1. liquid water, Mars is very dry and extremely short of water.
2. Oxygen, there is almost no oxygen on Mars, only carbon dioxide.
3. Atmospheric pressure, the pressure inside the human body is suitable for the earth. The atmospheric pressure of Mars is less than 1% of that of the Earth. If it is not directly protected in the external environment of Mars, people will soon die because of internal high pressure.
4. Temperature: The average temperature on the surface of Mars is 55 degrees below zero, and the maximum value of perihelion on the equator of Mars is only about 25 degrees during the day, but once the temperature drops sharply in the afternoon, it drops to tens of degrees below zero at night.
In the solar system, Titan is the most suitable place for human survival except the earth.