Wonders of the Solar System Text Only. Andrew Cohen

is a worthy member of this list. In 1858, Carrington made the first observation of an event that would eventually become known as a solar flare.

      This massive explosion in the Sun’s atmosphere releases a huge amount of energy and Carrington noticed that this event was followed by a geomagnetic storm, a massive disruption in the Earth’s magnetic field, the day after the eruption. Carrington was the first to suspect the two events may be connected. Beyond the weather in our swirling atmosphere, the solar wind creates another more tenuous atmosphere and weather system that surrounds our planet. We rarely notice this ethereal weather high above us, because by the time the solar wind reaches Earth it’s pretty diluted. If you went into space close to the Earth and held up your hand, you wouldn’t feel a thing. In fact, there are about five protons and five electrons for every sugar cube’s worth of space, but they’re travelling very fast, carrying a lot of energy – enough to severely damage our planet’s atmosphere, were it not for a defence system generated deep within the Earth’s core.

      On a beautiful sunny winter’s day in the Arctic, it’s hard to imagine that our star could be a threat. Yet, high above us deadly solar particles stream our way at speeds topping a million kilometres an hour and bombard the Earth.

      On a beautiful sunny winter’s day in the Arctic, it’s hard to imagine that our star could be a threat. Yet, high above us deadly solar particles stream our way at speeds topping a million kilometres an hour and bombard the Earth. Down here on the surface we’re protected from that intense solar wind by a natural shield that deflects most of it around us. To see that shield, you need nothing more than a compass. That’s because the Earth’s force field is magnetic, an invisible shell that surrounds the planet in a protective cocoon.

      The magnetic field emanates from deep within our planet’s spinning iron-rich core. It’s this gigantic force field, known as the magnetosphere, that deflects most of the lethal solar wind harmlessly away into space. However, the planet doesn’t escape completely; when the solar wind hits the Earth’s magnetic field, it distorts it. It stretches the field out on the night side of the planet and in some ways it’s like stretching a piece of elastic. More and more energy goes into the field and over time this energy builds up, stretching the tail until it can no longer hold on to it all. Eventually the energy is released, accelerating a stream of electrically charged particles down the magnetic field lines towards the poles. When these particles, energized by the solar wind, hit the Earth’s atmosphere, they create one of the most beautiful sights in nature: the aurora borealis, or Northern Lights.

      LIGHT FANTASTIC – THE AURORA BOREALIS

      The northern Norwegian city of Tromso is known as the gateway to the Arctic. At latitude seventy degrees North, deep inside the Arctic Circle, it has permanent sunlight from mid-May until the end of July, and permanent darkness from late November to mid-January. In late March the Arctic Ocean is a dark frosty blue, the white-crested waves matching the layers of snow and ice packed solid onto the wooden jetties and the well-weathered decks of the fishing boats. It was an utterly magical place to begin filming on 22 March 2009.

      We had gone to see the aurora borealis. Tromso is perfectly positioned on the auroral arc – the thin circle around the North Pole along which the elusive light show usually appears. March and September are the best months to see it, due to the alignment of the Earth’s magnetic field relative to the Sun, and we were told that, given clear skies, we would have a strong chance of glimpsing the Northern Lights.

      The Northern Lights reveal in exquisite beauty our planet’s connection with the rest of the Solar System. The Earth’s environment does not end at the edge of our atmosphere; it stretches at least to the Sun.

      Our guide told me of a Sami legend about the aurora. (The Sami are the people of the North, whose domain stretches from Tromso in the west, across northern Sweden and Finland and into Russia.) The legend has it that the aurorae are the spirits of women who died before they had children. Trapped between the frozen land and heaven, they are condemned to dance forever in the dark Arctic skies. As dusk fell, we rode snowmobiles out into the dense forests by the Fjord to get away from the city lights and settled down in the Sami camp with hot reindeer stew to wait.

      Just after midnight, the aurora came. I walked out into the frigid night air, enjoying the crunch of footsteps in fresh snow, and looked up. They came gently, a vague hint of green, but built quickly; sheets of colour drifted slowly then suddenly broke off and danced impossibly fast, a three-dimensional rain of light rising and falling between land and sky. They were mostly green, with hints of orange and red close to the horizon. They were like nothing I have ever seen, and as I turned to camera I realised that I didn’t care about the physics of what I was seeing. My reaction, composed whilst sitting at my desk in Manchester, was worthless in the face of Nature at its most magnificent. The Sami had it right – an aurora isn’t the light shaken out of atoms of nitrogen and oxygen as they are bombarded by high-energy particles from Earth’s ionosphere accelerated down magnetic field lines towards the poles, it is made of majestic, mournful, dancing spirits, trapped in the Arctic night.

      The Northern Lights reveal in exquisite beauty our planet’s connection with the rest of the Solar System. The Earth’s environment does not end at the edge of our atmosphere; it stretches at least to the Sun. We are bound to our star by the visible light that creates and nurtures life on Earth and the unseen, constant solar wind that only appears to us at night in special circumstances. Each and every planet in the Solar System shares this connection, and the same laws of physics apply. As the solar wind races out into the Solar System, wherever it meets a planet with a magnetosphere aurorae spring up. Jupiter’s magnetic field is the largest and most powerful in the Solar System, and the Hubble space telescope reveals that there are permanent aurorae over the Jovian poles. Jupiter’s moons, Io, Europa and Ganymede also have aurorae, created by Jupiter’s atmospheric wind interacting with the moons’ atmospheres. Saturn too puts on an impressive display, with aurorae at both its poles, but because Saturn’s magnetic field is uneven, the aurorae are smaller and more intense in the north.

      As the solar wind reaches the edge of the heliosphere it begins to run out of steam. Incredibly, there is a probe out there that will discover where these solar winds end.

      VOYAGERS’ GRAND TOUR

      In the autumn of 1977, a pair of identical 722-kilogramme (1,592-pound) spacecraft were launched from Cape Canaveral, Florida. Voyagers 1 and 2 were about to embark on a very special mission: to visit all four of the Solar System’s gas giants – Jupiter, Saturn, Uranus and Neptune. Normally such a journey would take thirty years to complete, but by a stroke of good fortune these spacecraft were designed at a time when the planets were uniquely aligned, allowing the probes to complete their grand tour in less than twelve years. Today, over thirty years after their launch, both spacecraft are alive and well, and remarkably Voyager 1 is still reporting back to Earth – the ultimate and most wonderful example of mission creep in the history of space exploration.

      Voyager 1 is currently the furthest man-made object from Earth. Travelling at seventeen kilometres (eleven miles) per second, this extraordinary spacecraft is just over seventeen billion kilometres (eleven billion miles) from home and delivering knowledge that it was never designed or expected to uncover. Listening to Voyager 1 is the sensitive ear of the Goldstone Mars station in the Mojave desert, California; one of the few telescopes in the world that is capable of communicating over such vast distances. Voyager is so far away that it takes the signal around fifteen hours to arrive, travelling at the speed of light. It may appear as little more than a blip on a screen, but the information Voyager is sending is providing the first data from the frontier of our solar system, from the edge of the heliosphere, and constantly measuring the solar wind as it fades away. Voyager 1 has now reached the point where this wind that emanated so powerfully from the surface of the Sun has literally run out of steam. The heliopause is the boundary at which the solar wind is no longer strong enough to push against the stellar winds of the surrounding stars. Beyond this point Voyager will leave its home and head off into interstellar space. With the batteries expected to struggle on until 2025, this spacecraft will continue to feed us data as it becomes the first man-made object to leave our solar system.

      FROM EARTH TO THE OORT CLOUD

      Our journey