Dead or Alive Wonders of the Solar System


Dead or Alive

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We live on a world of wonders,

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a place of astonishing beauty and complexity.

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We have vast oceans, incredible weather,

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giant mountains and spectacular landscapes.

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If you think that this

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is all there is, that our planet exists in magnificent isolation,

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then you're wrong.

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We're part of a much wider ecosystem that extends way beyond

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the top of our atmosphere.

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I think we're living through the greatest age of discovery our civilisation has known.

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We've voyaged to the farthest reaches of the solar system.

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We've photographed strange new worlds,

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stood in unfamiliar landscapes, tasted alien air.

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Now, the laws of physics are simple and they're universal.

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What applies here applies everywhere else up there.

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But it's fascinating that they can manifest themselves

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in so many different ways across the solar system.

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In this programme, I'm going to look at how the universal forces of nature

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that created all this can also wreak devastation across the solar system.

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How they can be the death of a planet...

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..and how they can keep other worlds alive.

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I can just see pieces of molten rock rising up just below my chin.

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These forces are so far reaching, they bridge the depths of space

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and transform a world long thought dead

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into a world of perpetual change and everlasting youth.

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The intense source of heat that powers that eternal change also

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drives one of the most spectacular sights in the solar system.

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I've come to one of Earth's natural wonders,

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the Grand Canyon in Arizona.

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It's a place to be humbled by nature.

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Well, this is undoubtedly

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one of the most beautiful places I've seen on Earth.

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From sunrise to sunset,

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the changing light brings this immense landscape to life.

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I hear stories of people coming here at sunrise with tears in their eyes

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at the majesty of the view, and I can see why.

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It's incredible to think that this enormous valley

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was etched and carved

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by the action of running water over just a few million years.

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Our knowledge of natural wonders like the Grand Canyon

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was once limited to our own planet.

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But the space age has brought new worlds into view.

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This is Mars, the Red Planet.

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Fourth rock out from the sun, it has a canyon so vast

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you could fit our own Grand Canyon into one of its side channels.

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Named after the space probe that first saw it,

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this is the Valles Marineris.

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8km deep and over 3,000km long,

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on Earth it would run all the way from Los Angeles to New York.

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We're beginning to get a deep and quite profound understanding

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of the way that Mars has evolved geologically because

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we are now there, because we now have eyes and ears on the surface.

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And there really is no substitute for actual exploration, for actually

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going somewhere and touching it and taking pictures of it.

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Look at this picture.

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This is a picture of a sunset.

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These are pictures of clouds.

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It's amazing to think these incredibly familiar-looking photographs

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were taken on the surface of Mars.

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This picture,

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or this amazing colour picture...

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I could have got a camera here and just snapped any picture

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and it would have looked exactly like this one.

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In the Grand Canyon, you can see the Colorado River

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running in the bottom of the valley

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so you can understand how this landscape was made.

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Whereas here on Mars, there's no sign of any water.

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So Mars is a puzzling place.

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Despite all the similarities between Mars and Earth,

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it's the differences between these two planets that are most telling.

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Mars is now a desolate dead wasteland,

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a world where the processes that sculpted its familiar landscapes

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seized up long ago.

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It's fascinating for me as a physicist to see how

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the same basic simple laws of nature can play out

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in such radically different ways, and produce such astonishingly

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varied and beautiful and violent and dead worlds

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out there, across the solar system.

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The Big Island of Hawaii, in the middle of the Pacific Ocean,

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holds the key to what happened to Mars.

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This is the perfect place to witness how a planet can be kept alive

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by nothing more than the simple flow of heat.

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You can smell the volcanic ash coming into the...

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into the helicopter. And everywhere you look, it looks like a...

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It's almost like an apocalyptic scene.

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This volcano is Kilauea, which means spewing.

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It's been erupting almost continuously since 1983.

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In fact, you can see molten rock flowing down the side

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of the mountain just cutting a swathe through the trees.

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This might look like widespread destruction,

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but volcanic eruptions are Earth's geological heartbeat.

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Active volcanoes make our planet a vibrant, living world.

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That is the most spectacular demonstration

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of our planet being geologically alive that I've ever seen.

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A few kilometres north of Kilauea,

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you can see just what volcanic action can produce,

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given enough time.

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The islands of Hawaii were built entirely by volcanoes.

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Today, these mountains are the largest volcanoes on our planet,

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and we've seen landscapes just like this, on Mars.

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It's quite an experience being 4km high.

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It makes you out of breath and you sniff a lot because your nose becomes...

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And makes you feel like you've had a few drinks.

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This is Mauna Kea,

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one of the five volcanoes that make up the Big Island of Hawaii.

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I've known about it since I was very little

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because it's one of the most famous observatories on the planet.

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Everywhere you look, surrounded by our eyes to the cosmos.

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Although this mountain is 4km above the surface of the Pacific,

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it's actually 10km above the surface of the Pacific floor.

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That makes it the highest mountain on Earth,

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over a kilometre higher than Mount Everest.

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But it is a tiny volcano compared to the biggest volcano on the surface of Mars.

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This is Olympus Mons,

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named after Mount Olympus, the mythical home of the Greek gods.

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This vast outpouring of lava stretches over 550km across,

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but it's the height of this volcano that is breathtaking.

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It soars 25km into the Martian sky,

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nearly three times the full height of Mauna Kea.

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But Olympus Mons isn't just the tallest volcano in the solar system,

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it's the highest mountain we know.

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There are striking similarities between the volcanic landscapes

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here on Hawaii and the giant volcanoes found on Mars.

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These similarities can be traced back billions of years

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to the fiery birth of the solar system.

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All this heat you can see driving this spectacular volcanic activity

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is a relic, a hangover of the Earth's formation.

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Now, all the rocky planets - Earth, Mars, Venus, Mercury - were formed in the same way.

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They came from a collapsing dust cloud over 4.5 billion years ago.

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With the ignition of the sun, our solar system was born.

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Little by little, the rocky bodies grew,

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falling together under their own gravity.

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This process not only generated immense amounts of heat,

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it also delivered radioactive material to the cores.

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These two ancient sources of heat power Earth's volcanoes to this day,

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but the volcanoes on Mars are little more than a petrified memory of a distant past.

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When we look down on the surface of Mars,

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we see no evidence of this kind of volcanic activity.

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As far as we can tell, Mars is a dead world.

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Mars must have had similar inner heat to Earth to build its volcanoes.

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Yet something obviously happened

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to stop the Red Planet's geological heartbeat.

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Now, as everyone who's left a hot cup of tea sat on the kitchen table knows,

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hot things lose heat to their cooler surroundings,

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and what's true for cups of tea, in physics is also true for planets.

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This is hot and that up there - space - is cold.

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So planets lose heat to space.

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Mars is a much smaller planet than the Earth.

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It's about half the diameter, it's an eighth of the volume,

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so there was much less heat trapped in there to begin with.

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Now, planets lose heat to space through their surfaces,

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and smaller things have a larger surface area

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in relation to their volume than big things.

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So that means that Mars will lose its heat to space much quicker than the Earth does.

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When the interior of Mars grew cold,

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the mighty volcanoes lost their lifeblood.

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The Red Planet's geological heart died,

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and millions of years ago, the surface of Mars ground to a halt.

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The fate of a whole planet was destined

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by the simplest of laws of physics.

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Since the dawn of human history, we've been able to gaze up into the night sky,

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but we're lucky because we're the first generation that's been able

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to build machines to actually go to those planets and moons.

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And we've found that they're more beautiful, more violent,

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more magnificent and fascinating

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than we could have possibly imagined.

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The more worlds we study, the more we realise

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that our solar system is a cosmic laboratory.

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Even the slightest differences in size or position

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can create a world radically different from its neighbours.

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So here on Earth, we have one beautiful manifestation of how those

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simple laws of nature can play out, how they can build a planet.

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In Mars we have another example.

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What happens when you take a planet that's smaller than Earth

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and move it further away from the sun?

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It loses its heat more quickly and it becomes geologically inactive.

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But what would happen if you took a planet just like the Earth

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and moved it a little closer to the sun?

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Well, we know of such a planet.

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It's the brightest point of light in our night sky.

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So similar in size to our own world,

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this planet has been called Earth's twin.

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This is Venus.

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Orbiting closer to the sun, Venus was named for its shining beauty.

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But our planetary twin hides its true identity

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beneath a thick blanket of cloud.

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Over the last 4.5 billion years,

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Venus has turned into an unimaginably oppressive world.

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The atmosphere is so dense that the pressure is crushing.

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It's 90 times atmospheric pressure here on Earth.

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Now, Venus takes 243 days to rotate once on its axis.

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That means its day is longer than its year.

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So Venus has the hottest average surface temperature,

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other than the sun's, anywhere in the solar system - 470 Celsius.

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I've come to India, to a place called the Deccan Traps.

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Hidden in this lush green landscape are tantalising clues

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to understanding how immense heat caused Venus to choke to death.

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When you look at this landscape today,

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it's incredibly peaceful and beautiful, rolling green hills,

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but I think it's astonishing to think

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that everything you see down there is lava.

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This whole landscape, half a million square kilometres of it, was created

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in an ongoing volcanic eruption that lasted for a million years.

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If you take away the green foliage, the underlying landscape of lava

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is actually very similar to what we see on Venus.

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Using radar to peer down through the clouds,

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the surface of Venus was finally revealed.

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It's covered with floods of solid lava, just like we see in India,

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but on a scale many thousands of times larger.

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We've also counted over 50,000 volcanoes,

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the most on any planet in the solar system.

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Venus is a similar size to Earth,

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so it may still have a hot geological heart

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powering its volcanoes but as yet we haven't witnessed any eruptions.

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The ancient floods of lava we see on Venus

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and here in India were created in much the same way.

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For both planets, this was volcanic activity in overdrive.

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The eruptions here in India 65 million years ago

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affected the Earth's climate so much that they're thought to have played

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a major role in the mass extinction events at the end of the cretaceous period,

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which wiped out over two-thirds of the species on Earth.

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Now, life on Earth recovered but Venus wasn't so lucky.

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The intense volcanic activity on both planets

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didn't just blast out molten rock.

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It also released copious amounts of gases, like carbon dioxide.

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But slight differences in the way the laws of physics played out

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on Venus helped push our cosmic twin down a path of no return.

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Venus and Earth reacted very differently to the same kind of volcanic cataclysm,

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and the reason for that is something that happens so often on Earth

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that we take it for granted, and just moan about it.

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Rain plays a significant role in keeping our planet a pleasant place to live.

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Acting as part of a global recycling system,

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rain keeps our atmosphere in balance,

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washing out the potent greenhouse gas, carbon dioxide,

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ready to be locked away in rocks in our oceans.

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But on Venus, the laws of physics have made it impossible

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for rainfall to cleanse its atmosphere.

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In fact, there's no liquid water at all.

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Venus lost its water essentially because it's hotter than the Earth.

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You see, temperature is just a measure of how fast things are moving around.

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So on Venus the oceans would have evaporated into the atmosphere

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and that water in the atmosphere would be moving around

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extremely quickly, simply because it's hot.

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And Venus is so close to the sun and so hot,

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those water molecules are moving so fast that the gravity of the planet

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can't continue to hold them in the atmosphere,

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and so they simply escape off into space.

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With no water, there is no rain on Venus.

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For billions of years, there has been nothing

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to temper the build-up of volcanic gases in its atmosphere.

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Venus ended up cocooned in a thick, high-pressure,

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dense blanket of carbon dioxide,

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and that made the temperature rise and rise and rise,

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turning Venus into the hell-like world we see today.

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Compared to scorched Venus and frozen Mars,

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our home is a very special ball of rock.

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Although governed by the same universal set of rules,

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our planet is not too big, not too small,

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not too hot, not too cold.

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Earth has been called the Goldilocks planet

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because everything is just right.

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Our world is unique but it doesn't exist in splendid isolation.

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It is intimately connected with its cosmic neighbours.

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Earth is not the master of its own destiny and it never has been.

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The life and death of our planet is influenced by forces

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emanating from the very depths of space.

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As we better understand our place in space,

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we've come to realise that our sharing of the same physical laws

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with the other worlds in the solar system

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isn't the only connection we have with them,

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because those same laws lead to a direct physical connection

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between the Earth and the other worlds out there

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that is subtle, is complicated, but can sometimes be extremely powerful.

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Out in the farthest reaches of the solar system are vast worlds

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that have a direct impact on our very existence.

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This is our sun from ten billion kilometres away -

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just another star in a sea of stars.

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But as you head towards the light, you enter a realm of giants.

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The furthest planet from the sun is icy Neptune,

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with its thick, blue methane atmosphere.

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Uranus comes next, the only planet that lies on its back.

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Further in towards the sun, and the planets get even bigger.

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Saturn, with its beautiful rings of ice.

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Finally we reach the king of the giants - Jupiter.

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Jupiter is the largest planet in the solar system,

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so big you could fit Earth inside it over 1,000 times.

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It's made up of the same stuff as our sun - hydrogen and helium -

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the most common elements in the universe.

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In its thick churning atmosphere,

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gigantic storms have raged for centuries.

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Now, astrologers have said for years that Jupiter influences our lives,

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but we now have scientific evidence that this mighty planet does have

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a significant connection with our own small world.

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Jupiter is so different to our planet -

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you know, a big ball of gas, half a billion kilometres away -

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it's difficult to see how it could have anything to do with us at all.

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But despite the fact that astrology is a load of rubbish,

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Jupiter can, in fact, have a profound influence on our planet

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and it's through a force that, well, surrounds us and penetrates us

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and binds the galaxy together - gravity.

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Gravity is one of the fundamental forces of nature.

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It exists between all objects, and the effects

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of a gravitational field extend way beyond the planet that creates it.

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Gravity is by far the weakest force of nature. But it's the only force

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that has an influence across the entire solar system,

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and that's because, although it's weak, it has an infinite range.

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It never quite goes away.

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So, no matter how far you go, you feel the force of gravity

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as a planet, although it drops and drops and drops away.

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Jupiter has the most powerful gravitational field of all the planets,

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and it's the gas giant's gravity that can directly influence

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the orbits of asteroids and other wandering space debris.

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Jupiter is so massive, by far the most massive planet in the solar system,

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that its gravitational field can have a profound influence on passing interplanetary stuff.

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It can do three things.

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Firstly, it can capture the stuff, literally hoover it up.

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Secondly, it can deflect the stuff,

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such that it throws it out of the solar system.

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But thirdly, and most importantly for us,

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it can deflect stuff onto a direct collision course with our planet.

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Influenced by Jupiter's gravity,

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today, right now, we're highly vulnerable from asteroid impacts.

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But we do have sentinels standing guard.

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On top of the mountain of Heleakala on the Hawaiian honeymoon island of Maui,

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I've come to see Professor Nick Kaiser, who's searching

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our solar system for potentially hostile space debris.

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The prime task is to try and find killer asteroids,

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things that are out there in the solar system

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that might hit the Earth.

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There's an air of Hollywood about it, isn't there, in some sense?

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Well, that's right. I would say a lot more resources have been spent

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on making movies about killer asteroids than actually finding them.

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Anything that's a kilometre in size, if it hit the Earth it would be devastating.

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It would probably kill nearly everyone on the planet.

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Each night, using a revolutionary billion-pixel digital sensor,

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the team scans a vast swathe of the sky.

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Mind your head!

0:29:020:29:04

They're looking for any unidentified objects that might be heading our way.

0:29:040:29:10

So any one of these points of light could in fact be an asteroid?

0:29:100:29:13

That's right. And it's very likely,

0:29:130:29:15

in fact, it's almost certain that there are asteroids in that image.

0:29:150:29:20

The problem is, how do you figure out which ones they are?

0:29:200:29:23

Yeah.

0:29:230:29:24

The camera captures several images of the same patch of sky taken minutes apart.

0:29:260:29:32

The team can then see if anything has moved,

0:29:320:29:35

relative to the background of stars.

0:29:350:29:37

What we've done here is taken two images and subtracted them,

0:29:370:29:41

and you see the stars have nearly all gone away.

0:29:410:29:44

There's a couple of interesting things left.

0:29:440:29:47

If you look over here, you see a dark thing and a white thing,

0:29:470:29:51

so that's something which was THERE in the first image

0:29:510:29:55

and THERE in the second image. And there's another one here.

0:29:550:29:59

So even on this tiny patch of sky, we've already detected two objects.

0:29:590:30:03

What that means is, when we do that kind of analysis

0:30:030:30:06

on a whole field of view, we'll detect hundreds of objects.

0:30:060:30:10

The beauty of our night sky belies the potential danger it holds in store.

0:30:140:30:20

Over 2,000 objects have been identified that pass close to the Earth,

0:30:200:30:26

with something like 400 that could be on a future collision course.

0:30:260:30:31

And all of these menacing lumps of rock, at some point,

0:30:330:30:37

come under Jupiter's gravitational influence.

0:30:370:30:41

Now, if you ever needed a demonstration of how congested the space is near the Earth,

0:30:410:30:48

just look at this movie of the near-Earth objects,

0:30:480:30:53

so here's Mercury, Venus, the Earth, Mars and out here is Jupiter.

0:30:530:30:58

Here's the asteroid belt, but look at the congestion in there.

0:30:580:31:02

Every one of those points of light is an asteroid that we know of.

0:31:020:31:08

Just look at the Earth swimming through them, so when you look up into the nice clear night sky and

0:31:080:31:13

you want to be reassured that we're all nice and safe,

0:31:130:31:16

just remember this movie.

0:31:160:31:18

Our planet is on a deadly journey.

0:31:220:31:26

Earth is trapped in a cosmic game of dodgeball as it orbits the sun,

0:31:260:31:31

a game where the gravitational stranglehold of Jupiter regularly throws asteroids our way.

0:31:310:31:39

Jupiter's gravitational influence on passing space debris

0:31:520:31:56

has made our planet a world under constant bombardment.

0:31:560:32:00

One of the most famous meteorite impact sites is the Barringer crater in Arizona.

0:32:020:32:07

50,000 years ago,

0:32:080:32:12

a 300,000 ton, 50 metre in diameter lump of iron and nickel entered the Earth's atmosphere

0:32:120:32:19

and made this crater, and it should remind us

0:32:190:32:23

that our environment doesn't just stop at the top of our atmosphere.

0:32:230:32:27

Our environment stretches out into the solar system,

0:32:270:32:31

to the very edges of the solar system, to wherever this rock came from.

0:32:310:32:34

In the grand scheme of things,

0:32:380:32:40

the asteroid that struck here was relatively small and innocuous.

0:32:400:32:46

But there are much larger impact craters hidden in Earth's landscapes

0:32:570:33:01

that have far more devastating tales to tell.

0:33:010:33:05

200 years ago, white settlers crossed the ancient Appalachian mountains here in America

0:33:100:33:17

to seek new land out west.

0:33:170:33:20

Little did they know what they were walking into.

0:33:200:33:23

Well, this place to me feels like the very definition of small town America.

0:33:250:33:30

It's on the border between Virginia, Kentucky and Tennessee.

0:33:300:33:34

It's the kind of town where you feel that

0:33:340:33:37

nothing much has changed for the last 100 years.

0:33:370:33:40

But this place was the site,

0:33:420:33:45

way back in history, of a violent cosmic intervention.

0:33:450:33:49

This is Middlesboro, Kentucky.

0:33:530:33:56

It's a town built inside a meteorite impact crater.

0:33:560:34:01

The asteroid that struck here would have been huge, about half a kilometre across,

0:34:060:34:12

hitting the Earth well over 200 million years ago.

0:34:120:34:16

I find it fascinating that when you look out of this view, you don't really see an obvious crater.

0:34:190:34:25

And indeed, it wasn't until the 1960s that anybody had any idea that there was

0:34:250:34:30

a colossal impact from space

0:34:300:34:33

just over there, centred right on the 18th hole of the golf course.

0:34:330:34:38

We now know where the giant asteroid that struck here could have come from.

0:34:430:34:48

Located between Jupiter and Mars is a vast reservoir of rocky debris that forms the asteroid belt,

0:34:560:35:04

and it's this ancient rubble that Jupiter, our neighbourhood giant, can nudge towards the Earth.

0:35:040:35:10

Well, here's my model of the solar system.

0:35:170:35:20

There's the sun in the middle,

0:35:200:35:23

then the Earth, Mars, Jupiter,

0:35:230:35:29

and the asteroids sort of scattered in between the big region

0:35:290:35:33

between Mars and Jupiter.

0:35:330:35:35

In fact they extend over 150 million miles,

0:35:350:35:38

which is further than the distance from the Earth to the sun.

0:35:380:35:43

This is my coffee, by the way, which doesn't represent anything.

0:35:440:35:48

I'll put it over there. But now and again,

0:35:500:35:53

because of collisions in the asteroid belt, a stray asteroid

0:35:530:35:56

will get thrown into the position where they keep rhythmically meeting Jupiter over and over again.

0:35:560:36:02

And because Jupiter is such a massive planet,

0:36:020:36:04

that means that it gets a kick, it gets a gravitational kick.

0:36:040:36:08

And that changes the orbit of these asteroids and over time, their orbit

0:36:080:36:12

can become, well, elongated or elliptical rather than circular.

0:36:120:36:17

That means that they can get thrown

0:36:170:36:19

into the inner solar system and cross the orbits

0:36:190:36:23

of the inner planets, including the orbit of the Earth.

0:36:230:36:27

And you get a potentially catastrophic collision.

0:36:270:36:30

Jupiter was once thought to be our protector,

0:36:370:36:41

its enormous gravity swallowing up dangerous asteroids.

0:36:410:36:47

Yet we now realise its gravitational influence can propel some of those asteroids in our direction.

0:36:470:36:53

But surprisingly, catastrophic impacts with space debris might not be a bad thing,

0:36:550:37:01

at least, in Earth's past.

0:37:010:37:04

Impacts from space shaped our planet.

0:37:070:37:10

They made our world what it is today.

0:37:100:37:12

Take life on Earth, for example.

0:37:120:37:15

Now, it's possible, or probable even,

0:37:150:37:18

that impacts on a colossal scale changed the climate so much

0:37:180:37:23

that huge swathes of life on Earth were wiped out,

0:37:230:37:26

creating ecological niches into which other species could evolve -

0:37:260:37:32

us, for example.

0:37:320:37:33

It's incredible to think that a planet

0:37:360:37:39

half a billion kilometres away could dictate the fate of our world.

0:37:390:37:45

Jupiter's immense gravity bridges the depths of space

0:37:450:37:50

and even though its power could one day devastate Earth,

0:37:500:37:54

that same gravitational field breathes life into other corners of the solar system.

0:37:540:38:02

For better or worse,

0:38:020:38:03

Jupiter's powerful gravitational field has had a direct influence on our planet.

0:38:030:38:09

We're part of a much wider ecosystem that extends to the very edges of the solar system,

0:38:090:38:15

and that ecosystem is bound together by the force of gravity,

0:38:150:38:20

and it's gravity that has power to bring worlds to life.

0:38:200:38:25

Our understanding of the solar system began much closer to home.

0:38:340:38:39

Gazing down at us, it was our moon, with its regularly changing face,

0:38:410:38:46

that first fired our interest in worlds beyond our own.

0:38:460:38:51

When we could look further out, we discovered the solar system was full

0:38:530:38:58

of moons, each invisibly connected to their parent planets by gravity.

0:38:580:39:04

Our moon is a cold, geologically dead world, but the powerful gravitational bond

0:39:090:39:15

that exists between another moon and its parent planet has done something astonishing.

0:39:150:39:23

It has brought this moon to life,

0:39:230:39:25

making it the most violent place in the solar system.

0:39:250:39:30

400 years ago, it was Galileo who first looked up at the night sky through a telescope.

0:39:310:39:38

Turning his attention to Jupiter, he noticed that this giant planet was not alone.

0:39:380:39:45

Oh, yeah!

0:39:480:39:50

Absolutely magnificent.

0:39:500:39:52

You see a disc surrounded by...

0:39:530:39:56

Well, I can see three points of light.

0:39:560:39:58

Galileo, over several nights, saw four points of light.

0:39:580:40:01

And he correctly surmised that those are actually moons, other worlds in orbit around Jupiter.

0:40:010:40:07

Jupiter's four largest moons are named after the four lovers of the Greek god Zeus.

0:40:130:40:19

Furthest out is Callisto.

0:40:210:40:24

Then there's huge Ganymede, the largest moon in the solar system.

0:40:240:40:29

Next is icy Europa,

0:40:310:40:34

and finally, the small, yellow-tinged moon nearest to Jupiter, Io.

0:40:340:40:40

So the legend goes, Zeus tried to protect his lover, Io, by turning her into a cow

0:40:430:40:48

to hide her from the jealous gaze of his wife, Hera.

0:40:480:40:52

But it didn't work, and Hera sent a gadfly to torment Io.

0:40:520:40:58

And it was prescient in a way to name that satellite Io, the tormented moon.

0:40:580:41:05

Because we've since learned that it is indeed an incredibly tormented world.

0:41:050:41:10

For 400 years, we expected Io to be as dead as our own moon.

0:41:140:41:19

But in the late 1970s, when the first spacecraft passed by Jupiter,

0:41:200:41:26

we finally saw Io up close.

0:41:260:41:29

But it didn't make any sense, as here was a moon with no meteorite impact craters.

0:41:320:41:39

Now, it's impossible to believe that Io could have escaped

0:41:420:41:46

the bombardment that we see on our moon and practically every

0:41:460:41:50

other body in the solar system, so the only explanation is that that surface is young.

0:41:500:41:55

It must have been recently produced, and that in turn means that Io,

0:41:550:42:01

that tiny moon of Jupiter out there, must be a geologically active world.

0:42:010:42:08

The truth about Io would blow us away.

0:42:100:42:14

We may not have stood on Io, but there are places we can go here on Earth to help unlock its secrets.

0:42:230:42:30

This is Ethiopia in East Africa.

0:42:330:42:35

We're being flown out by military helicopter to the very hot,

0:42:350:42:41

very inhospitable, Afar region in the north-east of the country.

0:42:410:42:46

And this is what I've come to see.

0:42:510:42:54

It's one of the rarest geological phenomena on our planet,

0:43:030:43:08

a volcano with a lake of molten lava.

0:43:080:43:11

As the sun goes down, the lava lake comes to life.

0:43:140:43:19

This volcano is called Erta Ale by the local Afar people.

0:43:250:43:30

It means "smoking mountain".

0:43:300:43:32

For many, this place is a vision of hell.

0:43:360:43:40

Yet it holds the key to understanding Io, a world over half a billion kilometres away.

0:43:460:43:53

This hot, tortured landscape of lava will be our home for the next three days.

0:43:550:44:01

Temperatures here reach 50 Celsius in the shade and we're camping right on top of the volcano.

0:44:010:44:08

But we're in good hands, as Io specialist Dr Ashley Davies is part of the team.

0:44:120:44:17

It is absolutely spectacular, isn't it?

0:44:210:44:24

-Extraordinarily beautiful.

-You feel like you're looking into the core of the planet.

0:44:240:44:29

It's a window into the interior of the Earth, so magma is rising up

0:44:290:44:34

from some kilometres down, circulating through the surface and then sinking back down again.

0:44:340:44:39

It is very difficult to breathe, it's very acidic and very bitter.

0:44:390:44:43

The magma has gases in it,

0:44:430:44:47

and as it comes up to the surface, just like when you pour

0:44:470:44:50

out a bottle of Coca-Cola, the gases come out.

0:44:500:44:54

So what we have here is sulphur dioxide, hydrogen sulphide,

0:44:540:44:58

water vapour, carbon dioxide, coming out of the magma

0:44:580:45:03

before the magma then cools and sinks down, and that's what we're breathing now, it's incredibly unpleasant.

0:45:030:45:08

This volcanic phenomenon is a product of immense amounts

0:45:130:45:16

of primordial heat escaping from inside our planet.

0:45:160:45:21

Yet we have seen something similar in the far reaches of the solar system.

0:45:230:45:28

Io is the same size as our moon and should be a cold, dead world.

0:45:320:45:37

Yet our first glimpses of Io revealed it as seething with heat, alive with volcanic activity.

0:45:420:45:49

Just one of the many lava lakes on Io releases more heat than all Earth's volcanoes put together.

0:45:510:45:58

If we were to stand on the surface of Io now,

0:46:050:46:07

what would be the similarities and what would be the differences?

0:46:070:46:11

The lake would probably appear very, very similar to this, except for the scale.

0:46:110:46:15

The lava lakes on Io are vastly larger.

0:46:150:46:18

The biggest one, we think, is 180km in diameter.

0:46:180:46:22

180km? So that would stretch way... obviously way beyond the horizon on Earth!

0:46:220:46:26

Yeah, it's almost beyond description,

0:46:260:46:29

to see something that size and it's just this huge pool of molten lava.

0:46:290:46:34

Io is the most volcanic place in the solar system,

0:46:390:46:43

endlessly pumping out heat into the cold vacuum of space.

0:46:430:46:49

But what's really interesting is that it's so small that it shouldn't be volcanic at all.

0:46:550:47:01

It was one of the greatest surprises of planetary science

0:47:080:47:11

when these massive volcanoes were discovered on Io.

0:47:110:47:14

Mighty planets like Mars - has big volcanoes.

0:47:140:47:17

They're not erupting anymore, they haven't erupted for a long time.

0:47:170:47:21

Venus, lots of volcanoes there, but they haven't been erupting in a long time, probably.

0:47:210:47:26

And here we have Io, which is just insanely volcanic.

0:47:260:47:29

It's just pumping out vast amounts of energy in a zone, in a part of

0:47:290:47:32

the solar system where it was thought that everything was dead.

0:47:320:47:36

Everything we now know about Io comes from looking at it from a distance,

0:47:430:47:48

but measuring the heat pumping out of this lava lake

0:47:480:47:51

will give us a better idea of the true scale of the heat loss on Io.

0:47:510:47:56

Far from being a benign, bubbling cauldron,

0:47:590:48:01

this volcano has the power to kick off at a moment's notice.

0:48:010:48:07

I can just see pieces of molten rock rising up just below my chin,

0:48:110:48:17

and with it a cloud of heat, absolutely overpowering heat.

0:48:170:48:21

There must be a hell... a hell of an eruption going on.

0:48:210:48:26

Seeing active volcanism like this on such a small moon like Io

0:48:310:48:35

changed our view of the workings of the solar system.

0:48:350:48:38

A world like Io, having such a powerful internal heat source, cries out for an explanation.

0:48:400:48:47

You see, Io is far too small a world to have retained any internal heat

0:48:470:48:54

to have the same heat source that powers the Earth's volcanoes.

0:48:540:49:00

So something else must be driving that powerful volcanism on Io.

0:49:000:49:06

New images sent back from recent space probes confirm that Io is a surprising and bizarre world.

0:49:100:49:17

Being so far from the sun, Io's surface is mostly very cold.

0:49:230:49:27

It is covered in frozen sulphur, which gives it its yellow colour.

0:49:290:49:32

Yet Io is pockmarked by cauldrons of molten lava.

0:49:350:49:40

You know, I think it is remarkable, and fortunate in a sense,

0:49:420:49:47

that you can come to a place like this on our planet and just

0:49:470:49:52

get the tiniest sense of what it must be like

0:49:520:49:56

to stand on the edge of one of those magnificent lava lakes on Io.

0:49:560:50:01

When we first saw hot volcanic action on Io,

0:50:040:50:07

it was quite a surprise for most planetary scientists.

0:50:070:50:11

But by considering simple laws of physics, it didn't surprise everyone.

0:50:110:50:16

Just weeks before Voyager arrived at Jupiter, three scientists made a prediction,

0:50:160:50:22

and it was one of those predictions that, when you see it, is almost obvious.

0:50:220:50:29

It was using physics that had been known for hundreds of years, but nobody had thought of it.

0:50:290:50:33

They predicted that Io should have an intense internal heat source because of its unique position

0:50:330:50:40

in the solar system, very close to a giant planet and surrounded by other large moons.

0:50:400:50:47

Io sits about the same distance from Jupiter as our own moon does from Earth,

0:50:520:50:58

but don't forget that orbiting outside Io are its sister moons, Europa and Ganymede.

0:50:580:51:04

Io is under the influence not just of the massive gravitational pull

0:51:060:51:10

of Jupiter, but also the additional pull of its neighbouring moons.

0:51:100:51:15

It's this gravitational tug of war that conspires to breathe life into Io.

0:51:150:51:22

Now, Io has a very interesting relationship with Europa and Ganymede,

0:51:240:51:29

because for every four orbits that Io makes around the planet,

0:51:290:51:34

Europa goes around almost exactly twice

0:51:340:51:39

and Ganymede goes around just once.

0:51:390:51:43

Periodically, they line up together, bang, bang, bang, and Io gets

0:51:430:51:48

a powerful gravitational kick on a very regular basis.

0:51:480:51:54

And that has the effect of moving Io out of the nice circular orbit

0:51:540:52:00

into an elliptical or an eccentric orbit.

0:52:000:52:03

Io comes close to Jupiter and then far away from Jupiter, and then close to Jupiter again.

0:52:030:52:09

And because Jupiter's gravity is so big, that has the effect of stretching and squashing Io.

0:52:090:52:15

Now, imagine it was a squash ball. If you stretch and squash and stretch and squash,

0:52:150:52:20

then it gets hot by friction, and the same thing happens to this moon.

0:52:200:52:23

The power of the gravitational interaction between Jupiter and Io is extraordinary.

0:52:230:52:30

It contorts the shape of this tiny moon, moving rock as if it were nothing more than water.

0:52:300:52:37

Now, this crater is about, what, 30 metres from the base

0:52:390:52:44

that you can see down there up to the edge of the rim.

0:52:440:52:48

Now, Io, when it orbits around Jupiter every 1.8 days,

0:52:480:52:53

flexes by something like 100 metres.

0:52:530:52:56

That's three times the height of that crater.

0:52:560:53:00

Remember, Io's surface is pretty much like this,

0:53:000:53:04

solid rock, so imagine how much energy that takes,

0:53:040:53:09

and all that energy comes from Jupiter's gravitational field,

0:53:090:53:13

and that is the energy that powers the volcanoes.

0:53:130:53:16

Io is a world beyond our imagination.

0:53:270:53:30

Its unique gravitational connections

0:53:300:53:34

provide a seemingly inexhaustible supply of heat.

0:53:340:53:38

As well as its huge lava lakes, the heat also powers

0:53:380:53:42

the largest volcanic eruptions in the solar system.

0:53:420:53:46

Molten rock and gas blasts out from the frigid surface.

0:53:540:53:59

The gas expands, shattering lava into a giant fountain of fine particles.

0:53:590:54:06

With weak gravity and a sparse atmosphere,

0:54:120:54:16

Io's volcanic plumes can reach 500 km above the moon's surface.

0:54:160:54:21

This incredible phenomenon, volcanism, comes from the simplest of laws of physics,

0:54:410:54:49

the law that says that heat contained in a planet

0:54:490:54:53

must eventually find a way to escape into the coldness of space.

0:54:530:54:58

But what a spectacular way for the laws of physics to play out.

0:54:580:55:03

In the most unexpected of places,

0:55:050:55:08

in the coldest reaches of the solar system,

0:55:080:55:11

the laws of physics created a fiery world of wonder,

0:55:110:55:16

and Io is not alone.

0:55:160:55:18

Many of the hundreds of moons in the solar system

0:55:180:55:22

are not dead, barren and uninteresting worlds,

0:55:220:55:27

but active, often violent and always beautiful worlds of wonder.

0:55:270:55:34

Io is fascinating.

0:55:380:55:41

It doesn't derive its energy from an internal heart source in the same way that the Earth does.

0:55:410:55:46

It extracts energy from its orbit around its giant parent planet,

0:55:460:55:51

Jupiter, and for all those reasons, Io is a wonder of the solar system.

0:55:510:55:57

Our exploration of the planets and moons orbiting our star

0:56:220:56:26

has given us valuable insights into the nature of our own world.

0:56:260:56:30

Our view of the Earth's place in space has been turned on its head.

0:56:330:56:39

Out there are many truly violent and hostile worlds,

0:56:390:56:46

but they're driven by the same laws that shape and control our own world.

0:56:460:56:53

And so, I suppose,

0:56:530:56:55

it's in many ways a miracle that we exist at all.

0:56:550:57:00

Our solar system is like a cosmic laboratory.

0:57:020:57:07

Until we went there, we had no idea of what the laws of nature could produce.

0:57:070:57:13

I think one of the most important lessons that our exploration

0:57:140:57:17

of the solar system has taught us is that the laws of nature

0:57:170:57:23

can create vastly different worlds with the tiniest of changes.

0:57:230:57:29

We now see how the life and death of planets and moons

0:57:320:57:37

is governed by interconnections which span the solar system,

0:57:370:57:42

and we wouldn't be here if it wasn't for those connections.

0:57:420:57:46

Subtitles by Red Bee Media Ltd

0:58:160:58:19

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0:58:190:58:22

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