10.宇宙生命之谜

The mystery of life in the universe

1. In ancient times, science was not developed, and people always aspired to the "heavenly world".

2. So, there are many stories: Chang'e running to the moon, fairies down to earth, peach event ...... Now, science has developed, people know that it is the myth made up by the ancients.

3. However, whether there is life in space beyond the Earth is still a - a fascinating question.

4. Theoretically, the universe is infinite.

The Earth is only one planet in the solar system, and the solar system is only a tiny part of the Milky Way, which is a drop in the ocean of the universe.

6. There are hundreds of billions of stars in the whole galaxy, and there are many celestial systems like the solar system, among which there must be planets similar to the Earth.

7. It can be guessed that the Earth is by no means the only celestial body where life exists.

8. However, mankind has not yet found another planet with life.

9. Which celestial bodies could have life on them?

10. What are the conditions that must be present in this celestial body?

11. After understanding the process of the origin of life, it is believed that there should be at least these conditions:

12. First, a temperature suitable for biological survival, generally should be between minus 50 degrees Celsius to minus 150 degrees Celsius;

13. Second, the necessary water, the vitality of living substances such as proteins, nucleic acids are closely related to water, without water, there would be no life;

14. Third, the appropriate composition of the atmosphere, although a few anaerobic bacteria have been found to survive in the absence of oxygen, but oxygen and carbon dioxide is extremely important for the existence of life; fourth, there should be enough light and heat to provide energy for the living system.

15. According to these conditions, scientists first analyzed the planets of the solar system other than the Earth.

16. Mercury is the closest to the Sun, and its surface temperature reaches three hundred to four hundred degrees Celsius when it is sunny, so it is impossible for life to exist.

17. Venus is a planet that lacks oxygen and water, and has a thick cloud cover. The sunlight radiation and the "greenhouse effect" caused by the clouds make the surface of Venus so hot that life is not possible.

18. Jupiter, Saturn, Uranus, and Neptune are far from the Sun, and their surface temperatures are generally below minus 140 degrees Celsius, so life is also unlikely to exist.

19. The only planet in the solar system where life may still exist is Mars.

20. Mars has many similarities with the Earth: one revolution of the Earth is 23 hours, 56 minutes and 4 seconds, and one revolution of Mars is 24 hours and 37 minutes;

21. The Earth's rotation axis has an inclination of 66 degrees 34 minutes to the orbital plane, and the inclination of Mars is about 66 degrees 1 minute, so the length of day and night of Mars and Earth are similar, and there are also four seasons.

22. More interestingly, in 1877, an Italian astronomer observed many vertical and horizontal black lines on the surface of Mars, which were speculated to be canals dug by Martians.

23. People also observed that the color of the Martian surface changed with the seasons, and some people thought that this was the Martian surface plants changed their colors with the seasons.

24. In order to unveil the mystery of Mars, scientists decided to use spacecraft to make a close observation of Mars.

25. In 1971, the U.S. launched the Mariner 9 spacecraft into orbit around Mars and took a large number of photographs of the planet.

26. These pictures showed that the so-called "canals" observed by Italian astronomers turned out to be a series of dark craters and dark patches.

27. Close observations also revealed that the previously observed seasonal changes in color on the surface of Mars were not caused by the growth and withering of plants, but by the wind blowing the dust around on the surface of Mars, which caused the changes in color.

28. Scientists have also found that Mars is a very dry planet, and although water vapor is found in its atmosphere, the amount is very small, only one percent of that found in desert areas on Earth;

29. The atmosphere of Mars is very thin, ninety-six percent carbon dioxide and very little oxygen;

30. The surface temperature of Mars is very low;

31. There is no magnetic field on Mars, and its atmosphere has no ozone layer, so it is not protected from ultraviolet light and various cosmic rays.

32. All these factors indicate that it is difficult for life to exist on Mars.

33. In order to further investigate Mars, in 1975, the United States launched two spacecraft named "Viking".

34. The two spacecraft landed on Mars, conducted a series of analysis and testing, and obtained two important results, one is that no organic molecules were detected in the Martian soil;

35. Secondly, in the culture of samples taken from the surface of Mars, the presence of microorganisms was not detected.

36. This proves that no life exists on the surface of Mars in the area where the spacecraft landed.

37. Scientists also asked whether life material could exist in the rock layers of Mars?

38. This is subject to further study.

39. People have not yet found life in space beyond Earth, but still believe that life exists in distant space.

40. In recent years, scientists have analyzed some meteorites that have fallen on Earth and found organic molecules on them, suggesting that life may exist in space.

41. Whether life exists beyond the Earth is a cosmic mystery that humans have been exploring.