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BBC – The Planets (2019) 2of5 The Two Sisters – Earth & Mars

BBC The Planets 2of5 The Two Sisters

Professor Brian Cox tells the extraordinary life story of our solar system. For four and a half billion years each of the planets has been on an incredible journey, filled with astonishing spectacle and great drama. Using the data from our very latest explorations of the solar system combined with groundbreaking CGI this series reveals the unimaginable beauty and grandeur of eight planets whose stories we are only just beginning to understand.

Part 1: A Moment in the Sun: The Terrestrial Planets
Traces the development of the four rocky worlds closest to the Sun: Mercury, Venus, Earth and Mars. Born together, they battled the unbelievable violence of the early solar system to become stable planets. For a while each had a moment of hope when they enjoyed almost earth-like conditions. Yet today Mercury is a scorched barren world. Venus is a runaway greenhouse world with a scorching atmosphere and Mars is a frozen desert. Only on Earth do oceans – and life – persist.

Why has Earth thrived whilst the others have faded away? The most advanced space missions ever mounted allow us to reveal the moments when the fate of each world turned. Mercury was flung across the solar system in a collision of unimaginable ferocity. A young Venus resplendent with oceans was locked in a battle with the sun. And an early wet Mars was robbed of the material it would need to survive.

Only Earth found itself far enough away from the sun for life to hold on. But it can’t last forever. Billions of years from now our world will follow the fate of its sister planets as the sun expands to become a red giant. But as it does other oases may awaken on the faraway moons of the gas giants – like Saturn’s moon Titan. In the far future, it too may enjoy its moment in the sun.


Part 2: The Two Sisters: Earth and Mars
Early in the story of the planets, there was a beautiful water world, an oasis of hope in a sterile universe. But this was not Earth – this was the young Mars. Professor Brian Cox continues his tour of the solar system revealing that it was once home to not one, but two blue planets.

For millions of years, Mars enjoyed oceans blanketed by a thick atmosphere and a temperature climate. Whilst at the same moment Earth was a far less favourable habitat. Our planet was toxic to life today, her atmosphere choked with carbon dioxide and her oceans, acidic.

And both planets were about to face another trial. As they reached the end of their adolescence, a solar system wide cataclysm threatened them both. Called the Late Heavy Bombardment, this event saw asteroids rain down on every inch of the planets for tens of millions of years, resurfacing vast areas of both worlds. But as the dust settled, both sister worlds emerged – ripe with the conditions for life to begin.

But deep inside the molten metal in Mars’ core was rapidly cooling. And in time the planet’s protective magnetic field would fail, causing Mars’ atmosphere to be slowly stripped away by the solar wind. As temperatures plummeted, Mars’ surface froze. Her oceans gone – for a while volcanic activity occasionally melts the ice, creating the largest waterfalls the solar system has ever seen.

Today, Mars is an arid desert world that long ago had the same potential as Earth. Which begs a big question: did life get a start on both worlds? In search of the answer, plans are afoot to take humans to the red planet – so perhaps one day soon we will become the Martians.


Part 3: The Godfather: Jupiter
Professor Brian Cox continues his exploration of the solar system with a visit to a planet that dwarfs all the others: Jupiter. Its enormous size gives it a great power that it has used to manipulate the other planets – a power both for good and bad that it wields to this day.

Jupiter is not only the biggest but also the oldest planet in the solar system. It alone witnessed the birth of the Sun and ever since its immense gravity has shaped the destiny of the other worlds. Soon after its birth, its orbit shifted inwards bringing it ever closer to the sun. As it moved, it created chaos in the the region of space that would become the asteroid belt, ensuring that no planet could form here, only a tiny failed planet Ceres, which remains today.

As it continued into the inner solar system, Jupiter used its power to throw raw material needed to form planets into the Sun, stunting the growth of Mars, a planet that might otherwise have grown as large as Earth. Indeed, Jupiter would have obliterated every last rocky world on its journey into the Sun, if a tussle with another giant – Saturn – had not brought it back from the brink.

Today Jupiter’s great mass continues to be felt. Its gravity torments its moon Io, creating the most volcanically active body in the solar system. And through the vice-like grip it exerts over the asteroid belt, Jupiter’s influence extends as far as Earth – where it retains the power to change the course of life on our planet. And where, as Brian reveals, it might even have created the conditions for humanity to inherit the Earth.


Part 4: Life Beyond the Sun: Saturn
Saturn is the jewel of the solar system, the most seductive of all the planets, but as Professor Brian Cox reveals – it wasn’t born that way.

Raised in the freezing outer reaches of the solar system, Saturn began life as a strange planet of rock and ice. Born outside the snow line, with an abundance of building materials, it soon grew to dwarf the Earth, drawing in colossal amounts of the hydrogen and helium that permeated the early solar system. In time Saturn was transformed into a gas giant, ring-less and similar looking to its great rival, Jupiter. As the gas giant grew, its original rocky form was lost forever, becoming part of the planet’s core, where temperatures are hotter than the surface of the sun, and pressures so intense that carbon there falls as diamond rain.

Saturn’s core isn’t the only part of it to change over time. As Nasa’s Cassini probe has discovered, the planet remained ring-less most of its life – until a fateful encounter changed everything. Less than a hundred million years ago, one of Saturn’s ice moons was drawn too close to the planet. In a truly cataclysmic event the entire moon was destroyed and the rings where born.

But Saturn’s true beauty may have remained hidden forever if it wasn’t for the decision to send Cassini on a risky close encounter with another moon, Enceladus. There we discovered an ocean with similar conditions to places on Earth where life thrives. Way out, far beyond the Sun, hydrothermal vents have been found, the very same habitat that we think life here on Earth may have got its start.


Part 5: Into the Darkness: Ice Worlds
Professor Brian Cox journeys to the remotest part of the solar system, a place that the most mysterious planets call home. These worlds remain shadowy for a simple reason. Beyond Saturn we have only ever visited the most distant planets once.

Uranus – barely visible to the naked eye – was once thought to be the furthest planet from the Sun. But with the telescope and some careful viewing we discovered it had a companion: Neptune. Thanks to a rare alignment of the planets in 1976, Voyager 2 was sent for our only flyby of these ice worlds. There we discovered far more vibrant planets than we ever imagined. Even at such cold temperatures, great storms whip around these frozen worlds that are home to spectacular moons and intricate ring systems. After a few hours of observation at each planet, Voyager 2 left them behind. We have never returned.

For decades that was as far as we got, until 2015 when Nasa’s New Horizons probe pushed the frontier even further into space with its extraordinary passage to the dwarf planet Pluto. Once again all our assumptions about this distant world were wrong. Pluto is alive with ice volcanoes, dunes, and geysers – even a subsurface ocean. What’s more, we discovered that Pluto isn’t alone out there – there is a plethora of weird icy companions, which are redefining everything we thought we knew about the strange, distant reaches of our solar system.

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