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Sci Adv. 2019 Feb 27;5(2):eaau9926. doi: 10.1126/sciadv.aau9926. eCollection 2019 Feb.

Direct evidence of nonstationary collisionless shocks in space plasmas.

Author information

1
Swedish Institute of Space Physics, P.O. Box 537, SE-751 21 Uppsala, Sweden.
2
Department of Earth Planetary and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095, USA.
3
Department of Physics, University of Maryland, College Park, MD 20742, USA.
4
LPC2E, CNRS-University of Orleans, Orleans, France.
5
Space Sciences Laboratory at University of California, 7 Gauss Way, Berkeley, CA 94720, USA.
6
Department of Automatic Control and Systems Engineering, University of Sheffield, Sheffield, UK.
7
Imperial College London, London SW7 2AZ, UK.
8
IRAP, Université de Toulouse, CNRS, UPS, CNES, Toulouse, France.
9
European Space Agency/European Space Research and Technology Centre (ESA/ESTEC), Noordwijk, Netherlands.
10
Finnish Meteorological Institute, Helsinki, Finland.
11
University of Michigan, Ann Arbor, MI 48109, USA.
12
Department of Physics, Ben-Gurion University, Beer-Sheva, Israel.
13
NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
14
Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, Espoo, Finland.

Abstract

Collisionless shocks are ubiquitous throughout the universe: around stars, supernova remnants, active galactic nuclei, binary systems, comets, and planets. Key information is carried by electromagnetic emissions from particles accelerated by high Mach number collisionless shocks. These shocks are intrinsically nonstationary, and the characteristic physical scales responsible for particle acceleration remain unknown. Quantifying these scales is crucial, as it affects the fundamental process of redistributing upstream plasma kinetic energy into other degrees of freedom-particularly electron thermalization. Direct in situ measurements of nonstationary shock dynamics have not been reported. Thus, the model that best describes this process has remained unknown. Here, we present direct evidence demonstrating that the transition to nonstationarity is associated with electron-scale field structures inside the shock ramp.

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