So he devoted the last few years of his life to finding the gas giant. He concluded it was there. Unfortunately, he died suddenly in 1916. At least in part, this was due to fatigue from his exploratio

So he devoted the last few years of his life to finding the gas giant. He concluded it was there. Unfortunately, he died suddenly in 1916. At least in part, this was due to fatigue from his explorations. The exploration was temporarily put on hold as Lowell's heirs quarreled over the inheritance. However, in 1929, partly to divert attention from the legend of the Martian canals (which by that time had become a huge embarrassment), the director of the Lowell Observatory decided to resume exploration and create a A young man named Clyde Tombaugh was brought in from Kansas. Tombaugh was not specifically trained to be an astronomer, but he was both diligent and smart. After a year of searching, he finally saw a dim point of light in the bright sky: Pluto. This is a miraculous discovery. What's more striking about this discovery is that it proves that Lowell's observations, which he had relied on to predict the existence of a planet beyond Neptune, were wrong, albeit understandably so. Tombaugh immediately realized that the new planet was not at all a giant balloon as Lowell had assumed - but any reservations he or others had about the nature of the new planet were lost in the excitement. Quickly swept away. In those excitable times, just about any major news story would stir up such emotions. 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 was named Pluto, at least in part, because its first two letters were a monogram of Lowell's initials. Lowell, who is no longer alive, is everywhere lauded as a genius of the first order, while Tombaugh has been largely forgotten, except among planetary astronomers, who tend to hold him in reverence. Affection.

Now, some astronomers continue to believe that there may be Planet (It gets so little sunlight that it reflects almost nothing.) They think it can't be an ordinary planet like Jupiter or Saturn—it's too far away to be that way; we speculate that there might be 72,000 Billions of kilometers away - and more like an unformed sun. Most star systems in the universe are in pairs (binary stars), which makes our single sun look a bit strange.

As for Pluto itself, no one knows exactly 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 really a planet, but just the largest object we have found in the ruins of the Milky Way known as the Kuiper Belt. The Kuiper belt theory was actually proposed in 1930 by an astronomer named F.G. Leonard, who used the name to commemorate Gerard Kuiper, a Dutchman working in the United States. Kuyper developed this theory. The Kuiper Belt is the source of so-called short-lived comets - stars that often flash by - the most famous of which is Halley's Comet. The longer-lived comets (among them the recently visited comets Hale-Bopp and Hyakutake) originate in the much more distant Oort cloud, as we will return to in a moment.

It is certainly true that Pluto behaves very differently from other planets. Not only is it small and fuzzy, but its motions are so variable that no one can tell where Pluto will be a century from now. The other planets rotate more or less on the same plane, but Pluto's orbit (seems to be) tilted. It is not on the same plane as the other planets, but forms an angle of 17 degrees, like someone wearing a hat on his head in a smart way. . Its orbit is very irregular, and during its lonely rotation around the sun, it is closer to us than Neptune for a considerable period of time each time it orbits. In fact, for much of the 1980s and 1990s, Neptune was actually the farthest planet in the solar system. It was only on February 11, 1999, that Pluto returned to its outer orbit, where it would stay for 228 years.

So, if Pluto is really a planet, it must be a weird one. It is very small, only four hundredth the size of Earth. If you put it over the United States, it would not cover half of the lower 48 states. This alone makes it appear extremely abnormal, indicating that our planetary system is composed of 4 rocky inner planets, 4 gaseous outer planets and 1 lonely small ice ball. And there's every reason to think we'll soon find other, larger pucks in the same space. Then, the problem came again. After Christie's discovery of Pluto's satellites, astronomers began to observe this part of the universe more carefully. As of early December 2002, more than 600 such objects had been discovered beyond Uranus, one of which was named Varuna. About the same size as Pluto's moons. Astronomers now believe there may be billions of such objects. The difficulty is that many of them are lackluster. Generally speaking, their reflectivity is only 4, which is about the same as the reflectivity of a piece of charcoal - of course, these "charcoal" are more than 6 billion kilometers away.

How far is it? It's almost unimaginable. You see, the space is huge—just huge. For the sake of understanding and entertainment, let's imagine that we are about to travel in a rocket vehicle. We won't go very far - just to the edge of our own solar system - but first we need to understand what a huge place space is and what a small part we occupy.

Oh, I'm afraid that's bad news, we can't go home for dinner. Even traveling at the speed of light (300,000 kilometers per second), it would take 7 hours to reach Pluto. And, of course, we can't travel at this speed. We had to go at spaceship speed. This speed is very slow. The highest speed any man-made object can achieve is the speed of the Voyager 1 and 2 spacecraft, which are currently flying away from us at 56,000 kilometers per hour.

The reason why the "Voyager" spacecraft was launched at that time (August and September 1977) was because Jupiter, Saturn, Uranus and Neptune were aligned in a straight line. This phenomenon only occurs every 175 years. Happens once. This allows the two Voyager spacecraft to use "gravitational assistance" technology to be continuously thrown from one gas giant to the next in a form of cosmic whiplash. Even then, it would take them nine years to reach Uranus and 12 years to cross Pluto's orbit. The good news is that if we wait until January 2006 (which is when NASA tentatively launches the New Horizons spacecraft to Pluto), we can take advantage of favorable Jupiter positioning methods, plus some With advanced technology, it will only take about 10 years to get there - although it may take quite a while to get back home again. Anyway, it was a long trip.

You may first realize that the name space is extremely appropriate. Space is an ordinary place. Within trillions of kilometers, the most vibrant thing is our solar system, and all that can be seen—the sun, the planets and their moons, the billions of tumbling rocks in the asteroid belt, comets, and other All kinds of floating rubble - filling only one trillionth of the existing space. You also quickly realize that the diagram of the solar system you see is not at all to scale. In most of the drawings in the classroom, the planets are close to each other—in many illustrations, the shadows of the outer giant stars actually fall on each other—but in order to draw all the planets on the same On paper, this kind of deception is also essential. Neptune is actually not a little beyond Saturn, but a long way beyond Saturn - it is five times further away from Saturn than Saturn is from us. It is so far outside that it receives only 3 times as much sunlight as Saturn.

In fact, the distances are so vast that it is impossible to draw a diagram of the solar system to scale. Even if you add lots and lots of foldouts to your textbook, or use ridiculously long slogan paper, you can't get close to this ratio.

On a scaled diagram of the solar system, if the diameter of the Earth were reduced to about the diameter of a bean, Saturn would be more than 300 meters away and Pluto would be 2.5 kilometers away (about the size of a bacterium, so You can't see it). Using the same proportions, Proxima Centauri, the closest star to us, would be 16,000 kilometers away. Even if you shrink everything so that Saturn is as small as an English period and Pluto is no larger than a molecule, Pluto is still more than 10 meters away.

So, the solar system is indeed huge. By the time we reach Pluto, we have traveled so far that the sun—our dear sun that warms us, tans our skin, and gives us life—has shrunk to the size of a pinhead. It is not much larger than a bright star. In such a deserted space, you begin to understand why even the most important objects - like Pluto's moons - escape attention. It's not just Pluto in this regard. Before the Voyager expedition, people thought that Neptune had only two satellites, and Voyager discovered 6 more. When I was a kid, people thought the solar system only had 30 moons. The total number of satellites now reaches at least 90, at least one-third of which were discovered in the past 10 years. When thinking about the universe as a whole, you certainly need to remember that we don't actually know the origins of our solar system yet.

Now, as we fly by Pluto, you'll notice something else: we're flying by Pluto. If you check the travel plans, you'll realize that the destination of this trip is the edge of our solar system, and I'm afraid we haven't reached it yet. Pluto may be the last object marked on the classroom wall chart, but the solar system doesn't end there. In fact, we are still far from the end. To reach the edge of the solar system, we have to pass through the Oort cloud, a vast sky filled with comets. And it will take us - and I feel bad about this - another 10,000 years to reach the Oort Cloud. Far from marking the outer reaches of the solar system, Pluto is only one fifty-thousandth of a million times away, as the classroom flip chart casually suggested.

Of course, we had no intention of going on such a trip. Traveling to the moon 386,000 kilometers away is still a great event for us. President Bush Sr. was temporarily confused and proposed to carry out a manned mission to Mars, but later fell through. Some estimate that this will cost US$450 billion, and it is likely that all crew members will die in the end (they will not be able to block high-energy solar particles, and their DNA will be torn to pieces).

Based on our current knowledge and sane imagination, no one will ever travel to the edge of our own solar system—ever. It's just too far away. In fact, even with Hubble, we can't see the Oort cloud, so we don't actually know it's there. Its existence is possible but entirely hypothetical.

This is all that can be said with certainty about the Oort Cloud: It begins beyond Pluto and stretches about two light-years into the universe. The basic unit of measurement in the solar system is the astronomical unit (Au), which represents the average distance between the sun and the earth. Pluto is about 40 AU from us, and the center of the Oort cloud is about 50,000 AU. In a word, it's very remote.

But let’s make another assumption: we have reached the Oort cloud. The first thing you notice is how peaceful it is. Now, we're very far away from anywhere - so far away from our own sun that it's not even the brightest star in the sky. It's incredible to think about how tiny that flickering bright spot in the distance is, yet it has enough gravity to drag down all these comets. This gravitational pull is not very strong, so these comets just move spectacularly slowly, at only about 354 kilometers per hour. From time to time one of these lonely comets is pushed out of its normal orbit due to subtle perturbations of gravity - perhaps from a passing star. Sometimes they are flicked into empty space, never to be seen again. However, sometimes they enter long orbits around the sun.

About three or four of these comets, so-called long-lived comets, pass sideways through the solar system every year. These lost visitors just happen to bump into something solid, like the Earth. That's why we're here now - because the comet we're seeing has just begun its long descent toward the center of the solar system. Among so many places, it's heading to Manson, Iowa. It would have taken a long time to get there—at least three to four million years—so we'll leave that aside and come back to it toward the end of the book.

This is your solar system. What else is there beyond the solar system? Heck, maybe nothing, maybe a lot, depending on how you look at the question.

In the short term, there is nothing. The most perfect vacuum created by humans is not as empty as interstellar space. There's a lot of "emptiness" there, until you get to the next "something." Our nearest neighbor in the universe is Proxima Centauri, which is part of the three-star cloud called Alpha. It is located 4.3 light-years away. This is only an insignificant amount of time in galaxy parlance, but it is still farther than traveling to the moon. 100 million times. It would take at least 25,000 years to go there by spaceship; even if you really make this trip, you still won't get anywhere, you will only see a cluster of lonely stars hanging in the middle of the vast space. To reach the next meaningful landmark, Sirius, there are still 4.6 light-years to travel. So, this is what would happen if you wanted to travel across the universe in an interstellar way. Even reaching the center of our own galaxy will take far longer than our human existence.

I repeat, space is huge. The average distance between stars exceeds 30 trillion kilometers. Even going there at close to the speed of light would be an extremely challenging distance for any individual wanting to travel. Of course, just for fun, aliens could travel billions of kilometers to plant crops in Wiltshire, or scare the hell out of some poor guy in a moving pickup truck on some deserted road in Arizona. , but that never seems to happen.

However, from a statistical perspective, it is still very likely that there are thinking creatures in outer space. No one knows how many stars there are in the Milky Way—estimates range from 100 billion to 400 billion—and the Milky Way is just one of about 140 billion galaxies, many of which are larger than our own. In the 1960s, a professor at Cornell University named Frank Drake was excited by such huge numbers and came up with a famous equation based on a series of shrinking probabilities, designed to calculate the number of times in the universe. The possibility of advanced life exists.

According to Drake's equation, you divide the number of stars in a certain part of the universe by the number of stars that may have planetary systems; then divide that quotient by the coefficient of planets that can theoretically support life; then use That quotient is divided by the coefficient of planets where life has emerged and life has been elevated to an intelligent state; and so on. With each such division, that number shrinks significantly - yet even with the most conservative inputs, the number of advanced civilizations in the Milky Way alone is always in the millions.

What an interesting and exciting view. We may be just one of millions of highly civilized societies. Unfortunately, space is vast, and it has been calculated 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 just say this. More explanations are needed. First, this means that even if those creatures know we are here and can see us through telescopes, all they are seeing is light that left Earth 200 years ago. So what they see is not you and me. What they saw was the French Revolution, Thomas Jefferson, and people in stockings and wigs—people who had no idea what atoms were or what genes were, rubbing a piece of fur against an amber rod to generate electricity and thinking it was fun. people. We receive cables from these observers, most likely beginning with "Dear Sir," congratulating us on our horses and our skill in using whale oil.

200 light years is so far away that we can hardly imagine it.

So even though we are not actually alone, we are actually quite alone. Carl Sagan calculated that there may be as many as 100 trillion planets in the universe - a number far beyond our imagination. But equally beyond our imagination is the scope of the universe in which they are scattered. “If we were randomly stuffed into the universe,” Sagan wrote, “the chances of you being on or near a planet would be less than one in a billion, billion, billion, or 10-33. The world is precious ”

So this may be good news: In February 1999, the International Astronomical Union officially ruled that Pluto is a planet. The universe is a big, lonely place. We have as many neighbors as we can have.