Life may take different forms, and they may have different requirements for the environment, which may be hellish for one organism and heaven for another. For example, before leaving the earth, how could Xiao Yu have thought that there was still a creature like a black worm on Titan?

Until now, Xiao Yu's spaceship still has some specimens of black insects. From the current point of view, Xiao Yu believes that these black insects should also be classified into the category of alien beast creatures, rather than ordinary creatures.

This situation has brought certain difficulties to Xiao Yu's exploration activities to find intelligent creatures. The reason is simple, because Xiao Yu does not have a unified means of defining which star systems are worth exploring closely. It is obviously not realistic to explore all the stars at once.

The stellar density here is slightly higher than where the solar system is located. Within 20 light-years, there are probably more than 1,000 stars. And Xiao Yu didn't think that his luck could be so good that he could find intelligent beings within these twenty light years.

Xiao Yu's psychological bottom line is within the range of 3,000 light years. Xiao Yu intends to spend no more than two thousand years to complete this task. The number of stars within a range of 3,000 light-years is an astronomical number, and if every star had to be explored at close range, even a tenfold increase in the time of 2,000 years would not be enough.

In order to deal with this situation, Xiao Yu gathered all the scientists under his command and held many discussions.

"First of all, I think there must be liquid matter on the living planet, whether it's liquid water, liquid methane, ethane. In short, there must be a liquid substance. This is because the energy exchange within the organism must be carried by liquid substances. ”

A scientist expressed his opinion.

"No, I don't agree with that." Another scientist objected, saying: "Although all of our more than 100 races use liquid matter as the carrier for energy exchange in the body, but in this universe, there can be no organisms that use gaseous matter as the carrier for energy exchange?" After all, in theory, gaseous matter can do the same. ”

The scientist's remarks caused a lot of discussion.

"This is questionable for the time being, and we can't prove it or deny it, so let's move on to the next discussion. Also about the exchange of substances, I think. A suitable planet for life must have a liquid core, and only the liquid core will have geological activity, there will be orogeny, and then. There also needs to be a satellite large enough to create tidal forces for it, to create winds. to form a global exchange of substances. ”

"I don't agree with that. I think. We can expand its scope a little more, and as long as a planet has an atmosphere, it is valuable enough. Under the illumination of stellar light, an imbalance in the temperature of the atmosphere causes atmospheric flows, which bring about the exchange of matter that is sufficient. ”

Another scientist has expressed his opinion.

"No, it doesn't have to be. weishenme must atmospheric flow and material exchange? Wouldn't a planet without an atmosphere be able to evolve life? I don't agree with that. I think this restriction can be removed. ”

…………

This discussion lasted for two months. Xiao Yu relaxed the restrictions again and again, combined with the environment of the respective needs of these more than 100 creatures, as well as the conditions of their home galaxy, and finally came to the following conclusions.

Xiao Yu thinks. These conclusions, at least in the Milky Way, should be universal. In other words, as long as there are intelligent creatures on the planet, the following conditions will generally be met. There will certainly be exceptions, but they will not be too numerous to be ignored. In the future search process, I will use these points as a guide to carry out actions.

First of all, the host star of a galaxy where living things can exist must be stable and can export energy smoothly and persistently. This excludes all stars that are in their last years and infancy. Because the stellar activity in the juvenile period is too strong, and the inner galaxy is too chaotic. An asteroid impact with a diameter of more than 10 kilometers can destroy the budding of a life. And in nascent star systems, this level of impact can only be considered trivial. Older stars become red giants, and the stellar activity becomes more intense.

Second, it must last long enough. Because only the lifespan of the main star is long enough to provide enough time for the slow evolution of living things. This point excludes all superstars.

Because the mass of a star is inversely proportional to its lifetime, the greater the mass, the shorter the lifetime. Stars that are tens of times more massive than the Sun may have a lifespan of only a few million years or less. On a cosmic scale, such a short period of time is fleeting. Such a short period of time is obviously not enough to evolve intelligent creatures.

Third, all living things should have appeared and evolved on planets. Although Xiao Yu could not rule out the possibility that there was life on the stars, this possibility was too small to be ignored. This excludes all star systems that do not have planets.

The remaining points, such as that the living planet must have a large enough moon to slow down its rotation and create tidal forces to form a material exchange, and for example, the outer layer of the living planet must have a large enough gaseous planet to protect it, or the distance from the star must be appropriate, and there must be liquid water on it, etc., because its universality cannot be proven, it was abandoned by Xiao Yu.

In other words, Xiao Yu believes that as long as a star system meets the above three conditions, then it has the value of getting closer to exploration.

The current state, age, mass, and lifetime of the star can be analyzed by reducing the light, and whether there are planets can be determined by oscillating and occultation. There is no distance limit or greatly increased detection range when it comes to detection by light, and Xiao Yu can make these explorations at any time on any galaxy within 20 light-years.

If it meets these three conditions, then Xiao Yu will change course and move closer to the star to use tachyon detection methods to detect it closely. If the results show that there is a sapient civilization surviving, the fleet will leave the faster-than-light voyage and settle down here, and if there is no sign of a sapient civilization surviving, it will continue to explore the next planet.

With such loose conditions, the number of eligible galaxies has increased dramatically, with basically one out of every 100 stars eligible. Massive stars and aging, juvenile stars are only a few after all, and the existence of planets is not as sparse as Xiao Yu originally expected. You must know that among the conditions set by Xiao Yu, there is no requirement that the planet must be a rocky planet. In other words, Xiao Yu believes that among the gaseous planets, there is also the possibility of intelligent life.

Xiao Yu does not expect to get results in a short period of time. This is a new round of needle in a haystack, and it takes Xiao Yu to pay a lot of energy and patience before he can gain something.

"This star is good, the size is moderate, the age is moderate, and the planet is still a rocky planet with a mass of 1.6 times the mass of the Earth...... Well, it's worth checking it out. During the long journey, a message from the probe caught Xiao Yu's attention.

Before this, Xiao Yu had searched for at least five hundred star systems, but each time the outcome was disappointment. The topography, geology and other circumstances of various planets are strange, not to mention intelligent and civilized creatures, even the most basic creature Xiao Yu has not found one.

Some of these planets are extremely close to their host star, and are constantly scorched by the flames of the stars, and under their own rotation, they are like roast ducks in the oven, for fear of not being roasted thoroughly enough. Some planets are directly locked by the gravitational pull of the star, and their rotation and orbit are synchronized, and they will always face the stars on the same side, just like Mercury in the solar system, with a fire hell on one side and an ice hell on the other.

Some planets are too chaotic, with no massive gaseous planets to protect them and no atmosphere to cushion them, they are subjected to constant interstellar shell bombardment all the time, causing craters and craters everywhere on their shells, just like the moon. Some are so far away from the stars that the whole planet is like an oversized ice cellar......

All kinds of different planets opened Xiao Yu's eyes and at the same time, he felt a deep disappointment.

"It turns out that in this universe, dead silence is the norm, and life is the exception. According to the calculation that there is one eligible star for every 100 stars, I have explored more than 500 stars, which means that 50,000 stars have been excluded, 50,000 stars, not a single living planet ......."

"Life, what a miraculous existence." Xiao Yu sighed deeply in his heart.

Through this search activity, Xiao Yu once again felt a conspiracy hand looming behind him. The reason is very simple, since the existence of life is so scarce, and intelligent life is even more unique, what is going on with all these civilizations that I have encountered one after another since I left the earth? Weishenme herself is so unlucky, or rather, she is so ...... Fortunate?

Xiao Yu didn't know what that meant.

"Again, be yourself first, and then talk about the rest." Xiao Yu sighed secretly, "I hope that this time the detection target will not disappoint me." ”

Xiao Yu once again changed the course of his fleet and sailed towards this star system. Tens of billions of kilometers behind him, the fourth-level beast still followed Xiao Yu looming like a kraft candy that couldn't be shaken off. (To be continued......)

PS: Today's fourth watch, this is the first change