Kelvin-Helmholtz Instability: Where and How to Find Them at Mars?!

Gang Kai Poh

The Catholic University of America ~ Physics Department
NASA Goddard Space Flight Center

Wed, September 4, 2024 - 4:00 PM

The Kelvin–Helmholtz (K–H) instability is a fundamental plasma process in many astrophysical plasma environments. Its development and growth is known to occur along the interface of two fluids in the presence of a velocity shear. As such, K–H instability is commonly observed along the flanks of globally magnetized planets, such as Mercury, Earth and Saturn. Extensive studies using spacecraft observations and numerical simulations have been conducted to understand the instability criteria, development and role in transporting mass, energy and momentum across plasma boundary layers during its non-linear stage. The K–H instability has also been thought to occur in the plasma environments of unmagnetized planets such as Venus and Mars. Unlike Earth and other magnetized planets, the Venusian and Martian ionosphere interacts directly with the solar wind due to the lack of an intrinsic planetary magnetic field, resulting in velocity shear along the boundary separating the magnetosheath and ionosphere where K–H instability could potentially develop. Despite previous attempts by earlier studies to apply our understanding of K–H instability at Venus to the Martian plasma environment, the excitation and evolution of K–H instability at Mars, and its contribution to the overall ionospheric escape remains largely unexplored and poorly understood. This can be attributed to (1) difficulties in observing fully developed vortices associated with K–H instability, (2) the lack of simultaneous in-situ magnetic field and plasma measurements before MAVEN, and (3) our poor understanding of how K–H instability could develop in Mars’ hybrid magnetosphere. Fundamental questions regarding the nature of K–H instability at Mars, such as (i) Where is the KH–unstable boundary at Mars?, (ii) What IMF and solar wind conditions are most conducive for the onset and growth of K–H instability?, and (iii) What has been the role of K–H on atmospheric loss at Mars throughout the history of the solar system?, remains as open questions. Although it is not the first spacecraft to observe and examine K–H instability in unmagnetized planets, the MAVEN spacecraft contains a comprehensive suite of instruments suited to further our physical understanding of K–H instability at Mars. In this seminar, we will discuss about the physics of K–H instability in magnetized fluid, and present observational and numerical results from earlier studies regarding its development, growth and late-stage evolution in the martian hybrid plasma environment. Results from ongoing research, implications of our understanding thus far and future efforts to improve our understanding of K–H instability at Mars will also be presented and explored.

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