The sun The sun is a star. It is a huge, spinning, glowing sphere of hot gas. The sun is just like the stars that you see in the night sky. It appears so much larger and brighter than the other stars because we are so close to it. The sun is the center of our solar system. All of the planets in our solar system, including Earth, orbit around the sun.

NINEPLANETS

MERCURY Since Mercury is the closest planet to the sun, spins slowly, and does not have much of an atmosphere to trap heat, its temperature varies greatly. Mercury's temperatures can go between -279 Fahrenheit (-173 Celsius) at night to 801 Fahrenheit (427 Celsius) during the day (This is hot enough to melt lead!).

THE EARTH Earth is thought to be between 4.5 and 4.8 billion years old. The age of Earth is found by measuring the age of very old Earth rocks.. Scientists have also measured the age of meteorites which have fallen onto Earth's surface, and the age of moon rocks brought back by the Apollo astronauts. Both the meteorites and the moon formed around the same time as Earth, and they show similar ages.

MARS Mars is more similar to Earth than any other planet in the solar system. There is also evidence that liquid water flowed on Mars in the past and that there is frozen water beneath the poles of Mars. In 1976, NASA's two Viking landers touched down on the surface of Mars to collect soil with a robotic arm and study it to see if there were any signs of life, such as bacteria. Thousands of images were taken of the surface of Mars as well, but so far no evidence of life has been found.

venus Venus is sometimes called Earth's twin because Venus and Earth are almost the same size, have about the same mass (they weigh about the same), and have a very similar composition (are made of the same material). They are also neighboring planets. However, Venus and Earth are also very different. Venus has an atmosphere that is about 100 times thicker than Earth's and has surface temperatures that are extremely hot. Venus does not have life or water oceans like Earth does.

Jupiter Jupiter has at least 63 known moons. The largest four are called Io, Europa, Ganymede and Callisto. These four moons are called the Galilean satellites because they were first seen in 1610 by the astronomer Galileo Galilei.

Jupiter We do not yet know if a solid surface exists on Jupiter. Jupiter's clouds are thought to be about 30 miles (50 km) thick. Below this there is a 13,000 mile (21,000 km) thick layer of hydrogen and helium which changes from gas to liquid as the depth and pressure increase. Beneath the liquid hydrogen layer is a 25,000 mile (40,000 km) deep sea of liquid metallic hydrogen. Beneath this, there might be a solid core which is about one and a half times the size of Earth, but thirty times more massive. We do not yet know if a solid surface exists on Jupiter. Jupiter's clouds are thought to be about 30 miles (50 km) thick. Below this there is a 13,000 mile (21,000 km) thick layer of hydrogen and helium which changes from gas to liquid as the depth and pressure increase. Beneath the liquid hydrogen layer is a 25,000 mile (40,000 km) deep sea of liquid metallic hydrogen. Beneath this, there might be a solid core which is about one and a half times the size of Earth, but thirty times more massive.

Saturn Saturn's rings probably formed when objects like comets, asteroids or even moons broke up in orbit around Saturn due to Saturn's very strong gravity. The pieces of these objects kept colliding with each other and broke into even smaller pieces. These pieces gradually spread around Saturn to form its rings.

Neptune Neptune's atmosphere is made up of hydrogen, helium and methane. The methane in Neptune's upper atmosphere absorbs the red light from the sun but reflects the blue light from the sun back into space. This is why Neptune appear blue