These days most of us are familiar with the term “space weather.” Actually, “solar weather” is a more accurate term because what we mean by space weather is what the sun is sending in our direction and what its effects are on our space neighbourhood, the Earth, and our activities. The main things we have to consider are the solar wind, solar flares, and coronal mass ejections.
The solar wind is a continuous and highly variable blast of particles and magnetic fields moving outward from the Sun at speeds ranging from hundreds to thousands of kilometres a second. Most of this is held away from the Earth by our planet’s magnetic field. If left alone that field should be shaped like a doughnut.
The solar wind blowing over and around it has shaped it into a long teardrop. How important our magnetic field is to us is shown by what we see on Mars. That planet’s magnetic field decayed long ago, and since then the solar wind has scoured away most of the planet’s atmosphere.
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The sun is a nuclear fusion powered ball of hot plasma threaded by magnetic fields. These emerge through the surface and form huge loops, filled with trapped, million-degree plasma. This “magnetoplasma” is rather like a mass of elastic.
It can be stretched, twisted or compressed. The constant motion of the solar surface leads to these loops getting tremendously stressed, and a colossal amount of energy stored in them. In most cases there are processes that can relax the stresses and release the energy slowly. However, on occasion instabilities develop which release that energy catastrophically, resulting in a huge explosion, known as a solar flare.
Huge bursts of high-energy radiation, such as X-rays are produced; electrons are accelerated to almost the speed of light and shot off into space, along with beams of other high-energy particles.
Here on the Earth’s surface, protected by our magnetic field and atmosphere, these hazards pose little threat. However, for those in space or flying over the poles at high altitudes, the radiation and high-energy particles from the sun can pose problems.
Coronal mass ejections, or “solar storms” are loops that have snapped off at the roots and catapulted out into space at thousands of kilometres a second. They are mostly stopped by the Earth’s magnetic field, but they can cause intense magnetic storms, which in turn cause power outages and other issues.
For us here on Earth, over history solar activity has, as far as we know, posed little threat to living things. The main thing was the occasional spectacular and beautiful displays of aurora.
However, over the last few decades, things have started to change. Our increasing dependence on high-tech infrastructure has made us more and more vulnerable to disruptions of our hi-tech lives.
A big question here is how big solar flares can get. Is it possible they could threaten our lives as opposed to our technical infrastructure?
Astronomers recently detected a flare on another star that released millions of times the energy of the biggest solar flare observed so far. This star, designated HD 283572 lies some 400 light years away. It is young star, only around 3 million years old, and is about 40% more massive than the Sun. If the Sun produced such an event, it is not clear that our atmosphere and magnetic field could protect us from the environmental damage it could produce.
Such flares could have devastating effects on life starting up on young planets. It looks as though when we are looking for life on planets orbiting other stars, we will need to consider the behaviour of those stars. Only one of these megaflares has been detected so far so we have no idea how rare they are.
Ken Tapping is an astronomer with the National Research Council’s Dominion Radio Astrophysical Observatory, Penticton.
