Alien Worlds – Science and Mysteries (Part 2)

Continuation of Part 1 - - - Losing about 10,000 tons of gas every second, this planet is, in effect, evaporating. It looks like a comet with a huge tail stretched out behind it.


Eventually that atmosphere's going to be gone, and all that's going to be left is a little molten core of what this planet used to be, orbiting nearby this bright star.

But these hot Jupiters are far too close to their stars to have formed there originally, so what happened? Scientists now believe these hot Jupiter solar systems began like ours, with the gas giants forming out past the snow line, but then the gravitational pull of the disk or of various planets or even passing stars caused the orbits of the gas giants to go haywire. They migrated inwards, spiralling toward their suns, and that process spelled doom for the smaller, Earthlike planets closer to the star. Well, you'd have the star over here. You'd have a Jupiter-size planet here, and as it moved in, the little, rocky planets would either be thrown into the star or thrown out of the solar system, or they could be captured by that big Jupiter and orbit around it like a moon.

The planets tossed out of the solar system are doomed to wander forever in deep space. Some researchers now believe that the galaxy holds billions of these dark, lost worlds. So it turns out that our orderly solar system, with the rocky planets close to the sun and the gas giants further out, may be a lucky exception. Earth has achieved a stability that allowed life to develop and evolve in a relatively un-hassled way for billions of years, and in many other planetary systems, that may not be the case.

But while the discovery of new planets has challenged some ideas of how solar systems evolve, it's confirming others, including the catastrophic idea of colliding worlds and even how the Earth will one day die. Many ancient ideas about planets seem simplistic... but around 400 BC, the Greek philosopher Democritus proposed ideas that seemed straight out of a modern science textbook, including ideas about fiery cataclysms in the Earth's past... and a terrifying idea about how the Earth will one day die. He was the first to come up with the idea that things were made of smaller things. He called them atoms, and they came together and grew and grew into stars, into planets, into everything that is around us. When it comes to planets, Democritus wrote that there are innumerable worlds of different sizes. In some, he wrote, there is neither sun nor moon. In others, their sun is larger than ours, and others have more than one sun"... all of which, amazingly, is true.

The interesting philosophical question is, how did he come up with this idea? It shows the uniqueness of the human mind to be able to project and ask, "What if?" And then, using logic, put together a philosophy of how everything works.

Today, as we discover planets around alien suns, many of Democritus' ancient ideas have been confirmed by modern science. For example, he wrote that some planets are destroyed by collision... and now we're actually watching that happen.


This is the hot Jupiter called WASP-18b, a planet caught in the act of plunging into its star. It's been orbiting for possibly 2 billion years, but within the next million years, it's going into its star, and the whole shape of this round world will be stretched like an egg. While WASP-18b confirms Democritus' idea of how planets can die, another new discovery confirms his ancient prediction that planets can crash head-on.

The planet HD 172555 is a world in the aftermath of a collision. What we think we're seeing is two large rocky planets which had just crashed into each other, thrown up a bunch of dust, melted rock kind of accreted together. Scientists have long speculated that a collision like this happened to the early Earth, tossing up debris that created our moon.

For decades, that was just a theory. Now they can actually watch it happen. Gases were given off. Glass was created. And now they're fusing back into this remain of this world that will be cooling down, but right before our very eyes. There's a space wreck right in front of us. Democritus' ancient theories about the death of planets are bolstered by another major discovery: a dying planet called Kepler-91b.

Scientists have long believed that in the distant future the Sun will swell up, engulfing the dying Earth in an inferno. And this isn't just a theory now because we think we see this with Kepler-91b. Kepler-91b's star, about the same mass as the Sun, has already swollen into a red giant. It's now about six times our Sun's radius and growing rapidly. If there were oceans here... they're already evaporated. If there is life, it's in trouble. On this world, if you wanted to see life, you'd be there at night. Everything would come out when it's cooler, it would disappear once again, and the most precious commodity on this world would be water. Everybody, everything would be looking for water, and yet this is our future. We're seeing it now.

Like Earth, Kepler-91b is doomed to be swallowed by its sun. Unlike Earth, its time is almost up, but could a planet survive that fate? Apparently we found one that did. V391 Pegasi is an example of an exoplanet that has physically survived the red giant stage of the star that it orbits. It's sun turned into a red giant and grew larger and larger and larger until it actually consumed this world. And then as its sun has shrunken back down, the world remains.

Since V391 Pegasi is still there, it's the first known planet to survive a close encounter with the kind of red giant that will one day threaten to destroy Earth... if you can call that survival. That world now is one burnt, rocky planet. Anything that was living is gone. It's disappeared. Newly discovered planets like these give us a glimpse into Earth's future, but there are other planets out there so strange, they seem ripped from an alternate universe. What is mankind's secret weapon for unmasking these mysterious worlds?

Less than 20 years ago, scientists were still struggling to discover a single planet outside our solar system. Today we've discovered thousands. How did we do all this and do it so quickly? The revolution begins in the 1990s. Scientists knew that planets cause their host stars to wobble and finally developed a way to detect this. We now have instruments with microelectronics, a spectrograph, that could act like a policeman's radar gun. We could take a look at a star, and we could see if it was moving towards us or away from us. Using that technique, scientists discovered something that had eluded not only the ancients, but even modern astronomers-- the very first planets outside our solar system. But were there even better ways to search? Once we knew there were planets around other stars, people suggested that there might be another way in which you could find planets.


That way was to look for little eclipses caused when the planets passed between their host stars and our vantage point on Earth. These tiny eclipses are called transits... like the transit of Venus we saw from Earth in 2012. This creates a tiny dip in the brightness of the star, which we can measure as it happens again and again as the exoplanet goes around in its orbit.

But from Earth's surface, the transit technique had serious limitations. You really need to monitor the star all the time without interruption in order to have a good chance of not missing any transits. That's where NASA's Kepler space telescope comes in. Launched high above Earth's distorting atmosphere, it pointed at just one spot in the sky-- a field of 150,000 stars, taking continuous pictures of that region over and over again for four years, with space-age precision. Would it find a sky brimming with planets or a dark and empty void? Lo and behold, planets started moving across their stars, and we started seeing their orbits. And we waited and waited-- another year, another crossing, another year, another crossing.

But scientists quickly turned to a larger question. Could any of these planets be similar to Earth? The majority of the stars in the Kepler field seemed to have planets, and Kepler was actually sensitive enough to detect a planet the same size or even smaller than the size of the Earth, and it found enough of those that we now know that small planets are much more common than large ones.

That, in fact, was Kepler's revolutionary purpose... To find Earthlike planets that could harbor life. In this mission, we found them, but we found a lot of other surprises too. But as scientists struggled to discover the total number of planets that exist in the galaxy, they ran up against Kepler's major limitation-- it can only spot planets that transit their star as seen from Earth, and most planets do not. If we have a transiting planet system, then we need the alignment to be perfect for that planet to go around its star and to block just a little bit of that light from getting to us from our point of view. However, if we took this system and we tilted it up such that that alignment no longer happened, then the planet would still be going around its star, but it would never block any of the star's light from getting to us, and we wouldn't see a transit at all. Scientists realized that the chances that an Earthlike planet will transit are 1 in 210. Using that ratio gives us a staggering estimate of how many planets actually exist.

What this tells us is that in our Milky Way galaxy, which has between 200 billion and 400 billion stars, there may be almost 230 million other planet Earths out there. Once Kepler detects a possible planet, scientists across the globe race into action. Another group of astronomers takes over with telescopes here on the Earth with huge spectrographs, and they take a look at this world and look for the star to wobble. We need both these processes now to determine what the planet is and how far away it is and what it looks like and even what it's made out of. 

Kepler roared into space in March 2009 on a Delta II rocket. In the first six weeks, it discovered five previously unknown worlds. Today it has discovered thousands. It's nearly impossible to describe how revolutionary Kepler was for exoplanets. Kepler made so many discoveries we never even expected. So far, some of the newly discovered planets have challenged and others have confirmed ancient theories of how worlds are born and die, but even the ancients never dreamed of the kinds of wondrous worlds we're discovering today.

How does the universe make a planet of solid diamond? Ancient philosophers like Democritus believed in a universe aglow with amazing planets. But today's planet hunters have discovered worlds far stranger than the ancients ever suspected. You are orbiting 55 Cancri e. It's mostly made of carbon, and due to extreme pressure and a surface temperature of 4,892 degrees Fahrenheit, it just might be a jeweler's dream. Now, think about this. What happens if you take a piece of carbon and you have the strength of Superman and you crush it like this? What do you get? A diamond.

If a diamond planet isn't strange enough, let's descend to another new discovery-- HD 189773b. Its blue color makes it look surprisingly like Earth, but in this case, looks can be deceiving. This is a glass planet. It has mostly silicon, and the silicon with the sunlight passing through it appears to be blue, and it's very hot. In fact, the temperatures near the surface are such that the silicate can condense into fine little particles of glass, so it might actually rain glass on this exoplanet. But that rain would move largely sideways because there are huge winds in the atmosphere, up to 4,000 miles an hour. And the ancients never predicted a planet covered with a seeming impossibility-- burning ice-- yet that's what we find on Gliese 436b. If you touched it, you would be burned. This is a world made of hot ice-- something we never imagined on Earth.

Diamond planets, planets of raining glass, worlds of burning hot ice-- thanks to projects like Kepler, the universe is proving far stranger than either the ancients or modern astronomers ever imagined, but more is soon to come. Scientists are bracing for the discoveries of TESS, the Transiting Exoplanet Survey Satellite, due to launch in 2017. Unlike Kepler, which looks at one patch of sky, TESS will scan only the stars that are so close, we might actually visit them someday. We're mapping the nearby stars for planets that we hope, eventually in the future, our descendants will actually be able to travel to. So we have a huge interest in trying to find planets orbiting stars that are very close to Earth.

Other new projects have actually begun searching not just for life but for intelligence and technology. One surprising key is to look for stars that twinkle and pulse in bizarre ways that could only be caused by advanced alien civilizations. - I used large databases of observations of stars to try and understand whether any of those stars could be varying in a way that was caused by something artificial.

But can we ever visit the planets we are now discovering in such abundance? - I'm hopeful that at one point, we'll eventually be able to send robotic probes to some of these nearby solar systems. Not everyone believes that it'll happen, but we're born explorers. We'll want to go. We have to have hope that, in the future, if there's a will, there's a way.

Whether such a thing will happen is anyone's guess, but one thing is certain... thanks to today's planet hunters, our views of the universe and of our place in it are undergoing one of the greatest revolutions in scientific history.   

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