From a distance from space, Earth is a blue planet, and since it happens to be within the habitable zone of the solar system, the surface of the Earth is covered with a thick layer of liquid water.
About 71 percent of the area is covered by oceans, with the remaining 29 percent being continents and islands. It is precisely because of so much water resources on earth that it has been able to give birth to millions of creatures that allow us to reproduce and live here forever. It can be said that water is the source of life, and without the existence of water resources, it is impossible to give birth to life on the earth!
When it comes to water, many people think that it is unique to the earth, but in fact, it is not so, in the universe water is actually widespread, only in our solar system, there are not a few planets with water, and even Saturn's rings have a lot of water resources.
In the solar system, there is a planet that is very unique, although it is smaller than the moon, but its water storage is far more than the earth, this planet is Europa
Europa is Jupiter's fourth largest moon, first discovered in 1610 by the famous astronomer Galileo Galilei, whose diameter is about 3138 kilometers and whose surface temperature can be as low as minus 163 degrees. Today's astronomers have found that Europa has extremely high water resources, equivalent to twice as much as the Earth
But from a distance, Europa is actually a giant ice hockey ball, and due to the extremely low temperature, there is no liquid water on the surface. Its liquid water is hidden under hundreds of kilometers of ice.
So why does Europa have a liquid ocean?
Scientists have speculated that europa may have had a liquid ocean because jupiter's huge tidal pull, so that his interior is constantly heated, so that the internal heat melts the solid ice, which can keep the water under the ice liquid all the time.
In 2016, scientists observed through hubble that there was a huge water vapor eruption in the cracks in Europa's surface ice, reaching a height of 200 kilometers, which is also the best proof of the liquid ocean under Europa's ice. Therefore, some people believe that Europa is the most likely planet in the current solar system to have extraterrestrial life other than Earth.
It should be known that although Europa only has a thin atmosphere, the conditions for life do not necessarily require oxygen. For example, the earliest primitive single-celled life on the earth was born at the hot spring mouth on the seabed, and the earth at that time did not have sufficient oxygen, and these life were anaerobic organisms. The same is true for Europa, which constantly generates heat inside, so many scientists believe that there is a great possibility of simple primitive single-celled organisms at the hot vent of Europa!
But then again, Europa is about 900 million kilometers away from us, so far humans have only been probes flying by, and observations through astronomical telescopes, and have not landed on the ground, so whether Europa has life or not is still unknown.