NASA’s Interstellar Mapping and Acceleration Probe (IMAP), scheduled for launch in September 2025 to a deep-space orbit around the Earth–Sun L1 point, will open a new observational window on particle acceleration throughout the heliosphere and on the connections between the Sun, the heliosphere, and the local interstellar environment. IMAP will also complement the existing fleet of near-Earth spacecraft, enabling coordinated multi-mission investigations with unprecedented detail.
For this session, we invite contributions from across the heliophysics and astrophysics communities, including theoretical studies, modelling efforts, and data analyses from both current and past missions. We particularly encourage work addressing particle acceleration from 1 au to the heliopause, sampling of interstellar material, and the dynamics of the heliospheric boundary regions. New results on Sun–heliosphere–interstellar coupling, multi-mission studies in near-Earth space, and early IMAP science findings are especially welcome.
Orals: Mon, 4 May, 10:45–12:30 | Room L1
NASA’s Interstellar Mapping and Acceleration Probe (IMAP) mission launched on 24 September 2025, inserted into L1 orbit on 8 January 2026, and began routine science operations on 1 February 2026. The spacecraft and all ten instruments are fully commissioned and operating well, which allows IMAP to provide its planned extensive and well-coordinated new observations of the inner and outer heliosphere and scientific closure on two of the most important topics in Heliophysics: 1) the acceleration of charged particles and 2) the interaction of the solar wind with the local interstellar medium. IMAP’s ten instruments provide complete and synergistic observations that examine particle energization processes at 1 au while simultaneously probing the global heliospheric interaction with the very local interstellar medium (VLISM). The in situ observations include solar wind electrons and ions from solar wind up through suprathermal ions, pickup ion, and energetic ions, as well as the interplanetary magnetic field. IMAP provides Energetic Neutral Atom (ENA) global imaging of the outer heliosphere via ENAs from 10s of eV up through 100s of keV, as well as observations of interstellar neutral atoms traversing the heliosphere. IMAP also directly measures interstellar dust that enters the heliosphere and the solar-wind-modulated ultraviolet glow. The IMAP mission also provides extensive new real-time measurements critical to Space Weather observations and predictions, and much more. This paper provides a brief mission overview, as well as some first light and early science observations.
How to cite: McComas, D. and the IMAP Mission team: The Interstellar Mapping and Acceleration Probe (IMAP) Mission, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3610, https://doi.org/10.5194/egusphere-egu26-3610, 2026.
In the coming years, New Horizons (NH) is expected to exit the heliosphere by crossing the solar wind termination shock (TS) and make the first measurements of pick-up ions (PUIs) across the TS boundary. To date, the only working spacecraft to have crossed the TS are Voyager 1 and 2, with Voyager 1 encountering the TS on day of year (DOY) 351, 2004 at ~94 AU, and Voyager 2 undergoing multiple crossings between DOY 243 and 344, 2007 at ~83.6 AU. Although NH is approximately aligned in heliolongitude with Voyager 2, its trajectory lies near the heliographic equator, in contrast to the higher northern and southern heliolatitudes of Voyager 1 and 2, respectively.
In this work, we analyze energetic particle observations (∼40–200 keV) from the Voyager Low Energy Charged Particle (LECP) instruments and the Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) onboard NH to characterize radial intensity variations in the outer heliosphere. Voyager 1 and 2 observations show a systematic decrease in energetic particle intensities with increasing heliocentric distance, followed by a recovery prior to their respective TS crossings, forming a heliospheric energetic particle “valley.” NH/PEPSSI observations from 5 to 60 AU exhibit a comparable radial decline but have yet to show the expected increase on the march toward the TS crossing.
To mitigate temporal variability associated with solar cycle effects, all observations are normalized using near-Earth energetic particle measurements from IMP-8/EPE and ACE/EPAM. The combined radial profiles from Voyager and NH are well described by a double power-law with a break at~33 AU. The combined radial profiles from Voyager and NH are well described by a power-law dependence with a distinct break beyond ~33 AU. This break likely reflects a transition in the dominant transport and/or acceleration mechanisms operating in the inner and outer regions separated by this radial distance. The presence of this break across multiple heliolatitudes suggests a global heliospheric feature, potentially reflecting changes in particle transport, acceleration, or local plasma conditions in the outer heliosphere. By scaling the Voyager observations to the NH measurements, we estimate a NH TS crossing between 2027 (~68 AU) and 2034 (~83 AU).
How to cite: Nikoukar, R., Hill, M. E., Dialynas, K., Krimigis, S. M., Brown, L., Kollmann, P., Decker, R. B., Manweiler, J. W., Reeve, W. S., Florinski, V., Zhang, M., Richardson, J., Opher, M., Giacalone, J., Adhikari, L., Brandt, P. C., carcaboso, F., Cooper, J. F., Elliott, H. A., and Gold, R. and the Romina Nikoukar: An Energetic Particle Valley in the Outer Heliosphere: Insights from Voyager and New Horizons and Implications for New Horizons’ Termination Shock Encounter, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15428, https://doi.org/10.5194/egusphere-egu26-15428, 2026.
The Interstellar Dust Experiment (IDEX) is a dust impact ionization Time-of-Flight (ToF) mass spectrometer launched onboard the Interstellar Mapping and Acceleration Probe (IMAP) on September 24, 2025. IMAP is in nominal science operations at the Sun-Earth Lagrange Point L1, with IDEX passively collecting cosmic dust grains at a cadence of roughly one interplanetary particle per week. IDEX will detect and analyze both Interstellar Dust Grains (ISDs) from the Local Interstellar Medium (LISM) as well as Interplanetary Dust grains (IDPs). ISD collection will begin in April 2026 as we enter the interstellar dust focusing season. IDEX will collect a variety of ISDs and IDPs over its lifetime, ranging from pristine to heavily processed particles that are a mixture of mineral and organic material.
We investigate how IDEX can be used to determine the degree of processing dust grains have undergone. These studies inform the analysis of IDEX flight data representative of organic and mineralogical cosmic dust grains. Assessments of aromaticity and the presence of functional groups can be used to determine the processing of organic species. Polycyclic aromatic hydrocarbons (PAHs) are the most pristine organic compounds. PAH destruction and processing lead to the production of heterocyclic compounds and decreasing aromaticity in organic species. Minerals can be appraised via the degree of serpentinization and conversion from crystalline to amorphous silicates. IDEX's large effective area combined with high mass resolution (m/dm > 200) and dynamic range make it well suited to assess minute variations in mass spectra pointing to pristine versus processed materials. Various campaigns from the last two years build and support the techniques presented here to analyze IDEX flight data.
How to cite: Mikula, R., Sternovsky, Z., Horyani, M., Armes, S., Ayari, E., Bouwman, J., Hillier, J., Khawaja, N., Postberg, F., Kempf, S., and Srama, R.: Measuring the processing of organic and mineral cosmic dust grains with the Interstellar Dust Experiment (IDEX) instrument, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14550, https://doi.org/10.5194/egusphere-egu26-14550, 2026.
Launched in September 2025, NASA’s Interstellar Mapping and Acceleration Probe (IMAP) now operates at the Sun–Earth L1 Lagrange point to investigate the interaction between the heliosphere and its interstellar environment. Among its ten-instrument payload is the Interstellar Dust Experiment (IDEX), which is designed to measure the flux, size distribution, and chemical, elemental, and isotopic composition of dust particles entering the solar system.
IDEX directly samples interstellar dust (ISD) originating in the local interstellar medium (LISM), providing unique insight into the composition of contemporary interstellar solid matter. A key scientific objective is to assess whether the present-day LISM dust population is compositionally consistent with the primordial material from which the solar system formed. In addition to ISD, IDEX measures interplanetary dust particles (IDPs) of cometary and asteroidal origin, including grains that may preserve pre-solar molecular cloud material as well as particles altered by solar system processing. These observations enable comparisons between interstellar, cometary, and asteroidal dust and help constrain the origins and evolutionary histories of organic-rich materials.
IDEX measurements of the directional and size distributions of ISD provide critical constraints on models of dust transport through the heliosphere, including the filtering effects of heliospheric magnetic fields and solar activity on small, charged grains. These data contribute to improved understanding of the heliospheric boundary and the processes governing the penetration of dust into the inner heliosphere.
IDEX is an impact-ionization time-of-flight mass spectrometer that analyzes ions generated by high-velocity dust impacts on a target surface. This presentation provides an overview of IDEX’s scientific objectives and measurement capabilities and reports on early in-flight performance and initial results, demonstrating IDEX’s role in linking interstellar and solar system material populations.
How to cite: Horanyi, M., Tucker, S., Sternovsky, Z., Knappmiller, S., Ayari, E., Mikula, R., Kempf, S., and Szalay, J.: First results of the Interplanetary Dust Experiment (IDEX) onboard the Interplanetary Mapping and Acceleration Probe (IMAP) Mission., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15635, https://doi.org/10.5194/egusphere-egu26-15635, 2026.
The IMAP-Hi Imager is one of three advanced imagers on the Interstellar Mapping and Acceleration Probe (IMAP) designed to remotely measure and detect energetic neutral atoms (ENAs) from the outer heliosphere. These ENAs are formed by charge exchange of ions in a hot plasma with cold ambient neutral atoms, travel in ballistic trajectories from the source plasma, and thus carry crucial information about their source plasma population, enabling observation of the global structure and dynamics of plasma domains across the outer heliosphere and beyond. IMAP-Hi was optimized to measure neutral Hydrogen over the energy range (500 eV – 15 keV) of core and suprathermal solar wind ion populations. IMAP-Hi is significantly more capable than its predecessor IBEX-Hi, with substantially improved energy range, energy resolution, imaging resolution, sensitivity, and background rejection. IMAP-Hi is comprised of two identical ENA imagers, enabling larger combined geometric factor, enhanced viewing near the ecliptic plane (heliospheric nose, tail, low-latitude ribbon, and flanks), and higher temporal cadence of viewing. Hi45 observes a 45° half-angle cone centered on the spin axis in an antisunward direction, whereas Hi90 views perpendicular to the spin axis. Observations from IMAP-Hi, IMAP-Lo and IMAP-Ultra will allow for a transformational advance in our understanding of the interaction between the heliosphere and the local interstellar medium (LISM), and the particle processes occurring in these regions. We give an overview of IMAP-Hi performance status on early flight operations of IMAP-Hi and present an initial look at the first IMAP-Hi ENA sky maps.
How to cite: Reisenfeld, D., Funsten, H., and Allegrini, F. and the IMAP-Hi Team: First Light from the IMAP-Hi Energetic Neutral Atom (ENA) Imager on the IMAP Mission, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15922, https://doi.org/10.5194/egusphere-egu26-15922, 2026.
Space Research Centre, Polish Academy of Sciences, Warsaw, Poland GLOWS (GLObal solar Wind Structure) is one of the experiments on a NASA mission IMAP (Interstellar Mapping and Acceleration Probe). The objective of GLOWS is to investigate the global heliolatitude structure of the solar wind and its evolution during the solar cycle. Additionally, GLOWS investigates the distribution of interstellar neutral hydrogen (ISN H) and the solar radiation pressure acting on ISN H. The objectives of GLOWS are accomplished by observation of the heliospheric hydrogen backscatter glow (the helioglow). The helioglow is created by resonant excitation of ISN H atoms within several au from the Sun by the intense solar electromagnetic radiation in the Lyman-α waveband 121.567 nm. The H atoms move in this region collisionless, and thus immediately after excitation of the photons from the Sun, they re-emit them in random directions. Those re-emitted photons form the helioglow. The intensity of the helioglow observed at ∼1 au varies across the sky, dependent on the location of the observer; it is on the order of 300–1000 Rayleigh. We present an update on the GLOWS instrument observations, carried on since November 2025, and the first latitudinal profiles solar wind speed and density obtained on the orbit.
How to cite: Kubiak, M., Bzowski, M., Porowski, C., Strumik, M., and Kowalska-Leszczynska, I.: Solar wind structure seen by IMAP/GLOWS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21088, https://doi.org/10.5194/egusphere-egu26-21088, 2026.
NASA’s Interstellar Mapping and Acceleration Probe (IMAP) mission is providing comprehensive observations of both the in situ magnetic field and charged particle environment as well as remotely exploring energetic neutral atoms (ENAs), dust particles, and ultraviolet photons that originate from the outer heliosphere and beyond. Collectively, these measurements will advance our understanding of particle acceleration throughout the solar system and how the solar wind and interstellar medium interacts with the boundary of our heliosphere. Here, we focus on heliospheric observations from the IMAP-Ultra (Ultra) instrument, which is one of three ENA imagers on IMAP. Ultra measures ~3 – 100 keV neutral atoms over its large ~96° × 120° field of view (FoV), achieving angular resolutions ≤ 6° above 10 keV for H. Since IMAP’s launch on September 24, 2025, both Ultra sensors have been fully commissioned and are collecting new and exciting observations of the heliosphere. In this presentation, we highlight the global heliospheric configuration of > 3.7 keV H ENAs with detailed investigations into its spectral variations, evolving heliotail structure as a function of energy, and high angular resolution structures (up to 2° for energies > 30 keV).
How to cite: Clark, G., Gkioulidou, M., Mitchell, D., Dutton, N., DeMajistre, R., Provornikova, E., Walia, N., McComas, D., Reisenfeld, D., Funsten, H., Schwadron, N., Allegrini, F., Möbius, E., Bzowski, M., Turner, D., and Christian, E.: IMAP-Ultra Observations of Heliospheric Energetic Neutral Atoms, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16060, https://doi.org/10.5194/egusphere-egu26-16060, 2026.
Voyager 1 observed a shock-like discontinuity in the magnetic field strength and proton density at 2020.4, where the compression ratio was 1.35 and 1.36, respectively, and there was no change in the magnetic field direction [Burlaga et al., 2023]. After the jump, the magnetic field strength remained at a higher level until recently, creating a magnetic hump or pileup region. A magnetic pileup boundary or ion composition boundary has been routinely observed between the cometary bow shock and the comet’s ionopause. Solar wind protons are reflected from and heavy cometary pickup ions (mainly water group ions) are transmitted through this boundary, also known as protonopause. A similar ion composition boundary is expected in the inner heliosheath. As the solar wind approaches the very local interstellar medium (VLISM), the density of interstellar pickup protons and pickup He+ is gradually increasing. At the ion composition boundary, solar wind protons are reflected from the potential barrier. However, heavier pickup He+ ions with higher kinetic energy are able to cross this boundary, separating solar wind protons from heavier interstellar pickup ions. The electrons carry the magnetic field across the ion composition boundary without change in the magnetic field direction. To maintain pressure balance, the transmitted pickup ions and the magnetic field are compressed, creating a magnetic pileup region. Such an ion composition boundary or magnetic pileup boundary was first suggested by Sauer et al. [1995] in the magnetosheath of comets, Mars, and Venus. We suggest that the magnetic pileup boundary observed by Voyager 1 in 2020 is associated with an ion composition boundary in the solar wind. We present multi-fluid simulations of the ion composition boundary in the inner heliosheath. We show that an ion composition boundary is formed when the generalized sonic Mach number has reached 1 from below. The generalized sonic Mach number can be increased by either accelerating the plasma or reducing the sonic speed. As the solar wind approaches the heliopause, interstellar He+ pickup ions gradually reduce the sonic speed until the generalized sonic Mach number reaches 1 and a new type of plasma boundary, the ion composition boundary is formed. Our results imply that Voyager 1 is still in the inner heliosheath, has not crossed the heliopause, and has not entered the VLISM yet. We predict that Voyager 1 will continue to observe a stronger magnetic field until the heliopause is reached, which is expected to be a tangential discontinuity with a rotation in the magnetic field. The heliospheric ion composition boundary could be verified by New Horizons or other interstellar missions in the future, such as Interstellar Probe.
How to cite: Zieger, B. and Opher, M.: The Ion Composition Boundary: A New Type of Plasma Boundary in the Inner Heliosheath, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15488, https://doi.org/10.5194/egusphere-egu26-15488, 2026.
The variability of solar wind properties directly impacts the outer heliosphere, which is expected to exhibit a time-dependent structure, driving a significant impact on the solar modulation of galactic cosmic rays. In addition to the Voyager probes that provided in-situ measurements of the outer heliosphere's properties, the New Horizons mission is currently offering valuable experimental data as it approaches the termination shock. Moreover, remote sensing observations of the outer heliosphere via energetic neutral atom (ENA) fluxes from the Interstellar Boundary Explorer (IBEX) clearly indicate long-term variations in the heliospheric boundaries. Soon, the Interstellar Mapping and Acceleration Probe (IMAP) will also contribute high-accuracy ENA flux observations. By employing a semi-analytical approach to solve the solar wind dynamics throughout the heliosphere, we have developed a data-driven model that leverages available in-situ and remote sensing data from the outer heliosphere to estimate the long-term, time-dependent distance of the termination shock from the Sun and the width of the heliosheath. Our predictions align closely with Voyager observations, differing by only a few astronomical units (AU). This will enhance our understanding of cosmic ray modulation in the heliosphere.
How to cite: La Vacca, G., Della Torre, S., and Gervasi, M.: A Data-Driven Model for the Long-Term Variations of the Heliospheric Boundaries, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12257, https://doi.org/10.5194/egusphere-egu26-12257, 2026.
Posters on site: Tue, 5 May, 10:45–12:30 | Hall X4
The Low Energy Charged Particle (LECP; Krimigis et al. 1977) detector on Voyager is capable of measuring both the intensities and directions of energetic ions inside the heliosphere, providing direct sampling of their anisotropies at seven positions separated by 45 deg within its scan plane (one sector is blocked and is used for calibration purposes). When expressed in terms of roughly parallel (azimuthal; T) and perpendicular (Radial; R) components to the magnetic field direction, these anisotropies can provide important insights on the ion flow properties in and beyond the heliosheath. The analysis of 40-139 keV ions obtained by the LECP on Voyager 1 (V1) have shown that the azimuthal ion anisotropy turns to -T inside the heliosheath and revealed (a) the existence of a region of ~9-10 au before the HP, consistent with an inward radial flow of suprathermal ions into the heliosheath, and (b) a region of ~30 au beyond the heliopause (HP), consistent with a radial outflow of suprathermal ions leaking from the HS into interstellar space (Dialynas et al. 2021; 2024). Beyond this point, both the azimuthal and radial anisotropies are nearly zero, which roughly coincides with an abrupt and prolonged increase in both the magnetic field intensity (Burlaga et al. 2023) and electron densities (Kurth, 2024), known as “second pressure front” (pf2). The confluence of these observations indicate that V1 may have entered a new region in the VLISM beyond ~152 au, progressively developing characteristics akin to the pristine IS medium. Recent magnetic field observations (Burlaga et al. 2024a) have shown that the magnetic field parameters are consistent with a clear separation of two regions in space beyond ~155 au, exhibiting different magnetic field properties. Burlaga et al. (2024b), argued that this is a solar cycle effect in the VLISM, most likely a manifestation of a prolonged compression/shock of solar origin (e.g. Gurnett et al. 2021), whereas Fisk & Gloeckler (2022) argue that the Voyager measurements before the “pf2” are indicative of the flow of ions through the so-called “heliocliff”. We will present an update on the Voyager 1 measurements and preliminary results from the analysis of the >28 keV ion anisotropies from Voyager 2.
References
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How to cite: Dialynas, K., Krimigis, S., Decker, R., Hill, M., Nikoukar, R., Opher, M., and Liokati, E.: Properties of suprathermal ion anisotropies from LECP on the Voyager inside the heliosheath and beyond the heliopause, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8009, https://doi.org/10.5194/egusphere-egu26-8009, 2026.
Research on the interstellar medium and its interaction with the solar system constitutes a significant topic in planetary and heliospheric physics. As the Sun traverses the local interstellar cloud, interstellar neutrals penetrate the heliosphere, forming the interstellar wind and scattering solar extreme ultraviolet (EUV) emission lines. The intensity of this scattered radiation serves as a key diagnostic for the characteristic parameters of the interstellar wind, which are crucial for characterizing the structure of the heliosphere and the properties of the very local interstellar medium (VLISM). Meanwhile, EUV emission is a powerful tool for studying stellar and heliospheric evolution. Due to strong absorption by the interstellar medium at EUV wavelengths, accurate modeling is essential for interpreting observations and understanding these interactions. In this study, we review classical modeling methods for the density distribution of interstellar helium atoms in the heliosphere and the corresponding intensity of the resonantly scattered 58.4 nm radiation. We establish distinct density and intensity models for different orbital positions of Earth. Our results show that when Earth enters the helium focusing cone in the downwind region, both the helium density and the 58.4 nm radiation intensity increase rapidly, with the temperature effect playing a particularly important role. The radiation intensity in the downwind direction can reach up to 170 times that in the upwind direction. For simplicity, some secondary factors such as solar line width and Doppler shift effects were omitted. This modeling work provides valuable insights into the heliosphere-VLISM interaction and large-scale heliospheric structure, and can aid in the analysis of current and future measurements of the outer heliosphere and interstellar boundary.
How to cite: Lyu, J., Yuan, C., He, F., and Ying, B.: The density distribution and 58.4 nm radiation intensity of interstellar helium in the heliosphere: a model simulation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9134, https://doi.org/10.5194/egusphere-egu26-9134, 2026.
The Interstellar Mapping and Acceleration Probe (IMAP) is a heliophysics NASA mission to study the acceleration of charged particles and the interaction of the solar wind with the local interstellar medium. IMAP combines images of the plasma boundary regions of the heliosphere by means of Energetic Neutral Atoms (ENAs) with in-situ measurements of the interstellar neutrals flowing into the heliosphere and of the local plasma and dust environment in the solar wind. IMAP was launched in September 2025 and begins its nominal science phase in February 2026. At the same time, the Interstellar Boundary Explorer (IBEX, launched in 2008, IMAP's predecessor in terms of ENA imaging) is still active and continues its observations of heliospheric ENAs. IBEX covers an energy range of roughly 10 eV to 6 keV whereas IMAP covers a wider energy range from roughly 10 eV to 300 keV with three different types of ENA instruments.
In this presentation, we concentrate on the energy spectrum of heliospheric ENAs measured at solar wind energies all the way down to the lowest energy bins of IMAP and IBEX. This energy spectrum is crucial to understand the plasma pressure balance of the heliosphere with respect to the surrounding Very Local Interstellar Medium and to understand the various plasma populations and acceleration mechanisms in the heliosphere. IBEX observations indicate ENA intensities 1-2 orders of magnitude higher than most heliospheric ENA model predictions at energies between 50 eV and 500 eV. The spectrum seems to drop below a power law and start rolling over near 100 eV, but a definite answer is thwarted by the large error bars below 100 eV. Before the advent of IMAP, three explanations have been investigated to explain the discrepancy between ENA measurements with IBEX and model predictions: Additional ENA sources from beyond the heliopause, heliosheath turbulence unaccounted for in models, and/or local foreground near IBEX or in the inner solar system. IMAP will help resolve these outstanding questions thanks to the improved geometric factors of its ENA instruments and the lower background levels expected for the IMAP location at L1 compared with IBEX in Earth orbit.
Based on the knowledge from the first few months of IMAP science observations, we show the first raw data of the ENA spectral intensities measured with IMAP between roughly 100 eV and 1 keV, and we discuss the necessary analysis steps to compare these data with the energy spectra measured with IBEX and those predicted by models. These steps include the correction for the spacecraft motion with respect to the Sun and the correction for ionization losses. Both corrections become more important at lower ENA energies: the typical ENA speed is no longer much faster than the speed of the spacecraft relative to the Sun, and an increasing fraction of ENAs does not reach IMAP or IBEX because they are ionized by charge-exchange, photo-ionization, or electron impact ionization on their years-long travel from the edge of the heliosphere toward the inner solar system.
How to cite: Galli, A. and the Interstellar Mapping and Acceleration Probe team for low energy ENAs: The Interstellar Mapping and Acceleration Probe: A glimpse at the first heliospheric ENA energy spectra measured below solar wind energy , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9945, https://doi.org/10.5194/egusphere-egu26-9945, 2026.
The Interstellar Dust Experiment (IDEX) is an impact-ionization time-of-flight mass spectrometer aboard NASA’s Interstellar Mapping and Acceleration Probe (IMAP), launched in September 2025 and operating at the Sun–Earth L1 Lagrange point. IDEX combines a large sensitive area (>600 cm²), high mass resolution (m/Δm > 200 at m = 100 u), and a wide dynamic range to measure the mass, flux, dynamics, and elemental and chemical composition of interstellar and interplanetary dust particles. The instrument’s performance has been validated through extensive laboratory calibration using iron, platinum-coated olivine, and aluminum particles with masses from approximately 3 × 10⁻¹⁸ to 10⁻¹⁴ kg and impact velocities of 4–50 km s⁻¹. In flight, IDEX operates in the ambient space environment, where it is exposed to interplanetary Lyman-α radiation and galactic cosmic rays. Many of the dust particles detected by IDEX in space are substantially larger than those achievable in laboratory accelerators and therefore generate significantly larger impact charges. This presentation provides an overview of the in-flight performance of IDEX, focusing on key instrument parameters and their comparison with laboratory calibration results.
How to cite: Sternovsky, Z., Horanyi, M., Tucker, S., Ayari, E., Hillier, J., Kempf, S., Knappmiller, S., Mikula, R., and Szalay, J. R.: Calibration and performance of the Interstellar Dust Experiment (IDEX) onboard the Interplanetary Mapping and Acceleration Probe (IMAP) Mission, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16857, https://doi.org/10.5194/egusphere-egu26-16857, 2026.
Solar wind features a latitudinal structure that evolves during the solar activity cycle. The only in-situ measurements of the solar wind speed and density available so far were performed by Ulysses at the turn of the 20th and 21st centuries. They showed the general behavior of the solar wind speed and density. However, details of possible asymmetries and regular structure evolution at shorter time scales could not be established because the measurements were performed in-situ along a highly elliptical orbit with a period of the order of half of the solar cycle.
Complementary methods of monitoring the solar wind latitudinal profiles include remote-sensing observations such as hydrogen Lyman-α backscatter glow observations. Helioglow maps observed by SOHO/SWAN suggested that the solar wind flux temporarily features flux maxima at mid-latitudes.
Insight from Ulysses resulted in a hypothesis that the energy flux of solar wind is latitudinally invariant, which cannot be verified without additional observations. A confirmation of this invariance would be an important milestone in the understanding of the solar wind emission mechanism and would provide a handy tool supporting the retrieval of the solar wind structure from observations of the helioglow.
GLObal solar Wind Structure (GLOWS) is a Lyman-α photometer onboard Interstellar Mapping and Acceleration Probe (IMAP), dedicated to helioglow observations optimized for the retrieval of the solar wind structure. We present how GLOWS observations will be used to infer the structure of the solar wind and to verify the hypothesis of latitudinal invariance of the solar wind energy flux.
How to cite: Kowalska-Leszczynska, I., Bzowski, M., Porowski, C., Strumik, M., and Kubiak, M. A.: From Hydrogen backscatter glow to solar wind structure – how we do it with IMAP/GLOWS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17718, https://doi.org/10.5194/egusphere-egu26-17718, 2026.
Since Voyager 2 crossed the termination shock in 2007 and the heliopause in 2018, the radial flow speed in the heliosheath () has remained uncertain due to persistent discrepancies between measurements from the Plasma Science (PLS) instrument and values inferred from energetic particle observations using the Compton–Getting (CG) effect. These differences are critical because they directly impact our understanding of heliosheath structure and dynamics and play a central role in validating global magnetohydrodynamic (MHD) models. In this work, we revisit the estimation of heliosheath flow speeds from Low-Energy Charged Particle (LECP) data by expanding the legacy CG-based method to account for anisotropic particle distributions in the plasma frame and by combining measurements from multiple energy channels. These refinements provide a more physically realistic interpretation of particle anisotropies and CG-derived flow speeds and offer a pathway toward reconciling plasma and particle measurements of heliosheath flows.
How to cite: Nikoukar, R., Hill, M. E., Dialynas, K., Krimigis, S. M., Richardson, J., and Opher, M.: Revisiting Heliosheath Flows from Voyager Observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20521, https://doi.org/10.5194/egusphere-egu26-20521, 2026.
We present new, multipoint observations of interplanetary shocks observed by six observatories around the first Sun-Earth Lagrange (L1) point. With IMAP, SWFO-L1, ACE, Wind, DSCOVR, and Aditya-L1, we investigate multiple interplanetary shocks associated with the passage of two coronal mass ejections (CMEs) on 11-12 November 2025. Inter-spacecraft separations range from 10s of Earth radii (Re) to ~200 Re, offering a number of different baselines and geometries for multipoint analysis. We analyze shock orientations and speeds and diagnose the interaction between the two CMEs. The 6-point observatories showcase how the CME shocks and sheaths are structured and allow for analysis of the interface between ejecta and ambient solar wind plasmas. We also show that spatial gradients of the structures can be resolved by combining different sets of tetrahedra within the constellation and discuss options for full volume reconstruction of the time-dependent plasma dynamics.
How to cite: Turner, D., Raptis, S., Horbury, T., Rankin, J., Cohen, C., Wilson, L., Christian, E., Szabo, A., Sankarasubramanian, K. S., Vassiliadis, D., Gkioulidou, M., and McComas, D.: Multipoint analysis of interplanetary shocks with 6-point observatories around Sun-Earth L1, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21785, https://doi.org/10.5194/egusphere-egu26-21785, 2026.
Impact-ionization time-of-flight mass spectrometry (II-TOF-MS) is a primary technique for in-situ compositional analysis of interplanetary and interstellar dust. However, quantitative elemental and isotopic interpretation requires laboratory validation against well-characterized standards across realistic encounter speeds.
We present hypervelocity dust-accelerator measurements of platinum-coated San Carlos olivine (Fo≈92) using the high-resolution reflectron-style Hyperdust II-TOF-MS. The olivine starting material was independently characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDX), providing ground-truth Mg, Si, and Fe abundances and confirming low grain-to-grain compositional variability. More than 500 individual olivine projectiles were accelerated to encounter speeds spanning the regime relevant to modern spaceborne dust analyzers (≈10–25 km s⁻¹).
Time-domain spectra were analyzed by identifying major multiplets and fitting isotopic peaks with exponentially modified Gaussian line shapes to obtain integrated peak areas. Isotopic multiplets for Mg, Si, and Fe are resolved, and accepted spectra reproduce terrestrial isotope ratios within a defined tolerance, enabling robust peak deconvolution and contamination control. Using EDX-normalized relative sensitivity factors (RSFs), we convert ion intensities to elemental ratios and compare single-impact and ensemble results to the EDX composition.
At higher encounter speeds (≈19–25 km s⁻¹), RSF-corrected Mg/Si and Fe/Si ratios agree with the EDX values within uncertainties and cluster along the olivine compositional trend, with dispersion smaller than the separation between olivine and pyroxene in Mg–Fe–Si space. Ratios involving Si show stronger speed dependence at lower velocities, consistent with ionization effects and potential isobaric contributions near the Si region, while Mg/Fe remains comparatively stable.
These results provide a quantitative calibration benchmark demonstrating that high-resolution II-TOF-MS can recover elemental and isotopic information for silicate dust and can discriminate mineral families at encounter speeds typical of upcoming and current missions, including IDEX (IMAP), SUDA (Europa Clipper), and DDA (DESTINY+).
How to cite: Ayari, E., Horanyi, M., Sternovsky, Z., Szalay, J., and Mikula, R.: Quantitative olivine elemental and isotopic ratios from hypervelocity impact ionization TOF mass spectrometry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21860, https://doi.org/10.5194/egusphere-egu26-21860, 2026.
The heliosphere can be considered as a plasma bubble formed by the solar wind as it flows outward from the Sun, carving through the local interstellar medium. Due to the relative motion of the heliosphere against the local interstellar medium, a continuous stream of interstellar neutrals (ISNs) enters the heliosphere with a defined speed and direction. Upon entering the heliosphere, ISNs are subjected to ionization processes, which further leads to the creation of interstellar pickup ions (PUIs). PUIs are continuously injected into the solar wind. In the velocity space, their velocity distribution (VDF) initially forms a torus-like shape.
The energies of interstellar pickup helium fall within the measurement range of the SupraThermal Electrons and Protons (STEP) sensor of the Energetic Particle Detector (EPD) onboard Solar Orbiter. By sacrificing mass information, STEP achieves a temporal resolution of up to 1 second. This work presents observations from STEP/EPD. We report several clear torus-shaped velocity distributions of interstellar pickup He⁺ observed at unprecedented temporal resolution.
How to cite: Gu, C., Berger, L., Wimmer-Schweingruber, R. F., Heidrich-Meisner, V., Seimetz, L., Jentsch, E., and Hecht, M.: Torus-shaped velocity distribution of interstellar pickup He+ observed at unprecedented resolution, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2590, https://doi.org/10.5194/egusphere-egu26-2590, 2026.
Posters virtual: Thu, 7 May, 14:00–18:00 | vPoster spot 4
EGU26-4233 | Posters virtual | VPS28
Effects of solar transients observed in the VLISMThu, 07 May, 14:12–14:15 (CEST) vPoster spot 4
The plasma wave instruments on both Voyager spacecraft have observed electron plasma oscillations in the very local interstellar medium (VLISM). The generally accepted explanation of these events is that the electron foreshock of shocks in the VLISM comprise electron beams in the range of 10 to 100 eV that are unstable to Langmuir waves, or electron plasma oscillations. Further, at least some of these events have been tied to solar transients departing the Sun more than a year earlier that evolve as they propagate outward. These disturbances are led by shocks and the impulse of these on the heliospause results in some of the shock impulse continuing into the VLISM. Previously, Voyager 1 had detected the most distant evidence of these transients at about 145 AU. In August 2025 Voyager 2 detected electron plasma oscillations near 140 AU. A simple model of the propagation of this disturbance suggests a transient from the Sun in 2022 as its source, near the beginning of the current solar maximum. New Horizons observed a series of shocks in 2022 – 2023 at heliocentric distances near 55 AU that could be related to the Voyager 2 event. Given these events occur early in solar cycle 25, it is possible additional shocks will be detected by Voyager and enable us to extend the distance over which these disturbances can travel in the VLISM.
We further relate some of the transients observed by the Voyager plasma wave instruments to global models of the VLISM density and magnetic field (Fraternale et al., 2026). For example, these models show the increased density and magnetic field associated with the so-called pf2 (pressure front 2) described by Burlaga et al. (2021). We can now show that the 2-3 kHz radio emissions observed by the Voyagers in the early 1980’s, 1990’s, and 2000’s are related to density structures just beyond the heliopause presumed to be associated with global merged interaction regions stemming from very active solar conditions.
How to cite: Kurth, W., Jaynes, A., Fraternale, F., Kim, T., and Pogorelov, N.: Effects of solar transients observed in the VLISM , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4233, https://doi.org/10.5194/egusphere-egu26-4233, 2026.
