Is there life on Mars, Zhihu?

Astrobiologists speculate that it is unlikely to find any life more complicated than simple bacteria on Mars.

Mars has always been considered as the most likely planet in the solar system to have extraterrestrial life. Since the second half of the last century, NASA has had many reconnaissance equipment, including Curiosity and Odyssey, which landed on or flew around Mars, and some of them are still working today.

These detection devices "saw" a desolate and lifeless land. The surface of Mars is basically desert, and there is no stable liquid water body. The atmosphere dominated by carbon dioxide is thin and cold, and sandstorms often occur. They dug up some soil and analyzed traces of microorganisms and organic compounds. And nothing was found. This red earth-like planet seems to be a frozen desert bathed in deadly ultraviolet radiation, and there seems to be no sign of life.

However, with the deepening of the exploration of Mars, scientists' views began to change. It may be too hasty to say that Mars is not the home of life. In recent years, more detailed photos from Mars have revealed some landforms that look like floods hitting plains and dry lake bottoms, and even the remains of ancient oceans.

The surface of Mars is terrible for any life with liquid water as its source. Although there is some ice at the poles, the temperature is too low to melt. Even if it melts, the liquid will evaporate quickly, because the atmosphere of Mars is less than 1% of that of the earth. It is estimated that Mars, which once had liquid water and warmth, ended about 3.5 billion years ago. Today, the best hope for finding life there is in the subsurface region. Because some microorganisms can live deep underground, their energy for survival comes not from sunlight, but from the chemical energy and heat energy of gases and minerals in the earth's crust, which are directly converted into biological energy, thus maintaining a food chain independent of terrestrial organisms.