Humans are the most intelligent species on Earth. With the continuous advancement of human technology, humans can now explore the universe beyond Earth.

This indicates that the pace of human technological development is still very rapid. After leaving Earth, humans discovered that Earth is just one of the planets in the solar system.

The solar system has eight major planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Beyond Neptune lies Pluto, which was once considered a planet in the solar system but was later reclassified due to its small size and mass. Outside Pluto, there is the Kuiper Belt and the Oort Cloud.

Currently, only Earth in the solar system has given birth to life. Scientists believe that the main reason Earth can sustain life is that it meets three essential conditions for life: suitable temperature, abundant water resources, and sufficient air. It is because Earth meets these three primary conditions that life has flourished.

Apart from Earth, two other planets in the solar system are also in the habitable zone: Venus and Mars. However, human exploration of Mars is more frequent than that of Venus. Why is this?

It's important to note that the average distance between Venus and Earth is only 41 million kilometres. The average distance between Mars and Earth is 120 million kilometres, with a closest approach of 54 million kilometres and a farthest distance of up to 400 million kilometres. In today's era, where the fuel for chemical propulsion spacecraft is costly, why do astronomers focus more on Mars despite its greater distance from Earth than Venus?

Venus is rightfully known as the "brightest star in the Earth's night sky." Astronomers later discovered that Venus appears so bright because its atmosphere is very thick. However, unlike Earth's atmosphere, Venus' atmosphere is almost entirely composed of greenhouse gases such as carbon dioxide, creating a harsh environment of high temperature and pressure.

The habitability of Venus is even lower than that of the Moon. After all, although the Moon lacks an atmosphere, it doesn't have the high-pressure environment found on Venus, potentially allowing scientists to establish bases on its surface or underground. However, the high temperature and pressure environment on the surface of Venus make it virtually impossible for astronauts to land and establish settlements.

The situation on Mars is much better than on Venus. After comprehensive exploration by dozens of probes, it's evident that Mars' environment is relatively favourable.

From these discoveries, it's clear that Mars' conditions are far better than Venus's, emphasizing Mars' value. Mars is the closest to Earth after Venus, among the eight major planets. Furthermore, Mercury is too close to the Sun and tidally locked, making it unsuitable for life and unlikely to harbour life. The outer planets of Jupiter, Saturn, Uranus, and Neptune are gas giants and are exceptionally distant from Earth. Therefore, Mars naturally becomes the primary focus of attention.

Interestingly, only Earth and Mars are in the habitable zone within the solar system. Hence, in the future, human migration to Mars could even become a possibility.