Wonders of the Solar System Text Only. Andrew Cohen

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СКАЧАТЬ 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 through the Sun’s Empire doesn’t end at this distant frontier, seventeen billion kilometres (eleven billion miles) away, where the solar wind meets the interstellar wind. The Sun has a final, invisible force that reaches out much further. Our star is by far the largest wonder in the Solar System. In fact, it alone makes up 99 per cent of the Solar System’s mass. It is this immensity that gives the Sun its furthest reaching influence – gravity.

      This is the full extent of the Sun’s empire; the lightest gravitational touch that retains a cloud of ice that encloses the Sun in a colossal sphere. Beyond this Oort cloud there is nothing. Only sunlight escapes; light that will take four years to reach even the Sun’s closest neighbour, Proxima Centauri – a red dwarf star among the 200 billion others that make up the Milky Way. And it’s by looking here, deep into our local galactic neighbourhood, that we’re learning to read the story of our own star’s ultimate fate.

      INVESTIGATING THE FUTURE OF OUR SUN

      The Sun’s empire is so vast and so ancient, and its power so immense, that it seems an audacious thought to imagine that we could even begin to comprehend its end – the death of our sun. However, that is exactly what astronomers are trying to do, and many of them head to the most arid and barren desert on Earth, the Atacama, in Chile, looking for answers.

      There, high up on an the sides of an extinct volcano at an altitude of 2,635 metres (8,643 feet), sits Paranal Observatory, home to the world’s most powerful array of telescopes. On arrival we were given ‘important information for a safe stay on Paranal’. As the observatory is about two and a half kilometres (one and a half miles) in the air, we were advised that if we experienced any of the following, we should consult a paramedic immediately: headache and dizziness, breathing problems, ringing or blocking of the ears, or seeing stars. It honestly said that if you saw stars at the Paranal Observatory you should consult a paramedic immediately!

      Perched high above the clouds is the reason why so many astronomers venture to this desert. Here, four colossal instruments make up the European Southern Observatory’s ‘Very Large Telescope’, or VLT. If you look up at the sky with these mighty machines you quickly notice that the stars are not just white points of light against the blackness of the sky, but are actually coloured. Through these lenses, orangey-red, yellow and bluey-white stars fill the clear Chilean sky.

      However, this beauty is not just one of the wonders of our night sky, it has also revealed something much deeper. To gaze upon the galaxy full of stars is to observe them at all the stages of their lives – from youthful bright stars to middle-aged yellow stars very similar to the Sun. Contained within the night sky we can see a colour code that allows us to plot the life cycle of every star, including our own.

      If you look up at the sky with these mighty machines you quickly notice that the stars are not just white points of light against the blackness of the sky, but are actually coloured. Through these lenses, orangey-red, yellow and bluey-white stars fill the clear Chilean sky.

      THE HERTZSPRUNG-RUSSELL DIAGRAM

      For the last 100 years astronomers have meticulously charted the nearest ten thousand stars to Earth and arranged each according to its colour and brightness. From this was born the Hertzsprung-Russell diagram; a powerful and elegant tool that allows astronomers to predict the history and evolution of stars, and in particular the future life of our sun. Most of the stars, including our own, are found in the ‘main sequence’ – the band of stars that runs from the top left to the bottom right. The Sun will spend most of its life there, steadily burning its vast reserves of hydrogen fuel, which will last for another five billion years. After which, it will pass through a Red Giant phase.

      THE DEATH OF THE SUN

      Eventually, like all stars, the Sun’s fuel will run out, its core will collapse and our star will begin its final journey. At this stage you may expect it to slowly burn out and splutter its way into oblivion, but there is a final, remarkable twist to our Sun’s ten-billion-year story.

      When the fuel does finally run out, the nuclear fusion reactions in the Sun’s core will grind to a halt and gravity will be master of our star’s fate once more. The Sun will no longer be able to support its own weight and it will begin to collapse. Just as in its formation, this collapse will start to heat the Sun once more, until the layers of plasma outside the core become hot enough for fusion to begin again – but this time on a much bigger scale. Our star’s brightness will increase by a factor of a thousand or more, causing it to swell to many times its current size. The Sun will then drift off the main sequence and into the top right-hand side of the Hertzsprung-Russell diagram, into the area known as the Giant Branch.

      As the outer layers expand, the temperature of the surface will fall and its colour will shift towards red. Mercury will be little more than a memory as it is engulfed by the expanding red sun, which will grow to two hundred times its size today. As it swells the Sun will stretch all the way out to the Earth’s orbit, where our own planet’s prospects are dim.

      So it seems that the wonder that has remained so constant throughout all of its СКАЧАТЬ