The Tandem Reconnection And Cusp Electrodynamics Reconnaissance Satellites (TRACERS) mission implemented a magnetics control plan to help meet its science objectives. TRACERS studies the variability of magnetic reconnection using two closely spaced spacecraft taking high-cadence plasma measurements through the northern magnetospheric cusp. Science measurements of the local AC and DC magnetic field and medium energy electrons can be degraded by local stray magnetic fields from the spacecraft and instruments. The measured low frequency and static magnetic field can be directly contaminated by static magnetic fields from magnetised or ferromagnetic materials while the AC magnetic fields are susceptible to contamination from time varying electrical currents. Incoming electrons can be deflected by local magnetic fields altering their apparent incoming direction at detection. TRACERS uses a combination of source control, physical separation, magnetic screening, and post-hoc signal processing to ensure it meets its measurement objectives.
The investigation and utilization of water-ice resources on extraterrestrial bodies represent a frontier of deep space exploration, carrying milestone significance for understanding the origin of the Solar System, assessing the potential for life, and enabling future human deep-space missions. This review systematically summarizes the exploration of extraterrestrial water ice, covering the historical development of exploration missions, the occurrence environments of water ice on representative extraterrestrial bodies, current sampling technologies, major technical challenges, and future development trends. It focuses on key ice-rich bodies, such as the lunar poles, Mars, and icy moons including Europa and Enceladus, and analyzes their unique environmental characteristics. The review further discusses the severe challenges posed by extreme low temperatures, vacuum conditions, weak gravity, and unknown mechanical properties for extraterrestrial water-ice exploration and sampling missions. Building on this context, the review examines a variety of sampling technologies designed for such environments, including mechanical drilling, thermal melting drilling, and surface sampling devices. Their working principles, performance in extraterrestrial environments, and respective advantages and limitations are assessed in detail. Finally, future trends are highlighted, identifying sample return, in-situ resource utilization, and deep drilling as major directions for continued development. It emphasizes that the development of lightweight, low-power, high-reliability, and multifunctional sampling systems with intelligent sensing and adaptive capabilities will be critical to future technological breakthroughs and deep-space exploration.
The search for life on exoplanets is difficult due to observational limitations stemming from vast separating distances. The Habitable Zone (HZ) is a simplifying framework for identifying exoplanets that may be suitable for life, given our observational limitations. The HZ framework is built on many simplifying assumptions and only attempts to bound the circumstellar regions where surface oceans are not precluded. In other words, HZ exoplanets are where surface oceans are possible, not necessarily where life is possible. Water is essential for life as we know it, however, life requires additional factors such as nutrients and a magnetosphere. Therefore, the criteria of the HZ framework is one step removed from assessing the suitability for life. This nuance is easily lost in translation and has caused confusion among researchers and the general public; as the term “Habitable Zone” implies that planets in the HZ are habitable and those outside are uninhabitable. Here we define a new term, euhabitable (suitable for life), that addresses this confusion. In brief, a euhabitable exoplanet can exist outside the HZ (e.g., a Europa-like planet), and an uninhabitable exoplanet can exist within the HZ (e.g., a desiccated planet). The “euhabitable” term can be used to discuss these cases explicitly, avoiding confusion between an exoplanet’s suitability for life and it’s position relative to the HZ. The euhabitable framework is informed by the advancements in astrobiology over the past three decades, and primes exoplanet science for the future by moving the habitability discussion beyond “follow the water.”
The Earth’s ionosphere involves long-standing plasma problems, such as instabilities and nonlinearity. The global ionospheric layers contain multi-scale irregular structures characterized by plasma density fluctuations and random permittivity. These ionospheric structures can degrade or even disrupt trans-ionospheric radio signals from satellite systems, and also disturb HF communications by altering the ionospheric properties. Ionospheric disturbance is one of the major problems in space weather, due to its unique role in the solar-terrestrial causal chain. To address these, the artificial ionospheric modification, achieved through the release of chemicals, enables a deeper understanding of physical mechanisms, provides a means to cope with ionospheric scintillations, and allows for the generation of artificial plasma clouds to tailor radio wave propagation. This paper analyzes the challenges, opportunities, and issues in the frontiers of artificially tailored radio wave propagation via ionospheric chemical releases. Some suggestions are also put forward for future experiments.
Ultraviolet (UV) observations provide a uniquely powerful window into the hot and evolved stellar populations that shape the structure, evolution and integrated light of star clusters. Because UV wavelengths are highly sensitive to massive main-sequence stars, blue straggler stars (BSS), extreme-horizontal-branch (extreme-HB) stars, post-AGB objects, interacting binaries and compact remnants, UV studies enable constraints on fundamental processes that are inaccessible at optical and infrared wavelengths. This review synthesises five decades of UV investigations of star clusters across the Milky Way, the Magellanic Clouds (MCs) and nearby galaxies, drawing on results from early space telescopes, wide-field surveys, high-resolution imagers and the recent capabilities of AstroSat/UVIT and Swift/UVOT. In Galactic open clusters, UV photometry has revealed diverse compact companions—including white dwarfs, hot subdwarfs and stripped stars—and has been essential for establishing the mass-transfer origins of BSS and related populations such as Blue Lurkers and yellow stragglers. In globular clusters, UV imaging is indispensable for identifying multiple stellar populations through UV-sensitive molecular bands, probing helium enrichment and mapping HB morphologies from cluster cores to tidal radii. Wide-field UVIT surveys have provided homogeneous catalogues of HB and post-HB stars, extending earlier Hubble Space Telescope results to full-cluster scales. In the MCs, UV observations have transformed our understanding of multiple populations in intermediate-age clusters, rotation-driven extended main-sequence turn-offs and the recently identified UV-dim phenomenon. UV spectroscopic surveys have advanced constraints on massive-star evolution, winds and binarity at low metallicity. Meanwhile, UV mapping of the Magellanic Bridge demonstrates ongoing massive-star formation in low-density tidal environments. Beyond the Local Group, UV studies of extragalactic clusters reveal star-formation histories, stellar feedback and population synthesis constraints in diverse galactic environments. Collectively, UV observations now form a cornerstone of star cluster astrophysics and will continue to do so with upcoming missions.
Magnetic switchbacks are large-amplitude fluctuations in the interplanetary magnetic field, and appear frequently in the near-Sun solar wind explored recently by Parker Solar Probe: these new observations have prompted many new studies into their properties and origins. Here, we first review what is known about how switchbacks evolve as they travel away from the Sun: both in terms of their expansion-driven growth and their decay due to various processes like turbulence, reconnection, dispersion, parametric instability, and interaction with interplanetary shocks. We then review the current state of knowledge on how switchbacks impact the physics of the solar wind as a whole: in terms of the turbulent cascade, acceleration and heating of the wind, modification of the open solar flux and scattering of energetic particles. Finally, we suggest future studies to further our understanding of switchback evolution and impacts on the heliosphere.
The plasma environment of our neighboring planets, Venus and Mars, differs significantly from Earth’s. Although neither of them possesses a dominant intrinsic dipolar magnetic field, there are still induced magnetospheres forming around the two planets, due to the interaction of the solar wind and the interplanetary magnetic field (IMF) with their conductive ionospheres, exospheres, and the localized crustal magnetic fields in the case of Mars. Induced magnetospheres, their associated plasma environments, and the physical processes within them are particularly susceptible to the changing upstream conditions. The increasing number of successful and long-lived missions during the last few decades has been key for describing the fundamental structures and processes comprising the induced magnetospheres of the two planets. Nevertheless, their induced magnetotails have been more challenging to probe, due to the restrictions of the orbital geometry of planetary missions. Here, we present the latest discoveries and a comprehensive comparison between the Venusian and Martian induced magnetotails, and we highlight the need for further exploration of these regions. Atmospheric escape and energy transfer processes and paths are inextricably linked with the climate history and the disappearance of water at Mars, though there are many unknowns still in the case of Venus. Past and current missions utilizing particle and fields instruments have explored a great part of the plasma environments of Venus and Mars. Several plasma boundaries, shaped by both internal and external factors, divide the planetary environments and magnetospheres into different plasma regimes and have been described by observations and models. Simulations and observations have also been utilized to investigate the magnetotail structure of the two planets, which appears to be governed mainly by the IMF, the solar wind dynamic pressure, and the crustal magnetic fields in the case of Mars. At Mars, the presence of the crustal magnetic fields, which are regions of crustal magnetization on the surface of the planet clustered mostly in the southern hemisphere, further complicates the interaction of the solar wind and the IMF with the planet’s plasma environment, thus justifying the term ‘hybrid’ – instead of induced – that is often used to describe the Martian magnetosphere. The existence of a magnetotail twist, as well as a first approach on mapping the structure of the current systems, has been reported at Mars, whereas different types of magnetotail current sheet flapping motion have been observed at both Mars and Venus. The magnetic topology, which describes the morphology of closed, open, and draped magnetic field lines over a planet, has also been inferred and explained for both planets. Escape processes, escape rates and their response to space weather have been reported, and we now have a better idea of the differences between the two planets. Escaping structures, contributing with a bulk removal of plasma, have also been observed in their magnetotails. Nevertheless, much still remains unknown, for example the specifics of how individual processes respond to solar drivers. Mars and Venus are not the only solar system bodies with no global intrinsic magnetic field. Induced magnetotails are formed around Saturn’s moon Titan and comets too. A comparison between those bodies and Venus and Mars will provide a broader and general picture of induced and hybrid magnetotails, which could help future investigations of the plasma environments and tails of exoplanets. Lastly, in this review paper, we also summarize the questions that remain unanswered, emphasizing the need for future missions.
The homopause marks the transition in a planetary atmosphere from turbulent mixing, which maintains a well-mixed composition, to molecular diffusion, which causes the diffusive separation of chemical species, impacting how these are distributed in the upper atmosphere and potentially escape to space. Here, we analyse simulations from the Mars Planetary Climate Model (Mars PCM) to investigate the variability of the Martian homopause in diurnal, seasonal and interannual timescales. The simulations reveal strong seasonal and latitudinal trends, with homopause altitudes peaking in the summer polar regions (∼120–130 km) and showing minimum values during the winter southern polar region (∼60–90 km). The simulations predict diurnal variations in the homopause altitude typically within 5–15 km and suggest that dust events can raise the value of the homopause altitude by 10–20 km, depending on the intensity of the event. When comparing the Mars PCM results with empirical estimates of the homopause altitude and density derived from Martian atmospheric data, we find that the model captures the overall magnitude and seasonal/latitudinal variability of the homopause, but appear to underestimate the strength of the diurnal cycle. Finally, we use the Mars PCM data to constrain the variability of the eddy diffusion coefficient, which can vary by one or two orders of magnitude across latitude and season. The derived parameterisation and variability of the eddy diffusion coefficient is suitable for use in one-dimensional models devoted to understanding seasonal difference in atmospheric photochemistry and escape.
Ultraviolet (UV) spectroscopy has played a central role in advancing our understanding of young planetary systems and their circumstellar environments. The UV domain uniquely probes hot plasmas, accretion shocks, magnetospheric accretion, stellar atmospheres, and outflows through spectral tracers that are otherwise inaccessible at optical or infrared wavelengths. Over the past several decades, space-based observatories have enabled high-resolution studies of resonance lines such as C IV, Si IV, N V, and Mg II, revealing the complex interplay between magnetospheric accretion, stellar activity, and mass outflows in pre-main-sequence stars. This review synthesizes observational results from major UV missions and examines how UV diagnostics constrain physical conditions in young stars, including temperature structure, mass accretion rates, wind kinematics, and magnetic topology. We discuss the evolution of theoretical models in light of UV data, identify persistent uncertainties, and highlight emerging directions for future instrumentation. UV spectroscopy remains indispensable for understanding stellar and planetary system formation.
We review the key observations and theories relevant to the internal structure and dynamics of the Galilean satellites. Key observations include: the bulk densities and degree-two gravity coefficients of the moons; the presence of conductive subsurface layers, as inferred from magnetic induction; and the surface compositions. All the moons, with the possible exception of Callisto, appear to be differentiated (denser components have separated from lighter components). Ganymede and Io have iron cores; Europa may have one. The outer three moons all likely possess subsurface oceans; for Europa the ocean overlies rock, while for the other two it overlies higher-pressure ice phases. Io is partially molten but does not possess a shallow magma ocean. Tidal heating is the dominant energy source at Europa and Io, and may have affected Ganymede’s long-term evolution. The dynamics of the subsurface oceans are of considerable theoretical interest but are only weakly tied to current or likely future observations. We identify seven outstanding questions regarding internal structures, some of which will be answered by the forthcoming JUICE, Europa Clipper and Tianwen-4 missions.
This article reviews the short-, medium-, and long-term prospects for characterizing rocky exoplanets, a central goal of contemporary astrophysics. The primary objectives are to determine whether these planets host atmospheres; if so, to constrain their molecular composition and search for potential biosignatures; if not, to infer their surface composition and thereby enabling a form of exo-geology. In the near term, the James Webb Space Telescope (JWST) will continue to lead this effort through photometric and spectroscopic observations of transits, eclipses, and phase curves, primarily targeting rocky exoplanets orbiting M dwarfs, including a limited number within their habitable zones. By the early 2030s, Giant Segmented-Mirror Telescopes (GSMTs) will provide the combination of high angular resolution, high contrast, and high spectral resolution needed to characterize rocky exoplanets around nearby M dwarfs via direct imaging, significantly broadening the accessible target sample and enabling detailed atmospheric and surface studies. Extending these investigations to rocky exoplanets orbiting solar-type stars, particularly those within habitable zones, will require the launch of next-generation space observatories in the 2040s, such as the Habitable Worlds Observatory (HWO), optimized for ultraviolet-to-near-infrared observations, and the Large Interferometer For Exoplanets (LIFE), designed for mid-infrared interferometry. In parallel, characterizing the broader planetary environment — including host stars and additional companions — will provide essential context. Missions such as Gaia (astrometric detection of companions), PLATO, Earth 2.0 (stellar characterization via asteroseismology), and Ariel (population-level atmospheric studies) will offer critical complementary insights into the architectures and habitability of nearby planetary systems.
The ultraviolet (UV) spectral domain occupies a unique position in stellar astrophysics, serving as the bridge between the thermal continuum of photospheres and the high-energy, non-thermal processes of stellar coronae and winds. This article provides a review of stellar physics in the UV, addressing both the theoretical framework and observational applications across the Hertzsprung-Russell diagram. We explicitly structure our discussion around key scientific questions, demonstrating that accurate spectral synthesis in this regime demands Non-LTE radiative transfer codes, which in turn rely on precise atomic collision and recombination rates. We highlight how a critical scarcity of modern laboratory astrophysics data limits these models, particularly for complex ions. Moving to observational diagnostics, we review how UV spectroscopy constrains diffusion and radiatively driven winds in hot subluminous stars, and traces shock dynamics and abundance patterns in Planetary Nebulae and Supernova Remnants. In the context of star clusters, we illustrate how UV sensitivity to light-element variations (C, N, O) allows us to disentangle multiple stellar populations that appear degenerate in optical bands. We conclude that future progress depends on facilities capable of high-resolution spectroscopy, time-domain monitoring, and polarimetry to recover these diagnostic tracers and resolve the physics of stellar feedback.
Hera is the European part of the Asteroid Impact Deflection Assessment (AIDA) international collaboration with NASA who is responsible for the DART (Double Asteroid Redirection Test) kinetic impactor spacecraft. Hera has been launched in October 2024 and will arrive at the binary asteroid (65803) Didymos, which includes the main body Didymos and its small moon Dimorphos, in fall 2026. The Hera mothercraft accommodates two 6U CubeSats, one of which is Milani, named after Professor Andrea Milani, for his unique contribution to asteroid science and visionary role in defining a viable planetary defence technique. The Milani CubeSat is developed by Tyvak International leading a consortium of European universities, research centers and firms from Italy, Czech Republic, Finland. During the cruise to Didymos (ongoing, the total duration is approx. 2 years), the Milani CubeSat is hosted inside the Hera mothercraft, periodically checked for health, and charged. At arrival it will be deployed and commissioned while Hera is performing the Didymos detailed characterization phase, at about 10 to 20 km distance from the asteroid. Milani mission objectives are defined to add scientific value to the Hera mission: i) Map the global properties of Didymos and Dimorphos, ii) Characterize the asteroids’ surface, iii) Evaluate the effects of the DART impact on the binary system and support gravity field determination, iv) Characterize the dust environment around the asteroid, enhancing the scientific return of the whole Hera mission. The instruments supporting the mission are “ASPECT” (VTT, Finland), a visible – near-infrared imaging spectrometer,“VISTA” (INAF, Italy), a thermogravimeter characterizing dust particles below 10 μm, and the NavCam (PoliMi/Tyvak, Italy), providing optical images in RGB bands.
We review the key observations and theories relevant to the origin and evolution of the Galilean satellites. Key observations include: the potentially undifferentiated nature of Callisto; the increasing ice fraction with semi-major axis; the present-day existence of the Laplace resonance; the potential resurfacing of Ganymede mid-way through its evolution; and the metal-enriched nature of Jupiter’s envelope. The most widely accepted theory for the formation of the satellites is the so-called “starved disk” model, although newer alternatives including decretion disks and pebble accretion have also been proposed. Models that allow slow satellite formation in a cold disk are preferred, based on the density progression and Callisto’s apparent differentiation state. Major model uncertainties include the angular momentum distribution of the material infalling to the circumplanetary disk, the source of the solids, and the thermal and viscosity structure of the disk. We identify six outstanding questions, some of which will be answered by JUICE, Europa Clipper and Tianwen-4. A major difficulty in answering some questions is overprinting of primordial characteristics by later events.
The Solar Wind Electron (SWE) instrument of the Interstellar Mapping and Acceleration Probe (IMAP) mission is designed to measure the in situ solar wind thermal and suprathermal electrons at the spacecraft. SWE contributes to the IMAP science objective to understand particle injection and acceleration processes near the Sun and in the heliosphere and heliosheath, and provides context for the IMAP measurements of energetic neutral atoms from the outer heliosphere. SWE measures the solar wind thermal and suprathermal electron distribution from 1–5000 eV in 24 log-spaced steps with energy resolution Δ E/E of 14
The IMAP-Hi Energetic Neutral Atom (ENA) Imager on NASA’s Interstellar Mapping and Acceleration Probe (IMAP) mission (McComas et al. 2018a, 2025) is designed to measure ENAs from the global interaction between the heliosphere and the local interstellar medium (LISM). These ENAs are initially plasma ions of solar wind origin that are neutralized by charge exchange with the cold neutral atoms of LISM that freely flow through the heliosphere-LISM interaction region. IMAP-Hi consists of two identical single-pixel sensors, each covering the ENA spectral range from 0.44 keV to 15.6 keV over nine contiguous energy passbands and having an approximately conical field-of-view (FOV) of 4.1o full width at half maximum (FWHM). The Hi-45 sensor points 45o relative to the spacecraft spin axis from the antisunward direction; each spacecraft spin, it measures ENA intensity over a circular swath with half-cone angle 45o centered on the ecliptic plane. The Hi-90 sensor points 90o relative to the spin axis; each spacecraft spin, it measures ENA intensity over a great circle in the sky, sampling both the north and south ecliptic poles. As the IMAP spin vector is re-pointed daily toward the Sun, the ecliptic longitude of the swaths moves daily by ∼1o such that a full sky map is acquired by Hi-90 every six months and a complete low latitude (−45o to +45o) map is acquired by Hi-45 annually. The IMAP-Hi sensor design has direct heritage from the IBEX-Hi imager on the Interstellar Boundary Explorer (IBEX) mission, with substantial improvements in energy range, energy resolution, angular resolution, signal-to-noise ratio, and, for ecliptic latitudes within ±45o, temporal resolution and exposure time. The global ENA maps acquired by IMAP-Hi partially overlap in energy and viewing with the ENA maps acquired by the IMAP-Lo and IMAP-Ultra ENA imagers, which we combine to answer fundamental questions about the structure and dynamics of the interaction of the heliosphere and the LISM.
NASA’s Mars Atmosphere and Volatile EvolutioN spacecraft carries an extensive suite of instruments for characterizing the Mars upper atmosphere. Of these, the NGIMS, IUVS, and EUVM instruments produce datasets for CO2 density and neutral atmosphere temperature. The different instruments and retrieval methods utilized provide an expansive view of the Mars upper atmosphere. To make full use of the geophysical coverage offered by these datasets, we undertake a systematic comparison of the datasets to understand where they are different and how any biases between datasets can be removed. We conduct pairwise comparisons between datasets, binning the data by geophysical and forcing parameters, to develop adjustment factors that can be used to adjust the measured CO2 density and neutral temperature of one dataset to nominal agreement with another. The determined adjustment factors are reported for use by the wider Mars aeronomy community.
Cosmic magnetic fields are typically inhomogeneous and often highly tangled due to large-scale plasma flows, turbulence, and instabilities. If the variations in the magnetic field occur on scales that are large compared to the gyro-radius of the plasma electrons, the electrons are primarily confined to gyro-centre trajectories along the field lines. Therefore, in-situ electron measurements help us map out the connectivity of the magnetic field in space plasmas. Gyro-centre drifts, wave-particle interactions, trapping, and cross-field diffusion are processes related to field inhomogeneities and fluctuations; they have the potential to modify or even disrupt the transport of electrons along field lines. We introduce the basic principles of electron transport in tangled magnetic fields and review the creation of tangled fields through turbulence and instabilities as well as the modulation of parallel electron transport through kinetic instabilities. We then describe trapping and de-trapping effects in inhomogeneous magnetic fields, as well as electron diffusion and energisation across the magnetic field. The transport of electrons in tangled fields results from a complex interplay of plasma processes that occur on a broad range of scales. A combination of in-situ plasma measurements, remote-sensing plasma observations, and plasma theory and simulations is required to resolve this contemporary challenge to the fields of heliophysics and astrophysics.
The magnetometer (MAG) is one of the ten scientific instruments on the Interstellar Mapping and Acceleration Probe (IMAP), which will take in situ and remote measurements from a Sun-Earth L1 halo orbit. MAG contributes to IMAP science goals of investigating the acceleration and propagation of energetic particles, as well as providing real-time space weather monitoring data. The magnetometer is a conventional dual sensor fluxgate instrument with a noise floor under 10 pT at 1 Hz, taking science measurements continuously at 2 vectors/s as well as a burst mode of 64 vectors/s for at least 8 hours per day. It also provides a real-time space weather monitoring product at 4 second cadence. We describe the requirements, design and performance of the instrument, including a novel lossless compression algorithm. Data products, processing and calibration plans are presented.
