Chapter 15 Chapter Ten Searching for Another Earth

The era of blindly seeking resources and settlements from the earth has passed, and human beings have begun to enter the second type of civilization.Cultivating and using the resources without gravity in the big sky is the biggest issue of human development at present. The number and nature of worlds in the universe have confused mankind for a long time. Polutarch once said: Alexander the Great was once angry because his friend Anaschas told him that there were countless worlds.Alexander shouted: Don't you think it's sad that there are so many numbers, but we can't conquer any of them.Bruno, one of the most forward-thinking philosophers in the Renaissance, challenged the deep-rooted concepts of that era. He said that every star is a sun, and every sun has planets.Worse than these heresies was the fact that around him always attracted many students to his lectures, while his colleagues left grumbling from the empty halls.In 1592 he was denounced by the court of Venice.In the words of a historian of science, no defendant has tried so hard to save his faith since Socrates. He laughed at the interrogating judges and kept talking to them. The judges were afraid of him. He was kidnapped. Burned alive at the stake, the first martyr to die for the multiverse theory.

The number of worlds in the universe is probably still limited to academic problems, even after thousands of years, and what happens this book wants to predict.Although our Milky Way is only one of billions of galaxies, it has a wide range, with a thousand suns, and it will take up a large part of human exploration time.The more practical question is how many habitable worlds are there in our galaxy?With the instruments Bruno lacked, we can guess the approximate number.Habitable means: a planet on which human settlers can live in reasonable comfort.Looking at our solar system, the conditions on most of the planets are unbearable, nine planets, they orbit a typical star which is considered quite typical, but only one planet is suitable for our life.The other planets cannot be inhabited without undergoing major environmental changes, which are costly and complicated.There are some calculations that allow us to estimate the number of planets with immediately habitable environments.let us see.

In the main sequence of the Hertz-Burning-Russell diagram, the sun is a moderately large star that exists for at least ten billion years.If the sun were larger than it is now, its lifetime would be shorter.The period of a star in the main sequence is the stable period of its life. This stable period is from when the internal temperature of the star rises enough to enable the thermonuclear reaction to start, until the star exhausts its hydrogen fuel and becomes a red giant or becomes a flaming star. Nova (if massive enough).Usually, the bigger it is, the shorter its lifespan.For example, the famous Betelgeuse has a mass 15 times greater than that of the sun and a brightness of about 50,000 times, but its existence period does not exceed 100 million years and is less than one fortieth of the age of the sun.Finding habitable planets on such a young star would be silly.When our sun was only 100 million years old, the earth was of course younger, with only some non-breathable carbon dioxide, ammonia, and methane in the atmosphere.Since very large stars exit the main sequence and become red giants, supernovae, or novae at about 150 million years old, they are unlikely to host habitable planets. (J Note: The above sentence pattern has been modified.) A habitable planet not only needs a sun with a reasonable stable time, but also needs plants to survive to provide the atmosphere with some breathable oxygen and nitrogen.Plants existed on the earth about 2 billion years ago, when the earth was between 2 billion and 2.5 billion years old.Therefore, even if it takes one billion years from the birth of the sun to the formation of the earth, we can say that any star younger than three billion years is an impossible object.Calculated from the diagram of Hertz-Plann and Russell, if a star is more than 1.43 times the mass of the sun, it cannot still exist in the main sequence at this age. (J Press: The above sentence patterns have been modified.)

It might be wrong to think of this chart as the Bible.We seem to follow beyond doubt by saying that unless a star has been shining steadily for three billion years, it cannot have habitable planets; glowing for so long.The Milky Way, with its 100 billion stars, is likely to have many exceptions that don't follow these two simple rules.The first is based only on our assumed knowledge of Earth's history (which may be wrong anyway), and the second is a statistical observation of an area of ​​far less than one percent of the galactic constellation.Undoubtedly, there may be planets with billions of stars in two billion years, where the stars may have two or three times the mass of the sun and are alive and well, and by some slow evolutionary process that is not yet understood, It remains in the main sequence after five billion years.In conclusion, this figure represents only an example of a cross-section of the Milky Way.It's a lot like a poll, just ask a small group of people who they're going to vote for, and then multiply that number to predict the outcome of the vote.Fortunately, stars are much simpler than people, they don't tell us elaborate lies, and we place more trust in graphs than in general polls.The search for habitable worlds can be guided by probability. If the map tells us that X is too young to have habitable planets, then it is better to abandon this star. Maybe the map will be wrong, but what does it matter?There are many, many older stars that are more promising!

In addition to unusually large and young stars, variable stars can also be omitted, which often flare up for a few days before returning to normal brilliance.The planets around it cannot endure such drastic changes.Stars like Alcyon and Cepheid, whose brightness changes regularly, should be avoided by settlers. A detailed three-dimensional map of the Milky Way, with hazardous stars and regularly or irregularly changing interstellar objects, periodic novas, supermassive stars, white dwarfs, neutron stars (pulsars), and black holes, should be in the library of all starships And in all interstellar commands.Only stars close to the mass and age of the Sun are safe to observe, even from hundreds of millions of miles away.By some estimates, this list of missized and dangerous stars contains 70 percent of the local Milky Way galaxy, or about 70 billion interstellar objects.

Now, the job of finding is much easier. Now that we know which stars to target and which to avoid, let's turn our attention to their planets.We know that a planet should have a lot of vegetation if it is to have a breathable atmosphere for humans.Usually there are only two types of planets we are interested in; Earth-type planets.With oceans, land and plants, this planet can be colonized immediately, and a Venus-type planet, with a rich carbon dioxide atmosphere, can be colonized after several years of algae treatment.However, the number of Earth-type planets in the Milky Way is likely to be in the billions, so that in the age of interstellar travel, algae disposal can be abandoned, and Venus-type planets are ignored.Shagang's plans for Venus are important only at this time because they may need to be completed before the development of human interstellar transportation.In a galaxy with enough worlds, we can choose the best among them. At present, we are limited to the solar system in a very small range, which makes us face many difficulties. In the vast and endless space of the galaxy, we don't have to work so hard. We can only limit ourselves to finding Earth-type planet.

As environmentalists often remind us, the habitability of the Earth, with its suitable climate, oceans, forests, mountains and continents, is the result of lucky chance.There is no law on the graph that says that a sun-sized star must have a habitable planet.Imagine how different the world would be if the Earth's mass, orbit, and motion were changed only slightly.It is important for the seeker to understand the acute effects of these factors. Assuming all other factors remain the same, the earth's mass is twice as large as it is now, and its surface gravity will be 1.4 times larger, and the added gravitational effect will be very extraordinary.The evolution of seabed organisms will take place more slowly, the migration of sea animals to land will be delayed by millions of years, and the evolution of life as a whole will be relatively delayed.The mountains will be lower and the bases will be wider than they are now.Trees will be smaller, with thicker trunks.Rivers are deeper because the water will be heavier and flow faster, with less alluvial impact on the land they pass.The waves in the sea will be lower, and the paths they will splash will be shorter.This will evaporate more slowly and the atmosphere will be drier.Assuming this heavier Earth is the same age as our world, the evolution of life is unlikely to go beyond the giant reptilian stage, and it will all be limited to squat, thick-legged creatures with long necks and legs, and animals like giraffes have no chance to evolve.Who can say what it was like when man last appeared millions of years ago?What is certain is that their physical and cultural forms were very different from today's.

Now assume instead that the Earth has only half the mass, and the gravity would be reduced by a factor of 0.7.Things are very different here.The mountains and woods will be taller and thinner, the atmosphere will be thinner, and the evolution of life will be very rapid; if the less atmosphere does not have any unforeseen effects, human beings will be far more advanced in technology than they are now, and many politically and psychological problems were solved a long time ago, the human body may evolve into a pure mind.Explorers should be careful when landing on a middle-aged planet with oxygen and water and a mass much smaller than that of the earth. The inhabitants on it are likely to have superb technology, beyond our imagination, and they may be able to make them and the whole world Industry disappears at the touch of a button.It would be unwise to rush to occupy such a planet unless the population's ability to resist invasion has been accurately assessed.

What would happen if the Moon was closer, say 95,000 miles away, instead of being 250,000 miles away from the Earth now?The force of the tides on the earth has been greatly increased, and the areas along our coasts are no longer inhabitable. They are flooded up to hundreds of feet every day. It is very difficult to develop the shipbuilding industry under these conditions. The area of ​​​​inhabitable land is much less. New York City It may have been built in the Adirondacks, and Paris may have been built on the plains of Arden.The earth's rotation relative to the moon is completely stopped. People who live on one side of the moon always face the moon, and people on the other side never see the moon.We can continue to play this game.Let the moon be the same size, but get closer, ten thousand miles or closer, and the moon will break up into small pieces, like Saturn's rings, which will block the sun's light for several days at a certain latitude.Move the earth 10 percent closer to the sun; the earth will be covered with carbon dioxide like Venus, and the surface temperature will be as high as hundreds of degrees; move it 30 percent away, and the temperature will be unbearably cold.

Assuming that some of the properties of the other planets in the solar system are different, how about increasing the mass of Jupiter by a factor of a thousand?At this time, the temperature on Jupiter rose to 100 million degrees Fahrenheit due to the pressure of gravity, and nuclear reactions began to take place.The earth will be orbiting between two suns of the same size. Although Saturn is far away from us, the heat transferred to the earth will increase the temperature by 6%. The ice sheets at the north and south poles may no longer exist or at least shrink a lot. The area will also be reduced a lot.

This second sun had a more serious impact on human culture.There are two suns in the sky, there must be no night for several months in a year, the progress of astronomy will be limited, the knowledge of cosmology and the development of nuclear energy will be delayed for a long time, the concept of a world running between two suns is not absurd; from Thousands of binary star systems are visible from Earth.Fifty years ago, when the complex orbital kinematics were poorly understood, it was generally believed that no planet, at least not a habitable one, could maintain a stable temperature in a binary galaxy.Today it is considered probable.American engineer Stephen.In his marvelous book The Habitable Planets of Man, Dooley calculates how far apart two stars should be so that a planet orbiting between them does not alternately freeze and scorch.This problem has been discussed theoretically by astronomers and mathematicians since Newton, and it is called the three-body problem.Until recently, the question asked was fairly simple: In what different ways do the three celestial bodies orbit each other in stable orbits?But restricting one of them to be a habitable planet, and the other two stars being about the same age and mass as the sun, the other two are about the same age and mass as the sun, which makes the problem very complicated. Dury's answer is that planets can be habitable in two ways: first, if the two suns are so close that only one habitable region exists in which the planets orbit, when the first sun eclipses, the second sun's Radiant light can replace the first one.In order for the emitted light to remain stable, both suns need to be of the same age and mass.In addition, if the distance between the two suns is about 480 million miles between the sun and Jupiter, the planets in them can also be habitable.Due to the existence of two suns in the sky, which hinders the progress of science, it is impossible to reach a high level of civilization very quickly, but this is not very important to the settlers with a high level of science.In multiple galaxies, with more than three stars orbiting each other or in complex ellipses, we can't be sure about our chances of finding planets.Bergomini would have said in beautiful terms: the three-star tango dance, the four-star Spanish dance, the multi-star mazeca dance are too complicated even for mathematicians. But if the binary system conforms to Dury's rules, the planets in it will be suitable for immigration.In addition to the habitability of the planet, the other most important question is whether there may be more intelligent beings on it, capable of destroying all colonists.I half-jokingly said earlier that a supercivilization might wipe out traces at will to trap settlers.If the appearance is very suitable, it is considered to be an ambush hiding danger, then we can never colonize that star, we only need to weigh the possibility a little bit to take the risk, and there are planets with a large mass in the binary system, it is worth the risk, Because their environment, for many reasons, would prevent the growth of nascent technologies. Numerous mathematical speculations have written the number of planets in the galaxy, habitable planets, planets with life, worlds with intelligent life and advanced planetary civilizations.These figures may be of interest to the reader who is not averse to simple statistical calculations based on the weakest data.Most people think that most of the main sequence stars have planets, this assumption has a proof, in 1969 Peter.Fan.Di.Kenca, from tiny fluctuations in Barnard's star six light-years from Earth, proved that it must have planets larger than Jupiter.Assuming that this situation is typical for the entire Milky Way, we can predict that the Milky Way has about 25 billion main-sequence stars older than 3 billion years, and contains about 5 billion planets of various types, assuming 100% of them Ninety-nine of them are uninhabitable, and we know that there are about 500 million habitable planets left. To sum up, a planet usually has the following characteristics before humans can land and colonize: One, it must have abundant plant life and vast oceans to maintain oxygen. 2. Its mass must be slightly greater than 0.4 times that of the earth to maintain the atmosphere, and its mass should be less than 2.35 times that of the earth; otherwise, the surface gravitational force will be unbearable. (On a planet of this mass, a human becomes 1.5 times his weight). 3. The age of its sun must be more than three billion years, and its mass should be less than 1.4 times that of our sun. 4. If the planet is in a binary system, the two suns must be very close or very far apart so that the orbit of the planet can be stable and the amount of radiation reaching the surface of the planet will not be too irregular. The conditions on the surface of the planet must be fairly well defined, and no one wants to live where the wind speed exceeds sixty miles unless he has some special reason.Frequent earthquakes, a steady stream of meteorites falling from adjacent star belts, or tilted axes causing large seasonal temperature changes can render a planet uninhabitable.Most importantly, some planets may be inhabited by intelligent life, which needs to be avoided.Astronomers and biologists estimate that there are between 1 million and 10 million intelligent civilizations in the Milky Way, representing 0.2 to 2 percent of the possible number of habitable planets.From experience on Earth, humans will have no difficulty dealing with lower life forms after all, even if the achievements of a few first expeditions will be wiped away by aggressive deadly microbes. All this sounds easy, imagine the program given on a ship in orbit around a star.Astronaut professor, I want you to point your binoculars at the target: tell us its mass, surface temperature, wind speed, axis slope, amount of plant life, etc., so that we can know whether it is safe to build a connected city in a moderate area, sure It has no intelligent inhabitants. How far away from the earth can a spacecraft in outer space be aware of which areas are natural and which are man-made?Cities like New York and London lit up at night can be seen with a telescope at a distance of five million miles, which is about twenty times the distance from the moon.Forests can be seen about 300 million miles away.The ocean, more dazzling in the sun, can be seen at a distance of 700 million miles, beyond which the earth does not appear even as a plate, but as a point with no three-dimensional effect, even with the largest telescopes.But human broadcasting capabilities in the high-frequency region have been detected far beyond the visible range, the most functional of which is the radar station of the Ballistic Missile Early Warning System, which transmits at a frequency of about 400 megahertz.At peak power, such a transmitter with one megawatt could detect its signal at a distance of up to 10 billion miles, about twice as far away as Pluto.Astronomer Frank.Braque calculated that traces of our UHF television broadcasts could be intercepted at distances of light-years (after years of transmission).One wonders if the computers of those probing aliens have translated these waves and don't want to get any closer to us. These and the previous chapters do not imply that human beings will begin interstellar travel before the year 2000.There are still many technical problems to be solved, and the resources of the most civilized nations are not enough to finance such a huge research development, but the situation will be very different in 2100, if the growth of technology, science and wealth maintains this At a rate of one hundred and fifty years, the first attempts to colonize another part of our galaxy will begin. Star Trek will undoubtedly have a dark side.If travel through hyperspace proves feasible and becomes quite common, wars and pollution will inevitably spread to other planets in the solar system, and the bloody history of war and war on Earth will repeat itself.The resistance of the alien society, which is losing ground militarily, is likely to be destroyed, and the conquerors from Earth will keep them in check with some valuable commodity.But such crimes will be rare, because the central government of the immigrants should be able to control them, conquerors with ships will be chased by policemen with ships of the same speed, of course, I assume that there is a planet that exercises this central control.Of course there are doubts that such central control can exist, because of the long history of anarchy in human history; however, all groups have an underlying tendency to subjugate another group, and the strongest of them will take central control and temporarily end anarchy.Some people envisioned a more peaceful and more commercial life, putting people on the stars.In 7000 AD, the eminent writer on astronomy, Strom, said that the wine in the sewage flowing from the earth's vineyards (J note: this sentence does not make sense) can be used as souvenirs with antiques from the fiery planets of the Orion star cluster Barter; jewels and medicines for a spoonful of dirt and a shining North Star, and rare insects for Arcturus velvet and distant sagittal arrows.If interstellar travel becomes a reality, a commercial venture of a kind never before seen on Earth is bound to unfold. Peacefully establish commercial markets or use war to completely destroy unsightly civilizations: these are the good and evil sides of the concept of economic expansion, both of which must happen when humans migrate into the galaxy and meet lower creatures. We can only hope that the former The method will be more than the latter method.It's hard to say what will happen when we meet beings whose civilization far surpasses ours, whose intelligence may be so high that they have evolved to a state of pure mind, and whose notions of our economic function and the conquest of galaxies are of no interest to them.The most interesting situation is that we meet about the same civilization as ours, and pursue the same expansion policy, if both sides want to own a particular star system because the planet has too few resources, or the star system is an important trade route It must be said that this confrontation is the main crisis of one human being or another, and the loser has to give up all his ego and become weak.Who will win in this competition?As at the beginning, I will answer with what Alexander the Great said before his death.According to his autobiography, the dying Alexander was asked by one of his officers: "Sire, which of us shall inherit the throne?"The conqueror opened his eyes for the last time and murmured a decisive word: whoever is the strongest shall be the successor!