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In the solar system, although there are only eight planets, there are more than 200 satellites. The earth is the fifth largest planet in the solar system, but there is only one satellite on the earth, which is the moon, but the volume and mass of the moon are quite large. Of all the satellites in the solar system, the moon can rank fifth, second only to Ganymede, Titan, Callisto and Io. Among them, Callisto is almost as big as Mercury, while both Callisto and Titan are bigger than Mercury.

According to Itar-Tass, Alexander Broshenko, executive director of Russian space future plan and scientific research project, said that Callisto, a satellite of Jupiter, is being considered as a possible human settlement, saying that "Callisto is the most suitable planet to build human settlements after the moon and Mars."

Now the world's space powers tend to explore the moon and Mars, because the distance to the moon is very close to the earth, and Mars is the planet with the most similar surface environment in the solar system and the earth. Relatively speaking, these two planets are more likely to undergo interstellar migration. On the other hand, Callisto is just a satellite of Jupiter. The moon and Mars are far away. Why does the Russian space department favor this planet?

Callisto is about 4820 kilometers in diameter, twice as large as the moon. There is a lot of water ice (frozen water) and frozen ammonia on this planet. Scientists believe that Callisto. There are ice layers with a thickness of 50~200 kilometers on the surface (the surface structure is not all ice layers, but some rocks), and there are oceans with a depth of 200~300 kilometers under the ice layers (presumably not all oceans, but there may be rocks). This structure is similar to Europa, but larger than Europa.

In addition to water shortage, Callisto's atmosphere is very thin, mainly composed of carbon dioxide, but there is also a small amount of oxygen. There is an active ionosphere around, so the cosmic background radiation is low. He is also a mother, the outermost star of Galileo's four satellites. It is far from Jupiter and is relatively less affected by Jupiter's magnetic field. Therefore, some scientists believe that Callisto is also an ideal interstellar settlement. The Russian Space Agency also announced that it has signed a plan to develop a nuclear-powered spacecraft, which will be used to carry out the Jupiter mission in 2030, when Callisto will be selected to land.

Russia is not the only country with such plans. In fact, long before Russia announced Saturn's orbital mission in 2030, NASA also announced the plan to carry out the manned mission of Callisto in 2040. It can be seen that Callisto is really an ideal place for human migration in the future.

References:

The newspaper, September 16, article "Russia considers building human settlements on Callisto, a planet with a lot of water ice and oceans".