There are numerous star systems in the Milky Way galaxy and in other galaxies. For all these star systems, the planets that are detected first are those that are as big as or even bigger than Jupiter. Thus, when an alien intelligent being looks towards this solar system, the planet that will be detected first will be Jupiter.

Obviously, the Jupiter is the biggest planet of the solar system. Jupiter’s diameter at the equator is about 142,984 km. Jupiter’s mass is 1.9 x 1027 kg or about 318 times more massive than planet Earth. From the sun, Jupiter is the fifth planet and about 778,330,000 km away.

This gigantic planet is named after Jupiter, the Roman God, who ruled Olympus. Many of the moons orbiting around the Jupiter were also named after the personalities that were involved with the Jupiter god. The four biggest moons of Jupiter are Io, Ganymede, Europa, and Callisto. These four moons are also called Galilean moons since they were discovered by Galileo in 1610.

If viewed from the Earth’s night sky, Jupiter is the second brightest planet, next only to Venus. And this fact earned Jupiter the name “wandering star”. Using a powerful astronomical telescope, one can detect horizontal colored bands wrapping the surface of Jupiter. There is also a great red spot on Jupiter that never seemed to dissipate.

Thus, when technological advancements finally allowed space explorations, the planet Jupiter was visited by several unmanned spacecrafts. These spacecrafts were sent to explore Jupiter and to solve the mystery of the great red spot. The first spacecraft sent to Jupiter was Pioneer 10, in 1973, followed by Pioneer 11, Voyager 1, Voyager 2, and Ulysses.

Exploration results revealed that Jupiter is a gas planet. That is, Jupiter has no solid ground like Earth. Many scientists would like to believe that Jupiter must have a solid rocky core which they estimate to have about 10 to 15 times the mass of Earth. But so far, what is definitely clear is that the bulk of Jupiter is pure metallic liquid hydrogen.

Another spacecraft, called Galileo, was sent to probe the atmosphere of Jupiter. The data sent back showed that Jupiter is about 90% hydrogen, 10% helium, and traces of methane, water, and ammonia. The colored bands of Jupiter were apparently created due to the high velocity winds that occur on the planet. Chemical differences and temperature conditions on Jupiter make the winds appear colored when viewed from space. The light colored bands are called zones and the dark colored bands are called belts. Winds at the belts move in directions opposite to those at the bands. According to the data gleaned by the Galileo probe, wind speeds reach the incredible velocities of 400 mph.

The great red spot of Jupiter, which has existed for more than three centuries, was found to be a high-pressure area with extremely low temperatures. Why it exists even until now still remains a mystery. But apparently, smaller and less obvious similar spots have appeared on other parts of Jupiter and on other planets, Saturn and Neptune. This implies that such spots could be normal phenomena on gas giants.

Like Saturn, Jupiter has rings. But these rings are less visible because these are dark. These Jupiter rings are dark because they are mainly composed of rocks.

In July 1994, the comet Shoemaker-Levy 9 collided with Jupiter. The debris from the collision can be seen even a year after.