In our solar system, there are four rocky planets, namely Mercury, Venus, Earth, and Mars. These four planets, which are composed of rocky and dense material, are called "Earth-like planets", as the name implies. There are also four gas planets, Jupiter, Saturn, Uranus, and Neptune. These four planets are composed of large amounts of low-density gas, and the lighter the element in the universe, the greater the number, so these gas planets are much larger and heavier than the Earth-like planets, which are called "Jupiter-like planets".
For a long time in the future, the main targets of human exploration will be Earth-like planets, because the environment of wood-like planets is generally very harsh, which will cause great obstacles to human exploration, and more crucially, the four Earth-like planets in our solar system are much closer to Earth.
Since humans began to explore the universe, the planets of the solar system have been explored many times, and the most explored planets are Venus and Mars, both of which are known as the "sister planets" of the Earth, and in the solar system, Venus and Mars have the highest similarity to the Earth.
Every stellar system has a "habitable zone," and planets in the habitable zone have a higher probability of harboring life, while planets in the habitable zone have relatively stable environments that can provide more complex evolutionary conditions for life.
The brightness of our sun increases by 10% about every billion years, and the increase in the sun's brightness causes the habitable zone of the solar system to move outward. Life on Earth was born about 4 billion years ago, but complex life began to appear only in the last billion years, probably because the sun was not bright enough 4 billion years ago, and the Earth did not fully enter the habitable zone of the solar system, and as the sun's brightness increased, the Earth's environment was gradually stabilized.
Venus and Mars are located in the habitable zone of the solar system, but Venus is closer to the Sun, Mars is farther away, but in the future, the Earth will gradually exit the habitable zone, the Sun becomes hotter, the Earth may become a fireball, then Mars will enter the habitable zone, so the main goal of human exploration is now Mars, the future of human may transform Mars into a second "Earth", to become the new home of mankind.
However, the influence of the habitable zone on planets is limited, and it is not certain that planets located within the habitable zone will give birth to life, nor is it impossible for planets outside the habitable zone to give birth to life; the presence of an ocean of liquid water on a planet is more important for life than being located within the habitable zone.
Take Venus and Mars, in fact, Venus is more like Earth than Mars, in terms of size and weight, Venus and Earth are more similar, Mars is smaller in size and mass, if we look at the appearance, Earth is blue, Venus is a dull yellow, Mars leans toward orange-red.
Scientists believe that when the solar system was first born, there was a large amount of liquid water on both Venus and Mars, and probes have proven that there is water in the lava of Venus, and there is a large amount of ice on Mars, and there are lakes of liquid water underneath the ice, which means that all three Earth-like planets in the solar system could have nurtured life, but in the end, only Earth succeeded.
According to the information sent back by the probe, Venus is a hot "fireball" with a high average temperature and an atmospheric pressure more than 90 times that of the Earth, while Mars is relatively "inhospitable" with a surface temperature of about -63 degrees Celsius, and sometimes Mars will scrape Mars storms that last for months.
Perhaps we are mistaken: Venus is more like the baby Earth, while the desolate Mars is a "dead" planet. Why do you say so? The first reason is that the core of Mars has cooled, which led to the loss of its own magnetic field, without the protection of the magnetic field, the solar wind directly blew away the atmosphere of Mars, resulting in the atmosphere of Mars became incredibly thin, most of the water on the entire surface of the planet evaporated, and slowly Mars became what it is today.
The magnetic field of Mars is only about 0.1%~0.2% of that of Earth, and the core of Venus is not cooled, but Venus also has only a weak magnetic field, this is because the rotation speed of Venus is too slow, plus the core of Venus although the volume is very similar to that of Earth, the core of Earth has a unique layered structure, plus the Earth has the moon as a satellite, the gravitational force of the moon will drive the core of Earth to move and form a stable magnetic field.
When the Earth was first born, and Mars is very similar, are the same hot, almost no oxygen in the atmosphere, after a number of "big oxidation events", the Earth's atmosphere is full of oxygen, so we say that Venus is the "baby" Earth This is why we say that Venus is a "baby" Earth. The core of Mars has been cooled, the future of human will be a lot of transformation of Mars still can not change the thin atmosphere and desolate environment, that is why we say that Mars has been "dead".
Unfortunately, Venus, although similar to the early Earth, has lost forever the possibility of becoming like the Earth, because the greenhouse effect of Venus has fallen into a vicious circle that cannot be contained, and coupled with the weak magnetic field of Venus, the thick atmosphere of Venus may also become thinner after the greenhouse effect is reduced.
Although Mars is "dead" and the environment is very harsh, but the environment is not as terrible as Venus, we can still give Mars a lot of transformation and move to this planet.
