We humans tend to take our existence for granted. Some of us have even become comfortably numb: In the middle of the night we can get something to eat at a nearby frituur or kebab shop. Even though it’s raining fiercely, we sleep underneath a roof and a warm blanket. Even if we lose our job, the government (or at least our friends) can help us out. Current conditions for life belong to the most stable since the existence of mankind. All of this gives us a blind assurance that the future will not differ much from today. Physicist Lenka Zychova would like to rid us of this illusion with this eight part series on the different ways life on Earth could be suddenly extinguished. The previous parts tackled mass extinctions and huge space rocks. This third episode will address solar radiation.
The weather forecast. The announcer breathes in and says in a calm, soothing voice: ‘Solar particle radiation and geomagnetic storms continue. While the severity of the radiation storm dropped to S4, the degree of the geomagnetic storm climbed to its maximum, G5. We expect further power outages, locally damaged transformers, and breakdowns on railway tracks. The train transport in Brussels has already collapsed, which was to be expected. Air traffic is still paralyzed by the radiation storm. We expect flight delays to be within several hours due to a reduction of flight altitudes for most flights within the Schengen Area. Transcontinental flights were canceled by most airlines. GPS navigation will be highly problematic in the upcoming days, especially in cities and densely populated areas. Tourists on all orbits have a strict ban on space walks. During the night we can expect to see northern lights all over Belgium. Tomorrow and the day after tomorrow, we expect a decline in the geomagnetic storm, but its effects are expected to last at least for one more week.’

Space weather means you’re going to miss the concert tonight. Image: Wendy Marijnissen, via Nieuwsblad.be

But on the flipside: you’ll get a free light show after sunset. Image: Pixabay

Science fiction? It depends. It is true that space tourism is not yet in full swing, but a geomagnetic or solar particle radiation storm is a reality that could hit us at any time. Moreover, as humanity is increasingly dependent on communication technologies and satellites circling the Earth, we have become more vulnerable to so-called space weather. As meteorologists predict storms on Earth, monitor precipitation and measure wind speed and direction, space weather scientists predict geomagnetic and solar particle radiation storms, monitor the flux of charged particles from both the Sun and the distant universe, and measure the speed and direction of the solar wind. Maybe you are wondering what this is all for? Our Earth has its magnetic field and an atmosphere that protects us. Well, Houston, that’s the problem. People are not strapped to the surface of the Earth anymore. Not only astronauts, but also passengers in airplanes can be endangered by the flood of charged particles from space. In addition, banking, security systems and navigation rely on satellites in orbit around the Earth. And such a dose of radiation can cause serious havoc to satellites .
‘As humanity is increasingly dependent on communication technologies and satellites circling the Earth, we have become more vulnerable  to so-called space weather.’

In this article, we look at one of the solar phenomena that can trigger a solar energetic particle event alarm, important not only for astronauts, but also spacecraft operators who have to alert the crew to an acute danger. This phenomenon is known as a solar flare.

The sun seen in visible light (left) and UV radiaton (right) – Image: NASA SDO

Through a solar telescope, the Sun looks like a calm, yellow disk with some darker sunspots here and there. However, when you look at UV images of the Sun, you will be surprised by the intricate structures that decorate the solar disk and its edges. These are coronal loops resulting from the complex magnetic field of the Sun and its interaction with the surrounding hot matter . Do you remember the classic school experiment with a magnet and sawdust? That’s exactly what the Sun’s magnetic field does NOT look like. Unlike your school’s magnet, the Sun is made up of very hot gas. The Sun is so hot that some atoms fall apart and lose their electrons. This means our Sun is made out of a huge amount of charged, swarming particles. The Sun not only rotates on its axis, its matter constantly bubbles up to the surface. And this movement of charged particles induces an extremely complex magnetic field which, to make things even more unpredictable, is constantly changing. Do you remember the joy when the sawdust magically jumped into the loops around the magnet? In the case of the Sun, it is not metal sawdust that forms the coronal loops, but particles of hot material (up to a million degrees) that surround the Sun. These particles flow along magnetic field lines, creating these beautiful curves and loops.

Metal shavings conform to the magnetic field that forms around a loop conducting electricity.

The sun’s magnetic field in 2014, during a period of intense solar activity. Image: NASA

In pictures and videos, the coronal loops seem to be charming and delicate, even fragile or harmless. However, they are a result of a strong local magnetic field, and if parts of an individual loop connect (we call this magnetic reconnection), an enormous amount of energy is released. It is vented in the form of unpalatable radiation. These so-called solar flares are producing gamma, ultraviolet and X radiation. In addition, solar flares produce energetically charged particles of high energy, which, along with electromagnetic radiation, are a huge threat to astronauts if they are not inside a protected area in for example their spacecraft or on the International Space Station.
Lucky for Apollo 16 and 17 that their missions were not hit by the solar particle radiation storm of August 1972. The Apollo 16 crew returned in April 1972 and the crew of Apollo 17 set off to the Moon at the beginning of December 1972. If any of the crew members had been hopping on the Moon’s surface at the time of the radiation storm in 1972, their lives would have been seriously endangered. There is a large possibility that a dose of about 4 Sv (Sievert) would have killed at least one of the crew members during the following month.
Maybe you feel safe because you are not spending your afternoon in an orbit around the Earth, or because you have decided to spend your vacation on Bali, not on the Moon. But honestly, have you ever used an airplane?

Maybe you feel safe because you are not spending your afternoon in an orbit around the Earth, or because you have decided to spend your vacation this year on Bali, not on the Moon. But honestly, have you ever used an airplane? Extremely energetic particles coming from the Sun and other parts of the distant universe produce a shower of secondary particles in the Earth’s atmosphere. Although the shower reaches its maximum at an altitude of about 18 km above the Earth’s surface, these particles are still present at common flight altitudes. So, there is a source of radiation and possible danger. Don’t worry, your flight will probably never be grounded because of solar activity. The radiation dose is not as huge as it sounds. But theoretically, if you were exposed daily for long durations during solar superstorms, you could accumulate a high dose, far exceeding the annual limit of 1 mSv (20 mSv for an aircraft crew). Luckily, storms of this intensity are very rare. Moreover, the amount of people with a long flight as their daily commute are even rarer.
This is why we have “space weathermen and -women”: scientists who monitor the space weather and spread alerts to all who need the information in time. From flight centers, through satellite operators, to astronauts. Therefore, if there were some active suspicious regions on the Sun and Elon Musk would at that moment decide to have a morning walk on Mars, there would be a whole team of scientists who would stop him. Sorry Elon, you’ll have to stay inside your Mars base for another day.
Space weather forecasting and research is fundamental for spacecraft operation, navigation, and aviation. Here in Belgium we have a whole institute devoted to space aeronomy, and space weather is one of the subjects that is pursued. This institute, known as the Royal Belgian Institute for Space Aeronomy (BIRA-IASB, http://www.aeronomie.be/), is a Belgian federal scientific research institute, focusing on research and public service in space aeronomy. One of the scientific research groups in the institute’s Space Physics Department is the Space Weather group. Its mission is to valorize scientific research within the field of space weather and effects through the provision of services to a broad range of end users including the general public. The group provides tools to forecast and model space weather during space missions. It also communicates with spacecraft operators, airlines and other users by managing the European Space Weather Helpdesk.

BIRA’s main building in Uccle. aeronomie.be

In the next episode, we will look at geomagnetic storms and their breathtaking sources.