In Situ Observations of the Formation of Periodic Collisionless Plasma Shocks from Fast Mode Waves

Lican Shan (1, 2) , Aimin D Du (2) , Bruce T Tsurutani (3) , Yasong Ge (1, 2) , Quanming Lu (4) , Christian Mazelle (5) , Can Huang (6, 2) , Karl-Heinz Glassmeier (7) , Pierre Henri (8)

1 EPP - CAS Key Laboratory of Earth and Planetary Physics
2 Innovation Academy for Earth Science
3 Independent Scholar
4 CAS Key Laboratory of Geospace Environment
5 IRAP - Institut de recherche en astrophysique et planétologie
6 CAS Key Laboratory of Basic Plasma Physics
7 Technische Universität Braunschweig = Technical University of Braunschweig [Braunschweig]
8 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace

It has been long theorized, but not directly observed, that low-frequency magnetosonic plasma waves can steepen and form shocks. We show an example of small-amplitude, sinusoidal magnetosonic waves at the proton gyrofrequency upstream of the Martian bow shock. We hypothesize that these waves are produced by an ion beam instability associated with the ionization of hydrogen atoms by charge exchange with solar wind protons, solar photoionization, and/or electron impact ionization. As the waves are convected toward the planet by solar wind flow, the wave amplitude grows due to additional free energy put into the system by further ion beam particles. Finally, the steepened waves form shocks. Because of their development, the shocks are periodic with the separation at the proton gyroperiod. These observations lead to the conclusion that newborn ions may play a crucial role in the formation process of some collisionless plasma shocks in astrophysical and space plasmas.

Keywords: Shocks; Pickup ions; Plasma physics; Unified Astronomy Thesaurus concepts: Shocks (2086); Pickup ions (1239); Plasma physics (2089)

Domains: Sciences of the Universe [physics]

Lican Shan, Aimin D Du, Bruce T Tsurutani, Yasong Ge, Quanming Lu, et al.. In Situ Observations of the Formation of Periodic Collisionless Plasma Shocks from Fast Mode Waves. The Astrophysical journal letters, 2020, 888 (2), pp.L17. ⟨10.3847/2041-8213/ab5db3⟩. ⟨insu-02514825⟩