Preprints
https://doi.org/10.5194/egusphere-2026-4440
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2026-4440
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
17 Aug 2026
| 17 Aug 2026
Status: this preprint is open for discussion and under review for Annales Geophysicae (ANGEO).
Dust in the Inner Heliosphere
Abstract. The inner heliosphere hosts a dynamically rich population of dust particles – the Zodiacal Dust Cloud – spanning sizes from nanometers to hundreds of micrometers and originating primarily from comets and asteroids. Over the past two decades, a generation of space missions has transformed our observational grasp of this environment. This review consolidates the advances enabled by the Wind, STEREO, Parker Solar Probe, and Solar Orbiter space missions, which together observe from heliocentric distances of 1 au down to less than 0.05 au. Two complementary observational approaches are addressed in detail. The first is in-situ dust detection via radio and plasma wave instruments, which commonly measure characteristic voltage pulses resulting from hypervelocity dust impacts on spacecraft. We describe the underlying physics, signal interpretation, dust particle mass calibration and machine-learning classification methods for this technique, which constitutes the only in-situ dust measurement capability on current inner-heliosphere missions. The second approach is remote sensing of the Zodiacal Light and F-corona through white-light coronagraph and heliospheric imagers. The combination of these approaches has yielded a consistent picture of the radial brightness profile of the cloud, provided the first observational evidence for a dust depletion zone developing sunward of 35 solar radii and a dust-free zone interior to 5 solar radii. The in-situ measurements established flux densities of dust in hyperbolic trajectories (β-meteoroids) across multiple missions, revealed variable fluxes of nanodust, and revealed solar-cycle modulation of the interstellar dust flux. This review presents these results, discusses their implications, and outlines the prospects offered by near-future missions.
How to cite. Zaslavsky, A., Mann, I. B., Howard, R. A., Sternovsky, Z., Anghel, S., Kvammen, A., Malaspina, D. M., Meyer-Vernet, N., Pantellini, F., Pérrone, A., Rackovic-Babic, K., Sterken, V. J., Szalay, J. R., Bale, S. D., Bothmer, V., DeForest, C. E., Gasque, L. C., Ishimaru, R., Kimura, H., Maksimovic, M., Morooka, M., Nieves-Chinchilla, T., Nouzák, L., Píša, D., Pokorný, P., Raouafi, N. E., Shen, M. M., Smith, A. M., and Stenborg, G.: Dust in the Inner Heliosphere, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2026-4440, 2026.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Annales Geophysicae.
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Arnaud Zaslavsky
CORRESPONDING AUTHOR
LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
Department of Physics and Technology, The Arctic University of Norway, Postboks 6050 Langnes, 9037 Tromsø, Norway
Russel A. Howard
The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, Maryland 20723, USA
Zoltan Sternovsky
Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder, Boulder, CO 80303, USA
Smead Aerospace Engineering Sciences Department, University of Colorado at Boulder, Boulder, CO 80303, USA
Simon Anghel
LTE, Observatoire de Paris, Université PSL, Sorbonne Université, Université de Lille, LNE, CNRS, 61 Avenue de l’Observatoire, 75014 Paris, France
Andreas Kvammen
Department of Physics and Technology, The Arctic University of Norway, Postboks 6050 Langnes, 9037 Tromsø, Norway
David M. Malaspina
Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder, Boulder, CO 80303, USA
Astrophysical and Planetary Sciences, University of Colorado, Boulder, Boulder, CO 80303, USA
Nicole Meyer-Vernet
LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
Filippo Pantellini
LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
Arthur Pérrone
Institute for Particle and Astroparticle Physics, ETH Zurich, Wolfgang-Pauli-strasse 27, 8093 Zürich, Switzerland
Kristina Rackovic-Babic
LPC2E, CNRS, Université d’Orléans, CNES, 3A Avenue de la Recherche Scientifique, 45071 Orléans, France
Veerle J. Sterken
Institute of Physics, Laboratory of Astrophysics (LASTRO), Ecole Polytechnique Federale de Lausanne (EPFL), Observatoire de Sauverny, CH-1290 Versoix, Switzerland
Institute for Particle and Astroparticle Physics, ETH Zurich, Wolfgang-Pauli-strasse 27, 8093 Zürich, Switzerland
Jamey R. Szalay
Department of Astrophysical Sciences, Princeton University, 4 Ivy Ln., Princeton, NJ 08540, USA
Stuart D. Bale
Physics Department, University of California, Berkeley, Berkeley, CA 94720-7300, USA
Space Sciences Laboratory, University of California, Berkeley, Berkeley, CA 94720-7450, USA
The Blackett Laboratory, Imperial College London, London SW7 2AZ, UK
Volker Bothmer
Institute for Astrophysics and Geophysics, University of Göttingen, Friedrich-Hund-Pl.1, 37077 Göttingen, Germany
deceased, 23 april 2026
Craig E. DeForest
Solar System Science and Exploration Division, Southwest Research Institute, Boulder, CO, 80302, USA
L. Claire Gasque
Space Sciences Laboratory, University of California, Berkeley, Berkeley, CA 94720-7450, USA
Ryo Ishimaru
Planetary Exploration Research Center (PERC), Chiba Institute of Technology, Tsudanuma 2-17-1, Narashino, Chiba 275-0016, Japan
Hiroshi Kimura
Planetary Exploration Research Center (PERC), Chiba Institute of Technology, Tsudanuma 2-17-1, Narashino, Chiba 275-0016, Japan
Milan Maksimovic
LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
Michiko Morooka
Swedish Institute of Space Physics, Uppsala, Box 537, SE-751 21 Uppsala, Sweden
Teresa Nieves-Chinchilla
Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
Libor Nouzák
Department of Surface and Plasma Science, Charles University, 180 00 Prague, Czech Republic
David Píša
Department of Space Physics, Institute of Atmospheric Physics of the Czech Academy of Sciences, 141 00 Prague, Czechia
Petr Pokorný
Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
Department of Physics, The Catholic University of America, Washington, DC 20064, USA
Nour E. Raouafi
The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, Maryland 20723, USA
Mitchell M. Shen
Department of Astrophysical Sciences, Princeton University, 4 Ivy Ln., Princeton, NJ 08540, USA
Austin Matheus Smith
Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder, Boulder, CO 80303, USA
Smead Aerospace Engineering Sciences Department, University of Colorado at Boulder, Boulder, CO 80303, USA
Guillermo Stenborg
The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, Maryland 20723, USA
Short summary
Small grains of dust, released by comets and asteroids, fill the space between the Sun and the planets. To learn how they behave near the Sun, we combined data from four spacecraft that either sense single grains hitting them or picture the sunlight scattered by the grains. Together, these observations build a consistent picture of where the dust sits and how it moves in the inner solar system, which helps us understand dust around other stars and grains coming from beyond our solar system.
Small grains of dust, released by comets and asteroids, fill the space between the Sun and the...
Recommendation
Major revision. This is a timely, ambitious, and potentially very useful review. It brings together remote-sensing observations of the Zodiacal cloud and in situ dust measurements obtained with radio/plasma-wave antennas, with substantial attention to the physics and calibration of antenna-based dust detection. The manuscript contains a great deal of valuable material and should be publishable after revision. My main concern is not the overall scientific value but the scope, balance, terminology, and the extent to which several quantitative conclusions are presented more definitively than the underlying measurement technique warrants.
Overall assessment
The strongest aspect of the review is its synthesis of STEREO, Wind, Parker Solar Probe (PSP), and Solar Orbiter observations, coupled to an unusually detailed discussion of impact-generated voltage signatures, laboratory calibration, electrostatic modeling, and machine-learning classification. The manuscript also provides a useful summary of the Zodiacal-light/F-corona results, including the radial brightness structure and the near-Sun dust depletion region.
However, the title “Dust in the Inner Heliosphere” implies a broader and more instrument-neutral review than the manuscript presently delivers. A large fraction of the paper is effectively a review of antenna-based dust detection. Dedicated dust detectors are acknowledged, but are largely treated as background even though they provide the direct mass, speed, and composition measurements against which antenna interpretations must ultimately be calibrated. This imbalance becomes especially important now that IMAP/IDEX is operating at L1, a point explicitly discussed later in the manuscript.
Major comments
The manuscript should either broaden the treatment of dedicated dust measurements or narrow the title/scope. The text states that antenna measurements constitute the “only in-situ dust measurement capability on current inner-heliosphere missions,” while later describing IMAP/IDEX as launched in 2025 and already beginning compositional measurements. In the present 2026 context, these statements are difficult to reconcile. I recommend explicitly distinguishing (i) current missions without dedicated dust instruments, such as PSP and Solar Orbiter, from (ii) the current inner-heliosphere measurement capability as a whole, which now includes IDEX. The abstract, Introduction, Section 3.2, Summary, and Section 5.4 should use consistent wording.
The review is strongest when it emphasizes that an antenna detects a voltage response to an impact rather than mass directly. This distinction should be carried consistently into the observational sections. The manuscript states that particle mass cannot be reliably determined from a single-antenna impact because the impact speed is not independently measured and the charge yield and the voltage-to-charge conversion are uncertain. Yet later sections sometimes quote size/mass ranges and fluxes with a precision that can give the impression of direct measurement. For every major population (bound grains, beta-meteoroids, nanodust, ISD), I suggest clearly separating measured observables (waveform amplitude, count rate, timing, spacecraft geometry) from model-dependent inferred quantities (mass, size, speed, flux and source population). A compact table would be very effective.
The manuscript discusses charge-yield uncertainty, spacecraft capacitance, antenna coupling, impact location, receiver selection, saturation, and assumed velocity distributions, but does not synthesize the consequences for reported fluxes quantitatively. A review should tell the reader not only that these uncertainties exist, but also their approximate magnitudes and which ones dominate. I recommend a table for STEREO, Wind, PSP, and Solar Orbiter listing the effective area, observability, detection/classification method, assumed speed or dynamical model, charge-yield calibration, approximate mass sensitivity, and dominant systematic uncertainty. This would make the cross-mission comparisons in Section 4 substantially more convincing.
Section 4.1.3 attempts to define the dynamical populations, but the notation/terminology needs careful editing. The text appears to use symbols that are rendered inconsistently in the supplied PDF, and the transition into Section 4.3 is confusing: the heading “4.3.1 epsilon-meteoroids” is followed immediately by a sentence stating that the beta-meteoroid population was previously characterized. Please check whether this is a heading/text mismatch. More generally, define beta unambiguously as the radiation-pressure-to-gravity ratio and distinguish the historical use of alpha/beta terminology from the manuscript’s chosen convention. The manuscript should avoid redefining established terminology unless there is a compelling reason.
The review highlights a dust depletion zone beginning at about 35 solar radii sunward and a largely dust-free region interior to about 5 solar radii. These are important results and deserve prominence, but the observational inference is based on line-of-sight white-light brightness, separation of F- and K-corona contributions, assumed scattering properties, and forward modeling. The wording should distinguish directly observed brightness depletion from inferred dust-number-density depletion. “Dust-free” should be qualified by the particle sizes/compositions to which the observations are sensitive and by the model assumptions. A short paragraph summarizing the principal degeneracies would improve the review.
The manuscript currently reads, in places, as two parallel reviews: one on antenna impacts and one on white-light imaging. The greatest value would come from explicitly connecting them. Which grain-size ranges dominate brightness, which dominate antenna counts, and where do these overlap? Can the radial profiles inferred from PSP/SolO impact rates be compared quantitatively with the density profiles inferred from WISPR/SECCHI brightness? Where are the apparent agreements genuine, and where do size-dependent dynamics prevent direct comparison? A synthesis figure spanning grain size, heliocentric distance, technique, and principal observable would greatly strengthen the paper.
Several interesting topics remain unsettled: single-hit amplification, magnetic impact signatures, long-duration events, CME/SIR effects, and short-term ISD modulation. The manuscript often acknowledges alternatives, but the review would benefit from a more systematic use of confidence language: established / strongly supported / plausible / unresolved. For example, the origin of single hits remains debated, and the relative roles of electron escape and ion-cloud expansion in magnetic signatures are not fully resolved. Similar caution is warranted when attributing changes in dust counts associated with solar-wind structures to physical dust depletion rather than to changes in detectability or spacecraft/plasma conditions.
The manuscript itself identifies co-located antennas and dedicated dust instruments as desirable for cross-calibration. I suggest making this a major conclusion. Antenna systems offer enormous effective collecting area and long time series; dedicated impact-ionization instruments offer calibrated mass, speed and composition. Their combination is far more powerful than either alone. IMAP/IDEX at L1, together with Wind and other contemporaneous measurements, provides an immediate opportunity to test antenna-derived mass distributions and ISD identification. This should be discussed more concretely as a near-term validation experiment rather than only as a general future recommendation.
The laboratory section is valuable, but the review should more clearly distinguish the empirical charge-yield relation Q = alpha m v^beta from a universal calibration. The coefficients depend on the target material, projectile properties, surface state, and velocity regime, and the manuscript notes an S-shaped normalized yield and substantial event-to-event scatter. A single commonly used alpha/beta pair should therefore be presented as an approximate historical parameterization rather than a generally applicable conversion. This is especially important because velocity enters with a high exponent and therefore dominates mass inference errors.
There are numerous grammatical problems, duplicated words, awkward constructions, inconsistent mission abbreviations (SO/SolO), spacing issues, and apparent symbol conversion errors in the PDF. Examples include “their their dust clouds,” “main sequence starts,” “seen with by Ulysses,” and several sentences with missing articles or subject-verb disagreement. These do not undermine the science, but at 80 pages they materially reduce readability. A careful line edit is needed before publication.
Specific and minor comments
Suggested additions
Recommended decision
The manuscript might be suitable for publication after major revision. The manuscript has the ingredients to become an authoritative review, especially because it combines the recent PSP/Solar Orbiter era with the long STEREO/Wind record and modern laboratory understanding of antenna impact signatures. The revision should focus on making the scope explicit, correcting the current-mission/dedicated-detector inconsistency, separating direct observables from inferred dust properties, quantifying systematic uncertainties, tightening the dynamical terminology, and integrating the remote-sensing and in-situ results into a more unified physical picture.