PHY569B – Astrophysical plasmas and space missions
The solar system provide an ideal laboratory to investigate fundamental physical processes (e.g., turbulence, magnetic reconnection, shocks) that underlie longstanding problems of heliophysics, such as the solar corona and solar wind heating problems, particle acceleration and radio emissions in planetary magnetospheres (e.g., aurora). The main reason is the availability of high quality in-situ data measured by various spacecraft that have been exploring these media for about a half century. These include the solar wind exploration by Voyager since the 1970s to the more recent ones, the NASA/Parker Solar Probe (launched in 2018) and the ESA/Solar Orbiter (launched in 2020), the near-Earth space exploration (ionosphere and magnetosphere) by multi-satellites missions such as the ESA/Cluster (2000) and NASA/MMS (2015), planetary exploration: NASA/Jupiter by Galileo, Juno (2016) and “soon” ESA/JUICE (launched in 2022, orbit insertion in 2030), NASA-ESA/Saturn (Cassini 1997-2017), Mercury by NASA/Messenger (2004) and ESA-JAXA/BepiColombo (launched in 2018, orbit insertion in December 2025). The achievements accomplished in the solar system allow us to extrapolate the results to other challenging problems of distant astrophysical objects, which are not (or much less) accessible to measurements. Examples are star formation in the interstellar medium (ISM), cosmic rays acceleration and magnetic field generation in galaxies and inter-cluster galaxy (ICG), angular momentum transport and accretion flows around compact objects (e.g., black holes).
In this lecture we will first introduce some major questions of astrophysical plasmas and explain how they can be tackled using the solar system as a laboratory to test modern existing theories. In the second part, we will recall some basic equations of plasma physics (kinetic and fluid-like descriptions, i.e. MHD and its extensions to small scales, e.g. Hall-MHD), before discussing examples of universal plasma processes such as turbulence and magnetic reconnection. We will expose the underlying theories of such processes and explain how they can help solving some of the questions addressed in the introduction of the course, with a particular focus on how the theoretical predictions can be tested in spacecraft observations.
The second part of the lecture we will deal with the description and design of space missions dedicated to space plasmas. We will describe the main in-situ instruments embedded on orbiting spacecraft (e.g., AC & DC magnetometers, Langmuir probes, plasma spectrometers –electrons and ions). We will explain their functioning principle, their constraints and limitations inherent to space exploration (cost, mass, power, telemetry). We will also introduce some signal processing techniques and methods used to analyze (single and multi-)spacecraft data and discuss their strengths and weaknesses.
In the last part we will present some current trends in space exploration dedicated to plasma physics (both in the solar wind and planetary magnetospheres). We will introduce new scientific questions that emerged in light of recent progress achieved from the current orbiting spacecraft, discuss the new concepts of space missions under preparation and highlight the new technical challenges faced.
Course language: English
- Profesor: Sahraoui Fouad