In short, there is nothing in the universe that astronomers can't find, as long as they are willing. So, it is even more incredible to remember why no one noticed that Pluto had moons before 1978. That summer, James Christie, a young astronomer at the U.S. Naval Observatory in Flagg, Arizona, was doing a routine inspection of Pluto's photos. Suddenly he found something there-something vague and uncertain, but it was definitely not Pluto. After a brief discussion with a colleague named Robert Harrington, he came to the conclusion that he was observing a satellite. This is not an ordinary satellite. Compared with that planet, it is the largest satellite in the solar system.
This is actually a blow to Pluto's planetary status, which has never been stable. At first, it was thought that this satellite occupied the same space as Pluto. This means that Pluto is much smaller than anyone thought-smaller than Mercury. In fact, the seven satellites of the solar system, including our own, are bigger than Pluto's satellites.
At this time, you will naturally ask why it took so long to find a satellite in our own solar system. The answer is: it has something to do with where astronomers aim their instruments and what instruments are designed to detect, and it has something to do with Pluto itself. The most important thing is where they aim the instrument. In the words of astronomer Clark Chapman: "Most people think that astronomers go to the observatory to scan the sky at night. This is not true. Almost all telescopes in the world are for observing tiny things in the distant sky, observing a quasar, or looking for a black hole, or observing a distant galaxy. The only telescope network that is really used to scan the sky is designed and manufactured by the military. "
Influenced by the artist's artistic expression, we think that the definition of the image is very high, which actually does not exist in astronomy. In Christie's photo, Pluto is dim and very vague-just a cosmic velvet flower-and its satellite is not like the sphere you will see in National Geographic magazine: the background is bright, very romantic, with clear lines, accompanied by Pluto; It's just a small, extremely vague lump. In fact, it is precisely because of this ambiguity that it took seven years for people to see this satellite again, thus confirming its independent existence.
The beauty of Christie's discovery is that it happened in Staffordshire, Frug, and Pluto was first discovered in 1930. This great discovery in astronomy is mainly attributed to astronomer percival Lowell. Lowell was born in one of the oldest and richest families in Boston (that is, the family mentioned in the famous song about Boston being the hometown of beans and cod). The lyrics say that the Lowell family only talks to the cabot family, and the cabot family only talks to God. He donated a famous observatory named after him, but people will never forget his view that Mars is full of canals built by hardworking Martians to store polar water and irrigate dry and fertile land near the equator.
Another unforgettable view of Lowell is that somewhere far from Neptune, there is an undiscovered ninth planet, which he named Planet X. Lowell's view is based on the irregularities he found in the orbits of Uranus and Neptune. So he devoted himself to finding this gas giant in the last few years of his life. He concluded that it was there. Unfortunately, he died suddenly on 19 16. At least to some extent, this is caused by his fatigue in exploration work. Lowell's heirs quarreled over the inheritance, and the exploration work was put on hold for the time being. However, in 1929, to some extent, in order to divert people's attention from the legend of the Mars Canal (by that time, it had become a very embarrassing thing), the head of Lowell Observatory decided to resume exploration and invited a young man named clyde tombaugh from Kansas for this purpose.
Tombo has no special training to be an astronomer, but he is diligent and clever. After a year of searching, he finally saw a dim light spot in the bright sky: Pluto. This is a miraculous discovery. What is more striking about this discovery is that it proves that Lowell's observations are wrong, although it is understandable that Lowell predicted the existence of a planet far from Neptune based on these observations. Tombaugh immediately realized that the new planet was not a huge balloon at all as Lowell thought-but any reservations he or others had about the nature of the new planet were quickly swept away in great excitement. In that excitable era, almost any major news will arouse this emotion. This is the first planet discovered by Americans. Some people think that it is actually just an ice particle in the distance, but no one will be distracted by this view. It is named Pluto, at least in part because its first two letters are interwoven with Lowell's initials. Lowell, who is no longer alive, is praised as a first-class genius everywhere, while Tobo has been basically forgotten by people, except for astronomers who study planets, who often have reverence for him.
Now, some astronomers continue to think that besides Pluto, there may be planet X, a real monster, perhaps 10 times that of Jupiter, but it is too far away for us to see. It gets too little sunlight and hardly reflects light. They don't think it will be an ordinary planet like Jupiter or Saturn-it's too far away to be like that; We speculate that it may be 7.2 trillion kilometers away-more like an unformed sun. Most star systems in the universe are in pairs, which makes our lonely sun look a bit strange.
As for Pluto itself, no one knows how big it is, what it is made of, what kind of atmosphere it has, or even what it is. Many astronomers believe that it is not a real planet, but only the largest celestial body (called Kepler belt) we found in the ruins of the Milky Way. Kepler belt theory was actually put forward by an astronomer named F.G. Leonard in 1930. He used this name to commemorate Gerald Cherpel, a Dutchman who worked in the United States. Cape developed this theory. The Keppel Belt is the source of so-called short-lived comets-the kind of stars that often flash by-the most famous of which is Halley's Comet. Longer-lived comets (including the recently visited comets of comet hale-bopp and Wu Bai) originated from Oort Cloud, which we will talk about later.
Pluto behaves quite differently from other planets, and this view is certainly correct. It is not only small and vague, but also changeable in its operation mode. No one can say where Pluto will be in a century. Other planets rotate more or less in the same plane, and Pluto's orbit is inclined, not in the same plane with other planets, but forms an angle of 17 degrees, just like someone wearing a hat on his head. Its orbit is very irregular, and in the process of its solitary rotation around the sun, each circle is closer to us than Neptune for a long time. In fact, Neptune was actually the farthest planet in the solar system for most of the 1980s and 1990s. Pluto returned to outer orbit on1February, 999 1 1 day, and will stay there for 228 years.
So, if Pluto is really a planet, it must be a very strange planet. It is very small, only 400 times as big as the earth. If it covers the United States, it is less than half of the 48 States in the United States. This alone makes it extremely abnormal, which shows that our planetary system is composed of four rocky inner planets, four gaseous outer planets and 1 lonely little ice hockey. Besides, we have every reason to believe that we will soon find other bigger hockey balls in the same space. Then, the problem came again. After Christie discovered Pluto's moon, astronomers began to observe this part of the universe more carefully. By the beginning of February 2002, more than 600 such objects had been found outside Uranus, one of which was named varuna, which was almost as big as Pluto's moon. Astronomers now think there may be billions of such objects. The hard part is that many of them are dull. Generally speaking, their reflectivity is only 4%, which is about equivalent to the reflectivity of a piece of charcoal-of course, these "charcoal" are more than 6 billion kilometers away.
How far is it? Almost unimaginable. You see, space is huge-it's huge. For the purpose of understanding and entertainment, let's imagine that we are going to travel by rocket plane. We won't go too far-only to the edge of our own solar system-but we must first understand how big the space is and how small the part we occupy.
Gee, I'm afraid it's bad news. We can't go home for dinner. Even at the speed of light (300,000 kilometers per second), it takes seven hours to reach Pluto. Besides, we certainly can't travel at this speed. We must move at the speed of a spaceship. This speed is very slow. The highest speed that any man-made object can reach is the speed of "Voyager 1" and "Voyager 2" spacecraft, which are now flying away from us at a speed of 56,000 kilometers per hour.
At that time (August and September of 1977), the Voyager spacecraft was launched because Jupiter, Saturn, Uranus and Neptune were in a straight line, which only happened once every 175 years. This enables the two Voyager spacecraft to be continuously thrown from one gas giant to the next in the form of cosmic whip by using the technology of "gravity help". Even so, it will take them nine years to reach Uranus and 12 years to cross Pluto's orbit. The good news is that if we wait until June 5438+ 10, 2006 (this is the time when NASA tentatively launches the "New Horizon" spacecraft to Pluto), we can use the favorable Jupiter positioning method and some advanced technologies, and it will only take about 10 years to get there-although it will take a long time to go home again. Anyway, it's a long trip.
You may first realize that the name space is extremely appropriate, and space is an inconspicuous place. Our solar system is the most active in the range of trillions of kilometers, and all visible things-the sun, planets and their satellites, hundreds of millions of rolling rocks, comets and other floating rubble in the asteroid belt-are only one trillion times less than the existing space. You soon realize that the map of the solar system you see is not drawn to scale at all. In most pictures in the classroom, the planets are close to each other-in many illustrations, the shadows of the outer superstars actually fall on each other-but this deception is also necessary in order to draw all the planets on the same paper. Neptune is actually not a little outside Saturn, but far away from Saturn-it is five times as far away from Saturn as Saturn is from us. It is too far away from Saturn and can only receive 3% of Saturn's sunlight.
In fact, the distance is so far that it is impossible to draw a map of the solar system to scale in any case. Even if you add a lot of folded pages to your textbook or use extremely long slogan paper, you can't get close to this ratio. On a scale map of the solar system, if the diameter of the earth is reduced to the diameter of a bean, Saturn is more than 300 meters away and Pluto is 2.5 kilometers away (about the size of a bacterium, so it can't be seen). According to the same proportion, the nearest star proxima centauri will be 1.6 million kilometers away. Even if you reduce everything to Saturn, Pluto is no bigger than a molecule, so Pluto is still above 10 meter.
So, the solar system is really big. By the time we reached Pluto, we had come so far, and the sun-our dear sun, which is warm, tanned and gives us life-has shrunk to the size of a needle tip. It is not much bigger than a bright star. In this empty space, you will begin to understand why even the most important celestial bodies, such as Pluto's moons, have escaped people's attention. In this respect, Pluto is by no means unique. Before Voyager's expedition, it was thought that Neptune had only two satellites, and Voyager discovered six more. When I was young, people thought that there were only 30 satellites in the solar system. At present, the total number of satellites is at least 90, of which at least one third was discovered in the past 10 year. Of course, when considering the whole universe, you need to remember that we don't really know the home of our solar system yet.
Now, when we fly over Pluto, you will notice another thing: we are flying over Pluto. If you check the travel plan, you will understand that the destination of this trip is the edge of our solar system, and I'm afraid we haven't arrived yet. Pluto may be the last object on the classroom wall chart, but the solar system is more than that. Actually, it's still far from the finish line. To reach the edge of the solar system, we must pass through the Oort Cloud, which is the vast sky where comets float. And we-I'm sorry about that-need/kloc-0.0 million years to reach the Oort Cloud. Pluto is far from being a sign of the outer edge of the solar system. As casually suggested on the wall chart in the classroom, it is only a millionth of a mile away.
Of course, we are not going to make such a trip. It is still a great event for us to travel to the moon 386,000 kilometers away. President George H.W. Bush was delirious for a moment, and proposed to send a man to mission to mars, but it was later dropped. Some people estimate that it will cost 450 billion dollars, and it is likely that all the crew will die in the end (the high-energy solar particles can't be stopped and the DNA will be torn to pieces).
According to our current knowledge and rational imagination, no one will go to the edge of our solar system-never. It's too far. In fact, even with the Hubble telescope, we can't see the Oort cloud, so we actually don't know where it is. Its existence is possible, but it is completely hypothetical.
As for the Oort cloud, we can only confidently say that it starts from Pluto and extends into the universe for about two light years. The basic unit of measurement of the solar system is the astronomical unit (Au), which represents the average distance between the sun and the earth. Pluto is about 40 astronomical units away from us, and the center of Oort Cloud is about 50,000 astronomical units away. In short, it's far away.
However, let's assume again that we have reached the Oort Cloud. The first thing you notice is that it is very quiet here. Now, we are far away from anywhere-so far from our own sun, it is not even the brightest star in the sky. Think about it, it's incredible that the bright spot that keeps flashing in the distance is so small, but there is enough gravity to hold all these comets. This gravity is not very strong, so these comets just move slowly and grandly, with a speed of only about 354 kilometers per hour. Due to the subtle disturbance of gravity-perhaps due to a passing star-one of these lonely comets will be pushed out of its normal orbit from time to time. Sometimes, they are bounced back into a vacuum and never seen again. However, sometimes they orbit the sun for a long time. About three or four such comets, the so-called longevity comets, pass through the inner side of the solar system every year. These lost tourists only occasionally bump into hard things, such as the earth. That's why we are here now-because the comet we saw has just begun to experience a long process of falling to the center of the solar system. Among so many places, its direction is Manson, Iowa. It will take a long time to get there-at least three or four million years-so let's put it aside and discuss it at the end of this book.
This is your solar system. What else is there outside the solar system? Well, maybe nothing, maybe a lot, depending on how you look at the problem.
In the short term, nothing. The perfect vacuum created by human beings is not as empty as interstellar space. Before you reach the next "something", there are many such "empty". Our nearest neighbor in the universe is proxima centauri, which is part of a Samsung cloud called Alpha Star, 4.3 light years away. This is only a negligible time in galaxy language, but it is still 65438+ billion times farther than traveling to the moon. It will take at least 25,000 years to go there by spaceship. Even if you do make this trip, you still can't go anywhere. You will only see a cluster of lonely stars hanging in the middle of the vast space. There are still 4.6 light-years to reach the next meaningful landmark Sirius. So, if you want to cross the universe by "crossing the stars", it will be like this. Even if we reach the center of our own galaxy, it will be much longer than our existence as human beings.
I repeat, there is plenty of room. The average distance between stars is more than 30 trillion kilometers. Even if you go there at a speed close to the speed of light, it is a very challenging distance for any individual who wants to travel. Of course, for fun, aliens may travel billions of kilometers to grow crops in Wiltshire, or go to a deserted road in Arizona to scare the shit out of some poor guys driving pickup trucks, but this kind of thing never seems to happen.
But from the statistical point of view, there is still a great possibility that there are thinking creatures in outer space. No one knows how many stars there are in the Milky Way-it is estimated that there are100 billion to 400 billion-and the Milky Way is only one of about140 billion galaxies, many of which are bigger than our own. In the 1960s, Frank Derrick, a professor at Cornell University, was excited about such a huge number. Based on a series of reduced probabilities, he came up with a famous equation to calculate the possibility of advanced life in the universe.
According to Drake equation, you divide the number of stars in a certain part of the universe by the number of stars that may exist in planetary systems; Then divide that quotient by the coefficient of theoretically possible life planets; Then divide this quotient by the planetary coefficient, which indicates that life has appeared and evolved into an intelligent state; And so on. Every time this division, the number is greatly reduced-however, even according to the most conservative input, only in the Milky Way, the number of advanced civilized societies is always millions.
How interesting and exciting this view is. We may be just one of millions of advanced civilized societies. Unfortunately, the space is vast. It is estimated that the average distance between any two civilized societies is at least 200 light years. In order to give you a clear idea, it is not enough to say so, but more explanations are needed. First of all, it means that even if those creatures know that we are here and can see us through telescopes, they will only see the light that left the earth 200 years ago. So, what they see is not you and me. What they saw was the French Revolution, Thomas Jefferson and people wearing stockings and wigs-people who didn't know what atoms and genes were, and people who rubbed a piece of fur against an amber stick to generate electricity and thought it was fun. We received telegrams from these observers, probably beginning with "Dear Adults", congratulating us on leading a good horse and skillfully using whale oil. 200 light years is such a long distance that we can hardly imagine.
So, even if we are not lonely, we are still lonely. Carl sagan calculated that there may be as many as 100 trillion planets in the universe-a number far beyond our imagination. However, what is also beyond our imagination is their scattered universe. "If we are randomly stuffed into the universe," Sagan wrote, "the probability that you are on or near a planet is less than one in a billion (that is, 10-33). The world is very precious. "
So, this may be good news:1In February, 999, the International Astronomical Union officially ruled that Pluto is a planet. The universe is a huge and lonely place. We need as many neighbors as possible.