Alien Worlds – Science and Mysteries (Part 1)
Unbelievable new worlds, planets made of diamond, planets of raining glass, worlds in collision... some plunging into stars... and others that just might harbor life. But had ancient astronomers as far back as the days of Greece and Rome already guessed what modern science is about to learn?
We are the generation of human beings that are going to know whether or not we're alone in the universe. Ancient mysteries shrouded in the shadows of time.
Now can they finally be solved by looking to the heavens? The truth is up there, hidden among the stars... in a place we call... Ancient Greece.
The greatest minds look up in wonder at the strangest objects in the night sky. Five brilliant points of light that look like stars but move in mysterious ways. - They noticed that some objects didn't behave like the stars and that they called them the wanderers, and they mapped them out in incredible detail. The ancient Greek word for "wanderers" is, "planets". 2,000 years later, the invention of the telescope added three more planets, bringing the accepted total to eight, but if anyone thought that these were the only planets in the universe, they were dead wrong.
The problem was, for years, there was simply no way to find any additional planets that theoretically might exist around alien stars. They didn't know how to find them because looking at them with a telescope-- they're just invisible to us. They're too small.
Scientists compared the challenge of finding such planets to placing a firefly next to a Hollywood spotlight. Now, imagine flying to New York City and taking your best camera, attaching it to your best telescope, and trying to take an image of that spotlight and that firefly all the way out here in Los Angeles, where you can see the firefly separate from the spotlight, and that's about the scale of how difficult it is to actually take a picture where you can see the planet next to the star.
Yet, in just the past few years, we've discovered hundreds of new planets whirling around alien suns. It's a collection of worlds that range from the bizarre to the eerily familiar-- a planet about to be swallowed by a dying star... Giant water worlds awash in global oceans... A planet in a death plunge into its star... Two planets in the fiery aftermath of a gigantic collision... And the holy grail-- Earthlike planets that just might harbor life.
Could this be one of the first places in the universe we find alien life-- a newly discovered planet called Gliese 667Cc? It orbits what's known as an M dwarf-- a star that's 1/3 less massive than our Sun and gives off a tiny fraction of the visible light, but for astronomers seeking both new worlds and life in the universe, it looms large, because planet Gliese 667Cc might actually be inhabited, even though it's eight times closer to its dim star than Earth is to the Sun.
If we on Earth were orbiting the Sun at that distance, we would get fried, but because Gliese 667 is a low-luminosity M dwarf, a dim star, the planet, 667Cc, that orbits it actually gets an amount of starlight that should make its temperatures somewhat comparable to those that we have on Earth. So what would it be like to stand on the surface of this world and look up into the sky?
Here we are on Earth. That's our Sun up there. It's so small, I can take my little finger and block it out, but on Gliese 667C, come on, the Sun is ten times larger.
The energy pouring onto the planet (nar) is not visible light like on Earth but infrared light, otherwise known as heat. Because the planet orbits so closely, it's locked in the tidal grasp of its star. It's the same side always that faces the star. It's like the Moon-- the same side of the Moon continually faces the Earth. Well, so, too, the same side of this planet continually faces Gliese 667C. Scientists once thought that such planets would be too hot for life on one side and too cold on the other, but simulations now suggest that heat from the hot side would flow to the dark side and vice versa, evening out the temperature. If life exists in this bath of infrared light, it must have evolved far differently from life on Earth, with eyes adapted to the infrared spectrum. If you imagine taking night vision goggles or something which lets you see infrared light, you would see that, in fact, everything around you is glowing and that the amount which it glowed varied depending on the temperature. Things which are hot will be brighter. Things which are cold will be fainter. Plants, too, would have evolved in ways hard to imagine.
On Earth, everything is green because that's the wavelength of light plants don't like. They take in the red, they take in the blue for energy, and they reject the green, so we live in a green world. But on one of these worlds, as the infrared wavelengths are brought into the plants, everything to us would look black. Could you imagine rolling fields of black grass, black trees?
But there's a problem for any potential life. M dwarf stars like Gliese 667C shoot out violent solar flares that can double the brightness of the star in minutes. Flares like this create gigantic bursts of radiation, the kind that can poison life and cause deadly mutations.
So the question is, could life survive on such a planet? In fact, some suspect that life might benefit in a surprising way. Most mutations are actually harmful to life, but some lead to advantages. Whether this would speed up evolution of life on that exoplanet or tend to kill off the life completely, I think we're not yet sure of.
If life can survive the turbulence of an M dwarf star like Gliese 667C, that would have profound implications for one of humanity's greatest questions-- How common is life in the universe?
The reason for that is that M dwarfs are the most common kinds of star. It might surprise you to learn that when you look up at the night sky, even if you're in a very dark place and you can see lots of stars, you can't see any of the stars that are the most common kinds of stars in the entire universe. 70% of the stars in our galaxy are what we call M dwarfs, very cool, small red stars that are half the size of the Sun or even smaller than that. Yet these dim suns, invisible to the naked eye, may be humming with life.
We've learned that these are the most likely stars to host planets that are roughly the size of Earth. At roughly the right distance away from their star, they receive similar amounts of light from their star that we receive here on Earth. One thing seems sure-- if life exists on Gliese 667Cc, it would have far more time to evolve than life does on Earth. Our Sun will only last a few billion more years before swelling into a red giant and sterilizing the planet. But M dwarfs are practically immortal. We think that there are some of these stars which live basically the age of the universe, so that's an advantage, because we know that our Sun isn't going to live forever.
Gliese 667Cc is just one of dozens of Earthlike planets that researchers have recently discovered... planets that finally confirm the beliefs of ancient philosophers who taught that there were countless alien worlds. But as we look at these new alien planets, an even bigger question emerges-- Is anyone looking back at us? We finally have the technology to find out.
As we search deep space for alien worlds, the ancient understanding of what it takes for a planet to support life is encoded much closer to home. When the Apollo mission landed on the Moon's Sea of Tranquility in 1969... many people wondered about the name. Tranquility Base here. Why Sea of Tranquility?
The answer goes back to an ancient belief about life on other worlds. In the first century AD, the Greek philosopher Plutarch wrote that the Moon was a planet like Earth and that it might even be inhabited. If so, he argued it would need oceans of water. - Even back to the days of Plutarch, we realized that water was necessary for life. Some people think wine is the elixir of life, but in the scientific world, we realize it's water.
Ancients like Plutarch looked for lunar oceans and thought they saw them in the dark splotches scattered across the Moon, so they named them the Latin word for "seas." So we have the Sea of Storms, the Sea of Tranquility, all these different seas. The idea that water was very critical to life goes way back in our historical records.
Today we know that the Moon's seas are simply large basins of dark volcanic rock, but Plutarch's original idea-- that to find life on other planets, look for liquid water-- has survived the test of time. All known life on Earth appears to require the presence of liquid water. Molecules can get bigger and can form complex structures. If life elsewhere is like life on Earth, then the mantra should be follow the water.
Water is common in the universe, but liquid water is rare. On the surface of planets, it only exists in the so-called Goldilocks, or habitable zone near a star, where things are not too hot and not too cold. The size of this habitable zone depends on the size and temperature of the star that the planets are circling. Our Sun is a fairly ordinary mid-size star, so our habitable zone, where Earth resides, is one astronomical unit away, way out here-- millions of miles. Now, in the case of low-mass stars, they're much smaller, and they have much less luminosity, or light output. So that means that the habitable zone goes from being way out here to being much closer in to the central star.
So life could exist on planets much closer to dim stars, and as we've seen, the universe is teeming with planets like that. Another key thing that affects the possibility of liquid water and life is the planet's size. If a planet is too small, we think it will lose its atmosphere because it does not have enough gravity to hold on to its atmosphere. That's what happened to Mercury and to some extent Mars. If the planet's too big, it becomes a gas giant, which, actually, are very hot planets as one would travel down into the atmosphere. So the planet has to be just the right size. So the habitable zone is actually the sum of two parts. One is being the right distance from the star, and the other is having the right kind of planet.
These, then, are the two requirements for life, but how often do they exist? It turns out they're everywhere, including here on this incredible, newly discovered planet called Kepler-22b. Kepler-22b is what we call a Super Earth. These are planets that are larger than Earth, but smaller than the planet Neptune. We don't have anything like that in our own solar system, yet these planets appear everywhere when we look at other stars.
As the list of planets that fit these precise requirements grows, the surprises keep coming. Consider an alien star only slightly smaller than our Sun that has not one but two planets that might be in the right spot and be the right size to harbor life. Kepler-62e and "f" are both Super Earths. They've got about 1 1/2 times the diameter of the Earth, and both of them are in, broadly speaking, the habitable zone. They're so close to each other that if technological beings evolved on one, they could easily visit the other. If you could travel on a rocket ship, it would take about 12 days to go between these two worlds.
That could only happen if these planets have dry continents, but some suspect that they're water worlds covered in a deep global ocean. These would be planets with a small, rocky core and then a very massive water envelope surrounding that, so that would certainly be an example of a kind of planet which is fundamentally different than anything we see in our own solar system. A water world might be great for life, even intelligent life, but technological civilization is probably impossible for a simple reason. You can't light a match under water. You can't have electricity. Probably intelligent life that is capable of making and building things wouldn't exist there because they can't use fire.
Still, this does not rule out life in the atmosphere. After all, some fish on Earth have evolved flight to escape predators, so scientists speculate that the skies of Kepler2e could swarm with alien birds. Planets like Kepler-22b and surprising twins like Kepler-62e and "f" are revolutionizing our understanding of what kinds of worlds might harbor life, but how does this strange class of planet make our solar system look like the freak of the universe?
As we search the heavens for new worlds, we expected to find solar systems that look like our own, but instead, we're discovering that our solar system might be a freak of nature, challenging a view of the cosmos that developed over thousands of years. Some astronomers in the ancient world correctly guessed that Earth was a globe that revolved around the Sun, but the most famous of all ancient philosophers strongly disagreed. In the 300s BC, Aristotle argued that the Earth was at the center of the universe, and his ideas were accepted for centuries.
The Catholic Church adopted this because it worked so well in their theology of how the universe worked. God had created man. Man was special. The Earth was special, and because of this, this was what everybody believed. It wasn't until the 1600s that Copernicus proposed that we inhabit a solar system with the Sun at the center and all the planets revolving around it, including Earth.
By the late 20th century, scientists believed that they fully understood the mechanics of how solar systems evolve. For many years, the only example of a solar system that we had was our solar system and the eight planets that orbit here around our Sun. We based our entire view of how solar systems are born on our own solar system... but the sudden discovery of thousands of exoplanets has shown that apparently we were wrong. Now we have a plethora of different systems, all of which are totally different and some very similar to ours and then some very alien.
The way our solar system formed produced essentially two kinds of planets. One type is the rocky planets. We call them terrestrial planets. The other would be giant planets like Jupiter and Saturn. This made sense because of how we thought solar systems evolve. When solar systems form, they collapse from a large cloud of gas, and the central mass of them becomes the star, whereas the disk of material that's left over around that central star becomes the planets. Close to the star's warmth, the most common elements, hydrogen and helium, are heated into gases and blown away by solar winds. So, near the star, the only materials left for making planets are heavier, rocky elements. This is where its warm enough that you can really only condense out rock and metal to form these little planets.
However, further out in the solar system, beyond what we call the snow line, temperatures are cool enough where you can condense gases and form these very large envelopes that eventually become planets like Jupiter and Saturn..
The tip-off for how wrong we were was the discovery of a class of exoplanets that theoretically can't exist, except they do, the so-called "hot Jupiters." - A lot of the first exoplanets found are what are called, hot Jupiters-- big, massive planets that actually orbit very close to a star, having a orbital period of a day or only a few days or ten days. HD 209458b zips around its Sun-like star in 3 1/2 days...
While our Sun's closest planet, Mercury, takes 88 days. HD 209458b is an iconic planet. We also think that the atmosphere's being blown off by interacting with the star and heating up and by wind from the star hitting the planet, and its atmosphere will be slowly whittled away.
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