Volatile loss from exoplanetary atmospheres and its possible implications for the longevity of habitable surface conditions is a topic of vigorous debate currently. The vast majority of the habitable zone terrestrial-like exoplanets known to date orbit low-mass M- and K-dwarf stars and are subject to the conditions drastically different to those of terrestrial planets in the Solar System. In particular, they orbit far closer to their host stars than similar planets around G-dwarfs similar to the Sun. Therefore they receive higher X-ray and UV fluxes, even though luminosities of M- and K-dwarfs are lower than those of heavier stars. Furthermore, due to their slower evolution, M-dwarfs retain high activity on the gigayear timescales. The combination of these two effects has led to claims that most terrestrial planets orbiting M-dwarfs may have their atmospheres stripped from the higher X-ray and UV fluxes of their host stars. Opposing this are researchers who point out that volatile inventories for terrestrial exoplanets are ill-constrained, and hence, they may be able to “weather the storm” of these higher X-ray and UV fluxes. In this article, we focus on exploring volatile loss in the upper atmospheres of terrestrial planets in our solar system and applications to those in exoplanetary systems around stars of different types.

We investigate the response of space weather events on Earth's upper atmosphere over the polar regions by studying their effect on the drag of the CHAMP and GRACE satellites. Increasing solar activity that results in heating and the expansion of the upper atmosphere threatens low Earth orbit (LEO) satellites. Auroral events are closely related to the stellar energy deposition of solar EUV radiation and precipitating energetic electrons, which influence photochemical processes such as the production of nitric oxide (NO) in the upper atmosphere. To study the production of NO molecules and their influence on the thermospheric structure and satellite drag, we first model Earth's background thermosphere structure with the 1D upper atmosphere model Kompot by considering the incident X-ray, EUV, and IR radiation during selected space weather events. For investigating the effect of electron precipitation in the production of NO molecules in the polar thermosphere, we apply a Monte Carlo model that takes into account the stochastic nature of collisional scattering of auroral electrons in collisions with the surrounding N2-O2 atmosphere, including the production of suprathermal N atoms. The observed effect of the atmospheric drag on the CHAMP and GRACE spacecraft during the two studied events indicates that a sporadic enhancement of NO molecule production in the polar thermosphere and its IR-cooling capability, which counteracts thermospheric expansion and can lead to an “overcooling” with decreased density after the space weather event, can have a protective effect on LEO satellites. Their production efficiency, however, is highly dependent on the energy flux of the precipitating electrons. Our results have direct implications for empirical satellite orbit prediction models, as our simulations highlight the need to consider precipitation-induced NO production to improve the predictive power of these models.

Context. Io, the innermost Galilean moon of Jupiter, is the main source of plasma in the Jovian magnetosphere. The neutral gas coming from the moon will get ionized through ultra-violet radiation and electron impacts. The newly created ions then get picked up by the Jovian magnetic field and start gyrating, thereby creating a ring-beam distribution in velocity space. This type of distribution is unstable with respect to the generation of ion cyclotron waves. Aims. The aim of this study is to characterize the escaping gas from Io's atmosphere into the Jovian magnetosphere. Methods. The Galileo magnetometer data have been investigated for the five Io flybys that have magnetometer data available. The ion cyclotron waves can be measured with magnetometers and through spectral analysis the specific pick-up ions can be determined. Assuming that the energy of the ions in the ring-beam distribution is fully transferred to the cyclotron waves, the pick-up ion densities can be estimated for all these species. Results. We found evidence of sulfur-bearing ions SO3+, SO2+, SO+, and S+, as well as either H2S+ or S-34(+) (which have the same mass-to-charge ratio and cannot be discerned), and for non-sulfur-bearing ions: Cl-35(+), Cl-37(+), K+, and Si+. We also present a first plausible detection of Io-genic phosphorous through the detection of P+ cyclotron waves. Conclusions. The main pick-up densities are related to SO2+ and SO+, varying with distance from Io between similar to 10(8) and similar to 10(6) m(-3), with the other ions exhibiting a similar variation, but their pick-up densities are lower by an order of magnitude.

Planetary exospheres are usually observed using transit spectroscopic methods, such as the Lyman-α line, which is mainly limited by interstellar medium absorption and airglow contamination from the geocorona when using low-orbit space telescopes or neutral and ion particle detectors and flight mass spectrometers. In this study, we discuss a complementary method that can be used for the characterization of exospheres based on the analysis of so-called ion cyclotron waves (ICWs) using magnetometers and plasma instruments. These ICWs are produced by pick-up ions from exospheric neutral atoms over a large spatial region upstream of planetary bodies. The newborn exospheric ions generate an unstable secondary ion population in the solar wind plasma, where the interaction between the exospheric and solar wind ion populations can produce plasma waves arising from various instabilities. The observed wave power can be used to derive the corresponding pick-up ion and related neutral particle densities. Because the ion pick-up density is balanced by the ion production rate, one can reconstruct the exospheric neutral number density. Various exospheric particles (i.e., H, H2, D, He, etc.) can be distinguished by identifying their masses via their different gyrofrequencies even when they are very close to each other. In this study, we will discuss and analyze available ICW data as a tool for the reproduction of neutral atom profiles of extended exospheres, such as those of Mercury, Venus, Mars, the Jovian satellites, and comets.

In the ongoing project ESPRIT, a goal is to investigate the contribution of the chemical composition and associated chemical reactions to the Earth’s upper atmosphere. This is realized through a combined analysis of thermospheric neutral density estimates and the exploration of external parameters of the interplanetary space, including variations in the magnetic field and the merged electric field. Regarding changes in the chemical composition of the Earth’s atmosphere, which might cause heating and cooling effects, we investigated TIMED/SABER measurements in conjunction with findings from the 1D first-principles hydrodynamic upper atmosphere model Kompot code, which shows some significant expansion in the density profile mainly based on the increased XUV flux from the Sun. The neutral mass densities were processed based on accelerometer measurements as well as on kinematic orbit information (Süsser-Rechberger et al. 2022). This allowed us to successfully process kinematic orbits for 19 different satellites at an altitude range of approximately 400 to 1300 km. Both approaches are realized using the in-house software package GROOPS. During the evaluation, significant improvements in the processing and parametrization could be achieved compared to previous solutions, especially through refined models for solar radiation pressure, the Earth’s re-radiation, the thermal radiation of the satellite itself and the consideration of the chemical composition of the atmosphere. Based on these new neutral density estimates, investigations regarding the effects of solar eruptions on the various satellites are performed and used for attempting to forecast the orbital decay of LEO satellites.

Mercury has an extended exosphere that consists of various species. Based on theoretical considerations, the existence of Lithium (Li) in the exosphere around Mercury is predicted to be less than 5x107 cm-2. Because these density values are well below the detection limits of remote observation instruments on board past missions, Li has never been directly observed. Here we show the first on-site determined altitude-density profile of atomic Li7, derived from in-situ magnetic field observations by the MESSENGER spacecraft. The results suggest that the source of Li at Mercury is most likely meteoritic ablation. The findings will help to interpret the remote observations of Mercury's exosphere that will be realized in the near future by the BepiColombo mission.

Mercury is known to possess a Magnetosphere that is highly responsive to the upstream Solar Wind conditions. Previous studies using MESSENGER data have contributed to understanding the dynamics of Mercury's respond to the upstream. However, the interactions between the Magnetospheric plasma and the Solar Wind is yet to be fully understood; and it is indeed one of the main focuses of the ESA/JAXA's current mission, BepiColombo. We report the observations of BepiColombo's flyby-3 at Mercury on 19th June 2023, using ion data from SERENA-PICAM and magnetic field data from MAG/MGF instruments. The preliminary analyses have given an insight into the rapidly changing plasma, at the inbound Magnetopause crossing. There is evidence that bursty reconnection could be the main contributor to such dynamic boundary.

The discovery of many low-mass exoplanets, including several planets within the habitable zone of their host stars, has led to the question of which kind of atmosphere surrounds them. Recent exoplanet detections have revealed the existence of a large population of low-mass planets (<3 M ⊕) with H2-dominated atmospheres that must have been accreted from the protoplanetary disk. As the gas disk usually has an ~10% fraction of helium, we model the possible enrichment of the primordial He fraction in the atmosphere of planets with mass between 0.75 M ⊕ and 3.0 M ⊕ that orbit in the classical habitable zone of Sun-like stars. Depending on the mass accreted by the planet during the gas disk phase and the stellar high-energy flux between ~10 and 120 nm, we find that Earth-like planets with masses between ~0.95 M ⊕ and 1.25 M ⊕ inside the habitable zone of Sun-like stars can end up with He-dominated primordial atmospheres. This finding has important implications for the evolution of Earth-like habitats, as these thick helium-enriched primordial atmospheres can inhibit the habitability of these planets. The upcoming generation of giant telescopes, such as the Extremely Large Telescope, may enable us to observe and explore these atmospheres.

In this work we present the first result of VLF/LF radio signals collected at the receivers of the INFREP network, and magnetic data acquired by the Swarm satellites during the months of January and February 2025. The aim of this study is to identify seismic precursors related to the seismic swarm occurred at the beginning of the year 2025 in the Dodecanese islands (Greece).

We investigate the recent earthquakes (EQs) that occurred on 06 February 2023 principally in the central southern part of Turkey and north western of Syria. The tectonic plate movements between Anatolian, Arabian and African plates are well known to be subject to EQs. The coordinate of the epicenter was 37.08°E and 37.17°N with depth in the order of 10 km and a magnitude Mw7.8. Beside aftershocks, a few hours later a strong Mw7.7 earthquake occurred in the same region . We consider in this analysis the Bafa VLF transmitter (TBB) signal emitting at frequency of 26.7 kHz and localized in the Anatolia region (Turkey) at longitude of 27.31°E and latitude of 37.40°N. TBB transmitter signal is daily monitored by the VLF Graz facility (Biagi et al., 2019; Galopeau et al., 2023) with a sufficient signal to noise ratio principally during night observations. We study the variations of the phase and amplitude of TBB signals, as detected by Graz facility (15.43°E, 47.06°N) few weeks before the earthquakes occurrence. It is essential to note that the geographical latitudes of the epicenter and the TBB transmitter are about 37°N, and the distance, in the order of 850 km, is found smaller than the radius of the earthquake preparation zone, as derived from Dobrovolsky et al. (1979), when considering the magnitude of the seismic event, i.e. Mw7.8. We have applied the terminator time (TT) method to make evident the presence of sunrise and sunset time shifts at terminators one week to ten days before EQs. We discuss essentially the anomalies, in the phase and the amplitude of TBB transmitter, which are probably linked to the electron density variations at the formation and the destruction of the ionospheric D-E-layers. References:Biagi et al., The INFREP Network: Present Situation and Recent Results, Open J. Earth. Research, 8, 2019.Dobrovolsky et al., Estimation of the size of earthquake preparation zones, Pageoph, 117, 1979.Galopeau et al., A VLF/LF facility network for preseismic electromagnetic investigations, Geosci. Instrum. Method. Data Syst., 12, 2023.

We study the amount, size distribution, and material composition of submicron aerosol particles in the lower Venus atmosphere <50 km. Our GGchem phase-equilibrium model predicts metal-chloride and metal-fluoride molecules to be present in the gas over the Venus surface in trace concentrations <2 × 10 ^−12 , in particular FeCl _2 , NaCl, KCl, and SiF _4 . Using an improved version of the DiffuDrift model developed by P. Woitke et al., we find that these molecules deposit to form solid potassium sulfate K _2 SO _4 , sodium sulfate Na _2 SO _4 , and pyrite FeS _2 above about 15.5, 9.5, and 2.4 km, respectively. These heights coincide well with the three potential haze layers found in the Pioneer Venus Large Probe neutral mass spectrometer data by R. Mogul et al. The particles with radius <0.3 μ m can be dredged up from the ground to reach the sulfuric acid cloud base from below by diffusion. The particle density decreases from ∼5000 cm ^−3 at ground level to ∼100 cm ^−3 at a height of 45 km. Particles larger than about 1 μ m are found to stay more confined to the ground, limited to about <10 km, indicating that the larger, so-called mode 3 particles, if they exist, cannot originate from the surface. All particles are expected to be coated by a thin layer of FeS _2 , Na _2 SO _4 , and K _2 SO _4 . We have included the repelling effect of particle charges on the coagulation, without which the model would predict much too steep gradients close to the surface, which is inconsistent with the measured opacities. Our models suggest that the particles must have at least 100 negative charges per micron of particle radius at ground level, and >50 μ m ^−1 at a height of 45 km.

Mariner 10 detected the existence of an exosphere around Mercury in 1974-1975 by remote spectrometric observations during flybys. More than four decades later the MErcury Surface, Space ENvironment, Geochemistry and Ranging (MESSENGER) spacecraft confirmed the existence of the exosphere. So far, the neutral helium (He) number density around Mercury’s exosphere was based on assumptions related to the spectroscopic observations, which are applied to exospheric models to derive an altitude-dependent density profile of the neutral helium around the planet. Here, we present the first on-site measured density profile of He, using in-situ magnetic field measurements from MESSENGER. These data were analyzed for the identification of Ion-Cyclotron Waves (ICWs) that originated from exospheric pick-up He+ ions. The results reveal an extended He-exosphere with a lower surface number density as expected by previous studies. To provide further context, the results are compared with measurements obtained by Mariner 10 and BepiColombo (first flyby), which shows that the measurements of the PHEBUS UV-instrument onboard of the MPO align very well with the determined density from this study.

This work presents an analysis of the sub-ionospheric VLF transmitter signal disturbances which were detected more than one week before the Turkey–Syria EQ occurrence. We have applied the multi-terminator method when considering amplitude and phase variations of the TBB transmitter signal (Turkey), selected because of a good signal to noise ratio for the amplitude, a stable phase variation, and a ray-path propagation crossing the pre-seismic sensitive region, estimated from the combination of the Dobrovolsky area and the Fresnel zone. New spectral features, i.e., inflexions and jumps, are considered in this study, besides the minima and maxima investigated in. The spectral occurrence probabilities are derived at three specific locations: Graz facility, TBB station and EQ epicenter. We show that two main precursors occurred from 27 to 30 January, and from 31 January to 3 February. More important are the prior precursors detected from 23 January to 25/26 January, where anomaly fluctuations were found to be similar to those at the EQ epicenter area, approximately. A forecasting model is proposed, in which the main steps can provide, in the presence of spectral anomalies, first hints regarding the longitudinal locations of the seismic preparation zone.

In this study, we suggest a model for the origin and abundance of exospheric Helium at Mercury. It was derived ab initio, assuming He-saturated regolith at the surface and a “steady-state” Helium exosphere. A 1D Monte Carlo computer simulation [1] was used to calculate the exospheric He density profiles according to the model. The Helium abundance in the Hermean exosphere was first constrained from UV Spectrometer measurements aboard Mariner 10 [2] and has been discussed extensively since, also in the light of probable analogies to the Lunar He environment. It is believed that there are two major sources for exospheric Helium: release of Solar Wind implanted He from the regolith of the Hermean surface and outgassing of radiogenic He from the interior [3]. However, there is no agreement on the quantitative contribution of the two possible origins. Through a larger volume and diversity of data, new insights concerning the origins and other aspects of the Hermean Helium system could be derived. Novel approaches are allowing the derivation of Helium density profiles from MESSENGER data [4], and soon the SERENA plasma/neutral particles package [5] on BepiColombo’s Mercury Planetary Orbiter (MPO) is expected to add the first ever in-situ density measurements to the picture. The presented model shows that the Helium exosphere is dominated by exospheric recycling. This term describes the process in which particles that have been released into the exosphere at energies below Eesc return to the surface and bounce back into the exosphere immediately at the energy corresponding to the local surface temperature. The Helium accumulates in the exosphere, where its abundance is eventually limited by the exospheric loss processes of Jeans escape and ionization. This model can build the foundation for an evaluation of future data and can allow a quantification of the two exospheric Helium sources. [1] Wurz, P. and Lammer, H. (2003). Icarus 164.1 (2003): 1-13.[2] Broadfoot, A. L., et al. (1976). Geophys. Res. Lett., 3: 577-580.[3] Hartle, R. E., et al. (1975), J. Geophys. Res., 80(25)[4] Weichbold, F., et al. (2024), in preparation.[5] Orsini, S., et al. (2021), Space Sci Rev 217,

Mercury's exosphere contains various neutral species, including hydrogen, helium, sodium, potassium, calcium, magnesium, aluminum, iron, and manganese. Although lithium has been predicted to exist, it had not been detected until now. Here, we demonstrate the presence of lithium in Mercury's exosphere, using data from the Mercury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft. The sporadic detection of lithium suggests its meteoritic origin, likely released through evaporation caused by sporadic meteoroid impacts. Our findings provide strong evidence supporting the hypothesis that (micro-)meteoroids and larger meteoroids, which have continuously and sporadically impacted Mercury's surface over billions of years, are a significant source of volatile elements and contributed substantially to Mercury's unexpectedly volatile-rich surface. This detection emphasizes the significant role of meteoroids in shaping Mercury's exosphere and provides insights into the planet's evolution and the history of volatile elements in the Solar System.

Coronal Mass Ejections (CMEs) are space weather phenomena capable of causing significant disruptions to both space- and ground-based infrastructure. The timely and accurate detection and prediction of CMEs is a crucial steps toward implementing strategies to minimize the impacts of such events. CMEs are commonly observed using coronagraphs and heliospheric imagers (HIs), with some forecasting methods relying on manually tracking CMEs across successive images in order to provide an estimate of their arrival time and speed. This process is time-consuming and results may exhibiting considerable interpersonal variation. We investigate the application of machine learning (ML) techniques to the problem of automated CME detection, focusing on data from the HI instruments aboard the STEREO spacecraft. HI data facilitates the tracking of CMEs through interplanetary space, providing valuable information on their evolution. Building on advances in image segmentation, we present the Solar Transient Recognition Using Deep Learning (STRUDL) model. STRUDL is designed to automatically detect and segment CME fronts in HI data. We address the challenges inherent to this task and evaluate the model's performance across a range of solar activity conditions. To complement segmentation, we implement a basic tracking algorithm that links CME detections across successive frames, thus allowing us to automatically generate time-distance profiles. Our results demonstrate the feasibility of applying ML-based segmentation techniques to HI data, while highlighting areas for future improvement, particularly regarding the accurate segmentation and tracking of faint and interacting CMEs.

The European Space Agency has selected PLATO (PLAnetary Transits and Oscillations of stars) for its M3 launch which is scheduled for 2026. With its extremely large field of view, PLATO is designed to obtain photometric measurements over an extended period for bright stars in order to detect and characterise (primarily) rocky planets in the habitable zones of solar type stars. The PLATO measurements will have sufficient sensitivity to determine the mass, radius and age of the host stars with unprecedented accuracy. The PLATO planet database will provide the first large-scale catalogue of accurately and homogeneously characterised small planets at intermediate orbital periods, which will can be used to severely constraint planet formation theories. This would facilitate large scale comparative exo-planetology. In addition the bright PLATO host stars will be ideal targets for atmospheric study with next generation facilities such as the ELT. The PLATO sensitivity will be sufficient to detect pulsations from stars across the HR diagram allowing a deep understanding of stellar structure and evolution to be developed using parameters determined from asteroseismology.

Since its detection by Mariner 10, helium has been a key focus in studies of Mercury's exosphere. Recently, Weichbold et al. (2025), https://doi.org/10.1029/2024je008679 provided the first in situ helium measurements, inferring density from Ion Cyclotron Wave (ICW) events observed by the MESSENGER spacecraft. This approach enables, for the first time, a helium density profile across a broad altitude range without relying on prior models. We present an ab‐initio model for a steady state, solar wind‐driven helium exosphere, which informed the interpretation of these ICW measurements. We discuss helium release processes and evaluate whether meteoroid impacts could account for specific instances of elevated helium measurements. We developed a global, semi‐analytical model based on a helium‐saturated regolith and an average helium source flux of He/s from solar wind ion implantation. We calculate the helium flux distribution using an analytical lateral transport model and then generate local radial density profiles from a numerical (Monte Carlo) radial transport model. Additionally, we applied the radial transport model to estimate the scale and duration of large, sporadic helium release events and assess the likelihood of detecting these events in situ. The strong agreement between our model and the novel measurements confirms that the measurable helium exosphere is dominated by thermally recycled particles. We show that elevated helium measurements can result from the vaporization and release of helium from large (1 m) meteoroid impacts, but it is statistically unlikely that more than one impact event is captured in the given set of measurements.

With its extended mission, JUNO is getting close to Io and performs moon flybys. It is therefore time to (re)analyse the already available magnetometer data from close flybys of Io by Galileo. Earlier studies of the J0 flyby showed the presence of ion cyclotron waves generated by the pick-up of SO2+ and determined the density of the picked-up ions. In this presentation we study all five Io flybys by Galileo and investigate the presence of ion cyclotron waves for three different species. SO2+, SO+ and S+. Through Fourier analysis and calculation of the cross-spectral matrix and strong criteria on power, polarization and ellipticity, we determine intervals of significant wave activity. Under the assumption of bi-spherical scattering of the pick-up ions in the velocity ring-distribution, an estimation of the pick-up ion density can be obtained. Through an assumption of the ionization frequency, this can be converted into a neutral density to obtain a value of the total neutral gas emitted per second and compare it to the usually assumed 1000 kg/s. Naturally, the five flybys will also give information about differences generated by local time, longitude and latitude.