The Persistent Mystery of Collisionless Shocks

TL;DR

This paper emphasizes the importance of a dedicated spacecraft mission to better understand the energy conversion processes and energy partitioning in collisionless shocks in space plasmas, which remain poorly understood due to observational limitations.

Contribution

It advocates for the first dedicated spacecraft mission to observe both terrestrial and interplanetary shocks to advance understanding of collisionless shock physics.

Findings

Current observations are limited by instrument and mission constraints.

Understanding of energy partitioning downstream of shocks is incomplete.

A dedicated mission could significantly improve shock physics knowledge.

Abstract

Collisionless shock waves are one of the main forms of energy conversion in space plasmas. They can directly or indirectly drive other universal plasma processes such as magnetic reconnection, turbulence, particle acceleration and wave phenomena. Collisionless shocks employ a myriad of kinetic plasma mechanisms to convert the kinetic energy of supersonic flows in space to other forms of energy (e.g., thermal plasma, energetic particles, or Poynting flux) in order for the flow to pass an immovable obstacle. The partitioning of energy downstream of collisionless shocks is not well understood, nor are the processes which perform energy conversion. While we, as the heliophysics community, have collected an abundance of observations of the terrestrial bow shock, instrument and mission-level limitations have made it impossible to quantify this partition, to establish the physics within the shock layer responsible for it, and to understand its dependence on upstream conditions. This paper stresses the need for the first ever spacecraft mission specifically designed and dedicated to the observation of both the terrestrial bow shock as well as Interplanetary shocks in the solar wind.