Jupiter Fact File


Planetary Fact Files
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This is the fifth planet from the Sun.

Jupiter is the largest planet in our solar system (the diameter at the equator is approximately 88,846 miles). The mass of Jupiter is 2.5 times larger than the mass of all the other planets in the solar system combined.

The planet is called a gas giant because it is made up primarily of hydrogen and helium gases. We do not know if there is any solid core to the planet or if it is gases all the way through.

The clouds around Jupiter are made up of ammonia crystals.

Not only is this the largest planet in our solar system, it is also the fastest spinning one. A single rotation on its axis (a Jupiter day) takes only 10 hours. However, it does take 12 Earth years to complete a single orbit of the Sun.

Due to the planet's size and spin speed it produces a magnetic field 14 times more powerful than Earth.

Jupiter has 79 known moons. The largest four are called Ganymede, Io, Europa and Callisto. Ganymede is also the largest moon in the solar system (slightly larger than Mercury). These four moons are so large that on a clear night you can see them with just a pair of binoculars.

Jupiter as imaged by the Voyager probe in 1979


Jupiter has been visited by seven of our spacecraft.

The first successful mission to Jupiter was a fly-by in 1973 by Pioneer 10 (a NASA space probe that became the first to leave our solar system). Since then there have been four other fly-bys en-route to other missions.

Galileo was the first spacecraft to enter the orbit of Jupiter in 1995. It remained in orbit until 2003. During that time it discovered data on the four main moons of Jupiter that indicated three of them had water present beneath there surfaces.

There is currently a NASA probe in orbit around Jupiter, called Juno. This craft entered Jupiter's orbit in 2016 (after travelling over 2 billion miles) and will continue its mission until 2021. One of the aims of this craft's data collection is to try and determine what the core structure of the planet is.


Use the information above to answer these questions:

  1. If Ganymede is larger than Mercury why is it called a moon rather than a planet?
  2. How many Jupiter days are in a Jupiter year?
  3. Why does NASA not want to risk crashing an orbiter, which could potentially carry Earth microbes, into one of Jupiter's main moons?
  4. Why does Jupiter have so many moons?


To check your answers please see the answer sheet. This should only be used after attempting all questions.

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