Compressive Structures in the Foreshock of Collisionless Shocks

Savvas Raptis; Domenico Trotta; Drew L. Turner; Xóchitl Blanco-Cano; Heli Hietala; Tomas Karlsson; Immanuel Christopher Jebaraj; Ivan Y. Vasko; Adnane Osmane; Kazue Takahashi; David Lario; Lynn B. Wilson; Gregory G. Howes; Robert F. Wimmer-Schweingruber

doi:10.3847/2041-8213/ae53e5

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Compressive Structures in the Foreshock of Collisionless Shocks

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Compressive Structures in the Foreshock of Collisionless Shocks

Savvas Raptis, Domenico Trotta, Drew L. Turner, Xóchitl Blanco-Cano, Heli Hietala, Tomas Karlsson, Immanuel Christopher Jebaraj, Ivan Y. Vasko, Adnane Osmane, Kazue Takahashi, …

Astrophysical journal. Letters, Vol.1000(2), L55

04/01/2026

DOI: 10.3847/2041-8213/ae53e5

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Abstract

Collisionless shocks are fundamental accelerators of energetic particles, yet the observations of nonlinear foreshock structures, which are essential in acceleration processes, differ significantly between interplanetary (IP) shocks and planetary bow shocks. We present a direct comparison of two high-Mach-number, quasi-parallel shocks: an IP shock observed by Solar Orbiter and the Earth’s bow shock measured by the Magnetospheric Multiscale mission during the 2024–2025 “string-of-pearls” campaign. We show that foreshock compressive structures (FCSs) initiate upstream of both shocks at similar normalized distances (≲50 ion inertial lengths, d i ) when the suprathermal (>10 keV) ion density exceeds ∼1% of the background. However, the IP shock lacks the fully evolved, high-amplitude short large-amplitude magnetic structures characteristic of the terrestrial foreshock. We demonstrate that the “growth zone” capable of sustaining these structures is spatially limited (∼135 d i ), which, due to the high speed of the propagating IP shock, corresponds to a brief observational window of <10 s. Beyond this observational constraint, we suggest an additional physical mechanism that can inhibit foreshock maturity at IP shocks. The lack of global curvature prevents the lateral supply (“cross talk”) of energetic ions from different shock regions. These findings suggest that while the fundamental physics of FCS initiation is unified across collisionless shocks, the achievement of full nonlinearity can be regulated by the unique shock geometry and upstream properties while ultimately remaining observationally challenging to identify.

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Title: Subtitle: Compressive Structures in the Foreshock of Collisionless Shocks
Creators: Savvas Raptis - Johns Hopkins University Applied Physics Laboratory
Domenico Trotta - European Space Astronomy Centre
Drew L. Turner - Johns Hopkins University Applied Physics Laboratory
Xóchitl Blanco-Cano - Universidad Nacional Autónoma de México
Heli Hietala - Queen Mary University of London
Tomas Karlsson - KTH Royal Institute of Technology
Immanuel Christopher Jebaraj - University of Turku
Ivan Y. Vasko - The University of Texas at Dallas
Adnane Osmane - University of Helsinki
Kazue Takahashi - Johns Hopkins University Applied Physics Laboratory
David Lario - Goddard Space Flight Center
Lynn B. Wilson - Goddard Space Flight Center
Gregory G. Howes - University of Iowa
Robert F. Wimmer-Schweingruber - Christian-Albrechts-Universität zu Kiel
Resource Type: Journal article
Publication Details: Astrophysical journal. Letters, Vol.1000(2), L55
DOI: 10.3847/2041-8213/ae53e5
ISSN: 2041-8205
eISSN: 2041-8213
Publisher: IOP
Grant note: Research Council of Finland (AKA): X-Scale, grant No. 371569 NASA divided by Science Mission Directorate (SMD): NNG04EB99C Deutsches Zentrum fr Luft- und Raumfahrt (DLR): 50OT2002 Royal Society (The Royal Society): URF\R1\180671 European Space Agency (ESA): ESA-SCI-E-LE-170
S.R. acknowledges funding from the MMS Early Career Award 80NSSC25K7353 and the Magnetospheric Multiscale (MMS) mission of NASA's Science Directorate Heliophysics Division via subcontract to the Southwest Research Institute (NNG04EB99C). S.R. also acknowledges the support of the International Space Sciences Institute (ISSI) team 555, "Impact of Upstream Mesoscale Transients on the Near-Earth Environment," and the useful discussions with Ahmad Lalti. X.B.C. thanks PAPIIT DGAPA IN106724 and SECIHTI CBF-2023-2024-852 grants. H.H. is supported by the Royal Society Award URF\R1\180671. URF\R \251031. I.C.J. acknowledges support from the Research Council of Finland (X-Scale, grant No. 371569). K.T. was supported by the Parker Solar Probe project under contract NNN06AA01C. R.F.W.-S. acknowledges support of Solar Orbiter's EPD by DLR grant 50OT2002. We also acknowledge support from ESA through the Science Faculty-Funding reference ESA-SCI-E-LE-170.
Language: English
Date published: 04/01/2026
Academic Unit: Physics and Astronomy
Record Identifier: 9985152088402771

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