Chapter 4 Chapter 2 Welcome to the Solar System

Today, astronomers can do the most amazing things.If someone strikes a match on the moon, they can see the flame.From the slightest pulsation and quiver of distant stars, they can deduce the size and properties, even the potential habitability, of planets that are too far away to be seen -- so far away that we It would also take 2.5 million years to get there by spaceship.They can pick up a tiny bit of radiation with radio telescopes, and this radiation is so faint that since the beginning of collecting (1951), all the energy from outside the solar system has been collected, in the words of Carl Sagan: " Less than the energy produced by a snowflake falling to the ground."

In short, there isn't much in the universe that astronomers can't discover if they want to.So it's all the more unusual to think about why no one had noticed that Pluto had a moon until 1978.That summer at the U.S. Naval Observatory in Flagstaff, Arizona, a young astronomer named James Christie was doing a routine review of photographs of Pluto when he noticed something there—a blurry, Not so sure, it's definitely not Pluto anyway.After a few moments of discussion with a colleague named Robert Harrington, he concluded that what he had observed was a satellite.It's no ordinary satellite.Relative to that planet, it is the largest moon in the solar system.

This was actually a blow to Pluto's planetary status, which was never secure.It was originally thought that the satellite occupied the same space as Pluto.This means that Pluto is much smaller than anyone thought -- even smaller than Mercury.In fact, all seven moons in the solar system, including our own, are larger than those of Pluto. At this point, you naturally ask why it took so long to discover a moon in our own solar system.The answer: It has to do with where astronomers point their instruments, what their instruments are designed to detect, and it has to do with Pluto itself.What matters most is where they point their instruments.In the words of astronomer Clark Chapman: "Most people think that astronomers go to observatories at night to scan the sky. This is not true. Almost all telescopes in the world are designed to observe very small things in the distant sky , observe a quasar, or look for a black hole, or observe a distant galaxy. The only networks of telescopes that actually scan the sky are designed and built by the military."

We are under the bad influence of the artist's artistic expression, thinking that the clarity of the image is very high, which does not exist in astronomy.In Christie's photo, Pluto is dark and very blurry - just a cosmic velvet - and its moons aren't the kind of spheres you'd see in National Geographic: the background is bright and very romantic , with clear lines, accompanying Pluto; but just a small, extremely vague blob.In fact, it was because of this ambiguity that it took 7 years to see the satellite again and confirm its independent existence. There's a twist to Christie's discovery: It happened in Flagstaff, where Pluto was first discovered in 1930.This major discovery in astronomy is largely due to the astronomer Percival Lowell.Lowell was born into one of the oldest and wealthiest families in Boston (the same family mentioned in the famous ballad about Boston being the home of beans and cod. The Lowells, it says, only spoke to the Cabots, The Cabots only talk to God).He donated the famous observatory bearing his name, but what people will never forget is his view that Mars is full of canals built by industrious Martians to store water from the poles for irrigation. The dry but productive land near the equator.

Another haunting observation of Lowell's was that somewhere beyond Neptune, there existed an undiscovered ninth planet, which he named Planet X.Lowell based this view on irregularities he discovered in the orbits of Uranus and Neptune.So he devoted the last few years of his life to finding the gas giant.He decided it was there. Unfortunately, he died suddenly in 1916.At least in part, this is due to the exhaustion of his exploration work.As Lowell's heirs squabbled over his inheritance, the exploration was temporarily put on hold.In 1929, however, in part to deflect attention from the legend of the Martian canals (which had become quite an embarrassment by that time), the head of the Lowell Observatory decided to resume exploration, and to So a young man named Clyde Tombaugh was invited from Kansas.

Tombaugh had no special training to be an astronomer, but he was hardworking and smart.After a year of searching, he finally spotted a faint point of light in the bright sky: Pluto.It was a miraculous discovery.What's even more remarkable about this finding is that it disproves Lowell's observations.Although understandable, Lowell had used these observations to predict the existence of a planet beyond Neptune.Tombaugh realized right away that the new planet was not at all the giant balloon that Lowell had expected--but any reservations he or others might have about the nature of the new planet were quickly overwhelmed by the overwhelming excitement. It's gone in no time.In that excitable age, almost any major news story stirred that emotion.It was the first planet discovered by Americans.Some people think it is really just a distant ice grain, but no one will be distracted by this idea.It was named Pluto, at least in part because its first two letters are a monogram of Lowell's initials.Lowell, now dead, is everywhere celebrated as a man of first-rate genius, while Tombaugh is largely forgotten, except among planetary astronomers, who tend to hold him in high esteem. Affection.

Now, some astronomers continue to think that beyond Pluto there may be Planet X—a real behemoth, perhaps 10 times the size of Jupiter, but it's too far away for us to see. (It receives so little sunlight that it reflects almost no light.) They don't think it's an ordinary planet like Jupiter or Saturn -- it's too far away to be that way; we figure maybe 72,000 billions of kilometers away—and more like an unformed sun.Most stellar systems in the universe come in pairs (binary stars), which makes our solitary sun seem a bit odd. As for Pluto itself, no one really knows how big it is, what it is made of, what kind of atmosphere it has, or even what it is.Many astronomers believe it's not really a planet, but just the largest object we've ever found in a belt of ruins in the Milky Way, known as the Kuiper Belt.The Kepper belt theory was actually proposed in 1930 by an astronomer named FG Leonard, who used the name in honor of Gerard Kepper, a Dutchman who worked in the United States.Kepper developed this theory.The Kuiper Belt is a source of so-called short-lived comets -- the kind of stars that often fly by -- the most famous of which is Halley's Comet.Longer-lived comets (among them the recent comets Hale-Bopp and Hyakutake) originate in the much more distant Oort cloud, as we'll get to in a moment.

Pluto behaves very differently from the other planets, and it's certainly true.Not only is it small and fuzzy, but the way it moves is so volatile that no one can tell where Pluto will be a century from now.The other planets rotate more or less on the same plane, while the orbit of Pluto (seems to be) is inclined, not in the same plane as the other planets, but forming an angle of 17 degrees, as if someone is wearing a hat on his head chicly .Its orbit is quite irregular, and during each of its lonely circles around the sun, it is closer to us than Neptune for a considerable amount of time.In fact, for most of the 1980s and 1990s, Neptune was the most distant planet in our solar system.It was only on February 11, 1999 that Pluto returned to its outer orbit, where it will remain for 228 years.

So if Pluto is a planet, it must be a weird one.It is very small, only four hundredth the size of the earth.If you put it on the United States, it can't cover half of the 48 states of the continental United States.That alone makes it extremely anomalous, suggesting that our planetary system is made up of 4 solid inner planets, 4 gaseous outer planets, and 1 lonely little ice ball.Then, the problem came again.After Christie discovered Pluto's satellite, astronomers began to observe this part of the universe more carefully. As of the beginning of December 2002, more than 600 objects were discovered outside Uranus, and one of them was named Varuna, which is almost the same as Pluto's moons are about the same size.Astronomers now think there may be billions of these objects.The difficulty is that many of them are dim.Generally speaking, their reflectivity is only 4%, which is about the same as that of a piece of charcoal-of course, these "charcoals" are more than 6 billion kilometers away.

How far is this?Almost unimaginable.You see, the space is incredibly large--impossibly large.For the sake of information and entertainment, let's imagine that we are about to travel in a rocket vehicle.We won't go very far -- only to the edge of our own solar system -- but first we need to understand: what a big place space is, and what a small part of it we occupy. Oops, I'm afraid it's bad news, we won't be home for dinner.Even traveling at the speed of light (300,000 kilometers per second), it would take seven hours to reach Pluto.And, of course, we can't travel at that speed.We had to go at the speed of a spaceship.This speed is very slow.The highest speed any human-made object can achieve is the speed of the Voyager 1 and Voyager 2 spacecraft, which are now flying away from us at 56,000 kilometers per hour.

The Voyager spacecraft were launched back then (August and September 1977) because Jupiter, Saturn, Uranus, and Neptune were aligned, a phenomenon that only happens every 175 years.This allows the two Voyager spacecraft to be continuously flung from one gas giant to the next, in a kind of cosmic whiplash, using "gravitational assistance" technology.Even then, they would take nine years to reach Uranus and 12 years to cross the orbit of Pluto.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 the favorable positioning of Jupiter, plus some Advanced technology, only 10 years or so to get there - although it may take quite a while to get back home again. Anyway, it's been a long trip. You may first realize that the space is a very aptly named space, that space is an unremarkable place.Within a few trillion kilometers, the most living thing is our solar system, and everything in sight—the sun, the planets and their moons, the billions of tumbling rocks in the asteroid belt, comets and others All sorts of floating rubble - just filling less than a trillionth of the existing space.You also quickly realize that the diagrams of the solar system you see are not made to scale at all.On most diagrams in the classroom, the planets are side by side, very close together—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 deception is also essential.Neptune is actually not a little bit beyond Saturn, but a very long way beyond Saturn - it is five times farther away from Saturn than Saturn is from us.It's so far out there that it receives only 3 percent as much sunlight as Saturn. In fact, the distances are so great that it is in any case impossible to draw a map of the solar system to scale.Even if you add tons and tons of folded pages to your textbook, or use ridiculously long banner paper, you won't be able to get close to this ratio.On a scaled solar system map, if the Earth were reduced to about the diameter of a bean, Saturn would be over 300 meters away, and Pluto would be 2.5 kilometers away (about the size of a bacterium, so You can't see it anyway).On the same scale, our closest star, Proxima Centauri, would be 16,000 kilometers away.Even if you zoomed everything out so that Saturn would be as small as a period in English and Pluto would be no bigger than a molecule, then Pluto would still be more than 10 meters away. So, the solar system is indeed huge.By the time we reach Pluto, we've come so far that the sun -- our dear sun that warms, tans and gives us life -- has shrunk to the size of a pinhead.It's not much bigger 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 by no means just Pluto in this regard.Before the "Voyager" expedition, people thought that Neptune had only two satellites, and the "Voyager" discovered 6 more.When I was a kid, people thought there were only 30 moons in the solar system.The total number of satellites is now at least 60, at least one-third of which were discovered in the past 10 years.When considering the universe as a whole, you certainly need to remember that we don't really know what our solar system is made of. Now, when we fly by Pluto, you'll notice another thing: We're flying by Pluto.If you look up travel plans, you'll understand that the destination of this trip is the edge of our solar system, which we're afraid we haven't reached yet.Pluto may be the last object to be put on the classroom wall chart, but the solar system doesn't end there.In fact, it is still far from the end.To reach the edge of the solar system, we have to pass through the Oort Cloud, a vast expanse of sky where comets roam.And we -- and I'm sorry for that -- will take another 10,000 years to get to the Oort Cloud.Far from being a marker of the outer reaches of the solar system, Pluto is only 1/50,000th of a way away, as casually suggested on the flipchart in the classroom. Of course, we had no intention of making such a trip.To make a 386,000-kilometer trip to the moon is still a big deal for us.President Bush Sr. once lost his head and proposed to carry out a manned mission to Mars, but it was never done.By some estimates, it would cost $450 billion, and would most likely end with the death of the entire crew (they couldn't shield the high-energy solar particles, and their DNA would be torn to shreds). Based on our current knowledge and sane imagination, there is absolutely no way for anyone to travel to the edge of our own solar system -- ever.It's just too far away.In fact, we can't see the Oort Cloud even with Hubble, so we don't actually know where it is.Its existence is possible, but entirely hypothetical. 1 There is only so much that can be said with certainty about the Oort Cloud: It begins beyond Pluto and extends 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 is very far away. But let's assume again: we've reached the Oort Cloud.The first thing you notice is how peaceful it is.Right now, we're so far away from anywhere—so far away from our own sun that it's not even the brightest star in the sky.When you think about it, it's incredible how tiny that twinkling point of light in the distance has enough gravitational pull to hold all these comets.This gravitational pull isn't very strong, so the comets move spectacularly slowly, at about 354 kilometers per hour.From time to time, one of these solitary comets is thrown out of its normal orbit due to a slight perturbation in gravity—perhaps due to a passing star.Sometimes, they're bounced 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 each year.These stray visitors only occasionally 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, its direction is Munson, Iowa.It's going to take a long time to get there—at least three or four million years—so we'll set that aside for a while until the end of the book. This is your solar system.What else is beyond our solar system?Heck, maybe nothing, maybe a lot, depending on how you look at the question. In the short term, nothing.The most perfect vacuum created by humans is not as empty as interstellar space. There's a lot of this "emptiness" out there until you get to the next "something".Our closest neighbor in the universe is Proxima Centauri, part of that three-star cloud called Alpha, located 4.3 light-years away, which is an insignificant amount of time in galactic parlance, but still farther than traveling to the moon 100 million times.To go there by spaceship will cost at least 25 000 years; even if you do take this trip, you still won't get anywhere, only a cluster of lonely stars hanging in the middle of the vast space.To reach the next significant landmark, Sirius, there is still 4.6 light-years to go.So this is what would be the case if you wanted to travel across the universe "by the stars".Even reaching the center of our own galaxy would take far longer than our human existence. I repeat again, the space is huge.The average distance between stars is more than 30 trillion kilometers.Even going there at the speed of light is an extremely challenging distance for any individual thinking of traveling.Of course, for fun, aliens could potentially travel billions of kilometers to plant crops in Wiltshire, or some poorly traveled road in Arizona, and scare some poor soul out of a moving pick-up truck Fly was terrified, but it never seemed like that would happen. Still, from a statistical point of view, the likelihood of sentient beings in outer space remains high.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 only about 1 One of 40 billion galaxies, many others larger than our Milky Way. In the 1960s, a professor at Cornell University named Frank Drake, excited by such gigantic numbers, came up with a famous equation designed to calculate the universe in terms of a series of ever-shrinking possibilities The possibility of advanced life in existence. According to Drake's equation, you divide the number of stars in a certain part of the universe by the number of planetary systems that stars may have; divide that quotient by the number of planets that could theoretically host life; divide that quotient by the number of planets that have already appeared , and planetary coefficients of life raised to an intelligent state; and so on.Each such division shrinks that number considerably -- yet even with the most conservative inputs, the number of advanced civilizations in the Milky Way alone is always in the millions. How interesting and exciting this view is.We may be only one of millions of advanced civilized societies. Unfortunately, space is vast. According to calculations, the average distance between any two civilizations is at least 200 light-years.In order to give you a clear idea, it is not enough to just say this, but more explanations are needed.First, it means that even if those creatures knew we were here and could see us through a telescope, all they saw was light that left Earth 200 years ago.So it's not you and me that they see.They see the French Revolution and Thomas Jefferson and people in stockings and wigs -- people who don't know what an atom is or what a gene is and make electricity by rubbing an amber rod with a piece of fur and think it's funny people.We receive telegrams from these watchers, likely beginning with "Dear Sir," congratulating us on our steeds and our skillful use of whale oil. 200 light-years is such a huge distance that we can hardly even imagine it. So even though we're not actually alone, we're actually alone.Carl Sagan calculated that there are as many as 100 trillion billion planets in the universe where life may exist-a number far beyond our imagination.But, also beyond our imagination, is the extent of the universe in which they are scattered. "If we were crammed at will into the universe," Sagan wrote, "the chances of you being on or near a planet would be less than one in a billion million million million million million million million (i.e. 10-33). Worlds are precious." of." So, perhaps here's the 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.