global navigation satellite system data. The tropospheric instability at long time scales is also significantly reduced, with most of the tracking passes now satisfying the Mercury orbiter radioscience experiment (MORE) requirements on two-way Doppler stability.

<p>The orbits and dynamics of exoplanet systems can unveil their tales of formation, migration, star-planet interactions, and atmospheric properties. Kepler, TESS, and soon PLATO deliver an unprecedented wealth of new photometric data on this matter, while ground-based follow-up and radial velocity instruments add valuable insights. Here, I will present how we can unite and untangle all this data on exoplanets' orbits and dynamics using allesfitter. This open-source python software enables flexible and robust inference of stars and exoplanets from photometric and radial velocity data. Allesfitter offers a rich selection of orbital and transit/eclipse models, accommodating multiple exoplanets, multi-star systems, transit-timing variations, and phase curves. It can also help mitigate and/or study stellar variability, starspots, and stellar flares. I will highlight some of allesfitter's science output on examples of exoplanet dynamics (e.g., TOI-270 and TOI-216) and orbital phase curves (e.g., WASP-18 and WASP-121). With TESS' extended mission and PLATO on the horizon, a wealth of new data soon face us, allowing TTV and phase curve studies of dozens of such systems over many years.</p>

<p>On our search for habitable worlds, we have to account for explosive stellar flaring and coronal mass ejections (CMEs) impacting exoplanets. These stellar outbursts are a double-edged sword. On the one hand, flares and CMEs are capable of stripping off atmospheres and extinguishing existing biology. On the other hand, flares might be the (only) means to deliver the trigger energy for prebiotic chemistry and initiate life. This talk will highlight our study of all stellar flares from the TESS primary mission, driven by a convolutional neural network. I will discuss our new insights on flaring as a function of stellar type, age, rotation, spot coverage, and other factors. Most importantly, I will link our findings to prebiotic chemistry and ozone sterilisation, identifying which worlds might lie in the sweet spot between too much and too little flaring. With future extended missions and increased coverage, flare studies and new exoplanet discoveries will ultimately aid in defining criteria for habitability.</p>

<p>The nearby TOI-270 system provides an unparalleled opportunity to observationally probe hypotheses for exoplanet formation and evolution. The system hosts one super-Earth and two sub-Neptunes near mean-motion resonances and transiting a bright (K-mag 8.25) M3V dwarf. Strangely, M-dwarf systems harbouring only super-Earths or only sub-Neptunes are ubiquitous. However, for still unknown reasons, systems with multiple planets spanning the radius valley are rare - and we know merely a handful of systems bright enough for precise mass measurements and atmospheric studies. To this end, TOI-270's planets are exceptionally favourable for detailed transit timing variation (TTV) and transmission spectroscopy observations. First, with the planets orbiting near low-order resonances (5:3 and 2:1), our extensive observing campaign with eight different observatories since 2018 yields clear TTV signals for planets c and d, with amplitudes of around 10 min and a super-period of circa 3 yr. Using dynamical models, we can thus significantly constrain their radii, mass ratios, and eccentricities. This adds to complementary radial velocity (RV) mass measurements from HARPS and ESPRESSO. Second, via HST and JWST transmission spectroscopy we can characterise and compare the atmospheres of two sub-Neptunes formed from the same protoplanetary nebula and test hypotheses like photoevaporation, core-powered mass-loss, and gas-poor formation. As one of the best-constrained small planet systems, TOI-270 can thus serve as a unique observational testbed for formation and evolution theories. </p>

This paper presents a robust tracking strategy for global navigation satellite system (GNSS) receivers in sounding rockets. The continuous tracking of sounding rockets using G NSS signals becomes challenging due to the high signal dynamics experienced, especially during lift-off. Therefore, robust tracking techniques are crucial to keep the lock of the satellite signals and achieve a continuous position, velocity, and time (PVT) solution of the sounding rocket. This research presents a robust adaptive tracking technique: the loop-bandwidth control algorithm (LBCA)-based frequency locked loop-assisted-phase locked loop (FAP). This technique is compared with state-of-the-art robust tracking techniques using fixed tracking configurations. Both methods are tested in a simulated rocket launch scenario. Results show that the LBCA-based FAP is a reliable option for sounding rocket scenarios due to its robustness against high dynamics.

The Sentinel-2 mission is a key element of the Copernicus Earth monitoring program of the European Union. The mission is currently composed of two satellites and provides a continuous observation of land and coastal areas at high spatial resolution and with a revisit time of 5 days at the equator. The geometric uncertainty of the Sentinel-2 product is a critical contributor to the performance of the mission. We present the approach used to calibrate the geometric performance of Sentinel-2 data and latest activities, especially related to the co-registration with the Global Reference Image (GRI). Generation of the GRI, coregistration algorithm, called geometric refinement, and preliminary results are presented.