Jupiter - the largest planet

General Information

Average distance from the Sun

778 million km
(483 million miles)

Length of year

11.9 Earth days

Average rotation period

9 hours 50 minutes

Diameter at equator

143,760 km
(89,350 miles)

Approximate surface temperature

- 150 0C

Jupiter is the largest planet of the Solar System: its mass is two and a half times the mass of all the other planets put together. Its diameter is eleven times the Earth's and its volume 1,300 times greater. This giant planet spins faster than any other. At the equator, the velocity due to the spinning motion is about 45,500 km/h. The equivalent velocity on Earth is about 420 km/h. Jupiter bulges at its equator because is not solid, and is spinning so fast.

Jupiter has no definite surface but, under the outer cloud layers, the gas thickens as the pressure gets greater, gradually becoming like a hot liquid. The atmosphere is stormy, with high winds and lightening which is probably quite violent.

Three faint rings of the particles circle Jupiter. They are only a few kilometers thick and cannot be seen from Earth even with the most powerful telescopes. They were first discovered on images returned by the spacecraft Voyager 1. The rings form a band about 50,000 km above Jupiter's cloud tops. At its center, Jupiter almost certainly has a small rocky core. The temperature there is around 20,000 - 30,000 0C.

In the layer over the core, the very high pressure makes the liquid hydrogen behave like a molten metal. Jupiter is mainly made of hydrogen (88 per cent) and helium (11 per cent). Small amounts of other chemicals give the clouds their variety of colors. Jupiter's Great Red Spot is thought to be a swirling storm cloud currently about 26000 km long and 12000 km wide. Since it was first observed in 1664, its length and color have varied. Why it is red is still a mystery. Small white clouds that get caught up around the swirling Red Spot take about 7 days to go right round it and then they merge in with the cloud bands.

Four of Jupiter's moons were discovered in 1610 by the Italian astronomer Galileo, when he first used a telescope; so they are known as the Galilean satellites. None is more than a tiny spot of light when viewed with even the most powerful telescopes.

Mars rotates round an axis tilted by 240. As a result Mars goes through seasons very similar to the ones we have on Earth. When it is winter in the northern hemisphere and summer in the southern hemisphere, the north polar cap is at its largest and the southern one at its smallest. After half a Martian year, the situation is reversed. The polar caps are a thin layer of frozen carbon dioxide and water.

Mars atmosphere is mainly carbon dioxide (95 per cent) with small amounts of
nitrogen (2.7 per cent), argon (1.6 per cent) and oxygen (0.2 per cent)

The only water now on Mars seems to be frozen, but images of the Martian landscape show channels and canyons that were obviously cut by water flowing in the past.

Mars is thought to have a core containing iron, but its precise size and composition are not known. The core is surrounded by a rocky mantle. Oxygen combined with silicon makes up 44 per cent of the soil sand iron oxide 19 per cent.

Mars has two tiny moons. Both are roughly potato-shaped and have craters on them. Deimos is about 16 km long and 12 km across. It orbits Mars at a distance of 23,500 km taking 1ľ Earth days. Phobos is about 28 km long and 20 km across. It orbits Mars at a distance of 9,340 km in just 8 (Earth) hours.

Jupiterís Structure

The atmosphereís top layer is broken by high winds into vast clouds. It forms a beautiful blend of red, brown, orange and yellow. The dark bands are gaps in the clouds. You can see through them to deeper, hotter layers of the planetís churning atmosphere. Inner layer is 17,000km (10,565 miles) thick. Made of hydrogen gas, it is so compressed that it behaves like liquid. Immediate next layer is also made of hydrogen. It is even more compressed and behaves like a solid. It is so heavy that it makes up over 77% of Jupiterís mass.

The core is solid and rocky. It is slightly larger than Earth.

Great Balls of gas

Jupiter is one of four planets that are made mostly of gas. The others are Saturn, Uranus and Neptune. Together, they are called the gas giants.

Jupiter is so vast that it exerts an enormous gravitational pull on things around it. Asteroids and meteoroids that come near it are sucked into its atmosphere. Jupiter is like a giant vacuum cleaner in space, sucking up pieces of space debris.