martes, agosto 24, 2010
Wonders of the Solar System - Order out of Chaos (II)
Episodio 2 – Order out of Chaos
Movimiento de la Tierra en el espacio
This is the Great Mosque city of Kairouan in Tunisia (…) For the last 14 centuries the relentless passing of the days has been celebrated by prairs, before dawn, sunrise, noon, sunset and in the evening. (…) But what we are really observing is the movement of the Earth through space.
If our axis wasn’t tilted by 23 degrees then there wouldn’t be any seasons. And if there were no seasons, then season flowers wouldn’t have evolved… and there wouldn’t be a flower market.
But it’s not just the Earth, the whole Solar System is full with rhythms. Each planet orbits the Sun at its own distinctive tempo (…) so regular, that the whole thing could be run by clockwork. It seems extraordinary that such a well ordered system could have come into being spontaneously. (…) I want to explain how the order emerged from the chaos of space.
Up there is Polaris, the North Star and it’s almost exactly aligned with the Earth’s spin axis, which means that as the Earth rotates, all the stars rotate through the sky around that point. (…) So it looks as if the Earth was at the centre of the Universe and the stars rotate around it and that’s of course what the ancients thought for thousands of years… and why not? Because it’s obvious… but wrong.
Movimiento de los planetas y modelo heliocéntrico
To understand the Earth’s real position in the Solar system, we need to look at the one set of bodies that doesn’t behave as predictably as the stars. The Greeks named them πλανήτης, or “wandering star”. This is Mars photographed once a week over a period of months (…) it occasionally changes direction and loops back on itself.
Understanding [this] didn’t come easy… that’s why it took over two thousand years to work out. The key thing is that the Earth is NOT at the center of the Solar System, Sun is.
What happens when the Earth overtakes Mars? Then, according to line of sights, Mars has moved back (…)
Once you have this picture of the (…) Sun surrounded by the orbiting planets, then you might start asking questions like, why is the Solar System so oordered and did that order come into existence? Well, the key lies in those sweeping circular motions.
Formación del Sistema Solar
The awesome spinning power of tornados is incredible destructive effect. But it’s the same phenomenon that is responsible for creating the stability of the solar system. Because it was the conservation of angular momentum that stopped the solar system collapsing completely.(…)
Oh my God, THAT’s gonna be violent!!
Los anillos de Saturno
There is a place where the processes that formed the Solar System are still in action today… (…) the planet Saturn.
All the rings are in motion, orbiting at immense speeds. (…) and while the rings appear solid, casting shadows onto the planet, they are also incredibly delicate. The main disc of the rings is over 100,000 kilometres across, but as little as 3 meters thick.
To try to understand the true nature of Saturn’s rings, I’ve come to this glacial lagoon in Iceland.
(…) So it’s either death or whisky.
(…) The structure of the rings is remarkably similar to the way these icebergs float in the lagoon, because despite appearances, the rings aren’t solid. Each ring is made up of hundreds of ringlets, and each ringlet is made up of billions of separate pieces
(…) But the similarity doesn’t end with the layout, it also lies in what the rings of the icebergs are made of, and that explains why the rings are so bright. (…) They are made of beautiful, pure water ice.
The key to understanding the rings can be found orbiting around them.
Dione is one of Saturn’s typical icy moons. (…)
Iapetus is known as the Ying and Yang moon, one half clean ice, the other coated in black dusty deposits. (…)
The giant moon Titan is bigger than the planet Mercury (…)
Hyperion is a moon unlike any other… it’s not even round, and it s battered surface has the texture of a sponge. (…)
But the moons of Saturn aren’t just a celestial freak show. They are the driving force behind the beauty and structure of the rings.
Enceladus y el anillo E
Enceladus [‘s] southern hemisphere is almost completely free from craters, which means that the surface is probably newly formed. (…) It all looks remarkably to the geology of Earth, but carved in ice rather than rock. And right over the south pole are the tiger stripes. (…) They look just like tectonic fold lines.
Cassini has found the unthinkable, it’s found that the southern tip of Enceladus is excessively warm. (…)
Then, one day in November 2005, Cassini fotographed Enceladus just as the sun was setting behind it. (…) images revealed giant fountains erupting from the south pole. Volcanoes blasting out ice, instead of rock.
This is one of Earth’s hot spots, where the volcanic heat of the planet’s core bubbles up to just below the surface. (…)
Geysers form when underground pockets of water suddenly boil, exploding to the air.
But Enceladus is far too small to have retained any minimum source of heat at its core, so where does that heat come from? (…)
The orbit from Enceladus is eccentric (…) and the gravitational pull changes as it moves in its orbit, so that means the body is flexing, and if it’s flexing it means it’s undergoing friction inside… this is a major process for injecting energy that turns into heat…
While this Geyser erupts every few minutes blasting boiling water 20 meters into the air, on Enceladus the plums are thought to be erupting constantly, and for them, the sky is the limit (…) they sore up into space, thousands of kilometres. (…) The ice fountains are creating one of Saturn’s ring as we watch. The whole E-ring is made from pieces of Enceladus.
División de Cassini y resonancia orbital
The behaviour of the sand in the desert can help us understand how the moons form the pattern in the rings.
At first sight the Sahara desert seems immensely chaotic place (…)
But if you look a little bit closer you start to see an immense amount of order. There are sand dunes as far as the eye can see, and the remarkable thing is that the angles of the front of all the sand dunes are exactly the same. In the Sahara the emergence of that order is driven by the desert winds blowing always in the same direction, day after day, year after year, moving the sand around.
In the Saturninan system the order (…) of the rings is driven, obviously not by wind, but by a different force, the force of gravity.
As the moons orbit Saturn, their gravitational influence sweeps through the rings. In these amazing images, we can actually see the moons as they work (…) distorting the shape of the rings
The F-ring, one of the outer rings, is twisted into a spiral shape by two moons, Prometheus and Pandora (…)
These short ranged gravitational effects account for many of the patterns in the rings. But sometimes the moons can exert their pull over much greater distances.
Here’s there’s a model of the Saturnian system. (…) the first thing you notice when you look at the rings is a huge gap, called the Cassini division… and what could possibly have caused that? (...)
Mimas orbits well outside the ring system. (…) it’s all due to a phenomenon called orbital resonance. Now, the particles in the Cassini division have an interesting relationship with the moon Mimas, because they orbit around Saturn twice for every single orbit of Mimas. And that has an interesting consequence.
Imagine there’s a particle in the Cassini division. Then, every second year they meet up with Mimas… they end up in the same place in space. And that means that this particle will get a kick from Mimas’s gravity on a regular basis, every second year… bang, bang, bang, and that alters the orbit, so that anything that is in the Cassini division and actually has the effect of throwing it out, clearing the gap in the rings.
Migración y bombardeo intenso tardío
There was one period, 3.6 billion years ago when the whole Solar system was turned inside out by the same forces of orbital resonance (…)
We now believe that the Giant planets formed much to the Sun than they are today. Their orbits drifted for hundreds of millions of years, until Jupiter and Saturn fell into a resonance pattern. Once every two cycles, the planets aligned in exactly the same spot, creating a gravitational surge that played havoc with the orbits of all the planets.
Neptune was catapulted outwards and smashed the ring of comets surrounding the Solar System, with dramatic consequences. For a 100 million years, the Solar System turned into a shooting gallery as a rain of comets ploughed through it.
It was called the late heavy bombardment. It created many of the craters that we see throughout the Solar System today. (…) It left scars all over our moon. And it had a lasting impact on the Earth as well. (…) Impact could have played a key role in the development of life on Earth.