When we talk about the universe, we mean not only the earth, the sun and the moon, but also the stars and space between them. There are millions of stars in our sky. The sun is one of them. Around it there are eight big planets moving, including the earth. The moon is our nearest neighbour in space. If you look at the sky on a clear night, it is possible to see about 3,000 stars. They look small, but they are really very big hot balls of burning(燃烧着的) gas. Some of them are huge, but others are much smaller like our planet Earth. The biggest stars are very bright, but they can only live for a short time. Every day new stars are born and old stars die.

All the stars are very far away. The light from the nearest star (except the sun) takes more than four years to reach the earth.

Hundreds of years ago, people used stars, like the North Star, to know which direction(方向) to travel in. Today you can still see that star.

From the moon to Mars, scientists have been looking for water — the key to life — in the solar system for many years. Recently, they have turned to Jupiter(木星)!

Jupiter is a gas giant(巨星). It doesn’t have an Earth-like surface. We can see strips(条纹) around it. They are actually cold, windy clouds.

On April 14, the European Space Agency’s (ESA) JUICE spacecraft successfully lifted off from French Guiana in South America. JUICE, short for “Jupiter Icy Moons Explorer”, will collect data(数据) from Jupiter and its three moons, Europa, Ganymede and Callisto.

The three moons are believed to have big oceans of liquid water(液态水) under their icy shells(壳). According to ESA, he water on those moons could be six times as much as the amount in Earth’s oceans. The mission “will change our understanding of the solar system”, wrote Scientific American.

In 1998, NASA’s Galileo spacecraft found that Europa might be ejecting(喷射) water as far as 160 kilometers into space. That gave scientists the idea of studying the icy moons of Jupiter.

The oceans under these moons are likely to be tens of kilometers deep. But they are also trapped under tens of kilometers of ice, making it very difficult to study them. Although JUICE cannot land on the surface, it has lots of high-tech equipment to study the moon’s environment, including spectral imaging(光谱成像) tools and radar(雷达). They could give more data on things like the thickness of the oceans, their salt content(含量), and their distance from the icy shells above, reported Phys.org.

“The main goal is to understand whether there are habitable (可居住的) environments among those icy moons and around a giant planet like Jupiter,” JUICE team member Olivier Witasse said during a press conference (发布会) on April 6.