English Across the Curriculum
Jupiter is the fifth planet from the sun and the largest in our solar system. It has 1 400 times the volume of our Earth, but is only 300 times as heavy because the planet must be made up of gas rather than rocks or metal.
It takes Jupiter almost 12 years to orbit the sun. But it rotates on its own axis very quickly - it completes one full turn every 10 hours. If you look at Jupiter closely, you can see stripes , probably clouds that are created by fast-moving winds.
We don't know very much about Jupiter because not very many spaceships have visited it. In 1979 two American Voyager spacecraft flew past Jupiter and gave us lots of new information. Today we know that most of the planet consists of gases - hydrogen and helium - and does not have a hard core , like the Earth. In 1994 a big comet crashed into Jupiter and stirred up the planet's atmosphere. Scientists could find out what kind of gases Jupiter's atmosphere is made up of.
In 1989 NASA launched an unmanned spacecraft to Jupiter - Galileo. After 6 years, Galileo reached the planet and went into orbit. It sent a small probe through the clouds of Jupiter to find out more about the atmosphere. It turned out to be very dense and filled with sulphur and other poisonous gases, impossible to breathe .
Jupiter has four large moons and many other smaller ones - over 60 moons have been found so far. Galileo discovered the four biggest moons in the 17th century. They are also called the Galilean moons. Ganymede, the biggest moon in the solar system is even larger than Mercury and would be an own planet if it didn't travel around Jupiter. Callisto is as big as Mercury. Both these moons have an icy surface. Io is a rocky, volcanic moon from which lava and sulphur come out. It is about as big as our moon and the innermost of Jupiter's moons. Europa is the smallest of the Galilean moons. It has a very smooth surface and a lot of lines and dots on it that may be frozen rivers or seas. Maybe there is even water underneath the surface of Europa.
Scientists discovered that, not only Saturn, but also Jupiter has a system of rings. They do not reflect the light from the sun because they are made of dark dust and pieces of rock. That's why they are not visible.