Xiao Yu did not visit Uranus, because at this time Uranus happened to be moving to the other side of the sun. However, it is estimated that after another 2 billion kilometers of flight, Xiao Yu's fleet will pass by Neptune when it reaches the orbit of Neptune, so as to have a rare opportunity to observe Neptune up close.

At this moment, the speed of Xiao Yu's fleet relative to the sun has reached 500 kilometers per second.

During the long journey, Xiao Yu arranged the fleet into the shape of a ball, the core of the sphere is three county-level spaceships, in addition, there are seventy township-level spaceships around, and further out, there are a thousand village-level spaceships, like the stars and the moon, guarding the county-level and township-level spaceships in the center.

Each spaceship is at least 500 kilometers apart from each other, and more than 1,000 spaceships constitute a large ball with a diameter of 10,000 kilometers.

In front of the fleet, the village-level spacecraft that served as a vigilance mission sent out lasers from time to time to vaporize the asteroids that stood in the way. Xiao Yu's fleet, like a crab, is rampaging through the solar system.

Ahead, Neptune, which was as blue as an ocean, had already entered Xiao Yu's field of vision. Here, Xiao Yu saw the spectacular big black spot on Neptune and observed Triton up close.

Triton was once a Kuiper Belt object that was captured by Neptune's strong gravitational pull, so Triton's orbit is retrograde, and it is slowly approaching Neptune. When it is beyond the Loch limit from Neptune, it will be torn apart by Neptune's strong gravitational pull, and then the fragments of Triton will hit Neptune.

Yes, this will be another huge impact event that is no less than the collision of the wood and the moon. However, due to its distance, it will not affect the inner planets much.

Xiao Yu didn't slow down his fleet. Now that he has made up his mind to leave the solar system, no matter what kind of scenery he has, he can no longer let Xiao Yu stop.

The encounter with Neptune was only a moment. Xiao Yu not only did not stop for Neptune, but with the help of Neptune's gravity, he accelerated the speed of his fleet to five hundred and twenty kilometers per second.

A month later, Xiao Yu's fleet reached the orbit of Pluto. After expressing sympathy for Pluto, which is 300 million kilometers away, through the telescope, Xiao Yu continued to fly towards the outer solar system.

This is already the territory of the Kuiper Belt. The Kuiper Belt is the main source of short-period comets in the solar system, for example, the famous Halley's Comet is thought to have come from here. However, Xiao Yu was not so lucky, and happened to encounter it. The current Halley's Comet does not know in which corner of the solar system it is dangling.

Here, six billion kilometers from the sun. Looking at the Sun here is only a little brighter than looking at Venus from Earth. She has become a point of light, losing all of her detailed features. But even at such a distance, she still dominates everything here. Yes, in the Kuiper Belt, Pluto, Xena, Sedna and other celestial bodies are still orbiting around that bright spot in the distance, along with countless cold stones.

Here, it's cold and dark. Loneliness is the eternal melody of the universe, and light is a rare scenery in the universe.

There are at least 100 million celestial bodies scattered within this vast space. But Xiao Yu couldn't see anything. Compared to this huge space, the density of matter is too thin.

Xiao Yu is still moving forward. In space, you don't notice that you're moving because you don't have a reference. Xiao Yu's huge fleet was quietly suspended in space without any movement.

Xiao Yu has been observing the strength of the solar wind. During this nine-month long journey, Xiao Yu saw that the speed of the solar wind was slowly decreasing, which meant that the influence of the sun on this place was getting weaker and weaker.

Gradually, gradually, the speed of the solar wind decreased from a few hundred kilometers per second to less than the speed of sound of 340 meters per second. Xiao Yu knew that he had come to the edge of the solar system.

Beyond will be the world of an infinite amount of interstellar medium. The sun, with its powerful energy, uses the solar wind to carve out a world of its own in the interstellar medium, and the place where Xiao Yu is located will be the border between the solar empire and the interstellar medium.

Here, there is the heliopause. Here, 18 billion kilometers from the sun.

Under the influence of the interstellar medium, the speed of the solar wind finally dropped below the speed of sound. The solar wind will be here, and the interstellar medium will have a fierce confrontation, and countless particles will collide violently in places that Xiao Yu can't see, and the temperature here is as high as several thousand degrees Celsius.

Yes, it's cold and dark here, and humans will be frozen into ice in an instant, but the temperature here is indeed as high as several thousand degrees Celsius.

Temperature is simply a physical quantity that measures the intensity of the thermal motion of an object's molecules. There are too few substances here, too thin, so although the temperature is high, it can't have any effect on Xiao Yu. It's like the Earth's ionosphere, where the temperature is more than 1,000 degrees Celsius, but there are still many man-made celestial bodies flying freely.

This is the final battleground. In the confrontation with the interstellar medium, the solar wind was defeated. Xiao Yu knew that after passing through here, the sun would no longer have any other means to influence this place except gravity.

It took Xiao Yu two days to pass through here and through the heliopause. Looking at the number of high-energy charged particles from the sun in the probe slowly decreasing to the point of finally disappearing, looking at the bright spot in the distance that was already a little dim and no longer much different from the rest of the stars in the universe, Xiao Yu had an indescribable feeling in his heart.

"Mother, dear mother, zaijian, zaijian." Xiao Yu muttered to himself, feeling the urge to cry.

Moving on, there will be the interstellar medium, that is, the world of hydrogen and helium from the Milky Way. The matter here is so thin that it is unimaginably thin, not even to the point of one atom per cubic centimeter. Such a density is equivalent to the density of a drop of water evenly distributed in a space of five million cubic kilometers.

What greeted Xiao Yu in front of him would be a lonely journey in such a space for more than 6,000 years.

After leaving the heliosphere top, Xiao Yu has been depressed for a year, during this year, Xiao Yu has been in a state of trance, the daily operation of the fleet, all handed over to the automatic program to do, Xiao Yu just through the telescope, every day obsessively looking at the direction of the sun, immersed in memories and unable to extricate himself. Fortunately, the route had already been set, and there was no need to worry about encountering an asteroid attack here, so Xiao Yu's fleet did not have an accident.

Here, it is already 35 billion kilometers away from the sun, and it takes 32 hours for the sun's rays to be transmitted here. But here, in such a distant place, Xiao Yu actually made a major discovery.

He discovered a planet.

Yes, having reached hydrostatic equilibrium and possessing enough mass to empty the rest of the small bodies in orbit, the planet, by all accounts, fits the astronomers' definition of a planet.

Its mass, which is one and a half times that of the Earth, is a rocky planet that orbits the Sun at an extremely slow pace and has a period of seven hundred and thirty-two years.

Looking at this planet, Xiao Yu's heart suddenly brightened up and understood many things.

Previously, mankind had been wondering if there was another large planet beyond Pluto's orbit, otherwise there would be no way to explain the strange orbits of many small bodies in the Kuiper Belt. Now, Xiao Yu has finally found the answer.

Here, indeed, there is a large planet. But because it's so small and it's so dark, humans haven't been able to spot it.

Xiao Yu named the planet "Lost Star". This is a lost land, which has never been traced in the written records of mankind.

Xiao Yu poured a lot of energy into the Lost Star. Xiao Yu even rushed to build a probe satellite and launched it in orbit around the Lost Star. In this way, even if Xiao Yu's fleet continues to leave, Xiao Yu can continue to observe the Lost Star.

The Lost Star has no atmosphere, but on the surface of the Lost Star, Xiao Yu observed a liquid that appeared to be liquid nitrogen, as well as a white solid like water ice. This suggests that if the right temperature allows the water ice to melt and liquid nitrogen sublimates, it can also have an atmosphere like the Earth.

Above the Lost Star, there are mountains, proving that it once had crustal movement, and there is crustal movement, proving that it has a liquid, fiery core. Perhaps, there will also be volcanic eruptions, hot springs caused by geothermal heat, and in the hot springs, there may be life.

Xiao Yu had a lot of thoughts in his heart.

Xiao Yu's observation of the Lost Star lasted for a year, and it was not until he could no longer receive the signal from the satellite that Xiao Yu had to regretfully give up his research on it.

The discovery of the Lost Star saved Xiao Yu from the slump, and Xiao Yu regained his spirit and had the desire to explore.

The compilation of the Heroes of the Sky Catalogue has resumed, and research on projects such as over-the-range communications, anti-gravity technology, and next-generation spacecraft engines has also been put on the agenda. The research of physical theory is also in full swing, and even the huge amount of science and technology has arranged the calculation schedule of the main computer to three hundred years later.

In other words, the data needed to be computed now is enough to run the host computer at full capacity for three hundred years. This result made Xiao Yu smile bitterly. However, there is time in the journey, and Xiao Yu is not in a hurry.

Time slipped away in this lonely, but fulfilling. Since his encounter with the Lost Star, Xiao Yu has not encountered any substance. This situation has been maintained for 600 years.

Six hundred years later, Xiao Yu arrived at a place.

Here, it's the Oort cloud, here, it's a light-year distance from the sun.

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