Popular Astronomy

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Jupiter from Cassini

Image: NASA/JPL/University of Arizona/





Amazing fact!

Jupiter is so ginormous, you could fit 1,317 Earth’s inside it and still have room left over for the odd moon!

     We are now moving into the outer Solar System – Jupiter is five times farther from the Sun than Earth is. Mighty Jupiter is the biggest planet in the Solar System, 142,984 kilometres across and 318 times as massive as Earth. Jupiter is what we call a gas giant – a planet made only from gas. Yes, Jupiter is nothing more than a giant gasbag! It doesn’t even have a surface to walk on.
      Jupiter is made up of mostly hydrogen gas, with some helium gas, and (relatively) small amounts of other gases such as methane, water vapour, oxygen, sulphur, neon and poisonous ammonia. We’re not really sure what is in the centre of Jupiter, but the pressure and temperature must be so high that scientists think it might be some kind

HST -- Jupiter's three spots
Jupiter now has three red spots

of liquid metallic hydrogen.
      What we can see of Jupiter are its cloud tops. It has distinctive bands of clouds, called zones and belts, which are driven by powerful winds and gigantic thunderstorms. The most famous storm is the Great Red Spot, which has constantly raged for centuries, and is so big that Earth could fit inside it several times over! Recently two new red spots have appeared, although these are smaller than the Great Red Spot.

      Jupiter has 63 moons in total, but most of them are very small. The four largest moons were discovered by Galileo, and are called Io, Europa, Ganymede and Callisto. Together they are known as the Galilean satellites. Io is the closest to Jupiter, and Jupiter’s strong gravity actually squeezes and stretches the moon, a bit like giving it an upset tummy. The result of this is that Io throws up a lot – it is absolutely covered in volcanoes chucking out lava.              Europa is completely covered in ice, but beneath the ice is an ocean of water that goes all around the moon. Scientists think that there could be aquatic forms of life swimming through this ocean. It would be a very dark ocean though, under all that ice, and Europan life would have to get its energy from deep-sea vents instead.
      Ganymede is the largest moon in the Solar System, and both it and Callisto might have oceans under their surfaces too.




The Galilean Satellites (not to scale!) All images from NASA.