CyberSec Research

Metric radio bursts are often said to be valuable diagnostic tools for studying the near-sun kinematics and energetics of the Interplanetary Coronal Mass Ejections (ICMEs). Radio observations also serve as an indirect tool to estimate the coronal magnetic fields. However, how these estimated coronal magnetic fields are related to the magnetic field strength in the ICME at 1 AU has rarely been explored. We aim to establish a relation between the coronal magnetic fields obtained from the radio observations very close to the Sun and the magnetic field measured at 1 AU when the ICME arrives at the Earth. We performed statistical analysis of all metric type II radio bursts in solar cycles 23 and 24, which were found to be associated with ICMEs. We estimated the coronal magnetic field associated with the corresponding CME near the Sun (middle corona) using a split-band radio technique and compared those with the magnetic fields recorded at 1 AU with in-situ observations. We found that the estimated magnetic fields near the Sun using radio techniques are not well correlated with the magnetic fields measured at 1 AU using in-situ observations. This could be due to the complex evolution of the magnetic field as it propagates through the heliosphere. Our results suggest that while metric radio observations can serve as effective proxies for estimating magnetic fields near the Sun, they may not be as effective close to the Earth. At least, no linear relation could be established using metric radio emissions to estimate the magnetic fields at 1 AU with acceptable error margins.

This article is an engineering note, and formal abstract is omitted in accordance with the requirements of the journal. The main idea of this note is as follows. In endoatmospheric landing of reusable rockets, there exist various kinds of disturbances that can induce the trajectory dispersion. The trajectory dispersion propagates with flight time and ultimately determines landing accuracy. Therefore, to achieve high-precision landing, this note proposes a novel online trajectory dispersion control method. Based on a Parameterized Optimal Feedback Guidance Law (POFGL), two key components of the proposed method are designed: online trajectory dispersion prediction and real-time guidance parameter tuning for trajectory dispersion optimization. First, by formalizing a parameterized probabilistic disturbance model, the closed-loop trajectory dispersion under the POFGL is predicted online. Compared with the covariance control guidance method, a more accurate trajectory dispersion prediction is achieved by using generalized Polynomial Chaos (gPC) expansion and pseudospectral collocation methods. Second, to ensure computational efficiency, a gradient descent based real-time guidance parameter tuning law is designed to simultaneously optimize the performance index and meet the landing error dispersion constraint, which significantly reduces the conservativeness of guidance design compared with the robust trajectory optimization method. Numerical simulations indicate that the trajectory dispersion prediction method can achieve the same accuracy as the Monte Carlo method with smaller computational resource; the guidance parameter tuning law can improve the optimal performance index and meet the desired accuracy requirements through directly shaping the trajectory dispersion.

First-principle studies of radiative processes aimed at explaining the origin of type II and type III solar radio bursts raise questions on the implications of downshifted electron beam plasma excitations with frequency (slightly) below the plasma frequency ($\omega\lesssim\omega_{pe}$) in the generation of radio emissions. Unlike the beam-induced Langmuir waves ($\omega \gtrsim \omega_{pe}$) in the standard radio emission plasma model, the primary wave excitations of cooler and/or denser beams have predominantly downshifted frequencies. Broadbands of such downshifted excitations are also confirmed by in situ observations in association with terrestrial foreshock and electron beams (in contrast to narrowband Langmuir waves), but their involvement in radiative processes has not been examined so far. We revisit three radiative scenarios specific to downshifted primary excitations, and the results demonstrate their direct or indirect involvement in plasma radio emission. Downshifted excitations of an electron beam primarily play an indirect role, contributing to the relaxation to a plateau-on-tail still able to induce Langmuir beam waves that satisfy conditions for nonlinear wave-wave interactions leading to free radio waves. At longer time scales, the primary excitations can become predominantly downshifted, and then directly couple with the secondary (backscattered) Langmuir waves to generate the second harmonic of radio emissions. Two counterbeams are more efficient and lead to faster radiative mechanisms, involving counterpropagating downshifted excitations, which couple to each other and generate intense, broadband and isotropic radio spectra of downshifted second harmonics. Such a long-lasting (second) radio harmonic can thus be invoked to distinguish regimes with downshifted ($\omega \gtrsim \omega_{pe}$) primary excitations.

Radio telescopes observe extremely faint emission from astronomical objects, ranging from compact sources to large scale structures that can be seen across the whole sky. Satellites actively transmit at radio frequencies (particularly at 10--20\,GHz, but usage of increasing broader frequency ranges are already planned for the future by satellite operators), and can appear as bright as the Sun in radio astronomy observations. Remote locations have historically enabled telescopes to avoid most interference, however this is no longer the case with dramatically increasing numbers of satellites that transmit everywhere on Earth. Even more remote locations such as the far side of the Moon may provide new radio astronomy observation opportunities, but only if they are protected from satellite transmissions. Improving our understanding of satellite transmissions on radio telescopes across the whole spectrum and beyond is urgently needed to overcome this new observational challenge, as part of ensuring the future access to dark and quiet skies. In this contribution we summarise the current status of observations of active satellites at radio frequencies, the implications for future astronomical observations, and the longer-term consequences of an increasing number of active satellites. This will include frequencies where satellites actively transmit, where they unintentionally also transmit, and considerations about thermal emission and other unintended emissions. This work is ongoing through the IAU CPS.

The modulation of low-energy galactic cosmic rays reflects interplanetary magnetic field variations and can provide useful information on solar activity. An array of ground-surface detectors can reveal the secondary particles, which originate from the interaction of cosmic rays with the atmosphere. In this work, we present an investigation of the low-threshold rate (scaler) time series recorded in 16 years of operation by the Pierre Auger Observatory surface detectors in Malargue, Argentina. Through an advanced spectral analysis, we detected highly statistically significant variations in the time series with periods ranging from the decadal to the daily scale. We investigate their origin, revealing a direct connection with solar variability. Thanks to their intrinsic very low noise level, the Auger scalers allow a thorough and detailed investigation of the galactic cosmic-ray flux variations in the heliosphere at different timescales and can, therefore, be considered a new proxy of solar variability.

The solar wind is a medium characterized by strong turbulence and significant field fluctuations on various scales. Recent observations have revealed that magnetic turbulence exhibits a self-similar behavior. Similarly, high-resolution measurements of the proton density have shown comparable characteristics, prompting several studies into the multifractal properties of these density fluctuations. In this work, we show that low-resolution observations of the solar wind proton density over time, recorded by various spacecraft at Lagrange point L1, also exhibit non-linear and multifractal structures. The novelty of our study lies in the fact that this is the first systematic analysis of solar wind proton density using low-resolution (hourly) data collected by multiple spacecraft at the L1 Lagrange point over a span of 17 years. Furthermore, we interpret our results within the framework of non-extensive statistical mechanics, which appears to be consistent with the observed nonlinear behavior. Based on the data, we successfully validate the q-triplet predicted by non-extensive statistical theory. To the best of our knowledge, this represents the most rigorous and systematic validation to date of the q-triplet in the solar wind.

Thermodynamics of solar wind bulk plasma have been routinely measured and quantified, unlike those of solar energetic particles (SEPs), whose thermodynamic properties have remained elusive until recently. The thermodynamic kappa (\(\kappa_{\rm EP}\)) that parameterizes the statistical distribution of SEP kinetic energy contains information regarding the population's level of correlation and effective degrees of freedom (\({\rm d_{eff}}\)). At the same time, the intermittent kappa (\(\kappa_{\Delta B}\)) that parameterizes the statistical distribution of magnetic field increments contains information about the correlation and \({\rm d_{eff}}\) involved in magnetic field fluctuations. Correlations between particles can be affected by magnetic field fluctuations, leading to a relationship between \(\kappa_{\rm EP}\) and \(\kappa_{\Delta B}\). In this paper, we examine the relationship of \({\rm d_{eff}}\) and entropy between energetic particles and the magnetic field via the spatial variation of their corresponding parameter kappa values. We compare directly the values of \(\kappa_{\rm EP}\) and \(\kappa_{\Delta B}\) using Parker Solar Probe IS\(\odot\)IS and FIELDS measurements during an SEP event associated with an interplanetary coronal mass ejection (ICME). Remarkably, we find that \(\kappa_{\rm EP}\) and \(\kappa_{\Delta B}\) are anti-correlated via a linear relationship throughout the passing of the ICME, indicating a proportional exchange of \({\rm d_{eff}}\) from the magnetic field to energetic particles, i.e., \(\kappa_{\Delta B} \sim (-0.15 \pm 0.03)\kappa_{\rm EP}\), interpreted as an effective coupling ratio. This finding is crucial for improving our understanding of ICMEs and suggests that they help to produce an environment that enables the transfer of entropy from the magnetic field to energetic particles due to changes in intermittency of the magnetic field.

Modeling the internal structure of self-gravitating solid and liquid bodies presents a challenge, as existing approaches are often limited to either overly simplistic constant-density approximations or more complex numerical equations of state. We present a detailed analysis of a tractable and physically motivated model for perfectly elastic, spherically symmetric self-gravitating bodies in hydrostatic equilibrium. The model employs a logarithmic equation of state (logotropic EOS) with a non-zero initial density and constant bulk modulus. Importantly, scaling properties of the model allow all solutions to be derived from a single, universal solution of an ordinary differential equation, resembling the Lane-Emden and Chandrasekhar models. The model provides new insights into stability issues and reveals oscillatory asymptotic behavior in the mass-radius relation, including the existence of both a maximum mass and a maximum radius. We derive useful, simple analytical approximations for key properties, such as central overdensity, moment of inertia, binding energy, and gravitational potential, applicable to small, metallic bodies like asteroids and moons. These new approximations could aid future research, including space mining and the scientific characterization of small Solar System bodies.

The Combined Release and Radiation Effects Satellite (CRRES) observed the response of the Van Allen radiation belts to peak solar activity within solar cycle 22. This study analyses the occurrence and loss timescales of relativistic electrons within the CRRES High Energy Electron Fluxometer (HEEF) dataset, including during several large geomagnetic storms that flooded the slot region with multi-MeV electrons and which allow the first definitive multi-MeV lifetimes to be calculated in this region. The HEEF loss timescales are otherwise broadly in agreement with those from later solar cycles but differences include longer-lasting sub-MeV electrons near the inner region of the outer belt and faster decaying multi-MeV electrons near geosynchronous orbit. These differences are associated with higher levels of geomagnetic activity, a phenomenon that enables the spread in the results to be parameterised accordingly. The timescales generally appear well-bounded by Kp-dependent theoretical predictions but the variability within the spread is however not always well-ordered by geomagnetic activity. This reveals the limits of pitch-angle diffusion in accounting for the decay of elevated electron fluxes following geomagnetic storms.

A density structure within the magnetic cloud of an interplanetary coronal mass ejection impacted Earth and caused significant perturbations in plasma boundaries. We describe the effects of this structure on the magnetosheath plasma downstream of the bow shock using spacecraft observations. During this event, the bow shock breathing motion is evident due to the changes in the upstream dynamic pressure. A magnetic enhancement forms in the inner magnetosheath and ahead of a plasma compression region. The structure has the characteristics of a fast magnetosonic shock wave, propagating earthward and perpendicular to the background magnetic field further accelerating the already heated magnetosheath plasma. Following these events, a sunward motion of the magnetosheath plasma is observed. Ion distributions show that both the high density core population as well as the high energy tail of the distribution have a sunward directed flow indicating that the sunward flows are caused by magnetic field line expansion in the very low $\beta$ magnetosheath plasma. Rarefaction effects and enhancement of the magnetic pressure in the magnetosheath result in magnetic pressure gradient forcing that drives the expansion of magnetosheath magnetic field lines. This picture is supported by a reasonable agreement between the estimated plasma accelerations and the magnetic pressure gradient force.

With humans returning to the Moon under the Artemis program, understanding and mitigating effects from Plume Surface Interactions (PSI) will be essential for the protection of personnel and equipment on the Moon. To help characterize the underlying mechanics associated with viscous erosion and crater formation, experimental measurements using regolith simulants and subsonic, non-reacting flows were completed using compressed air in a splitter plate, plume cratering setup. More specifically, these investigations examined the underlying effects of bulk density, cohesion, and exhaust flow characteristics on viscous erosion rates and crater formation using Lunar highlands simulant (LHS-1), Lunar mare simulant (LMS-1), LHS-1D (Dust) simulants, and 40-80 um glass beads in atmosphere. Results show that particle size distribution can ultimately influence crater shapes and erosion rates, likely owing to internal angle of friction. Measurements show that increasing bulk density, especially from an uncompacted to a slightly compacted state, decreases erosion rate by as much as 50%. While cohesion of granular material can mitigate erosion rates to some extent, higher levels of cohesion above 1,000 Pa may actually increase viscous erosion rates due to particle clumping. A modified version of Metzger's (2024a) equation for volumetric erosion rate is presented, with limitations discussed. These modified equations for viscous erosion, with limitations noted, show that geotechnical properties play an important role in viscous erosion and should be considered in PSI computer models for future mission planning.

Naturally-occurring whistler-mode waves in near-Earth space play a crucial role in accelerating electrons to relativistic energies and scattering them in pitch angle, driving their precipitation into Earth's atmosphere. Here, we report on the results of a controlled laboratory experiment focusing on the excitation of whistler waves via temperature anisotropy instabilities--the same mechanism responsible for their generation in space. In our experiments, anisotropic energetic electrons, produced by perpendicularly propagating microwaves at the equator of a magnetic mirror, provide the free energy for whistler excitation. The observed whistler waves exhibit a distinct periodic excitation pattern, analogous to naturally occurring whistler emissions in space. Particle-in-cell simulations reveal that this periodicity arises from a self-regulating process: whistler-induced pitch-angle scattering rapidly relaxes the electron anisotropy, which subsequently rebuilds due to continuous energy injection and further excites wave. Our results have direct implications for understanding the process and characteristics of whistler emissions in near-Earth space.

Foundation Models, pre-trained on large unlabelled datasets before task-specific fine-tuning, are increasingly being applied to specialised domains. Recent examples include ClimaX for climate and Clay for satellite Earth observation, but a Foundation Model for Space Object Behavioural Analysis has not yet been developed. As orbital populations grow, automated methods for characterising space object behaviour are crucial for space safety. We present a Space Safety and Sustainability Foundation Model focusing on space object behavioural analysis using light curves (LCs). We implemented a Perceiver-Variational Autoencoder (VAE) architecture, pre-trained with self-supervised reconstruction and masked reconstruction on 227,000 LCs from the MMT-9 observatory. The VAE enables anomaly detection, motion prediction, and LC generation. We fine-tuned the model for anomaly detection & motion prediction using two independent LC simulators (CASSANDRA and GRIAL respectively), using CAD models of boxwing, Sentinel-3, SMOS, and Starlink platforms. Our pre-trained model achieved a reconstruction error of 0.01%, identifying potentially anomalous light curves through reconstruction difficulty. After fine-tuning, the model scored 88% and 82% accuracy, with 0.90 and 0.95 ROC AUC scores respectively in both anomaly detection and motion mode prediction (sun-pointing, spin, etc.). Analysis of high-confidence anomaly predictions on real data revealed distinct patterns including characteristic object profiles and satellite glinting. Here, we demonstrate how self-supervised learning can simultaneously enable anomaly detection, motion prediction, and synthetic data generation from rich representations learned in pre-training. Our work therefore supports space safety and sustainability through automated monitoring and simulation capabilities.

Many aspects of our societies now depend upon satellite telecommunications, such as those requiring Global Navigation Satellite Systems (GNSS). GNSS is based on radio waves that propagate through the ionosphere and experience complicated propagation effects caused by inhomogeneities in its electron density. The Earth's ionosphere forms part of the solar-terrestrial environment, and its state is determined by the spatial distribution and temporal evolution of its electron density. It varies in response to the "space weather" combination of solar activity and geomagnetic conditions. Notably, the radio waves used in satellite telecommunications suffer due to the dispersive nature of the ionospheric plasma. Scales and indices that summarise the state of the solar-terrestrial environment due to solar activity and geomagnetic conditions already exist. However, the response of the ionosphere to active geomagnetic conditions, its geoeffectiveness, and its likely impact on systems and services are not encapsulated by these. This is due to the ionosphere's intrinsic day-to-day variability, persistent seasonal patterns, and because radio wave measurements of the ionosphere depend upon many factors. Here we develop a novel index that describes the state of the ionosphere during specific space weather conditions. It is based on propagation disturbances in GNSS signals, and is able to characterise the spatio-temporal evolution of ionospheric disturbances in near real time. This new scale encapsulates day-to-day variability, seasonal patterns, and the geo-effective response of the ionosphere to disturbed space weather conditions; and can be applied to data from any GNSS network. It is intended that this new scale will be utilised by agencies providing space weather services, as well as by service operators to appreciate the current conditions in the ionosphere, thus informing their operations.

One of hot topics in the solar physics are the so-called 'stealth' coronal mass ejections (CME), which are not associated with any appreciable energy release events in the lower corona, such as the solar flares. It is often assumed recently that these phenomena might be produced by some specific physical mechanism, but no particular suggestions were put forward. It is the aim of the present paper to show that a promising explanation of the stealth CMEs can be based on the so-called 'topological' ignition of the magnetic reconnection, when the magnetic null point is produced by a specific superposition of the remote sources (sunspots) rather than by the local current systems. As follows from our numerical simulations, the topological model explains very well all basic features of the stealth CMEs: (i) the plasma eruption develops without an appreciable heat release from the spot of reconnection, i.e., without the solar flare; (ii) the spot of reconnection (magnetic null point) can be formed far away from the location of the magnetic field sources; (iii) the trajectories of eruption are usually strongly curved, which can explain observability of CMEs generated behind the solar limb.

We describe physical processes affecting the formation, trapping, and outgassing of molecular oxygen (O2) at Europa and Ganymede. Following Voyager measurements of their ambient plasmas, laboratory data indicated that the observed ions were supplied by and would in turn impact and sputtering their surfaces, decomposing the ice and producing thin O2 atmospheres. More than a decade later, Europa's ambient O2 was inferred from observations of the O aurora and condensed O2 bands at 5773 and 6275 angstroms were observed in Ganymede's icy surface. More than another decade later, the O2 atmosphere was shown to have a dusk/dawn enhancement, confirmed by Juno data. Although the incident plasma produces these observables, processes within the surface are still not well understood. Here we note that incident plasma produces a non-equilibrium defect density in the surface grains. Subsequent diffusion leads to the formation of voids and molecular products, some of which are volatile. Although some volatiles are released into their atmospheres, others are trapped at defects or in voids forming gas bubbles, which might be delivered to their subsurface oceans. Here we discuss how trapping competes with annealing of the radiation damage. We describe differences observed at Europa and Ganymede and roughly determine the trend with latitude of O2 bands on Ganymede's trailing hemisphere. This understanding is used to discuss the importance of condensed and adsorbed O2 as atmospheric sources, accounting for dusk/dawn enhancements and temporal variability reported in condensed O2 band depths. Since plasma and thermal annealing timescales affect the observed O2 variability on all of the icy moons, understanding the critical physical processes of O2 can help determine the evolution of other detected oxidants often suggested to be related to geological activity and venting.

The arrival of a series of coronal mass ejections (CMEs) at the Earth resulted in a great geomagnetic storm on 10 May 2024, the strongest storm in the last two decades. We investigate the kinematic and thermal evolution of the successive CMEs to understand their interaction en route to Earth. We attempt to find the dynamics, thermodynamics, and magnetic field signatures of CME-CME interactions. Our focus is to compare the thermal state of CMEs near the Sun and in their post-interaction phase at 1 AU. The 3D kinematics of six identified Earth-directed CMEs were determined using the GCS model. The flux rope internal state (FRIS) model is implemented to estimate the CMEs' polytropic index and temperature evolution from their measured kinematics. The thermal states of the interacting CMEs are examined using in-situ at 1 AU. Our study determined the interaction heights of selected CMEs and confirmed their interaction that led to the formation of complex ejecta identified at 1 AU. The plasma, magnetic field, and thermal characteristics of magnetic ejecta (ME) within the complex ejecta and other substructures, such as interaction regions (IRs) within two ME and double flux rope-like structures within a single ME, show the possible signatures of CME-CME interaction in in-situ observations. The FRIS-model-derived thermal states for individual CMEs reveal their diverse thermal evolution near the Sun, with most CMEs transitioning to an isothermal state at 6-9 Rsun, except for CME4, which exhibits an adiabatic state due to a slower expansion rate. The complex ejecta at 1 AU shows a predominant heat-release state in electrons, while the ions show a bimodal distribution of thermal states. On comparing the characteristics of CMEs near the Sun and at 1 AU, we suggest that such one-to-one comparison is difficult due to CME-CME interactions significantly influencing their post-interaction characteristics.

Cosmic rays (CR), both solar and Galactic, have an ionising effect on the Earth's atmosphere and are thought to be important for prebiotic molecule production. In particular, the $\rm{H_2}$-dominated atmosphere following an ocean-vaporising impact is considered favourable to prebiotic molecule formation. We model solar and Galactic CR transport through a post-impact early Earth atmosphere at 200Myr. We aim to identify the differences in the resulting ionisation rates, $\zeta$, particularly at the Earth's surface during a period when the Sun was very active. We use a Monte Carlo model to describe CR transport through the early Earth atmosphere, giving the CR spectra as a function of altitude. We calculate $\zeta$ and the ion-pair production rate, $Q$, as a function of altitude due to Galactic and solar CR. The Galactic and solar CR spectra are both affected by the Sun's rotation rate, $\Omega$, because the solar wind velocity and magnetic field strength both depend on $\Omega$ and influence CR transport. We consider a range of input spectra resulting from the range of possible $\Omega$, from $3.5-15\, \Omega_{\rm{\odot}}$. To account for the possibility that the Galactic CR spectrum outside the Solar System varies over Gyr timescales, we compare top-of-atmosphere $\zeta$ resulting from two different scenarios. We also consider the suppression of the CR spectra by a planetary magnetic field. We find that $\zeta$ and $Q$ due to CR are dominated by solar CR in the early Earth atmosphere for most cases. The corresponding $\zeta$ at the early Earth's surface ranges from $5 \times 10^{-21}\rm{s^{-1}}$ for $\Omega = 3.5\,\Omega_{\rm{\odot}}$ to $1 \times 10^{-16}\rm{s^{-1}}$ for $\Omega = 15\,\Omega_{\rm{\odot}}$. Thus if the young Sun was a fast rotator, it is likely that solar CR had a significant effect on the chemistry at the Earth's surface at the time when life is likely to have formed.