{"id":517303,"date":"2026-06-03T23:51:12","date_gmt":"2026-06-03T23:51:12","guid":{"rendered":"https:\/\/www.europesays.com\/ie\/517303\/"},"modified":"2026-06-03T23:51:12","modified_gmt":"2026-06-03T23:51:12","slug":"relativistic-electron-acceleration-at-the-bow-shock-of-jupiter-and-beyond","status":"publish","type":"post","link":"https:\/\/www.europesays.com\/ie\/517303\/","title":{"rendered":"Relativistic electron acceleration at the bow shock of Jupiter and beyond"},"content":{"rendered":"<p>Data<\/p>\n<p>Observations for this study are from the Juno spacecraft of NASA<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 32\" title=\"Bolton, S. J. et al. The Juno mission. Space Sci. Rev. 213, 5&#x2013;37 (2017).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR32\" id=\"ref-link-section-d74689692e1268\" rel=\"nofollow noopener\" target=\"_blank\">32<\/a>. The energetic particle data are provided by the JEDI<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 47\" title=\"Mauk, B. H. et al. The Jupiter Energetic Particle Detector Instrument (JEDI) investigation for the Juno mission. Space Sci. Rev. 213, 289&#x2013;346 (2017).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR47\" id=\"ref-link-section-d74689692e1272\" rel=\"nofollow noopener\" target=\"_blank\">47<\/a>, which measures ions and electrons from about 30\u2009keV to 1\u2009MeV with an energy resolution of around 20%. JEDI consists of three identical sensor heads (JEDI90, JEDI180 and JEDI270) distributed around the spacecraft to optimize pitch angle coverage over a 160\u00b0\u2009\u00d7\u200912\u00b0 field of view with an angular resolution of about 18\u00b0. The first two energy bins of JEDI used in this study are contaminated and are not included in the analysis, resulting in four energy bins covering approximately 100\u2009keV to 1\u2009MeV, as shown in Fig. <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#Fig2\" rel=\"nofollow noopener\" target=\"_blank\">2<\/a>. Lower-energy ion and electron observations are obtained from the JADE<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 48\" title=\"McComas, D. J. et al. The Jovian Auroral Distributions Experiment (JADE) on the Juno mission to Jupiter. Space Sci. Rev. 213, 547&#x2013;643 (2017).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR48\" id=\"ref-link-section-d74689692e1279\" rel=\"nofollow noopener\" target=\"_blank\">48<\/a>. JADE consists of two electron sensors (JADE-E) and an ion sensor (JADE-I), both measuring ions with energy per charge from 10\u2009eV\u2009q\u22121 to 46.5\u2009keV\u2009q\u22121 across 64 energy channels and electrons with energy per charge from 30\u2009eV\u2009q\u22121 to 32\u2009keV\u2009q\u22121, with a time resolution that is mode dependent and corresponds to about 2\u2009min in the presented event. Magnetic field vector data are sourced from the Magnetic Field Investigation (MAG) instrument<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 49\" title=\"Connerney, J. E. P. et al. The Juno Magnetic Field Investigation. Space Sci. Rev. 213, 39&#x2013;138 (2017).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR49\" id=\"ref-link-section-d74689692e1292\" rel=\"nofollow noopener\" target=\"_blank\">49<\/a>, which uses two fluxgate magnetometers to provide measurements with a temporal resolution of 1\u2009s. All data are presented in the JSO coordinate system, a Jupiter-centred frame in which the x-axis points to the Sun, the y-axis is in the anti-direction of the orbital motion of Jupiter and the z-axis completes the right-handed system<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 50\" title=\"Bagenal, F. et al. Magnetospheric science objectives of the Juno mission. Space Sci. Rev. 213, 219&#x2013;287 (2017).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR50\" id=\"ref-link-section-d74689692e1306\" rel=\"nofollow noopener\" target=\"_blank\">50<\/a>.<\/p>\n<p>Data post-processing and density calculations<\/p>\n<p>The raw instrument data were processed to generate the products used in this analysis. The JEDI energy-time spectrograms (Fig. <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#Fig1\" rel=\"nofollow noopener\" target=\"_blank\">1c<\/a>) were created by averaging data from all three sensors and all look directions. During the observation period, the instrument operated in a low-resolution mode, binning counts into six logarithmically spaced energy channels from about 30\u2009keV to 1\u2009MeV and into 300\u2009s time bins. The count rates associated with the transient event, ranging from about 20 to 60 counts per second, are considered statistically significant. The electron energy efficiency correction detailed in ref.\u2009<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 51\" title=\"Mauk, B. H. et al. Diverse electron and ion acceleration characteristics observed over Jupiter&#x2019;s main aurora. Geophys. Res. Lett. 45, 1277&#x2013;1285 (2018).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR51\" id=\"ref-link-section-d74689692e1321\" rel=\"nofollow noopener\" target=\"_blank\">51<\/a> was applied, although its effect is minimal in the low-radiation environment near the magnetospheric boundary of Jupiter. For JADE, proton densities were derived from JADE-I data using a numerical integration method on SPECIES=3 data<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 52\" title=\"Wilson, R. J. Error analysis for numerical estimates of space plasma parameters. Earth Space Sci. 2, 201&#x2013;222 (2015).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR52\" id=\"ref-link-section-d74689692e1325\" rel=\"nofollow noopener\" target=\"_blank\">52<\/a>. Although JADE-I is not optimized for solar wind measurements<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 53\" title=\"Wilson, R. J. et al. Solar wind properties during Juno&#x2019;s approach to Jupiter: data analysis and resulting plasma properties utilizing a 1-D forward model. J. Geophys. Res. Space Phys. 123, 2772&#x2013;2786 (2018).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR53\" id=\"ref-link-section-d74689692e1329\" rel=\"nofollow noopener\" target=\"_blank\">53<\/a>, this method has been shown to be consistent with forward-modelled Maxwellian fits for similar events<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 28\" title=\"Valek, P. W. et al. Hot flow anomaly observed at Jupiter&#x2019;s bow shock. Geophys. Res. Lett. 44, 8107&#x2013;8112 (2017).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR28\" id=\"ref-link-section-d74689692e1333\" rel=\"nofollow noopener\" target=\"_blank\">28<\/a>. The omnidirectional differential number intensities for JADE-E were calculated by averaging the observed intensities over 48 look directions, which are binned onboard in the low rate science mode of the instrument<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 48\" title=\"McComas, D. J. et al. The Jovian Auroral Distributions Experiment (JADE) on the Juno mission to Jupiter. Space Sci. Rev. 213, 547&#x2013;643 (2017).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR48\" id=\"ref-link-section-d74689692e1338\" rel=\"nofollow noopener\" target=\"_blank\">48<\/a>.<\/p>\n<p>Bow shock and foreshock transient characterization<\/p>\n<p>In Extended Data Fig. <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#Fig4\" rel=\"nofollow noopener\" target=\"_blank\">1<\/a>, a magnified timeseries of the foreshock transient interval (11:30\u201313:30 UTC) is shown. Energetic particle intensification and plasma density depletion begin at about 12:30 UTC, with a localized compression marking the trailing edge of the structure at approximately 12:50 UTC, typical features of foreshock transients<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 4\" title=\"Turner, D. L. et al. Autogenous and efficient acceleration of energetic ions upstream of Earth&#x2019;s bow shock. Nature 561, 206&#x2013;210 (2018).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR4\" id=\"ref-link-section-d74689692e1353\" rel=\"nofollow noopener\" target=\"_blank\">4<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 5\" title=\"Raptis, S. et al. Revealing an unexpectedly low electron injection threshold via reinforced shock acceleration. Nat. Commun. 16, 488 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR5\" id=\"ref-link-section-d74689692e1356\" rel=\"nofollow noopener\" target=\"_blank\">5<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 22\" title=\"Zhang, H. et al. Dayside transient phenomena and their impact on the magnetosphere and ionosphere. Space Sci. Rev. 218, 40 (2022).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR22\" id=\"ref-link-section-d74689692e1359\" rel=\"nofollow noopener\" target=\"_blank\">22<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 54\" title=\"Kajdi&#x10D;, P. et al. Transient upstream mesoscale structures: drivers of solar-quiet space weather. Front. Astron. Space Sci. 11, 1436916 (2024).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR54\" id=\"ref-link-section-d74689692e1362\" rel=\"nofollow noopener\" target=\"_blank\">54<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 55\" title=\"Kajdi&#x10D;, P., Blanco-Cano, X., Rojas-Castillo, D. &amp; Omidi, N. Different transient phenomena at the edges of traveling foreshocks. J. Geophys. Res. Space Phys. 131, e2025JA034777 (2026).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR55\" id=\"ref-link-section-d74689692e1365\" rel=\"nofollow noopener\" target=\"_blank\">55<\/a>.<\/p>\n<p>To better characterize the global environment during this encounter, we use the local magnetic field conditions and the shock normal vector estimated in ref.\u2009<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 56\" title=\"Joy, S. P. et al. Probabilistic models of the Jovian magnetopause and bow shock locations. J. Geophys. Res. Space Phys. 107, SMP 17-1&#x2013;SMP 17-17 (2002).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR56\" id=\"ref-link-section-d74689692e1372\" rel=\"nofollow noopener\" target=\"_blank\">56<\/a>. Using this, we obtain a normal vector of [0.77,\u00a00.45,\u00a0\u22120.44], consistent with the duskward Juno location. The orientation of the magnetic field with respect to this normal is shown in Extended Data Fig. <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#Fig4\" rel=\"nofollow noopener\" target=\"_blank\">1e<\/a>, suggesting that the shock orientation transitions from an oblique or quasi-parallel to a quasi-perpendicular one. Specifically, during the formation and observation of the transient itself, the orientation becomes even more quasi-parallel. This shock geometry (with \u03b8Bn \u2272 60\u00b0) is expected to produce substantial populations of foreshock suprathermal particles<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Karlsson, T., Raptis, S., Trollvik, H. &amp; Nilsson, H. Classifying the magnetosheath behind the quasi-parallel and quasi-perpendicular bow shock by local measurements. J. Geophys. Res. Space Phys. 126, e2021JA029269 (2021).\" href=\"#ref-CR57\" id=\"ref-link-section-d74689692e1387\">57<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Koller, F., Raptis, S., Temmer, M. &amp; Karlsson, T. The effect of fast solar wind on ion distribution downstream of Earth&#x2019;s bow shock. Astrophys. J. Lett. 964, L5 (2024).\" href=\"#ref-CR58\" id=\"ref-link-section-d74689692e1387_1\">58<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 59\" title=\"Svenningsson, I., Yordanova, E., Khotyaintsev, Y. V., Andr&#xE9;, M. &amp; Cozzani, G. Classifying the magnetosheath using local measurements from MMS. J. Geophys. Res. Space Phys. 130, e2024JA033272 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR59\" id=\"ref-link-section-d74689692e1390\" rel=\"nofollow noopener\" target=\"_blank\">59<\/a> associated with the formation of foreshock transients<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 4\" title=\"Turner, D. L. et al. Autogenous and efficient acceleration of energetic ions upstream of Earth&#x2019;s bow shock. Nature 561, 206&#x2013;210 (2018).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR4\" id=\"ref-link-section-d74689692e1394\" rel=\"nofollow noopener\" target=\"_blank\">4<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 5\" title=\"Raptis, S. et al. Revealing an unexpectedly low electron injection threshold via reinforced shock acceleration. Nat. Commun. 16, 488 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR5\" id=\"ref-link-section-d74689692e1397\" rel=\"nofollow noopener\" target=\"_blank\">5<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 22\" title=\"Zhang, H. et al. Dayside transient phenomena and their impact on the magnetosphere and ionosphere. Space Sci. Rev. 218, 40 (2022).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR22\" id=\"ref-link-section-d74689692e1400\" rel=\"nofollow noopener\" target=\"_blank\">22<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 54\" title=\"Kajdi&#x10D;, P. et al. Transient upstream mesoscale structures: drivers of solar-quiet space weather. Front. Astron. Space Sci. 11, 1436916 (2024).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR54\" id=\"ref-link-section-d74689692e1403\" rel=\"nofollow noopener\" target=\"_blank\">54<\/a>.<\/p>\n<p>Particle data further support this interpretation. The presence of diffuse, isotropic suprathermal ions and electrons indicates that the spacecraft is residing within the foreshock region<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 60\" title=\"Balogh, A. &amp; Treumann, R. A. Physics of Collisionless Shocks: Space Plasma Shock Waves (Springer, 2013).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR60\" id=\"ref-link-section-d74689692e1410\" rel=\"nofollow noopener\" target=\"_blank\">60<\/a>. Specifically, the pitch angle distributions (PADs) of ions and especially electrons show a clear isotropic population of accelerated particles. These PADs demonstrate that particles are distributed across all pitch angles, a signature of well-scattered populations within the foreshock. This is in agreement with characteristics of accelerated electrons observed during foreshock transients at Earth<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 5\" title=\"Raptis, S. et al. Revealing an unexpectedly low electron injection threshold via reinforced shock acceleration. Nat. Commun. 16, 488 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR5\" id=\"ref-link-section-d74689692e1414\" rel=\"nofollow noopener\" target=\"_blank\">5<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 18\" title=\"Liu, T. Z., Angelopoulos, V. &amp; Lu, S. Relativistic electrons generated at Earth&#x2019;s quasi-parallel bow shock. Sci. Adv. 5, eaaw1368 (2019).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR18\" id=\"ref-link-section-d74689692e1417\" rel=\"nofollow noopener\" target=\"_blank\">18<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 19\" title=\"Shi, X., Artemyev, A., Angelopoulos, V., Liu, T. &amp; Wilson, L. B. III Compound electron acceleration at planetary foreshocks. Nat. Commun. 16, 77 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR19\" id=\"ref-link-section-d74689692e1420\" rel=\"nofollow noopener\" target=\"_blank\">19<\/a>. An illustration of the environment and associated transient is shown in Extended Data Fig. <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#Fig5\" rel=\"nofollow noopener\" target=\"_blank\">2<\/a>.<\/p>\n<p>Focusing on the foreshock transient (12:30\u201312:50 UT), the electron PAD signature shows a progression as the transient passes through the spacecraft. This signature suggests that particles are accelerated in the approaching region, peaking within the transient and ceasing as the spacecraft exits the structure and the field rotates to a quasi-perpendicular regime after 12:50 UT. This strongly supports a local acceleration mechanism because if the source was external, energetic electrons would be observable over wider intervals. Instead, their strict localization to the transient structure implies they are generated in situ rather than being remote-sensed. Regarding the broader spatial context, based on spacecraft speed (about 4\u2009km\u2009s\u22121) and the interval duration, we estimate that Juno was residing approximately 1RJ upstream of the bow shock (Fig. <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#Fig2\" rel=\"nofollow noopener\" target=\"_blank\">2<\/a>, inset). This serves as an approximate estimate, as the bow shock at planetary flanks can change location rapidly. This estimate is consistent with observations at Earth, in which transients are observed at around 1\u22124RE (refs.\u2009<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 19\" title=\"Shi, X., Artemyev, A., Angelopoulos, V., Liu, T. &amp; Wilson, L. B. III Compound electron acceleration at planetary foreshocks. Nat. Commun. 16, 77 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR19\" id=\"ref-link-section-d74689692e1444\" rel=\"nofollow noopener\" target=\"_blank\">19<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 61\" title=\"Chu, C. et al. THEMIS satellite observations of hot flow anomalies at Earth&#x2019;s bow shock. Ann. Geophys. 35, 443&#x2013;451 (2017).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR61\" id=\"ref-link-section-d74689692e1447\" rel=\"nofollow noopener\" target=\"_blank\">61<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 62\" title=\"Turc, L. et al. Interplay between a foreshock bubble and a hot flow anomaly forming along the same rotational discontinuity. Geophys. Res. Lett. 52, e2025GL116473 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR62\" id=\"ref-link-section-d74689692e1450\" rel=\"nofollow noopener\" target=\"_blank\">62<\/a>).<\/p>\n<p>To determine the exact geometry and scale of the observed foreshock transient, we first established its orientation using minimum variance analysis (MVA) on the magnetic field vector data in the JSO coordinate system<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 63\" title=\"Sonnerup, B. U. O. &amp; Scheible, M. in Analysis Methods for Multi-Spacecraft Data (eds Paschmann, G. &amp; Daly, P. W.) 185&#x2013;220 (International Space Science Institute, 1998).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR63\" id=\"ref-link-section-d74689692e1458\" rel=\"nofollow noopener\" target=\"_blank\">63<\/a>. This technique identifies the principal axes of the variance of the magnetic field by finding the eigenvalues (\u03bbmax\u2009\u2265\u2009\u03bbint\u2009\u2265\u2009\u03bbmin) and the corresponding eigenvectors of the covariance matrix of the magnetic field over the interval containing the transient crossing. The eigenvector associated with the minimum eigenvalue (<b>n<\/b>MVA) is interpreted as the normal direction to the boundary of the transient, assuming a quasi-planar structure. The validity of this normal was confirmed by ensuring a large ratio of the intermediate to minimum eigenvalues (\u03bbint\/\u03bbmin \u226b 1). With the boundary normal established, we then estimated the scale size of the transient, L, along this direction using the single-spacecraft timing method. The scale is calculated as L\u00a0=\u00a0|<b>v<\/b>sw \u22c5 <b>n<\/b>MVA|\u00a0\u00d7\u00a0\u0394t, where <b>v<\/b>sw is the upstream solar wind velocity and \u0394t is the measured duration of the passage of the spacecraft through the structure. Finally, the convection electric field \u2212<b>V<\/b>\u00a0\u00d7\u00a0<b>B<\/b> points towards the transient sheet, which allows particles to concentrate and form the observed transient. The overall methodological approach we followed is a standardized process typically done when single spacecraft in situ observations are available<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 4\" title=\"Turner, D. L. et al. Autogenous and efficient acceleration of energetic ions upstream of Earth&#x2019;s bow shock. Nature 561, 206&#x2013;210 (2018).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR4\" id=\"ref-link-section-d74689692e1519\" rel=\"nofollow noopener\" target=\"_blank\">4<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 5\" title=\"Raptis, S. et al. Revealing an unexpectedly low electron injection threshold via reinforced shock acceleration. Nat. Commun. 16, 488 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR5\" id=\"ref-link-section-d74689692e1522\" rel=\"nofollow noopener\" target=\"_blank\">5<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 18\" title=\"Liu, T. Z., Angelopoulos, V. &amp; Lu, S. Relativistic electrons generated at Earth&#x2019;s quasi-parallel bow shock. Sci. Adv. 5, eaaw1368 (2019).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR18\" id=\"ref-link-section-d74689692e1525\" rel=\"nofollow noopener\" target=\"_blank\">18<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 28\" title=\"Valek, P. W. et al. Hot flow anomaly observed at Jupiter&#x2019;s bow shock. Geophys. Res. Lett. 44, 8107&#x2013;8112 (2017).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR28\" id=\"ref-link-section-d74689692e1528\" rel=\"nofollow noopener\" target=\"_blank\">28<\/a>. Specifically, for our case, we used a typical upstream solar wind velocity of <b>v<\/b>sw\u00a0=\u00a0[400,\u00a00,\u00a00]\u2009km\u2009s\u22121 in JSO coordinates, which is in agreement with estimations of velocity during that interval, and calculated the scale as L\u00a0=\u00a0|<b>v<\/b>sw \u22c5 <b>n<\/b>MVA|\u00a0\u00d7\u00a0\u0394t, where \u0394t was taken as a 15-min duration of the passage of the spacecraft during the transient event. It should be noted that this 15-min interval, while relatively conservative, provides a realistic range of values for the spatial scale analysis (described below). The outcome of this analysis is provided in Extended Data Table <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"table anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#Tab1\" rel=\"nofollow noopener\" target=\"_blank\">1<\/a>.<\/p>\n<p>Finally, a power-law fitted to the energetic tail of the JADE and JEDI data (\u226510\u2009keV) during the foreshock transient results (Fig. <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#Fig2\" rel=\"nofollow noopener\" target=\"_blank\">2b<\/a>) in a spectral index of P\u00a0\u2248\u00a0\u22121.85\u00a0\u00b1\u00a00.2 with the exact 95% confidence interval being determined using a non-parametric bootstrap analysis with 1,000 iterations<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 64\" title=\"Davison, A. C. &amp; Hinkley, D. V. Bootstrap Methods and Their Application. Cambridge Series in Statistical and Probabilistic Mathematics (Cambridge Univ. Press, 1997).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR64\" id=\"ref-link-section-d74689692e1569\" rel=\"nofollow noopener\" target=\"_blank\">64<\/a>. This value suggests an acceleration process with a signature and efficiency similar to that of DSA. The obtained index is well-bounded by the canonical DSA limit of P = \u22121.5, a feature of efficient acceleration, and is also consistent with the expected spectral softening from \u22121.5 (non-relativistic) towards \u22122 for electrons at relativistic energies at \u22731\u2009MeV, as they are above the electron rest mass energy<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 65\" title=\"Haggerty, C. C. &amp; Caprioli, D. dhybridr: a hybrid particle-in-cell code including relativistic ion dynamics. Astrophys. J. 887, 165 (2019).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR65\" id=\"ref-link-section-d74689692e1576\" rel=\"nofollow noopener\" target=\"_blank\">65<\/a>.<\/p>\n<p>Spatial scales and energy limits<\/p>\n<p>The maximum energy attainable by a charged particle is fundamentally constrained by the physical properties of the accelerating environment. This limit is known as the Hillas criterion<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 3\" title=\"Hillas, A. M. The origin of ultra-high-energy cosmic rays. Annu. Rev. Astron. Astrophys. 22, 425&#x2013;444 (1984).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR3\" id=\"ref-link-section-d74689692e1588\" rel=\"nofollow noopener\" target=\"_blank\">3<\/a>, which relates the maximum particle energy to the available potential drop across the system. For a characteristic magnetic field B and flow velocity V, the induced motional electric field creates a potential difference across a scale L that ultimately limits the maximum attainable energy of a particle, with charge q, to Emax\u00a0=\u00a0qBLV.<\/p>\n<p>In the specific context of diffusive shock acceleration, this limit can be expressed as a confinement condition requiring that the upstream diffusion length of the particle, Ld, remains comparable to or smaller than the system size L (ref.\u2009<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 34\" title=\"Oka, M., Makishima, K. &amp; Terasawa, T. Maximum energy of particles in plasmas. Astrophys. J. 979, 161 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR34\" id=\"ref-link-section-d74689692e1628\" rel=\"nofollow noopener\" target=\"_blank\">34<\/a>). The diffusion length (Ld) can be estimated through the expression Ld\u00a0\u2248\u00a0D\/Vsh, where D is the spatial diffusion coefficient for the maximum energy, and Vsh is the velocity of the shock. For strong scattering, as is often assumed in the foreshock regions of planetary bow shocks<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 2\" title=\"Caprioli, D. &amp; Spitkovsky, A. Simulations of ion acceleration at non-relativistic shocks. III. Particle diffusion. Astrophys. J. 794, 47 (2014).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR2\" id=\"ref-link-section-d74689692e1656\" rel=\"nofollow noopener\" target=\"_blank\">2<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 5\" title=\"Raptis, S. et al. Revealing an unexpectedly low electron injection threshold via reinforced shock acceleration. Nat. Commun. 16, 488 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR5\" id=\"ref-link-section-d74689692e1659\" rel=\"nofollow noopener\" target=\"_blank\">5<\/a>, the scattering approaches the Bohm limit, at which the diffusion coefficient is \\(D\\approx \\frac{1}{3}v{r}_{{\\rm{g}}}\\), with v being the relativistic velocity of the particle and rg its gyroradius. By equating the diffusion length to the system size (L\u00a0\u2248\u00a0Ld), we recover the velocity dependence inherent in the Hillas criterion: \\(L\\approx \\frac{1}{3}\\frac{v}{{V}_{{\\rm{sh}}}}{r}_{{\\rm{g}}}\\).<\/p>\n<p>To derive a quantitative expression for the maximum energy from this relationship, we express the velocity v of the particle and gyroradius rg\u00a0=\u00a0p\/(qB) in terms of its total energy Etotal\u00a0=\u00a0Emax\u00a0+\u00a0mc2, where p is the momentum of the particle, q is the particle charge and B is the magnetic field magnitude. The relativistic relations p\u00a0=\u00a0\u03b3mv and \\({E}_{\\,{\\rm{total}}}^{2}={(pc)}^{2}+{(m{c}^{2})}^{2}\\) imply \\(p=\\sqrt{{E}_{\\,{\\rm{total}}}^{2}-{(m{c}^{2})}^{2}}\/c\\) and v\u00a0=\u00a0pc2\/Etotal. Substituting these into the confinement condition gives <\/p>\n<p>$$L=\\frac{1}{3}\\frac{1}{{V}_{\\mathrm{sh}}}\\frac{{E}_{\\mathrm{total}}^{2}-{(m{c}^{2})}^{2}}{{E}_{\\mathrm{total}}\\,qB},$$<\/p>\n<p>\n                    (1)\n                <\/p>\n<p>which leads to the quadratic equation for the particle\u2019s total energy, <\/p>\n<p>$${E}_{\\,\\mathrm{total}}^{2}-(3qBL{V}_{\\mathrm{sh}}){E}_{\\mathrm{total}}-{(m{c}^{2})}^{2}=0.$$<\/p>\n<p>\n                    (2)\n                <\/p>\n<p>Solving this equation for the positive energy root provides the exact solution for the maximum total energy that a size-limited shock acceleration region can produce: <\/p>\n<p>$${E}_{{\\rm{max,}}{\\rm{total}}}=\\frac{1}{2}\\,[A+\\sqrt{{A}^{2}+4{(m{c}^{2})}^{2}}],$$<\/p>\n<p>\n                    (3)\n                <\/p>\n<p>where the term A\u00a0=\u00a03qBLVsh describes the properties of the accelerator. The maximum kinetic energy is then found by subtracting the rest mass energy of the particle, Emax\u00a0=\u00a0Emax,total\u00a0\u2212\u00a0mc2. In the ultrarelativistic limit (v\u00a0\u2192\u00a0c and Etotal \u226b mc2), this relation reduces to the simple linear form Emax \u2243 \u03b1L, with \u03b1 \u2243 3qBVsh.<\/p>\n<p>The calculation of energy limits in equation (<a data-track=\"click\" data-track-label=\"link\" data-track-action=\"equation anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#Equ3\" rel=\"nofollow noopener\" target=\"_blank\">3<\/a>) requires three parameters: the local upstream magnetic field strength (B), the shock velocity (Vsh) and the characteristic system size (L). In this study, we use the upstream magnetic field for B and the relative velocity between the transient and the primary shock for Vsh. The acceleration region size (L) is described by the spatial extent of the transient, which is adequately equated to the precursor or foreshock region.<\/p>\n<p>To model the relationship between the acceleration region size (L) and the characteristic system size (S) as shown in Fig. <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#Fig3\" rel=\"nofollow noopener\" target=\"_blank\">3<\/a>, we assumed a power-law dependency of the form L\u00a0=\u00a0k \u22c5 Sm (ref.\u2009<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 28\" title=\"Valek, P. W. et al. Hot flow anomaly observed at Jupiter&#x2019;s bow shock. Geophys. Res. Lett. 44, 8107&#x2013;8112 (2017).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR28\" id=\"ref-link-section-d74689692e2461\" rel=\"nofollow noopener\" target=\"_blank\">28<\/a>). Two separate power-law models based on planetary observations are developed: a \u2018typical\u2019 model and an \u2018extreme\u2019 model. For the typical model, we used the standoff distance of each planet as the system size (S) and its typical observed acceleration region size as the associated value for Ltyp. For the extreme model, we used the same standoff distances (S) but paired them with the maximum observed acceleration region sizes (Lext). We performed a linear fit for each model in the log\u2013log space using ordinary least squares as implemented by the statsmodels (v.0.14.4) of Python library. The resulting fits are shown in Fig. <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#Fig3\" rel=\"nofollow noopener\" target=\"_blank\">3a<\/a>.<\/p>\n<p>The extension from planetary to astrophysical scales follows three points of reasoning: (1) We establish empirically that the acceleration region size (L) scales systematically with the global shock size (S) across planetary environments, where in situ observations confirm that large-scale foreshock transients are the primary acceleration sites. (2) We apply the Hillas criterion to relate this acceleration scale (L) to the maximum particle energy (Emax), a relationship validated through the presented Juno observations, previous research and recently shown to be applicable at planetary scales<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 5\" title=\"Raptis, S. et al. Revealing an unexpectedly low electron injection threshold via reinforced shock acceleration. Nat. Commun. 16, 488 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR5\" id=\"ref-link-section-d74689692e2502\" rel=\"nofollow noopener\" target=\"_blank\">5<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 34\" title=\"Oka, M., Makishima, K. &amp; Terasawa, T. Maximum energy of particles in plasmas. Astrophys. J. 979, 161 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR34\" id=\"ref-link-section-d74689692e2505\" rel=\"nofollow noopener\" target=\"_blank\">34<\/a>. (3) We combine these scaling relations under the premise that foreshock transient-driven acceleration operates universally across collisionless shocks, independent of whether the system is a planetary bow shock, protostellar jet or supernova remnant. This final step represents an extrapolation beyond what is testable with in situ experimentation and relies on theoretical expectations regarding the physics of collisionless shocks in different astrophysical contexts, further discussed below. To model the maximum particle energies for the planetary systems shown in Fig. <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"figure anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#Fig3\" rel=\"nofollow noopener\" target=\"_blank\">3(b)<\/a>, we set the acceleration size (L) to the maximum observed value (Lext). For the astrophysical objects, where direct observations of L are unavailable, we used our extreme fit model to estimate a value. Specifically, we calculated the upper boundary of the 95% prediction interval for a new observation at the object\u2019s system size (S). This interval accounts for both the uncertainty in the fitted model and the inherent variability in the data. The resulting energy range for each object, therefore, reflects the uncertainty propagated from its local shock speed and magnetic field parameters<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 66\" title=\"Heskes, T. Practical confidence and prediction intervals. In Proc. Advances in Neural Information Processing Systems Vol. 9 (NeurIPS, 1996).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR66\" id=\"ref-link-section-d74689692e2527\" rel=\"nofollow noopener\" target=\"_blank\">66<\/a>. This approach provides an estimate for the maximum achievable energy that is constrained by direct observation for the planets and by a robust statistical extrapolation for the astrophysical shocks.<\/p>\n<p>Physical justification for astrophysical applicability<\/p>\n<p>The extension of the planetary-derived scaling to astrophysical environments necessarily involves an extrapolation beyond verifiable limits, as in situ measurements of foreshock localized processes at kiloparsec distances are not feasible for the foreseeable future. However, several physical arguments support this extrapolation as a reasonable theoretical expectation, grounded in our understanding of collisionless shock physics and the properties of astrophysical environments.<\/p>\n<p>First, the astrophysical shocks that we consider (the protostellar jet HH 211 and the supernova remnants SN 1987A and SN 1006) represent curved, collisionless shocks, known from numerical simulations and indirect observational evidence to exhibit notable foreshock regions in their quasi-parallel geometries<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 2\" title=\"Caprioli, D. &amp; Spitkovsky, A. Simulations of ion acceleration at non-relativistic shocks. III. Particle diffusion. Astrophys. J. 794, 47 (2014).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR2\" id=\"ref-link-section-d74689692e2543\" rel=\"nofollow noopener\" target=\"_blank\">2<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 8\" title=\"Giuffrida, R. et al. The supernova remnant SN 1006 as a galactic particle accelerator. Nat. Commun. 13, 5098 (2022).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR8\" id=\"ref-link-section-d74689692e2546\" rel=\"nofollow noopener\" target=\"_blank\">8<\/a>. The curved geometry of these shocks ensures that quasi-parallel configurations are naturally present across substantial portions of the shock surface, similar to planetary bow shocks.<\/p>\n<p>Second, although the predicted acceleration region scales of 108\u20131010\u2009km for these astrophysical systems cannot be directly resolved, our estimates represent conservative lower bounds. These values are consistent with independent estimates of foreshock sizes<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 67\" title=\"Laming, J. M., Hwang, U., Ghavamian, P. &amp; Rakowski, C. Electron heating, magnetic field amplification, and cosmic-ray precursor length at supernova remnant shocks. Astrophys. J. 790, 11 (2014).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR67\" id=\"ref-link-section-d74689692e2557\" rel=\"nofollow noopener\" target=\"_blank\">67<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 68\" title=\"Katsuda, S. et al. Spatially resolved spectroscopy of a balmer-dominated shock in the cygnus loop: an extremely thin cosmic-ray precursor? Astrophys. J. Lett. 819, L32 (2016).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR68\" id=\"ref-link-section-d74689692e2560\" rel=\"nofollow noopener\" target=\"_blank\">68<\/a>. The consistency between our extrapolated predictions and these observational constraints provides support for the validity of our scaling approach, even in the absence of direct spatial resolution of the acceleration regions themselves.<\/p>\n<p>Third, the formation of large-scale foreshock transient can arise spontaneously through plasma instabilities and wave-particle interactions, whereas transient formation is also facilitated by large-scale discontinuities in the upstream medium<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 22\" title=\"Zhang, H. et al. Dayside transient phenomena and their impact on the magnetosphere and ionosphere. Space Sci. Rev. 218, 40 (2022).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR22\" id=\"ref-link-section-d74689692e2567\" rel=\"nofollow noopener\" target=\"_blank\">22<\/a>. These variable upstream media are an expected feature of astrophysical quasi-parallel shock environments. The turbulent interstellar medium contains magnetized filaments and structures extending to parsec scales<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Dickey, J. M. et al. Structure in the magnetic field of the Milky Way disk and halo traced by Faraday rotation. Astrophys. J. 940, 75 (2022).\" href=\"#ref-CR69\" id=\"ref-link-section-d74689692e2571\">69<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Ntormousi, E., Vlahos, L., Konstantinou, A. &amp; Isliker, H. Strong turbulence and magnetic coherent structures in the interstellar medium. Astron. Astrophys. 691, A149 (2024).\" href=\"#ref-CR70\" id=\"ref-link-section-d74689692e2571_1\">70<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 71\" title=\"Beattie, J. R., Federrath, C., Klessen, R. S., Cielo, S. &amp; Bhattacharjee, A. The spectrum of magnetized turbulence in the interstellar medium. Nat. Astron. 9, 1195&#x2013;1205 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR71\" id=\"ref-link-section-d74689692e2574\" rel=\"nofollow noopener\" target=\"_blank\">71<\/a>. Furthermore, supernova shock waves are expected to interact with complex circumstellar structures created by the progenitor star itself. These include stellar wind-blown bubbles and previously ejected dense shells of material, which can extend to parsec scales<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Martizzi, D., Faucher-Gigu&#xE8;re, C.-A. &amp; Quataert, E. Supernova feedback in an inhomogeneous interstellar medium. Mon. Not. R. Astron. Soc. Lett. 450, 504&#x2013;522 (2015).\" href=\"#ref-CR72\" id=\"ref-link-section-d74689692e2578\">72<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Moriya, T. J., Yoon, S.-C., Gr&#xE4;fener, G. &amp; Blinnikov, S. I. Immediate dense circumstellar environment of supernova progenitors caused by wind acceleration: its effect on supernova light curves. Mon. Not. R. Astron. Soc. Lett. 469, L108&#x2013;L112 (2017).\" href=\"#ref-CR73\" id=\"ref-link-section-d74689692e2578_1\">73<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 74\" title=\"Bykov, A. M., Ellison, D. C., Marcowith, A. &amp; Osipov, S. M. Cosmic ray production in supernovae. Space Sci. Rev. 214, 41 (2018).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR74\" id=\"ref-link-section-d74689692e2581\" rel=\"nofollow noopener\" target=\"_blank\">74<\/a>. When the expanding supernova shock encounters these pre-existing structures, it can generate large-scale magnetic field discontinuities. These encounters provide ideal conditions for seeding transient phenomena and driving particle acceleration through transient processes. Finally, the very high shock speeds observed at supernova remnants allow Alfv\u00e9nic Mach numbers (MA) to reach values of the order of 102\u2013103, causing particularly strong foreshock regions upstream of their quasi-parallel geometries that are highly favourable for the formation and persistence of large-scale foreshock structures. We note, however, that the maximum extent of these structures may be regulated by the coherence length of the upstream magnetic field (LB). For remnants in the galactic disk (for example, SN 1572), in which the shock radius can exceed LB, the acceleration region might be affected by the coherence scale, possibly creating a plateau in the acceleration scale length. This is in contrast to high-latitude systems such as SN 1006 or young SRNs such as SN7D21987A, in which LB\u00a0&gt;\u00a0S. Overall, the interplay between tangled fields and foreshock development in the regime in which S\u00a0&gt;\u00a0LB remains an open question for future investigation.<\/p>\n<p>Although these arguments establish the physical plausibility of extending our planetary framework to astrophysical scales, we emphasize that this extrapolation remains tentative in the absence of direct observational confirmation. Nevertheless, the internal consistency of our framework, validated at planetary scales and yielding predictions for SN 1006 that match observed maximum energies of about 100\u2009TeV, provides encouraging support for the underlying physical picture.<\/p>\n<p>Parameters of Solar System planets<\/p>\n<p>To apply our acceleration model, we first defined the physical parameter space for each environment. This space consists of the characteristic size (S), the acceleration region scale size (L), the shock speed (Vsh) and the upstream magnetic field strength (B) of the system. For the planetary environments, the system size S is the standoff distance of the bow shock, and L is the typical scale of a foreshock transient. These values were adopted from established literature<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 28\" title=\"Valek, P. W. et al. Hot flow anomaly observed at Jupiter&#x2019;s bow shock. Geophys. Res. Lett. 44, 8107&#x2013;8112 (2017).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR28\" id=\"ref-link-section-d74689692e2657\" rel=\"nofollow noopener\" target=\"_blank\">28<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 75\" title=\"Uritsky, V. M. et al. Active current sheets and candidate hot flow anomalies upstream of Mercury&#x2019;s bow shock. J. Geophys. Res. Space Phys. 119, 853&#x2013;876 (2014).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR75\" id=\"ref-link-section-d74689692e2660\" rel=\"nofollow noopener\" target=\"_blank\">75<\/a>, with the dataset for Jupiter supplemented by the event presented in this work. Minor refinements to the values have been made on the basis of the most recent standoff distance statistics and observations from each planetary environment<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Winslow, R. M. et al. Mercury&#x2019;s magnetopause and bow shock from messenger magnetometer observations. J. Geophys. Res. Space Phys. 118, 2213&#x2013;2227 (2013).\" href=\"#ref-CR76\" id=\"ref-link-section-d74689692e2664\">76<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Sulaiman, A. H., Masters, A. &amp; Dougherty, M. K. Characterization of saturn&#x2019;s bow shock: magnetic field observations of quasi-perpendicular shocks. J. Geophys. Res. Space Phys. 121, 4425&#x2013;4434 (2016).\" href=\"#ref-CR77\" id=\"ref-link-section-d74689692e2664_1\">77<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Gruesbeck, J. R. et al. The three-dimensional bow shock of Mars as observed by maven. J. Geophys. Res. Space Phys. 123, 4542&#x2013;4555 (2018).\" href=\"#ref-CR78\" id=\"ref-link-section-d74689692e2664_2\">78<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Xu, S. et al. Closed magnetic topology in the Venusian magnetotail and ion escape at Venus. Nat. Commun. 15, 6065 (2024).\" href=\"#ref-CR79\" id=\"ref-link-section-d74689692e2664_3\">79<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 80\" title=\"Rutala, M. J. et al. New models of Jupiter&#x2019;s magnetopause and bow shock through the Juno prime mission: probabilistic location, shape, and internally-driven variation. J. Geophys. Res. Space Phys. 130, e2025JA033842 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR80\" id=\"ref-link-section-d74689692e2667\" rel=\"nofollow noopener\" target=\"_blank\">80<\/a>. A full range for the shock speed, Vsh, was selected for all environments to account for the variety of dynamic conditions observed at interplanetary shocks. This range is based on the typical relative speeds between the solar wind plasma and transient compressive structures, as documented in several previous works, with the upper limit essentially describing typical solar wind speed<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 4\" title=\"Turner, D. L. et al. Autogenous and efficient acceleration of energetic ions upstream of Earth&#x2019;s bow shock. Nature 561, 206&#x2013;210 (2018).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR4\" id=\"ref-link-section-d74689692e2675\" rel=\"nofollow noopener\" target=\"_blank\">4<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 5\" title=\"Raptis, S. et al. Revealing an unexpectedly low electron injection threshold via reinforced shock acceleration. Nat. Commun. 16, 488 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR5\" id=\"ref-link-section-d74689692e2678\" rel=\"nofollow noopener\" target=\"_blank\">5<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 28\" title=\"Valek, P. W. et al. Hot flow anomaly observed at Jupiter&#x2019;s bow shock. Geophys. Res. Lett. 44, 8107&#x2013;8112 (2017).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR28\" id=\"ref-link-section-d74689692e2681\" rel=\"nofollow noopener\" target=\"_blank\">28<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 81\" title=\"Turner, D. L. et al. Direct multipoint observations capturing the reformation of a supercritical fast magnetosonic shock. Astrophys. J. Lett. 911, L31 (2021).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR81\" id=\"ref-link-section-d74689692e2684\" rel=\"nofollow noopener\" target=\"_blank\">81<\/a>. Finally, the range for the upstream magnetic field, B, at each planet was estimated using the Parker spiral model, which describes the evolution of the heliospheric magnetic field strength with increasing distance from the Sun<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 82\" title=\"Owens, M. J. &amp; Forsyth, R. J. The heliospheric magnetic field. Living Rev. Sol. Phys. 10, 5 (2013).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR82\" id=\"ref-link-section-d74689692e2692\" rel=\"nofollow noopener\" target=\"_blank\">82<\/a>.<\/p>\n<p>Parameters for HH 211<\/p>\n<p>HH 211 lies at approximately 1,000 light years away and drives a narrow bipolar jet with an associated bow shock. James Webb Space Telescope measurements showed speeds of about 80\u2013100\u2009km\u2009s\u22121 (figure 5 in ref.\u2009<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 7\" title=\"Ray, T. P. et al. Outflows from the youngest stars are mostly molecular. Nature 622, 48&#x2013;52 (2023).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR7\" id=\"ref-link-section-d74689692e2706\" rel=\"nofollow noopener\" target=\"_blank\">7<\/a>). Polarimetric ALMA\/SMA observations have shown envelope magnetic fields of 40\u2013100\u2009\u03bcG (4\u201310\u2009nT) within about 700\u2009AU (refs.\u2009<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 83\" title=\"Lee, C.-F. et al. Magnetic field structure in the flattened envelope and jet in the young protostellar system HH 211. Astrophys. J. Lett. 797, L9 (2014).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR83\" id=\"ref-link-section-d74689692e2713\" rel=\"nofollow noopener\" target=\"_blank\">83<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 84\" title=\"Lee, C.-F. et al. Unveiling a magnetized jet from a low-mass protostar. Nat. Commun. 9, 4636 (2018).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR84\" id=\"ref-link-section-d74689692e2716\" rel=\"nofollow noopener\" target=\"_blank\">84<\/a>). The projected separation from the protostar to the bow shock is about 1,000\u2009AU (figure 1 in ref.\u2009<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 7\" title=\"Ray, T. P. et al. Outflows from the youngest stars are mostly molecular. Nature 622, 48&#x2013;52 (2023).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR7\" id=\"ref-link-section-d74689692e2724\" rel=\"nofollow noopener\" target=\"_blank\">7<\/a>), which we take as the effective standoff distance. To account for variability, we took 700\u2009AU as the system size (S), and a shock speed between 50\u2009km\u2009s\u22121 and 150\u2009km\u2009s\u22121 based on the observed outer shock. The relatively cold environment upstream of these propagating jets allows the local Alfv\u00e9n Mach number (MA) to be relatively high, subsequently causing the formation of a strong foreshock precursor.<\/p>\n<p>Parameters of SN 1987A<\/p>\n<p>SN 1987A in the Large Magellanic Cloud has been extensively monitored through radio and X-ray observations. During the interaction with the dense equatorial ring, the forward shock decelerated to around 2,300\u2009km\u2009s\u22121, later re-accelerating to 3,500\u20133,600\u2009km\u2009s\u22121 (refs.\u2009<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Manchester, R. N. et al. Imaging of the radio remnant of SN 1987A at 12 mm wavelength. Astrophys. J. 628, L131 (2005).\" href=\"#ref-CR85\" id=\"ref-link-section-d74689692e2755\">85<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" title=\"Gaensler, B. M. et al. Fifteen years of high-resolution radio imaging of supernova 1987A. AIP Conf. Proc. 937, 86&#x2013;95 (2007).\" href=\"#ref-CR86\" id=\"ref-link-section-d74689692e2755_1\">86<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 87\" title=\"Zanardo, G. et al. High-resolution radio observations of the remnant of SN 1987A at high frequencies. Astrophys. J. 767, 98 (2013).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR87\" id=\"ref-link-section-d74689692e2758\" rel=\"nofollow noopener\" target=\"_blank\">87<\/a>); for our analysis, we used a conservative range between 2,000\u2009km\u2009s\u22121 and 4,000\u2009km\u2009s\u22121. For the upstream interstellar magnetic field, we expect values of the order of 1\u20135\u2009\u03bcG (0.1\u20130.5\u2009nT)<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 88\" title=\"Berezhko, E. G. &amp; Ksenofontov, L. T. Cosmic rays, radio and gamma-ray emission from the remnant of supernova 1987A. Astron. Lett. 26, 639&#x2013;656 (2000).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR88\" id=\"ref-link-section-d74689692e2767\" rel=\"nofollow noopener\" target=\"_blank\">88<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 89\" title=\"Berezhko, E. G. &amp; Ksenofontov, L. T. Magnetic field in supernova remnant SN 1987A. Astrophys. J. Lett. 650, L59&#x2013;L62 (2006).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR89\" id=\"ref-link-section-d74689692e2770\" rel=\"nofollow noopener\" target=\"_blank\">89<\/a>. Finally, for an equivalence of a standoff distance of the expanding shock (or arc), we used the radius of the blast wave of 0.1\u2009pc, resulting in an approximately 200,000\u2009AU system size (S).<\/p>\n<p>Parameters of SN 1006<\/p>\n<p>SN 1006 is a young, shell-type supernova remnant that provides compelling evidence for efficient particle acceleration to very high energies, similar to other historical remnants, such as Tycho<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 90\" title=\"Morlino, G. &amp; Caprioli, D. Strong evidence for hadron acceleration in Tycho&#x2019;s supernova remnant. Astron. Astrophys. 538, A81 (2012).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR90\" id=\"ref-link-section-d74689692e2788\" rel=\"nofollow noopener\" target=\"_blank\">90<\/a>, Cas A<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 91\" title=\"Cao, Z. et al. Broadband &#x3B3;-ray spectrum of supernova remnant Cassiopeia A. Astrophys. J. Lett. 982, L33 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR91\" id=\"ref-link-section-d74689692e2792\" rel=\"nofollow noopener\" target=\"_blank\">91<\/a> and RX J1713.7\u20133946<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 92\" title=\"Aharonian, F. et al. A detailed spectral and morphological study of the gamma-ray supernova remnant RX J1713.7&#x2013;3946 with HESS. Astron. Astrophys. 449, 223&#x2013;242 (2006).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR92\" id=\"ref-link-section-d74689692e2796\" rel=\"nofollow noopener\" target=\"_blank\">92<\/a>. Its shock velocity has been well-constrained by observations of its expansion, with estimates typically placing it in the range of 3,500\u20134,500\u2009km\u2009s\u22121. The strength of the upstream ambient magnetic field values is taken to be between 1\u2009\u03bcG and 2\u2009\u03bcG (0.1\u20130.2\u2009nT). The system size of the remnant is approximately 9\u201310\u2009parsecs, which translates to a system size (S) of roughly 2 \u00a0\u00d7\u00a0106\u2009AU. A unique feature of SN 1006 is the strong observational evidence, derived from its X-ray synchrotron and TeV emission, that particles are being accelerated to energies of the order of 100\u2009TeV within its shocks<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 8\" title=\"Giuffrida, R. et al. The supernova remnant SN 1006 as a galactic particle accelerator. Nat. Commun. 13, 5098 (2022).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR8\" id=\"ref-link-section-d74689692e2811\" rel=\"nofollow noopener\" target=\"_blank\">8<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 36\" title=\"Lemoine-Goumard, M., Acero, F., Ballet, J. &amp; Miceli, M. Hadronic particle acceleration in the supernova remnant SN 1006 as traced by Fermi-LAT observations. Astron. Astrophys. 693, A193 (2025).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR36\" id=\"ref-link-section-d74689692e2814\" rel=\"nofollow noopener\" target=\"_blank\">36<\/a>,<a data-track=\"click\" data-track-action=\"reference anchor\" data-track-label=\"link\" data-test=\"citation-ref\" aria-label=\"Reference 38\" title=\"Koyama, K. et al. Evidence for shock acceleration of high-energy electrons in the supernova remnant SN1006. Nature 378, 255&#x2013;258 (1995).\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#ref-CR38\" id=\"ref-link-section-d74689692e2817\" rel=\"nofollow noopener\" target=\"_blank\">38<\/a>. This makes SN 1006 an ideal test case for evaluating acceleration frameworks and provides a direct benchmark for the predictions of our model.<\/p>\n<p>The very high speeds observed at SN shocks allow Alfv\u00e9nic Mach numbers (MA) to reach values of the order of 103\u2212104 causing a particularly strong foreshock upstream of their quasi-parallel geometry. This parameter range estimation is difficult to constrain as expanding SN shocks change during their lifetime. However, the parameter space above provides a reasonable order of magnitude estimate and uncertainty range for the maximum obtainable particle energy. The parameters for the planetary environments that were used for the fitting are shown in Extended Data Table <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"table anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#Tab2\" rel=\"nofollow noopener\" target=\"_blank\">2<\/a>, and all parameters used for our generalized maximum energy model are summarized in Extended Data Table <a data-track=\"click\" data-track-label=\"link\" data-track-action=\"table anchor\" href=\"http:\/\/www.nature.com\/articles\/s41586-026-10473-z#Tab3\" rel=\"nofollow noopener\" target=\"_blank\">3<\/a>. It should be noted that the obtained shock speed range for each planetary environment is predominantly driven by the relative speed of the solar wind with respect to the shock, whereas for astrophysical objects, it is primarily dictated by the outward shock expansion to the relatively stable interstellar medium. Finally, although the upstream magnetic field values used in this study may be elevated by compression effects within the foreshock or precursor region, the acceleration regions themselves are characterized by local magnetic depressions. Consequently, the magnetic field within these transient structures is expected to be notably weaker than in the surrounding environment.<\/p>\n","protected":false},"excerpt":{"rendered":"Data Observations for this study are from the Juno spacecraft of NASA32. The energetic particle data are provided&hellip;\n","protected":false},"author":2,"featured_media":517304,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":"","_share_on_mastodon":"0"},"categories":[271],"tags":[85847,18,174762,1099,19,17,1100,452,133,127415],"class_list":["post-517303","post","type-post","status-publish","format-standard","has-post-thumbnail","category-physics","tag-astrophysical-plasmas","tag-eire","tag-high-energy-astrophysics","tag-humanities-and-social-sciences","tag-ie","tag-ireland","tag-multidisciplinary","tag-physics","tag-science","tag-space-physics"],"share_on_mastodon":{"url":"https:\/\/pubeurope.com\/@ie\/116688865811779677","error":""},"_links":{"self":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts\/517303","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/comments?post=517303"}],"version-history":[{"count":0,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/posts\/517303\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/media\/517304"}],"wp:attachment":[{"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/media?parent=517303"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/categories?post=517303"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.europesays.com\/ie\/wp-json\/wp\/v2\/tags?post=517303"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}