(ESTD. BY GOVERNMENT OF TAMILNADU)


Jupiter


Jupiter is the fifth planet from the Sun and it is the largest planet in the Solar System. Jupiter is more than twice as massive as all the other planets combined. The mass of Jupiter is 318 times that of Earth.

The Romans named the planet Jupiter after their king of the gods. The Greeks referred to the planet as Zeus, who was the king in their mythology. Indian mythology considers it as Prahaspati, the Guru of Gods.

It orbits the Sun at a distance of about 78 crore kms. It completes one rotation around the Sun in about 11.9 years. Even though it is 1330 times bigger than Earth, it completes one rotation on its axis in 9.8 hours. Jupiter is the third brightest object in the night sky after the Moon and Venus.

In 1610 when Galileo first pointed a telescope at the sky he discovered Jupiter's four large moons, Io, Europa, Ganymede and Callisto. They are now known as the Galilean moons. Ganymede is the largest Moon in the solar system. It is bigger than the planets Mercury and Pluto.

Jupiter was first visited by Pioneer 10 in 1973 and later by Pioneer 11, Voyager 1, Voyager 2 and Ulysses. The spacecraft Galileo orbited Jupiter for eight years. Its orbiter and probe have revolutionised knowledge of the planet.

Jupiter is one of the four 'gas giant' planets. Unlike rocky worlds like the Earth, Jupiter is composed almost entirely of gas. Inside this spinning ball of gas lies a small core of solid rocky material amounting to something like 10 to 15 Earth-masses.

Above the core lies the main bulk of the planet in the form of liquid metallic hydrogen. The outermost layer is composed primarily of ordinary molecular hydrogen and helium. The layer is liquid in the interior and gaseous further out. The atmosphere what we see when looking at this planet is the tops of clouds high in their atmospheres Jupiter is about 90% hydrogen and 10% helium with traces of methane, water, ammonia and "rock". This is very close to the composition of the primordial Solar Nebula from which the entire solar system was formed.

The bright colours in Jupiter's clouds are caused by complex interactions of various simple gases.

Jupiter and the other gas planets have high velocity winds, which are confined in wide bands of latitude. The winds blow in opposite directions in adjacent bands. Between the bands are vortices where wind speeds reach 600km per hour.

The Great Red Spot is a vast thunderstorm that has raged on the planet's surface for over 300 years. The spot is over twice the size of Earth and is the largest thunderstorm in the Solar System. It is Jupiter's most prominent feature and is even visible from the Earth. How such a huge storm has survived for so long remains a mystery.

Jupiter radiates more energy into space than it receives from the Sun. The interior of Jupiter is hot. The core is probably about 20,000 K. The heat is generated by the slow gravitational compression of the planet. This interior heat probably causes convection deep within Jupiter's liquid layers and is responsible for the complex motions seen in the cloud tops.

Like Saturn, Jupiter also has a system of rings. They're very faint when viewed with the naked eye. Unlike Saturn's rings, Jupiter's do not contain ice crystals. They are probably composed of debris from meteor collisions on Jupiter's moons. Jupiter has a multitude of large moons. And there is evidence that there may be many more smaller satellites. Presently we have found 63 moons orbiting the planet. Jupiter has more moons than any other planet.

The origin of these smaller moons remains a mystery. Many are in 'retrograde orbit', which means that they circle in the opposite direction to the major moons. So these odd moons may be asteroids that have been captured from the asteroid belt by Jupiter's immense gravity.

Jupiter has an immense magnetic field.