There is More Than Just One “Corona” That Can Kill Us All

Michaela Brchnelová 1
1 Centre for Mathematical Plasma Astrophysics, Department of Mathematics, Catholic University Leuven
* Corresponding author:
Key words:
magnetohydrodynamics, computational fluid dynamics, solar physics, solar atmosphere
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When most people hear the phrase "space exploration", they imagine preparing the colonisation of Mars, studying distant planets, searching for alien life or studying exotic black holes. Many times, however, mankind tends to leap before looking and focus on the exotic and the interesting instead of that which might not seem that special to most of us, but which which can be crucial for our survival. This way, many major and important issues in astrophysics - and sciences in general - can become overlooked and take very long to resolve. One such major issue in astrophysics is the behaviour of our closest star, the Sun. While we generally assume that we have a good idea about the most significant processes in the solar interior acting as its main energy source, our attempts at explaining the dynamics and structure of the solar atmosphere (the so-called corona) are still merely an educated guesswork at best. Due to several of the magnetohydrodynamic processes which we do not yet fully understand, the temperature of the solar atmosphere is very high compared to the layers underneath and reaches millions of Kelvins. Since this is where the major mass ejections occur, some of which might be directed towards the Earth causing geomagnetic storms, it is crucial that we start not only to fully understand these processes, but also to be able to accurately predict their outcomes. As will be shown in this text however, it is not only our limited understanding of the physics which prevents us from doing that; it is also the lack of computational resources. This paper firstly briefly discusses the basic physics behind the behaviour of the solar coronal plasma. Afterwards, it discusses the coronal heating problem in more detail and finally, it outlines the major challenges we currently face which seem to prevent us from efficient simulation and complete understanding of the behaviour of our closest star.
Our Sun is a highly complex object made out of high-temperature rotating plasma, undergoing periodic cycles of activity. Despite the fact that compared to the majority of stellar types out there, our Sun belongs to the category which we generally consider to be "calm" and "average", its activity must still be something that we concern ourselves with greatly. Stars similar to our Sun have been observed to produce enormous ejections of energy and mass, some of which could make our survival on Earth challenging if not outright impossible if one such event hit the Earth directly. Even though the Sun is our closest star, we still know embarrassingly little about it. We are not even close to fully understanding the processes which happen in the solar plasma. The fact that we cannot directly observe most of the Sun's internal and atmospheric layers or send a probe to its close vicinity is not helping us on that quest. From the observations that we have, we can only create approximations about its composition and thermodynamic variations; we can tell very little about what exactly is causing these variations and how they will evolve in the future. At the same time, our lives directly depend on the Sun's activity. Without a warning, a stronger solar storm can destroy satellites, electrically charge railways, corrode pipelines, overload transformers degrading power grids and even hinder radio communication. Just in 2012, a massive solar storm narrowly avoided the Earth - one which could have resulted in serious damage all over the globe as well as in space. Similar events in the past have created radio blackouts, destroyed satellite systems, caused power outages and hindered railway traffic. We must have a system to issue warnings about such events, despite not fully understanding how the physics that leads to them. In this paper, I make a short introduction into the physics of the solar plasma; the principles and laws governing its dynamics along with some of the assumptions that we currently make when resolving it. I also introduce one of the most important solar phenomena which we are still yet to sufficiently explain - the coronal heating problem - along with some of the proposed explanations by the different groups of physicists. Naturally, from this arises the discussion about how come that we still cannot explain phenomena such as this. I briefly touch upon some of the challenges that we face which are preventing us from fully resolving how the Sun works and from making predictions on its behaviour in the future. I conclude with an outlook highlighting some of the steps that we, as a community, must further undertake to help us understand the Sun and, by extension, to help us protect our society.
Michaela Brchnelova is a PhD researcher at KU Leuven in Belgium at the Centre for Mathematical Plasma Astrophysics. She obtained her Master and Bachelor degrees in Aerospace Engineering with Cum Laude from Delft University of Technology in the Netherlands and has work experience from the European Space Agency (ESTEC) and the German Aerospace Centre. Currently, she works on creating global numerical models of the Sun and simulating plasma waves in its atmosphere.