jueves, octubre 14, 2010

Wonders of the Solar System - Dead or Alive (IV)

Episodio 4 - Dead or Alive

The Grand Canyon, in Arizona (…) It’s incredible to think that this enormous valley was etched and carved by the action of running water over just a few million years.

This is Mars, the red planet. Fourth rock out from the Sun. It has a canyon so vast, you could fit our own Grand Canyon into one of its side channels. (…) This is Vallis Marineris. Eight kilometres deep and over 3,000km long.

Despite all the similarities between Mars and Earth, it’s the differences between these two planets that are most telling. Mars is now a desolate dead wasteland. A world where the processes that sculpted its familiar landscapes ceased up long ago.

The big island of Hawaii in the middle of the Pacific ocean, holds the key to what happened to Mars. This is the perfect place to witness how a planet can be kept alive by nothing more than a simple flow of heat. (…) It looks like an apocalyptic scene! This volcano is Kiloueia, which means spewing. It’s been erupting almost continuously since 1983. (…) This might look like widespread destruction, but volcanic eruptions are Earth’s geological heartbeat. Active volcanoes make our planet a vibrant, living world.

Today these mountains are the largest volcanoes on our planet, and we’ve seen landscapes just like this on Mars.

This is Olympus Mons, named after Mount Olympus, the mythical home of the Greek Gods. This vast outpouring of lava stretches over 550km across. But it’s the height of this volcano that is breathtaking. It sores 25km into the martian sky.

All this heat you can see driving all this spectacular volcanic activity is relic, a hangover of the Earth’s formation. All the rocky planets, Erath, Mars, Venus, Mercury were formed in the same way. They came from a collapsing dust cloud about 4.5 billion years ago. (…) Little by little the rocky bodies grew falling together under their own gravity. This process not only generated immense amounts of heat. It also delivered radioactive materials to the cores. These two ancient sources of heat power volcanoes to this day. But the volcanoes on Mars are little more than a petrified memory of a distant past. (…) Something obviously happened to stop the Red Planet’s geological heartbeat.

Mars is a much smaller planet than the Earth, about half the diameter, 1/8 of the volume. So there is much less heat trapped there to begin with. Now, planets loose heat to space through their surfaces. And smaller thing have a larger surface area in relation to their volume than big things. So that means than Mars would loose its heat to space much quicker than the Earth does.

Tierra vs. Venus

It’s the brightest point of light in our night sky. So similar in size to our own world, this planet has been called Earth’s twin. This is Venus. Orbiting closer to the Sun, Venus was named for its shining beauty. But our planetary twin hides its true identity beneath a thick blanket of clouds. (…) The atmosphere is so dense that the pressure is crushing. It’s 90 times the atmospheric pressure here on Earth. Venus takes 243 days to rotate on its axis. That means its day is longer than its year. And Venus has the hottest average surface temperature other than the Sun’s, anywhere in the Solar System, 470ºC.

I’ve come to India, to a place called the Deccan Traps. Hidden in this lush green landscape, a tantalizing clue to understanding how immense heat caused Venus to choke to death. If you see this landscape today it’s incredibly peaceful and green (…) But everything you see down there is lava,. This whole landscape, half a million square kilometres of it was created on an ongoing volcanic eruption, and it lasted for a million years.

If you take away the green foliage, the underlying landscape of lava is actually very similar to what we see on Venus. Using radar to peer down through the clouds the surface of Venus was finally revealed. It’s covered with floods of solid lava. Just like we see in India. But in a scale many thousands of time larger. We’ve also counted over 50,000 volcanoes, the most of any planet in the Solar System. Venus has a similar size to Earth, so it may still have a hot geological heart powering its volcanoes But as yet, we haven’t witnessed any eruptions.

For both planets this was volcanic activity in overdrive. The eruptions here in India 65 million years ago affected the Earth’s climate so much, that they’re thought to have played a major role in the mass extinction event at the end of the Cretaceous period, which wiped out over two thirds of the species on Earth. Now, life on Earth recovered, but Venus wasn’t so lucky. The intense volcanic activity on both planets (…) also released copious amounts of gases, like carbon dioxide. But slight differences (…) pushed our cosmic twin into a path of no return.

Rain plays a significant role in keeping our planet a pleasant place to live. Acting as part of the global recycling system, rain keeps our atmosphere in balance, washing out greenhouse gases, ready to be locked away in rocks in our oceans. On Venus the laws of physics have made it impossible for rainfalls to cleanse its atmosphere. In fact, there is no liquid water at all. Venus lost its water, escentially because it’s hotter than the Earth. (…) Venus ended up cocooned in thick high pressure dense blanket of carbon dioxide. And that made the temperature rise, rise, rise. Turning Venus into the hell-like world we see today.

Our planet is not too big, not too small, not too hot, not too cold (…) Everything is just right. Our world is unique. But it doesn’t exist in splendid isolation. It is intimately connected with its cosmic neighbours. (…) Out in the farthest reaches of our Solar System, vast worlds have a direct impact on our very existence.

Asteroides e influencia de Júpiter.

Despite the fact that astrology is a load of rubbish, Jupiter CAN, in fact, have a profound influence on our planet, and it’s through gravity. (…) Jupiter has the most powerful gravitational field of all the planets. And it’s the gas giant gravity that can directly influence the orbits of asteroids and other wondering space debris. (…) Firstly, it can capture the stuff, literally hover it up. Secondly, it can deflect the stuff so that it throws it out of the Solar System. But thirdly (…) it can deflect stuff onto a direct collision course with our planet.

But we do have sentinels standing guard. -The prime task is to try and find killer asteroids, things that are out there in the Solar System that might hit the Earth.
-There’s an air of Hollywood about it, isn’t there, in some sense?
-Well, that’s right. I would say a lot more resources have been spent on making movies about killer asteroids than in actually finding them. Anything that’s a kilometre in size… if it’d hit the Earth, it would be devastating. It would probably kill nearly everyone on the planet.

Each night (…) the team scans a vast sway of the sky. They are looking for any unidentified objects that might be heading our way. (…) It’s almost certain that there are asteroids in that image. The problem is, how do you figure out which one they are. The camera captures several images of the same patch of sky taken minutes apart. The team can then see if anything has moved relative to the background of stars. -What we’ve done here is, we’ve taken two images, substracted them and, you see, the stars have nearly all gone away. But there’s a couple of interesting things left (..) That’s something which was there in the first image, and there in the second image.

Over 2,000 objects have been identified that pass close to the Earth, with something like 400 that could be on collision course. And all of these menacing lumps of rock come under Jupiter’s gravitational influence. (…) Jupiter regularly throws asteroids our way.

One of the most famous meteorite impact sites is the Barringer crater in Arizona. 50,000 years ago a 300,000 ton, 50m in diameter lump of iron and nickel entered the Earth’s atmosphere and made this crater.(…) But the asteroid that struck here was relatively small and innocuous.

But there are much larger impact craters hidden in Earth’s landscapes that have far more devastating tales to tell. (…) This is Middlesbrough, Kentucky. It’s a town built INSIDE a meteorite impact crater The asteroid that struck here would have been huge, around half a kilometre across, hitting the Earth well over 200 million years ago. But when you look at this view is not obvious (…)

Located between Jupiter and Mars is a vast reservoir of rocky debris that forms the asteroid belt. And it’s this ancient rubble that Jupiter can nudge towards the Earth.


For four hundred years we’ve expected Io to be as dead as our own moon. But in the late 1970’s (…) we’ve finally seen Io up close. But it didn’t make any sense, as Io was a moon with no meteorite impact craters. (…) The only explanation is that the surface is young, it must have been recently produced. And that in term means that Io (…) must be a geologically active world.

We may not have stood on Io, but there are places we can go here on Earth to unlock its secrets. This is Ethiopia, in East Africa. We’re being flown out by a military helicopter to the very hot, very inhospitable Afar region (…) And this is what I’ve come to see. It’s one of the rarest geological phenomena in our planet. A volcano with a lake of molten lava. This volcano is called Erta-Ale by the local afar people. It means smoking mountain.
-It’s a window into the interior of the Earth

Io is the size of our moon and should be a cold, dead world. Yet our first glimpses of Io revealed it (…) alive with volcanic activity. Just one of the many lava lakes on Io releases more heat than all Earth’s volcanoes put together.
-If we were to stand in the surface of Io, what would be the similarities and what the differences?
-It would be very, very similar to this. Except for the scale. The lava lakes in Io are vastly larger. The biggest we think is 180km in diameter.

Io is the most volcanic place in the Solar System. But what is interesting is that it is so small, that it shouldn’t be volcanic at all. (…) Something else must be driving that powerful volcanism on Io. (…)
Io sits about the same distance from Jupiter as our own Moon does from Earth. But don’t forget that orbiting outside Io are its sister moons, Europa and Ganymede. Io is under the influence not just of the massive gravitational pull from Jupiter but also from the additional pull of its neighbouring moons. It’s this gravitational tug-of-war that conspires to bring life into Io. (…) Periodically they line up together… bang, bang, bang! (…) That has the effect of stretching and squashing Io (…) and it gets hot by friction.

With weak gravity and a sparse atmosphere Io’s volcanic plumes can reach 500km above the moon surface.

1 comentario:

Silvi dijo...

Sigue siendo súper interesante. Y explicado con bastante simpleza para lo complicado del caso. Y muy buenos paralelos con lo conocido de la tierra. Me gusta.