In the entire solar system, when it comes to the largest star, then the first thing that comes to people's minds must be Jupiter, in addition to the sun, the largest is Jupiter, and the number of Jupiter's moons is also very large, after so many years of in-depth exploration of human beings, a total of 79 natural satellites have been discovered.
At one time, it was thought that Jupiter had the largest number of moons in the entire solar system, but this record was eventually broken by Saturn, and today we are going to talk about one of the moons of Jupiter.
One of the characteristics of this moon is that it is very large, how big is it, let's say, this moon is even bigger than a planet in the solar system.
Even some scientists say that if it hadn't revolved around Jupiter, if it had orbited the sun, it might have become a planet in the solar system.
It is also the only moon in the solar system that has a magnetosphere, I believe you must have guessed which moon it is, it is the extremely mysterious Ganymede, and after research, scientists also think that this moon has something very suitable for the emergence of life.
So do you know how the moon Ganymede was discovered, in 1610, Galileo observed three stars approaching Jupiter, and then he found that these three stars actually shifted, and then the fourth star appeared, this star is the callisto we are going to talk about today.
But he was not the first to discover this star, the first to discover the moon of Jupiter, in fact, we Chinese, as early as 400 BC to 360 BC, the continent was in the Warring States period, there was a man named Gander who had discovered Gander.
It was in the middle of the 4th century B.C. that we observed Jupiter's largest moon, more than 2,000 years before Galileo.
If Ganymede is mainly composed of silicate rocks and ice, the stars are clearly layered, and have an iron-rich fluid core, if this is reasoned, then it is very likely that 200 kilometers below the surface of Ganymede, there is probably a saltwater ocean sandwiched between two layers of ice.
Let's move on to the volume of Europa, as mentioned earlier, the volume of Europa is larger than the volume of some planets, don't believe it, just look at its diameter, which reaches 5262 kilometers.
It is even larger than Mercury at 4,878 kilometers in diameter and only slightly smaller than Mars, with an orbit of about 1.04 million kilometers from Jupiter, which takes about seven days to orbit around Jupiter.
First of all, the surface topography of Ganymede is divided into two types, the darker areas account for about one-third of Ganymede, and these areas are full of impact craters, and the geological age is about 4 billion years.
The remainder of the brighter areas are home to a large number of interlaced trenches and ridges, and the cause of these fragmented geological formations remains a mystery to this day, with some experts suggesting that they may have been caused by tidal heat.
We all know that the earth has a magnetosphere, the earth has a magnetic field, our compass can clearly distinguish the direction, in addition, the magnetosphere can also protect the radiation from the effects of space radiation.
You may not know that harmful space radiation will corrode our atmosphere, and once the atmosphere is damaged, our surface will be directly exposed to radiation and the sun's ultraviolet rays, and the damage to the human body is huge.
Ganymede also has a magnetosphere, and between 1995 and 2000, Galileo made a total of six flyovers of Ganymede, only to find that the moon was a magnetic moment that had existed for a long time independent of Jupiter's magnetic field.
The magnetic dipole and Ganymede have an axis of rotation at an angle of 176°, and the magnetic poles are facing Jupiter's magnetic field, and the long-standing magnetic poles form a small magnetosphere around Ganymede.
In 1970, scientists proposed the existence of an ocean deep in the surface of Ganymede, and later used spacecraft to confirm it, and even came up with convincing evidence that Ganymede's ocean depth can reach 100 kilometers.
But the ocean is between two layers of ice, but there is no liquid water on its surface, so there is certainly no life on the surface of this moon, but it is possible that life may be hidden in the ocean beneath the surface.
Later, it was discovered that there was a thin atmosphere on Ganymede, and it was all oxygen, which scientists believe was due to the separation of the ice on Europa's surface into hydrogen and oxygen when exposed to sunlight.
The hydrogen atom in it is relatively light, and the gravitational pull of Ganymede is not enough to bind it.
So only part of the gaseous oxygen remains. And Europa also possesses an ionosphere. This makes Europa very similar to Earth in many ways.