Jupiter, the most massive planet.

Jupiter, the 4th brightest natural object in the sky, is the most massive planet in the solar system.

Jupiter is so large that it can hold 1,321 planet Earths inside (to give you perspective, Saturn, the second largest planet, would only fit 737 planet Earths).

It's mass is 1.8981 x 1027 kg, that is 1,898,130,000,000,000,000,000,000,000 kg.

Jupiter is 2 and 1/2 times the mass of all the other planets put together. In laymen's terms: it's enormous.

Earth compared to Jupiter
(if they were really that close it would be the end of the Earth!)

The only object bigger than Jupiter in our Solar System is the Sun.

Jupiter is far from the Sun at 778 million km (483 million miles) away.

Earth seems amazingly close to the sun, in comparison, at a mere 149 million kilometers (92 million miles) away.

"Jovian" refers to Jupiter, so we might say "The Jovian atmosphere".


Because of its distance from the Sun, it should come as no surprise that Jupiter is an extremely cold planet. The average temperature is a cool -148°C (-234°F).


Because Jupiter is such a large planet, you will weigh more there than on any other planet.

Example: Kilograms measure mass, which does not change, and a person weighing 45 kilograms (100 pounds) on Earth would be 114 kilograms (253 pounds) on Jupiter, that is if you could get there, or even stand on the planet, which you can't, as we will see.


Gas Giant

Jupiter is mostly hydrogen and helium. It is classified as a Gas Giant.

Unlike Mercury, Venus, Earth or Mars, which have hard surfaces, Jupiter is mostly gaseous-liquid, making the boundary between the atmosphere and the planet hard to tell.

So there is no surface for anything or anyone to land on!

The atmosphere is about 1000 km thick, then it becomes liquid hydrogen which goes on for another 20,000 kilometers.

Even deeper, we think the hydrogen becomes a metallic liquid because of the extremely high pressure (over 3 million bars).

The electrical currents that run through the liquid metallic hydrogen generate Jupiter's huge magnetic field. This field is so large that it actually sends billions of watts of energy into Earth's own magnetic field every day.

Finally, the core is thought to be an iron-nickel alloy (plus other material), at a temperature over 20,000 °C.

The Great Red Spot

Jupiter has another interesting feature called The Great Red Spot.

This spot is actually a giant rotating storm that is wider than 3 earth diameters.

It has existed for at least 100 years.

Jupiter also has stripes across the planet that are caused by 400 mph winds that blow alternately in opposite directions east to west, or west to east, and the winds change shape within hours or days. They are thought to be caused by Jupiter's internal heat. Jupiter radiates more energy than it receives from the sun, and outside of the sun itself, the second hottest place in the solar system is the core of Jupiter.


Jupiter, besides being the largest planet, also rotates faster than any of the planets in the Solar System.

Jupiter spins so fast it only takes about 10 hours to complete one Jovian day.

Such a huge planet, but it spins more than twice as fast as Earth!

And because it is made of gases and liquids, Jupiter does not rotate as a whole part. The top and bottom of the planet, the poles, flatten slightly from the speed and it takes the poles 5 minutes longer to rotate than it does at the equator. The equator, or middle of the planet bulges out from the speed of the rotation. Jupiter has been said to look like a "squashed ball" at times.


Due to its distance from the sun it takes 11.86 Earth years to orbit once around the sun (although Neptune has it beat at a slow crawling 165 Earth years to orbit the sun!)



In 1610 Galileo Galilei made some improvements to his telescope and discoverd four moons circling Jupiter (now called the "Galileans"):

  • Europa is 3,130 kilometers (1,945 miles) in diameter.
  • Io is 3,642 kilometers (2,263 miles) in diameter.
  • Ganymede is 5,260 kilometers (3,268 miles) in diameterm a bit larger than Mercury.
  • Callisto is 4,820 kilometers (2,995 miles) in diameter, almost exactly the size of Mercury.

Overall Jupiter has more than 50 moons, most of them fairly small though.

Imagine the beautiful view of Jupiter you would get from Europa.



Mercury, Venus, Earth, Mars,
the Gas Giants Jupiter, Saturn, Uranus and Neptune

(Images courtesy NASA.)