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The interstellar flux gap: From dust to kilometer-scale objects

Eloy Peña-Asensio, Darryl Z. Seligman

TL;DR

The paper tests whether a single power-law size-frequency distribution can bridge interstellar dust detected in situ with kilometer-scale interstellar objects, using flux data from spacecraft, radar, and optical meteor surveys. By evaluating $r$-space power laws and computing a $3I$-like interstellar flux, the study finds that the ISD flux is $2$–$7$ orders of magnitude larger than meteor-survey constraints would permit, and that a simple $ISD$–$ISO$ extrapolation overpredicts interstellar impactors. Slopes restricted by meteor data ($r^{-2.7}$–$r^{-2.3}$) imply interplanetary-to-interstellar flux ratios of $10^{3}$–$10^{6}$, reinforcing the breakdown of a universal power-law. The results reveal a gap between LIC submicron dust and macroscopic ISOs, suggesting distinct origins or processing, and motivate improved trajectory-resolving dust instruments and velocity-resolved meteor surveys to disentangle interstellar from interplanetary populations.

Abstract

Context. Three kilometer-sized interstellar objects (ISOs) have been detected transiting the Solar System, and spacecraft have directly measured micrometer-scale interstellar dust (ISD). Yet no intermediate-size interstellar meteoroids have been identified in current meteor surveys. Aims. We test whether a power-law flux extrapolation connecting spacecraft ISD and kilometer-scale ISOs is consistent with meteor surveys, and we quantify the expected interstellar impacting flux based on various observational reports. Methods. We compiled differential fluxes and limits from spacecraft ISD, radar and optical meteor surveys, and theoretical estimates. We evaluated the power-law size-frequency fits, computed the 3I-like flux, and compared measured fluxes to predictions. Results. The spacecraft-measured dust flux exceeds extrapolations constrained by meteor surveys and kilometer-scale ISOs by $\sim$2-7 orders of magnitude. An $r^{-3.0}$ fit combining spacecraft ISD detections with kilometer-scale ISOs overpredicts the number of meteors with hyperbolic orbits, whereas slopes of $r^{-2.7}$-$r^{-2.3}$ (derived from radar and optical meteor upper limits, respectively) instead yield interplanetary-to-interstellar flux ratios of $10^{3}$-$10^{6}$. Conclusions. A simple power-law from ISD to ISOs is inconsistent with meteor survey constraints and yields unrealistic predictions for interstellar meteoroids. The data reveal a gap between submicron dust entrained in the Local Interstellar Cloud (LIC) and macroscopic bodies ejected from planetary systems. This gap may reflect distinct origins and destruction-transport processes rather than a continuous size-frequency distribution. This would imply either the dominance of a small-particle LIC component or the need to reassess spacecraft dust fluxes.

The interstellar flux gap: From dust to kilometer-scale objects

TL;DR

The paper tests whether a single power-law size-frequency distribution can bridge interstellar dust detected in situ with kilometer-scale interstellar objects, using flux data from spacecraft, radar, and optical meteor surveys. By evaluating -space power laws and computing a -like interstellar flux, the study finds that the ISD flux is – orders of magnitude larger than meteor-survey constraints would permit, and that a simple – extrapolation overpredicts interstellar impactors. Slopes restricted by meteor data (–) imply interplanetary-to-interstellar flux ratios of –, reinforcing the breakdown of a universal power-law. The results reveal a gap between LIC submicron dust and macroscopic ISOs, suggesting distinct origins or processing, and motivate improved trajectory-resolving dust instruments and velocity-resolved meteor surveys to disentangle interstellar from interplanetary populations.

Abstract

Context. Three kilometer-sized interstellar objects (ISOs) have been detected transiting the Solar System, and spacecraft have directly measured micrometer-scale interstellar dust (ISD). Yet no intermediate-size interstellar meteoroids have been identified in current meteor surveys. Aims. We test whether a power-law flux extrapolation connecting spacecraft ISD and kilometer-scale ISOs is consistent with meteor surveys, and we quantify the expected interstellar impacting flux based on various observational reports. Methods. We compiled differential fluxes and limits from spacecraft ISD, radar and optical meteor surveys, and theoretical estimates. We evaluated the power-law size-frequency fits, computed the 3I-like flux, and compared measured fluxes to predictions. Results. The spacecraft-measured dust flux exceeds extrapolations constrained by meteor surveys and kilometer-scale ISOs by 2-7 orders of magnitude. An fit combining spacecraft ISD detections with kilometer-scale ISOs overpredicts the number of meteors with hyperbolic orbits, whereas slopes of - (derived from radar and optical meteor upper limits, respectively) instead yield interplanetary-to-interstellar flux ratios of -. Conclusions. A simple power-law from ISD to ISOs is inconsistent with meteor survey constraints and yields unrealistic predictions for interstellar meteoroids. The data reveal a gap between submicron dust entrained in the Local Interstellar Cloud (LIC) and macroscopic bodies ejected from planetary systems. This gap may reflect distinct origins and destruction-transport processes rather than a continuous size-frequency distribution. This would imply either the dominance of a small-particle LIC component or the need to reassess spacecraft dust fluxes.

Paper Structure

This paper contains 4 sections, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Flux comparison
  3. Conclusion
  4. Additional material

Figures (4)

  • Figure 1: Eccentricity versus inclination for hyperbolic fireballs reported in the EN catalog Borovicka2022AA667A158B, hyperbolic meteor detections from CMOR radar surveys Froncisz2020PSS19004980F, and the three known ISOs 1I/‘Oumuamua, 2I/Borisov, and 3I/ATLAS JPLHorizonsOumuamuaJPLHorizonsBorisovJPLHorizonsATLAS. Marginal histograms display the distribution of inclination (top) and eccentricity (right) for each dataset in logarithmic scale using colors consistent with the scatter plot. The dashed horizontal line marks $e=1$.
  • Figure 2: Differential flux versus size based on Ulysses and Galileo spacecraft confident ISD detections Baalmann2025AA, hyperbolic meteor radar 3$\sigma$ constraint in CMOR Froncisz2020PSS19004980F, estimated $>$100 $\mu$m objects impacting the Earth from $\alpha$ Centauri GreggWiegert2025, optical meteor upper limit in GMN Wiegert2025, estimated flux at Earth of objects from asymptotic giant branch (AGB) stars, young stellar objects (YSOs), and young main-sequence stars Murray2004, observed sporadic meteors on Earth with interplanetary orbits Ceplecha1988BAICz39221C, 1I/‘Oumuamua-like object flux Hajdukova2019, and 3I/ATLAS‐like object (this work). Linear fit fluxes are depicted for $r^{-3.0}$Jewitt2023ARAA, $r^{-2.7}$ to match 1I and 3I with hyperbolic radar meteors, and $r^{-2.3}$ to match 1I and 3I with upper limit hyperbolic optical meteors.
  • Figure 3: Ratio of the measured differential flux of ISD detections by spacecraft to the corresponding derived power-law fit for interstellar impactors. Linear fit fluxes are depicted for $r^{-2.7}$ to match 1I and 3I with hyperbolic radar meteors and for $r^{-2.3}$ to match 1I and 3I with upper limit hyperbolic optical meteors (see Figure \ref{['fig:fluxes']}).
  • Figure 4: Interplanetary-to-interstellar ratio of the measured differential flux of observed meteors on Earth to the corresponding derived power-law fit for interstellar impactors. The linear fit fluxes are depicted for $r^{-3.0}$Jewitt2023ARAA to match 1I and 3I with ISD detections by spacecraft, $r^{-2.7}$ to match 1I and 3I with hyperbolic radar meteors, and $r^{-2.3}$ to match 1I and 3I with upper limit hyperbolic optical meteors (see Figure \ref{['fig:fluxes']}).